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description | The present invention first of all relates to an applicator means for x-ray radiation therapy according to the preamble of patent claim 1. In addition, the invention also relates to a fastening means for attaching an applicator means according to the preamble of patent claim 9. In addition, the invention also relates to a radiation therapy device. The present invention, in particular, lies in the field of radiation therapy, and is particularly associated with the irradiation of tumors or the like. Radiation therapy devices usually are made up of a radiation source means, the operation of which gives rise to radiation, for example, x-ray radiation. The radiation that is generated is guided to the site to be irradiated by means of a probe tip or a radiation source element. For this purpose, so-called applicator means are generally used. An applicator means, for example, comprises an an applicator element, which is designed for taking up a probe tip or a radiation source element of a radiation therapy device. This means that the probe element or the radiation source element of the radiation therapy device is introduced, for example, inserted, into the applicator element. These types of applicator elements are already known in the prior art. For example, an applicator means is described in Patent Application DE 10 2008 030 590 A1 of the Applicant, in which the applicator element provides a base body that comprises a number of different regions. A first region is formed by the foot region. It serves for the uptake of at least one component of a radiation therapy device, for example, at least one probe tip or one radiation source element, which represents one component of the radiation therapy device. A largely cylindrical guide region is adjacent to the foot region and this guide region serves for taking up and guiding a probe tip or a radiation source means. A transition region is provided between foot region and guide region. Finally, at its distal end, the applicator provides a head region, where, in particular, the radiation required for an irradiation is released. In the operation of the radiation therapy device, radiation arises in the probe tip or in the radiation source element, which is released at least in the guide region of the applicator means. Using the applicator means, it can be achieved that body tissue can be directly irradiated at the site of a tumor. The known applicator means is used in order to make possible an irradiation in very constricted body regions, in particular, in channels or ducts. Applicator means, however, may also serve for the purpose of irradiating surfaces, for example, the skin or the surfaces of organs. The object of the present invention is to further develop an applicator means, a fastening means, as well as a radiation therapy device of the type named initially so that they are suitable in a particular way also for the irradiation of surfaces. This object is achieved according to the invention by the applicator means with the features according to the independent patent claim 1, the fastening means with the features according to the independent patent claim 9, as well as the radiation therapy device with the features according to the independent patent claim 13. Further features and details of the invention can be taken from the subclaims, the description and the drawings. In this case, features and details that are named in connection with the applicator means according to the invention are valid, of course, also in connection with the fastening means according to the invention as well as the radiation therapy device according to the invention, and vice versa correspondingly in each case. According to the first aspect of the present invention, an applicator means for radiation therapy, in particular for x-ray radiation therapy for the irradiation of surfaces is provided, having an applicator element for taking up a probe tip or a radiation source element of a radiation therapy device. The applicator means is characterized according to the invention in that the applicator element for adjusting different beam characteristics has at least one element for influencing the beam which is disposed in an exchangeable manner at/in the applicator element. In particular, the applicator means is also characterized according to the invention in that the element for influencing the beam is formed as a lens element or as a combination of lens elements. The irradiation of surfaces in this case particularly involves an irradiation up to a depth of 1 cm or of approximately 1 cm. An applicator means, which permits and makes possible different beam characteristics by exchanging of at least one element for influencing the beam is thus the foundation of the present invention. It was previously known in the prior art to produce different beam characteristics in order to irradiate tissue at different depths by having at hand different applicator elements. This was not only complicated, but also expensive. Now, the different beam characteristics can be provided by exchanging the at least one element for influencing the beam. The applicator means as such, however, can also still be utilized, in addition. For this purpose, the element for influencing the beam can be disposed or designed particularly in a detachable manner at/in the applicator element. The applicator means according to the invention is particularly suitable for the irradiation of the skin or of surfaces of organs, for example, for the surface irradiation of lesions or tumors. The applicator means may involve, in particular, a surface applicator for radiotherapy. Basically, the invention is not limited to specific types of elements for influencing the beam, or, however, to a specific number of such elements. Preferably, at least one element for influencing the beam can be designed as a lens element or as a combination of lens elements. The lens element can be designed in one piece or have multiple parts. Several lens elements can be assembled into a combination of lens elements. It is preferably provided that the applicator means having at least one exchangeable lens is equipped for changing the beam characteristic. Several preferred embodiment examples for the configuration of the lens element or the combination of lens elements are described below. Preferably, the lens element or the combination of lens elements can be designed as an element or as a combination of elements with a different mass distribution in one plane crosswise to the direction of expansion of the x-ray radiation. Preferably, the mass distribution of the lens element or the combination of lens elements can be adapted or can be made adaptable to the radiation characteristic of a radiation source means. The mass distribution is a determining factor for influencing the x-ray radiation. Due to the mass of the element in the radiation path for the x-ray radiation, the radiation is attenuated, whereby a larger mass causes a greater attenuation. The mass distribution in this case can be varied both by the shape as well as also by the selection of materials of the lens element or of the combination of lens elements. Preferably, the lens element or the combination of lens elements can be designed for generating a radiation characteristic for the applicator means that is independent of the type of radiation source means. For example, a flat or spherical radiation characteristic can be produced in a targeted manner, independently of whether a spherical radiation source or a directed radiation source, such as, for example, a linear accelerator, is used. For example, the lens element or the combination of lens elements and/or the applicator element—the latter at least in regions—may have a round shape, or a quadrangular shape, or an octagonal shape, or a shape that is adapted to a tumor to be treated. For example, the lens element or the combination of lens elements may comprise one or at least two different materials. Preferably, the lens element or the combination of lens elements may have at least one positively curved surface and/or at least one neutral surface and/or at least one negatively curved surface. For example, it may be provided that the two surfaces are identically designed. It is also possible, however, that the surfaces are designed differently from one another. Positively curved surfaces, for example, may be convex surfaces, surfaces with continuous contour, surfaces with a pyramid structure, e.g., a step pyramid structure or the like. Neutral surfaces are, in particular, smooth planar surfaces. Negatively curved surfaces, for example, may be concave surfaces or the like. Various examples of different lens elements are described in connection with FIGS. 5 to 19, and reference is made here also to the full disclosure content thereof. In this case, the embodiment examples that are shown may be produced individually, but also in any desired combination. In addition, the invention is also not limited to specific embodiments of the applicator means. For example, the applicator means may have an applicator element that first provides a foot region, by means of which the applicator element can be attached to a radiation source means. Thus, the radiation source means and the applicator means can be moved in common. A guide region, particularly a cylindrical guide region, can be connected to the foot region. The guide region, in particular, has an uptake space, into which can be introduced a probe element or a radiation source element of a radiation therapy device. Likewise, the foot region can also have a corresponding uptake space. In particular, it can be provided that the applicator element is designed as a cylinder, at least in regions. The applicator element can have a first, free end, which, in particular, opposes a second end. For example, the second end serves for attaching the applicator means to the radiation source means. The first, free end, for example, serves for the purpose of being placed on the surface to be irradiated. In such a case, it can preferably be provided that the element for influencing the beam is provided in the region of the first end of the applicator element. In the above-named case, the irradiation, or the delivery of radiation, in particular, takes place via the first, free end of the applicator element. That is, the delivery of radiation is made toward the front. Of course, the invention is not limited to this example of embodiment. For example, it can also be provided that the delivery of the radiation takes place in other regions of the applicator element. For example, a lateral irradiation can be provided. Of course, it is also conceivable that the delivery of the radiation is made not only in one region, but in several different regions of the applicator element. In previously known applicator means, which are used for the irradiation of surfaces, the problem existed that the applicator means usually could be fastened to the surface to be irradiated only in a very complex manner. This problem may also be eliminated with the present invention. According to a second aspect of the invention, or, however, as another preferred embodiment of the applicator means according to the invention, a fastening means is provided for the attachment onto a surface to be treated of an applicator means for radiation therapy, in particular, for x-ray radiation therapy, particularly for the irradiation of surfaces, which is characterized in that the fastening means has an uptake opening for taking up at least one region of the applicator means. In this way, the applicator means can be inserted into the uptake opening of the fastening means, for example, by means of its applicator element, in which a probe tip or a radiation source element of a radiation therapy device has been introduced. The fastening means in turn can be attached to the surface to be irradiated. The fastening means preferably has a base body, which is disposed on or attached to the surface to be treated. In addition, the fastening means has an uptake opening which is formed in a particular way in the base body and, for example, penetrates through it. In such a case, the side walls of the uptake opening that penetrates the base body, at least in regions, serve for supporting and attaching the applicator means in the fastening means. In this case, the invention is neither limited to specific embodiments of the fastening means, nor to specific possibilities of attachment. Several advantageous, but non-exclusive examples will be explained in more detail in the further course of the description. The fastening means according to the invention, in particular, is also characterized in that it is formed as a fastening ring. Preferably, the uptake opening has an inner contour, which corresponds to the outer contour of the region of the applicator means that is to be taken up. Due to the fact that the uptake opening of the fastening means has an inner contour that corresponds to the outer contour of the region of the applicator means to be taken up, it can be assured that the applicator means has a solid seating in the fastening means, which is particularly resistant to slipping out of place. In this case, the invention is not limited to specific embodiments of the uptake opening. For example, it may be provided that the fastening means has a round uptake opening, and that the round uptake opening has a diameter that corresponds to the outer diameter of a cylindrical applicator means that is to be taken up. Of course, other embodiments are also conceivable. Thus, the uptake opening can also be designed, for example, quadrangular, preferably square, while the region of the applicator means to be taken up has, for example, a round, cylindrical cross section. The side lengths of the quadrangle may then preferably correspond to the diameter of the round segment, so that the applicator means can be securely attached and fixed in the uptake opening and thus in the fastening means. Of course, other geometries are also conceivable. It is only important that the applicator means can be introduced into the uptake opening of the fastening means and can be held therein. If the irradiation or the delivery will take place toward the front, i.e., via the first, free end of the applicator element, the fastening means is preferably designed, for example, as a fastening ring, in the above-named way. If an irradiation or the delivery of the radiation is to take place via other regions of the applicator element, for example, laterally, the fastening means can be designed in suitable ways, which makes possible a lateral delivery of the radiation. For example, the fastening means could be made L-shaped in such a case. The fastening means is fastened onto the surface to be treated. This can be accomplished in different ways. For example, it may be provided that the fastening means can be attached and fixed directly onto the surface to be irradiated, for example, with double-sided adhesive tape. Preferably, it can be provided that the fastening means has at least one outwardly projecting fastening tab on at least one of its outer sides. Of course, several such fastening tabs may also be provided. With the presence of such fastening tabs, it can be provided, for example, that these can be attached and fixed onto the surface to be irradiated with normal adhesive tape. Preferably, at least one fastening tab can have at least one fastening opening. In this way, it is made possible, in particular, that the fastening means can also be sewn in order to fix it in place. This may be of advantage, for example, in the irradiation of organs. According to a third aspect of the invention, a radiation therapy device is provided with a radiation source means, in particular for x-ray irradiation, particularly for irradiation of surfaces The radiation therapy device has an applicator means for taking up a probe tip or a radiation source element of the radiation source means, whereby the applicator means is designed in the above-described way according to the invention, so that in this respect, reference is made to the full content of the above statements relating to the applicator means. Alternatively or additionally, the radiation therapy device may have a fastening means according to the invention, as described above, for fastening an applicator means for radiation therapy onto a surface to be treated, so that, in this respect also, reference is made to the full content of the above statements relating to the fastening means. The radiation therapy device may be used particularly for the irradiation of surfaces, for example, for the irradiation of the skin or of the surface of an organ. The radiation therapy device first has a radiation source means, by means of which the radiation doses necessary for the irradiation will be produced. In particular, the radiation source means is designed for generating radiation for radiotherapy. The applicator means is disposed at the radiation source means. A radiation therapy device 10 is shown in FIGS. 1 to 3. Radiation therapy device 10 has a radiation source means 11, which is designed for generating radiation for radiotherapy. A radiation source element 12 is provided for applying the generated radiation. Radiation therapy device 10 serves for x-ray radiation therapy. As is shown further in FIGS. 1 to 3, an applicator means 20 according to the invention has a cylindrically shaped applicator element 21. Applicator element 21 comprises a foot region 22 and a guide region 23 connecting thereto. In particular, the radiation source element 12 of radiation source means 11 of radiation therapy device 10 is found in irradiation operation, as is illustrated particularly also in FIG. 3. For this purpose, guide region 23 of applicator element 21 has a corresponding uptake space 24. Applicator element 21 has a second end 25 in foot region 22, by means of which applicator element 21, and thus applicator means 20, can be attached to radiation source means 11. The first end 26 of applicator element 21, which lies opposite to the second end 25, involves the free end of applicator element 21, which terminates the guide region 23 of applicator element 21, and the radiation dose can be applied by first end 26, for example, onto the surface to be irradiated. In order to be able to generate different beam characteristics with applicator means 20, for example, in order to be able to irradiate a tissue to be irradiated at different depths, applicator means 20 has an element 27 for influencing the beam in the example of embodiment shown in FIGS. 1 to 3. Element 27 for influencing the beam is advantageously designed as a lens 27 for changing the beam characteristic. It is preferably exchangeable, i.e., detachably disposed on applicator element 21, preferably in the region of its first free end 26. In FIG. 2, the radiation therapy device 10 according to FIG. 1 is shown in a state in which applicator means 20 and radiation therapy device 10 are assembled. FIG. 3 shows a cross-sectional view of the radiation therapy device 10, which is assembled as shown in FIG. 2. In particular, FIG. 3 shows how applicator means 20 is attached via its foot region 22 to radiation source means 11. Radiation source means 11 and applicator means 20 form components of radiation therapy device 10. Radiation, for example, radiation for radiotherapy is produced in radiation source means 11 and is applied onto the surface to be irradiated via radiation source element 12, which is connected to radiation source means 11 and which is found in uptake space 24 inside applicator element 21. In particular, if a surface is to be irradiated, it is often difficult to configure applicator means 20 so that it can be attached to the site that is to be irradiated. In order to eliminate this problem, a special fastening means 30 is provided, which is described in more detail below in connection with FIG. 4. Fastening means 30 is designed as a fastening ring, by means of which the applicator means 20 can be attached and fixed onto the surface to be treated. Fastening ring 31 has an uptake opening 36 for applicator element 21, whereby uptake opening 36 has an inner diameter 31, which corresponds to outer diameter 28 of applicator element 21 in the region of its first end 26, as this is also illustrated in FIGS. 1 and 3. In this way, applicator means 20 can be inserted into fastening ring 30 and can be held therein so that it cannot slip out of position. Fastening ring 30, in turn, can be attached and fixed onto the surface to be treated, for example, the skin, e.g., with the use of double-sided adhesive tape. Alternatively, it can be provided that fastening ring 30 has at least one fastening tab projecting outwardly from its outer side 32. Two such fastening tabs 33, 34 are shown in FIG. 4, whereby the number may vary according to the application. In such a case, fastening ring 30 can be attached and fixed via fastening tabs 33, 34 onto the surface to be treated also with normal adhesive tape. If fastening openings 35 are found in fastening tabs 33, 34, fastening ring 30 can also be solidly sewn in place for attachment, for example. This may be of advantage, for example, in the irradiation of organs. On the basis of FIGS. 5 to 19, different embodiment examples of elements 27 for influencing the beam are shown, which can be used in an applicator means 20 as described above. Elements 27 involve lens elements. A lens element in the sense of the Patent Application in this case is, in particular, an element with a different mass distribution in a plane crosswise to the expansion direction of the x-ray radiation. The mass distribution of lens element 27 is thus ideally adapted to the radiation characteristic of radiation source means 11. The mass distribution is a determining factor for influencing the x-ray radiation. Due to the mass of lens element 27 in the beam path of the x-ray radiation, the radiation is attenuated, whereby a larger mass causes a greater attenuation. The mass distribution in this case can be varied both by the shape as well as also by the selection of materials of lens element 27. In this way, a radiation characteristic of applicator means 20 that is independent of the type of radiation source means 11 can be adapted. In the following, different embodiment examples for lens elements 27 with different mass distributions are described, which can be used for applicator means 20 shown in FIGS. 1 to 3. FIG. 5 shows an element 27 for influencing the beam in the form of a lens element that comprises one material and has a round shape. One surface 27a of lens element 27 in this case has a positive curvature in the form of a continuous contour. FIG. 6 shows an element 27 for influencing the beam in the form of a lens element that comprises one material and has a round shape. One surface 27a of lens element 27 in this case has a positive curvature in the form of a contour in the shape of a step pyramid. The individual steps of the step pyramid in this case could also comprise different materials, at least in part. FIG. 7 shows a similar example of embodiment, except that the lens element has a quadrangular shape. FIG. 8 shows an element 27 for influencing the beam in the form of a lens element that comprises one material and has a round shape. One surface 27a of lens element 27 in this case has a negative curvature in the form of a concave contour. The other surface 27d has a neutral, smooth contour. The depicted element involves a focus element. FIG. 9 shows a similar example of embodiment, except that the element comprises two different materials 27b, 27c. The example of embodiment shown in FIG. 10 is similar to the example of embodiment shown in FIG. 9, whereby the surface is designed as neutral in the form of a smooth surface. This can be produced, for example, by means of a refilling. FIG. 11 shows an element 27 for influencing the beam in the form of a lens element that comprises one material and has an octagonal shape. One surface 27a of lens element 27 in this case has a negative curvature in the form of a concave contour. The other surface 27d has a neutral, smooth contour. The depicted element involves a focus element. FIG. 12 shows a similar example of embodiment, except that the element comprises two different materials 27b, 27c. FIG. 13 shows an element 27 for influencing the beam in the form of a lens element that comprises one material and has a round shape. Both surfaces 27a, 27d of lens element 27 in this case have a negative curvature in the form of a concave contour. The depicted element involves a focus element. FIG. 14 shows an element 27 for influencing the beam in the form of a lens element that comprises one material and has a round, flat shape. Both surfaces 27a, 27d of lens element 27 in this case have a neutral, smooth contour. FIG. 15 shows an element 27 for influencing the beam in the form of a lens element that has a round shape. One surface 27a of lens element 27 in this case has a positive curvature in the form of a continuous contour. Element 27 comprises several materials. In the example of embodiment shown, element 27 comprises materials with decreasing density. FIG. 16 shows an element 27 for influencing the beam in the form of a lens element that has a round shape. One surface 27a of lens element 27 in this case has a positive curvature in the form of a continuous contour. The other surface 27d has a neutral, smooth contour. Element 27 comprises several materials 27b, 27c. FIG. 17 shows another example of embodiment for an element 27 for influencing the beam in the form of a lens element that comprises two different materials 27b, 27c. In this case, element 27 is designed as a ring. FIG. 18 shows yet another example of embodiment of an element 27 for influencing the beam in the form of a lens element with an unusual shape. Finally, in FIG. 19, an example of embodiment is shown, in which applicator means 20, and alternatively or additionally, element 27 for influencing the beam is/are adapted to the shape of a tumor 13 to be treated. The embodiment examples described above and shown in the Figures are particularly suitable for the irradiation of surface lesions or tumors, in particular on the skin or on the surface of organs. 10 Radiation therapy device 11 Radiation source means 12 Radiation source element 13 Tumor 20 Applicator means 21 Applicator element 22 Foot region 23 Guide region 24 Uptake space 25 Second end of the applicator element 26 First end of the applicator element 27 Element for influencing the beam (lens element) 27a Surface 27b Material 27c Material 27d Surface 28 Outer diameter 30 Fastening means (fastening ring) 31 Inner diameter 32 Outer side 33 Fastening tab 34 Fastening tab 35 Fastening opening 36 Uptake opening |
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abstract | A multi-beam e-beam system employs a set of independently controllable (for blanking and deflection) subsystems placed in a solenoid field, each system having a demagnifying lens comprising at least one passive pole piece, so that the final image demagnifies imperfections in the upstream electron beam. Upper and lower sections of the system employ the focusing effect of the solenoid field to form an image at a shaping aperture and a demagnified image of the beam at the shaping aperture on the workpiece. Small focus corrections due to magnetic lens field non-uniformity and/or target height variations, are accomplished with an electrostatic unipotental lens built into the pole pieces and target voltage variations. |
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056132409 | abstract | A method for immobilizing waste chloride salts containing radionuclides and hazardous nuclear material for permanent disposal starting with a substantially dry zeolite and sufficient glass to form leach resistant sodalite with occluded radionuclides and hazardous nuclear material. The zeolite and glass are heated to a temperature up to about 1000.degree. K. to convert the zeolite to sodalite and thereafter maintained at a pressure and temperature sufficient to form a sodalite product near theoretical density. Pressure is used on the formed sodalite to produce the required density. |
abstract | An X-ray arrangement is suitable to record absorption, phase contrast, and dark field images of an object. The visibility of low absorbing specimens is improved and required radiation dose is reduced. The assembly includes an X-ray source; two or more gratings; a position-sensitive detector with spatially modulated detection sensitivity; a recorder for recording the images; an evaluator for evaluating the intensities for each pixel to identify the characteristic of the object for each individual pixel as an absorption and/or a differential phase contrast and/or an x-ray scattering dominated pixel. Images are collected by rotating from 0 to n or 2n either the sample or the assembly. The gratings are produced with planar geometry. The X-rays pass through the gratings parallel to the substrate. The grating structures extend along the X-ray path which determines the phase shift. The attenuation of the X-rays caused by the grating structures is no longer given by the thickness, but by the length of the grating structures. |
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claims | 1. A system for generating and maintaining a magnetic field with a field reversed configuration (FRC) comprisinga confinement chamber,first and second diametrically opposed FRC formation sections coupled to the confinement chamber, the formation section comprising modularized formation systems for generating an FRC and translating the FRC toward a midplane of the confinement chamber,first and second divertors coupled to the first and second formation sections,first and second axial plasma guns operably coupled to the first and second divertors, the first and second formation sections and the confinement chamber,a plurality of neutral atom beam injectors coupled to the confinement chamber and oriented normal to the axis of the confinement chamber,a magnetic system comprising a plurality of quasi-dc coils positioned around the confinement chamber, the first and second formation sections, and the first and second divertors, first and second set of quasi-dc mirror coils positioned between the confinement chamber and the first and second formation sections, and first and second mirror plugs position between the first and second formation sections and the first and second divertors,a gettering system coupled to the confinement chamber and the first and second divertors,one or more biasing electrodes for electrically biasing open flux surface of a generated FRC, the one or more biasing electrodes being positioned within one or more of the confinement chamber, the first and second formation sections, and the first and second divertors,two or more saddle coils coupled to the confinement chamber, andan ion pellet injector coupled to the confinement chamber. 2. The system of claim 1 wherein the mirror plug comprises a third and fourth sets of mirror coils between each of the first and second formation sections and the first and second divertors. 3. The system of claim 2 wherein the mirror plug further comprises a set of mirror plug coils wrapped around a constriction in the passageway between each of the first and second formation sections and the first and second divertors. 4. The system of claim 1 wherein the first and second formatting sections include an elongate quartz tube with a quartz liner. 5. The system of claim 1 wherein the formation systems are pulsed power formation systems. 6. The system of claim 1 wherein the formation systems comprise a plurality of power and control units coupled to individual ones of a plurality of strap assemblies to energize a set of coils of the individual ones of the plurality of strap assemblies wrapped around the elongate tube of the first and second formation sections. 7. The system of claim 6 wherein individual ones of the plurality of power and control units comprising a trigger and control system. 8. The system of claim 7 wherein the trigger and control systems of the individual ones of the plurality of power and control units being synchronizable to enable static FRC formation wherein the FRC is formed and then injected or dynamic FRC formation wherein the FRC is formed and translated simultaneously. 9. The system of claim 1 wherein the plurality of neutral atom beam injectors comprises one or more RF plasma source neutral atom beam injectors and one or more arc source neutral atom beam injectors. 10. The system of claim 1 wherein the plurality of neutral atom beam injectors are oriented with an injection path tangential to the FRC with a target trapping zone within separatrix of the FRC. 11. The system of claim 1 wherein the gettering system comprises one or more of a Titanium deposition system and a Lithium deposition system that coat the plasma facing surfaces of the confine chamber and the first and second divertors. 12. The system of claim 1 wherein biasing electrodes includes one or more of one or more point electrodes positioned within the containment chamber to contact open field lines, a set of annular electrodes between the confinement chamber and the first and second formation sections to charge far-edge flux layers in an azimuthally symmetric fashion, a plurality of concentric stacked electrodes positioned in the first and second divertors to charge multiple concentric flux layers, and anodes of the plasma guns to intercept open flux. 13. A system for generating and maintaining a magnetic field with a field reversed configuration (FRC) comprisinga confinement chamber,first and second diametrically opposed FRC formation sections coupled to the confinement chamber,first and second divertors coupled to the first and second formation sections,one or more of a plurality of plasma guns, one or more biasing electrodes and first and second mirror plugs, wherein the plurality of plasma guns includes first and second axial plasma guns operably coupled to the first and second divertors, the first and second formation sections and the confinement chamber, wherein the one or more biasing electrodes being positioned within one or more of the confinement chamber, the first and second formation sections, and the first and second divertors, and wherein the first and second mirror plugs being position between the first and second formation sections and the first and second divertors,comprising a gettering system coupled to the confinement chamber and the first and second divertors,a plurality of neutral atom beam injectors coupled to the confinement chamber and oriented normal to the axis of the confinement chamber, anda magnetic system comprising a plurality of quasi-dc coils positioned around the confinement chamber, the first and second formation sections, and the first and second divertors, first and second set of quasi-dc mirror coils positioned between the confinement chamber and the first and second formation sections. 14. The system of claim 13 wherein the mirror plug comprises third and fourth sets of mirror coils between each of the first and second formation sections and the first and second divertors. 15. The system of claim 14 wherein the mirror plug further comprises a set of mirror plug coils wrapped around a constriction in the passageway between each of the first and second formation sections and the first and second divertors. 16. The system of claim 15 further comprising first and second axial plasma guns operably coupled to the first and second divertors, the first and second formation sections and the confinement chamber. 17. The system of claim 15 further comprising two or more saddle coils coupled to the confinement chamber. 18. The system of claim 15 further comprising an ion pellet injector coupled to the confinement chamber. 19. The system of claim 15 wherein the formation section comprises modularized formation systems for generating an FRC and translating it toward a midplane of the confinement chamber. 20. The system of claim 13 wherein biasing electrodes includes one or more of one or more point electrodes positioned within the containment chamber to contact open field lines, a set of annular electrodes between the confinement chamber and the first and second formation sections to charge far-edge flux layers in an azimuthally symmetric fashion, a plurality of concentric stacked electrodes positioned in the first and second divertors to charge multiple concentric flux layers, and anodes of the plasma guns to intercept open flux. |
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claims | 1. A system comprising:an enclosure comprising:a first end and a second end that is opposite from the first end; anda midpoint that is substantially equidistant between the first and second ends of the enclosure;two superconducting internal magnetic coils suspended within an interior of the enclosure and coaxial with a center axis of the enclosure, the two internal magnetic coils each having a toroidal shape, the two internal magnetic coils comprising:a first internal magnetic coil located between the midpoint and first end of the enclosure; anda second internal magnetic coil located between the midpoint and the second end of the enclosure;wherein the internal coils each have a radius configured to balance the relative field strength between a plurality of point cusps and a plurality of ring cusps;a plurality of encapsulating magnetic coils co-axial with a center axis of the enclosure, the encapsulating magnetic coils having a larger diameter than the internal magnetic coils, the plurality of encapsulating magnetic coils comprising;at least two first encapsulating magnetic coils located between the midpoint and the first and of the enclosure; andat east two second encapsulating magnetic coils located between the midpoint and the second end of the enclosure;a center magnetic coil co-axial with a center axis of the enclosure and located proximate to the midpoint of the enclosure; andtwo mirror magnetic coils co-axial with a center axis of the enclosure and comprising:a first mirror magnetic coil located proximate to the first end of the enclosure;a second mirror magnetic coil located proximate to the second end of the enclosure;one or more coil systems configured to supply the magnetic coils with electrical currents, to form magnetic fields for confining plasma within a magnetized sheath in the enclosure, wherein the magnetized sheath and plasma confined within the magnetized sheath encircle each of the two internal magnetic coils;wherein the center magnetic coil is disposed outside the interior of the enclosure. 2. The system of claim 1, wherein the one or more coil systems comprise:a center coil system configured to supply first electrical currents flowing in a first direction through the center magnetic coil;an internal coil system configured to supply second electrical currents flowing in a second direction through each of the two internal magnetic coils;an encapsulating coil system configured to supply third electrical currents flowing in the first direction through each of the plurality of encapsulating magnetic coils; anda mirror coil system configured to supply fourth electrical currents flowing in the first direction through each of the two mirror magnetic coils. 3. The system of claim 1, wherein the enclosure comprises an outer blanket and an inner blanket, the outer blanket comprising steel or iron and the inner blanket comprising beryllium or a mixture of lithium fluoride (LiF) and beryllium fluoride (BeF2)(FLiBe). 4. The system of claim 1, wherein each of the two internal magnetic coils comprises:a core comprising a plurality of coil windings;an inner shield surrounding the core;a protective layer surrounding the inner shield; andan outer shield surrounding the protective layer. 5. A system comprising:an enclosure comprising:a first end and a second end that is opposite from the first end; anda midpoint that is substantially equidistant between the first and second ends of the enclosure;two superconducting internal magnetic coils suspended within an interior of the enclosure, each internal magnetic coil positioned on an opposite side of the midpoint of the enclosure from the other internal magnetic coil;wherein the internal coils each have a radius configured to balance the relative field strength between a plurality of point cusps and a plurality of ring cusps;one or more encapsulating magnetic coils positioned on each side of the midpoint of the enclosure, each encapsulating magnetic coil being coaxial with the internal magnetic coils;a center magnetic coil co-axial with the center of the enclosure and located proximate to the midpoint of the enclosure;two mirror magnetic coils coaxial with the internal magnetic coils, each mirror magnetic coil positioned on an opposite side of the midpoint of the enclosure from the other mirror magnetic coil; andone or more coil systems configured to supply the magnetic coils with electrical currents, to form magnetic fields for confining plasma within a magnetized sheath in the enclosure, wherein the magnetized sheath and plasma confined within the magnetized sheath encircle each of the two internal magnetic coils;wherein the center magnetic coil is disposed outside the interior of the enclosure. 6. The system of claim 5, further comprising a center magnetic coil located proximate to the midpoint of the enclosure, the center magnetic coil being coaxial with the internal magnetic coils. 7. The system of claim 6, wherein:the two internal magnetic coils comprises:a first internal magnetic coil located between the center magnetic coil and the first end of the enclosure; anda second internal magnetic coil located between the center magnetic coil and the second end of the enclosure;the one or more encapsulating magnetic coils positioned on each side of the midpoint of the enclosure comprises:a first set of two encapsulating magnetic coils located between the first internal magnetic coil and the first end of the enclosure; anda second set of two encapsulating magnetic coils located between the second internal magnetic coil and the second end of the enclosure; andthe two mirror magnetic coils comprises:a first mirror magnetic coil located proximate to the first end of the enclosure; anda second mirror magnetic coil located proximate to the second end of the enclosure. 8. The system of claim 5, wherein the enclosure comprises an outer blanket and an inner blanket, the outer blanket comprising steel or iron and the inner blanket comprising beryllium or a mixture of lithium fluoride (LiF) and beryllium fluoride (BeF2)(FLiBe). 9. The system of claim 5, wherein each of the two internal magnetic coils comprises:a core comprising a plurality of coil windings;an inner shield surrounding the core;a protective layer surrounding the inner shield; andan outer shield surrounding the protective layer. 10. The system of claim 5, wherein the one or more coil systems comprise:a center coil system configured to supply first electrical currents flowing in a first direction through the center magnetic coil;an internal coil system configured to supply second electrical currents flowing in a second direction through each of the two internal magnetic coils;an encapsulating coil system configured to supply third electrical currents flowing in the first direction through each of the plurality of encapsulating magnetic coils; anda mirror coil system configured to supply fourth electrical currents flowing in the first direction through each of the two mirror magnetic coils. 11. The system of claim 5, wherein the encapsulating magnetic coils are external to the enclosure. |
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048851230 | abstract | The present invention provides an apparatus for handling core constituent elements of a reactor that comprises a core having as core constituent elements control rod assemblies each containing a control rod and fuel assemblies each containing nuclear fuel, a small rotating plug rotatably provided on the core, and a control rod drive mechanism provided on the small rotating plug, the control rod drive mechanism being characterized by comprising a plurality of grippers each having a hook projecting inwards so as to be able to engage with a handling head of the control rod and a hook projecting outwards so as to be able to engage with a handling head of each of the core constituent elements as a distance in the longitudinal direction; an operational head for opening and closing the grippers; and a third elevating drive mechanism for vertically driving the operational head; a second elevating frame for supporting the third elevating drive mechanism and the grippers; a second elevating drive mechanism for vertically driving the second elevating frame; a first elevating frame for supporting the second elevating drive mechanism and the second elevating frame; a first elevating drive mechanism for vertically driving the first elevating frame; and a frame which supports the first elevating drive mechansim and is provided on the small rotating plug. |
055662170 | abstract | A spacer includes a plurality of ferrules welded to one another to form a structural integral matrix for locating fuel rods in a fuel bundle. Each ferrule has a pair of stops along one side of the ferrule and a central opening along its opposite side. An elongated flat spring having openings straddling a central cross-piece is disposed along an outer edge of the ferrule with the spring openings receiving band portions of the ferrule above and below the opening through the ferrule. The intermediate cross-piece bears against an adjoining ferrule whereby the end portions of the spring bear against the rod in the one ferrule, biasing it against the opposite stops. Thus ferrule/spring construction reduces the quantity of material of the ferrule, thereby improving performance without sacrificing structural integrity. |
abstract | A boiling water reactor having a reactor pressure vessel with two recirculation loops hydraulically connected thereto is decontaminated by installing plugs in the outlets of jet pump ram""s head manifolds located within the reactor pressure vessel to isolate the recirculation loops from the reactor pressure vessel. A monitoring gas is bubbled into some of the ram""s head manifolds through the plugs to monitor the process pressure within the manifolds and riser pipes connected with the manifolds. The level of the decontamination solution in the riser pipes can be determined by determining the differential pressure due to the vertical height of the decontamination solution in the loops. |
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claims | 1. A method of medical imaging comprising:rotating a first X-ray source-detector pair through a first set of angles around an axis of rotation;simultaneously rotating a second X-ray source-detector pair through a second set of angles around said axis of rotation, wherein said first set of angles and said second set of angles do not overlap;acquiring image data from said first X-ray source-detector pair and said second X-ray source-detector pair during rotation; andstoring said image data to form a computed tomography dataset. 2. The method of claim 1 wherein said first set of angles and said second set of angles each comprise at least 90 degrees. 3. The method of claim 1 further comprising:completing rotation of the first X-ray source-detector pair through the first set of angles and the second X-ray source-detector pair through the second set of angles in less than 3 seconds. 4. The method of claim 1 further comprising:fixing positions of said first X-ray source-detector pair and said second X-ray source-detector pair at a predetermined angle of separation; andacquiring images from said first X-ray source-detector pairs and said second X-ray source-detector pair while stationary. 5. The method of claim 4 further comprising:utilizing said computed tomography dataset for registration of said images. 6. The method of claim 1 wherein source of said first X-ray source-detector pair is configured to emit radiation from a plurality of discrete locations on its face. 7. The method of claim 1 wherein source of said first X-ray source detector-pair is a point source. 8. A method of medical imaging comprising:rotating two X-ray source-detector pairs around an imaging volume, wherein sources of said X-ray source-detector pairs are configured to emit radiation from pluralities of discrete locations on their faces;acquiring a computed tomography dataset during rotation of said two X-ray source-detector pairs;fixing said two X-ray source-detector pairs at a predetermined angle relative to one another;acquiring image data from said two X-ray source-detector pairs while stationary at said predetermined angle relative to one another;reconstructing a three-dimensional image from said image data; andutilizing said computed tomography dataset as a prior for reconstruction of said three-dimensional image. 9. The method of claim 8 wherein said prior is a Bayesian prior. 10. The method of claim 8 wherein said predetermined angle is between 80 and 100 degrees, inclusive. 11. The method of claim 8 further comprising:reconstructing said three-dimensional image using a maximum-likelihood expectation maximization in voxel space. 12. The method of claim 8 further comprising:reconstructing said three-dimensional image using an ordered-subset expectation maximization framework. 13. The method of claim 8 further comprising:reconstructing said three-dimensional image using a maximum likelihood algorithm for transmission tomography. 14. The method of claim 8 further comprising:correcting artifacts in said three-dimensional image using said computed tomography dataset. |
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044252978 | description | DETAILED DESCRIPTION OF PREFERRED EMBODIMENT Referring now to the drawings in detail, FIG. 1 illustrates a typical boiling water reactor installation, generally referred to by reference numeral 10, for a gamma radiation type of sensor, generally referred to by reference numeral 12. The sensor 12 is inserted into the reactor from the top by means of a gripping cone 14, in a manner already known in the art. When inserted, the lower end of the sensor projects from the bottom wall 16 of the reactor vessel through a high pressure gland 18 and is connected by means of a pin socket coupling 20 to a signal cable 22 extending to the instrumentation site for the reactor. The sensor 12 is vertically positioned as shown between adjacent fuel assemblies 24 having vertically enlongated channels 26 enclosing bundles of fuel rods 28. These fuel assemblies extend vertically within the reactor vessel between a top fuel guide structure 30 and a lower grid 32 below which the sensor projects. Some of the fission products from the fuel rods during power generation, in the form of gamma radiation is detected by the sensor 12 at a plurality of vertically spaced measurement zones. In practice, there are between four and ten of such measurement zones from which local power generation measurements are obtained through each sensor. The outer diameter of the sensor is made as large as practically possible for the available space between the adjacent fuel assemblies, and is externally exposed to a body of coolant within the reactor vessel in order to establish a uniform heat sink temperature therefor. As more clearly seen in FIGS. 2 and 3, showing an enlarged portion of the gamma sensor 12, an elongated monolithic gamma radiation absorbing body 34 is provided made of a material such as stainless steel No. 316 or zircaloy which generates heat when exposed to gamma radiation, without any change in its properties. The heat so generated flows radially outward to the external surface 36 of the body 24 which is maintained at a heat sink temperature by the coolant, such as water, in direct contact therewith throughout. A plurality of double junction thermocouple cables 38 is mounted internally within the body 34 and is connected to the instrument cable 22, in order to measure differential temperatures at the axially spaced measuring zones, one of which is shown in FIGS. 2 and 3. The sensor, therefore, has associated therewith differential thermocouple junctions 40 and 42 for each measuring zone as shown in FIG. 3. The thermocouple cables are mounted within a central bore 44 formed in the elongated body 34 through which its longitudinal axis extends. The body is generally cylindrical and of a constant diameter along a major portion thereof interrupted at reduced cross-sectional area portions 46 located within each measuring zone. The axial interruptions in the otherwise constant diameter of the body at the reduced diameter portions 46 form cold regions within which the thermocouple junctions 42 are located. As a result of such configuration, the temperature gradient in the measurement zone follows the curve 48 shown in FIG. 4. As shown in FIGS. 3 and 4, the cold junction 44 is located approximately midway within the cold region surrounding the reduced diameter portion 46. The hot junction 40 adjacent the tip of the thermocouple cable 38 is aligned with the constant diameter portion of the body 34 adjacent to the reduced diameter portion 46 in axially spaced relation to cold junction 42. Thus, temperature measurements made through the thermocouple cable will be influenced by one-dimensional, radial heat flow through the body 34 during reactor power operation at the axial locations of the thermocouple junctions 40 and 42. The temperature differential (.DELTA.T) between the interior of body 34 and the heat sink surface for such a radial heat flow arrangement is approximately .DELTA.T=(9r.sup.2 /4K), as compared to the equation applicable to an axial heat flow arrangement; .DELTA.T=(qL.sup.2 /8K). In the foregoing equations, (q) is the rate of heat generated by gamma ray absorption, (r) is the radius of the major portion of the body, (k) is its thermal conductivity and (L) is the axial length of the reduced diameter portion of the body. Thus, for both pressurized and boiling water types of reactors, the temperature differential signal obtained from an axial flow type sensor is a function of axial length of the reduced diameter portion of the heater body of the sensor. When utilizing a radial heat flow type of sensor in accordance with the present invention, the differential temperature signal obtained is a function of the outer diameter or radius (r) of the sensor body. Accordingly, by use of a larger diameter sensor for the larger space available in a boiling water reactor as compared to a pressurized water reactor, a larger differential signal output is theoretically possible. In practice, the differential temperature measurement through the raidal heat flow sensor is up to 4.degree. C. in a pressurized water reactor and is up to 22.degree. C. in a boiling water reactor. The foregoing equations are approximate in that they omit a negligible factor depending on the radius of the reduced diameter portion of the sensor body and disregard those heat losses which are mimimal only for the radial heat flow type of sensor. Such heat losses are avoided because the entire external surface of the body 34 is in direct thermal contact within the coolant establishing a uniform heat sink temperature throughout. Thus, more accurate and reliable differential signal measurement of local power generation is achieved. The only drawback may reside in the limitation on the magnitude of the temperature differential imposed by the more restricted space for the sensor in a pressurized water reactor. Whether such a drawback is significant will depend on the signal noise level to be encountered. In the design and construction of the sensor 12, the dimensions of the reduced diameter portions 46 are not significant, as hereinbefore demonstrated, in so far as signal level is concerned, but do affect the structural strength of the sensor. In order to strengthen the sensor and offset the weakening effect of the reduced diameter portions, radial fins 50 are provided as more clearly seen in FIG. 2. These fins are made of material having a high structural strength and a high thermal conductivity so as to have a negligible affect on heat sink temperature and the radial flow of heat. The accuracy of the measurements obtained through the sensor 12 will also depend on its calibration before installation. Calibration is effected by passing an electric current longitudinally through the sensor body 34 by connection to an electrical power source 52, as diagrammed in FIG. 5, causing internal electrical heating of the body. A non-uniform volt drop ordinarily occurs along the length of the sensor body as indicated by curve 54 in FIG. 6, because of the higher electrical resistance of the reduced diameter portions 46. The volt drop is therefore modified to render it uniform as indicated by curve 56, by establishing current paths in parallel with the reduced diameter portions 46 of the body during electrical heating for calibration purposes. Toward that end an annular filler ring 58 is fitted about the reduced diameter portions of the body as shown in FIG. 5. The filler is made of a material having high thermal and electrical conductivity as well as a low melting point temperature. Thus, silver solder, etc., may be suitable. The quantity of the filler utilized in such as to equalize the volt drop per unit length of the reduced diameter portion 46 with the major diameter portions to obtain the uniform volt drop curve 56 shown in FIG. 6. The high conductivity of the filler will avoid any additional heating affect on the body 34. The low melting point for the filler will enable it to be readily removed by melting after calibration is completed. Once the body 34 is electrically heated after being prepared as herein described, a differential temperature signal (.DELTA.T) is obtained across the thermocouple junctions 40 and 42 as shown in FIG. 5 and the heating current varied in order to plot the signal (.DELTA.T) versus the heating effect of the current as indicated by the calibration curves 60 in FIG. 7. The slopes of these curves plotted for each sensor individually, represent sensitivity factors in terms of .degree.C. per watt, per gram. In practice, the sensitivity factors for the radial heat flow sensors is between 4 and 40.degree. C./watt/gram. |
description | This application is a continuation of U.S. patent application Ser. No. 15/176,025 filed Jun. 7, 2016, which is a continuation-in-part of U.S. patent application Ser. No. 15/167,617 filed May 27, 2016, which is: a continuation-in-part of U.S. patent application Ser. No. 15/152,479 filed May 11, 2016, which: is a continuation-in-part of U.S. patent application Ser. No. 14/216,788 filed Mar. 17, 2014, which is a continuation-in-part of U.S. patent application Ser. No. 13/087,096 filed Apr. 14, 2011, which claims benefit of U.S. provisional patent application No. 61/324,776 filed Apr. 16, 2010; and is a continuation-in-part of U.S. patent application Ser. No. 13/788,890 filed Mar. 7, 2013; is a continuation-in-part of U.S. patent application Ser. No. 14/952,817 filed Nov. 25, 2015, which is a continuation-in-part of U.S. patent application Ser. No. 14/293,861 filed Jun. 2, 2014, which is a continuation-in-part of U.S. patent application Ser. No. 12/985,039 filed Jan. 5, 2011, which claims the benefit of U.S. provisional patent application No. 61/324,776, filed Apr. 16, 2010; is a continuation-in-part of U.S. patent application Ser. No. 14/860,577 filed Sep. 21, 2015, which is a continuation of U.S. patent application Ser. No. 14/223,289 filed Mar. 24, 2014, which is a continuation-in-part of U.S. patent application Ser. No. 14/216,788 filed Mar. 17, 2014, which is a continuation-in-part of U.S. patent application Ser. No. 12/985,039 filed Jan. 5, 2011, which claims the benefit of U.S. provisional patent application No. 61/324,776, filed Apr. 16, 2010; and is a continuation-in-part U.S. patent application Ser. No. 15/073,471 filed Mar. 17, 2016, which claims benefit of U.S. provisional patent application No. 62/304,839 filed Mar. 7, 2016, is a continuation-in-part of U.S. patent application Ser. No. 14/860,577 filed Sep. 21, 2015, which is a continuation of U.S. patent application Ser. No. 14/223,289 filed Mar. 24, 2014, which is a continuation-in-part of U.S. patent application Ser. No. 14/216,788 filed Mar. 17, 2014, which is a continuation-in-part of U.S. patent application Ser. No. 13/572,542 filed Aug. 10, 2012, which is a continuation-in-part of U.S. patent application Ser. No. 12/425,683 filed Apr. 17, 2009, which claims the benefit of U.S. provisional patent application No. 61/055,395 filed May 22, 2008, now U.S. Pat. No. 7,939,809 B2; all of which are incorporated herein in their entirety by this reference thereto. This invention relates generally to imaging and/or treatment of solid cancers. More particularly, the invention relates to control of a charged particle beam state, such as charged particle position, direction, intensity, density, energy, and/or distribution and/or positioning control of a patient. Cancer Treatment Proton therapy works by aiming energetic ionizing particles, such as protons accelerated with a particle accelerator, onto a target tumor. These particles damage the DNA of cells, ultimately causing their death. Cancerous cells, because of their high rate of division and their reduced ability to repair damaged DNA, are particularly vulnerable to attack on their DNA. Patents related to the current invention are summarized here. Proton Beam Therapy System F. Cole, et. al. of Loma Linda University Medical Center “Multi-Station Proton Beam Therapy System”, U.S. Pat. No. 4,870,287 (Sep. 26, 1989) describe a proton beam therapy system for selectively generating and transporting proton beams from a single proton source and accelerator to a selected treatment room of a plurality of patient treatment rooms. Imaging P. Adamee, et. al. “Charged Particle Beam Apparatus and Method for Operating the Same”, U.S. Pat. No. 7,274,018 (Sep. 25, 2007) and P. Adamee, et. al. “Charged Particle Beam Apparatus and Method for Operating the Same”, U.S. Pat. No. 7,045,781 (May 16, 2006) describe a charged particle beam apparatus configured for serial and/or parallel imaging of an object. K. Hiramoto, et. al. “Ion Beam Therapy System and its Couch Positioning System”, U.S. Pat. No. 7,193,227 (Mar. 20, 2007) describe an ion beam therapy system having an X-ray imaging system moving in conjunction with a rotating gantry. C. Maurer, et. al. “Apparatus and Method for Registration of Images to Physical Space Using a Weighted Combination of Points and Surfaces”, U.S. Pat. No. 6,560,354 (May 6, 2003) described a process of X-ray computed tomography registered to physical measurements taken on the patient's body, where different body parts are given different weights. Weights are used in an iterative registration process to determine a rigid body transformation process, where the transformation function is used to assist surgical or stereotactic procedures. M. Blair, et. al. “Proton Beam Digital Imaging System”, U.S. Pat. No. 5,825,845 (Oct. 20, 1998) describe a proton beam digital imaging system having an X-ray source that is movable into a treatment beam line that can produce an X-ray beam through a region of the body. By comparison of the relative positions of the center of the beam in the patient orientation image and the isocentre in the master prescription image with respect to selected monuments, the amount and direction of movement of the patient to make the best beam center correspond to the target isocentre is determined. S. Nishihara, et. al. “Therapeutic Apparatus”, U.S. Pat. No. 5,039,867 (Aug. 13, 1991) describe a method and apparatus for positioning a therapeutic beam in which a first distance is determined on the basis of a first image, a second distance is determined on the basis of a second image, and the patient is moved to a therapy beam irradiation position on the basis of the first and second distances. Problem There exists in the art of charged particle irradiation therapy a need to know and/or control position, direction, energy, intensity, and/or cross-sectional area or shape of the charged particle beam relative to a patient position, where the controls are individualized to individual patients and/or individual tumor shapes. The invention comprises a motion control system used to control a charged particle beam shape and direction relative to a patient and/or imaging system. Elements and steps in the figures are illustrated for simplicity and clarity and have not necessarily been rendered according to any particular sequence. For example, steps that are performed concurrently or in different order are illustrated in the figures to help improve understanding of embodiments of the present invention. The invention relates generally to control of a charged particle beam shape and direction relative to a patient position and/or an imaging surface, such as a scintillation plate of a tomography system. In one embodiment, multiple linked control stations are used to control position of elements of a beam transport system, nozzle, and/or patient specific beam shaping element relative to a dynamically controlled patient position and/or an imaging surface, element, or system. In another embodiment, a tomography system is optionally used in combination with a charged particle cancer therapy system. Optionally and preferably, a common injector, accelerator, and beam transport system is used for both charged particle based tomographic imaging and charged particle cancer therapy. In one case, an output nozzle of the beam transport system is positioned with a gantry system while the gantry system and/or a patient support maintains a scintillation plate of the tomography system on the opposite side of the patient from the output nozzle. In another example, a charged particle state determination system, of a cancer therapy system or tomographic imaging system, uses one or more coated layers in conjunction with a scintillation detector or a tomographic imaging system at time of tumor and surrounding tissue sample mapping and/or at time of tumor treatment, such as to determine an input vector of the charged particle beam into a patient and/or an output vector of the charged particle beam from the patient. In another example, the charged particle tomography apparatus is used in combination with a charged particle cancer therapy system. For example, tomographic imaging of a cancerous tumor is performed using charged particles generated with an injector, accelerator, and guided with a delivery system. The cancer therapy system uses the same injector, accelerator, and guided delivery system in delivering charged particles to the cancerous tumor. For example, the tomography apparatus and cancer therapy system use a common raster beam method and apparatus for treatment of solid cancers. More particularly, the invention comprises a multi-axis and/or multi-field raster beam charged particle accelerator used in: (1) tomography and (2) cancer therapy. Optionally, the system independently controls patient translation position, patient rotation position, two-dimensional beam trajectory, delivered radiation beam energy, delivered radiation beam intensity, beam velocity, timing of charged particle delivery, and/or distribution of radiation striking healthy tissue. The system operates in conjunction with a negative ion beam source, synchrotron, patient positioning, imaging, and/or targeting method and apparatus to deliver an effective and uniform dose of radiation to a tumor while distributing radiation striking healthy tissue. In another embodiment, a treatment delivery control system (TDCS) or main controller is used to control multiple aspects of the cancer therapy system, including one or more of: an imaging system, such as a CT or PET; a positioner, such as a couch or patient interface module; an injector or injection system; a radio-frequency quadrupole system; a ring accelerator or synchrotron; an extraction system; an irradiation plan; and a display system. The TDCS is preferably a control system for automated cancer therapy once the patient is positioned. The TDCS integrates output of one or more of the below described cancer therapy system elements with inputs of one or more of the below described cancer therapy system elements. More generally, the TDCS controls or manages input and/or output of imaging, an irradiation plan, and charged particle delivery. In yet another embodiment, one or more trays are inserted into the positively charged particle beam path, such as at or near the exit port of a gantry nozzle in close proximity to the patient. Each tray holds an insert, such as a patient specific insert for controlling the energy, focus depth, and/or shape of the charged particle beam. Examples of inserts include a range shifter, a compensator, an aperture, a ridge filter, and a blank. Optionally and preferably, each tray communicates a held and positioned insert to a main controller of the charged particle cancer therapy system. The trays optionally hold one or more of the imaging sheets configured to emit light upon transmission of the charged particle beam through a corresponding localized position of the one or more imaging sheets. Charged Particle Beam Therapy Throughout this document, a charged particle beam therapy system, such as a proton beam, hydrogen ion beam, or carbon ion beam, is described. Herein, the charged particle beam therapy system is described using a proton beam. However, the aspects taught and described in terms of a proton beam are not intended to be limiting to that of a proton beam and are illustrative of a charged particle beam system, a positively charged beam system, and/or a multiply charged particle beam system, such as C4+ or C6+. Any of the techniques described herein are equally applicable to any charged particle beam system. Referring now to FIG. 1A, a charged particle beam system 100 is illustrated. The charged particle beam preferably comprises a number of subsystems including any of: a main controller 110; an injection system 120; a synchrotron 130 that typically includes: (1) an accelerator system 132 and (2) an internal or connected extraction system 134; a beam transport system 135; a scanning/targeting/delivery system 140; a patient interface module 150; a display system 160; and/or an imaging system 170. An exemplary method of use of the charged particle beam system 100 is provided. The main controller 110 controls one or more of the subsystems to accurately and precisely deliver protons to a tumor of a patient. For example, the main controller 110 obtains an image, such as a portion of a body and/or of a tumor, from the imaging system 170. The main controller 110 also obtains position and/or timing information from the patient interface module 150. The main controller 110 optionally controls the injection system 120 to inject a proton into a synchrotron 130. The synchrotron typically contains at least an accelerator system 132 and an extraction system 134. The main controller 110 preferably controls the proton beam within the accelerator system, such as by controlling speed, trajectory, and timing of the proton beam. The main controller then controls extraction of a proton beam from the accelerator through the extraction system 134. For example, the controller controls timing, energy, and/or intensity of the extracted beam. The controller 110 also preferably controls targeting of the proton beam through the scanning/targeting/delivery system 140 to the patient interface module 150. One or more components of the patient interface module 150, such as translational and rotational position of the patient, are preferably controlled by the main controller 110. Further, display elements of the display system 160 are preferably controlled via the main controller 110. Displays, such as display screens, are typically provided to one or more operators and/or to one or more patients. In one embodiment, the main controller 110 times the delivery of the proton beam from all systems, such that protons are delivered in an optimal therapeutic manner to the tumor of the patient. Herein, the main controller 110 refers to a single system controlling the charged particle beam system 100, to a single controller controlling a plurality of subsystems controlling the charged particle beam system 100, or to a plurality of individual controllers controlling one or more sub-systems of the charged particle beam system 100. Referring now to FIG. 12B, a first example of the internal pendant 1218 is provided. In this example, in place of and/or in conjunction with a particular button, such as a first button 1270 and/or a second button 1280, moving or selecting a particular element, processes are optionally described, displayed, and/or selected within a flow process control unit 1260 of the internal pendant 1218. For example, one or more display screens and/or printed elements describe a set of processes, such as a first process 1261, a second process 1263, a third process 1265, and a fourth process 1267 and are selected through a touch screen selection process or via a selection button, such as a corresponding first selector 1262, second selector 1264, third selector 1266, and fourth selector 1268. Referring now to FIG. 1B, an example of a charged particle cancer therapy system 100 is provided. A main controller receives input from one, two, three, or four of a respiration monitoring and/or controlling controller 180, a beam controller 185, a rotation controller 147, and/or a timing to a time period in a respiration cycle controller 148. The beam controller 185 preferably includes one or more or a beam energy controller 182, the beam intensity controller 340, a beam velocity controller 186, and/or a horizontal/vertical beam positioning controller 188. The main controller 110 controls any element of the injection system 120; the synchrotron 130; the scanning/targeting/delivery system 140; the patient interface module 150; the display system 160; and/or the imaging system 170. For example, the respiration monitoring/controlling controller 180 controls any element or method associated with the respiration of the patient; the beam controller 185 controls any of the elements controlling acceleration and/or extraction of the charged particle beam; the rotation controller 147 controls any element associated with rotation of the patient 830 or gantry; and the timing to a period in respiration cycle controller 148 controls any aspects affecting delivery time of the charged particle beam to the patient. As a further example, the beam controller 185 optionally controls any magnetic and/or electric field about any magnet in the charged particle cancer therapy system 100. One or more beam state sensors 190 sense position, direction, intensity, and/or energy of the charged particles at one or more positions in the charged particle beam path. A tomography system 700, described infra, is optionally used to monitor intensity and/or position of the charged particle beam. Referring now to FIG. 2, an illustrative exemplary embodiment of one version of the charged particle beam system 100 is provided. The number, position, and described type of components is illustrative and non-limiting in nature. In the illustrated embodiment, the injection system 120 or ion source or charged particle beam source generates protons. The injection system 120 optionally includes one or more of: a negative ion beam source, an ion beam focusing lens, and a tandem accelerator. The protons are delivered into a vacuum tube that runs into, through, and out of the synchrotron. The generated protons are delivered along an initial path 262. Focusing magnets 230, such as quadrupole magnets or injection quadrupole magnets, are used to focus the proton beam path. A quadrupole magnet is a focusing magnet. An injector bending magnet 232 bends the proton beam toward a plane of the synchrotron 130. The focused protons having an initial energy are introduced into an injector magnet 240, which is preferably an injection Lamberson magnet. Typically, the initial beam path 262 is along an axis off of, such as above, a circulating plane of the synchrotron 130. The injector bending magnet 232 and injector magnet 240 combine to move the protons into the synchrotron 130. Main bending magnets, dipole magnets, turning magnets, or circulating magnets 250 are used to turn the protons along a circulating beam path 264. A dipole magnet is a bending magnet. The main bending magnets 250 bend the initial beam path 262 into a circulating beam path 264. In this example, the main bending magnets 250 or circulating magnets are represented as four sets of four magnets to maintain the circulating beam path 264 into a stable circulating beam path. However, any number of magnets or sets of magnets are optionally used to move the protons around a single orbit in the circulation process. The protons pass through an accelerator 270. The accelerator accelerates the protons in the circulating beam path 264. As the protons are accelerated, the fields applied by the magnets are increased. Particularly, the speed of the protons achieved by the accelerator 270 are synchronized with magnetic fields of the main bending magnets 250 or circulating magnets to maintain stable circulation of the protons about a central point or region 280 of the synchrotron. At separate points in time the accelerator 270/main bending magnet 250 combination is used to accelerate and/or decelerate the circulating protons while maintaining the protons in the circulating path or orbit. An extraction element of an inflector/deflector system is used in combination with a Lamberson extraction magnet 292 to remove protons from their circulating beam path 264 within the synchrotron 130. One example of a deflector component is a Lamberson magnet. Typically the deflector moves the protons from the circulating plane to an axis off of the circulating plane, such as above the circulating plane. Extracted protons are preferably directed and/or focused using an extraction bending magnet 237 and extraction focusing magnets 235, such as quadrupole magnets along a positively charged particle beam transport path 268 in a beam transport system 135, such as a beam path or proton beam path, into the scanning/targeting/delivery system 140. Two components of a scanning system 140 or targeting system typically include a first axis control 142, such as a vertical control, and a second axis control 144, such as a horizontal control. In one embodiment, the first axis control 142 allows for about 100 mm of vertical or y-axis scanning of the proton beam 268 and the second axis control 144 allows for about 700 mm of horizontal or x-axis scanning of the proton beam 268. A nozzle system 146 is used for imaging the proton beam, for defining shape of the proton beam, and/or as a vacuum barrier between the low pressure beam path of the synchrotron and the atmosphere. Protons are delivered with control to the patient interface module 150 and to a tumor of a patient. All of the above listed elements are optional and may be used in various permutations and combinations. Proton Beam Extraction Referring now to FIG. 3, both: (1) an exemplary proton beam extraction system 300 from the synchrotron 130 and (2) a charged particle beam intensity control system 305 are illustrated. For clarity, FIG. 3 removes elements represented in FIG. 2, such as the turning magnets, which allows for greater clarity of presentation of the proton beam path as a function of time. Generally, protons are extracted from the synchrotron 130 by slowing the protons. As described, supra, the protons were initially accelerated in a circulating path, which is maintained with a plurality of main bending magnets 250. The circulating path is referred to herein as an original central beamline 264. The protons repeatedly cycle around a central point in the synchrotron 280. The proton path traverses through a radio frequency (RF) cavity system 310. To initiate extraction, an RF field is applied across a first blade 312 and a second blade 314, in the RF cavity system 310. The first blade 312 and second blade 314 are referred to herein as a first pair of blades. In the proton extraction process, an RF voltage is applied across the first pair of blades, where the first blade 312 of the first pair of blades is on one side of the circulating proton beam path 264 and the second blade 314 of the first pair of blades is on an opposite side of the circulating proton beam path 264. The applied RF field applies energy to the circulating charged-particle beam. The applied RF field alters the orbiting or circulating beam path slightly of the protons from the original central beamline 264 to an altered circulating beam path 265. Upon a second pass of the protons through the RF cavity system, the RF field further moves the protons off of the original proton beamline 264. For example, if the original beamline is considered as a circular path, then the altered beamline is slightly elliptical. The frequency of the applied RF field is timed to apply outward or inward movement to a given band of protons circulating in the synchrotron accelerator. Orbits of the protons are slightly more off axis compared to the original circulating beam path 264. Successive passes of the protons through the RF cavity system are forced further and further from the original central beamline 264 by altering the direction and/or intensity of the RF field with each successive pass of the proton beam through the RF field. Timing of application of the RF field and/or frequency of the RF field is related to the circulating charged particles circulation pathlength in the synchrotron 130 and the velocity of the charged particles so that the applied RF field has a period, with a peak-to-peak time period, equal to a period of time of beam circulation in the synchrotron 130 about the center 280 or an integer multiple of the time period of beam circulation about the center 280 of the synchrotron 130. Alternatively, the time period of beam circulation about the center 280 of the synchrotron 130 is an integer multiple of the RF period time. The RF period is optionally used to calculated the velocity of the charged particles, which relates directly to the energy of the circulating charged particles. The RF voltage is frequency modulated at a frequency about equal to the period of one proton cycling around the synchrotron for one revolution or at a frequency than is an integral multiplier of the period of one proton cycling about the synchrotron. The applied RF frequency modulated voltage excites a betatron oscillation. For example, the oscillation is a sine wave motion of the protons. The process of timing the RF field to a given proton beam within the RF cavity system is repeated thousands of times with each successive pass of the protons being moved approximately one micrometer further off of the original central beamline 264. For clarity, the approximately 1000 changing beam paths with each successive path of a given band of protons through the RF field are illustrated as the altered beam path 265. The RF time period is process is known, thus energy of the charged particles at time of hitting the extraction material or material 330, described infra, is known. With a sufficient sine wave betatron amplitude, the altered circulating beam path 265 touches and/or traverses a material 330, such as a foil or a sheet of foil. The foil is preferably a lightweight material, such as beryllium, a lithium hydride, a carbon sheet, or a material having low nuclear charge components. Herein, a material of low nuclear charge is a material composed of atoms consisting essentially of atoms having six or fewer protons. The foil is preferably about 10 to 150 microns thick, is more preferably about 30 to 100 microns thick, and is still more preferably about 40 to 60 microns thick. In one example, the foil is beryllium with a thickness of about 50 microns. When the protons traverse through the foil, energy of the protons is lost and the speed of the protons is reduced. Typically, a current is also generated, described infra. Protons moving at the slower speed travel in the synchrotron with a reduced radius of curvature 266 compared to either the original central beamline 264 or the altered circulating path 265. The reduced radius of curvature 266 path is also referred to herein as a path having a smaller diameter of trajectory or a path having protons with reduced energy. The reduced radius of curvature 266 is typically about two millimeters less than a radius of curvature of the last pass of the protons along the altered proton beam path 265. The thickness of the material 330 is optionally adjusted to create a change in the radius of curvature, such as about ½, 1, 2, 3, or 4 mm less than the last pass of the protons 265 or original radius of curvature 264. The reduction in velocity of the charged particles transmitting through the material 330 is calculable, such as by using the pathlength of the betatron oscillating charged particle beam through the material 330 and/or using the density of the material 330. Protons moving with the smaller radius of curvature travel between a second pair of blades. In one case, the second pair of blades is physically distinct and/or is separated from the first pair of blades. In a second case, one of the first pair of blades is also a member of the second pair of blades. For example, the second pair of blades is the second blade 314 and a third blade 316 in the RF cavity system 310. A high voltage DC signal, such as about 1 to 5 kV, is then applied across the second pair of blades, which directs the protons out of the synchrotron through an extraction magnet 292, such as a Lamberson extraction magnet, into a transport path 268. Control of acceleration of the charged particle beam path in the synchrotron with the accelerator and/or applied fields of the turning magnets in combination with the above described extraction system allows for control of the intensity of the extracted proton beam, where intensity is a proton flux per unit time or the number of protons extracted as a function of time. For example, when a current is measured beyond a threshold, the RF field modulation in the RF cavity system is terminated or reinitiated to establish a subsequent cycle of proton beam extraction. This process is repeated to yield many cycles of proton beam extraction from the synchrotron accelerator. In another embodiment, instead of moving the charged particles to the material 330, the material 330 is mechanically moved to the circulating charged particles. Particularly, the material 330 is mechanically or electromechanically translated into the path of the circulating charged particles to induce the extraction process, described supra. In this case, the velocity or energy of the circulating charged particle beam is calculable using the pathlength of the beam path about the center 280 of the synchrotron 130 and from the force applied by the bending magnets 250. In either case, because the extraction system does not depend on any change in magnetic field properties, it allows the synchrotron to continue to operate in acceleration or deceleration mode during the extraction process. Stated differently, the extraction process does not interfere with synchrotron acceleration. In stark contrast, traditional extraction systems introduce a new magnetic field, such as via a hexapole, during the extraction process. More particularly, traditional synchrotrons have a magnet, such as a hexapole magnet, that is off during an acceleration stage. During the extraction phase, the hexapole magnetic field is introduced to the circulating path of the synchrotron. The introduction of the magnetic field necessitates two distinct modes, an acceleration mode and an extraction mode, which are mutually exclusive in time. The herein described system allows for acceleration and/or deceleration of the proton during the extraction step and tumor treatment without the use of a newly introduced magnetic field, such as by a hexapole magnet. Charged Particle Beam Intensity Control Control of applied field, such as a radio-frequency (RF) field, frequency and magnitude in the RF cavity system 310 allows for intensity control of the extracted proton beam, where intensity is extracted proton flux per unit time or the number of protons extracted as a function of time. Still referring FIG. 3, the intensity control system 305 is further described. In this example, an intensity control feedback loop is added to the extraction system, described supra. When protons in the proton beam hit the material 330 electrons are given off from the material 330 resulting in a current. The resulting current is converted to a voltage and is used as part of an ion beam intensity monitoring system or as part of an ion beam feedback loop for controlling beam intensity. The voltage is optionally measured and sent to the main controller 110 or to an intensity controller subsystem 340, which is preferably in communication or under the direction of the main controller 110. More particularly, when protons in the charged particle beam path pass through the material 330, some of the protons lose a small fraction of their energy, such as about one-tenth of a percent, which results in a secondary electron. That is, protons in the charged particle beam push some electrons when passing through material 330 giving the electrons enough energy to cause secondary emission. The resulting electron flow results in a current or signal that is proportional to the number of protons going through the target or extraction material 330. The resulting current is preferably converted to voltage and amplified. The resulting signal is referred to as a measured intensity signal. The amplified signal or measured intensity signal resulting from the protons passing through the material 330 is optionally used in monitoring the intensity of the extracted protons and is preferably used in controlling the intensity of the extracted protons. For example, the measured intensity signal is compared to a goal signal, which is predetermined in an irradiation of the tumor plan. The difference between the measured intensity signal and the planned for goal signal is calculated. The difference is used as a control to the RF generator. Hence, the measured flow of current resulting from the protons passing through the material 330 is used as a control in the RF generator to increase or decrease the number of protons undergoing betatron oscillation and striking the material 330. Hence, the voltage determined off of the material 330 is used as a measure of the orbital path and is used as a feedback control to control the RF cavity system. In one example, the intensity controller subsystem 340 preferably additionally receives input from: (1) a detector 350, which provides a reading of the actual intensity of the proton beam and/or (2) an irradiation plan 360. The irradiation plan provides the desired intensity of the proton beam for each x, y, energy, and/or rotational position of the patient/tumor as a function of time. Thus, the intensity controller 340 receives the desired intensity from the irradiation plan 350, the actual intensity from the detector 350 and/or a measure of intensity from the material 330, and adjusts the amplitude and/or the duration of application of the applied radio-frequency field in the RF cavity system 310 to yield an intensity of the proton beam that matches the desired intensity from the irradiation plan 360. As described, supra, the protons striking the material 330 is a step in the extraction of the protons from the synchrotron 130. Hence, the measured intensity signal is used to change the number of protons per unit time being extracted, which is referred to as intensity of the proton beam. The intensity of the proton beam is thus under algorithm control. Further, the intensity of the proton beam is controlled separately from the velocity of the protons in the synchrotron 130. Hence, intensity of the protons extracted and the energy of the protons extracted are independently variable. Still further, the intensity of the extracted protons is controllably variable while scanning the charged particles beam in the tumor from one voxel to an adjacent voxel as a separate hexapole and separated time period from acceleration and/or treatment is not required, as described supra. For example, protons initially move at an equilibrium trajectory in the synchrotron 130. An RF field is used to excite or move the protons into a betatron oscillation. In one case, the frequency of the protons orbit is about 10 MHz. In one example, in about one millisecond or after about 10,000 orbits, the first protons hit an outer edge of the target material 130. The specific frequency is dependent upon the period of the orbit. Upon hitting the material 130, the protons push electrons through the foil to produce a current. The current is converted to voltage and amplified to yield a measured intensity signal. The measured intensity signal is used as a feedback input to control the applied RF magnitude or RF field. An energy beam sensor, described infra, is optionally used as a feedback control to the RF field frequency or RF field of the RF field extraction system 310 to dynamically control, modify, and/or alter the delivered charge particle beam energy, such as in a continuous pencil beam scanning system operating to treat tumor voxels without alternating between an extraction phase and a treatment phase. Preferably, the measured intensity signal is compared to a target signal and a measure of the difference between the measured intensity signal and target signal is used to adjust the applied RF field in the RF cavity system 310 in the extraction system to control the intensity of the protons in the extraction step. Stated again, the signal resulting from the protons striking and/or passing through the material 130 is used as an input in RF field modulation. An increase in the magnitude of the RF modulation results in protons hitting the foil or material 130 sooner. By increasing the RF, more protons are pushed into the foil, which results in an increased intensity, or more protons per unit time, of protons extracted from the synchrotron 130. In another example, a detector 350 external to the synchrotron 130 is used to determine the flux of protons extracted from the synchrotron and a signal from the external detector is used to alter the RF field, RF intensity, RF amplitude, and/or RF modulation in the RF cavity system 310. Here the external detector generates an external signal, which is used in a manner similar to the measured intensity signal, described in the preceding paragraphs. Preferably, an algorithm or irradiation plan 360 is used as an input to the intensity controller 340, which controls the RF field modulation by directing the RF signal in the betatron oscillation generation in the RF cavity system 310. The irradiation plan 360 preferably includes the desired intensity of the charged particle beam as a function of time and/or energy of the charged particle beam as a function of time, for each patient rotation position, and/or for each x-, y-position of the charged particle beam. In yet another example, when a current from material 330 resulting from protons passing through or hitting material is measured beyond a threshold, the RF field modulation in the RF cavity system is terminated or reinitiated to establish a subsequent cycle of proton beam extraction. This process is repeated to yield many cycles of proton beam extraction from the synchrotron accelerator. In still yet another embodiment, intensity modulation of the extracted proton beam is controlled by the main controller 110. The main controller 110 optionally and/or additionally controls timing of extraction of the charged particle beam and energy of the extracted proton beam. The benefits of the system include a multi-dimensional scanning system. Particularly, the system allows independence in: (1) energy of the protons extracted and (2) intensity of the protons extracted. That is, energy of the protons extracted is controlled by an energy control system and an intensity control system controls the intensity of the extracted protons. The energy control system and intensity control system are optionally independently controlled. Preferably, the main controller 110 controls the energy control system and the main controller 110 simultaneously controls the intensity control system to yield an extracted proton beam with controlled energy and controlled intensity where the controlled energy and controlled intensity are independently variable and/or continually available as a separate extraction phase and acceleration phase are not required, as described supra. Thus the irradiation spot hitting the tumor is under independent control of: time; energy; intensity; x-axis position, where the x-axis represents horizontal movement of the proton beam relative to the patient, and y-axis position, where the y-axis represents vertical movement of the proton beam relative to the patient. In addition, the patient is optionally independently translated and/or rotated relative to a translational axis of the proton beam at the same time. Beam Transport The beam transport system 135 is used to move the charged particles from the accelerator to the patient, such as via a nozzle in a gantry, described infra. Charged Particle Energy The beam transport system 135 optionally includes means for determining an energy of the charged particles in the charged particle beam. For example, an energy of the charged particle beam is determined via calculation, such as via equation 1, using knowledge of a magnet geometry and applied magnetic field to determine mass and/or energy. Referring now to equation 1, for a known magnet geometry, charge, q, and magnetic field, B, the Larmor radius, ρL, or magnet bend radius is defined as: ρ L = v ⊥ Ω c = 2 Em qB ( eq . 1 ) where: v⊥ is the ion velocity perpendicular to the magnetic field, Ωc is the cyclotron frequency, q is the charge of the ion, B is the magnetic field, m is the mass of the charge particle, and E is the charged particle energy. Solving for the charged particle energy yields equation 2. E = ( ρ L qB ) 2 2 m ( eq . 2 ) Thus, an energy of the charged particle in the charged particle beam in the beam transport system 135 is calculable from the know magnet geometry, known or measured magnetic field, charged particle mass, charged particle charge, and the known magnet bend radius, which is proportional to and/or equivalent to the Larmor radius. Nozzle After extraction from the synchrotron 130 and transport of the charged particle beam along the proton beam path 268 in the beam transport system 135, the charged particle beam exits through the nozzle system 146. In one example, the nozzle system includes a nozzle foil covering an end of the nozzle system 146 or a cross-sectional area within the nozzle system forming a vacuum seal. The nozzle system includes a nozzle that expands in x/y-cross-sectional area along the z-axis of the proton beam path 268 to allow the proton beam 268 to be scanned along the x-axis and y-axis by the vertical control element and horizontal control element, respectively. The nozzle foil is preferably mechanically supported by the outer edges of an exit port of the nozzle 146. An example of a nozzle foil is a sheet of about 0.1 inch thick aluminum foil. Generally, the nozzle foil separates atmosphere pressures on the patient side of the nozzle foil from the low pressure region, such as about 10−5 to 10−7 torr region, on the synchrotron 130 side of the nozzle foil. The low pressure region is maintained to reduce scattering of the circulating charged particle beam in the synchrotron. Herein, the exit foil of the nozzle is optionally the first sheet 760 of the charged particle beam state determination system 750, described infra. Charged Particle Control Referring now to FIG. 4A, FIG. 4B, FIG. 5, FIG. 6A, and FIG. 6B, a charged particle beam control system is described where one or more patient specific beam control assemblies are removably inserted into the charged particle beam path proximate the nozzle of the charged particle cancer therapy system 100, where the patient specific beam control assemblies adjust the beam energy, diameter, cross-sectional shape, focal point, and/or beam state of the charged particle beam to properly couple energy of the charged particle beam to the individual's specific tumor. Beam Control Tray Referring now to FIG. 4A and FIG. 4B, a beam control tray assembly 400 is illustrated in a top view and side view, respectively. The beam control tray assembly 400 optionally comprises any of a tray frame 410, a tray aperture 412, a tray handle 420, a tray connector/communicator 430, and means for holding a patient specific tray insert 510, described infra. Generally, the beam control tray assembly 400 is used to: (1) hold the patient specific tray insert 510 in a rigid location relative to the beam control tray 400, (2) electronically identify the held patient specific tray insert 510 to the main controller 110, and (3) removably insert the patient specific tray insert 510 into an accurate and precise fixed location relative to the charged particle beam, such as the proton beam path 268 at the nozzle of the charged particle cancer therapy system 100. For clarity of presentation and without loss of generality, the means for holding the patient specific tray insert 510 in the tray frame 410 of the beam control tray assembly 400 is illustrated as a set of recessed set screws 415. However, the means for holding the patient specific tray insert 510 relative to the rest of the beam control tray assembly 400 is optionally any mechanical and/or electromechanical positioning element, such as a latch, clamp, fastener, clip, slide, strap, or the like. Generally, the means for holding the patient specific tray insert 510 in the beam control tray 400 fixes the tray insert and tray frame relative to one another even when rotated along and/or around multiple axes, such as when attached to a charged particle cancer therapy system 100 dynamic gantry nozzle 610 or gantry nozzle, which is an optional element of the nozzle system 146, that moves in three-dimensional space relative to a fixed point in the beamline, proton beam path 268, and/or a given patient position. As illustrated in FIG. 4A and FIG. 4B, the recessed set screws 415 fix the patient specific tray insert 510 into the aperture 412 of the tray frame 410. The tray frame 410 is illustrated as circumferentially surrounding the patient specific tray insert 510, which aids in structural stability of the beam control tray assembly 400. However, generally the tray frame 410 is of any geometry that forms a stable beam control tray assembly 400. Still referring to FIG. 4A and now referring to FIG. 5 and FIG. 6A, the optional tray handle 420 is used to manually insert/retract the beam control tray assembly 400 into a receiving element of the gantry nozzle or dynamic gantry nozzle 610. While the beam control tray assembly 400 is optionally inserted into the charged particle beam path 268 at any point after extraction from the synchrotron 130, the beam control tray assembly 400 is preferably inserted into the positively charged particle beam proximate the dynamic gantry nozzle 610 as control of the beam shape is preferably done with little space for the beam shape to defocus before striking the tumor. Optionally, insertion and/or retraction of the beam control tray assembly 400 is semi-automated, such as in a manner of a digital-video disk player receiving a digital-video disk, with a selected auto load and/or a selected auto unload feature. Patient Specific Tray Insert Referring again to FIG. 5, a system of assembling trays 500 is described. The beam control tray assembly 400 optionally and preferably has interchangeable patient specific tray inserts 510, such as a range shifter insert 511, a patient specific ridge filter insert 512, an aperture insert 513, a compensator insert 514, or a blank insert 515. As described, supra, any of the range shifter insert 511, the patient specific ridge filter insert 512, the aperture insert 513, the compensator insert 514, or the blank insert 515 after insertion into the tray frame 410 are inserted as the beam control tray assembly 400 into the positively charged particle beam path 268, such as proximate the dynamic gantry nozzle 610. Still referring to FIG. 5, the patient specific tray inserts 510 are further described. The patient specific tray inserts comprise a combination of any of: (1) a standardized beam control insert and (2) a patient specific beam control insert. For example, the range shifter insert or 511 or compensator insert 514 used to control the depth of penetration of the charged particle beam into the patient is optionally: (a) a standard thickness of a beam slowing material, such as a first thickness of Lucite, (b) one member of a set of members of varying thicknesses and/or densities where each member of the set of members slows the charged particles in the beam path by a known amount, or (c) is a material with a density and thickness designed to slow the charged particles by a customized amount for the individual patient being treated, based on the depth of the individual's tumor in the tissue, the thickness of intervening tissue, and/or the density of intervening bone/tissue. Similarly, the ridge filter insert 512 used to change the focal point or shape of the beam as a function of depth is optionally: (1) selected from a set of ridge filters where different members of the set of ridge filters yield different focal depths or (2) customized for treatment of the individual's tumor based on position of the tumor in the tissue of the individual. Similarly, the aperture insert is: (1) optionally selected from a set of aperture shapes or (2) is a customized individual aperture insert 513 designed for the specific shape of the individual's tumor. The blank insert 515 is an open slot, but serves the purpose of identifying slot occupancy, as described infra. Slot Occupancy/Identification Referring again to FIG. 4A, FIG. 4B, and FIG. 5, occupancy and identification of the particular patient specific tray insert 510 into the beam control tray assembly 400 is described. Generally, the beam control tray assembly 400 optionally contains means for identifying, to the main controller 110 and/or a treatment delivery control system described infra, the specific patient tray insert 510 and its location in the charged particle beam path 268. First, the particular tray insert is optionally labeled and/or communicated to the beam control tray assembly 400 or directly to the main controller 110. Second, the beam control tray assembly 400 optionally communicates the tray type and/or tray insert to the main controller 110. In various embodiments, communication of the particular tray insert to the main controller 110 is performed: (1) directly from the tray insert, (2) from the tray insert 510 to the tray assembly 400 and subsequently to the main controller 110, and/or (3) directly from the tray assembly 400. Generally, communication is performed wirelessly and/or via an established electromechanical link. Identification is optionally performed using a radio-frequency identification label, use of a barcode, or the like, and/or via operator input. Examples are provided to further clarify identification of the patient specific tray insert 510 in a given beam control tray assembly 400 to the main controller. In a first example, one or more of the patient specific tray inserts 510, such as the range shifter insert 511, the patient specific ridge filter insert 512, the aperture insert 513, the compensator insert 514, or the blank insert 515 include an identifier 520 and/or and a first electromechanical identifier plug 530. The identifier 520 is optionally a label, a radio-frequency identification tag, a barcode, a 2-dimensional bar-code, a matrix-code, or the like. The first electromechanical identifier plug 530 optionally includes memory programmed with the particular patient specific tray insert information and a connector used to communicate the information to the beam control tray assembly 400 and/or to the main controller 110. As illustrated in FIG. 5, the first electromechanical identifier plug 530 affixed to the patient specific tray insert 510 plugs into a second electromechanical identifier plug, such as the tray connector/communicator 430, of the beam control tray assembly 400, which is described infra. In a second example, the beam control tray assembly 400 uses the second electromechanical identifier plug to send occupancy, position, and/or identification information related to the type of tray insert or the patient specific tray insert 510 associated with the beam control tray assembly to the main controller 110. For example, a first tray assembly is configured with a first tray insert and a second tray assembly is configured with a second tray insert. The first tray assembly sends information to the main controller 110 that the first tray assembly holds the first tray insert, such as a range shifter, and the second tray assembly sends information to the main controller 110 that the second tray assembly holds the second tray insert, such as an aperture. The second electromechanical identifier plug optionally contains programmable memory for the operator to input the specific tray insert type, a selection switch for the operator to select the tray insert type, and/or an electromechanical connection to the main controller. The second electromechanical identifier plug associated with the beam control tray assembly 400 is optionally used without use of the first electromechanical identifier plug 530 associated with the tray insert 510. In a third example, one type of tray connector/communicator 430 is used for each type of patient specific tray insert 510. For example, a first connector/communicator type is used for holding a range shifter insert 511, while a second, third, fourth, and fifth connector/communicator type is used for trays respectively holding a patient specific ridge filter insert 512, an aperture insert 513, a compensator insert 514, or a blank insert 515. In one case, the tray communicates tray type with the main controller. In a second case, the tray communicates patient specific tray insert information with the main controller, such as an aperture identifier custom built for the individual patient being treated. Tray Insertion/Coupling Referring now to FIG. 6A and FIG. 6B a beam control insertion process 600 is described. The beam control insertion process 600 comprises: (1) insertion of the beam control tray assembly 400 and the associated patient specific tray insert 510 into the charged particle beam path 268 and/or dynamic gantry nozzle 610, such as into a tray assembly receiver 620 and (2) an optional partial or total retraction of beam of the tray assembly receiver 620 into the dynamic gantry nozzle 610. Referring now to FIG. 6A, insertion of one or more of the beam control tray assemblies 400 and the associated patient specific tray inserts 510 into the dynamic gantry nozzle 610 is further described. In FIG. 6A, three beam control tray assemblies, of a possible n tray assemblies, are illustrated, a first tray assembly 402, a second tray assembly 404, and a third tray assembly 406, where n is a positive integer of 1, 2, 3, 4, 5 or more. As illustrated, the first tray assembly 402 slides into a first receiving slot 403, the second tray assembly 404 slides into a second receiving slot 405, and the third tray assembly 406 slides into a third receiving slot 407. Generally, any tray optionally inserts into any slot or tray types are limited to particular slots through use of a mechanical, physical, positional, and/or steric constraints, such as a first tray type configured for a first insert type having a first size and a second tray type configured for a second insert type having a second distinct size at least ten percent different from the first size. Still referring to FIG. 6A, identification of individual tray inserts inserted into individual receiving slots is further described. As illustrated, sliding the first tray assembly 402 into the first receiving slot 403 connects the associated electromechanical connector/communicator 430 of the first tray assembly 402 to a first receptor 626. The electromechanical connector/communicator 430 of the first tray assembly communicates tray insert information of the first beam control tray assembly to the main controller 110 via the first receptor 626. Similarly, sliding the second tray assembly 404 into the second receiving slot 405 connects the associated electromechanical connector/communicator 430 of the second tray assembly 404 into a second receptor 627, which links communication of the associated electromechanical connector/communicator 430 with the main controller 110 via the second receptor 627, while a third receptor 628 connects to the electromechanical connected placed into the third slot 407. The non-wireless/direct connection is preferred due to the high radiation levels within the treatment room and the high shielding of the treatment room, which both hinder wireless communication. The connection of the communicator and the receptor is optionally of any configuration and/or orientation. Tray Receiver Assembly Retraction Referring again to FIG. 6A and FIG. 6B, retraction of the tray receiver assembly 620 relative to a nozzle end 612 of the dynamic gantry nozzle 610 is described. The tray receiver assembly 620 comprises a framework to hold one or more of the beam control tray assemblies 400 in one or more slots, such as through use of a first tray receiver assembly side 622 through which the beam control tray assemblies 400 are inserted and/or through use of a second tray receiver assembly side 624 used as a backstop, as illustrated holding the plugin receptors configured to receive associated tray connector/communicators 430, such as the first, second, and third receptors 626, 627, 628. Optionally, the tray receiver assembly 620 retracts partially or completely into the dynamic gantry nozzle 610 using a retraction mechanism 660 configured to alternatingly retract and extend the tray receiver assembly 620 relative to a nozzle end 612 of the gantry nozzle 610, such as along a first retraction track 662 and a second retraction track 664 using one or more motors and computer control. Optionally the tray receiver assembly 620 is partially or fully retracted when moving the gantry, nozzle, and/or gantry nozzle 610 to avoid physical constraints of movement, such as potential collision with another object in the patient treatment room. For clarity of presentation and without loss of generality, several examples of loading patient specific tray inserts into tray assemblies with subsequent insertion into an positively charged particle beam path proximate a gantry nozzle 610 are provided. In a first example, a single beam control tray assembly 400 is used to control the charged particle beam 268 in the charged particle cancer therapy system 100. In this example, a patient specific range shifter insert 511, which is custom fabricated for a patient, is loaded into a patient specific tray insert 510 to form a first tray assembly 402, where the first tray assembly 402 is loaded into the third receptor 628, which is fully retracted into the gantry nozzle 610. In a second example, two beam control assemblies 400 are used to control the charged particle beam 268 in the charged particle cancer therapy system 100. In this example, a patient specific ridge filter 512 is loaded into a first tray assembly 402, which is loaded into the second receptor 627 and a patient specific aperture 513 is loaded into a second tray assembly 404, which is loaded into the first receptor 626 and the two associated tray connector/communicators 430 using the first receptor 626 and second receptor 627 communicate to the main controller 110 the patient specific tray inserts 510. The tray receiver assembly 620 is subsequently retracted one slot so that the patient specific ridge filter 512 and the patient specific aperture reside outside of and at the nozzle end 612 of the gantry nozzle 610. In a third example, three beam control tray assemblies 400 are used, such as a range shifter 511 in a first tray inserted into the first receiving slot 403, a compensator in a second tray inserted into the second receiving slot 405, and an aperture in a third tray inserted into the third receiving slot 407. Generally, any patient specific tray insert 510 is inserted into a tray frame 410 to form a beam control tray assembly 400 inserted into any slot of the tray receiver assembly 620 and the tray assembly is not retracted or retracted any distance into the gantry nozzle 610. Tomography/Beam State In one embodiment, the charged particle tomography apparatus is used to image a tumor in a patient. As current beam position determination/verification is used in both tomography and cancer therapy treatment, for clarity of presentation and without limitation beam state determination is also addressed in this section. However, beam state determination is optionally used separately and without tomography. In another example, the charged particle tomography apparatus is used in combination with a charged particle cancer therapy system using common elements. For example, tomographic imaging of a cancerous tumor is performed using charged particles generated with an injector, accelerator, and guided with a delivery system that are part of the cancer therapy system, described supra. In various examples, the tomography imaging system is optionally simultaneously operational with a charged particle cancer therapy system using common elements, allows tomographic imaging with rotation of the patient, is operational on a patient in an upright, semi-upright, and/or horizontal position, is simultaneously operational with X-ray imaging, and/or allows use of adaptive charged particle cancer therapy. Further, the common tomography and cancer therapy apparatus elements are optionally operational in a multi-axis and/or multi-field raster beam mode. In conventional medical X-ray tomography, a sectional image through a body is made by moving one or both of an X-ray source and the X-ray film in opposite directions during the exposure. By modifying the direction and extent of the movement, operators can select different focal planes, which contain the structures of interest. More modern variations of tomography involve gathering projection data from multiple directions by moving the X-ray source and feeding the data into a tomographic reconstruction software algorithm processed by a computer. Herein, in stark contrast to known methods, the radiation source is a charged particle, such as a proton ion beam or a carbon ion beam. A proton beam is used herein to describe the tomography system, but the description applies to a heavier ion beam, such as a carbon ion beam. Further, in stark contrast to known techniques, herein the radiation source is preferably stationary while the patient is rotated. Referring now to FIG. 7, an example of a tomography apparatus is described and an example of a beam state determination is described. In this example, the tomography system 700 uses elements in common with the charged particle beam system 100, including elements of one or more of the injection system 120, accelerator 130, targeting/delivery system 140, patient interface module 150, display system 160, and/or imaging system 170, such as the X-ray imaging system. One or more scintillation plates, such as a scintillating plastic, are used to measure energy, intensity, and/or position of the charged particle beam. For instance, a scintillation plate 710 is positioned behind the patient 730 relative to the targeting/delivery system 140 elements, which is optionally used to measure intensity and/or position of the charged particle beam after transmitting through the patient. Optionally, a second scintillation plate or a charged particle induced photon emitting sheet, described infra, is positioned prior to the patient 730 relative to the targeting/delivery system 140 elements, which is optionally used to measure incident intensity and/or position of the charged particle beam prior to transmitting through the patient. The charged particle beam system 100 as described has proven operation at up to and including 330 MeV, which is sufficient to send protons through the body and into contact with the scintillation material. Particularly, 250 MeV to 330 MeV are used to pass the beam through a standard sized patient with a standard sized pathlength, such as through the chest. The intensity or count of protons hitting the plate as a function of position is used to create an image. The velocity or energy of the proton hitting the scintillation plate is also used in creation of an image of the tumor 720 and/or an image of the patient 730. The patient 730 is rotated about the y-axis and a new image is collected. Preferably, a new image is collected with about every one degree of rotation of the patient resulting in about 360 images that are combined into a tomogram using tomographic reconstruction software. The tomographic reconstruction software uses overlapping rotationally varied images in the reconstruction. Optionally, a new image is collected at about every 2, 3, 4, 5, 10, 15, 30, or 45 degrees of rotation of the patient. In one embodiment, a tomogram or an individual tomogram section image is collected at about the same time as cancer therapy occurs using the charged particle beam system 100. For example, a tomogram is collected and cancer therapy is subsequently performed: without the patient moving from the positioning systems, such as in a semi-vertical partial immobilization system, a sitting partial immobilization system, or the a laying position. In a second example, an individual tomogram slice is collected using a first cycle of the accelerator 130 and using a following cycle of the accelerator 130, the tumor 720 is irradiated, such as within about 1, 2, 5, 10, 15 or 30 seconds. In a third case, about 2, 3, 4, or 5 tomogram slices are collected using 1, 2, 3, 4, or more rotation positions of the patient 730 within about 5, 10, 15, 30, or 60 seconds of subsequent tumor irradiation therapy. In another embodiment, the independent control of the tomographic imaging process and X-ray collection process allows simultaneous single and/or multi-field collection of X-ray images and tomographic images easing interpretation of multiple images. Indeed, the X-ray and tomographic images are optionally overlaid to from a hybrid X-ray/proton beam tomographic image as the patient 730 is optionally in the same position for each image. In still another embodiment, the tomogram is collected with the patient 730 in the about the same position as when the patient's tumor is treated using subsequent irradiation therapy. For some tumors, the patient being positioned in the same upright or semi-upright position allows the tumor 720 to be separated from surrounding organs or tissue of the patient 730 better than in a laying position. Positioning of the scintillation plate 710 behind the patient 730 allows the tomographic imaging to occur while the patient is in the same upright or semi-upright position. The use of common elements in the tomographic imaging and in the charged particle cancer therapy allows benefits of the cancer therapy, described supra, to optionally be used with the tomographic imaging, such as proton beam x-axis control, proton beam y-axis control, control of proton beam energy, control of proton beam intensity, timing control of beam delivery to the patient, rotation control of the patient, and control of patient translation all in a raster beam mode of proton energy delivery. The use of a single proton or cation beamline for both imaging and treatment facilitates eases patient setup, reduces alignment uncertainties, reduces beam state uncertainties, and eases quality assurance. In yet still another embodiment, initially a three-dimensional tomographic proton based reference image is collected, such as with hundreds of individual rotation images of the tumor 720 and patient 730. Subsequently, just prior to proton treatment of the cancer, just a few 2-dimensional control tomographic images of the patient are collected, such as with a stationary patient or at just a few rotation positions, such as an image straight on to the patient, with the patient rotated about 45 degrees each way, and/or the patient rotated about 90 degrees each way about the y-axis. The individual control images are compared with the 3-dimensional reference image. An adaptive proton therapy is subsequently performed where: (1) the proton cancer therapy is not used for a given position based on the differences between the 3-dimensional reference image and one or more of the 2-dimensional control images and/or (2) the proton cancer therapy is modified in real time based on the differences between the 3-dimensional reference image and one or more of the 2-dimensional control images. Charged Particle State Determination/Verification/Photonic Monitoring Still referring to FIG. 7, the tomography system 700 is optionally used with a charged particle beam state determination system 750, optionally used as a charged particle verification system. The charged particle state determination system 750 optionally measures, determines, and/or verifies one of more of: (1) position of the charged particle beam, (2) direction of the charged particle beam, (3) intensity of the charged particle beam, (4) energy of the charged particle beam, and (5) a history of the charged particle beam. For clarity of presentation and without loss of generality, a description of the charged particle beam state determination system 750 is described and illustrated separately in FIG. 8 and FIG. 9A; however, as described herein elements of the charged particle beam state determination system 750 are optionally and preferably integrated into the nozzle system 146 and/or the tomography system 700 of the charged particle treatment system 100. More particularly, any element of the charged particle beam state determination system 750 is integrated into the nozzle system 146, the dynamic gantry nozzle 610, and/or tomography system 700, such as a surface of the scintillation plate 710 or a surface of a scintillation detector, plate, or system. The nozzle system 146 or the dynamic gantry nozzle 610 provides an outlet of the charged particle beam from the vacuum tube initiating at the injection system 120 and passing through the synchrotron 130 and beam transport system 135. Any plate, sheet, fluorophore, or detector of the charged particle beam state determination system is optionally integrated into the nozzle system 146. For example, an exit foil of the nozzle 610 is optionally a first sheet 760 of the charged particle beam state determination system 750 and a first coating 762 is optionally coated onto the exit foil, as illustrated in FIG. 7. Similarly, optionally a surface of the scintillation plate 710 is a support surface for a fourth coating 792, as illustrated in FIG. 7. The charged particle beam state determination system 750 is further described, infra. Referring now to FIG. 7, FIG. 8, and FIG. 9A, four sheets, a first sheet 760, a second sheet 770, a third sheet 780, and a fourth sheet 790 are used to illustrated detection sheets and/or photon emitting sheets upon transmittance of a charged particle beam. Each sheet is optionally coated with a photon emitter, such as a fluorophore, such as the first sheet 760 is optionally coated with a first coating 762. Without loss of generality and for clarity of presentation, the four sheets are each illustrated as units, where the light emitting layer is not illustrated. Thus, for example, the second sheet 770 optionally refers to a support sheet, a light emitting sheet, and/or a support sheet coated by a light emitting element. The four sheets are representative of n sheets, where n is a positive integer. Referring now to FIG. 7 and FIG. 8, the charged particle beam state verification system 750 is a system that allows for monitoring of the actual charged particle beam position in real-time without destruction of the charged particle beam. The charged particle beam state verification system 750 preferably includes a first position element or first beam verification layer, which is also referred to herein as a coating, luminescent, fluorescent, phosphorescent, radiance, or viewing layer. The first position element optionally and preferably includes a coating or thin layer substantially in contact with a sheet, such as an inside surface of the nozzle foil, where the inside surface is on the synchrotron side of the nozzle foil. Less preferably, the verification layer or coating layer is substantially in contact with an outer surface of the nozzle foil, where the outer surface is on the patient treatment side of the nozzle foil. Preferably, the nozzle foil provides a substrate surface for coating by the coating layer. Optionally, a binding layer is located between the coating layer and the nozzle foil, substrate, or support sheet. Optionally, the position element is placed anywhere in the charged particle beam path. Optionally, more than one position element on more than one sheet, respectively, is used in the charged particle beam path and is used to determine a state property of the charged particle beam, as described infra. Still referring to FIG. 7 and FIG. 8, the coating, referred to as a fluorophore, yields a measurable spectroscopic response, spatially viewable by a detector or camera, as a result of transmission by the proton beam. The coating is preferably a phosphor, but is optionally any material that is viewable or imaged by a detector where the material changes spectroscopically as a result of the charged particle beam hitting or transmitting through the coating or coating layer. A detector or camera views secondary photons emitted from the coating layer and determines a current position of the charged particle beam 269 or final treatment vector of the charged particle beam by the spectroscopic differences resulting from protons and/or charged particle beam passing through the coating layer. For example, the camera views a surface of the coating surface as the proton beam or positively charged cation beam is being scanned by the first axis control 142, vertical control, and the second axis control 144, horizontal control, beam position control elements during treatment of the tumor 720. The camera views the current position of the charged particle beam 269 as measured by spectroscopic response. The coating layer is preferably a phosphor or luminescent material that glows and/or emits photons for a short period of time, such as less than 5 seconds for a 50% intensity, as a result of excitation by the charged particle beam. The detector observes the temperature change and/or observe photons emitted from the charged particle beam traversed spot. Optionally, a plurality of cameras or detectors are used, where each detector views all or a portion of the coating layer. For example, two detectors are used where a first detector views a first half of the coating layer and the second detector views a second half of the coating layer. Preferably, at least a portion of the detector is mounted into the nozzle system to view the proton beam position after passing through the first axis and second axis controllers 142, 144. Preferably, the coating layer is positioned in the proton beam path 268 in a position prior to the protons striking the patient 730. Referring now to FIG. 1 and FIG. 7, the main controller 110, connected to the camera or detector output, optionally and preferably compares the final proton beam position 269 with the planned proton beam position and/or a calibration reference to determine if the actual proton beam position 269 is within tolerance. The charged particle beam state determination system 750 preferably is used in one or more phases, such as a calibration phase, a mapping phase, a beam position verification phase, a treatment phase, and a treatment plan modification phase. The calibration phase is used to correlate, as a function of x-, y-position of the glowing response the actual x-, y-position of the proton beam at the patient interface. During the treatment phase, the charged particle beam position is monitored and compared to the calibration and/or treatment plan to verify accurate proton delivery to the tumor 720 and/or as a charged particle beam shutoff safety indicator. Referring now to FIG. 10, the position verification system 172 and/or the treatment delivery control system 112, upon determination of a tumor shift, an unpredicted tumor distortion upon treatment, and/or a treatment anomaly optionally generates and or provides a recommended treatment change 1070. The treatment change 1070 is optionally sent out while the patient 730 is still in the treatment position, such as to a proximate physician or over the internet to a remote physician, for physician approval 1072, receipt of which allows continuation of the now modified and approved treatment plan. Referring still to FIG. 12B, a second example of the internal pendant 1218 is provided. In this example, one or more buttons or the like, such as the first button 1270, and/or one or more of the processes, such as the first process 1261, are customizable, such as to an often repeated set of steps and/or to steps particular to treatment of a given patient 730. The customizable element, such as the first button 1270, is optionally further setup, programmed, controlled, and/or limited via information received from the patient treatment module 1290. In this example, a button, or the like, operates as an emergency all stop button, which at the minimum shuts down the accelerator, redirects the charged particle beam to a beam stop separate from a path through the patient, or stops moving the patient 730. In place of and/or in conjunction with a particular button, such as the first button 1270 and/or the second button 1280, moving or selecting a particular element, processes are optionally described, displayed, and/or selected within a flow process control unit 1260 of the internal pendant 1218. For example, one or more display screens and/or printed elements describe a set of processes, such as a first process 1261, a second process 1263, a third process 1265, and a fourth process 1267 and are selected through a touch screen selection process or via a selection button, such as a corresponding first selector 1262, second selector 1264, third selector 1266, and fourth selector 1268. Referring still to FIG. 12B, as illustrated for clarity and without loss or generalization, the first process 1261 and/or a display screen thereof operable by the first selector 1262 selects, initiates, and/or processes a set of steps related to the beam control tray assembly 400. For instance, the first selector 1262, functioning as a tray button: (1) confirms presence a requested patient specific tray insert 510 in a requested tray assembly; (2) confirms presence of a request patient specific tray insert in a receiving slot of the control tray assembly; (3) retracts the beam control tray assembly 400 into the nozzle system 146; (4) confirms information using the electromechanical identifier plug, such as the first electromechanical identifier plug 530; (5) confirms information using the patient treatment module 1290; and/or (6) performs a set of commands and/or movements identified with the first selector 1262 and/or identified with the first process 1261. Similarly, the second process 1263, corresponding to a second process display screen and/or the second selector 1264; the third process 1265, corresponding to a third process display screen and/or the third selector 1266; and the fourth process 1267, corresponding to a fourth process display screen and/or the fourth selector 1268 control and/or activate a set of actions, movements, and/or commands related to positioning the patient 730, imaging the patient 730, and treating the patient 730, respectively. Still yet another embodiment includes any combination and/or permutation of any of the elements described herein. Herein, any number, such as 1, 2, 3, 4, 5, is optionally more than the number, less than the number, or within 1, 2, 5, 10, 20, or 50 percent of the number. The particular implementations shown and described are illustrative of the invention and its best mode and are not intended to otherwise limit the scope of the present invention in any way. Indeed, for the sake of brevity, conventional manufacturing, connection, preparation, and other functional aspects of the system may not be described in detail. Furthermore, the connecting lines shown in the various figures are intended to represent exemplary functional relationships and/or physical couplings between the various elements. Many alternative or additional functional relationships or physical connections may be present in a practical system. In the foregoing description, the invention has been described with reference to specific exemplary embodiments; however, it will be appreciated that various modifications and changes may be made without departing from the scope of the present invention as set forth herein. The description and figures are to be regarded in an illustrative manner, rather than a restrictive one and all such modifications are intended to be included within the scope of the present invention. Accordingly, the scope of the invention should be determined by the generic embodiments described herein and their legal equivalents rather than by merely the specific examples described above. For example, the steps recited in any method or process embodiment may be executed in any order and are not limited to the explicit order presented in the specific examples. Additionally, the components and/or elements recited in any apparatus embodiment may be assembled or otherwise operationally configured in a variety of permutations to produce substantially the same result as the present invention and are accordingly not limited to the specific configuration recited in the specific examples. Benefits, other advantages and solutions to problems have been described above with regard to particular embodiments; however, any benefit, advantage, solution to problems or any element that may cause any particular benefit, advantage or solution to occur or to become more pronounced are not to be construed as critical, required or essential features or components. As used herein, the terms “comprises”, “comprising”, or any variation thereof, are intended to reference a non-exclusive inclusion, such that a process, method, article, composition or apparatus that comprises a list of elements does not include only those elements recited, but may also include other elements not expressly listed or inherent to such process, method, article, composition or apparatus. Other combinations and/or modifications of the above-described structures, arrangements, applications, proportions, elements, materials or components used in the practice of the present invention, in addition to those not specifically recited, may be varied or otherwise particularly adapted to specific environments, manufacturing specifications, design parameters or other operating requirements without departing from the general principles of the same. Although the invention has been described herein with reference to certain preferred embodiments, one skilled in the art will readily appreciate that other applications may be substituted for those set forth herein without departing from the spirit and scope of the present invention. Accordingly, the invention should only be limited by the Claims included below. In a fourth example, the gantry comprises at least two imaging devices, where each imaging device moves with rotation of the gantry and where the two imaging devices view the patient 730 along two axes forming an angle of ninety degrees, in the range of eighty-five to ninety-five degrees, and/or in the range of seventy-five to one hundred five degrees. Pendant Referring still to FIG. 12A and referring now to FIG. 12B, a pendant system 1250, such as a system using the external pendant 1216 and/or internal pendent 1218 is described. In a first case, the external pendant 1216 and internal pendant 1218 have identical controls. In a second case, controls and/or functions of the external pendant 1216 intersect with controls and/or function of the internal pendant 1218. Particular processes and functions of the internal pendant 1218 are provided below, without loss of generality, to facilitate description of the external and internal pendants 1216, 1218. The internal pendant 1218 optionally comprises any number of input buttons, screens, tabs, switches, or the like. The pendant system 1250 is further described, infra. |
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abstract | A pattern drawing method of drawing a desired pattern on a base material by irradiating an electronic beam and scanning the base material with the electronic beam with a predetermined dose amount, comprising: a first step of drawing a first region on the base material by scanning with the electronic beam with a first dose amount; a second step of drawing a second region on the base material by scanning with the electronic beam with a second dose amount; and a inclining step of inclining a boundary between the first region and the second region to form an inclined surface by conducting a first scanning to scan with the electronic beam with the first dose amount and a second scanning to scan with the electronic beam with the second does amount in a mixed arrangement. |
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description | The invention relates to a spacer grid for a fuel assembly in a light-water-cooled nuclear reactor. Light-water-cooled nuclear reactors and in particular pressurized-water-cooled nuclear reactors use fuel assemblies comprising a bundle of fuel rods held in place by a framework in mutually parallel arrangements. The fuel assembly framework comprises, in particular, a plurality of spacer grids distributed along the length of the fuel assembly, in the axial direction of the bundle of rods. The spacer grids ensure transverse retention of the rods and comprise a set of juxtaposed cells arranged in a regular lattice, generally with square lattice cells, the cells themselves having a square cross section in a transverse plane of the spacer grid perpendicular to the axis of the rods. Each of the cells is bounded and separated from the adjacent cells by a peripheral wall having the shape of the lateral surface of a square-based parallelepiped. The cells of the spacer grid are open at their two ends in the axial direction of the cells, so that each of the cells can receive a rod in a central position, in which the axis of the rod is placed along the axis of the cell. The fuel rods have a substantially smaller diameter than the sides of the square cells, so that a free space remains around the rod, between the cylindrical external surface of the rod and the peripheral wall of the cell in which the rod is engaged axially. The spacer grid includes, in each of the cells intended for housing a fuel rod, bearing and retaining means intended to come into contact with the external surface of the fuel rod, in order to ensure that the rod is held in place in transverse directions perpendicular to the axis of the rod and of the cell, while still permitting the rod to move in the axial direction, for example owing to the effect of expansion inside the core of the nuclear reactor. The means for bearing on and retaining the fuel rods in the cells of a spacer grid generally comprise dimples projecting toward the inside of the cell relative to the peripheral wall, which are produced by cutting and pushing back the wall, and resilient leaf springs, also projecting toward the inside the cell relative to the wall, which are produced by cutting and pushing back a part of the wall, or which are added and fastened to the peripheral wall. In general, two dimples are provided on each of two adjacent faces of the parallelepipedal peripheral wall and two leaf springs on the faces opposite the faces having the dimples. The fuel rod is contained inside the cell at six points, by the four dimples and the two leaf springs, the leaf springs and the dimples being produced so as to come in contact with the fuel rod in a region of small area, that can be likened to a contact point. In addition to the transverse retention of the rods of the fuel assembly bundle, the spacer grids ensure mixing and stirring of the reactor cooling water that flows in contact with the fuel rods along the axial longitudinal direction. The spacer grids for the fuel assemblies consist of metal plates of rectangular shape that are cut at mid-width in order to fit one over the other and assembled by welding, in the form of a lattice of square lattice cells. To ensure that the cooling water is mixed and stirred upon leaving the spacer grid, the plates of the spacer grids are cut along their edge intended to come into the upper part of the spacer grid, in order to constitute mixing vanes that are folded over toward the inside the cells, alternately in one direction and in the other, so as to guide the fluid leaving one cell into a neighboring cell, and thus mixing the various fluid flows in contact with the fuel rods. The plates used to produce a spacer grid must therefore be cut in a particular design and stamped or pushed back in order to form the dimples and leaf springs. In the case of leaf springs attached to the walls of the cells, it is also necessary to provide cuts for fastening the leaf springs and then to fit and weld the leaf springs, which may be made of a metal material different from that of the plates. For example, the plates may be made of a zirconium alloy and the leaf springs of a nickel alloy. Construction of the spacer grids is therefore complex, because they requires many cutting, stamping, fitting and welding operations. In addition, the six-point retention of the fuel rods inside each of the cells may result in local wear of the rod cladding in contact with the dimples or leaf springs, by friction because the reactor cooling water sets the rods in vibration inside the spacer grids. This phenomenon, which is generally called “fretting wear”, may result, over long periods of use of the nuclear reactor, in the cladding of the rods being punctured in the contact regions. Finally, the ability of the vanes cut along the upper edges of the spacer grids to provide mixing is limited, so that perfect temperature homogenization of the cooling water flowing in the fuel assembly is not achieved. This may result in hot spots in contact with the rods in certain regions, where the boiling crisis phenomenon, that is to say the local formation of vapor bubbles in the cooling water, is observed to occur. The objective of the invention is therefore to propose a spacer grid for a fuel assembly in a light-water-cooled nuclear reactor, for providing the transverse retention of a bundle of fuel rods in mutually parallel arrangements, comprising an array of cells juxtaposed and placed in a regular lattice, each bounded and separated from neighboring cells by at least one peripheral wall which is open at two opposed ends, along the direction of an axis of the cell, so as to receive a fuel rod of cylindrical general shape passing along the cell along its axis parallel to the peripheral wall, and an arrangement for supporting and retaining the rod in a central position in which the axis of the rod lies along the axis of the cell, a free space being left between the cylindrical external surface of the fuel rod and the peripheral wall of the cell, in which the arrangement for bearing on and retaining the fuel rod in each of the cells housing a fuel rod comprise at least one element in a helical arrangement around the axis of the cell, comprising a wall having the form of a helical sheet extending transversely in the free space between the external surface of the fuel rod and the peripheral wall of the cell, so as to bear on the fuel rod over a substantial part of the height of the cell in the direction of its axis, this spacer grid being of simple construction and very effective as regards retaining the rods, while still limiting the phenomenon of fretting wear and having a very high capacity to mix the cooling water within the spacer grid and upon leaving it. For this purpose, the at least one element in a helical arrangement of the arrangement for supporting and retaining a fuel rod consists of a part of the peripheral wall of the cell cut in the peripheral wall along a direction inclined to the axis of the cell and folded so as to constitute a blade-shaped first part of direction transverse to the peripheral wall and a second part approximately parallel to the wall of the cell and constituting a bearing surface for the external surface of the fuel rod, which second part is joined to the peripheral wall of the cell via the transverse first part constituting a spring leaf for retaining the rod and for guiding a cooling fluid in a helical arrangement around the axis of the cell. FIG. 1 illustrates a fuel assembly for a pressurized-water-cooled nuclear reactor, denoted overall by the reference numeral 1. The fuel assembly 1 consists of a bundle of substantially cylindrical fuel rods 2 consisting of a metal cladding in which fuel pellets are stacked, the cladding being closed off at its ends by plugs. The fuel rods 2 of the fuel assembly bundle are held in place by a framework, which comprises a plurality of spacer grids 3 distributed along the longitudinal direction of the fuel assembly, in the axial direction of the rods 2, guide tubes 4, which are placed inside the bundle of fuel rods 2 and joined to the grids 3, and an upper nozzle 5a and a lower nozzle 5b that are rigidly fastened to the ends of the guide tubes 4, the length of which is greater than the length of the fuel rods 2 of the bundle. The spacer grids, which ensure transverse retention of the fuel rods 2 of the fuel assembly bundle, comprise, as can be seen in FIG. 2, cells 6 of square cross section that are arranged in a regular lattice with square lattice cells. Each cell 6 has a peripheral wall 7 in the form of a square-based parallelepiped open at its two ends in the direction of the axis 6′ of the cell, perpendicular to the plane of FIG. 2 and passing through the center of the square section of the cell. The peripheral walls 7 of the cells 6 of the spacer grid 3 are formed by plates intersecting at right angles, constituting two families of mutually parallel plates 8a and 8b. The plates 8a and 8b of the two families of plates are cut from metal sheets, for example made of zirconium alloy, and include, at distances corresponding to the sides of the cells 6, slots at mid-width that allow them to be assembled by mutual engagement in 90° arrangements, as shown in FIG. 2. The assembled plates are then welded along the assembly lines constituting the edges of the cells 6 of the spacer grid. Prior to their assembly, the plates 8a and 8b are cut and stamped in order to form dimples 9 projecting toward the inside of the cells 6. The plates 8a and 8b also include openings that are cut at regular intervals, so as to fit and fasten leaf springs 10, which also project toward the inside of the cells 6. Each of the cells has two adjacent 90° walls, in each of which are produced, by cutting and pushing back the metal of the plates, two dimples 9 spaced apart along the axial direction of the cell. The other two walls of the cell, which are adjacent and at 90° , house leaf springs 10. In this way, six points of contact are provided inside each of the cells 6 for a fuel rod 2 inserted along the direction of the axis 6′ in a centered position inside the cell 6. The outside diameter of the fuel rod 2 is substantially less than the length of a side of a cell 6, such that a free space 11 is left around the cylindrical external surface of the rod 2, inside the peripheral wall 7 of the cell in which the rod is held in a centered position by the dimples 9 and the leaf springs 10. The plan view of FIG. 2 is a top view of a spacer grid and this illustrates that the plates 8a and 8b constituting the spacer grid are cut along their upper edge in order to form the vanes 12 for mixing the cooling water flowing inside the cells in contact with the external surface of the fuel rods 2. The mixing vanes 12 are folded over toward the inside of the cells so as to direct the cooling water as it leaves each of the cells toward a neighboring cell. This thus produces a mixing effect on the water flowing in contact with each of the fuel rods along the axial direction. The plates 8a and 8b of the spacer grid 3 must be stamped in order to produce projecting dimples on their two faces, each of the plate portions ensuring, at each cell, the separation of two neighboring cells in which the dimples are produced on the same plate. The construction of a spacer grid is therefore complex and requires many cutting, forming and assembling operations. In addition, the retention of the fuel rod 2 inside a cell 6 of the spacer grid is provided only in six regions of small area constituting points of contact. Furthermore, within the lattice of cells, it is necessary to produce cells 6a of special type that allow the passage, and possible fastening, of the fuel assembly guide tubes 4. FIGS. 3A and 3B show a cell of a spacer grid according to the invention, which can be used as a replacement for a spacer grid according to the prior art as shown in FIG. 2. In general, the spacer grid 3 according to the invention is produced in a manner similar to the spacer grid according to the prior art, from metal plates 8 that are assembled and fastened together by welding at right angles in order to constitute a lattice of cells 6 of square cross section, each bounded by a peripheral wall 7 in the form of a square-based parallelepiped formed by plate portions 8 joined together at right angles. Produced on each of the plate portions constituting one of the faces of the peripheral wall 7 of a cell 6, by cutting and bending, are two elements for bearing on and retaining a fuel rod which are arranged in general along a helix having as axis the axis 6′ of the cell 6. The four faces of the peripheral wall 7 of the cell 6, having the shape of a parallelepiped of square cross section, are denoted by 7a, 7b, 7c and 7d. Produced in the metal of the face 7a, by cutting and bending, are two elements 14a and 14′a which are arranged, in the case of the first one (14a), in the lower end part and, in the case of the second one (14′a), in the upper end part of the face 7a of the wall 7. Likewise, respective bearing and retaining elements 14b, 14′b, 14c, 14′c and 14d, 14′d, respectively, are produced on the successive faces 7a, 7b, 7c and 7d by cutting and bending. The bearing and retaining elements 14a, 14b, 14c and 14d lie in the lower part and the elements 14′a, 14′b, 14′c and 14′d are produced by cutting and bending in the upper part of the peripheral wall 7 of the cell 6. The view shown in FIG. 3B represents an axial cross section through the opposed faces 7b and 7d. As illustrated in FIGS. 3A and 3B, the elements for bearing on and retaining a rod 2 in the cell 6 are produced by cutting one face of the wall 7 in a direction inclined to the axis 6′ of the cell 6, so that the cuts are all directed upward, when the cell 6 is rotated about the axis 6′ in the direction going from the right to the left in FIG. 3A, this direction corresponding to the direction of winding of the upwardly directed helices formed by the successive bearing and retaining elements of the cell 6. The successive cuts in the faces of the peripheral wall 7 of the cell 6 have generally rectangular shapes, the short sides of the rectangular cuts being directed along directions parallel to the axis 6′ of the cell and the cut having a single inclined long side directed along the direction of winding of the helix of the bearing and retaining elements of the cell, the cut being joined to the wall via its second long side along which the bending of the wall takes place. This long side and the cut make an angle of around 30° with the direction of the axis 6′ of the cell 6. The successive bearing and retaining elements 14a, 14′a, through 14d, 14′d are produced by bending the corresponding cuts along directions approximately parallel to the long side of the cut joining the wall. The successive bearing and retaining elements 14a, 14′a, through 14d, 14′d are produced by bending the cuts out of the plane of the face of the wall 7 in which the-cut is made. The cut is firstly bent (for example at 45°) with respect to the plane of the face of the wall and secondly bent upward toward the top of the cell, along lines of bending approximately parallel to the long side of the cut and lying substantially along helix portions wound in the desired direction about the axis 6′ of the cell. What is thus obtained is a wall (for example 15a or 15b) of the corresponding bearing and retaining element 14a or 14b directed transversely with respect to the axis 6′ and to the face of the wall 7, and a second wall (16a or 16b) substantially parallel to the face of the wall 7 of the cell. The cuts are bent successively toward the inside and toward the outside of the cell 6 for successive cuts along the direction of the axis 6′ and along the direction of winding of the helix in which the bearing and retaining elements are arranged. Thus, the first wall 15a of the first bearing and retaining element 14a is bent toward the inside of the cell 6 and the second wall 16a of the first element 14a folded parallel to the face 7a of the wall inside the cell 6. In contrast, the first wall 15b of the second bearing and retaining element 14b is folded toward the outside of the cell 6, in a cell neighboring the cell 6, and the second wall 14b of the second bearing and retaining element 14b is folded in an arrangement substantially parallel to the face 7b of the wall 7, in the cell neighboring the cell 6. The bearing and retaining element 14′a, lying in the upper part of the first face 7a of the wall 7 of the cell 6 in the axial alignment of the bearing and retaining element 14a lying in the lower part of the face 7a of the wall 7 is folded in the opposite direction to the bearing and retaining element 14a, that is to say toward the outside. Each of the successive bearing and retaining elements, along the axial direction or along the direction of the helix in which the bearing and retaining elements are wound, is therefore folded in a different direction from the previous one. Consequently, the element 14c is folded inward and the element 14b folded outward, the element 14′b, located in the upper part of the cell 6, is folded inward, whereas the successive elements 14′c and 14′d are folded toward the outside and toward the inside of the cell 6, respectively. The second walls, such as 16a, 16b or 16d visible in FIG. 3, of the respective bearing and retaining elements 14a, 14b, and 14′d are bent so as to have the shape of a ring portion having a diameter approximately equal to the diameter of a rod 2 of the fuel assembly. These second walls, such as 16a, 16b or 16′d are intended to come into contact with the external surface of a rod 2 inserted into the cell 6 or into a neighboring cell. The bearing and retaining elements cut in the upper part of the faces 7a, 7b, 7c and 7d of the peripheral wall 7 of the cell 6 are produced in the form of vanes projecting upward with respect to the upper edge of the peripheral wall 7 of the cell 6. To do this, parts of the plates projecting from one of the edges of the plates are cut, these plates being folded on one side of the plate in order to constitute the two walls of the bearing and retaining elements that also constitute a vane for guiding and mixing of the fuel assembly cooling water. The vanes such as 14′a or 14′c, which are folded toward the outside of the cell 6, include an upper end part (in the direction of winding of the helical retaining elements) which is directed toward a neighboring cell of the cell 6. The first walls, such as 15a or 15b of the bearing and retaining elements, which are bent in a direction perpendicular or inclined to the face of the wall in which the cut is produced, constitute blades of direction transverse to the walls of the cell, lying along helix portions wound in the direction of winding of the successive retaining elements cut in the walls of the cell 6. The first walls or blades 15a, 15′b, 15c and 15′d, directed toward the inside of the cell, constitute blades of transverse direction between the plane of the face of the corresponding wall and a bearing surface of the fuel rod which can be inserted into the cell 6, which surface is formed by the curved internal surface of the second wall 16a, 16′b, 16c or 16′d of the corresponding bearing and retaining element. When a fuel rod 2 is inserted into the cell 6 along the axis 6′ of the cell 6, as shown in FIG. 4, the external surface of the rod 2 comes into contact with the second surfaces 16a, 16′b, 16c and 16′d of the four bearing and retaining elements folded toward the inside of the cell 6. The corresponding first walls 15a, 15′b, 15c and 15′d of transverse direction, having the shape of a helix portion, which extend between the peripheral wall 7 of the cell 6 and the second wall bearing on the external surface of the rod, exhibit elasticity allowing them to ensure resilient retention of the rod 2, the bearing and retaining elements 14a, 14′b, 14c and 14′d directed toward the inside of the cell 6 being folded so that the internal bearing surfaces of the second walls 16a, 16′b, 16c and 16′d lie on a cylindrical surface having as axis the axis 6′ of the cell and having a slightly smaller diameter than the diameter of the rod. When the rod 2 is inserted along the axis 6′ of the cell 6, into the cell 6, the rod 2 moves the bearing surfaces slightly apart, using the elasticity of the transverse blades in the form of helix portions. The four bearing surfaces of the second walls 16a, 16′b, 16c and 16′d come into contact with the rod 2, in two regions, the total height of which, along the axial direction 6′ of the cell 6, is approximately equal to or slightly less than the total height of the cell 6 along the direction of the axis 6′. The rod is thus retained in contact with bearing surfaces over a total height approximately equal to the height of the cell 6, that is to say to the height of the spacer grid. The total area of the four bearing regions of the four retaining and bearing elements 14a, 14′b, 14c and 14′d inside the cell 6 is therefore large and substantially greater than the total bearing area of the four dimples and two leaf springs of a cell of a spacer grid according to the prior art. Thus, the bearing pressure on the rod 2 and the risk of fretting wear, on the assembly in service in the nuclear reactor, are reduced. Moreover, the reactor cooling water flowing vertically in contact with the outer surface of the fuel rod 2 is guided by the first transverse walls in the form of helical blades of the four inwardly folded elements of the cell, so as to constitute a helical stream around the rod 2, in the free space between the external surface of the rod and the peripheral wall 7 of the cell 6. The bottom vane 14a and top vane 14′b located on two adjacent faces of a cell ensure successive guiding of the fluid each over one quarter of a turn, so that the cooling water describes a portion of a helix over approximately 180° , on passing through the cell; the vanes 14c and 14′d have a similar effect. As a result, the fluid is guided inside the cell 6, promoting heat exchange with the external surface of the rod 2. In addition, the bearing and retaining elements produced in the upper parts of the peripheral wall 7 of the cell 6 which are directed either toward the inside of the cell 6 or toward the outside and toward neighboring cells ensure very good stirring and very good mixing of the stream flowing in contact with the rod inside the cell 6 and of the streams flowing in contact with the fuel rods located in the cells neighboring the cell 6. Furthermore, the production of a spacer grid according to the invention requires only simple cutting and bending operations on the various plates intended to form the spacer grid by fitting them together at right angles and welding them, as in the case of the prior art. In addition to the bearing and retaining elements 14a, 14′a, through 14d, 14′d that constitute resilient dimples for bearing on the rods, rigid dimples such as 21a and 21b may be produced by cutting and pushing back the metal of the walls of the cell. Two dimples, such as 21a and 21b produced on two adjacent walls of the cell 6 may be pushed back toward the outside of the cell 6 and two dimples produced on the other two adjacent walls of the cell 6 may be pushed back toward the inside of the cell. Each cell therefore has two rigid dimples for bearing on the rod, for example in the bottom part. FIG. 5 shows in plan view part of the spacer grid 3 according to the first embodiment, this part of the spacer grid comprising five rows of five cells 6. Inside two cells 6, and indicated by reference numerals similar to those used in FIG. 3, are the bearing and retaining elements 14a, 14′b, 14c and 14′d folded toward the inside of the cell, the elements 14a and 14c being produced in a lower part of the peripheral wall 7 of the cell and the elements 14′b and 14′d in upper parts of the wall 7 of the cell. Throughout the view shown in FIG. 5, the reference H denotes the helical bearing, retaining and fluid-guiding elements cut in an upper part of the wall of a cell and the reference B denotes the bearing, retaining and guiding elements cut in a lower part of the wall 7 of a cell. Owing to the fact that, in each of the faces of the peripheral wall 7 of a cell, a bearing and retaining element is cut in a lower part of the face of the wall and a bearing, retaining and guiding element is cut in an upper part of the face of the peripheral wall of the cell, these elements being folded on either side of the wall, such as toward the inside and toward the outside of the cell 6 in question, each face of a peripheral cell wall allows a bearing, retaining and guiding element to be produced either in the top part or bottom part of the cell, said element being arranged along a helix having a clockwise or counterclockwise winding direction along the direction of flow of the fluid through the spacer grid, such as from the bottom upward, and a second bearing, retaining and guiding element inside a cell neighboring the cell, in a helix having a direction of winding opposite the direction of winding of the helix of the first cell. FIG. 5 shows the directions of guiding of the fluid flow by helical bearing, retaining and guiding elements in the twenty-five cells 6 shown in adjacent positions. The direction of rotation of the fluid in each of the cells 6 alternates from one cell to any neighboring cell. This flow characteristic of the fluid favors mixing and prevents a resultant torque being applied to the spacer grid, due to the flow of the fluid. To optimize the fuel rod retention characteristics and the cooling water mixing characteristics, the following parameters may be adjusted: the angle of inclination of the helix to the vertical direction of the axis of the cells; the relative height of the top and bottom helices in each of the faces of the peripheral wall of the cells; the position of the helical retaining and guiding elements with respect to the bottom of the plates constituting the spacer grid; the height above the upper edge of the spacer grid of the projecting part of the retaining and guiding elements lying in the upper part of the cells of the spacer grid; the width of the transverse blade constituting the flexible region of the helical retaining and guiding element; and the length of the region for contact between the helical retaining and guiding element and the rod 2 placed inside a cell. In each of the cells of the spacer grid intended to house a fuel rod, it is possible to produce, on at least one wall of the cell, by stamping the plate constituting the wall, at least one stamped feature projecting into the cell, such as a dimple. Thus the movement of the rod in the cell is limited and its embedment is reinforced. In the case of the alternative embodiment shown in FIGS. 4A and 4B (the elements corresponding to those shown in FIGS. 3A and 3B being assigned the same reference numerals), the vanes such as 14a and 14′a, 14b and 14′b, 14c and 14′c, 14d and 14′d lying in bottom and top respective parts of the walls of a cell 6 of the spacer grid 3 are folded alternately toward the inside and toward the outside of the cell in the same manner as the vanes shown in FIGS. 3A and 3B. However, unlike the vanes of the cell shown in FIGS. 3A and 3B, the first walls such as 15′a, 15c, 15′b or 15′d of the vanes, in the form of transverse blades, are folded downward (for example at 45° ) and not upward. Likewise, the second walls such as 16′a, 16b, 16c or 16d, which ensure that the rod bears on a cylindrical bearing surface, are folded downward. When cooling water is flowing through the cell 6, the bearing surfaces of the vanes are pressed against the rod under the effect of the hydraulic forces. Hydraulic exchange inside the cell is also promoted. The top and bottom vanes may be cut in the walls of the cell at a certain distance from the upper edges of these walls. The invention is not strictly limited to the embodiment that has been described. Thus the helical retaining and guiding elements may make an angle of inclination to the axis of the cell or of the fuel rod different from 30° and the retaining and fluid-guiding element of each of the cells of the spacer grid may be produced in a manner different from those that have been described. The invention applies in general to any spacer grid for a fuel assembly of a light-water-cooled nuclear reactor ensuring transverse retention of the rods constituting a bundle in which the rods are mutually parallel. |
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abstract | The invention relates to a final, ready to use, spacer grid for a nuclear boiling water reactor. The final spacer grid comprises: i) a spacer grid structure made of an alloy that has been formed and assembled such that it constitutes a spacer grid, and ii) an outer oxide coating on the surface of the spacer grid structure. Said alloy is a Ni base alloy that consists of the following: (table) The invention also relates to a method of manufacturing the final spacer grid according to the invention. |
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claims | 1. An apparatus comprising:an apparatus that generates ions and directs said ions to a workpiece; anda laser source that generates a laser, said laser projected above said workpiece in a line, said line disposed above a portion of said workpiece and blocking a fraction of said ions. 2. The apparatus of claim 1, wherein said laser source generates a plurality of lasers, each of said plurality of lasers projected above said workpiece in a line. 3. The apparatus of claim 1, further comprising at least one reflector, said reflector reflecting said laser whereby said laser forms a plurality of lines above said workpiece. 4. The apparatus of claim 1, wherein said ions are disposed in an ion beam. 5. The apparatus of claim 1, wherein said ions are disposed in an ion sheath. 6. A method of workpiece processing comprising:generating a laser above a workpiece;directing ions toward said workpiece;blocking a fraction of said ions with said laser; andimpacting said workpiece with said ions in a first region. 7. The method of claim 6, further comprising pulsing said laser. 8. The method of claim 6, wherein said generating said laser and said directing said ions are at least partially simultaneous. 9. The method of claim 8, wherein said directing said ions occurs at least partly while said laser is not being generated. 10. The method of claim 9, wherein said generating of said laser is stopped thereby forming a wake, and wherein said ions fill said wake. 11. The method of claim 9, wherein said directing said ions comprises applying a bias to said workpiece. 12. The method of claim 6, further comprising generating a second laser above said workpiece and focusing said ions toward said workpiece. 13. The method of claim 6, further comprising biasing said workpiece. 14. The method of claim 13, wherein said biasing occurs during a first period when said directing said ions occurs and further comprising depositing said ions during a second period when said workpiece is not biased, said depositing occurring primarily in a region shadowed by said laser. 15. The method of claim 6, further comprising:generating a second laser configured to shadow said first region;directing a second species of ions toward said workpiece, said second species of ions different from said ions;blocking a fraction of said second species of ions with said second laser; andimpacting said workpiece with said second species of ions in a second region adjacent said first region. 16. A method of workpiece processing comprising:generating a laser above a workpiece;directing ions toward said workpiece; andblocking a fraction of said ions directed through said laser whereby said workpiece is implanted to a first dose in a first region of said workpiece shadowed by said laser and a second dose in a second region of said workpiece. 17. The method of claim 16, further comprising stopping said laser from being generated above said workpiece and implanting all of said workpiece with said ions. 18. The method of claim 16, wherein said workpiece is a solar cell. |
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051125692 | summary | BACKGROUND OF THE INVENTION The subject-matter of this invention consists of an intrinsic-safety nuclear reactor of the pressurized water type. Canadian patent no. 1.070.860 describes a nuclear reactor of the type with pressurized light water, called the intrinsic-safety type. According to said patent, the vessel containing the reactor core, made of steel and externally insulated, is immersed in a pool provided with its own containment shell. The reactor vessel has at the top an output header for the water which has crossed through the core and got heated, and which, by means of a suitable delivery pipe is conveyed outside the pool to a heat exchanger. From the heat exchanger, the water is conveyed back through a suitable return pipe to an input header located below the core, in the reactor vessel. On the primary circuit return pipe, furthermore, there is a circulation pump. The reactor core, the two headers, the output pipe and the return pipe with the relevant circulation pump, and finally the heat exchanger, form the reactor primary circuit. In the Canadian patent mentioned above, intrinsic safety is ensured by the fact that the water in the pool is pressurized, and there are means of connection which, in emergency conditions, allow the water from the pool to flow freely into the lower header on the one hand, and means of connection which allow the free flow of the water in the upper header towards the pool, on the other. The emergency conditions envisaged could consist, for example, of a failure of the primary circuit circulation pump, with a consequent increase of the temperature inside the reactor. The means of connection between the water in the pool and the lower header consist of a pneumatic seal or even an open pipe in which a flow rate of nil is ensured, in normal operating conditions, by means of a suitable play of pressures, as explained below. The means of connection between the upper header and the water of the pool consist of a bell of gas or steam under pressure, installed on top of a fairly high chamber, also full of gas or steam: the height of said chamber must be such that the corresponding head of liquid contained in the pool is equal to the pressure drop in the primary liquid circulating in the reactor. In this way the lower header of the reactor and the surrounding water of the pool are the same pressure, and there is no difference in pressure between the two areas: in spite of the fact that these two areas communicate freely, since their pressures are the same, the flow rate of liquid between one and the other is nil. In case of failure of the circulation pump, the pressure drop between the lower header and the upper header is eliminated; in particular, the pressure in the upper header increases and the water of the reactor is pushed into the chamber full of gas, and from here into the pool. At the same time, the water from the pool enters the lower header and from here passes into the core. The water of the reactor is therefore replaced by the water from the pool, which is colder: it has already been said that the walls of the reactor are insulated. In addition to this, the water in the pool is borated water so that on reaching the reactor core it gradually stops the reaction. The volume of water present in the pool is relatively large, and this allows quite a number of hours of primary fluid circulation pump failure without the rector core heating over the pre-established safety limits. From a strictly technical point of view, the operation of the intrinsic-safety reactor described above and claimed in Canadian patent no. 1.070.860 is unexceptionable. This known reactor, however, has the drawback that it entails a complex construction in the event of using a high-temperature reactor. Indeed, the pressure of the liquid contained in the pool must be higher that the pressure corresponding to the saturation temperature of the fluid on leaving the core, and therefore: either the quantity of water in the pool is limited, and in this case shut-down of the reactor is ensured but cooling of the core is ensures only in the short term, PA1 or the quantity of water in the pool is large, and in this case complex reinforced concrete structures are needed to guarantee containment of said fluid under pressure. BRIEF SUMMARY OF THE INVENTION The purpose of the invention described here is to overcome this drawback, allowing construction of a pool with non-pressurized walls, the size of which may be increased at a considerably lower cost than is called for with the Canadian patent mentioned above. According to this invention, the reactor vessel is inserted inside a pressurized metal container which contains a neutron-absorbing liquid under pressure, and which is equipped with all the components called for by the known solution described above. This pressurized metal container is in turn immersed in a neutron-absorbing fluid, at atmospheric pressure, contained in a large pool equipped with a reinforced concrete containment shell. The neutron-absorbing fluid both inside and outside the pressurized metal container may be borated water. Since this time the pool is not pressurized, its size may be increased at a reasonable cost in relation to the corresponding increase in safety. In addition to the above, the solution according to the invention allows installation in one single pool of serveral modular-sized reactors; this gives rise to greater operational flexibility, as well as shorter construction times and lower construction costs, due to easy recourse to standardization. |
claims | 1. A near infrared ray-absorbing synthetic resin composition comprising a synthetic resin, and the following component (A) and/or component (B) dispersed in the synthetic resin: Component (A): a component composed of a copper ion and a phosphate compound represented by the following formula (1); and/or Component (B): a component composed of a compound obtained by reacting a phosphate compound represented by the following formula (1) with a copper salt wherein groups R independently mean a group represented by the following formula (2) or (3), and n is 1 or 2: wherein R 1 denotes an alkyl group having 1 to 20 carbon atoms, R 2 represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and m is an integer of 1 to 6. 2. The near infrared ray-absorbing synthetic resin composition according to claim 1 , wherein the component (B) is composed of the phosphate copper compound represented by the following formula (6) or (7): claim 1 wherein groups R independently mean a group represented by the following formula (2) or (3), and M denotes a copper ion: wherein R 1 denotes an alkyl group having 1 to 20 carbon atoms, R 2 represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and m is an integer of 1 to 6. 3. The near infrared ray-absorbing synthetic resin composition according to claim 1 , wherein the content of the copper ion is 0.1 to 5% by weight based on the total weight of the composition. claim 1 4. The near infrared ray-absorbing synthetic resin according to claim 1 , wherein R 2 in the formulae (2) and (3) representing the group R in the phosphate compound represented by the formula (1), is a hydrogen atom or an alkyl group having 1 to 4 carbon atoms. claim 1 5. The near infrared ray-absorbing synthetic resin composition according to claim 1 , wherein m in the formulae (2) and (3) representing the group R in the phosphate compound represented by the formula (1), is an integer of 1 to 3. claim 1 6. The near infrared ray-absorbing synthetic resin composition according to claim 1 , wherein the content of the copper ion is 0.3 to 4% by weight based on the total weight of the composition. claim 1 7. A near infrared ray-absorbing synthetic resin composition according to claim 1 , wherein the content of the copper ion is 0.5 to 3% by weight based on the total weight of the composition. claim 1 8. The near infrared ray-absorbing synthetic resin composition according to claim 1 , wherein the synthetic resin is acrylic resin. claim 1 9. The near infrared ray-absorbing synthetic resin composition according to claim 2 , wherein the synthetic resin is acrylic resin. claim 2 10. The near infrared ray-absorbing synthetic resin composition according to claim 3 , wherein the synthetic resin is acrylic resin. claim 3 11. The near infrared ray-absorbing synthetic resin composition according to claim 4 , wherein the synthetic resin is acrylic resin. claim 4 12. The near infrared ray-absorbing synthetic resin composition according to claim 11 , wherein m in the formulae (2) and (3) representing the group R in the phosphate compound represented by the formula (1), is an integer of 1 to 3. claim 11 |
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description | This application is a US 371 Application from PCT/RU2015/000839 filed Dec. 1, 2015, which claims priority to Russia Application 2014151527 filed Dec. 19, 2014, the technical disclosures of which are hereby incorporated herein by reference. The invention relates to nuclear engineering and is designed for controlled reactor start-up by rising the reactor to the working power level after normal and abnormal shutdowns. In order to improve the reactor safety and its dynamic properties, as well as to reduce consequences of start-up reactivity accidents, it is feasible to implement engineering measures to prevent “blind” start-up, because in subcritical reactor the neutron flux is the only and the most important variable parameter at reactivity rise. The controlled start-up means the possibility to measure the neutron flux in the reactor core depending on the position of standard control equipment compensating rods. The amount of neutrons generated in the core as a result of spontaneous uranium fission (˜2 103 n/s), is not sufficient to provide a controlled neutron flux in measuring chambers during the start. The reactor subcriticalilty and power control is one of the most important nuclear safety tasks. In order to provide controlled reactor start-up, it is essential to ensure that the core neutron power is consistent with the response of ionization chambers monitoring the neutron flux which are located in a specific area near the core. In order to ensure the control, the neutron flux in a subcritical reactor shall be increased significantly, or the start-up equipment response shall be increased accordingly. The most appropriate solution of the reliable power control problem of reactors (in the initial subcritical state) equipped with pulse start-up equipment is the allocation of neutron sources in the core. Neutron sources designed as cluster assemblies are currently in use. The assembly includes two types of rods: rods with antimony filling, and rods with a hot-pressed beryllium bed. Such designs are very large and occupy a considerable area in the core. Neutron sources based on antimony-beryllium composition pellets enclosed in a single housing are currently in use. At present, such neutron source design is used at naval nuclear facilities. The shortage of this design is potential antimony melting during the source manufacture and operation, resulting in the stratification of the antimony-beryllium composition and source efficiency degradation. A monoenergetic neutron source is currently in use, disclosed in Patent RU No. 1762676, MPK G21G4/00 of Aug. 30, 1994. This neutron source is designed as radioactive antimony in a beryllium enclosure which is placed in the iron layer, with varying thickness of the beryllium and ferrum layers, which thickness is determined by the calculated ratios. The device contains a photon source, cylinder-shaped antimony, a photoneutron source, beryllium shaped as a cylindric tube, a neutron filter, barrel-shaped ferrum, in which an antimony-beryllium system is placed, and then capped with an iron plug. The shortage of this design is also potential antimony melting during the source manufacture and operation, resulting in the stratification of the antimony-beryllium composition and source efficiency degradation. The invention solves the task of improving the reliability of the operational neutron source. The technical result of the invention is the provision of additional safety barriers between the coolant and neutron source active part materials, the improvement of fail-free operation of the neutron source, its reliability and durability. The above technical results are achieved by the following distinctive features of the invention. As a solution to the stated problem, we claim an operational neutron source designed as an enclosure of a durable material, such as steel, inside of which there is an ampule containing active elements: antimony and beryllium with separate antimony and beryllium cavities positioned coaxially. The antimony is housed in the central ampule enclosure made of a material which does not react with the antimony during filling and operation, for example, a niobium-based alloy. The central enclosure of the ampule is leak tight. A beryllium powder bed is located between the antimony enclosure and the ampule enclosure. The beryllium powder bed porosity is 45%, with particle size from 60 to 200 micron. The ampule enclosure is made of a material poorly reacting with beryllium, for example, martensite-ferrite grade steel. An upper gas collector is located above the ampule, which serves as a compensation volume collecting gaseous fission products. The gas collector is pressed against the ampule through washers with a spring. At the bottom, the ampule is supported by a reflector and a bottom gas collector. The gas collectors, the reflector and the washers are made of a durable material, such as martensite-ferrite grade steel. The neutron source enclosure inner cavity is filled with helium to ensure heat transfer. The neutron source enclosure is sealed with two shanks: upper and lower ones. It is sealed by argon arc welding. The ampule is placed in the neutron source enclosure with a 0.1 mm clearance. The ampule is positioned in a four-ribbed enclosure in order to provide an additional safety barrier. The operational neutron source ensures controlled reactor start-up from the subcritical state with fully submerged CPS rods at any time during the entire service life of the core, except for its initial start-up. The container-type Secondary Startup operational neutron source has an enclosure 1 made of ferritic martensitic grade steel with a diameter of 12 mm in the smooth part, and the wall thickness of 0.4 mm, with four spiral ribs 13 shown in FIGS. 1 and 3 located on the outer side of the enclosure. The diameter along the ribs 13 is 13.5 mm, the rib winding pitch is 750 mm. The enclosure houses an ampule 4 with active elements: antimony and beryllium. The active components are located in separate antimony and beryllium cavities of coaxial design. An upper gas collector is located above the ampule 5, which serves as a compensation volume collecting gaseous fission products. The gas collector 5 is pressed against the ampule through washers 7 with a spring 6. At the bottom, the ampule is supported by a reflector 8 and a bottom gas collector 9. The neutron source enclosure inner cavity is filled with helium to ensure heat transfer. The neutron source enclosure is sealed with two shanks: upper shank 2 and lower shank 3. It is sealed by argon arc welding. The source enclosure, gas collectors, reflector and washers are made of martensite-ferrite grade steel. FIG. 2 shows the ampule of a coaxial design with the antimony 10 in the ampule central enclosure 11. The ampule central enclosure 11 is made of a niobium-based alloy which does not react with antimony during filling and operation. A beryllium bed 14 (shown in FIG. 3) is located between the ampule central enclosure 11 and the ampule enclosure 12. Beryllium is a powder with particle size from 60 to 200 micron, and the beryllium powder bed porosity is 45%. The ampule enclosure 12 is made of martensite-ferrite steel poorly reacting with beryllium. The central ampule enclosure containing the antimony is leak tight. The ampule central enclosure and its elements may be made, for example, of the VN-2AE alloy. The ampule 4 is placed in the enclosure 1 of martensite-ferrite grade steel with a 0.1 mm clearance. The length of the ampule active part is 190 mm, the overall length of the operational neutron source (active part) is 1,720 mm. Due to provision of additional safety barriers between the coolant and the source active part materials, the operational neutron source ofthe claimed design, its active part, provides reliable operation of the reactor plant for a campaign of 53,000 effective hours (approximately 8 years). |
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054597684 | abstract | A safety device against overpressure failure of a nuclear reactor pressure vessel in case of inadequate core cooling, includes a pressure relief system responding as a function of temperature. A differential-pressure-loaded pressure relief valve set in a wall or an immediately adjacent pipeline of the pressure vessel which is exposed to primary pressure, has a closure piece that is preferably a differential-pressure piston being mounted so as to be longitudinally displaceable and being sealingly retained in a closure position thereof by a fusible stop. When an upper threshold temperature is reached in the interior of the reactor, which causes the fusible stop to melt due to a threshold temperature heat flow reaching the stop, the differential-pressure piston is moved into an opened position thereof. With correspondingly lower cross-sectional dimensions of the pressure relief valve and lines connected thereto, the pressure relief line may alternatively be constructed as a control line for a separate relief valve. |
claims | 1. A structure, comprising:a middle portion comprising a rigid member, the middle portion extending along a longitudinal dimension of the structure; andan outer portion configured to contact a bodily surface, the outer portion coupled to the middle portion by way of a plurality of ribs, the plurality of ribs configured to space the middle portion away from the bodily surface;wherein the structure is configured to absorb and displace energy upon impact. 2. The structure of claim 1, wherein the middle portion, the outer portion, and the plurality of ribs define a plurality of voids, 3. The structure of claim 1, wherein the outer portion and the middle portion each have a width, and wherein the width of the outer portion is wider than the width of is the middle portion. 4. The structure of claim 1, wherein the rigid member is relatively more rigid than the outer portion and the plurality of ribs, 5. The structure of claim 1, wherein the outer portion comprises a top end and a bottom end, and wherein the plurality of ribs extend from the middle portion in an angular direction toward the top end of the outer portion. 6. The structure of claim 1, further comprising:at least one securing tab positioned on or coupled to the outer portion, the at least one securing tab configured to receive a second structure so that the structure can be held in place upon a user's body when the second structure is received thereby. 7. The structure of claim 1, wherein the middle portion further comprises an outer layer positioned external to the rigid member, the outer layer defining an outer surface and the rigid member defines an inner surface. 8. The structure of claim 7, wherein the outer layer is over-molded upon the rigid member. 9. The structure of claim 1, wherein the rigid member comprises a polycarbonate material. 10. The structure of claim 1, wherein the outer portion comprises a material selected from the group consisting of a flexible material and a rubber-like material. 11. The structure of claim 1, wherein the rigid member comprises a first material, wherein the outer portion and the plurality of ribs comprise a second material, and wherein the first material is relatively more rigid than the second material. 12. The structure of claim 1, wherein the structure is configured as an athletic supporter. 13. The structure of claim 1, wherein the structure is configured as a shin guard. 14. The structure of claim 1, wherein the structure is configured for placement upon a user's body at an area selected from the group consisting of the user's shoulder, the user's shin, the user's knee, the user's elbow, and the user's hip. 15. A structure, comprising:a middle portion comprising a rigid member, the middle portion extending along a longitudinal dimension of the structure; andan outer portion configured to contact a bodily surface, the outer portion coupled to the middle portion by way of a plurality of ribs, the plurality of ribs configured to space the middle portion away from the bodily surface;wherein the middle portion, the outer portion, and the plurality of ribs define a plurality of voids;wherein the rigid member is relatively more rigid than the outer portion and the plurality of ribs; andwherein the structure is configured to absorb and displace energy upon impact. 16. The structure of claim 15, wherein the outer portion comprises a top end and a bottom end, and wherein the plurality of ribs extend from the middle portion in an angular direction toward the top end of the outer portion. 17. The structure of claim 15, wherein the rigid member comprises a first material, wherein the outer portion and the-plurality of ribs comprises a second material, and wherein the first material is relatively more rigid than the second material, 18. The structure of claim 15, wherein the structure is configured as a shin guard, 19. A shin guard, comprising:a middle portion comprising a rigid member, the middle portion extending along a longitudinal dimension of the shin guard; andan outer portion configured to contact a bodily surface, the outer portion coupled to the middle portion by way of a plurality of ribs, the plurality of ribs configured to space the middle portion away from the bodily surface;wherein the middle portion, the outer portion, and the plurality of ribs define a plurality of voids; andwherein the shin guard is configured to absorb and displace energy upon impact. 20. The shin guard of claim 19, further comprising:at least two securing tabs positioned on or coupled to the outer portion, the at least two securing tabs configured to receive a structure so that the shin guard can be held in place upon a user's body when the second structure is received thereby. |
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claims | 1. A computer-implemented method of optimizing at least one of a design, production or testing process in a mass manufacturing process, the method comprising steps of:collecting error data relating to a product at a plurality of points along its design, production and distribution chain, wherein the error data comprises both test data found during production testing of the product, as well as post production customer service events;classifying the error data into categories of errors to provide classified error data;analyzing relationships among the classified error data; andrecommending modifications to an end user for at least one of the design, production, delivery, or testing processes based on the analysis, the recommending step comprising steps of:recommending modifications to the design of the product if the error data is collected after design but before manufacture of the product, and if a design error is found;recommending modifications to the delivery process if the error data is collected after delivery, and if an error is found;recommending modifications to the production process if the error data is collected after producing part of the product and if a part error is found;recommending modifications to the process of making a subsystem of the part if the error data is collected after producing the subsystem of the product comprising the part; andrecommending modifications to the mass manufactuing process if the error data is collected after mass manufacturing, but before delivery, and if a mass manufacturing error is found. 2. The method of claim 1, wherein the categories of errors include at least one of the following:errors found during product development;errors found in instances of the product after manufacturing, but before delivery;errors that occur as a result of the transportation process; anderrors found by a product service provider. 3. The method of claim 1 wherein the modifications include a correction of problems in one or more of the following: design, test, manufacturing, and transportation in the mass manufacturing process. 4. The method of claim 1 wherein the method is performed in a plurality of iterations to ensure continuous improvement. 5. The method of claim 1, wherein the error data is at least one selected from the following attribute types: phase when found, vehicle identification, unique identifier, revealing condition, open date, close date, customer impact, ownership duration, product impact, non-product impact, scope of fix, corrective action, responsible agent, part history, part hierarchy, part number, number of hits affect, and complexity level. 6. The method of claim 1, further comprising steps of:mapping a symptom to a revealing condition;mapping the revealing condition to a test type, andmapping a scope of a fix to phases of error injection mapping. 7. The method of claim 1, wherein error data and analysis from a parts supplier can be used for a more comprehensive analysis of an organization that uses the supplied parts. 8. The method of claim 1, wherein classifications are derived automatically. 9. The method of claim 8, wherein the classifications are based on one or more of a scope of fix, action, and a duration of ownership, and phase of error injection. 10. The method of claim 1, further comprisingperforming an analysis of aspects of the mass manufacturing development process and product, including at least one of: evaluating testing effectiveness; evaluating mass manufacturing process; evaluating; transportation process; identifying safety concerns; comparing in-process with post sales problems. 11. The method of claim 10, wherein the analysis of a given aspect of the mass manufacturing process includes the generation of two or more graphical representations of the classified error data. 12. The method of claim 11, wherein each graphical presentation includes one or more interpretations, including text. 13. The method of claim 1 further comprising a step of enabling the end user to provide the method steps of collecting, classifying, analyzing and recommending for a second user. 14. The method of claim 13 further enabling the end user to provide the steps of collecting, classifying, analyzing and recommending on a continuing basis to the second user. 15. The method of claim 13 further enabling the end user to update the steps or analysis techniques or both. 16. The method of claim 1 wherein the product of the mass manufacturing development process includes integrated software, hardware, and electronics. 17. The method of claim 1 wherein error data and analysis are used as a reliability measure for the overall quality of the process and product. |
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054141958 | summary | BACKGROUND OF INVENTION This invention relates to a system and method for monitoring and controlling the level of heavy metal contamination in the slurry of a soil or other particulate material washing process. BACKGROUND OF THE INVENTION Contamination of soil and other particulate materials, such as for instance sludges, sediments, scrap yard dust and the like, is becoming a more common environmental problem. Often the particulate material is contaminated with heavy metals such as, for instance, cadmium, copper, lead, mercury, radium, uranium and thorium. Various methods and systems have been developed for reducing the concentration of these heavy metal contaminants in the particulate material to acceptable levels, typically well below 1000 ppm and generally below 100 ppm. One such technique is disclosed in commonly owned related U.S. patent application Ser. No. 07/529,092 filed May 25, 1990 now U.S. Pat. No. 5,128,068 entitled "Method and Apparatus for Cleaning Contaminated Particulate Material." In this process, the soil or other particulate material is first washed with a leachate or surfactant to mobilize soluble and dispersible contaminants. Large particles are mechanically separated, washed and returned to the site. The fines in which the heavy metals are concentrated, are together with the leachate and solubilized contaminants, then separated from the intermediate sized particles by a counterflow of washwater to produce a waste slurry which is disposed of or further treated. The slurry of separated intermediate sized particles and wash water is dewatered to produce additional recovered particulate material. The size of the fines separated from the intermediate sized particles can be varied (more fines recovered with the intermediate sized particles or more diverted in the waste slurry) to adjust the level of contamination remaining in the recovered particulate material. There is a need for a reliable on-line system and method for monitoring the concentration of the heavy metal contaminants in the recovered particulate material for assuring that the required reduction in contamination level has been realized and to control the process to achieve such a result. One of the difficulties is that it is the residual concentration of the heavy metal contaminants in the recovered particulate matter which must meet the required standards, not the slurry. There is a further need therefore for such a system and method which can determine on-line the concentration for residual heavy metal contaminants in the solids fraction of a slurry. SUMMARY OF THE INVENTION These and other needs are satisfied by the invention which is directed to a system and method for on-line measurements and control of the concentration of heavy metal contamination in a soil or other particulate material washing process in which a slurry of washed particulate material having residual heavy metal contamination is produced. In order to determine the concentration of the residual heavy metal contamination in the particulate material in the slurry, energy is applied to the slurry at a level to produce electromagnetic radiation which is characteristic of the constituents of the slurry including at least the residual heavy metal contaminants. The electromagnetic radiation is analyzed to measure the amount of heavy metal contaminants and the amount of particulate material in the portion of the slurry to which the energy has been applied and from these amounts the concentration of residual heavy metal contaminants can be determined. In accordance with one embodiment of the invention, the energy is applied to the slurry in the form of x-rays at a wavelength which causes secondary emission or x-ray fluorescence of the heavy metal contaminants. The Compton scatter at wavelengths adjacent the characteristic wavelength emitted by the heavy metal contaminant is also determined and used as a measure of the mass of the particulate material irradiated which in turn is used to calculate the concentration of the heavy metal contaminant in the recovered particulate material. In another embodiment of the invention, employing prompt neutron activation, energy is applied to the slurry by a thermal neutron field. Thermal neutrons captured by nuclei of elements in the slurry transmute the element to another isotope in an excited state. These nuclei de-excite promptly emitting gamma rays. The residual heavy metal contaminants emit gamma rays of readily identifiable characteristic energies. The magnitude of gamma rays at the characteristic energy levels is a measure of the number of atoms of the heavy metal contaminant present in the slurry within the neutron field. The hydrogen in the water phase of the slurry also emits gamma rays of characteristic energy levels, so that the water content of the slurry can be determined. The mass of particulate material is determined using a density measurement and the amount of water present. This prompt neutron activation technique measures the concentration of residual contaminants in a larger volume than the x-ray fluorescence technique which can only measure contamination near the surface of the slurry. A third embodiment of the invention employs laser induced breakdown in which energy is applied to the slurry through a laser beam causing dielectric breakdown of the elements in the slurry which in turn emit light of characteristic energies. Characteristic light emitted by the heavy metal contaminant and reference elements which have been established statistically from samples to be substantially uniformly present in the particulate matter being treated, is measured and used to calculate the concentration of the heavy metal in the particulate material. As another aspect of the invention, a neural network trained with slurry samples with varying concentrations of contaminants and varying water content can be used to analyze the characteristic emitted radiation. When used to control the soil washing process, the network need only output a signal indicating whether the concentration of contaminant in the particulate material fraction of the slurry is within or not within, with an appropriate margin, a specified required level. |
claims | 1. An X-ray inspection system, comprising the following elements disposed sequentially along a central axis: an X-ray source capable of projecting a beam of radiation along said central axis; a first collimator disposed coaxially with said central axis at a first location along said central axis, said first collimator having a first slit-shaped aperture having a first dimension in a first direction perpendicular to said central axis; a second collimator disposed coaxially with said central axis at a second location along said central axis, said second collimator having a second slit-shaped aperture having a second dimension in said first direction; and means for causing said central axis to pass through a selected inspection zone of a target, wherein said second location of said second collimator and said second dimension of said second aperture are selected such that the portion of said target actually illuminated by said beam measured in said first direction is substantially equal to the size of said selected inspection zone measured in said first direction. 2. The X-ray inspection system of claim 1 further comprising: claim 1 an X-ray detector disposed adjacent said target and opposite said second collimator; and a third collimator disposed between said target and said detector. 3. The X-ray inspection system of claim 2 wherein said third collimator has a third aperture, said third aperture being oriented perpendicular to said central axis and to said first direction. claim 2 4. The X-ray inspection system of claim 1 wherein said second dimension of said second aperture is adjustable. claim 1 5. A X-ray inspection method, comprising: providing an X-ray source capable of projecting a beam of radiation along a central axis; providing a first collimator disposed coaxially with said central axis at a first location along said central axis, said first collimator having a first slit-shaped aperture having a first dimension in a first direction perpendicular to said central axis; providing a second collimator disposed coaxially with said central axis at a second location along said central axis, said second collimator having a second slit-shaped aperture having a second dimension in said first direction; providing means for causing said central axis to pass through a selected inspection zone of a target, wherein said step of providing said second collimator includes selecting said second location and said second dimension of said second aperture such that the portion of said target actually illuminated by said beam measured in said first direction is substantially equal to the size of said selected inspection zone measured in said first direction. 6. The X-ray inspection method of claim 5 further comprising: claim 5 providing an X-ray detector disposed adjacent said target and opposite said second collimator; and providing a third collimator disposed between said target and said detector. 7. The X-ray inspection method of claim 6 wherein said third collimator has a third aperture, said third aperture being oriented perpendicular to said central axis and to said first direction. claim 6 8. An X-ray inspection system, comprising the following elements disposed sequentially along a central axis: an X-ray source capable of projecting a beam of radiation along said central axis; a first collimator disposed coaxially with said central axis at a first location along said central axis, said first collimator having a first slit-shaped aperture oriented in a first direction; a second collimator disposed coaxially with said central axis at a second location along said central axis, said second collimator having a second slit-shaped aperture oriented in said first direction; and means for supporting a target, wherein said second collimator is positioned as close as possible to said means for supporting said target without interfering with said target. 9. The X-ray inspection system of claim 8 further comprising: claim 8 an X-ray detector disposed adjacent said target and opposite said second collimator; and a third collimator disposed between said target and said detector. 10. The X-ray inspection system of claim 9 wherein said third collimator is oriented perpendicular to said first direction. claim 9 11. The X-ray inspection system of claim 8 wherein said second aperture is adjustable is said first direction. claim 8 |
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abstract | In one embodiment, a system and method for dry storage comprises removing spent fuel rods from their fuel rod assemblies and placing the freed fuel rods in a storage cell of a dry storage canister with a high packing density and without a neutron absorber material present. |
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claims | 1. An X-ray output apparatus, comprising:an X-ray output unit includes a plurality of X-ray sources and configured to output parallel X-ray beams;a shield on which positions that block the output parallel X-ray beams and positions that transmit the parallel X-ray beams are variable; anda control unit configured to:control the output of the parallel X-ray beams in the X-ray output unit and the positions through which the parallel X-ray beams are transmitted in the shield. 2. The X-ray output apparatus according to claim 1,wherein, on the shield, grid-shaped regions are set, andwherein the control unit is further configured to block concurrent transmission of the parallel X-ray beams in positions corresponding to adjacent regions among the grid-shaped regions on the shield. 3. The X-ray output apparatus according to claim 2,wherein the X-ray output unit further includes a plurality of collimators that form the parallel X-ray beams, andwherein the grid-shaped regions on the shield correspond to the plurality of collimators in a one-to-one relation. 4. The X-ray output apparatus according to claim 1,wherein the shield includes a transmission hole to transmit the parallel X-ray beams, andwherein the control unit is further configured to control the positions, through which the X-rays are transmitted, based on a movement of the shield to shift a position of the transmission hole. 5. The X-ray output apparatus according to claim 4,wherein, based on the movement of the shield, the control unit is further configured to control the X-ray output unit to stop the output of the parallel X-ray beams, andwherein, upon completion of the movement of the shield, the control unit is further configured to control the X-ray output unit to output the parallel X-ray beams. 6. The X-ray output apparatus according to claim 4, wherein the transmission hole has a shape including at least a curved part. 7. The X-ray output apparatus according to claim 6, wherein the shape of the transmission hole is an asymmetric shape. 8. The X-ray output apparatus according to claim 7, wherein the asymmetric shape is a shape in which, based on a rectangular shape used as a reference, asymmetry in a corner portion of the rectangular shape is smaller than asymmetry in a center portion of the rectangular shape. 9. The X-ray output apparatus according to claim 6, wherein the shape in the transmission hole includes at least one of an arc shape, a convex shape, a concave shape, or an uneven shape. 10. The X-ray output apparatus according to claim 1,wherein, on the shield, grid-shaped regions are set,wherein the shield includes, in each region of the grid-shaped regions, a shield member opening-closing mechanism to one of open or close shield members to selectively transmit the parallel X-ray beamswherein the control unit is further configured to control the positions through which the parallel X-ray beams are transmitted, based on a state of the shield member opening-closing mechanism of each region of the grid-shaped regions, andwherein the state comprises one of state in which the shield members are open or a state in which the shield members are closed. 11. The X-ray output apparatus according to claim 10, wherein a shape of the grid-shaped regions includes at least a curved part. 12. The X-ray output apparatus according to claim 11, wherein the shape of the grid-shaped regions is an asymmetric shape. 13. The X-ray output apparatus according to claim 11, wherein the shape of the curved part includes at least one of an arc shape, a convex shape, a concave shape, or an uneven shape. 14. The X-ray output apparatus according to claim 10, wherein, based on a change in the positions through which the parallel X-ray beams are transmitted, the control unit is further configured to set all the shield member opening-closing mechanisms in the shield to a state in which the shield members are closed, and then set a shield member opening-closing mechanism corresponding to a specific position in the shield to a state in which the shield members are open. 15. The X-ray output apparatus according to claim 14, wherein the control unit is further configured to control the X-ray output unit to continuously output the parallel X-ray beams. 16. The X-ray output apparatus according to claim 10,wherein, based on a change in the positions through which the parallel X-ray beams are transmitted, the control unit is further configured to control the X-ray output unit to stop the output of the parallel X-ray beams until the change in the positions through which the parallel X-ray beams are transmitted is completed. 17. The X-ray output apparatus according to claim 1, wherein the control unit is further configured to control the X-ray output unit to output the parallel X-ray beams only for a position corresponding to the positions through which the parallel X-ray beams are transmitted in the shield. 18. The X-ray output apparatus according to claim 1,wherein the shield is in an output direction of the parallel X-ray beams in the X-ray output unit, andwherein the shield is in between the X-ray output unit and a subject to which the parallel X-ray beams are radiated. 19. The X-ray output apparatus according to claim 1,wherein the control unit is further configured to control an apparatus to display an image corresponding to control of the output of the parallel X-ray beams and of the positions through which the parallel X-ray beams are transmitted, andwherein the image is based on X-ray detection data of the parallel X-ray beams transmitted through the shield. |
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046882421 | abstract | An X-ray imaging system has an X-ray source, an X-ray image detection section, an X-ray mask member, a drive unit, a memory, a calculating section, and an image output unit. An X-ray image is detected by the X-ray image detection section. The X-ray mask member has X-ray shielding regions, distributed in a predetermined pattern, which locally shield the X-ray. The mask member is driven by the drive unit so that it is inserted in or removed from an X-ray radiation field between the X-ray image detection section and the X-ray source, and is sequentially displaced to predetermined positions in the radiation field. The calculating section calculates scattered X-ray intensity distribution data based on a plurality of transmission X-ray data obtained by irradiating an object with X-rays with the mask member located at different positions in the radiation field, and transmission X-ray data obtained by irradiating the object with X-rays with the mask member located outside this field. The calculating section then calculates X-ray image data from the scattered X-ray intensity distribution data and transmission X-ray data obtained with the mask member located outside the radiation field. |
claims | 1. A radiation therapy delivery system comprising a plurality of measurement devices configured to measure a direction to and a distance from a plurality of fixed landmarks and at least one of a moveable radiation nozzle and a moveable patient positioner, the system configured to calculate a current spatial position and angular orientation of at least one of the radiation nozzle and the patient positioner with reference to the plurality of fixed landmarks, the system further configured to determine movement commands to induce at least one of the radiation nozzle and the patient positioner to move from the current spatial position and angular orientation to a desired spatial position and angular orientation. 2. The system of claim 1, wherein the plurality of measurement devices are configured to measure a direction to and a distance from a plurality of markers on at least one of the moveable radiation nozzle and the moveable patient positioner. 3. The system of claim 2, wherein each measurement device is configured to independently determine a current spatial position and angular orientation of the measurement device with reference to the plurality of fixed landmarks, and wherein the system is further configured to calibrate the plurality of measurement devices by correlating the current spatial position and angular orientation of each measurement device. 4. The system of claim 1, wherein the plurality of measurement devices are configured to independently measure a direction to and a distance from at least one of the radiation nozzle and the patient positioner from multiple perspectives, wherein the system is configured to determine a direction vector from each measurement device to at least one of the radiation nozzle and the patient positioner, and wherein the system is configured to calculate the point in space where the vectors from each measurement device intersect to calculate a current spatial position and angular orientation of at least one of the radiation nozzle and the patient positioner with reference to the plurality of fixed landmarks. 5. The system of claim 1, further comprising one or more moveable imagers arranged to obtain image data of at least a portion of the patient positioner, wherein the plurality of measurement devices are further configured to determine a current three-dimensional spatial position and an angular orientation of the one or more imagers with reference to the plurality of fixed landmarks. 6. The system of claim 5, wherein the system is further configured to determine a movement envelope for the one or more imagers using the current spatial position and angular orientation of the one or more imagers. 7. The system of claim 1, wherein the plurality of measurement devices include cameras, laser measurement devices, or radio-location devices. 8. The system of claim 1, further comprising one or more feedback devices in communication with at least one of the radiation nozzle and the patient positioner, the one or more feedback devices configured to independently determine the current position of at least one of the radiation nozzle and the patient positioner, and wherein the system is configured to determine movement commands based on current position information received from the plurality of measurement devices and the one or more feedback devices. 9. The system of claim 1, wherein the system receives position signals from one or more movable imagers indicative of a spatial position of a target iso-center of a patient affixed to the patient positioner, and wherein the system is configured to determine movement commands to induce at least one of the radiation nozzle and the patient positioner to align the target iso-center at a desired translation and rotation position. 10. A radiation therapy delivery system comprising:means for measuring a direction to and a distance from a plurality of fixed landmarks and at least one of a moveable radiation nozzle and a moveable patient positioner;means for calculating a current spatial position and angular orientation of at least one of the radiation nozzle and the patient positioner with reference to the plurality of fixed landmarks; andmeans for determining movement commands to induce at least one of the patient positioner and the radiation nozzle to move from the current spatial position and angular orientation to a desired spatial position and angular orientation. 11. The system of claim 10, wherein the means for measuring includes at least one of a camera, a laser measurement device, and a radio-location device. 12. The system of claim 10, wherein the means for calculating includes a 6-D module configured to receive location measurements from the measuring means and to determine a 6-dimensional spatial position and angular orientation of at least the radiation nozzle and the patient positioner with respect to the fixed reference objects. 13. The system of claim 10, wherein the means for determining movement commands includes a command and control module in communication with the means for calculating and at least one of the radiation nozzle and the patient positioner. 14. A method of controlling movement of a patient positioner in a radiation therapy delivery system, the method comprising:measuring a direction to and a distance from a plurality of fixed landmarks and at least one of a moveable radiation nozzle and a moveable patient positioner;calculating a current spatial position and angular orientation of at least one of the radiation nozzle and the patient positioner with reference to the plurality of fixed landmarks; anddetermining movement commands to induce at least one of the radiation nozzle and the patient positioner to move from the current spatial position and angular orientation to a desired spatial position and angular orientation. 15. The method of claim 14, further comprising:measuring the position of a plurality of markers on at least one of the radiation nozzle and the patient positioner from multiple perspectives; andcalibrating the measured position of the plurality of markers with respect to each other and the plurality of fixed landmarks. 16. The method of claim 14, further comprising moving at least one of the radiation nozzle and the patient positioner based on the movement commands. 17. The method of claim 16, further comprising:recalculating the spatial position and angular orientation of at least one of the radiation nozzle and the patient positioner with reference to the plurality of fixed landmarks; anddetermining whether the desired spatial position and angular orientation of at least one of the radiation nozzle and the patient positioner has been achieved. 18. The method of claim 14, further comprising:determining a current three-dimensional spatial position and an angular orientation of at least one of a movable radiographic imager and a moveable x-ray source; anddetermining a movement envelope for at least one of the imager and the x-ray source using the current spatial position and angular orientation information. 19. The method of claim 14, further comprising independently performing second local position measurements of at least the radiation nozzle and the patient positioner. 20. The method of claim 19, wherein movement commands are determined based on the current spatial position and angular orientation of at least one of the radiation nozzle and the patient positioner and the second local position measurements. |
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summary | ||
description | Field of the Invention Example embodiments relate generally to nuclear reactors, and more particularly to a method and apparatus for a Boiling Water Reactor (BWR) jet pump inlet mixer compliant stop clamp assembly that applies a controlled lateral force to an inlet mixer. Related Art A reactor pressure vessel (RPV) of a boiling water reactor (BWR) typically has a generally cylindrical shape and is closed at both ends (for example by a bottom head and a removable top head). A top guide typically is spaced above a core plate within the RPV. A core shroud, or shroud, typically surrounds the core and is supported by a shroud support structure. Particularly, the shroud has a generally cylindrical shape and surrounds both the core plate and the top guide. There is a space or annulus between the cylindrical reactor pressure vessel and the cylindrically shaped shroud. In a BWR, hollow tubular jet pumps positioned within the shroud annulus provide the required reactor core water flow. The upper portion of the jet pump, known as the inlet mixer, is laterally positioned and supported against two opposing rigid contacts within jet pump restrainer brackets by a gravity actuated wedge. Conventionally, set screw gaps may be formed by movement of either the main wedge or the inlet mixer. Additionally, vibration may cause wear of the main wedge and/or set screws. Set screw gaps allow the inlet mixer to experience flow induced vibration (FIV), causing excessive wear to jet pump components. Furthermore, the conventional jet pump assembly may also experience slip joint leakage (i.e., leakage between the mechanical connection of the inlet mixer and diffuser). Example embodiments provide a method and an apparatus for a BWR jet pump inlet mixer compliant stop that may apply a controlled, reduced horizontal force to the side of the inlet mixer to stabilize the inlet mixer. The inlet mixer compliant stop, in conjunction with two other non-compliant stops, may provide a three-point contact to mitigate inlet mixer flow induced vibration (FIV) and slip joint leakage. The three-point contact may be used along with an existing (i.e., conventional) main wedge and set screws, or it may be used in lieu of an existing main wedge and set screws (i.e., an existing main wedge and/or existing set screws may be removed). Detailed example embodiments are disclosed herein. However, specific structural and functional details disclosed herein are merely representative for purposes of describing example embodiments. Example embodiments may, however, be embodied in many alternate forms and should not be construed as limited to only the embodiments set forth herein. Accordingly, while example embodiments are capable of various modifications and alternative forms, embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that there is no intent to limit example embodiments to the particular forms disclosed, but to the contrary, example embodiments are to cover all modifications, equivalents, and alternatives falling within the scope of example embodiments. Like numbers refer to like elements throughout the description of the figures. It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and, similarly, a second element could be termed a first element, without departing from the scope of example embodiments. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. It will be understood that when an element is referred to as being “connected” or “coupled” to another element, it may be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being “directly connected” or “directly coupled” to another element, there are no intervening elements present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., “between” versus “directly between”, “adjacent” versus “directly adjacent”, etc.). The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises”, “comprising,”, “includes” and/or “including”, when used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. It should also be noted that in some alternative implementations, the functions/acts noted may occur out of the order noted in the figures. For example, two figures shown in succession may in fact be executed substantially concurrently or may sometimes be executed in the reverse order, depending upon the functionality/acts involved. FIG. 1 is a perspective view of a conventional boiling water nuclear reactor (BWR) jet pump assembly. The jet pump assembly includes a large riser pipe 1 between two inlet mixers 2. The inlet mixers 2 inject water into diffusers 4. A restrainer bracket assembly 6 may be used to conventionally restrain movement and vibration of the inlet mixers 2. The restrainer bracket assembly 6 may also be used to conventionally mitigate slip joint leakage that occurs between the interface of the inlet mixers 2 and diffusers 4. FIG. 2 is an enlarged view of a conventional BWR jet pump restrainer bracket assembly 6. The conventional restrainer bracket assembly 6 generally includes a restrainer bracket encircling the inlet mixer and pressing against a side wall of the riser pipe 1. The restrainer bracket provides three points of contact for each inlet mixer 2 via a main wedge 8 and two set screws 14 (see FIG. 5A, showing the position of the two set screws 14 for each inlet mixer 2). Guide ears 12 vertically project from the restrainer bracket 10 at the location of each set screw 14. FIG. 3 is an enlarged, side view of a conventional BWR jet pump assembly restrainer bracket assembly 6. Note that set screws 14 contact a belly band 18 encircling the inlet mixer 2 (also shown in FIG. 5A). Restrainer bracket contoured wall 10a hugs a side wall of riser pipe 1. Conventionally, a pocket 16 exists between riser pipe 1 and inlet mixer 2 (more particularly, the pocket 16 exists between contoured wall 10a of restrainer bracket 10 and belly band 18). FIG. 4 is a detailed view of a jet pump inlet mixer compliant stop 20, in accordance with an example embodiment of the invention. The compliant stop 20 may include a main body 22 bracketed by two C-clamp frames 28. A foot 24 may be provided to extend longitudinally across a rear surface of the main body 22 (shown in more detail in FIG. 4A). Main body 22 may include an arced cold spring 22a structure attached to the main body 22. The cold spring 22a may be located toward a mid-section of the main body 22 and may project beyond a front surface of the main body 22. The cold spring 22a may include a swivel contact pad 32 attached to a distal end of the cold spring 22a. The swivel contact pad 32 may be held on the distal end of the cold spring 22a by a shoulder screw 50. At least one jacking bolt 30 may run through main body 22 and foot 24 (shown in better detail in FIGS. 6 and 15). Preferably, one jacking bolt 30 may be located on either side of cold spring 22a. Threads on the jacking bolts 30 may mate with threaded connections in the main body, allowing a tightening of the jacking bolts 30 to separate foot 24 from main body 22 (as described herein, in more detail). Ratchet keeper 26 may be included on a top surface of foot 24 (shown in better detail in FIG. 6A). C-clamps on either end of main body 22 may include an outer C-clamp frame 28 and an inner C-clamp body 34. The C-clamp body 34 may be held in place in the C-clamp frame 28 via socket head cap screws 36 (explained in more detail, herein). Note that a sloped face 28a of C-clamp frame 28 contacts a sloped face 22b of main body 22, providing both vertical and horizontal stabilization of the main body 22 between the two C-clamps (as described in more detail, herein). The angle of the slope may be a moderate angle from a horizontal plane (the horizontal plane may be the flat top surface of the main body 22 or the foot 24), such as a 17 degree slope, for instance. FIG. 4A is a rear view of the jet pump inlet mixer compliant stop 20 of FIG. 4, in accordance with an example embodiment of the invention. FIG. 4A shows the ratchet keeper 26 extending along a top surface of foot 24 (the purpose of the ratchet keeper 26 described, herein). FIG. 4A also shows a shape of an inner surface 24a of foot 24 that may cause foot 24 to somewhat follow a shape of contoured wall 10a of the restrainer bracket 10, as shown in FIG. 5. A sloped face 24h may also be provided on foot 24, allowing sloped face 28a of C-clamp frame 28 to provide both vertical and horizontal stabilization for foot 24 (similar to the way in which the sloped face 28a of C-clamp frame 28 also engages sloped face 22b of main body 22, shown in FIG. 4). The sloped face 24h of foot 24 may be a moderate angle from a horizontal (similar to the description of FIG. 4), such as 17 degrees. FIG. 5 is a detailed view of a jet pump inlet mixer compliant stop 20 installed on a BWR restrainer bracket assembly 6, in accordance with an example embodiment of the invention. The C-clamp frames 28 and C-clamp bodies 34 may attach to restrainer bracket 10 and hold the compliant stop 20 in place in pocket 16 (see pocket 16, shown in FIG. 3). Jacking bolts 30 may be used to adjust the force the cold spring 22a applies to belly band 18 of inlet mixer 2. Once the desired force of cold spring 22a is reached by tightening jacking bolts 30 (explained in more detail, herein; see discussion related to FIG. 15, in particular), the jacking bolts 30 may be held in place via ratchet keeper 26. Notice that the general shape of foot 24 generally matches the shape of contoured wall 10a of restrainer bracket 10, so as to fit snuggly within pocket 16. The jet pump inlet mixer compliant stop 20 may be installed with two non-compliant stops 38 (placement of the additional non-compliant stops 38 are best shown in FIG. 5A) to provide the jet pump inlet mixer compliant stop 20 structure with three points of contact. The jet pump inlet mixer compliant stop 20 may provide a reaction force (i.e., a firm point of contact for the riser pipe 2 to rest against, as compliant stop 20 applies the lateral force on the riser pipe 2) that causes the inlet mixer 2 to shift away from the riser pipe 1, thereby reducing the deleterious impact of set screw gaps (gaps between belly band 18 and set screws 14) that may cause chattering and damage. The lateral force the compliant stop 20 imparts on the riser pipe 2 may be in a direction that is opposite from the force that may be provided by an existing wedge 8. In other words, the lateral force provided by the compliant stop 20 may be additive with the inlet mixer 2 hydraulic loads already experienced by an inlet mixer with a conventional restrainer bracket assembly 6. However, because the lateral force applied by the compliant stop 20 may be in a direction that is opposite the direction of the force created by wedge 8, undesirable motion of the inlet mixer 2 (such as flow induced vibration of the inlet mixer 2) and restrainer bracket assembly 6 components (such as chattering of the gravity wedge 8 and/or set screws 14) may be eliminated, thereby reducing potential damage to component parts. The adjustable feature of hard stops 38 coupled with the lateral force of the compliant stop 20 may provide an accurately controlled preload capable of preventing slip joint flow induced vibration (SJFIV), which may eliminate the need for slip joint clamps or other conventional structure used to mitigate undesired component vibration. Optionally, if the non-compliant stops 38 are used, the wedge 8 and/or set screws 14 may be removed. Also, alternatively to using two non-compliant stops 38, the jet pump inlet mixer compliant stop 20 may be used with the existing wedge 8 and set screws 14. The two non-compliant stops 38 may be adjustable hard stops (such as ADJUSTABLE HARD STOPS FOR NUCLEAR REACTOR RESTRAINER BRACKETS AND METHODS OF USING THE SAME, disclosed in U.S. application Ser. No. 12/980,010), and incorporated by reference it its entirety. The non-compliant stops 38 may provide a reaction force on either side of the location of wedge 8. The two non-compliant stops 38 may provide horizontal constraints between the restrainer bracket 10 and the inlet mixer 2, thereby causing the jet pump inlet mixer compliant stop 20 and two non-compliant stops 38 to provide three points of contact that, in essence, may take the place of the three points of contact that may be conventionally provided by the wedge 8 and set screws 14. The two non-compliant stops 38 may also be set screws, or any other structure capable of pushing (or, horizontally constraining) the restrainer bracket 10 away from the inlet mixer 2 and allowing three points of contact that include the jet pump inlet mixer compliant stop 20 as one of the point s of contact. FIG. 5A is a top view of the jet pump inlet mixer compliant stop 20 installed on a BWR restrainer bracket assembly 6 (shown in FIG. 5), in accordance with an example embodiment of the invention. FIG. 5A shows the swivel contact pad 32 on a distal end of cold spring 22a contacting belly band 18 to place a controlled lateral force on the inlet mixer 2 (i.e., the cold spring 22a may impart the lateral force toward a centerline of the inlet mixer 2 and away from a centerline of the riser pipe 1). FIG. 5A also shows the placement of non-compliant stops 38 that may be used to provide a three-point contact (along with jet pump inlet mixer compliant stop 20) to stabilize movement of the inlet mixer 2. The location of the swivel contact pad 32 contacting the inlet mixer 2 and the locations of non-compliant stops 38 contacting the inlet mixer 2 may be spaced apart such that they are approximately 120 degrees apart from each other on the inlet mixer 2. FIG. 6 is a detailed view of a jet pump inlet mixer compliant stop 20 shown without C-clamps, in accordance with an example embodiment of the invention. Note that a gap G (also shown in FIG. 15) exists between main body 22 and foot 24. This gap G allows the lateral force that is imparted on inlet mixer 2 (via cold spring 22a) to be finely adjusted through the tightening of jacking bolts 30. Specifically, as jacking bolts 309 are tightened, gap G widens, forcing main body 22 to move apart from foot 24 and then cause compression in cold spring 22a to increase (as swivel contact pad 32 presses up against inlet mixer 2), thereby placing a controlled lateral force on inlet mixer 2. FIG. 6A is an exploded view of the jet pump inlet mixer compliant stop 20 of FIG. 6, in accordance with an example embodiment of the invention. Jacking bolts 30 are free to rotate within foot 24, as the distal ends of each jacking bolt may be held in place by bolt keeper 42. Bolt keepers 42 may be held in place on foot 24 via flat head screws that may include a retaining pin 44a (retaining pin 44a may be inserted to lock the position of flat head screw 44 into a desired position). As described above, tightening of jacking bolts 30 may cause main body to be forced apart from foot 24 (through the use of threaded connections 22e in main body 22), which ultimately cause compression of cold spring 22a that imparts the lateral force on inlet mixer 2. Jacking bolts 30 may be locked into place via ratchet keeper 26. Specifically, ratchet teeth 46 (on each end of ratchet keeper 26) may engage ratchet teeth 30a (shown in FIG. 13) of the jacking bolts 30, offering anti-rotational structure to hold each jacking bolts in a desired position. Flat head screw 40 may be used to hold ratchet keeper 26 in place on foot 24, and retaining pin 40a may be used to lock flat head screw 40 into place once screw 40 is sufficiently tightened to ensure ratchet keeper 26 is held in place on foot 24. FIG. 7 is a detailed view of a ratchet keeper 26 of a jet pump inlet mixer compliant stop 20, in accordance with an example embodiment of the invention. Tapped hole 40b may be provided to allow flat head screw 40 to hold ratchet keeper 26 in place on a top surface of foot 24. Note that ratchet teeth 26 may be provided on either end of ratchet keeper 26, for anti-rotational purposes (to ensure that a desired position of jacking bolts 30 may be retained within foot 24). FIG. 8 is a detailed view of a main body 22 of a jet pump inlet mixer compliant stop 20, in accordance with an example embodiment of the invention. Spherical seat 22c may be provided on an outer surface of the distal end of the cold spring 22a. The spherical seat 22c may accept a convex spherical face 32a (shown in FIG. 9) of swivel contact pad 32 to pivot on a distal end of cold spring 22a. Concave spherical seat 22c allows swivel contact pad 32 to readjust positioning throughout installation of jet pump inlet mixer compliant stop 20, including the point in time when jacking bolts 30 (shown in at least FIG. 6) are being tightened and compression is being placed on cold spring 22a (thereby causing some shift and movement of the distal end of cold spring 22a which may require minute repositioning of the swivel contact pad 32 throughout this adjustment/installation period). Alignment channels 22d may also be provided to capture self-alignment rib 32b (shown in FIG. 9) of swivel contact pad 32, to reduce actual rotation of swivel contact pad 32 during remote installation and use of the jet pump inlet mixer compliant stop 20. FIG. 9 is a rear view of a swivel contact pad 32 of a jet pump inlet mixer compliant stop 20, in accordance with an example embodiment of the invention. Shoulder screw hole 32c accepts shoulder screw 50 (shown in at least FIG. 6), to secure swivel contact pad 32 to cold spring 22a. As described in relation to FIG. 8 (above), convex spherical face 32a allows swivel contact pad 32 to pivot within concave spherical seat 22c of FIG. 8. Self-alignment ribs 32b align with alignment channels 22d (of FIG. 8) to cause swivel contact pad 32 to resist rotation during installation and use. FIG. 10 is a detailed view of the swivel contact pad 32 (shown in FIG. 9) of a jet pump inlet mixer compliant stop 20, in accordance with an example embodiment of the invention. Shoulder screw pocket 32c1 may accept and retain the head of shoulder screw 50 (shown in at least FIG. 6). Concave cylindrical surface 32d may be provided to allow swivel contact pad 32 to conform to an outer rounded surface of belly band 18 of inlet mixer 2. FIG. 11 is a rear view of a foot 24 of a jet pump inlet mixer compliant stop 20, in accordance with an example embodiment of the invention. Tapped hole 24b may be provided to accept flat head screw 40 (shown in FIG. 6A). Ratchet teeth slots 24c may be provided to accept ratchet teeth 46 of ratchet keeper 26 (also shown in at least FIG. 6A). Inspection port 24d may be provided as a way of verifying that spherical pad 48 (shown in FIG. 15) is in place in within jacking bolt retention hole 24g (shown in FIG. 11A). FIG. 11A is a detailed view of the foot 24 (shown in FIG. 11) of a jet pump inlet mixer compliant stop 20, in accordance with an example embodiment of the invention. Pocket 24e may be provided to accept bolt keeper 42 (shown in FIG. 6A). Tapped holes 24f may be provided to accept flat head screws 44 (also shown in FIG. 6A). As described above, jacking bolt retention holes 24g may be provided in a front surface of foot 24 (the surface of the foot facing the main body 22) to allow jacking bolts 30 (shown in FIG. 6A) to freely rotate within foot 24 (bolt keeper 42, shown in FIG. 6A, may be provided simply to retain a distal end of each jacking bolt 30). FIG. 12 is a detailed view of a bolt keeper 42 of a jet pump inlet mixer compliant stop 20, in accordance with an example embodiment of the invention. Notice the arced portion 42b of bolt keeper 42 that hugs the side of jacking bolt 30 (shown in FIG. 6A) and causes a distal end of jacking bolt 30 to be retained within jacking bolt retention hole 24g (shown in FIG. 11A). Holes 42a may accept flat head screws 44, as shown in FIG. 6A. FIG. 13 is a detailed view of a jacking bolt 30 of a jet pump inlet mixer compliant stop 20, in accordance with an example embodiment of the invention. Ratchet teeth 30a may be provided on jacking bolt 30 to allow the ratchet teeth 46 of ratchet keeper 26 to engage the teeth 30a for anti-rotational purposes (as shown in FIG. 6A). Note that ratchet teeth 30a are larger than the diameter of the rest of jacking bolt 30, thereby providing a physical stop that allows a distal end 30c of jacking bolt 30 to remain within jacking bolt retention hole 24g (see FIG. 11A for retention hole 24g) of foot 24. Specifically, the arced portion 42b (see FIG. 12) of bolt keeper 42 may provide a physical stop that may contact the enlarged diameter of jacking bolt 30 (which includes ratchet teeth 30a) to retain the jacking bolt 30 within foot 24, as shown for instance in FIG. 6A. Outer hex 30b may also be provided on jacking bolt 30 to apply a necessary torque to jacking bolt 30 to effectively place compression on cold spring 22a (as described above, related to the discussion of FIG. 6). FIG. 14 is a detailed view of a C-clamp of a jet pump inlet mixer compliant stop 20, in accordance with an example embodiment of the invention. Cavity 28b may be provided on C-clamp frame 28 to allow overhang 28c to extend over the top of restrainer bracket 10 and contact main body 22. Specifically, sloped face 28a of C-clamp frame 28 may contact sloped face 22b of main body 22 (as shown in FIG. 4). The sloped nature of sloped faces 28a and 22b allow the C-clamp frames 28 (on both sides of jet pump inlet mixer compliant stop 20) to offer both vertical and horizontal stabilization of main body 22 within pocket 16 (see pocket 16, in FIG. 3) when field installed. C-clamp body 34 may slide in and out of C-clamp frame 28, via the use of the male dovetail slot portion 34a (which engages female dovetail slot portion 28e, in FIG. 14A), to allow C-clamp frame 28 and C-clamp body 34 to be fashioned to restrainer bracket 10 (see the installed jet pump inlet mixer compliant stop, in FIG. 5). An upward projecting portion 34c and an arced portion 34b of the C-clamp body may be provided to allow the C-clamp body 34 to cradle a bottom portion of restrainer bracket 10, to securely fasten both the C-clamp frame 28 and C-clamp body 34 to the restrainer bracket. Socket head cap screw 36 may penetrate both C-clamp frame 28 and C-clamp body 34, allowing the position of C-clamp body 34 to be locked into place within frame 28. Ratchet teeth 36b on cap screw 36 and ratchet keeper 36a may be used for anti-rotational purposes, to lock cap screw 36 into place once a desired position of C-clamp body 34 has been determined. FIG. 14A is a detailed view of the C-clamp frame 28 (shown in FIG. 14) of a jet pump inlet mixer compliant stop 20, in accordance with an example embodiment of the invention. Thru hole 28d may be provided to accept cap screw 36 (shown in FIG. 14). Female dovetail slot 28e may be provided, to engage male dovetail slot 34a of C-clamp frame 28 (shown in FIG. 14), allowing C-clamp body 34 of the C-clamp to slide in and out of C-clamp frame 28. The upper portion of hole 28d may be tapped to accept ratchet keeper 36a. FIG. 14B is a detailed view of a C-clamp body 34 (shown in FIG. 14) of a jet pump inlet mixer compliant stop 20, in accordance with an example embodiment of the invention. Tapped hole 34d may be provided to accept cap screw 36 (shown in FIG. 14). FIG. 14B shows more detail of male dovetail slot 34a which may engage the female dovetail slot 28e of FIG. 14A, allowing C-clamp body to slide in and out of C-clamp frame 28, as shown in FIG. 14. FIG. 15 is a cut-away view of a jet pump inlet mixer compliant stop 20, in accordance with an example embodiment of the invention. This cut-away view shows a gap T between protruding boss 22f (located on a front surface of main body 22) and protruding boss 22a1 (located on an inner surface of the distal end of cold spring 22a). When installing compliant stop 30, jacking bolts 30 may be tightened to increase the gap G between foot 24 and main body 22, placing compression on cold spring 22a as swivel contact pad 32 presses against inlet mixer 2 (as shown in FIG. 5A). Therefore, as jacking bolts 30 are tightened, gap T decreases (as gap G increases). During initial installation of the compliant stop 20 (at temperatures that are below jet pump assembly normal operating temperatures), gap T should be approximately zero, or close to zero (for instance, gap T could be 0.1 inches, or it could be less). With a gap T of zero, or near zero, selection of the width and thickness of the cold spring 22a may ensure that cold spring 22a provides a preload (i.e., “spring load”) that counteracts flow induced vibration (FIV) that may occur at the inlet mixer. For instance, the preload of the cold spring 22a may be in the range of 2,000 to 4,000 lbs. The actual preload of spring 22a may be sized based on FIV loads that may be plant specific. By selecting a wider spring 22a (with a higher relative spring rate), a higher preload (and, a higher lateral force, during operation) may be imparted by the spring 22a. By selecting a narrower spring (with a lower relative spring rate), a lower preload (and, a lower lateral force, during operation) may be imparted by the spring 22a. Therefore, by selecting a cold spring 22a that may provide a desired preload force (and, assuming that gap T is at zero, or near zero, during initial operation), a precise lateral force may ultimately be imparted on the inlet mixer 2 by the compliant stop 20. As compliant stop 20 becomes warmer, during normal plant operation (and during warming of the jet pump assembly, which occurs during normal plant operation), thermal expansion of the compliant stop 20 may cause gap T to increase slightly (a more detailed discussion of the materials of construction of component parts, and the associated thermal expansion of these parts, is included herein). The existence of the small gap T (which may be 3/1000 of an inch) may allow cold spring 22a to act as a moderate shock absorber, during heavy system vibration. The existence of the small gap T may also allow protruding bosses 22f and 22a1 to slightly shift in a horizontal direction during system vibration. The jacking bolt retention holes 24g (shown also in FIG. 11A) may differ, from the standpoint that a spherical backstop 24g2 may be provided for one retention holes 24g, while a flat backstop 24g3 may be provided for another retention hole 24g. The shape of the spherical backstop 24g2 matches the shape of a distal end of the jacking bolt 30, allowing the distal end of jacking bolt 30 to mate with the spherical backstop 24g2. Use of the spherical backstop 24g2 and flat backstop 24g3 may mitigate potential binding, while torque is applied to the jacking bolts 30. Specifically, spherical pad 48 may fit against flat backstop 24g3, with small gaps P on either lateral side of pad 48 (i.e., the diameter of the pad 48 is smaller than the diameter of retention hole 24g). The spherical surface of pad 48 also matches a distal end of jacking bolt 30, allowing the spherical pad 48 to mate with the distal end of jacking bolt 30. As uneven torque may be applied to each jacking bolt 30, the distal end 30c of the jacking bolt 30 on the right side of FIG. 15 may pivot slightly within jacking bolt retention hole 24g, causing spherical pad 48 to slightly shift along the flat backstop 24g3 of the retention hole 24g (shifting of pad 48 may occur, due to the existence of gaps P on either side of pad 48). In this sense, potential binding due to uneven torque between the two jacking bolts 30 may be avoided. It should also be understood that the spherical backstop 24g2 and the spherical pad 48 helps mitigate or eliminate bolt 30 bending, during installation and operation. FIG. 15 also depicts placement of bolt keeper 42 within foot 24. Bolt keeper 42 acts as a physical stop (by abutting ratchet teeth 30a of jacking bolts 30) to ensure that a distal end 30c of the jacking bolts 30 may remain inside retention hole 24g. As described above, the distal end 30c is free to rotate within retention holes 24g. Therefore, as jacking bolts 30 are tightened, the distal end 30c of each jacking bolt 30 remains in place within retention holes 24g while the threads of each jacking bolt 30 cause main body 22 to be forced apart from foot 24 (thereby increasing the size of gap G, and ultimately decreasing the size of gap T as swivel contact pad 32 is pressed against inlet mixer 2, as shown in FIG. 5A). Materials of construction of the component parts of the jet pump inlet mixer compliant stop 20 (with the exception of cold spring 22a) and non-compliant stops 38 may be either 300 series stainless steel or type XM-19 stainless steel. More specifically, all components parts of the jet pump inlet mixer compliant stop 20 (with the exception of cold spring 22a) and non-compliant stops 38 may match the materials of construction of existing restrainer bracket assembly components such as the main wedge 8 and the restrainer bracket 10 (which, often are 300 series stainless steel or XM-19). This ensures that potential thermal expansion of the jet pump inlet mixer compliant stop 20 and non-compliant stops 38 match, to some degree, the thermal expansion of existing restrainer bracket assembly components. However, materials of construction for cold spring 22a are preferably alloy X-750, or another suitable high-yield and high-temperature spring material that may expand less than either 300 series stainless steel or XM-19. The lower thermal expansion of cold spring 22a causes a small gap T (see FIG. 15) between preload limit bosses 22a1/22f. The small gap T allows the spring 22a to function (move) during operation, as described above. Example embodiments having thus been described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the intended spirit and scope of example embodiments, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims. |
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claims | 1. A nuclear fuel, comprising:an assembly of nuclear fuel particles;nano-scale ligaments extending between the nuclear fuel particles; andcontinuous open channels defined between at least some of the nuclear fuel particles and between the ligaments,wherein the channels are structurally characterized as being capable of allowing fission gasses produced in an interior of the assembly to escape from the interior of the assembly to an exterior thereof without causing swelling of the assembly,wherein the assembly has a density of at least about 68% of a theoretical maximum density thereof. 2. The nuclear fuel of claim 1, wherein the fuel particles are unsintered. 3. The nuclear fuel of claim 1, wherein the assembly has a density of between about 68% and 80% of a theoretical maximum density thereof. 4. The nuclear fuel of claim 1, wherein the assembly is a compressed aerogel, xerogel, or ambigel. 5. The nuclear fuel of claim 1 , wherein the nuclear fuel is characterized as being usable in a nuclear reactor as a fuel that does not impart mechanical loading on cladding materials cladding the nuclear fuel. 6. The nuclear fuel of claim 1, wherein the nano-scale ligaments are formed at least in part of the nuclear fuel particles. 7. The nuclear fuel of claim 1, wherein the nano-scale ligaments have a length in a range of about 0.1 nanometer to about 1000 microns. 8. The nuclear fuel of claim 7, wherein the nano-scale ligaments have a length in a range of about 1 nanometer to about 10 nanometers. 9. The nuclear fuel of claim 7, wherein the nano-scale ligaments have a length in a range of about 5±2 nanometers to about 10±2 nanometers. 10. The nuclear fuel of claim 1, wherein the nuclear fuel particles are comprised of UO2. 11. The nuclear fuel of claim 10, wherein the nuclear fuel particles consist of UO2. 12. The nuclear fuel of claim 7, further comprising cladding encasing the assembly of fuel particles, wherein the fuel particles in the cladding are unsintered, wherein the assembly has a density of between about 68% and 80% of a theoretical maximum density thereof. 13. The nuclear fuel of claim 8, wherein the nano-scale ligaments have a length in a range of about 1 nanometer to about 10 nanometers. 14. The nuclear fuel of claim 2, further comprising cladding encasing the unsintered fuel particles. 15. A method for fabricating a nuclear fuel, comprising:consolidating a precursor of a nuclear fuel to produce an open nanoscale porosity material having a density of at least about 68% of a theoretical maximum density of the material,the material comprising:an assembly of nuclear fuel particles;nano-scale ligaments extending between the nuclear fuel particles; andcontinuous open channels defined between at least some of the nuclear fuel particles and between the ligaments,wherein the channels are structurally characterized as being capable of allowing fission gasses produced in an interior of the assembly to escape from the interior of the assembly to an exterior thereof without causing swelling of the assembly,wherein the assembly has a density of at least about 68% of a theoretical maximum density thereof. 16. The method of claim 15, wherein the assembly of fuel particles comprises nano-scale ligaments. 17. The method of claim 15, wherein the structure is a compressed aerogel, xerogel, or ambigel. 18. The method of claim 15, further comprising reducing the precursor to a nuclear fuel. 19. The method of claim 18, wherein the material, after reduction, maintains about the same overall volume, defined by an outer periphery thereof, during a nuclear fission chain reaction involving the nuclear fuel thereof. 20. The method of claim 15, further comprising synthesizing the precursor of the nuclear fuel. 21. The method of claim 15, wherein the precursor is consolidated by at least one of direct compression, isostatic pressing and spark plasma sintering. |
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050283790 | summary | FIELD OF THE INVENTION This invention relates to an improvement in the mechanical means for refueling power generating nuclear reactor plants such as the conventional water cooled and moderated boiling water and pressure water system. The invention comprises a unique composite apparatus for handling nuclear fuel bundle units underwater within the nuclear reactor vessel, including a remotely operable grapple provided with a viewing camera for grasping and transfer fuel bundles submerged underwater. BACKGROUND OF THE INVENTIONS Typical water cooled and moderated nuclear reactor plants for power generation comprise a large pressure vessel containing cooling and neutron moderating water, and have a heat generating core of fissionable fuel submerged a substantial distance beneath the surface of the cooling and moderating water. The submerged fissionable fuel of the core must be periodically replaced, including the removal of spent fuel and replacement with new fuel, as well as rearranging partially spent fuel within the core. Due to the high levels of radioactivity within the nuclear reactor pressure vessel, the means for handling the water submerged fuel must be remotely controlled by an operator from out beyond the water containing reactor pressure vessel. Conventional fuel handling systems comprise a fuel handling mast or pole extending down from above an open top of the water containing reactor pressure vessel with a grapple head affixed to the lower end of the mast. The system is designed for attachment to fuel bundles and their transfer while submerged in the reactor vessel to remove spent fuel and introduce new fuel, and rearrange fuel bundles within the core. The fuel handling mast is frequently supported on and operated from a movable platform which can travel back and forth over an open top of the water containing reactor vessel above the fuel core. Typically the fuel handling mast is mechanically telescoping downward from the supporting movable platform to facilitate reciprocal travel of the grapple head affixed to the lower end of the mast down into and back up from the interior of the reactor vessel. This arrangement provides greater versatility for transferring fuel bundles within and about the reactor vessel. To facilitate operating personnel in manipulating such fuel handling systems with the grappling devices submerged a substantial depth below the surface of the water containing reactor vessel from a safe position above the open top of the reactor vessel, underwater viewing means are commonly employed. For example, underwater periscopes or television cameras suspended on a pole and connected to an above surface monitoring screen have been utilized for enabling remotely located operators to more accurately and clearly observe their underwater manipulation and relative location of the grappling head on the mast with respect to fuel assemblies to be transferred, and its application to fuel bundles. However, controlling the manipulation of two distinct underwater units and their coordination by a remotely located operator is cumbersome and slow, and space limitations sometimes impede positioning of such underwater viewing mechanisms in conjunction with the fuel handling means. Fuel bundles for typical water cooled and moderated nuclear reactor plants used to generate power commonly consist of a multiplicity of small diameter sealed tubes elements enclosing fissionable fuel which are grouped, spaced apart, into an assembled unit. Each assembled unit of the grouped tube elements is provided with an upper and lower end piece having sockets to receive and secure the end portions of the grouped tube elements, and the overall assembled unit is substantially surrounded with an open ended housing or channel. A handle or bail is provided on the uppe end piece of the assembled units for convenient and effective grasping and secure attachment of a transferring means such as a grapple device. The identification number of each assembled unit or fuel bundle is stamped on the top of its boil. The grouping of a multiplicity of the fuel containing tube elements in assembled units greatly facilitates the transfer of fuel in reloading operations, among other benefits. SUMMARY OF THE INVENTION This invention comprises an improved system for handling fuel bundles within the water containing vessel of a nuclear reactor plant. The invention comprises a composite system of a mast with a grapple head mounted on the lower end thereof and having a viewing camera enclosed within the grapple head, for observing submerged fuel bundles and transferring the bundles underwater. OBJECTS OF THE INVENTION It is a primary object of this invention to provide an improved fuel handling system for nuclear reactor plants. It is another object of this invention to provide a unique fuel handling system for transferring fuel bundles underwater within the housing vessel of a water cooled and moderated nuclear reactor plant. It is a further object of this invention to provide a fuel handling system for water cooled and moderated nuclear reactor plants incorporating means for viewing underwater when carrying out the transfer of fuel bundles submerged within the water containing vessel of the nuclear reactor. It is a still further object of this invention to provide a composite system for handling fuel bundles underwater within a nuclear reactor including an underwater grappling means containing a viewing camera integrated therein. It is also an object of this invention to provide an underwater fuel handling system for nuclear reactors having an internal camera for close viewing of all underwater work performed with the handling system. |
claims | 1. A composition for use in preparing radiopharmaceuticals comprising from 4 Ci to 15 Ci of copper-64 (64Cu) and having a specific activity of about 350 mCi 64Cu/μg Cu up to about 3800 mCi 64Cu/μg Cu. 2. The composition of claim 1, wherein the composition is obtained from a single cyclotron run. 3. The composition of claim 1, wherein the composition comprises from 4 Ci to 5 Ci of 64Cu at the end of bombardment (EOB) of a single cyclotron run of about 2 h to about 4 h. 4. The composition of claim 1, wherein the composition comprises from about 5 Ci to about 9 Ci of 64Cu at the end of bombardment (EOB) of a single cyclotron run of about 6 h. 5. The composition of claim 1, wherein the composition comprises from 4 Ci to 15 Ci of 64Cu at the end of bombardment (EOB) of a single cyclotron run of about 8 h to about 12 h. 6. The composition of claim 1, wherein the composition has a specific activity from about 350 mCi 64Cu/μg Cu to about 2300 mCi 64Cu/μg Cu. 7. The composition of claim 1, wherein the composition has a total content of trace metals of less than about 5 parts per million (ppm), the trace metals being cobalt, copper, gold, iron, lead, mercury, nickel, and zinc. 8. The composition of claim 1, wherein the composition comprises a solution of hydrochloric acid (HCI) having a molarity of about 0.001 M to about 3 M. 9. The composition of claim 7, wherein the molarity of the HCI is about 0.05 M. 10. The composition of claim 9, wherein the 64Cu exists as [64Cu]CuCl2. 11. The composition of claim 9, wherein the composition further comprises a chelating agent or a bifunctional chelating agent in which the 64Cu is coordinated therein, and the chelating agent or the bifunctional chelating agent is a macrocyclic compound, a bridged macrocyclic compound, a bicyclic compound, or an acyclic compound. 12. The composition of claim 11, wherein the bifunctional chelating agent is DOTA. |
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H00006890 | summary | BACKGROUND AND SUMMARY OF THE INVENTION This invention relates generally to a liquid metal nuclear reactor fuel pin, and more particularly to a fuel pin having an improved metallic fuel arrangement. Conventional metallic fuel pin assemblies typically include pressure cast fuel alloys which are loaded into cylindrical cladding tubes sealed at their ends. Mechanical interaction during fission between the fuel and cladding is prevented by a large radial gap. Typically this gap takes up about 25% of the volume within the cladding tube. Also included in the pin is a fission gas plenum in the form of a chamber which receives fission gases released by the fuel during operation of the reactor. Because of the high thermal conductivity of metallic fuels (20 W/m-k) and their relatively low melting points (approximately 2200.degree. F.), the existence of the large gas gaps, without any coolant bond, could cause excessive fuel temperature and perhaps even fuel melt. This is undesirable because it would redistribute the fuel to the bottom of the fuel column, which would disturb the porosity balance and render the location of the fuel material somewhat unpredictable. To preclude fuel melting, prior designs have provided a sodium thermal bond between the fission material and the cladding. The high thermal conductivity of the sodium, compared to gas, keeps fuel temperatures acceptable. During operation, metallic fuel swelling closes the gap between fuel and cladding, and this displaces the sodium away from the fuel and into the fission gas plenum. This displacement reduces the available fission gas plenum volume, which diminishes the capacity of the system, or requires additional fuel pin length. Any such increase in length dramatically increases reactor containment costs. Another limitation of conventional fuel pin designs is that the use of a sodium thermal bond normally requires that the fission gas plenum be disposed above the fuel, in an upper part of the fuel pin. This leads to inefficient utilization of fission gas plenum space because the reactor coolant system circulates coolant upwardly between the various fuel pins. Thus, system coolant passes the fuel region before it passes the plenum. The resulting heating of the coolant prior to contact with the plenum increases the fission gas plenum pressure and temperature, or requires additional fuel pin length. This length increase again dramatically increases reactor containment costs. There are other drawbacks with the use of sodium or another coolant as a thermal bond between the fuel and the cladding. Because of the proximity of the coolant to the metallic fuel, it is an additional contaminated waste product which must be dealt with in reprocessing the fuel elements. Clean up and/or storage of such waste products is very expensive and troublesome. Finally, the requirement of a fuel pin thermal bond also increases the expense of the system. Another disadvantage with existing metallic fuel systems is that there is typically far more power being generated from the areas near the axial center of the fuel stack than is being generated near the ends of the fuel stack. This is because the neutron concentration is greater near the axial center of the fuel stack than at the ends of the fuel stack where neutron leakage occurs. It has long been thought that if there was a way to increase the power output adjacent the ends of the fuel stack, then a dramatic increase in power output could be realized. Yet another typical feature of existing systems is a tag gas capsule which contains a tag gas comprising specific mixtures of different isotopes of gases that can readily be sensed from a position outside of the reactor core. Thus, if there is leakage from one or more of the fuel pins, such leakage can readily be determined. It is also possible to use different gas mixtures for each fuel assembly position so that the tag gas sensor can determine in which fuel assembly position there is a leak as well as the presence of a leak. In one embodiment of the present invention, there is disclosed a fuel pin design which includes a temperature sensitive tag gas capsule that releases tag gas into the fuel pin during reactor operation. By releasing tag gas into the fuel pin during reactor operation, the power-to-melt characteristics during reactor start up is improved. Another embodiment of the invention discloses a fuel design which permits the elimination of the tag gas capsule while still providing pin leakage sensing capability. Eliminating of the tag gas capsule reduces the cost of the reactor both by eliminating an additional component and by decreasing the necessary length of the fuel pin. It is an object of the present invention to avoid the drawbacks and limitations in the prior art. More specifically, the invention has as objects the following: (1) to develop a fuel system for a nuclear reactor which does not require a thermal bond between the fuel material and the cladding; (2) the provision of a fuel pin design which increases the effective amount of plenum space to receive fission gases, without increasing the size of the fuel pin; (3) to provide a nuclear power plant which generates less contaminated waste than conventional designs; (4) to provide a fuel pin design which results in more effective transfer of heat from the fuel pin to the reactor coolant system; (5) to develop a fuel pin which effectively increases the amount of power generated adjacent the ends of the fuel stack; (6) to provide a tag gas capsule which is temperature sensitive and releases tag gas within the fuel pin during reactor operation; (7) the provision of a fuel design which permits the elimination of the tag gas capsule, while still providing pin leakage sensing capability; and (8) to provide various fuel system alternatives which maximize reactor output while permitting a simplification of plant design. The present invention achieves the above objects by providing various means for adding porosity to the fuel stack. Another way to describe the invention is to provide means for decreasing the effective smear density of the fuel. Such means could take the form of one or more axially extending channels extending through the fuel. They could take the form of spaced, axially extending peripheral flutes. Another alternative would be to provide small radial gaps or voids within the stack, or to form fuel spheroids which would provide the desired porosity. Because the invention permits elimination of the annular fuel-to-cladding gap, radial transfer of heat from the pin to the reactor coolant system is enhanced, thus preventing fuel melt and resulting axial relocation. Expansion of the fuel is facilitated by the axial channels or the initial porosity of the fuel; that is, the channels or gaps in the fuel merely fill with the expanding fuel as fission is taking place. A particular advantage of the use of spheroids or some other configuration which exhibits internal radial porosity is that means can be provided for exerting pressure on the end regions of the fuel stack. This pressure does not typically pass through the entire stack, so that the end regions are compacted more than the center region, thus increasing the amount of fuel at those portions. This permits a flattening of the axial fuel pin power distribution curve which can result in significant increases in reactor power output without any meaningful increase in assembly or operating expense. Another advantage of the porous fuel stack of the present invention is that tag gas can be injected directly into the fuel region of the pin. Thus, as the fuel swells during fission, that gas is passed into the fission gas plenum. If there is leakage in the pin, the tag gas will pass out of the pin, just as though a separate tag gas capsule was provided. Other objects, features and advantages of the present invention will become apparent upon reading the following detailed description in conjunction with the accompanying drawings. |
050254642 | abstract | A transmission grating in which the vertical supports are equidistantly sed from each other in each of the horizontal rows but have their positions relative to each vertical support in all of the other rows determined by a pseudo-random integer of the spacings between the grating wires. As a result, all of the artifacts produced by the vertical supports are eliminated from the diffraction plane. |
051606941 | summary | BACKGROUND OF THE INVENTION The invention relates to a fusion reactor having a reaction zone surrounded by a magnetic field with magnetic flux lines which viewed from the reaction zone are curved in a convex manner. THE PRIOR ART Such a magnetic field, surrounding the reaction zone and having magnetic flux lines curved in a convex manner when viewed from the reaction zone, had already been proposed for controlled nuclear fusion by the doyen of nuclear fusion, Edward Teller, during the Sherwood Conference in Princeton U.S.A. in October 1954 because only with such a magnetic field is it possible to achieve stability during the containment--essential for eliminating contacts between reactants and material reactor parts in the vicinity of the reaction zone--of the high-energy reactants in the reaction zone ("Project Sherwood", Addison-Wesley Publishing Company Inc., Reading, Mass., U.S.A., by A. S. Bishop, p. 85-87). At the same conference, J. L. Tuck put forward a proposal, which fulfilled E. Teller's stability criterion and became known as the "picket fence concept", for the basic construction of a fusion reactor of the type mentioned initially in which the magnetic field is generated by magnetic flux lines, which are curved in a convex manner towards the reaction zone, of several circulating currents which flow parallel to one another and axially apart from one another, each in the opposite current direction to the adjacent circulating current, about the same axis and surround the reaction zone or the plasma of high-energy reactants with the magnetic field they generate ("Project Sherwood", p. 86-89, in particular p. 89). Teller's contribution to the 1954 Sherwood Conference led during the conference itself to an in-depth discussion of the stability problems of containing high-energy plasmas for, apart from the picket fence concept first submitted at this conference, there was not a single concept for a fusion reactor which met Teller's stability criterion, i.e. where the reaction zone was surrounded by a magnetic field with magnetic flux lines curved, when viewed from the reaction zone, in a convex manner, rather all the concepts put forward at that time and all the experimental reactors under development--and especially the various embodiments of the Stellarator and the so-called Mirror machines--were provided with a magnetic field with magnetic flux lines curved in a concave manner viewed from the reaction zone and were, according to Teller's stability criterion, unstable. Nevertheless, during this conference the hope still prevailed that instabilities owing to non-fulfilment of Teller's stability criterion would arise in the experimental reactors under development and especially in the Stellarator and the Mirror machines only at relatively high values of the ratio .beta. of plasma pressure to magnetic pressure upon the plasma and that non-fulfilment of Teller's stability criterion was not an effective barrier to continued development of these experimental reactors. In the ensuring period, however, theoretical studies conducted in particular by E. A. Frieman, H. Grad and C. L. Longmire have demonstrated that Teller's stability criterion is universally valid so that the Stellarator and the Mirror machines are unstable, and are so not only at high but also at low values of the ratio of plasma pressure to magnetic pressure upon the plasma ("Project Sherwood", p. 85-88). Despite these findings, however, the Stellarator and Mirror programmes were continued ("Project Sherwood", p. 106-131), initially probably for the main reason that a great deal of money had already been invested in experimental reactors and there was a wish to use the, in some cases, almost completed experimental reactors at least to check out the, hitherto only theoretically predicted, instabilities by conducting practical stability tests. But otherwise these findings led, not for example to a rethink in the development of fusion reactors on the basis of stable plasma containment as a priority, but on the contrary to a second series of pinch concepts (fast pinch, B.sub.z -stabilized pinch, srew-dynamic pinch, triaxial pinch; "Project Sherwood", p. 90-105) aimed no longer at achieving stability but the fastest possible heating of the plasma to fusion temperatures within the period up to the occurrence of instabilities and the maximum extension of this period. However, because of the abandonment of stability, these concepts even if successful could at best have led to pulsed-mode operation fusion reactors and consequently to an adverse energy balance so that the actual aim of producing energy by nuclear fusion would have been no nearer achievement. Whereas, even after the discovery that all the experimental reactors of the Stellarator, Mirror and Pinch programmes were unstable, practical testing was still carried out for an extended period both with earlier developed experimental reactors and particularly with new developements (e.g. within the framework of the above-mentioned second series of Pinch concepts) although on the basis of this discovery it was already established that these means could not bring us any nearer to achieving the aim of producing energy by nuclear fusion, an aim achievable only with the precondition of continuous reactor operation and hence stable plasma containment, the only concept to guarantee stability and hence at least not to rule out from the start the possibility of achieving the aim of producing energy by nuclear fusion, i.e. the picket fence concept, was after only a short time dropped on the basis of a theoretical study by a small group of scientists in Los Alamos on the grounds that this concept could in fact achieve stability but not containment of a plasma, that particularly in the mid-planes between the circulating currents generating the magnetic field for containing the plasma a high particle loss could be expected, in other words that such a system was not tight ("Project Sherwood", p. 90-91). Although another group working in New York under the direction of H. Grad was also able from theoretical studies to prove in respect of a simplified modification of the picket fence concept, known as cusped geometry and having only two circulating currents generating the magnetic field for plasma containment, that at least in the case of high .beta. values or relatively high plasma pressure in relation to the magnetic pressure upon the plasma such high particle losses were not to be expected, this only concept to guarantee stability was never practically realised despite completion of a series of theoretical preliminary studies for a fusion reactor suitable for energy production based on this cusped geometry concept because the programme was discontinued in the concluding phase shortly before practical realisation and those working on the programme were assigned to different tasks, in particular to theoretical investigation of a modification to the Stellarator which held out the promise of stability in continuous reactor operation ("Project Sherwood", p. 139-142). This modification to the Stellarator consisted, according to a proposal by L. Spitzer, of superimposing upon the original confining field having magnetic flux lines extending within the discharge tube substantially parallel to the axis thereof a stabilising magnetic field with magnetic flux lines extending within the discharge tube substantially perpendicular to the axis thereof, said stabilising magnetic field being generated by six conductors extending like a sextuple thread with a very large lead helically about the discharge tube and carrying the same current ("Project Sherwood", p. 110-113). Since a twisted magnetic field of decreasing twist towards the axis is produced within the discharge tube as a cumulative field from the paraxial confining field and the stabilising magnetic field extending perpendicular to the axis ("Project Sherwood", p. 113) and the individual helical magnetic flux lines of this twisted magnetic field (unlike paraxial magnetic flux lines extending always on the same side of the axis) wind about the axis and hence successively extend now on one side of the axis then below it, now on the other side of the axis and then above it, the original configuration of the discharge tube of the Stellarator in the form of an 8 (which had been chosen so that the magnetic flux lines extending externally in one curve of the 8 extend in the other curve of the 8 internally and hence, so to speak, on the other side of the axis) was no longer necessary so that, with the introduction of the stabilising magnetic field proposed by L. Spitzer, it was simultaneously possible to go over again to toroidal discharge tubes, and this purely secondary effect of the efforts to stabilise the Stellarator in practice became a primary factor determining the whole course of further development and finally resulted in the gradual suspension of experiments with non-toroidal discharge vessels and the adoption of the toroidal discharge vessel as the basic prerequisite so to speak of new developments which, for the following reasons outlined below, must have contributed in no small way to the lack of success experienced up till now with controlled nuclear fusion. The stabilising magnetic field was however unable to fulfil its actual main purpose, namely stable plasma containment, since in the case of a relatively high plasma pressure in relation to the magnetic pressure upon the plasma or in the case of relatively high .beta. values it was already theoretically unsuitable for stabilisation purposes and the possibility held out by theoretical investigations of a stabilisation at relatively low values of less than c. 20% ("Project Sherwood", p. 112, esp. footnote) was at first in any case impossible to realise in practice. The main reason for this was that the modification of the Stellarator originally suggested by L. Spitzer with six currents of equal intensity and the same direction running helically round the discharge tube was, in view of the then standard resistive heating of the plasma by means of a direct voltage pulse induced in the discharge tube and directed in the axial direction of said tube ("Project Sherwood", p. 114, para. 2), so conceived that the stabilisation theoretically possible at .beta. values below 20% only intercepted or confined in the stable region axial plasma streams in the flow direction predetermined by the direct voltage pulse but excluded axial plasma streams in the reverse flow direction from the stable region. For the six currents of equal intensity running helically round the discharge tube, given the same direction, generate within the discharge tube a "stabilising magnetic field" which has magnetic flux lines extending substantially circularly around the tube axis and which, if the intensity of the helical currents is high enough, is more powerful than the magnetic field generated by the axial plasma stream with magnetic flux lines running similarly circularly around the tube axis and so, given the same direction of the helical currents and of the plasma stream, cancels out the magnetic field generated by the plasma stream and replaces it with a magnetic field of inverse magnetic flux direction so that, upon constriction of the plasma stream at one point and the resultant increase in the field intensity of the magnetic field generated by the plasma stream at this point, the field intensity of the cumulative field made up of the stabilising magnetic field and the magnetic field generated by the plasma stream, owing to the greater intensity of the stabilising magnetic field and the opposing field strength directions of the two magnetic fields at the constriction point, does not rise but falls and the magnetic pressure upon the plasma stream consequently also falls at the constriction point and the constriction therefore disappears by itself, whereas the constriction in contrast to this in the absence of the stabilising magnetic field on account of the increasing magnetic field intensity of the plasma stream generated magnetic field at the constriction point and the consequently increasing magnetic pressure upon the plasma stream at the constriction point continues to grow until the stream at the constriction point breaks away, causing a constriction instability or a so-called bulge-type instability to occur. Since the so-called kink instabilities, i.e. the bulging of the plasma stream towards the discharge tube wall with similarly ensuing breaking away of the stream, were practically excluded by the confining field acting as an axial guidance field for the plasma stream, it was hoped that, with the exclusion of constriction instabilities by the stabilising magnetic field, all the essential causes for the occurrence of instabilities in the axial plasma stream had been eliminated. The fact that the constriction instabilities were however only excluded with opposing field intensity directions of the stabilising magnetic field and of the plasma stream generated magnetic field and hence only with identical direction of the helical currents generating the stabilising magnetic field and of the axial plasma stream, while with an opposing direction of the helical currents and of the axial plasma stream and hence identical field strength directions of the stabilising magnetic field and of the plasma stream generated magnetic field no stabilisation but, on the contrary, a destabilisation was anticipated, was at first not at all recognised as a possible disruptive factor because the flow direction of the axial plasma stream seemed to be fixed in advance by the direct voltage pulse driving said stream. However, when the modification suggested by L. Spitzer was put into practice, there arose not only a series of foreseeable problems but also unexpected new problems associated with the stability of the plasma. The foreseeable problems were basically difficulties attributable to the very low plasma pressure permissible with this modification such as, for example, technical difficulties associated with the very high vacuum, necessary on account of the very low plasma pressure, to which the discharge vessel has to be evacuated prior to introduction of the reaction gas forming the plasma, difficulties with the necessary, quite substantial reduction in the plasma contamination arising from gas pockets in the discharge vessel wall which was absolutely essential on the one hand because of the very low plasma pressure and, given a foreign gas quantity, the correspondingly high ratio of foreign gas quantity to plasma gas quantity and on the other hand because of the extended discharge times and the rising quantity, associated with the longer period of release of foreign gases from the discharge vessel wall, of released foreign gases located in the plasma, and difficulties associated with the high radiation losses caused by contamination of the plasma in particular with foreign gases of a relatively high molecular weight and with the resultant considerable cooling of the plasma and the associated further increase in gas release from the discharge vessel wall ("Project Sherwood", p. 114, para. 2). Over and above these and various other foreseeable problems, in the experiments with the newly created modified Stellarator which was regarded as stable, a new problem which was totally unexpected in view of the hoped-for stability arose however in the form of a new, never before observed type of instability of the plasma containment during heating of the plasma with the above-mentioned direct voltage pulse ("Project Sherwood", p. 116, para. 2). The causes of this new type of instability could not at first be explained with the result that for a long time, while an attempt was made to explain these instabilities, all that there was to go on were suppositions of varying validity. One of these suppositions was that the instabilities were attributable to the so-called runaway electrons arising with the direct voltage pulse ("Project Sherwood", p. 116, para. 3). It was thought that the electrons of the plasma, which were accelerated by the direct voltage pulse over random, relatively long, free path lengths to, in relation to the mean energy of the electrons, very high kinetic energies, were able because of their high energies to "pierce" the magnetic confining field and so reach the discharge vessel wall where they would release their energy, so that throughout the period of heating of the plasma by the direct voltage pulse energy was being conveyed from the plasma to the discharge vessel wall ("Project Sherwood", p. 188, para. 6 in conjunction with p. 114, para. 2). Only much later was it discovered that what caused these instabilitites were axial plasma vibrations which were triggered by the sudden change in the field intensity at the beginning of the axial direct voltage pulse and led to the axial plasma stream in the discharge tube flowing during the axial plasma vibrations temporarily in the opposite direction to the direction of the direct voltage pulse and hence also in the opposite direction to that of the helical currents generating the stabilising magnetic field, causing the stabilising magnetic field during these phases of reverse flow direction to have not a stabilising but a destabilising effect. A modification in the helical currents generating the stabilising magnetic field was then carried out to the effect that, of the original six currents running in the same direction helically around the discharge tube, three currents each offset relative to one another by 120.degree. in a peripheral direction of the discharge tube were driven in the reverse direction so that the remaining three helical currents running in the original direction are responsible for stabilisation when the axial plasma stream is flowing in the same direction as the direct voltage pulse and the three helical currents running in the opposite direction are responsible for stabilisation when the axial plasma stream is flowing in the opposite direction to the direct voltage pulse. This change in the modification of the Stellarator originally suggested by L. Spitzer made it possible to achieve substantial improvements in stability in the form of much longer discharge times throughout which stable plasma containment could be sustained. Similar successes have been achieved with modifications of the Stellarator changed in this manner, especially at the University of Princeton, U.S.A., and the Max-Planck Institute of Plasma Physics in Garching, Germany. These successes with the Stellarator led to the use in other concepts with toroidal discharge tubes, such as, for example, the so-called theta pinch concept (a further development of the original collapse concept described in "Project Sherwood, p. 68-71), of stabilising magnetic fields of a similar type to that used in the Stellarator which were generated by an even number of currents running helically around the discharge tube, with half flowing in one direction and half flowing in the other direction, e.g. in the said theta pinch concept by four currents running helically around the discharge tube, of which two flow in one direction and two in the other direction. However, scant account was taken of the fact that the really effective stabilising effect of these stabilising magnetic fields (generated by two equal-sized groups of currents flowing in opposite directions helically around the discharge tube) was in no way primarily based on the considerations which had led to these stabilising magnetic fields, rather the main reason why these stabilising magnetic fields permitted stable plasma containment over extended discharge times was that they fulfilled Teller's stability criterion and were in principle magnetic fields with a magnetic field configuration similar to that of the picket fence concept (the similarity in the magnetic field configuration is evident from a cross-section through the discharge tube with the currents uniformly distributed along its periphery and flowing alternately out of the sectional plane and into said plane: for if the circular line of circumference with the currents distributed along it is imagined as a straight line, a current and magnetic field configuration is obtained similar to the upper half of the illustration of the picket fence concept in FIG. 9-2 on page 89 of "Project Sherwood"). It therefore emerges that the picket fence concept, largely ignored by specialists in the field and dropped after only a relatively short period of theoretical investigation in 1955/56 as insufficiently promising, in reality was--at any rate until the development of the so-called Tokamac--the only concept with which in practice an effective stabilising effect could actually be achieved and this concept remains to this day the only concept offering the prospect of realising an indefinite period of stable plasma containment and hence of realising a continuous operation fusion reactor suitable for energy production. For the concept known as Tokamac, with which in practice, e.g. in the PLT (Princeton Large Torus) and the ASDEX (Axial-symmetrical Divertor Experiment), similarly effective stabilising effects (PLT: 1978 0.18 s, 60 million .degree.C.; ASDEX: 1980 3 s) have been able to be achieved, is unsuitable for continuous reactor operation and hence also for energy production by nuclear fusion because in this concept the currents generating the stabilising magnetic field are driven by voltages induced in a metal discharge tube wall (and not as in, for example, the Stellarator by a separate direct current source) and these induced voltages must always point in the same direction owing to the unacceptability of a collapse of the stabilising magnetic field and the resultant ban on zero crossings of the currents generating the stabilising magnetic field and voltages of permanently fixed direction cannot be induced for an indefinite length of time because, with a preset voltage to be induced, the size of the magnet core required for induction increases in proportion to the square of the time during which the voltage to be induced must be sustained. That effective stabilising effects have been able to be achieved at all with the Tokamac concept is due to the fact that this concept in principle represents the ideal implementation of the modification of the Stellarator originally proposed by L. Spitzer: for if in this modification, instead of six conductors running helically around the discharge tube and carrying the same current, so great a number of conductors running directly adjacent to one another helically around the discharge tube and carrying the same current were to be provided that the entire surface of the discharge tube was covered by such conductors running directly adjacent to one another helically around the discharge tube and carrying the same current, then this plurality of conductors may also be replaced by a metal tube if at the same time provision is made for voltages, which have the same characteristic as previously the conductors running adjacent to one another, to be induced in the metal tube. In the Tokamac concept, such helically running voltages are induced in the toroidal metal discharge tube in that the metal torus forming the discharge tube and the annular plasma inside the metal torus each form a secondary winding of a shell-type transformer, which has a transformer core extending along the torus axis and a shell externally enclosing the torus and in whose core a constantly increasing current flowing through the primary winding generates a constantly increasing magnetic flux which in turn induces in the two secondary windings, i.e. in the metal torus and the annular plasma, rotational voltages of the same level and direction running parallel to the tube axis of the torus. The induced rotational voltage sets the plasma moving in the direction of the tube axis of the torus, thereby producing an axial plasma stream which in turn generates a magnetic field which surrounds the plasma and has circular magnetic flux lines concentric to the tube axis of the torus. Super-imposition of this magnetic field generated by the axial plasma stream by the confining field whose magnetic flux lines run parallel to the tube axis of the torus and hence perpendicular to the magnetic flux lines of the magnetic field generated by the axial plasma stream produces a cumulative field with magnetic flux lines running helically around the tube axis of the torus. The individual charge carriers of the plasma set in motion by the induced rotational voltage then follow these helical magnetic flux lines with the result that the axial plasma stream contains, besides its axial component pointing in the direction of the tube axis of the torus, an additional azimuthal component pointing in the direction of rotation about the tube axis of the torus, and the magnetic field generated by this azimuthal component of the axial plasma stream finally induces in the metal torus an annular voltage which runs around the tube axis of the torus and whose superimposition by the rotational voltage induced by the shell-type transformer and running parallel to the tube axis of the torus produces a helical characteristic in the voltages in the metal torus forming the discharge tube. The voltages running helically about the tube axis of the torus in the metal torus in turn drive helical currents in the metal torus which, if the system and its operating parameters are suitably dimensioned, may together be of the same magnitude as the sum of the six individual currents running helically around the discharge tube in the Stellarator and may also have the same characteristic as these. Thus, the Tokamac concept allows the same current and magnetic field configurations as the modification to the Stellarator originally proposed by L. Spitzer and hence also the stability, which according to the theoretical studies of L. Spitzer was to be achievable with such current and magnetic field configurations, but it excludes the possibility, which still exists in practice in this modification of the Stellarator for the reasons mentioned above, of the occurrence of axial plasma vibrations and plasma instabilities caused thereby because in this concept, in contrast to the electrically non-conductive discharge tube of the Stellarator, an electrically conductive metal torus is provided as a discharge tube which, because of the permanent coupling effected by said shell-type transformer between the annular plasma forming the one secondary winding of this transformer and the metal torus forming the other secondary winding of the transformer, acts as a strong damper which is connected in parallel to the annular plasma and does not allow the axial plasma vibrations to occur in the first place. With the Tokamac concept, it is therefore possible to realise in practice the stability which in theory should have already been a feature of the modification to the Stellarator proposed by L. Spitzer and for this reason an effective stabilising effect has in practice also been achievable with the Tokamac concept (and not only with the above-described changed modification of the Stellarator with two equal-sized groups of currents flowing in opposite directions around the discharge tube or the picket fence concept realised therein). The drawback of the Tokamac concept is however that this stabilising effect is in practice limited in time because the currents generating the stabilising magnetic field in the Tokamac concept are driven by the voltages induced in the metal discharge tube wall and the size of the magnet core required to induce these voltages and hence of course also the size and cost of the entire fusion system as already mentioned increase in proportion to the square of the sustenance time of the induced voltages. For since, according to the Lawson criterion, ignition of the plasma can only occur when the product of the sustenance time and the particle density lies above 3.times.10.sup.14 s/cm.sup.3 and the particle density has a ceiling imposed by the maximum achievable magnetic pressure upon the plasma and the maximum permissible .beta. values, ignition of the plasma can in practice only be achieved by increasing the sustenance time, and since the size and cost of the fusion system increase in proportion to the square of the sustenance time, the limit of what is technically and financially feasible here is very quickly reached. This is clearly evident from the size and cost development of experimental reactors for controlled nuclear fusion for, whereas initially the experimental plants still operating according to the Stellarator concept, such as, for example, the Stellarator C developed in Princeton with a size of around 20 m.sup.3 and an outlay of around 10 million U.S.$ or the Wendelstein in Garching with a size of around 100 m.sup.3 and an outlay of around 50 million U.S.$, were still within the budgetary scope of the relevant research institutes or the universities to which the research institutes belonged, the experimental plants operating according to the Tokamac concept, such as the ASDEX constructed in Germany with a size of around 200 m.sup.3 and an outlay in excess of 150 million U.S.$ or the JET currently under construction and jointly financed by the Western European states with a size of around 750 m.sup.3 and a projected cost in excess of 500 million U.S.$ and finally the INTOR joint venture by the U.S.A., U.S.S.R., Japan and Western Europe with a size of over 2500 m.sup.3 and estimated cost in excess of 2000 million U.S.$, can only be financed on a national or international scale. Bearing in mind that the size of the biggest planned experimental system, i.e. the INTOR, is around 100 times the size of the Stellarator C dating from the early days of research into nuclear fusion and that such a size ratio in the Tokamac concept only makes possible an increase in the sustenance time by the factor 10, then it becomes clear that the drawback of the stabilising effect in the Tokamac concept being in practice limited in time is serious enough to cast doubt on the ability of the Tokamac concept to achieve the aim of energy production by nuclear fusion. This is also already evident from the results of the planning stage of the INTOR which reveal that with the INTOR nuclear fusion itself and ignition of the plasma should be achievable but that the power gain through nuclear fusion at 5 to 10 MW is only 2.5 to 5% of the power consumption of around 200 MW required to operate the INTOR. And since this fairly negative power balance could only be improved to the extent where an acceptable positive power balance of less than 50% own consumption by the fusion reactor of the power generated by nuclear fusion could be anticipated by increasing the planned containment time for the INTOR of 6 to 12 seconds to a period of several minutes and such an increase in the containment time would make the costs for the fusion reactor soar immeasurably, then even if energy production through nuclear fusion were theoretically attainable with the Tokamac concept, such a solution would be impracticable on the grounds of cost. In practical terms, this means that the Tokamac concept is also ruled out for energy production by nuclear fusion and is ruled out in the end for the same reason that made all the other concepts tried out in the course of nuclear fusion development unsuitable for energy production by nuclear fusion, namely that none of these concepts guarantees the stability of the plasma over periods of indefinite length which is required to sustain the plasma containment for an unlimited time, in other words none of these concepts is inherently stable. The question then arises of the correctness of the decision taken mid-1956 during the initial development phase of nuclear fusion to drop the only inherently stable concept, i.e. the picket fence concept and its modification known as cusped geometry, and instead to pursue other projects which may at the time have appeared more promising but in no way fulfilled Teller's stability criterion. For in view of the fact that in the intervening three decades, despite an enormous scientific and technical input throughout the world, it has proved impossible to find a satisfactory solution to the stability problem with the concepts practically tested in the course of nuclear fusion development, it seems fair to say that an absence of stability in a concept is a problem which cannot in practical terms--at any rate at a reasonable cost--be solved, whereas the question whether the deficiencies of the only inherently stable concept, i.e. mainly the problem of particle loss and the non-tight plasma containment in the picket fence concept and the cusped geometry based thereon, can be satisfactorily eliminated has remained largely unanswered owing to the above-mentioned decision to abandon the concept. Admittedly, during the course of the above-mentioned theoretical studies of cusped geometry, various suggestions have been made to reduce particle loss but the question, whether within the scope of this concept a plasma with a non-decreasing particle number can be achieved for an indefinite length of time and whether the particle loss problem can be completely eliminated, remained unanswered in these studies too. SUMMARY OF THE INVENTION. The aim of the invention was therefore, on the basis of the only inherently stable concept, to provide a fusion reactor of the type mentioned initially with a reaction zone which is surrounded by a magnetic field with magnetic flux lines curved in a convex manner viewed from the reaction zone, in which reactor the particle loss problem is solved and there is always in the reaction zone a sufficient number of reactant ions to sustain the fusion process with sufficient kinetic energy for fusion. This aim is achieved according to the invention with a fusion reactor of the type mentioned initially which is characterised by a potential pot surrounding the reaction zone for the conversion of kinetic energy from ionized reactants escaping from the reaction zone into potential energy thereof and for the subsequent return of the ionized reactants into the reaction zone with reconversion of their potential energy into kinetic energy. The reaction zone expediently lies in the centre of the electric potential pot, to the upper edge of which ionized reactants are supplied and accelerated by the potential difference between edge and centre up to a kinetic energy sufficient for fusion and upon not meeting another reactant in the reaction zone pass the centre at a high speed corresponding to their kinetic energy and at the opposite side of the potential pot to their supply side again run against the potential difference at a decreasing speed towards the edge of the potential pot until their kinetic energy, shortly before reaching the potential pot edge, is again converted into potential energy, so that the process of accelerated movement towards the potential pot centre and the subsequent decelerated movement towards the potential pot edge may be repeated any number of times up to a fusion reaction in the reaction zone and consequently a large portion of the reactants supplied to the potential pot edge may be brought into fusion reaction, with the portions, which extend in the potential pot, of the magnetic flux lines of the magnetic field surrounding the reaction zone in the region between potential pot edge and reaction zone running substantially perpendicular to the equipotential lines of the electric field forming the potential pot and substantially parallel to the field lines of the electric field so that the substantially linear acceleration of the ionized reactants towards the reaction zone is not disrupted by the magnetic field surrounding the reaction zone. The main advantage of the present fusion reactor is that it offers for the first time the possibility of indefinite continuous reactor operation and hence attainment of the goal of energy production by nuclear fusion. In principle, this possibility results from the inherent stability of the plasma containment in nuclear fusion reactors of the type mentioned initially with a reaction zone which is surrounded by a magnetic field having magnetic flux lines curved in a convex manner viewed from the reaction zone, as well as from the ability by means of the electric potential pot of the present fusion reactor to achieve complete elimination of the particle loss problem or the lack of tightness of the plasma containment which, in the known proposals for fusion reactors of the type mentioned initially (picket fence concept, cusped geometry), was regarded as an insoluble problem (Picket fence concept, "Project Sherwood", p. 91) to which partial solutions in the sense of a reduction in particle losses were conceivable only in discontinuous reactor operation (Cusped geometry, "Project Sherwood", p. 410). In the present fusion reactor, this particle loss problem is overcome with the aid of a technical trick in that removal of the particles from the direct vicinity of the reaction zone is deliberately permitted but the removing particles are returned by means of the electric potential pot with the same energy back into the reaction zone, with only one conversion of the kinetic energy of the removing particles into potential energy and one reconversion of this potential energy into kinetic energy upon the return of the particles into the reaction zone occurring in the potential pot holding the particles captive. The electric potential pot of the present fusion reactor moreover has the critical advantage of rendering superfluous the compression of the plasma required in the known fusion reactors, because the ionized reactants supplied at the upper edge of the potential pot are compressed towards the reaction zone in the centre of the potential pot in inverse proportion to the cube of the distance from the centre so that, e.g. with a reaction zone diameter of one tenth of the potential pot diameter, "compression" to the level of .times.1000 occurs in the reaction zone. This advantage is of critical importance in so far as, in all known fusion reactors, compression of the plasma is effected by magnetic compression which necessitates a steep increase in the magnetic field containing the plasma or in the current generating said magnetic field and this increase inevitably leads to pulsed-mode operation of the fusion reactor if stability of the compressed plasma contained by the magnetic field as well as tight containment of said plasma are not guaranteed. However, as the stability of the plasma in the known fusion reactors with a toroidal discharge vessel decreases with increasing compression of the plasma because the originally doughnut-shaped plasma is compressed by the magnetic compression into a thin circular plasma thread and such a thin plasma thread naturally is more inclined to break, the thinner it is, magnetic compression in fusion reactors with a toroidal discharge vessel leads perforce to a restriction to pulsed-mode operation and hence to unattainability of the goal of energy production by nuclear fusion. The electric potential pot of the present fusion reactor therefore not only ensures the above-mentioned complete elimination of the particle loss problem as yet unsolved in the proposed fusion reactors of the type mentioned initially (picket fence concept, cusped geometry) but also, owing to the fact that its compression of the reactants in the reaction zone is effected without magnetic compression, fulfils all the other preconditions for continuous reactor operation, i.e. overcomes the pulsed-mode operation previously unavoidable in all the known fusion reactors, including the proposed fusion reactors of the type mentioned initially, on account of magnetic compression of the plasma and eliminates the stability problems occurring in fusion reactors with a toroidal discharge vessel on account of magnetic compression of the plasma, so that only by equipping fusion reactors of the type mentioned initially with such a potential pot will the transition from discontinuous to continuous reactor operation and hence to energy production by nuclear fusion be possible. The non-magnetic compression of the reactants in the reaction zone by the electric potential pot plays a positive role in that the magnetic field containing the plasma in the reaction zone may, because there is no longer any need for magnetic compression, be held constant or left at a constant magnetic field intensity during operation of the reactor, which in conjunction with generation of the magnetic field by means of superconducting coils opens up the possibility of reducing the energy required to sustain the magnetic field containing the plasma during operation of the reactor virtually to zero and so improving the energy balance of the present fusion reactor to the extent that the aim of energy production by nuclear fusion can be achieved. In connection with the high density of reactants in the reaction zone achievable by means of the electric potential pot, it is also an important advantage that the present fusion reactor may be operated with a much higher particle density in the reaction zone than the known fusion reactors of the Stellarator or Tokamac types because, as already mentioned, for stability reasons fusion reactors of the Stellarator or Tokamac types have to be operated with very low values of the ratio .beta. of plasma pressure to magnetic pressure upon the plasma and with correspondingly low particle densities in the reaction zone, whereas fusion reactors of the type mentioned initially, as demonstrated above by the example of cusped geometry, are preferably operated with high .beta. values and correspondingly large particle densities in the reaction zone. The advantage of such a high particle density in the reaction zone or a correspondingly high permissible plasma pressure is the elimination of all the aforementioned problems which arise in Stellarator or Tokamac type fusion reactors on account of the very low plasma pressure permissible in them, in particular the elimination of the cited technical problems occurring in Stellarator or Tokamac type fusion reactors with the very high vacuum required on account of the low permissible plasma pressure and with the correspondingly necessary, extremely low plasma impurities from gas pockets in the discharge vessel wall and the high radiation losses caused by such plasma impurities. In the present fusion reactor, the vacuum which is required is in contrast much lower and serious problems with plasma impurities and associated radiation losses no longer arise. Further advantages of the present fusion reactor accrue from the basic concept of fusion reactors of the type mentioned initially realised in principle in the above-mentioned cusped geometry. In this basic concept, the reaction zone basically takes the shape of a double cone acted upon from outside by magnetic pressure and such a formation is, in a similar fashion to a hollow sphere acted upon from outside by mechanical pressure, largely insensitive to disturbances or changes suddenly occurring inside it, such as an abrupt increase in the nuclear fusion rate, because the effects of such changes suddenly occurring at any point inside it are almost immediately evenly spread over the total interior or the total reaction zone whereas, in the case where a thin circular plasma thread forms the reaction zone as in fusion reactors with a toroidal discharge vessel, the effects of such sudden changes remain localised and the plasma thread is therefore inclined to break at the point of such a sudden change. The basic concept of the present fusion reactor therefore offers not only the inherent static stability provided by the--viewed from the reaction zone--convex curvature of the magnetic flux lines of the magnetic field containing the reaction zone but also inherent dynamic stability of the plasma contained by the magnetic field in the reaction zone. One other property of said basic concept is however of critical importance for the production of nuclear fusion reactions in the reaction zone. This is that, in this basic concept, the magnetic field intensity in the centre of the reaction zone enclosed by the magnetic field is praticularly zero with the result that in the centre of the reaction zone no magnetic forces whatsoever and--since the centre of the reaction zone coincides with the centre of the electric potential pot and the electric field strength in the centre of an electric potential pot is similarly zero--no electrical forces either act upon the ionized reactants so that the reactants in the centre of the reaction zone are freely movable in all three degrees of freedom. Such free mobility of the reactants in all three degrees of freedom is however, besides the required temperature of the plasma and the required mean kinetic energy of the reactants, a basic requirement for producing nuclear fusions and this basic requirement has not up till now been fulfilled in any of the practically realised fusion reactors because the reaction zone in all these fusion reactors is permeated by a magnetic field used i.a. for stabilisation and compression of the plasma and the ionized reactants in the reaction zone are therefore freely movable only in the direction of the magnetic flux lines of this magnetic field and hence only in one and not all three degrees of freedom and this may well be one of the main reasons why, despite decades of considerable effort, nuclear fusion has up till now been unattainable with the practically realised fusion reactors. In the present fusion reactor, means may advantageously be provided for supplying the reactor with a reaction gas preferably consisting at least partially of deuterium as well as for ionizing and supplying said gas to the upper edge of the potential pot. The advantage of such supply means is a continuous feed of new reactants which take the place of the reactants which have reacted, and such a continuous feed, while not being essential for nuclear fusion itself, may well be for continuous reactor operation. As means for ionizing and supplying the reaction gas to the reactor, there may advantageously be disposed at the upper edge of the potential pot a glow discharge chamber which is provided with means for supplying ionized reactants to the potential pot in the form of canal rays, preferably with a metal foil designed in the manner of a Lenard tube and permeable to the canal rays as a cathode. The advantage of such a glow discharge chamber as an ion source is a relatively low energy consumption for producing the ionized reactants in conjunction with the desired large-area distribution of the ion source at the upper edge of the potential pot. To achieve relatively high ion concentrations at the upper edge of the potential pot, means for producing a current-intensive glow discharge according to B. Berghaus may be provided in the glow discharge chamber. The electric potential pot may in the present fusion reactor advantageously take the form of a rotationally symmetrical cavity having a cross-section substantially in the form of two opposing sectors of a circle, with the cusps of the two sectors which form the cross-section coinciding with the axis of symmetry of the rotationally symmetrical cavity and a median dividing said two sectors each into two identical parts standing vertically on said axis of symmetry and said upper edge of the electric potential pot lying in the region of the arc of the sectors. The apex angle of the sectors may advantageously be between 10.degree. and 80.degree., preferably between 30.degree. and 50.degree.. The advantage of such a shape for the electric potential pot over other possible shapes, such as a circular disc-shaped cavity, is increased compression of the reactants in the reaction zone. Particularly advantageously, there may be provided, at the substantially cone-shaped side surfaces of the rotationally symmetrical cavity spatially defining the electric potential pot, means for lateral electric screening of the potential pot as well as for achieving a potential profile along the screening which is higher than or approximately the same as the potential profile along said median depending upon the distance from the potential pot centre. This has the advantage that the ionised reactants moving back and forth inside the potential pot from the region of the upper edge through the centre towards the opposite upper edge run in a kind of potential trough and so cannot reach the lateral screening of the potential pot, thereby preventing the ionised reactants from coming into contact with the material walls forming the lateral screening. The means for screening and for achieving said potential profile may advantageously comprise stacked rings made of an electrically conducting material, each of which is substantially in the shape of a short truncated cone and fits on top of the preceding ring in the stack in such a way that the ring edges of all the stacked rings together define at one side one of said substantially cone-shaped side surfaces of the rotationally symmetrical cavity. The rings may advantageously be electrically insulated from one another, preferably by means of electrically non-conducting coatings, and may be individually connected to direct voltage sources each supplying the intended potential of the ring. This has the advantage that the potential profile along the screening is independent of the movement and density of the ionised reactants moving inside the potential pot but does require a not inconsiderable technical effort on account of the individual connection of the rings to direct voltage sources each supplying the intended potential of the ring. This effort may advantageously be avoided in that the rings PG,24 are electrically connected to one another by high-resistance resistors preferably formed by electrically poorly conducting coatings and means are provided for generating a current which flows through the stack and produces at the high-resistance resistors the voltage drops required to achieve said potential profile. The price which has to be paid for the advantage thereby achieved, namely removal of the technical effort associated with individual connection of the rings, is however the energy consumption of the current flowing through the stack and, provided said energy consumption is kept down by a relatively low current flowing through the stack, the dependence of the potential profile along the screening upon voltages induced in the rings as a result of the space charge of the ionised reactants moving in the potential pot. In a preferred embodiment of the present fusion reactor, for generating the magnetic field surrounding the reaction zone, two coils with a substantially triangular winding cross-section are advantageously provided disposed coaxially to the reaction zone and the potential pot and on either side of the reaction zone and potential pot, with currents of at least approximately the same magnitude flowing in opposite directions through said coils. This embodiment has the advantage of the absolute minimum number of coils required to generate a magnetic field with magnetic flux lines curved in a convex manner viewed from the reaction zone and, because of the substantially triangular winding cross-section of the coils, the advantage of optimum adaptation of the profile of the magnetic flux lines of the magnetic field generated by the coils to the profile of the field lines of the electric field in the potential pot. To increase the magnetic field intensity in the reaction zone and in particular between the reaction zone and the material walls surrounding it, in the present thermo-nuclear reactor and in particular in said preferred embodiment thereof, a substantially hollow sphere-shaped reactor shell which encloses the coils and the potential pot and is made of a ferromagnetic material, preferably soft iron, may advantageously be provided, with one side of the substantially triangular winding cross-section of the coils advantageously being adjacent to the reactor shell inner wall and extending approximately parallel thereto and a linear extension of the median between the other two sides of the triangular winding cross-section extending through the centre of the reaction zone. The advantage of such a reactor shell made of ferromagnetic material is, with a predetermined coil current, an increase in the magnetic field intensity in the reaction zone and, with a predetermined magnetic field intensity in the reaction zone, a reduction in the coil current for generating the magnetic field surrounding the reaction zone. In the present fusion reactor and in particular in said preferred embodiment thereof, the coils may particularly advantageously be superconducting coils comprising tubular windings through which a cooling medium preferably formed by a liquefied gas flows and keeps the current-conducting walls of said windings at a temperature within the superconductivity range of the material of said walls, with means for supplying the cooling medium to the coils being provided and each of the two coils being surrounded by a heat-insulating shell preferably constructed in the manner of a Dewar flask. The advantage of such superconducting coils is that the energy consumption for generating the magnetic field surrounding the reaction zone may be kept so low that it no longer has any significant influence upon the energy balance of the fusion reactor. The substantially triangular winding cross-section of the coils in said preferred embodiment of the present thermo-nuclear reactor may advantageously basically take the form of an equilateral triangle, with the windings of the coils being formed by preferably tubular conductors, the cross-section of which conductors preferably likewise has the external shape of an equilateral triangle, and with the median between the two triangle sides, pointing approximately towards the reaction zone, of the substantially triangular winding cross-section of the coils making an angle in the region of 30.degree. to 50.degree., preferably between 37.degree. and 43.degree., with the axis of the coaxially disposed coils. The advantage of such a winding cross-section section in the form of an equilateral triangle is that the conductor cross-section of the coil windings may also take the form of an equilateral triangle so that almost complete utilisation of the winding space of the coils and consequently a maximum magnetic field intensity in the vicinity of the coils and hence also in the outer regions of the reaction zone may be achieved. For the capture and chemonuclear conversion of neutrons released in nuclear fusion reactions, there may advantageously be provided in the present fusion reactor a blanket which surrounds the reaction zone and the potential pot and in which in liquid lithium flows from a storage tank, disposed in the region of the upper edge of the pot and covering the potential pot in this region, along the side surfaces of the potential pot into the region surrounding the reaction zone and from there approximately in the direction of the axis of the reaction zone and potential pot into a collecting tank, the collecting tank being connected to the storage tank by a separating device, preferably a tritium stripper, and a first heat exchanger as well as by a lithium pump for circulating the liquid lithium through the blanket. Advantageously, the flow cross-section for the liquid lithium may be at least approximately constant in the portions of the blanket extending along the side surfaces of the potential pot and approximately in the direction of the axis of reaction zone and potential pot in order to achieve a substantially constant flow rate of the lithium in said portions of the blanket and the width of the, in said portions of the blanket, annular flow cross-section may for this purpose be at least approximately inversely proportional to the mean diameter of the annular flow cross-section or to the mean distance of the flow cross-section from the axis of reaction zone and potential pot. The blanket surrounding both the reaction zone and the potential pot has the advantage that almost no neutrons can escape from the fusion reactor, and the advantage of a constant flow cross-section for the lithium in the blanket lies in the fact that it allows a combination of a high flow rate with laminar, non-turbulent flow of the lithium and that as a result the width of the annular flow cross-section and consequently the capture effect of the lithium is greatest at the point where the most neutrons are to be captured, i.e. in the vicinity of the reaction zone. Said first heat exchanger in the lithium circuit may give up its heat advantageously to a potassium circuit passing through a second heat exchanger and a potassium turbine, the potassium turbine driving a first generator for generating electric energy, and the second heat exchanger advantageously gives up its heat to a water/steam circuit leading through a steam turbine as well as a condenser and a pump, the steam turbine driving a second generator for generating electric energy. The advantage of such a two-stage heat exchange with a potassium circuit in the first stage is the adaptability of the potassium circuit to the temperature in the lithium circuit. In the present fusion reactor, means may also advantageously be provided for supplying reactants to the reaction zone and for discharging reaction products and excess reaction gas from the reaction zone, said means comprising at least one gas reservoir for gas to be supplied to the reaction zone, supply means, preferably with a supply channel coaxial to the axis of the reactor, for supplying reaction gas from at least one gas reservoir to the reaction zone, discharge means, preferably with a discharge channel coaxial to the axis of the reactor, for carrying reaction products and excess reaction gas away from the reaction zone, a gas separating system, preferably in the form of a gas fractionator, for the gas coming from the reaction zone and a gas pump, preferably a vacuum pump, for conveying gas out of the reaction zone as well as preferably in the circuit through the gas separating system, gas reservoir, supply means, reaction zone and discharge means. Besides carrying reaction products away from the reaction zone, such gas supply and discharge means have the advantage of opening up the possibility of supplying to the reaction zone un-ionised reactants which are ionized in the reaction zone and whose electrons released during said ionization, together with the ions thereby produced and the ionized reactants from the potential pot, form a true plasma of ions and electrons in the reaction zone. A further advantage of such means is the movement of the supplied atoms in the axial direction of the reactor for, since this direction of movement is substantially perpendicular to the direction of movement of the ionized reactants passing from the potential pot into the reaction zone, there is a much greater chance of collisions between ionized reactants from the potential pot and ionized reactants from the supply channel with subsequent fusion reaction than there is of collisions of the ionized reactants from the potential pot with one another because, just as with sustaining an unstable equilibrium, there is virtually no chance of a frontal collision between atomic nuclei moving towards one another in a straight line because atomic nuclei of like electrical charge avoid one another while a similar avoiding process with atomic nuclei moving at right angles to one another quite often does not rule out a collision of the atomic nuclei. |
050646036 | description | DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic block diagram of a hydroball string sensing system embodying the present invention. In FIG. 1, a nuclear reactor vessel 10 includes a core region 15. The nuclear reactor vessel 10 contains a pressurized, high temperature fluid such as water. The fluid pressure within the core region 15 is in the range of, for example, 1,200 psi to 2,000 psi. The core region 15 has positioned therein fuel rods and a number of stainless steel tubes such as a tube 20 shown in FIG. 1. Each of the tubes 20 is connected to the nuclear reactor vessel 10 and contains the pressurized water at substantially the same pressure as within the core region 15. Basically, each of the tubes 20 functions as an extension of the nuclear reactor vessel 10. Because the tubes 20 are subjected to the same high temperature (e.g., 600.degree. F.), high pressure water that exists within the core region 15, the tubes 20 are structure of thick stainless steel walls (e.g., 0.05 inch). The hydroball string 25 comprises a string member 30 with objects including hydroballs 35 and bullet members 40. The hydroballs 35 are positioned along the string member 30 with a specified spacing between each hydroball 35. As shown in FIG. 1, the bullet members 40 are positioned at opposing ends of the string member 30. The hydroballs 35 can comprise, for example, 304 stainless steel with 2% manganese or 18-8 austenitic stainless steel. The bullet members 40 can comprise a ferritic stainless steel such as 17-4 PH. The structure and operation of a hydroball string is known to those skilled in the art and discussed in, for example, copending U.S. patent application Ser. No. 07/042,183 and entitled Hydro-Ball In-Core Instrumentation System and Method of Operation which is assigned to the same assignee as this application. Briefly, the hydroball string 25 is moved within the stainless steel tube 20 by pumping water into or out of the reactor vessel 10, depending upon whether it is desired to move the hydroball string 25 into or out of the reactor vessel 10. Sensors (described below) at location A sense the presence of the objects on the hydroball string 25, such as bullet members 40. This sensing indicates whether the hydroball string 25 has entered into or exited from the nuclear reactor 10. With this information, the amount of time that the hydroball string 25 spends within the nuclear reactor 10 can be measured together with the amount of time that elapses after the hydroball string 25 leaves the reactor vessel 10 and before the string 25 reaches a location C and counter station 45. In practice, there is only one counter station for the many stainless steel tubes 20. Consequently, a multiport valve 50 determines which of the stainless steel tubes 20, and therefore which hydroball string 25 housed therein is connected to a tube 55 located adjacent the counter station 45. FIG. 2 is a schematic block diagram of the counter station 45 shown in FIG. 1. In FIG. 2, a first sensor 60 is positioned outside a first segment 65 of the tube 20. The first sensor 60 (described in detail below) senses objects, such as a hydroball 35 being within the first segment 65. The first sensor 60 provides a first sensing signal on signal line 70. The first sensing signal is responsive to the first sensor 60 sensing an object, such as hydroball 35, being within the first segment 65. In a manner similar to the first sensor 60, a second sensor 75 is positioned outside a second segment 80 of the tube 20 that is spaced a given distance along the tube 20 from the first sensor 60. The second sensor 75 provides a second sensing signal on signal line 85 that is responsive to the second sensor sensing an object such as hydroball 35 being within the second segment 80. The details of the first and second sensors (60, 75) are discussed below. Typically, the spacing between the first and second sensors (60, 75) is approximately 1/2 inch, and the spacing between the hydroballs 35 is approximately 2 inches. These particular dimensions are not required, but merely presented as examples. As shown in FIG. 2, the first and second signal lines (70, 85) are connected to a controller 90. The controller 90 drives a variable speed pump 95. The controller 90 also determines the amount of time elapsing between the first sensor 60 sensing a first hydroball 35 being within the first segment 65, and the first sensor 60 sensing an adjacent hydroball 35 being within the first segment. Since the spacing between adjacent hydroballs 35 is known, the average velocity of the hydroball string 25 is calculated by controller 90 using the determined elapsed time and the known spacing between hydroballs 35. If the velocity determined by the controller 90 is less than a desired velocity, then the controller 90 increases the speed of the variable speed pump 95. This increases the flow of fluid within tube 20; thus, increasing the velocity of the hydroball string 25. Alternatively, if the velocity determined by the controller 90 is larger than the desired velocity, then the controller 90 decreases the speed of the variable speed pump 95. This reduces the flow rate of fluid within the tube 20; thus, reducing the velocity of the hydroball string 25 within the tube 20. In FIG. 2, reference numeral 100 identifies a gamma ray scintillation counter. The structure and operation of such a counter is well known to those skilled in the art and therefore is not discussed here. The counter 100 detects the gamma ray radiation emitted from one of the hydroballs 35 during the time that the hydroball 35 is between the first and second sensors (60, 75). The time during which the counter 100 operates is controlled by controller 90. For example, when the first sensor 60 indicates, on signal line 70, that a hydroball 35 is in the first segment, the controller 90 initiates counting by the counter 100 via signal line 105. When the controller 90 determines that this same hydroball 35 is within the second segment 80, via signal line 85, the controller 90 stops the counting of the counter 100 via signal line 105. Thus, the count developed by counter 100 indicates the amount of radiation emitted from the hydroball 35 during the time that the hydroball 35 is between the first and second sensors (60, 75). In a preferred embodiment of the present invention, the first and second sensors (60, 75) comprises ultrasonic transducers. Referring to FIG. 2, ultrasonic transducer transmitters 110 and 115 respectively transmit ultrasound into the first segment 65 and the second segment 80. Ultrasonic transducer receives 120 and 125 respectively receive ultrasound passing through the first segment 65 and the second segment 85. Basically, when a hydroball 35 is in, for example, the first segment, the amount of ultrasound received by ultrasonic transducer receiver 120 is substantially less than that received when there is no hydroball in the segment. Thus, a signal provided by the ultrasonic transducer receiver 120 varies in dependence upon the presence or absence of a hydroball 35 from the first segment 65. The ultrasonic transducers 120, 125 operate in the same way. FIG. 3 is a schematic block diagram of a signal processing portion of the FIG. 1 system that is included in the controller 90. In FIG. 3, a clock circuit 130 controls an RF pulse generator 135 so as to gate RF pulses so as to provide bursts of RF pulses to the first and second transducers (60, 75). In a preferred embodiment the clock pulses occur at, for example, point 0.01 seconds, and the RF frequency is 5 Mhz. This frequency and pulse timing is only one example and used here only to discuss an embodiment of the present invention. Typically, the diameter of the transducer should a fraction of the diameter of the tube, and the length of the transducer along the tube 20 should be on the order of the size of a hydroball 35 or less in order to accurately sense the location of a hydroball. Each of the ultrasonic transducer receivers (120, 125) is connected to signal processing and gating circuitry within controller 90. The processing and gating circuitry for each of the ultrasonic transducer receivers (120, 125) is the same, and therefore, only circuitry connected to ultrasonic transducer receiver 120 is discussed below. The ultrasonic transducer receiver 120 converts the received ultrasound into electrical pulses. Typically, such electrical pulses have an amplitude of less than 1 mv. If a hydroball 35 is interposed between the ultrasonic transducer transmitter 110 and the ultrasonic transducer receiver 120, then the pulses provided by the ultrasonic transducer receiver 120 are much smaller than the 1 mv. The pulses provided by ultrasonic transducer receiver 120 are processed by a typical ultrasonic signal processing system. The signal processing system includes an amplifier 140 which amplifies the pulses by 30 to 50 db. A filter 145 filters the 5 Mhz pulses, and an envelope detector 150 converts a bipolar train of 5 Mhz pulses to an envelope. For example, the envelope detector can comprise a simple rectifying and filtering circuit. The output of the detector 150 is applied to a threshold circuit 155 such as a Schmitt trigger. This provides some noise immunity, wave shaping and a signal as shown in FIG. 4. In FIG. 4, the large pulses on the lefthand side of the waveform (b) and (c) represent the ultrasound being transmitted by, for example, ultrasonic transducer transmitter 110. In waveform (b) two smaller pulses represent ultrasound being received by the ultrasonic transducer receiver 120. The absence of the two smaller pulses in waveform (c), indicates that a hydroball 35 is positioned between the ultrasonic transducer transmitter 110 and the ultrasonic transducer receiver 120. The clock circuit 130 also drives a gate circuit 160. The clock signal, shown in waveform (a) of FIG. 4, ensures that only the signal representing the ultrasound received by ultrasonic transducer receiver 120 is presented to a peak sense and hold circuit 165. The peak sense and hold circuit 165 detects the peak of the pulses shown in waveform (b) of FIG. 4 that occur during the clock signal, waveform (a). A microprocessor 170 detects the output of the peak sense and hold circuit 165, and when a pulse is sensed at the output of peak sense and hold circuit 165, the microprocessor identifies that there is no hydroball 35 between the ultrasonic transducer transmitter 110 and the ultrasonic transducer receiver 120. FIG. 5A is a partial cross-sectional view of an alternative embodiment of the first and second sensors (60, 75). In FIG. 5A, a magnet 175 is attached to a ceramic fiber insulation 177 positioned about a double walled stainless steel tube 20. It will be recognized that it is not necessary to the present invention that a double walled tube be used. Pole pieces (180, 185) are positioned adjacent the ceramic fiber insulation 177 and located opposite the magnet 175. The pole pieces 180 and 185 guide a portion of the magnetic field provided by the magnet 175. A Hall effect transducer 190 is positioned between the pole pieces 180 and 185 to sense the magnetic field guided by the pole pieces 180 and 185. FIG. 5B is a graph illustrating a waveform provided by the Hall effect transducer 190 shown in FIG. 5A when a bullet member disturbs the magnetic field guided by the pole pieces 180 and 185. A ferritic object such as the bullet member 40 disturbs the magnetic field provided by the magnet 175. Essentially, the bullet member 40 shunts a significant portion of the magnetic field guided by the pole pieces 180, 185. Typically, the hall effect transducer 190 provides approximately 60 mv change in output when a bullet member 40 passes the sensor with about 1.1 inches between the pole pieces (180, 185) and the magnet 175. It will be recognized that larger signals can be obtained as the gap between the pole pieces (180, 185) and magnet 175 is reduced. As will be appreciated by those skilled in the art, when using the sensor shown in FIG. 5A, the filter 145 and the envelope detector 150 shown in FIG. 3 are not needed. FIG. 6A is a partial cross-sectional view of an alternative embodiment of the first and second sensors (60, 75). The sensor shown in FIG. 6A detects a rate of change of a magnetic field. In FIG. 4, a magnetically permeable or highly magnetically permeable material pole piece 200 guides a portion of the magnetic field provided by the magnet 175. A sense coil 205 is wound about the steel pole piece 200. The sense coil 205 senses the change in magnetic flux passing through the steel pole piece 200. The output of the sensed coil 205 can be applied to, for example, the amplifier 140 shown in FIG. 3, or can be displayed on a display device such as oscilloscope 210. FIG. 6B illustrates a waveform of a signal provided by the sense coil 205 when a ferritic object such as a bullet member 40 passes through the position shown in FIG. 6A. When using a rate of change sensor such as shown in FIG. 4, it is desirable to detect a zero crossing to accurately identify the position of an object such as the bullet member 40. Thus, the sense and hold circuit of FIG. 3 would be replaced by a zero crossing detection circuit and there is no need for the envelope detector 150. While the present invention has been described with respect to a specific embodiments, these embodiments are not intended to limit the scope of the present invention which is instead defined by the following claims. |
description | This disclosure relates generally to impeller devices and, more specifically, to a system and method for determining health indicators for impellers. Impellers are routinely used in various industries. One type of impeller includes a rotor used to increase the pressure and flow of a fluid inside a cylinder, tube, or other conduit. Impellers are often used, for example, in the process control industry. However, impellers routinely suffer from various failures. Example failure modes of an impeller can include vane breakage, one or more cracks in the impeller, and wear in the impeller. It is often necessary or desirable to monitor the health of an impeller in a process control system or other system in order to properly schedule maintenance for the impeller. However, it is often difficult to monitor the health of impellers because of the wide variety of impellers in use. This disclosure provides a system and method for determining health indicators for impellers. In a first embodiment, an apparatus includes an input interface configured to receive an input signal associated with at least one stage of an impeller. The apparatus also includes a processor configured to identify a fault in the impeller using the input signal. The apparatus further includes an output interface configured to provide an indicator identifying the fault. The processor is configured to identify the fault by determining a family of frequencies related to at least one failure mode of the impeller, decomposing the input signal using the family of frequencies, reconstructing an impeller signal using the decomposed input signal, and comparing the reconstructed impeller signal to a baseline signal. The family of frequencies includes a vane pass frequency and its harmonics. In a second embodiment, a system includes a plurality of sensors configured to measure one or more characteristics of an impeller. The system also includes an impeller condition indicator device, which includes a plurality of sensor interfaces configured to receive input signals associated with at least one stage of the impeller from the sensors. The impeller condition indicator device also includes a processor configured to identify a fault in the impeller using the input signals and an output interface configured to provide an indicator identifying the fault. The processor is configured to identify the fault by determining a family of frequencies related to at least one failure mode of the impeller, decomposing the input signals using the family of frequencies, reconstructing an impeller signal using the decomposed input signals, and comparing the reconstructed impeller signal to a baseline signal. The family of frequencies includes a vane pass frequency and its harmonics. In a third embodiment, a method includes receiving an input signal having vibration and/or speed information corresponding to at least one stage of an impeller. The method also includes determining a family of frequencies corresponding to at least one failure mode of the impeller, where the family of frequencies includes a vane pass frequency and its harmonics. The method further includes decomposing the input signal using the family of frequencies and reconstructing an impeller signal using the decomposed input signal. In addition, the method includes comparing the reconstructed impeller signal to a baseline signal and outputting an indicator identifying a fault when the reconstructed impeller signal differs from the baseline signal by a threshold amount. Other technical features may be readily apparent to one skilled in the art from the following figures, descriptions, and claims. FIGS. 1 through 9, discussed below, and the various embodiments used to describe the principles of the present invention in this patent document are by way of illustration only and should not be construed in any way to limit the scope of the invention. Those skilled in the art will understand that the principles of the invention may be implemented in any type of suitably arranged device or system. Also, it will be understood that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some elements in the figures may be exaggerated relative to other elements to help improve the understanding of various embodiments described in this patent document. FIGS. 1A through 1G illustrates example impeller configurations. In FIGS. 1A through 1D, impellers 100a-100b include a rotor inside a cylinder, tube, or other conduit 105. The rotor is used to increase the pressure and flow of a fluid inside the conduit 105. The conduit 105 includes an open inlet 110 (often referred to as an “eye”) that accepts incoming fluid. Vanes 115 push the fluid radially within the conduit 105. The vanes 115 can, for example, represent backward curved blades 115a, radial blades 115b, or forward inclined blades 115c. A splined, keyed, or threaded bore 120 accepts a driveshaft 125, which causes the vanes 115 to rotate. The impellers 100a-100b can be made of iron, steel, bronze, brass, aluminum, plastic, or other suitable material(s). The impeller 100a represents an axial flow impeller, and the impeller 100b represents a mixed flow impeller. As shown in FIG. 1E, an impeller 100c also can be used as the rotating component of a centrifugal pump 130. The impeller 100c transfers or converts rotating and/or kinetic energy from a motor that drives the pump 130 into potential energy of the pumped fluid by accelerating the fluid outwards from the center of rotation. The velocity achieved by the impeller 100c translates into pressure when a pump casing 135 confines the outward movement of the fluid. FIGS. 1F and 1G illustrate additional types of impellers. In particular, FIG. 1F illustrates an open impeller 100d, a semi-open impeller 100e, and a closed impeller 100f. FIG. 1G illustrates a single suction impeller 100g and a double suction impeller 100h. In addition to selecting a particular type of impeller, the design of the particular impeller can be varied to alter its performance characteristics. For example, an impeller with a large number of vanes or with vanes having large angles may have an increased “head” of the fluid. Also, an impeller with a low number of vanes or with large vane outlet angles may have poor vibration characteristics or heavy loads at the tips. Further, a larger clearance between an impeller and its casing may decrease vibration but result in an increase in size, weight, and cost. One hydraulic phenomenon associated with the use of impellers is cavitation, which is illustrated in FIGS. 2A and 2B. Cavitation is a phenomenon where vapor bubbles form in a flowing liquid in or around a region where the pressure of the liquid falls below its vapor pressure. FIG. 2A illustrates cavitation located at the discharge of an impeller, while FIG. 2B illustrates cavitation located at the suction of an impeller. Cavitation can be divided into two classes of behavior, namely inertial (or transient) cavitation and noninertial cavitation. Inertial cavitation is the process where a void or bubble in a liquid rapidly collapses, producing a shock wave. Noninertial cavitation is the process where a bubble in a fluid is forced to oscillate in size or shape due to some form of energy input, such as an acoustic field. Both types of cavitation can occur when using impellers. Moreover, the shock waves formed by cavitation may be strong enough to significantly damage moving parts, which can facilitate the erosion of an impeller and its casing or other damage to the impeller. It is often difficult to monitor the health of a number of impellers due, among other things, to the various types of impellers that are in use. In accordance with this disclosure, an impeller health monitoring system is provided that can monitor the health of one or more impellers and provide an indication when a particular impeller is suffering from wear or other problems. FIG. 3 illustrates an example table 300 for impeller failure mode rules according to this disclosure. The embodiment of the table 300 shown in FIG. 3 is for illustration only. Other embodiments of the table 300 could be used without departing from the scope of this disclosure. In this example, the table 300 includes five failure conditions. The failure conditions include high flow cavitations 302, low flow cavitations 304, impeller wear 306, impeller cracking 310, and impeller vane breakage 312. The table 300 identifies the effects of these failure conditions on various frequencies associated with operation of the impeller. The impeller frequencies include the rotating shaft speed frequency (fr) 322, the vane pass frequency (fvane) 324, the shaft sideband frequencies (fvane−fr) 326 and (fvane+fr) 328, and background noise 330. If high flow cavitations 302 or low flow cavitations 304 occur, the frequencies fvane 324, fvane−fr326 and fvane+fr 328 decrease, and the background noise 330 increases. If impeller wear 306 occurs, the frequency fvane 324 increases, while the frequencies fvane−fr 326 and fvane+fr 328 decrease. Impeller cracking 310 results in an increase in each of the frequencies fr 322, fvane−fr 326, and fvane+fr 328, and the frequency fvane 324 decreases. An impeller vane breakage 312 increases the frequencies fr 322, fvane−fr 326, and fvane+fr 328 while causing a decrease in the frequency fvane 324. With these rules in mind, an impeller health monitoring system can monitor the health of one or more impellers and can identify a specific failure mode for each impeller (if any). FIG. 4 illustrates an example Impeller Condition Indicator (ICI) device 400 according to this disclosure. The embodiment of the ICI device 400 shown in FIG. 4 is for illustration only. Other embodiments of the ICI device 400 could be used without departing from the scope of this disclosure. In this example, the ICI device 400 includes a user configuration portion 402. The user configuration portion 402 provides a user interface that facilitates operator interaction with the ICI device 400. For example, the user configuration portion 402 may enable an operator to enter impeller configuration information. As particular examples, the user configuration portion 402 may allow the operator to enter a machine configuration 404. The machine configuration 404 may include a pump rating, one or more types of pumps, one or more types of impellers, and one or more natural frequencies of the machine. The operator may also enter a filter specification 406. The filter specification 406 may include a filter type, an order of the filter, a higher frequency limit, and a lower frequency limit. Data Acquisition (DAQ) specifications 408 may further be entered by the operation in the user configuration portion 402. The DAQ specification 408 may include a sampling frequency, a number of samples, and a voltage range. In addition, the operator may enter sensor specifications 410 and additional user inputs 412. The sensor specifications 410 may include types of sensors, sensor ranges and sensitivities, and sensor dynamic ranges and natural frequencies. The additional user inputs 412 may include sampling frequency, a number of samples, and a class of machine. The ICI device 400 also includes a sensor signal portion 420. The sensor signal portion 420 provides an interface for receiving inputs from sensors coupled to, or otherwise associated with, an impeller and/or a centrifugal pump or other device that includes an impeller. In this example, the sensor signal portion 420 includes interfaces to an accelerometer 422 and a tachometer 424. The accelerometer 422 detects, measures, and records a vibration 426 of an impeller or device containing the impeller. The tachometer 424 can be a sensor input device such as a tachogenerator or Once Per Revolution (OPR) device. The tachometer 424 detects, measures, and records speed 428 of an impeller or device containing the impeller. The sensor signal portion 420 also can store baseline signals 430 for the impeller or device containing the impeller. The ICI device 400 further includes an Artificial Intelligence (AI) portion or other processing portion 440. In this example, the AI portion 440 includes an analog-to-digital converter 441, a pre-processing filter 442, and a vibration signature processor 444. The vibration signature processor 444 can include one or more processors or other components adapted to perform FFT analysis 446, Frequency/Frequency Bandwidth Selection (FFBS) 448, signal reconstruction 450, statistical features recordation 452, and normalization 454. The AI portion 440 is also able to perform Fuzzy Rule-Based Diagnostics 456 and Rule-Based Diagnostics 458. The Fuzzy Rule-Based Diagnostics 456 include Fuzzification, Rules, Aggregation and De-fuzzification operations. These functions are described in more detail below. In addition, the ICI device 400 includes an output interface 470. The output interface 470 represents an interface configured to send information to another system or device, such as a computer or a display. The output interface 470 could also represent a single display (e.g., a monitor) or multiple displays. In this example, the output interface 470 includes an impeller wear indicator 472, an impeller crack indicator 474, a cavitations indicator 476, and an impeller health indicator 478. These indicators 472-478 identify the health of the impeller being monitored. The ICI device 400 can be implemented in any suitable manner. For example, the ICI device 400 can be implemented as an Analog/Digital (A/D) card, an embedded system, a display system, a central processing unit, a personal computer, or a digital signal processor. The ICI device 400 detects and measures the effects resulting from various types of impeller failures. For example, the ICI device 400 measures the changes in amplitudes of the frequencies 322-330 shown in FIG. 3. Based on those changes, the ICI device 400 classifies the impeller failure. In one aspect of operation, an operator can enter a machine configuration 404 for an impeller or a device with an impeller via the user configuration portion 402. The operator can also enter a pump rating (if any), a type of pump (if any), a type of impeller, and one or more natural frequencies. The operator can further enter information relating to the filter specification 406, the DAQ specification 408, and the sensor specification 410. In addition, the operator can enter additional user inputs 412, such as a sampling frequency, a number of samples, and class of machine, that the ICI device 400 will use to monitor the impeller. The ICI device 400 receives sensor input signals from sensors coupled to the ICI device 400 via a number of sensor interfaces. The ICI device 400 measures and records the sensor input signals associated with normal operation of the impeller. The ICI device 400 stores the sensor input signals corresponding to normal operation of the impeller as the set of baseline signals 430. The ICI device 400 continues to monitor the performance of the impeller based on the sampling frequency included in the additional user inputs 412. The ICI device 400 filters the input signals from the sensors using the filter 442. The vibration signature processor 444 applies the FFT analysis 446 to all of the component characteristics (e.g., frequencies) in the filtered signals. The FFT analysis 446 may yield only the relevant frequencies related to the impeller being monitored. The FFBS 448 isolates one or more frequencies and amplitudes that will be used in signal reconstruction 450 to reconstruct the signal. Once the signal is reconstructed using those selected frequencies and amplitudes, the vibration signature processor 444 determines statistical features 452 of the reconstructed signal. In some embodiments, the statistical feature 452 is a Root Mean Square (RMS) value. Thereafter, the vibration signature processor 444 produces a normalized signal by performing a normalization 454 of the reconstructed signal with respect to the baseline signal 430. The ICI device 400 can then apply various rules to the normalized signal. These rules may include Fuzzy Rule-Based Diagnostics 456 and/or Rule-Based Diagnostics 458. The ICI device 400 presents an output of the results via the output interface 470. In some embodiments, the output interface 470 only provides an output when the ICI device 400 has determined that a fault condition exists (such as when the normalized signal differs from the baseline signals 430 by one or more threshold values). In these embodiments, the output interface 470 can provide the output by flagging, illuminating, or otherwise displaying the indicator associated with the failure (e.g., via the impeller wear indicator 472, the impeller crack indicator 474, the cavitations indicator 476, or the impeller health indicator 478). FIG. 5 illustrates a more detailed view of an example ICI first stage operation 500 for monitoring the health of an impeller according to this disclosure. The embodiment of the ICI first stage operation 500 shown in FIG. 5 is for illustration only. Other embodiments of the ICI first stage operation 500 could be used without departing from the scope of this disclosure. During a configuration stage, the operator enters data related to an impeller to be monitored, such as the filter specification 406, signal details (e.g., additional user inputs 412), the DAQ specification 408, the sensor specification 410, and the impeller specification (e.g., machine configuration 404). In this example, the operator can enter a type of impeller 502, a number of stages 504, a number of vanes 505 for each stage, a high-pass filter frequency FH 506, a maximum sampling frequency fdaq 507 and a maximum number of samples Ndaq 508 for data acquisition, a maximum sampling frequency fdaq 510 for each sensor, and a sampling frequency fs 511 and a number of samples Ns 512. The ICI device 400 also determines a Family of Frequencies (FoF) 520 for the impeller (or for each stage of the impeller if multiple stages are monitored). For example, the AI portion 440 can determine the vane pass frequency fvane 324 and at least three harmonics for each vane pass frequency fvane 324. The AI portion 440 can also determine the shaft frequency fr 322 and shaft sidebands fvane−fr 326 and fvane+fr 328 around the vane pass frequency fvane 324. It will be understood that although three harmonics for each vane pass frequency fvane 324 are illustrated, embodiments with other than three harmonics could be used. In addition, the AI portion 440 can determine a natural frequency for the impeller. The AI portion 440 also determines if the operator has entered appropriate values for FH 506, fs 511, and Ns 512. For example, the AI portion 440 compares fs 511 to FH 506 during a comparison 530. If fs 511 is less than twice FH 506 (fs<2FH), the AI portion 440 triggers an increase fs 511 indicator 532 in the output interface 470 of the ICI device 400. The increase fs indicator 532 provides a visual or audible cue to the operator that the value entered for fs 511 is too low and should be increased. If the AI portion 440 determines that a sufficient fs 511 has been entered (e.g., fs 511 is not less than twice FH 506 such that fs≧2 FH), the AI portion 440 compares fs 511 to fdaq 507 during a comparison 536. If fs 511 is greater than to fdaq 507 (fs>fdaq), the AI portion 440 triggers a decrease fs indicator 534 in the output interface 470. The decrease fs indicator 534 provides a visual or audible cue to the operator that the value entered for fs 511 is too high and should be decreased. The AI portion 440 also compares Ns 512 against Ndaq 508 during a comparison 540. If Ns 512 is greater than Ndaq 508 (Ns>Ndaq), the AI portion 440 triggers an decrease Ns indicator 542 in the output interface 470. The decrease Ns indicator 542 provides a visual or audible cue to the operator that the value entered for Ns 512 is too high and should be increased. If Ns 512 is less than or equal to Ndaq 508 (Ns≦Ndaq), the AI portion 440 either disables the decrease Ns indicator 542 (if the decrease Ns indicator 542 is enabled) or does nothing (if the decrease Ns indicator 542 is not enabled). FIG. 6 illustrates a more detailed view of an example ICI second stage operation 600 for monitoring the health of an impeller according to this disclosure. The embodiment of the ICI second stage operation 600 shown in FIG. 6 is for illustration only. Other embodiments of the ICI second stage operation 600 could be used without departing from the scope of this disclosure. After the AI portion 440 has computed the Family of Frequencies 520 for the sensor input signals, the AI portion 440 processes the FoF 520 through the low-pass filter 442 and applies the FFT analysis 446. The low-pass filter 442 can be a Butterworth filter, a wavelet-based filter, or any other low pass filter. The FoF 520 is passed through the FFBS 448, which, in this example, includes a number of band-pass filters paths 605a-605c. A 2 Hz band (e.g., from f+1 Hz to f−1 Hz) 605a is applied to the signals from the FFT analysis 446 whose value is less than 1000 Hz (f<1000 Hz). A 3 Hz band (e.g., from f+1.5 Hz to f−1.5 Hz) 605b is applied to the signals from the FFT analysis 446 whose value is less than 2000 Hz but greater than or equal to 1000 Hz (1000 Hz≦f<2000 Hz). A 4 Hz band (e.g., from f+2 Hz to f−2 Hz) 605c is applied to the signals from the FFT analysis 446 whose value is greater than or equal to 2000 Hz (f≧2000 Hz). The AI portion 440 computes the minimum and maximum amplitudes for each band 605a-605c. The AI portion 440 then combines each of the maximums from the bands 605a-605c to generate a matrix of maximum amplitudes and frequencies 610. The AI portion 440 also combines each of the minimums from the bands 605a-605c to generate a matrix of minimum amplitudes and frequencies 615. The AI portion 440 creates a union 620 of all frequencies in the FoF 520 to identify the impeller component frequencies. The AI portion 440 applies statistical features 452 to the union 620 and the matrix of min amplitudes and frequencies 615. The statistical features 452 can include determining the RMS or norm of each FoF 520. Thereafter, the AI portion 440 performs signal reconstruction 450 for the impeller component and noise frequencies to generate reconstructed signals for the impeller. In this example, the reconstructed signals represent an acceleration. In particular, the AI portion 440 can reconstruct a signal for the vane and harmonics, a signal for the shaft and shaft sideband frequencies, and a signal for noise frequencies. Each of the reconstructed signals is passed through an RMS level detector 630, a normalized RMS level detector 635, and one of three fuzzy membership functions 640. The outputs of the fuzzy membership functions 640 are passed through fuzzy rules 645 to produce a fuzzy rule signal. The AI portion 440 compares the fuzzy rule signal to a number of indexes within an RMS or norm baseline signal 650 to produce one or more impeller or pump conditions 655. Note that the fuzzy membership functions 640 and fuzzy rules 645 could be replaced by other logic, such as when the rule-based diagnostics 458 are used. The impeller or pump conditions 655 provide an indication that reflects the health of an impeller or pump based on, in this example, a sensed vibration. The ICI device 400 can output an impeller or pump condition that identifies impeller wear, impeller crack, and/or cavitations using the output interface 470. In some embodiments, the ICI device 400 includes a number of threshold values stored in a memory, and the ICI device 400 can compare the identified conditions 655 to the threshold values stored in memory to determine whether to initiate an alarm or other action. The memory can be any computer readable medium, such as any electronic, magnetic, electromagnetic, optical, electro-optical, electromechanical, and/or other memory device that can contain, store, communicate, propagate, or transmit data. In particular embodiments, the threshold values could include a warning threshold and an alarm threshold for each condition 655 calculated by the ICI device 400. The warning threshold could trigger a warning that an impeller condition 655 is high, while an alarm threshold could trigger an alarm that a fault has been detected in an impeller. FIG. 7 illustrates an example process 700 for monitoring an impeller according to this disclosure. The embodiment of the process 700 shown in FIG. 7 is for illustration only. Other embodiments of the process 700 could be used without departing from the scope of this disclosure. Also, for ease of explanation, the process 700 is described with respect to the ICI device 400, although the process 700 could be used with any suitable device or system. In this example, the ICI device 400 uses vibration and speed signals, as processed and compared to the thresholds, to alert an operator to possible damage in an impeller. The vibration and speed signals are received by the ICI device 400 at step 705. The ICI device 400 stores the vibration and speed signals obtained during normal operation of the impeller as baseline signals at step 710. The ICI device 400 determines the relevant family of frequencies for the impeller at step 715. This may include, for example, determining the FoF 520 for each of the failure modes of the impeller. The FoF 520 can include a vane pass frequency and its harmonics, a shaft rotating frequency, sidebands of the shaft rotating frequencies around the vane pass frequency and its harmonics, and background noise. The ICI device 400 can measure the vibration signals and estimate the frequencies of the vibration signals using any available technique, such as FFT analysis. The ICI device 400 continues to receive vibration and speed signals and performs signal processing at step 720. This may include, for example, decomposing the vibration and speed signals. The signal processing may also include a low-pass filter operation and an FFT analysis. In some embodiments, deconstruction (e.g., decomposition) is accomplished using a Fourier series, a Laplace transform, or a Z-transform. The ICI device 400 performs frequency/frequency bandwidth selection using the processed signals at step 725. This may include, for example, isolating frequencies and obtaining minimum and maximum frequencies and amplitudes. The ICI device 400 reconstructs the signal at step 730, such as by reconstructing an overall signal and reconstructing signals for the vane pass frequencies and its harmonics, the shaft sidebands, and the background noise. The ICI device 400 identifies one or more features from the reconstructed signal in step 735. For example, the ICI device 400 can determine features such as RMS and Kurtosis values. The ICI device 400 also identifies corresponding features in the base line signal in step 740 and the current signal in step 745. The reconstructed signals are normalized with respect to the features of the baseline signals or other indices at step 750. For example, the reconstructed signals can be normalized by dividing the features from the current signal, found in step 745, by the features from the baseline, found in step 750. The normalizing helps to generalize the model with respect to the size of a mechanical system and application type. In the event a reconstructed signal exceeds one of the thresholds, the ICI device 400 outputs the appropriate indicator (e.g., the impeller wear indicator, impeller crack indicator, and/or cavitations indicator) in step 755. The ICI device 400 applies fuzzy-rule based diagnostics to determine if the reconstructed signal exceeds one of the thresholds. In some embodiments, the vibration and speed signals stored are for an impeller that currently is experiencing wear or currently includes a crack. In such embodiments, the ICI device 400 provides a warning or alarm based on a change in the signals resulting from additional wearing or further cracking of the impeller. FIGS. 8 and 9 illustrate example impeller health indicators 478 according to this disclosure. The embodiments of the impeller health indicators 478 shown in FIGS. 8 and 9 are for illustration only. Other embodiments of the impeller health indicator 478 could be used without departing from the scope of this disclosure. In these examples, the impeller health indicator 478 is constructed using a feature fusion of statistics on the basis of Fuzzy, Dempter-Shafer, or Bayesian theory. The health indicator 478 provides a severity index varying between a value of 0 and a value of 1. The impeller health indicator 478 includes a time 805 and two threshold values 810 and 815. Although the figures above have illustrated various embodiments, any number of modifications could be made to these figures. For example, any suitable types of impellers could be monitored, and any suitable types of faults could be detected. Also, various functions shown as being performed by the ICI device 400 could be combined, further subdivided, or omitted and additional functions could be added according to particular needs. In addition, while FIG. 7 illustrates a series of steps, various steps in FIG. 7 could overlap, occur in parallel, occur multiple times, or occur in a different order. In some embodiments, various functions described above are implemented or supported by a computer program that is formed from computer readable program code and that is embodied in a computer readable medium. The phrase “computer readable program code” includes any type of computer code, including source code, object code, and executable code. The phrase “computer readable medium” includes any type of medium capable of being accessed by a computer, such as read only memory (ROM), random access memory (RAM), a hard disk drive, a compact disc (CD), a digital video disc (DVD), or any other type of memory. It may be advantageous to set forth definitions of certain words and phrases used throughout this patent document. The term “couple” and its derivatives refer to any direct or indirect communication between two or more elements, whether or not those elements are in physical contact with one another. The terms “include” and “comprise,” as well as derivatives thereof, mean inclusion without limitation. The term “or” is inclusive, meaning and/or. The phrases “associated with” and “associated therewith,” as well as derivatives thereof, may mean to include, be included within, interconnect with, contain, be contained within, connect to or with, couple to or with, be communicable with, cooperate with, interleave, juxtapose, be proximate to, be bound to or with, have, have a property of, or the like. While this disclosure has described certain embodiments and generally associated methods, alterations and permutations of these embodiments and methods will be apparent to those skilled in the art. Accordingly, the above description of example embodiments does not define or constrain this disclosure. Other changes, substitutions, and alterations are also possible without departing from the spirit and scope of this disclosure, as defined by the following claims. |
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abstract | A plurality of signal anomalies are identified in a number of tubes in a steam generator. Since the geometry of the steam generator is known, the location of each signal anomaly along each tube is converted into a location within the interior of the steam generator. If a plurality of signal anomalies are at locations within the steam generator that are within a predetermined proximity of one another, such a spatial confluence of signal anomalies is determined to correspond with a loose part situated within the steam generator. Additional methodologies can be employed to confirm the existence of the loose part. Historic tube sheet transition signal data can be retrieved and subtracted from present signals in order to enable the system to ignore the relatively strong eddy current sensor signal of a tube sheet which would mask the relatively weak signal from a loose part at the tube sheet transition. |
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summary | ||
description | It is evident from FIG. 1 that two drive units 1, 2 are connected by a ceramic profile that is part of a linear guidance system 3. The ceramic profile of linear guidance system 3 carries a nonmagnetic retention system 4 for a substrate, in this case e.g. for a wafer. Retention system 4 is arranged displaceably on linear guidance system 3. Linear guidance system 3, inclusive of retention system 4, is to be displaced by means of the two drive units 1, 2 in a direction parallel to the substrate surface, and guided and driven in all directions in zero-backlash fashion with little elastic resilience, as will be shown below. What is achieved according to the present invention is that retention system 4, by way of the two drive units 1, 2 that are spaced apart from one another by the length of linear guidance system 3 and are also magnetically shielded separately from one another, can be positioned in all six spatial degrees of freedom with high precision and dynamics in the vacuum chamber of a device that serves for exposure of the wafer and/or for measurement on the wafer by means of radiation. In the installed state, drive units 1, 2 can of course assume any position in the chamber, although a horizontal orientation is preferred. The direction of motion of retaining system 4 is in that case oriented vertically, i.e. in the direction of gravity, along linear guidance system 3. The ceramic profile of linear guidance system 3 serves as a guide element and can simultaneously receive drive elements that are necessary for triggering the displacement motion of retention system 4 (not depicted in the drawing). FIG. 2 indicates that the two drive units 1, 2 are embodied as linear motors, the air gap between stator 5, 6 and rotor 7, 8 being modifiable in each case. Located on rotors 7, 8 are magnetic bridges having permanent magnets, to compensate for the weight of the guided unit. They are configured in such a way that the electromagnets integrated into rotors 7, 8 must generate comparatively small forces for positional stabilization, and thermal loads are thus reduced. The two drive units 1, 2 are magnetically guided in each of four degrees of freedom. In the remaining two degrees of freedom, guidance is accomplished by the linear motors, in which no mechanical contact points exist between stator 5, 6 and rotor 7, 8. The highly dynamic fine adjustment motion is implemented within the range of motion by controlling the air gap of the magnetic guides in degrees of freedom Y, Z, RX, and RY, and by positioning the linear motors in degrees of freedom X, RZ. Measurement of the position of rotors 7, 8 is accomplished by means of two plane mirror interferometers 9, 10 operating independently of one another. Capacitative sensors (not depicted in the drawing), which are used together with plane mirror interferometers 9, 10 to measure the position of retention system 4, are additionally provided. Also provided for each drive unit are magnetic shielding walls 11 to protect the particle beam region from interfering magnetic fields; these are each embodied in multiple layers, the slots necessary for motion transfer being offset laterally from one another in the individual layers, thus creating a meander-shaped magnetic seal which makes possible a rigid connection between rotors 7, 8 and the zero-magnetic-field retention system 4. For the sake of clarity, in FIG. 2 magnetic shielding walls 11 are shown only on drive unit 2. In order to eliminate disruptive thermal expansion of the subassemblies of drive units 1, 2, and in particular also of the subassemblies of retention system 4, the frame-mounted coils of the linear motors, with their mount, are water-cooled. This mount and also the surfaces of rotors 7, 8 are moreover equipped with a suitable surface coating so that effective radiative cooling is implemented in order to dissipate the heat of the magnetic bearings (not depicted in the drawing). The linear motors and magnetic bearings are advantageously arranged outside the particle beam region, i.e. outside the region in which the radiation used for exposure and/or measurement travels, and are not mounted directly on retention system 4 for the substrate. They are arranged around this particle beam region, a symmetrical arrangement being preferred. It is also evident from FIG. 2 that retention system 4 is equipped with a wafer chuck 12 for receiving the wafer with the wafer surface oriented vertically. A stepping motor drive 13 allows (coarse) positioning over an adjustment range of approximately 320 mm in the vertical Y axis. Wafer chuck 12, on which the wafer is retained electrostatically, is fabricated with high precision from temperature-stable Zerodur. Machined laterally onto wafer chuck 12 are mirror surfaces that are used for ascertaining and monitoring the chuck position with a six-beam laser interferometer arrangement 14 (resolution: 0.6 nm) in all spatial degrees of freedom except the Z coordinate. The position of the wafer with respect to the Z coordinate is ascertained directly on the wafer surface with the aid of three highly accurate capacitative sensors (not depicted). The measured signals thereby obtained are also referred to hereinafter as xe2x80x9cglobalxe2x80x9d signals, since they represent the immediate position of the wafer to be exposed. Wafer chuck 12 is coupled in stress-free fashion onto a frame made of titanium profiles which is guided vertically with the aid of lubrication-free ceramic ball bearings along the ceramic profile of linear guidance system 3. The vertical motion for retention system 4 with wafer chuck 12 is coupled in, as already explained, via a Bowden cable driven by a fast stepping motor 13. With the aid of piezoactuators (not depicted), the frame can be clamped in any desired vertical Y coordinate in a range of xc2x1160 mm with an accuracy of approx. xc2x110 xcexcm. This yields repeatabilities in the range of a few xcexcm/xcexcrad in all other coordinates. Once the desired vertical position of the wafer is reached, the wire of the Bowden cable is detensioned to minimize its influence on drive units 1, 2. The electrodynamic direct drives or linear motors provided in drive units 1, 2 are magnetically guided and triply shielded (shielding walls 11). They make possible a highly accurate horizontal X motion of xc2x1160 mm, which is measured with the aid of the two plane mirror interferometers 9, 10, with a resolution of 5 nm, on the upper and lower linear motors. A controlled asynchronous movement of the two linear motors results in the RZ rotation. Each drive unit 1, 2 is equipped with a total of five electromagnetic actuators 1.1, 1.2, 1.3, 1.4, 1.5 and 2.1, 2.2, 2.3, 2.4, 2.5, of which four in each case (actuators 1.1, 1.2, 1.3, 1.4 and 2.1, 2.2, 2.3, 2.4) serve to implement adjustment motions in the Z direction, and one in each case (actuators 1.5 and 2.5) to implement adjustment motions in the Y direction. FIG. 3 depicts the arrangement of actuators 1.1, 1.2, 1.3, 1.4, and 1.5 in drive unit 1. Each of these actuators 1.1, 1.2, 1.3, 1.4, 1.5 and 2.1, 2.2, 2.3, 2.4, 2.5 possesses its own xe2x80x9clocalxe2x80x9d capacitative measurement system for highly accurate measurement of the air gap between stator and rotor, or between the working surface of the actuator and the guide surface on the stator, in a range of xc2x10.5 mm at a resolution of 20 nm. Motion in coordinates Y, Z, RY, and RX is made possible by influencing the width of the air gap in controlled fashion. Actuators 1.5 and 2.5 are in this case of hybrid design, i.e. they possess built-in permanent magnets that compensate without power dissipation for the predominant portion of the weight (approx. 50 kg) of the mass to be moved. If, in other embodiments of the invention, the Z coordinate rather than the Y coordinate should point in the direction of gravity, actuators 1.1, 1.2, 1.3, 1.4 and 2.1, 2.2, 2.3, 2.4 are designed accordingly. Taking into consideration the geometric data of the arrangement as indicated in FIG. 3 and the resolution of the measurement systems of the individual xe2x80x9clocalxe2x80x9d actuators 1.1, 1.2, 1.3, 1.4, 1.5 and 2.1, 2.2, 2.3, 2.4, 2.5, the following (theoretical) displacement ranges and positional resolutions are obtained in the individual coordinates: Xxc2x1160 mm (5 mn); Yxc2x1160 mm as total displacement range and xc2x10.5 mm as parallel shift (20 nm); Zxc2x10.5 mm (5 nm); RXxc2x10.4 mrad (16 nrad); RYxc2x14 mrad (160 nrad); RZxc2x15 mrad (6 nrad). The manner in which the adjustment motions are achieved in the degrees of freedom X, Y, Z, RX, RY, and RZ will be explained once again with reference to FIG. 4. The symbolically depicted linear guidance system 3; drive unit 1 having stator 5, rotor 7, and actuators 1.1, 1.2, 1.3, 1.4, 1.5; and drive unit 2 having stator 6, rotor 8, and actuators 2.1, 2.2, 2.3, 2.4, 2.5, are evident. Actuators 1.1, 1.2, 1.3, 1.4 are provided to modify the width measured in direction Z of the air gap between stator 5 and rotor 7 on drive unit 1, and actuators 2.1, 2.2, 2.3, 2.4 to modify the width measured in direction Z of the air gap between stator 6 and rotor 8 on drive unit 2. Actuator 1.5 on drive unit 1 and actuator 2.5 on drive unit 2 serve to modify the width of the air gap measured in direction Y. The adjustment motions are implemented as follows: Parallel displacement in coordinate X in one or the other direction by synchronous activation of the linear motors (rotor 7 in drive unit 1 and rotor 8 in drive unit 2); Parallel displacement in coordinate Y in one or the other direction by synchronous activation of actuators 1.5 and 2.5; Parallel displacement in coordinate Z in one or the other direction by synchronous activation of actuator pairs 1.1/1.2 and 1.3/1.4 and actuator pairs 2.1/2.2 and 2.3/2.4; Rotation RX about coordinate X by activation of actuator pairs 1.1/1.2 and 1.3/1.4 asynchronously with activation of actuator pairs 2.1/2.2 and 2.3/2.4 (and thus modification in opposite directions of the air gaps on the linear motors); Rotation RY about coordinate Y by activation of actuator pairs 1.1/1.2 and 2.1/2.2 asynchronously with activation of actuator pairs 1.3/1.4 and 2.3/2.4 (and thus modification in opposite directions of the air gaps within the two linear motors); Rotation RZ about coordinate Z by activation of the linear motor in drive units 1 asynchronously with activation of the linear motor in drive units 2. The arrangement selected has the following advantages: A self-contained unit can be moved with high precision in all six spatial degrees of freedom. It is magnetically guided and xe2x80x9cfloatsxe2x80x9d in three dimensions in almost noncontact fashion (aside from electrical supply lines and the influence of the Bowden cable), i.e. is largely free of friction and wear. The drives, representing potential interference field sources, are comparatively far away (more than half a meter) from the exposure location. The field proceeding from the drives can be further drastically reduced by suitable (in the present case, triple) shielding. A further region around the ion beam used for exposure is iron-free, thereby minimizing distortion of the exposure. As a result of the permanent-magnet-based weight compensation in the magnetic guidance system, the electromagnetic actuators of the guidance system can be operated with almost zero static current, resulting in low power conversion and thus little heating of the drives in vacuum. The coils in the direct drives for rapid and accurate horizontal positioning are statically mounted and therefore easy to cool. Large working air gaps in the magnetic guidance system are needed in order to ensure a sufficient movement range in the rotation axes, in particular RX. This results in lower resolution for the rotation axes with a smaller base spacing, in this case RY. Advantageously, drive units 1, 2 are each located in a housing made of steel. This steel housing is at the same time the first layer of the magnetic shielding; two further layers of mu metal are applied once drive units 1, 2 are completely installed and aligned. Each shield is equipped with a labyrinth seal for the magnetic interference field proceeding from drive units 1, 2 through which motion passes outward. Experiments in a shielding chamber have shown that with the three-layer shielding, it is possible to reduce the magnetic field proceeding from a drive to 10 nT (static) and 5 pT (dynamic) at the exposure location. The problem of outgassing and heating of the drive elements was also investigated. Aluminum foil equipped on all sides with an oxide coating is used as the coil material. The coil cores, also equipped with an oxide coating, largely prevent the formation of eddy currents and thus result in less heating and a short time constant for the coils. The heat created in the coils of the electrodynamic direct drives is dissipated at the ends of the coil cores through copper blocks having channels for a cooling fluid. These additionally impart a stable T-shape to the stator of the direct drive. A different approach was used for the electromagnets and their coils that are present in the actuators of the direct drives. To minimize the number of supply lines to the moving part, cooling lines were dispensed with here. The electromagnets were instead optimized for a low current/force ratio and a high force/mass ratio. As a result, the electromagnets of the Z guidance system achieve, at a force of 100 N and a 1-mm air gap, a power dissipation of only 3 W at a weight of 0.6 kg each, while the figures for the Y electromagnetsxe2x80x94more heavily loaded because their weight compensation is not quite completexe2x80x94are 1.4 kg and 1.3 W at 100 N and a 1-mm air gap. The aforesaid forces are needed, however, only with strong accelerations and usually at smaller air gaps (approx. 0.5 mm). Since the electromagnets are operated with almost zero static current (aside from small forces that must always be applied to compensate for torques and residual weight), the average power consumption is considerably lower, being in total approximately 0.5 W in the entire magnetic guidance system of a direct drive. The overtemperature in the immediate vicinity of the electromagnet coils that can be estimated therefrom is 3 K, decreasing to less than 1 K in the immediate vicinity of the coils. Since both the actuator and the stator in the direct drive are equipped with a black aluminum oxide coating, the power consumed in the guidance systems is at least partially emitted as thermal radiation to the cooled stator. In summary, this example of a positioning system describes a magnetically guided, electromagnetically driven, high-precision vertical wafer stage that emits very low magnetic interference fields and is suitable for use in high vacuum. With this stage, despite a difficult system environment, positioning smoothness and accuracy values in the sub-micrometer or -xcexcrad range, and moreover particularly good synchronization of the wafer stage, are achieved. |
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claims | 1. An x-ray chopper wheel assembly comprising:a disk chopper wheel configured to rotate about a rotation axis thereof, the rotation axis perpendicular to a rotation plane of the disk chopper wheel, the disk chopper wheel having a solid cross-sectional area in the rotation plane, the disk chopper wheel configured to absorb x-ray radiation received from an x-ray source at a source side of the disk chopper wheel, the disk chopper wheel defining one or more radial slit openings configured to pass x-ray radiation from the source side of the disk chopper wheel to an output side of the disk chopper wheel;a source-side scatter plate having a solid cross-sectional area in a plane substantially parallel to the rotation plane of the disk chopper wheel, the source-side scatter plate configured to absorb x-ray radiation and defining an open slot therein configured to pass x-ray radiation, wherein the solid cross-sectional area of the source-side scatter plate is substantially smaller than the solid cross-sectional area of the disk chopper wheel; anda support structure configured to secure the source-side scatter plate in the plane substantially parallel to the rotation plane of the disk chopper wheel with a source-side gap between the source-side scatter plate and the source side of the disk chopper wheel wherein the disk chopper wheel and source-side scatter plate are arranged relative to each other to cause a substantial confinement of x-rays that are scattered from the disk chopper wheel. 2. The assembly of claim 1, wherein the solid cross-sectional area of the source-side scatter plate in the plane parallel to the rotation plane of the disk chopper wheel is less than 50%, less than 25%, or less than 10% of the cross-sectional area of the disk chopper wheel. 3. The assembly of claim 1, wherein the source-side gap is in a range of approximately 0.5 mm to approximately 1.0 mm. 4. The assembly of claim 1, wherein the source-side scatter plate comprises tungsten or another high-Z material and has a thickness on the order of 1.0 mm. 5. The assembly of claim 1, wherein the cross-sectional area of the source-side scatter plate is in a range of about 100% to about 5,000% larger than an open cross-sectional area of one of the one or more radial slit openings in the rotation plane of the disk chopper wheel. 6. The assembly of claim 1, wherein the source-side scatter plate has a plate width in a direction parallel to a radial direction of the disk chopper wheel, the plate width being in a range of about 10% to about 70% greater than a slit length of one of the one or more radial slit openings in the radial direction of the disk chopper wheel. 7. The assembly of claim 1, wherein the source-side scatter plate is formed of pure or alloyed lead, tin, iron, or tungsten. 8. The assembly of claim 1, further comprising an output-side scatter plate having a solid cross-sectional area in a plane parallel to the rotation plane of the disk chopper wheel, the output-side scatter plate configured to absorb x-ray radiation and defining an open slot therein configured to pass x-ray radiation, wherein the solid cross-sectional area of the output-side scatter plate in the plane parallel to the rotation plane of the disk chopper wheel is substantially smaller than the solid cross-sectional area of the disk. 9. The assembly of claim 8, wherein the support structure is further configured to secure the output-side scatter plate substantially parallel to the rotation plane of the disk chopper wheel with an output-side gap between the output-side scatter plate and the disk chopper wheel. 10. The assembly of claim 1, wherein the support structure is further configured to secure the disk chopper wheel at the rotation axis thereof. 11. The assembly of claim 1, wherein the support structure includes an inner portion configured to secure the disk chopper wheel at the rotation axis thereof, the support structure further including one or more radial spokes extending from the inner portion and configured to secure the source-side scatter plate. 12. The assembly of claim 1, wherein the support structure includes a source-side portion and an output-side portion, the source-side and output-side portions configured to be connected together and to secure the disk chopper wheel therebetween. 13. The assembly of claim 1, wherein the support structure is formed of aluminum. 14. The assembly of claim 1, wherein the support structure is configured to be mounted within a handheld x-ray scanner. 15. The assembly of claim 1, wherein the support structure is configured to be mounted within a fixed-mount or mobile x-ray scanning system. 16. The assembly of claim 1, further comprising a shield structure configured to enclose the x-ray radiation in a region of travel between the x-ray source and the source-side scatter plate. 17. The assembly of claim 1, wherein the x-ray source is configured to output x-rays having an energy in a range of about 120 kiloelectron volts (keV) to about 450 keV. 18. The assembly of claim 1, wherein the source-side scatter plate is configured to output a fan beam of x-rays through the open slot therein, and wherein the assembly is configured to output a pencil beam of x-rays. 19. The assembly of claim 1, wherein the substantial confinement limits leakage of scattered radiation to no more than 10% of scattered radiation or to a dose of no more than 0.5 milli-Rem per hour at a distance of 5 cm away from the outer surface of the assembly, whichever is greater. 20. An x-ray chopper wheel assembly comprising:a disk chopper wheel configured to absorb x-ray radiation received, at a source side of the disk chopper wheel, from an x-ray source; anda source-side scatter plate arranged relative to the disk chopper wheel to cause a substantial confinement of x-rays that are scattered from the disk chopper wheel. 21. The assembly of claim 20, wherein the substantial confinement further limits leakage of scattered radiation to no more than 10% of scattered radiation or to a dose of no more than 0.5 milli-Rem per hour at a distance of 5 cm away from the outer surface of the assembly, whichever is greater. 22. The assembly of claim 20, wherein:the disk chopper wheel is configured to rotate about a rotation axis thereof, the rotation axis perpendicular to a rotation plane of the disk chopper wheel, the disk chopper wheel having a solid cross-sectional area in the rotation plane;the source-side scatter plate has a solid cross-sectional area in a plane substantially parallel to the rotation plane of the disk chopper wheel; andthe solid cross-sectional area of the source-side scatter plate is less than 50% of the cross-sectional area of the disk chopper wheel. 23. The assembly of claim 22, wherein the solid cross-sectional area of the source- side scatter plate is less than 25% of the cross-sectional area of the disk chopper wheel. 24. The assembly of claim 23, wherein the solid cross-sectional area of the source- side scatter plate is less than 10% of the cross-sectional area of the disk chopper wheel. 25. The assembly of claim 20, wherein the source-side scatter plate is secured in the plane substantially parallel to the rotation plane of the disk chopper wheel with a source- side gap between the source-side scatter plate and the source side of the disk chopper wheel, the source-side gap being in a range of approximately 0.5 mm to approximately 1.0 mm. 26. The assembly of claim 20, wherein the source-side scatter plate comprises tungsten or another high-Z material and has a thickness on the order of 1.0 mm. 27. The assembly of claim 20, the disk chopper wheel defining one or more radial slit openings configured to pass x-ray radiation from the source side of the disk chopper wheel to an output side of the disk chopper wheel, and wherein the cross-sectional area of the source-side scatter plate is in a range of about 100% to about 5,000% larger than an open cross-sectional area of one of the one or more radial slit openings in the rotation plane of the disk chopper wheel. 28. The assembly of claim 20, the disk chopper wheel defining one or more radial slit openings configured to pass x-ray radiation from the source side of the disk chopper wheel to an output side of the disk chopper wheel, and wherein the source-side scatter plate has a plate width in a direction parallel to a radial direction of the disk chopper wheel, the plate width being in a range of about 10% to about 70% greater than a slit length of one of the one or more radial slit openings in the radial direction of the disk chopper wheel. 29. The assembly of claim 20, wherein the source-side scatter plate is formed of pure or alloyed lead, tin, iron, or tungsten. 30. The assembly of claim 20, wherein:the disk chopper wheel is configured to rotate about a rotation axis thereof, the rotation axis perpendicular to a rotation plane of the disk chopper wheel, the disk chopper wheel having a solid cross-sectional area in the rotation plane,the assembly further comprising an output-side scatter plate having a solid cross-sectional area in a plane parallel to the rotation plane of the disk chopper wheel, the output-side scatter plate configured to absorb x-ray radiation and defining an open slot therein configured to pass x-ray radiation, wherein the solid cross-sectional area of the output-side scatter plate in the plane parallel to the rotation plane of the disk chopper wheel is substantially smaller than the solid cross-sectional area of the disk. 31. The assembly of claim 20, further comprising a support structure including an inner portion configured to secure the disk chopper wheel at a rotation axis thereof, the support structure further including one or more radial spokes extending from the inner portion and configured to secure the source-side scatter plate. 32. The assembly of claim 20, further comprising a support structure including a source-side portion and an output-side portion, the source-side and output-side portions configured to be connected together and to secure the disk chopper wheel therebetween. 33. The assembly of claim 20, further comprising a support structure configured to secure the source-side scatter plate in a plane substantially parallel to a rotation plane of the disk chopper wheel, and wherein the support structure is configured to be mounted within a handheld x-ray scanner. 34. The assembly of claim 20, further comprising a support structure configured to secure the source-side scatter plate in a plane substantially parallel to a rotation plane of the disk chopper wheel, and wherein the support structure is configured to be mounted within a fixed-mount or mobile x-ray scanning system. 35. The assembly of claim 20, further comprising a shield structure configured to enclose the x-ray radiation in a region of travel between the x-ray source and the source-side scatter plate. 36. The assembly of claim 20, wherein the x-ray source is configured to output x-rays having an energy in a range of about 120 kiloelectron volts (keV) to about 450 keV. 37. The assembly of claim 20, wherein the source-side scatter plate is configured to output a fan beam of x-rays through an open slot defined therein, and wherein the assembly is configured to output a pencil beam of x-rays. |
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040244059 | description | DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, there is shown an X-ray eye shield 10 in place on the head of a patient. As can be seen, the eye shield 10 with frame 12 closely fits the contours of the head and radiopaque lens cups 14a and 14b fit comfortably against the eye socket. The lens cups 14a and 14b shield the opening of the eye socket from all angles. FIGS. 2-4 show eye shield 10 in more detail. Thus, it is seen to have a frame 12 with a bridge portion 16 and temple pieces 18 and 20. These three parts are attached at hinges 22a and 22b. The hinges 22a and 22b may be spring-loaded so that the temple pieces 18 and 20 are biased against the temples as shown by directional arrows 24 and 26. Other arrangements to obtain a close fit may also be used. Frame 12 is made of a radiolucent plastic material of any type commonly used in spectacle frames. However hinges 22a and 22b are metal and would distort a radiopgraph taken in the area over which the hinges are positioned. Therefore, it is desirable to have hinges 22a and 22b coextensive with lens cups 14a and 14b so that only the sensitive eye area is blocked from X-ray radiation. Likewise, no metal reinforcement as commonly found in spectacle frames in used. Lens cups 14a ad 14b are made of a material which will prevent passage of X-ray radiation. Typical of such materials is lead film encased in a plastic material, for example, a 0.030 - 0.040 inch or more thickness lead film. Other materials which prevent the passage of X-ray radiation could also be used. The structure of the preferred laminated lens cup is best shown in FIG. 5. There lead film 28 is surrounded by plastic 30, which may be ABS, acrylic, vinyl, polyamide or other know rigid plastics. For support a thin metal wire or rod 32 is located around the periphery of the lens cups, althoug this is not necessary if the plastic material is strong enough to have the hinges embedded therein without the need for further support. Similarly, an exterior frame could be used rather than a embedded wire. In any event, lens cup 14a and 14b are attached via the plastic (reinforced or not), or lens cup frame etc., to frame 12. Thus, referring again to FIG. 2, there is shown hinges 34a to 34b by which lens cups 14a ad 14b are attached to the frame 12. Preferably, these hinges are passive so that the dentist, hygienist, or dental assistant can position the lens cups 14a and 14b snugly against the eye socket as desired. That is, for effective protection of the eye tissue against X-ray radiation a fairly snug fit is required. This is made possible by adjustment or movement of the individual lens cups as shown by directional arrows 36 and 38. It should be noted, as memtioned previously, that bridge portion 16, having nose pads 40, is located lower than normally found in ordinary spectacles. This is best seen in FIGS. 1 and 3-4. The reason for this is that certain X-ray machines used by dentits i.e., panograph and cephalometric, have a guide portion that rests on the bridge of the nose to stabilize the patient's head during radiography. In order to accomodate use of this type of X-ray machine, the bridge porton 16 is located as shown in the figures. As is apparent, these features make eye sield 10 ideally suited for use during preparation of dental radiographs. However, eye shield 10 could also be used at any other time it is desired to protect sensitive eye tissue from X-ray or other types of radiation. While the article herein described constitutes a preferred embodiment of the invention, it is to be understood that the invention is not limited to this precise article, and that changes may be made therein without departing from the scope of the invention. |
041742575 | abstract | A fuel assembly for a nuclear reactor has a pressure plate attached to the lower end thereof. The upper side of the pressure plate is exposed to the ambient pressure of the reactor coolant. The lower side of the pressure plate is exposed to a pressure from another location in the reactor, selected so that the pressure above the pressure plate is greater than that below the pressure plate. |
053655540 | description | The probe comprises a cage-like inner support structure 10 which houses and supports the instrumentation of the probe. The support structure 10 is attached to a pair of inner perforate end plates 11, 12 with an array of dummy fuel pencil stubs 13 which are attached to actual fuel bundle end plates 14, 15. The outer periphery of the probe consists of an array of active fuel pencils 16 extending longitudinally between the end plates 14, 15 and connected thereto at their ends. Thus the probe can be configured to simulate a fuel bundle of the reactor in which it is to be used. The instrumentation includes sensors each of which is responsive to a physical parameter to be measured. In the illustrated device there is a mechanical pressure sensor 17 responsive to fluid pressure and an end plate displacement sensor 18, the latter being in the form of a rod which is connected to the end plate 15 and extends longitudinally therefrom. The instrumentation may include other sensors (not shown), each being responsive to a respective physical parameter to be recorded. Each sensor carries a scribe 19, 20, or equivalent writing device which cooperates with a recording device for recording the measurements of the parameters over time. In the illustrated embodiment of the invention the recording device is a rotary drum 21, but it may take any other suitable form such as a rotary disc or a travelling tape. The drum 21 is driven at a constant speed to provide a time base. As shown, the device for rotating the drum 21 comprises a rotary shaft 22 carrying an impeller 23 which is responsive to the fluid flow along the fuel channel so as to rotate the shaft 22. The shaft 22 serves as the input shaft of a speed reducing mechanism 24, the latter having an output shaft 25 on which the rotary drum 21 is mounted. Since the fluid flow in the reactor fuel channel is normally held constant, the drum 21 is rotated at a constant speed. In certain applications, however, where the fluid flow may not be constant, the speed of the drum can be kept constant simply by governing the speed of the impeller to the speed corresponding to the lowest flow rate expected. In order to clarify the structure of the probe and to show essential components, certain elements have been omitted from the drawing. In particular, a part of the inner and outer rings of fuel pencils has been omitted to reveal the instrumentation. The sensors, scribes, recording drum and gear reducing mechanism are conventional, and are supported within the cage-like support structure. The drum 21 and the speed reducing mechanism 24, which may be a gear reduction train, are arranged coaxially within the cage, one end of the rotary shaft 22 being journalled in a bearing mounted centrally on the end plate 11. |
summary | ||
059096543 | abstract | A method and apparatus for the volume reduction and processing of solid organic waste, in particular ion exchange media from nuclear facilities containing sulfur or chlorine. A method and apparatus for the volume reduction of nuclear waste is disclosed comprising: subjecting the waste to pyrolysis in a pyrolysis vessel, and gasifying the solid pyrolysis residue in a steam reformer to remove residual carbon. A further method and apparatus for the processing of nuclear waste is disclosed comprising: grinding the nuclear waste, addition of iron powder, pyrolysis, gasification of the pyrolysis residue, and combustion in a submerged bed heater. An evaporator cools gases from the submerged bed heater. Off gases from the evaporator are treated by a fiber bed scrubber to remove acids. |
description | The current application claims priority to and incorporates by reference in its entirety U.S. Provisional Patent Application No. 60/602,041, entitled METHODS FOR ANALYZING TARGET EMISSIONS, filed Aug. 17, 2004. This application also incorporates by reference in its entirety U.S. patent application Ser. No. 11/033,552, entitled, SYSTEM AND METHOD FOR MEASURING AND ANALYSING TARGET EMISSIONS, filed Jan. 12, 2005. 1. Field of the Invention The invention relates generally to the field of target inspection to determine the contents thereof through radiation detection. The invention relates more specifically to the use of inspection systems and methods. 2. Description of the Related Art Preventing the trafficking of illegal and dangerous substances, as well as the security of various localities, rests in the ability to assess the contents of a suspected target, such as a vehicle or cargo. These targets may contain a variety of materials, including explosives, chemical agents, or illicit drugs. Successful safety and homeland security requires confronting the trafficking of these targets, which may also include weapons of mass destruction and the fundamental building blocks thereof, i.e., fissionable materials, that are increasingly being trafficked. Inspection stations are established to reduce the flow or entry of illicit contraband. The role of the current inspection systems at the inspection stations is now being amplified to look not only for illicit drugs, but also for explosives and weapons of mass destruction. Currently, these inspection systems are “anomaly” detectors. When an anomaly is detected, it can only be identified through an intrusive manual inspection, which is inherently limited by the ability, condition, and initiative of inspection personnel. Other conventional methods for assessment of whether a vehicle, container, or other target contains dangerous or illicit materials may be limited to external markings and visual examination by trained experts. Often, the target is weathered or corroded and the markings and external visual cues are deteriorated or absent. Alternatively, the target may conceal the dangerous material. If a conservative approach is used and all questionable targets are treated as explosive or chemical filled, the cost of clearance operations is greatly increased. If a less conservative approach is used, accidents can occur that lead to injury or loss of life. The time to visually inspect and assess a target is an inefficient process. This costly and time consuming operation exposes inspection personnel to serious risks and has resulted in increasing delays. Often, the system lacks the specificity to clearly identify the nature of an anomaly, thereby necessitating additional resources and/or the destruction of unverifiable suspect items. There is currently a need for the ability to inspect targets, e.g., vehicles and cargo, to determine whether the target contains dangerous or illicit materials in order to prevent the movement or entry of the illegal contraband. There is a need for a more efficient inspection system to rapidly assess a target and make a determination of the contents of the target. Additionally, a system is desired that is more accurate, providing fewer false alarms and relying less on human interaction. A means of rapidly and correctly determining the contents of a target is needed to allow rapid disposition and proper handling of explosive or chemical material. Additionally, a method and system is needed for non-intrusively identifying targets in-situ for more cost-effective and safer environmental remediation. It is also desired to have a system and method to provide the nation's domestic security forces with an optionally portable system to identify threat material. The focus is typically on explosives, with additional capabilities of identifying chemicals, radiological isotopes, and drugs. For example, a desired system and method can recognize and identify explosives hidden in common packages such as boxes and briefcases, identify contents of improvised explosive devices (“IEDs”) such as pipe bombs, detect caches of explosives in car trunks or van interiors, and detect hidden illicit drugs. The system and method can also identify concealed targets, such as a detection of mines in the ground. The solution system and method described herein are based on neutron interrogation used to inspect targets, e.g., vehicles and cargo, for prohibited materials including, inter alia, explosives, chemical warfare agents, illicit drugs, and other hazardous materials. In a first embodiment of the present invention, a method for analyzing target interrogation data is described. The method comprises collecting target interrogation data, wherein the target interrogation data comprises spectra that is representative of the contents of the target; performing a primary analysis of the spectra according to a least squares analysis to determine a first set of elemental intensities representative of the contents of the target; performing a secondary analysis of the spectra utilizing the first set of elemental intensities by comparing the first set of elemental intensities from the target to a second set of elemental intensities for known spectra; and classifying the contents of the target based on the secondary analysis comparison. In a second embodiment of the present invention, a method for analyzing target interrogation data is described. The method comprises collecting target interrogation data, wherein the target interrogation data comprises spectra that is representative of the contents of the target; performing a primary analysis of the spectra according to a principal component analysis to determine a first set of vectors representative of the contents of the target; performing a secondary analysis of the spectra utilizing the first set of vectors be comparing the first set of vectors from the target to a second set of vectors for known spectra; and classifying the contents of the target based on the secondary analysis comparison. In a third embodiment of the present invention, an interrogation system for determining the contents of a target is described. The interrogation system comprises at least one detector configured to provide spectra representative of the target; a primary analysis application to perform a least squares analysis of the spectra to determine a first set of elemental intensities representative of the contents of the target; and a secondary analysis application to perform an analysis of the spectra utilizing the first set of elemental intensities by comparing the first set of elemental intensities from the target to a second set of elemental intensities for known spectra; wherein the system classifies the contents of the target based on the secondary analysis application comparison. In a fourth embodiment of the present invention, an interrogation system for determining the contents of a target is described. The interrogation system comprises at least one detector configured to provide spectra representative of the target; a primary analysis application to perform a principal component analysis to determine a first set of vectors representative of the contents of the target; and a secondary analysis application to perform an analysis of the spectra utilizing the first set of vectors be comparing the first set of vectors from the target to a second set of vectors for known spectra; wherein the system classifies the contents of the target based on the secondary analysis application comparison. Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings. It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed. Reference will now be made in detail to the preferred embodiments of the present invention, examples of which are illustrated in the accompanying drawings. The system and method of the present invention analyze data regarding the contents of a target to determine whether the target contains dangerous or illicit contents. Further, the system and method provide a classification to discern whether the contents contain an improper substance for handling, removing, isolating, or other future action. For example, the contents of the target can be classified as “explosive” or “inert,” or as “containing illicit drugs” or “not containing illicit drugs,” and the like. The system may also classify the contents as “unknown.” Although the present invention can be applied to a variety of target contents, the description herein often describes the method of determining whether the target is “explosive” or “inert.” However, references to these classifications are merely exemplary and the present invention is not intended to be limited only to the detection of explosive targets. Given the fact that chemical elements and elemental ratios are quite different for innocuous substances, drugs, explosives, chemical warfare agents, etc., the system and method described herein are applicable in a variety of situations, e.g., identification of filler of shells, differentiating chemical agents from innocuous or high explosive fillers, confirming buried landmines, etc. More specifically, the inspection is intended to be used in a variety of applications including, but not limited to, improvised explosive devices (“IEDs”) and radiological dispersal devices (“RDDs”), chemical warfare agents (“CWA”) in various containers, drugs (e.g., cocaine) in sea vessels, drug stimulant in a pallet, explosives, confirmation sensor for humanitarian demining, shells over a range of sizes and fills, and detecting a bomb in a vehicle. Examples of target contents to be identified include, but are not limited to, explosives (e.g., RDX, TNT, PETN, ANFO, black powder, smokeless, Pyrodex), radioactive isotopes (e.g., Cobalt (60Co), Cesium (137Cs), depleted Uranium (238U), Americium (241Am)), and miscellaneous or innocuous contents (e.g., ammonia, bleach, water, gasoline, diesel fuel). The system can recognize these contents in a plurality of different targets used as a concealment including, but not limited to, metal toolboxes filled with tools, canvas gym bags filled with clothes, cardboard and plastic boxes, rolling suitcases filled with clothes, leather briefcases filled with papers, and metal/pvc/abs pipe bombs. Additionally, the system can also identify a background such as metal tables, concrete, dirt, carpet, and sand. High explosives (e.g., TNT, RDX, C-4) are composed primarily of the chemical elements hydrogen, carbon, nitrogen, and oxygen. Similarly, illicit drugs are typically composed of high amounts of hydrogen and carbon and, in many instances, show a strong chlorine signature. Many innocuous materials are also primarily composed of these same elements, but the elemental ratios and concentrations are unique to each material. The table below shows the atomic density of elements for various materials along with the atomic ratios. The problem of identifying explosives and illicit drugs is thereby reduced to the problem of elemental identification. Nuclear techniques exhibit a number of advantages for non-destructive elemental characterization. These include the ability to examine bulk quantities with speed, high elemental specificity, and no memory effects from the previously measured object. Densityor RatioHCNOClC/OC/NCl/ONarcoticsHighHighLowLowMediumHigh >3HighVeryHighExplosivesLow-MediumHighVeryMediumLow <1Low <1Low toMediumHighto NoneMediumPlasticsMedium-HighHigh toMediumMediumMediumVery—HighLowto NoneHigh Nuclear interrogation can provide a means of rapidly and correctly determining the contents, thereby allowing rapid disposition and proper handling of explosive or chemical filled material. Nuclear interrogation allows the system to non-intrusively and quickly identify the contents of a target in-situ for more cost-effective and safer environmental remediation. Referring to FIG. 1, a process 10 for inspecting a target according to an embodiment of the present invention is shown. Hardware 20 irradiates the target. Spectra 30 emits from the target due to the radiation. The hardware 20 detects and analyzes the spectra 30 in a primary analysis application 40. The primary analysis application 40 provides elemental intensities 50, vector scores, or the like, which is representative of the contents of the target. A secondary analysis application 60 analyzes the data from the primary analysis application 40 to render a decision 70 regarding the contents of the target. The chemical elements of interest for the detection of illicit drugs or explosives require different neutron energies in order to be observed. Elements such as H, Cl, and Fe are best observed through nuclear reactions initiated from very low energy neutrons. Other elements, such as C and O, need neutron energies of several MeV to be observed reliably. To satisfy this range of neutron energies, a neutron source is required that can produce the high-energy neutrons for measurement of elements such as C and O, as well as low energy neutrons (e.g., energy less than 0.025 eV) for elements such as H and Cl. This can be accomplished with the use of a pulsed neutron generator. The pulsed neutron generator emits penetrating neutrons that interact with the nuclei of the chemical elements in the target. As a result of these interactions, the chemical agents in the target material, e.g., H, C, N, and O, emit characteristic gamma-rays that are the “fingerprints” of those elements. The gamma ray energy is characteristic of the nuclei with which the reaction occurred, and can therefore be used as an indicator of a particular atomic species. Because different interactions produce prompt or delayed emission, neutron pulses and gated detectors have the advantage of providing more than one spectrum, as compared to continuous neutron fluxes. Thus, the system can separate the fast inelastic, capture, and activation components, and make available more information that can be used to infer the elemental composition of the irradiated target. By examining the elemental composition of the object, the system is able to automatically differentiate and classify the item into various categories, such as explosives, illicit drugs, industrial chemical agents, and the like. This classification process provides a safe mechanism for the non-intrusive and non-destructive testing of many hazardous materials. Referring to FIG. 2(a), a schematic figure of a conventional inspection system 200 is shown. The system 200 has a neutron source 210, such as a pulsed neutron generator, that irradiates a target 220 with pulsed neutrons 230. However, any neutron source or interrogation process may be used, such as those disclosed in exemplary processes described in U.S. Pat. Nos. 5,982,838 and 6,563,898, which are incorporated herein by reference in their entirety. Irradiating a substance with pulsed neutrons 230 results in several types of interactions that cause the emission of gamma rays 250. The energy of these gamma rays 250 is characteristic of the nuclei with which the reaction occurred and can, therefore, be used as an indicator of the presence of an atomic species. Additionally, the pulsed neutron generator 210 makes it possible to separate the gamma spectra into inelastic and capture components that are easier to interpret. The pulsed neutron generator 210 produces neutrons by creating deuterium ions and accelerating these ions onto a tritiated target. The neutrons are generated by applying a DC high voltage (e.g., of the order of 100 kV) between the cathode and the tritiated target. Deuterium atoms are emitted from the cathode when it is heated. These atoms are then ionized and accelerated in a high voltage field of up to about 100 kV to impinge on tritium atoms in the target. The fusion of deuterium and tritium nuclei creates neutrons with an energy of about 14 MeV. The deuteron beam is pulsed by applying a gated voltage, e.g., 2-3 kV, between the cathode and an intermediate electrode. The neutrons are produced isotropically and diffuse through the target. The system is controllable between three detection/timing modes. The modes comprise, for example, when the neutron generator is “off” for a predetermined amount of time (Mode 1), the neutron generator pulsing at 10 Hz/10 microseconds (Mode 2), and the neutron generator pulsing at 200-400 kHz/25-200 microseconds (Mode 3). Utilizing the system in these three modes to inspect a target facilitates data collection in both passive and active modes for both passive and stimulated emissions of gamma and neutron radiation. The neutron generator, operating at 14 MeV, can be configured to pulse neutrons approximately 2-10 μs wide in a first frequency range of approximately 5,000-10,000 Hz, in order to excite and detect gamma radiation from a first class of prohibited materials, e.g., explosives, chemical warfare agents, and illicit drugs. The emitted gamma radiation from the target is detected and subjected to chemical elemental analysis. A detailed description of an exemplary chemical elemental analysis method is described below, as well as in U.S. Pat. Nos. 5,982,838 and 6,563,898. The same neutron generator also uses pulsed neutrons that are approximately 25-200 μs wide in a second frequency range, e.g., 200-400 Hz, in order to excite and detect neutron radiation from a second class of prohibited materials, e.g., nuclear materials such as 235U or 240Pu. The system can also be utilized in a passive mode in order to detect gamma and/or neutron radiation emitted from the target without the need for active interrogation. Neutrons can initiate several types of nuclear reactions (e.g., (n,n′γ), (n,pγ), (n,γ), etc.) on the interrogated target. The gamma rays (γ) from these reactions are detected by at least one detector. During the (Mode 2) neutron pulse, the gamma ray spectrum is primarily composed of prompt gamma rays from the (n,n′γ) and (n,pγ) reactions of fast neutrons with elements such as C, O, and N. This spectral data is stored at a particular memory within the data acquisition system. Between pulses, some of the fast neutrons that are still within the object lose energy by collisions with light elements composing the object. When the neutrons have energy less than 1 eV, they are captured by such elements as H, S, N, Cl, and Fe through (n,γ) reactions. The prompt gamma rays from this set of reactions are detected by the same at least one detector, but stored at a different memory address within the data acquisition system. The procedure can be repeated with a different frequency, e.g., 10 kHz. After a predetermined number of pulses, there is a longer period that allows the detection of gamma rays emitted from the elements, such as O, Al, Si, and P, that have been activated. Therefore, by utilizing fast neutron reactions, neutron capture reactions, and activation, a large number of elements contained in an object can be identified in this remote, non-invasive technique. With respect to Mode 3, the neutron generator produces neutrons, i.e., frequency of 200-400 Hz for between 25-200 μs, that interact with fissionable materials, e.g., 235U and 239Pu, within a target. At the end of the neutron pulse, neutrons emitted by any fissionable materials will be detectable and identifiable according to their characteristic decay curves. Based on the resulting emissions from pulsed neutrons, the system identifies key elements, e.g., H, C, N, and O, which cannot be done with radioisotopic neutron sources. Advantageously, pulsed neutrons permit the separation—in time—of the gamma ray spectra/signatures produced by inelastic neutron scatter, neutron radiative capture, and induced activation. Referring to FIGS. 3(a) and (b), a graph is shown depicting the gates associated with the gamma rays during the time after a neutron burst. The pulsed neutron technology provides both fast neutron 370 and thermal neutron 380 capture analysis, which gives the broadest possible range of elemental identification. The “fast” neutron time 310 during a neutron burst and emission of inelastic gamma rays is characterized as an inelastic gate 320, and has a duration of approximately 10 μs. The “thermal neutron” time 330 during capture of the gamma rays and thermal neutrons is characterized as a capture gate 340, and has a duration of approximately 90 μs. The time when the level of capture gamma rays falls below activation gamma rays 350 is characterized as an activation gate 360. The reactions happen immediately and are eliminated as soon as the neutron generator is turned “off.” Between pulses, some of the fast neutrons are slowed down and thermalized, and may eventually be captured by nuclei in the target, producing gamma rays with different characteristic energies. The neutron generator can be switched “on” or “off,” with no external radiation in the “off” position. An advantage to using the neutron generator is that the neutrons are produced “on demand.” Because the neutrons are only produced when the high voltage is applied on the generator, there is no external radioactivity when there is no high voltage. Additionally, neutrons have high penetrability and can traverse with ease the part of the cargo volume concealing a suspected anomaly. The incident neutrons interact with the nuclei of the various chemical elements in the anomaly, emitting the characteristic gamma rays, which act as the fingerprints of the various chemical elements. The incident neutrons interact with both the chemical elements in the anomaly and the surrounding cargo material. These interactions result in gamma rays that constitute the background of the measurement. It is necessary to use an appropriate configuration of the system to maximize the signal to background ratio. A gamma ray detector 240 collects spectra data, e.g., gamma rays, from the target 220. The gamma ray detector 240 comprises a bismuth germinate (“BGO”) or NaI scintillator coupled to a photomultiplier tube (not shown) to detect the gamma rays emitted by the target and its surroundings. The detector is gated to independently acquire the fast spectrum and the thermal spectrum. The neutron pulse duration is, e.g., 10 microseconds with a frequency of 10 kHz. The spectra can be acquired by counting for a period of time, e.g., 1 to 5 minutes, depending on the target type and size and container makeup. After converting the gamma ray signals from the BGO to digital energy information, they are collected in an energy spectrum histogram. The gamma ray detector 240 is protected from the direct output of the pulsed neutron generator 210 by a line of sight shield stack or neutron shielding 260. During the neutron pulse, the gamma ray spectrum is primarily composed of gamma rays from inelastic scattering and neutron capture reactions on elements, e.g., C and O, and is stored at a particular memory location within the data acquisition system. An embedded controller 270 communicates the data with a remote computer or control pad 280, such as a laptop computer or handheld computer, for operation by a user. Embedded controller 270 comprises a computer system including a power supply and battery backup. In one example, the neutron pulse generator emits 14.2 MeV neutrons in 10 μs pulses at a rate of 10,000 pulses per second. The neutrons excite the nuclei within the target (e.g., the nuclei of H, C, N, O, Si, Cl, Ca, Fe, and Al), which emit characteristic gamma rays detected by the gamma ray detectors. The gamma rays for each element have different energies, so it is possible to measure elemental ratios such as C/H, C/O, and H/Cl. For illicit drugs, these elemental ratios are distinctly different from those of innocuous materials and, therefore, pallets containing narcotics can be readily identified. The ability to obtain reliable elemental information and induced gamma spectra depends on many factors, including size of the sample, available neutron flux, and detector resolution. Practical limitations inherent to field instruments make it difficult to interpret the spectra directly from published nuclear data. Accordingly, one relies on some form of calibration using spectra of known substances as a reference. Conventionally, data analysis of the resulting gamma-ray spectra is performed with a program known as a spectrum deconvolution code. To utilize the program, one must first measure the response of the detector in question to γ rays from pure elements. For example, a block of pure graphite is used to determine the detector's response to the C γ rays. To determine the detector's response to elemental H, a response is measured from a water sample. In the absence of any sample placed in front of the detector, the detector records γ rays emanating from the material surrounding the detector, as well as from the materials inside and around the neutron generator. This spectrum is known as the background spectrum. The counts of the ith channel of the spectrum of a sample, S, can be represented by the equation: S i = k * B i + ∑ j = 1 n c j * E i , j where Bi is the background spectrum at the ith channel and k is its coefficient, Ei,j is the response of the jth element at the ith channel and cj is its coefficient, and n is the total number of elements utilized to fit the spectrum. A least squares algorithm is used to fit this equation. Primarily, identification of a substance is performed through examining the atomic ratios, e.g., the ratio of carbon atoms to oxygen atoms (C/O). The measurement of C/O is performed by taking the ratio of intensities for carbon and oxygen γ rays and then applying the ratio of the (n,n′γ) cross-sections for these elements. The properties can then be analyzed using a decision tree, which is a set of rules or inequalities on the elemental intensities that is developed through inspection of the data along with trial and error. The development of a decision tree can be a laborious process because one needs to visualize data in multidimensional space. The decision tree code sets boundary limits for elemental responses and for characteristic elemental ratios. The decision tree progresses logically to deduce a result such as “Explosive Threat!”, “TNT!”, or “Drugs!”. The responses can be dependent on the material of the container and its physical properties and other objects in the container that affect them. Attention is given to the background and the container, particularly if the amount of substance to be analyzed is small. Referring to FIG. 4, a conventional decision tree is shown for an ammonium nitrate fuel oil (“ANFO”) bomb. Decision trees are not the same for all of the various conditions under which explosives can be found. For example, a decision making tree for an explosive ordnance on the ground is different than a decision tree for an explosive ordnance in water. In the present invention, spectral analysis can be performed in two steps. First, the system extracts from the spectra a robust set of indicators. Second, the indicators can be correlated to the properties of the substance in question. The system produces raw data and processed data. The raw data consists of spectra and the processed data may consist of elemental intensities. In certain situations, the signal due to the target is only a small fraction of the total measured signal. When the system is used to inspect explosive targets, especially if the targets are on the ground rather than on a table or other support, the background is a large portion of the sample spectrum. It is essential that the background effects be included in the analysis. Accordingly, the raw data for a target comprises a fast spectrum and a thermal spectrum for each the signal and the background. Visual inspection of signal and background spectra is useful to identify potential problems with the data and to check that the energy calibration is correct. For a particular sample, one usually considers the combination of two spectra, one with the sample present (i.e., signal) and one taken in similar conditions without the sample (i.e., background). Spectral analysis reduces the information to a smaller set of numbers, which are known as “indicators,” e.g., elemental intensities, which can be used as features to classify, identify, or otherwise characterize the sample. One approach may be based on an underlying physical model (i.e., some assumptions are made) and auxiliary measurements of the response functions must be available. The processed data, e.g., elemental intensities, are based on the assumption of a linear model and rely on the definition of elemental response functions. While the concept of elemental intensities has great appeal, mainly because it is based on nuclear arguments, the model from which it is derived is an approximation and its validity can be questioned. As an alternative, the raw data (i.e., spectra) from an ensemble of measurements of known items can be used without any model or fit. The spectrum comprises a vector with a large number of components and contains information that allows for an inference of the nature of the substance in a container, e.g., explosive or inert, and identifies the substance. One simply uses the shape of the spectra in a pattern recognition mode without any attempt to interpret them according to a model. Various methods for analyzing spectral data are described herein. In a first exemplary processing embodiment, once the gamma ray and neutron emission data is collected by the detector, the spectra is processed to identify contraband hidden among innocuous objects within the target. The spectra data are analyzed using a primary analysis application by performing a least squares analysis (“LSA”), which uses a library of gamma ray (and neutron) spectra for several chemical elements that are expected to be either in the background (e.g., other parts of the target) or in the target to be interrogated. The LSA extracts the contribution of different elemental species present in the sample. Spectral data analyzed using model dependent LSA requires measured response functions of each element and results in intensities of C, N, O, H, etc. The decision making process using deterministic rules based on elemental intensities and ratios is developed manually and can change depending on types of targets or the environment. The LSA method does not rely on any particular chemical element. Instead, LSA utilizes all chemical elements that are present or, in certain cases, absent from a spectrum. For each measured spectrum and associated background, the output of the LSA provides a number of elemental intensities. For small amounts of explosive material or, in general, when the sample spectrum is not very different from the background, the elemental intensities are not directly proportional to the fraction of elements in the target. However, the intensities are useful indicators of elements represented in the spectra, and display correlation with some properties, e.g., explosive or inert, of the substances that produced the spectra. Utilizing collected spectra data, based on the assumed linear model, a generic spectrum |s> can be written as follows:|S>=c1|R1>+c2|R2>+ . . . +cn|Rn>where the ci are coefficients and |R1>. . . |R>are generalized responses (in particular |R1>is the background). The equation above can be written as a matrix vector product, as follows:|S>=R|c>where R is a known matrix. If R were a square matrix, the solution would be|c>=R−1|S>Since R is not a square matrix, e.g., R may have four or five columns and hundreds of lines, corresponding to the channels in the spectrum, the system of equations is over determined. The matrix RTR, where T indicates the transpose, is a square matrix, and the system can be solved in the least squares sense, as follows:|c>=(RTR)−1RT|S>The vector |c>contains the indicators based on the LSA method. The LSA primary analysis application provides the results in counts/second for each chemical element of importance. The results are then used in a secondary analysis application to identify the target. In a second exemplary processing embodiment, rather than requiring a model and response functions in the primary analysis application, features can be determined directly from a number of spectra of substances of interest, e.g., explosives and hazardous chemicals. The principal component analysis (“PCA”) can be used to obtain indicators from the spectra. Decomposition of the spectra into principal components is an alternative to the characterization of the spectra by elemental intensities. In PCA, one relies on general features of the accumulated spectrum and not on the particular chemical elemental content of the anomaly under interrogation. PCA is based on a particular expansion in terms of orthonormal functions. PCA uses an eigenvector approach to derive sets of indicators directly from the spectra, eliminating the need for a model and elemental response functions. The indicators are representative of the spectra and display correlation to the properties. The PCA method relies on general features of the accumulated spectrum and not on the particular chemical elemental content of the “anomaly” under interrogation. For a particular sample, one usually considers the combination of two spectra, one with the sample present (i.e., signal) and one taken in similar conditions without the sample (i.e., background). Every spectrum (or the difference between signal and background) can be represented as a weighted sum of basis vectors. If an adequate representation of a spectrum can be attained with only a small number of basis vectors, the coefficients of the expansion form a feature vector that can also be used to characterize the sample. Advantageously, this approach is completely heuristic and, accordingly, does not require any auxiliary measurements or underlying models. This means that, where the system is well trained, it is possible to analyze a target without relying on spectral deconvolution. The PCA technique allows for threat classification by directly responding to the data pattern classic to that type of target. This makes a PCA system more flexible and more responsive to a broader variety of targets. More particularly, any vector, including a spectrum|s>, can be decomposed into a sum of vectors as follows:|s>=c1|P1>+c2|P2>+ . . . +cn|Pn>where the c1 . . . cn coefficients are numbers, and the vectors |P>. . . |P>form an orthonormal basis. The above equation is true for any orthonormal set. Many vectors |S>can be arranged to form a matrix X. This matrix is not square, however. The matrix XTX that is proportional to the covariance of the matrix X (provided that the data has been mean centered) is square. The eigenvectors of this square covariance matrix by definition form an orthonormal set. They can be ordered in descending order according to the magnitude of the corresponding eigenvalues. The advantage of this procedure is that one does not need all of the eigenvectors to expand the spectra. Instead, a relatively small number of components may be sufficient for the spectral expansion, and most of the variance in the data is captured by the first few principal components. Once the principal components have been determined, a particular spectrum is represented by a small number of indicators, also known as “vector scores,” which are obtained by projecting the vector onto the principal components, as follows:ci=>Pi|S>Accordingly, applying the PCA method described above to the spectra data, a matrix of all the spectra data is formed, which also accounts for the background. The covariance of this matrix is calculated. The set of eigenvectors of the covariance matrix is computed and they are ordered in descending order by eigenvalue. A smaller subset of eigenvectors from the top of the ordered list is selected as the principal components. Finally, the data vector (spectrum) is projected on the above components. The PCA method extracts the group of indicators, i.e., vector scores, for each data vector. The PCA vector scores replace the elemental intensities obtained from the least squares approach, which are then processed by the secondary analysis application to classify the target contents. In order to maximize the reliability of the results from the inspection system, the system utilizes a secondary analysis application that maximizes probability of detection and minimizes probability of false alarms. The secondary analysis application can use a generalized likelihood ratio test or support vector machines to render a decision on the contents of the target. Based on LSA, PCA, or other spectral analysis, the generalized likelihood ratio test (“GLRT”) offers a simpler and automated way of correlating the indicators to the material properties. The GLRT is a statistical analysis tool that allows hypothesis testing based on a ratio of two likelihoods: the likelihood that the data point of the target being evaluated is inert and the likelihood that the target is a real threat or contraband item. Applying GLRT to the detected data from the primary analysis application in conjunction with known materials, the target inspection system optimizes the probability of detection and minimizes the probability of false alarms. The training data sets are based on an elemental concentrations data bank established by interrogating a large number of innocuous objects as well as drugs, explosives, weapons of mass destruction, etc., i.e., known targets. Based on elemental concentrations, as well as several elemental ratios, the target inspection system is “trained” to distinguish contraband from innocuous objects. To apply the tool, one needs a set of representative data to train on, after which one selects a threshold and applies the tool to the stream of data points that follow. By moving the threshold, one can develop a receiver operating characteristic (“ROC”) curve, which is a good indicator of the detection capability of the system. The ROC curve is a plot of detection probability versus false alarms. By comparing the result of the declarations to the known state (e.g., explosive or inert) of the sample one can calculate the detection probability (“DP”) and the probability of false alarms (“FA”) for that particular threshold. The ROC curve is a global way of assessing the performance of both primary and secondary analysis applications. The GLRT method can then be used for making decisions on new data. If enough information is available for a range of different substances, the GLRT parameter can also be used for substance identification. The substance is identified as belonging to the class (e.g., explosive or inert) corresponding to the highest confidence. GLRT separately calculates the probability density functions (“PDF”) from different elements, e.g., explosive and inert. The ratio of the PDF of an explosive to an inert is substantially proportional to the likelihood that the interrogated sample is an explosive. This requires some a priori knowledge of target types that are desired to be identified. For each data point, which consists of measured elemental intensities, the quantity λ can be computed. The quantity λ is the logarithm of the ratio of two likelihoods, more specifically, the likelihood that a data point corresponds to an inert or an explosive. Since it is a statistical property, it can be computed from the statistical properties, e.g., mean and covariance, of the inert and explosive data sets. The value of λ can be used as a threshold and can represent a surface in the multi-dimensional space. The data points that fall on one side of the surface, e.g., above the threshold, can be declared explosives, while the remaining ones are considered inert. The distance of a point from the surface is an indication of the confidence in the decision. When a point lies exactly on the surface confidence is 50%. The procedure for a decision is as follows. By way of example, using data from a PCA, a sample may comprise of a vector, W, with four components (C, H, N, and O intensities). The samples can include all of the measurements or a subset, e.g., all of the measurements made on a particular type of environment, such as on a concrete surface. The mean (μ) and covariance (Cov) matrix for the explosives and inert items, respectively, are computed. Statistics under H0 (inert) are represented by μ0 and C0. Statistics under H1 (explosive) are represented by μ1 and C1. For a generic vector, W, compute:λ=(W−μ1)T(Cov1)−1(W−μ1)−(W−μ0)T(Cov0)−1(W−μ0)where T indicates the transpose. The decision statistic, λ, is applied to each data vector, W, and then the decision statistics are compared to a threshold level in a ROC curve. An advantage of the GLRT approach is that it provides a natural way of assessing performance through the ROC curve. If λ is less than the threshold level, the decision is explosive. If λ is greater than the threshold level, the decision is inert. A threshold value of λ is selected that corresponds to an acceptable level on the ROC curve, e.g., 10% false alarm, 80% detection probability. Advantages to GLRT include the application to a number of dimensions, the parameters determining the decision can be obtained with a completely automated analysis, the method generates well-defined boundaries, and a confidence level can be associated with the decision once a threshold has been selected. The decision is associated with the following confidence level: Confidence = 0.50 + 0.50 erf ( abs ( λ - Threshold ) 4 2 ) where erf ( x ) = 2 π ∫ 0 I ⅇ - f 1 ⅆ t The confidence so defined varies from 0.50, i.e., when we are exactly at the threshold, to 1. The conventional decision procedure for a two hypothesis problem is to compare the algorithm output, λ, to a fixed threshold, β, and declare H1 if λ>β or H0 if λ<β. Because there are only two decision regions, H0 and H1, only one threshold is required to separate them. Typical PDFs and decision regions, as well as the decision outcomes, are illustrated in FIGS. 5(a)-(c). There are four possible decision outcomes: (1) Correct Rejection—Declare H0 when the measurement results from H0; (2) False Alarm—Declare H1 when the measurement results from H0; (3) Miss—Declare H0 when the measurement results from H1; and (4) Detection—Declare H1 when the measurement results from H1. Associated with each of these outcomes is the probability that it will occur. The probabilities are denoted as follows: probability of a correct rejection (“PCR”); probability of false alarm (“PFA”); probability of miss (“PM”); and probability of detect (“PD”). FIG. 5(a) depicts a PDF of λ for all data. If λ is greater than threshold β, H1 is chosen. If λ is less than threshold β, then H0 is chosen. FIG. 5(b) depicts a PDF of λ for H0 data. If λ is greater than threshold β, it is a false alarm. If λ is less than threshold β, it is a correct reject. FIG. 5(c) depicts a PDF of λ for all H1 data. If λ is greater than threshold β, it is a proper detection. If λ is less than threshold β, it is a miss. The ROC curve evaluates algorithm performance for a binary hypothesis test. Even though there are four decision outcomes and, therefore, four probabilities to assess performance, the two probabilities PD and PFA capture all of the information about the performance of the algorithm since PCR=1−PFA and PM=1−PD. In practice, the ROC curve is found by determining PD and PFA for a set of thresholds. The conventional ROC curve for the binary decision PDFs shown in FIGS. 5(a)-(c) is plotted in FIG. 6(a). The usual performance goal is to maximize the probability of making a correct decision, which is equivalent to maximizing detections while minimizing false alarms. Therefore, the closer a ROC curve is to the upper left corner of the graph, the better the algorithm performance. The perfect algorithm produces 100% detection with no false alarms. An alternate algorithm performance measure is an ROC curve which plots PD versus PCR, as illustrated by FIG. 6(b). For this performance measure, improved performance is indicated by the ROC curve being closer to the upper right corner of the graph since it is desirable to maximize detection while maximizing correct rejections. The perfect algorithm has 100% detection with 100% correct rejection. An equally valid alternate performance measure is PM versus PFA. For this convention, better-improved performance is indicated by lower PM and PFA, or being closer to the bottom left corner of the graph. For a PM versus PFA ROC curve, perfect performance is no misses and no false alarms. In an alternative embodiment, a tertiary hypothesis test is utilized in place of the binary hypothesis test, where the decision is either “explosive” (“EX”) or “inert” (“IN”). Utilizing a tertiary hypothesis test, the decision would include at least a third choice, such as “Unknown” or “Don't Know” (“DK”). DK is declared when confidence in an IN/EX decision is low. Because there are only two underlying hypotheses, e.g., inert or explosive, the classification algorithms are developed as they would be for the traditional binary hypotheses test. However, performance evaluation (e.g., ROC curves) must be modified. Tertiary decision changes scoring procedure, not algorithms. The tertiary decision introduces the third possible decision, DK, for a fixed percentage of the data. Two thresholds, which assign 25% of the data to the DK decision, β0 and β1, and the resulting decision regions and decision outcomes, are shown in FIGS. 7(a)-(c). FIG. 7(a) depicts a PDF of λ for all data. If λ is greater than threshold β1, H1 is chosen. If λ is less than threshold β0, then H0 is chosen. If λ is between β0 and β1, then it is a “Don't Know.” FIG. 7(b) depicts a PDF of λ for H0 data. If λ is greater than threshold β1, it is a false alarm. If λ is less than threshold β0, it is a correct reject. If λ is between β0 and β1, then it is a “Don't Know.” FIG. 7(c) depicts a PDF of λ for all H1 data. If λ is greater than threshold β1, it is a proper detection. If λ is less than threshold β0, it is a miss. If λ is between β0 and β1, then it is a “Don't Know.” The decision outcomes illustrate that a ROC curve (PD v. PFA) does not take the DK decision into account since both probabilities are determined with respect to β1. It is necessary to assess performance using both thresholds so the impact of the third decision, i.e., DK, can be determined. Since PCR depends on β0 while PD depends on β1, the alternate convention, PD v. PCR, is appropriate for measuring algorithm performance. However, the alternate convention ignores a portion of the available data when determining PD and PCR. Consequently, performance improves because the region in which it is most difficult to distinguish between the two hypotheses is the region in which the data is ignored. As the percentage of the data ignored decreases, the ROC curve falls, until it becomes identical to the binary decision ROC when none of the data is ignored. Referring to FIG. 8, exemplary tertiary decision ROC curves are obtained when 25%, 10%, and 0% of the data is declared DK. Note that when 0% of the data is ignored, the ROC is identical to the ROC for the binary decision in FIG. 6(b). In an exemplary embodiment, FIGS. 9(a)-(c) depict distributions of elemental intensities for a plurality of targets placed in various concealments and situated on concrete. A “+” represents a target with explosives. A “o” represents a target without explosives. FIG. 9(d) depicts a corresponding ROC curve obtained by the GLRT method for the set of exemplary data taken with the targets interrogated in FIGS. 9(a)-(c). In these measurements, the concealment was not included in the background. This situation is considered more realistic because, in the field, a concealment matching that containing the target may not be readily available for the background measurement. An alternative to GLRT is support vector machines (“SVMs”). One issue with the use of the likelihood ratio for decision making is the necessity for determining the probability density functions that describe the data under each condition of uncertainty. These probability density functions are used to define the decision boundary that separates target decisions from non-target decisions. This involves developing a probability density function describing the count data for at least each type of explosive. As an alternative, SVMs are alternative means of determining decision boundaries. SVMs map their multi-dimensional input space nonlinearly into a high dimensional feature space. In this high dimensional feature space, a linear classifier is constructed. Thus, once training is performed, execution of the algorithm is computationally inexpensive. SVMs can perform binary decision tasks, and the associated relevance vector machines (“RVMs”) can be used to formulate decision tasks. SVMs have been shown to provide excellent performance and to be robust to limited training sets. When the data is analyzed, a computer screen can provide the results of the secondary analysis application to the user. In one exemplary embodiment, a computer screen can display the interrogation results and alert the user to the presence of contraband by stating “Contraband Detected!” In another exemplary embodiment, the computer screen identifies the material and provides its chemical composition for the confirmation of the operator, along with an indication of the confidence level of the reading. The embodiments described above are intended to be exemplary. One skilled in the art recognizes that numerous alternative components and embodiments that may be substituted for the particular examples described herein and still fall within the scope of the invention. |
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053176154 | description | DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be explained in conjunction with the drawings. FIG. 1 is a sectional view showing the structure of a major part of a first embodiment of the present invention. Denoted in the drawing at 4 are aperture blades (light blocking means) for limiting the exposure region. Each blade comprises a metal plate having a sufficient thickness to prevent transmission of first light, consisting of X-rays (soft X-rays) to be used for the exposure. Denoted at 402 are aperture stages for moving corresponding aperture blades 4. Each aperture stage 402 comprises a single axis stage and is operable to set an associated aperture blade 4 at a predetermined position, corresponding to a desired view angle (range). Four aperture blades 4 and four aperture stages 402 are provided in this example, in association with the four sides of the view angle, respectively. Driving means for the aperture stage 402 comprises a pulse motor drive or a DC motor drive with an encoder, and the quantity of movement is controlled in response to a signal supplied from a drive control (not shown). Denoted at 6 are position detecting devices each for measuring a positional deviation between a pattern already formed on a wafer 2 and a pattern formed on a mask 1 which is held by a mask chuck 8. Generally, the positional deviation detection is effected by detecting a positional deviation of an alignment mark formed at a peripheral part around the circuit pattern. The mask-to-wafer alignment to be effected in this embodiment may be made in a manner such as disclosed in Japanese Laid-Open Patent Application No. 100311/1990 or European Patent Application No. EPA 0,336,537. More specifically, it may be effected by detecting positional deviations between alignment marks (not shown) on the wafer 2 and alignment marks 101 formed around the circuit pattern area 102 on the mask 1. In consideration of a possibility that each positional deviation detecting means is able to detect a positional deviation only in one direction, four positional deviation detecting devices 6--6 are provided in this example. These positional deviation detecting devices 6--6 correspond to four alignment marks 101, respectively, formed at four peripheral sides of the circuit pattern area 102. Denoted at 601 is the axis of emission for a laser beam to be projected from a corresponding positional deviation detecting device 6, for obtaining a positional deviation detection signal. The laser beam is emitted by a laser light source (not shown) of a corresponding positional deviation detecting device. Denoted at 602 is the axis of light reception for the laser beam to be received by a light emitting element (optical detection means), not shown, of a corresponding positional deviation detecting device 6, after the laser beam is influenced by an alignment mark 101 on the mask substrate and an alignment mark (not shown) on the wafer such that it bears a positional deviation signal, representing mutual positional deviation of these alignment marks. In order to obtain a positional deviation signal with good precision, the emitted laser beam should be projected on the alignment mark 101 with a predetermined positional precision. The size of the circuit pattern area 102 is variable with cases, and the disposition of the alignment mark 101 is variable with masks. In consideration of this, the positional deviation detecting device 6 is equipped with a stage 603 which is movable in two directions, whereby an alignment mark, if it is in a predetermined region, can be caught by the positional deviation detecting device. The stage 603, the aperture stage 402 and the mask chuck 8 are mounted on a frame 5 of the exposure apparatus. Also, broken lines 7 in FIG. 1 depict the range of projection of the exposure X-rays. The aperture blade 4 of the present embodiment is formed with an opening for allowing passage of the laser beam projected from the positional deviation detecting device 6. The opening is covered by a plate 401 adhered thereto and made of a material which does not transmit exposure X-rays but transmits a laser beam as described above. Usable examples are X-ray resistive glasses such as BK-7R available from OHARA Inc. Japan and BK-7G25 available from JENAer GLASWERK SCHOTT & GEN. Denoted at 403 is a piping for temperature control of the aperture blade 4, through which cooling water is circulated between it and an external water tank (not shown), such that a temperature control means is constituted thereby. With this arrangement, the aperture blade 4 can be controlled always at a constant temperature. The operation of this embodiment will be explained. FIG. 2 shows a state in which a positional deviation between the mask 1 and the wafer 2 is being detected. The aperture blade 4 is at a position sufficiently retracted from the alignment mark 101 so as not to interfere with impingement of the laser beam 601 on the alignment mark 101. FIG. 3 shows a state in which, after completion of the mask-to-wafer alignment operation based on a positional deviation signal, the aperture blade 4 is just going to cross the path of the laser beam. FIG. 5 is a plan view corresponding to this. In the state shown in FIG. 3, the signal processing at the light receiving portion of the positional deviation detecting device 6 is set in a mode different from that for the positional deviation detection, such as a mode for discriminating presence/absence of a light reception signal, for example. When the aperture blade 4 comes to a position covering the alignment mark 101 against the laser beam, namely, at the very moment at which the blade 4 crosses the laser beam, a corresponding signal is supplied from the signal processing portion of the positional deviation detecting device 6 to the drive control for the aperture stage 401. Namely, a signal representing the arrival of the edge of the blade at the position of the path of the laser beam, is produced and supplied. Since the position of the alignment mark with respect to the path of emitted light (axis 601) has been fixed, positional information of the aperture blade 4 with respect to the alignment mark 101 is obtained at this time. FIG. 4 shows the position of the aperture blade 4 to be assumed for the exposure (circuit pattern transfer) FIG. 6 is a plan view corresponding to this. In this state, the aperture blade 4 is protruded as compared with the FIG. 3 state. The beam of X-rays for the exposure passes by the edge of the aperture blade 4. The aperture blade 4 covers the alignment mark 101 against the exposure X-rays 7, but it does not cover the circuit pattern area 102. Also, the laser beam from the positional deviation detecting device 6 can pass through the window 401 of the aperture blade 4 and impinge on the alignment mark 101. As a result, the circuit pattern area 102 can be exposed to the X-rays while, on the other hand, the alignment mark 101 is not exposed to the X-rays. Thus, it is still possible to effect the positional deviation detection during the exposure process. Since the moving distance from the FIG. 3 position to the FIG. 4 position is fixed, it is possible to calculate the moving distance beforehand. In this embodiment, in the state shown in FIG. 2, a positional deviation between the alignment mark 101 formed on the mask 1 and an alignment mark formed in a zone of a wafer 2, to be exposed at the first time, is detected and then the initial positioning is effected. After this, in the state shown in FIG. 3, signal detection is effected for the positioning of the aperture blade 4. Subsequently, the aperture blade 4 is protruded by using the detection signal to a position such as shown in FIG. 4, whereby the limitation of the exposure region for the exposure of the wafer 2, is accomplished. After this, if another zone of the wafer 2 is to be exposed, the aperture blade 4 is kept in the state shown in FIG. 4, and by using the laser beam projected through the window 401, a positional deviation between the alignment mark 101 of the mask 1 and another alignment mark formed in that exposure zone of the wafer 2 is detected and, then, the positioning is effected. In the present embodiment, as described above, for step-and-repeat exposures, the positioning is effected by using the laser beam projected through the window 401. However, there is a possibility that, depending on the material or thickness of the plate 401, the optical path length changes largely or non-negligible refraction is caused. If this occurs, then the optical system is different between a case where the alignment laser beam passes through the window and a case where it does not pass therethrough. In order to compensate for this, the signal processing of the positional deviation detecting device 6 may be made to operate alternately in different modes for these cases, to execute positional deviation detection. For example, in the case where the laser beam goes through the window, the signal processing may be made in consideration of the effect of refraction or the like. FIG. 7 is a plan view showing a major part of a second embodiment of the present invention. In this embodiment, each aperture blade 703 is provided with a window 704 of a width substantially equal to the full length of a side of a maximum view angle to be defined for the exposure. This makes it possible to effect the positioning for the step-and-repeat exposures, independently of the position of each alignment mark 702 to be provided on a scribe line of a wafer 701. The remaining portion of this embodiment is similar to the first embodiment. FIG. 8 is a plan view showing a major part of a third embodiment of the present invention, and FIG. 9 is a sectional view of the same. In this embodiment, for simplification of structure, a single aperture member 801 is mounted on the top of a mask frame 805. The portion of the aperture member 801 corresponding to a circuit pattern area 804 defined on the mask frame 805 is shaped into a rectangular opening, and four small positioning windows each for allowing passage of a positioning laser beam are formed adjacent the centers of the four sides of the rectangular opening, respectively. Each positioning window is covered by a plate 802 adhered thereto and made of a similar material as the plate 401 of the first embodiment. The remaining portion of this embodiment is similar to the first embodiment. In the present embodiment, the positioning laser beam can always pass through the window and, therefore, the same condition such as refraction or the like is assured. Thus, the positioning at the time of initial exposure (first shot) and the positioning at the step-and-repeat exposures, can be made in the same condition. As a result, no change occurs in the positioning reference (the position of incidence of the laser beam upon a light receiving element where there is no positional deviation) between the positioning operation at the initial exposure and the positioning operation at the step-and-repeat exposure, due to the effect of refraction of the window 802. Since in this embodiment the temperature of the aperture member 801 is not controlled, it is preferable to use a metal material having a large heat conductivity so that produced heat is easily transmitted to the mask chuck. FIGS. 10 and 11 are a sectional view and a plan view, showing the structure of a portion around an aperture in an X-ray aligner according to a fourth embodiment of the present invention. Denoted in the drawings at 901 is a mask having a circuit pattern (exposure region) 902 to be transferred; denoted at 903 is a wafer onto which the circuit pattern of the mask is to be transferred; denoted at 904 is a base on which the mask is held fixed; denoted at 905 is a wafer chuck with which the wafer is held fixed on a wafer stage (not shown); denoted at 906a-906d are pickups each comprising a semiconductor laser for projecting light onto alignment marks AM formed on the mask and the wafer, a CCD line sensor for detecting diffraction light or the like from the alignment marks, which light contains positional deviation information and the like; and at La-Ld are paths for the alignment lights. In this X-ray aligner, as the wafer 903 is brought to the exposure position, a positional deviation between the mask 901 and the wafer 903 with reference to a predetermined standard positional relationship is detected on the basis of the outputs from the pickups 906a-906d Then, on the basis of results of positional deviation detection, the wafer stage is driven to correct a positional deviation (gap, parallelism and the like) of the mask 901 and the wafer 903 in the Z-axis direction as well as a positional deviation of them in respect to the X, Y and .theta. directions. After such positional deviation correction, exposure light such as X-rays emitted from a SOR (synchrotron orbit radiation) source, for example, is projected from the above to the below in the Z direction in FIG. 10, namely, in a direction perpendicular to the sheet of the drawing of FIG. 11, whereby an image of the pattern of the mask is printed on the wafer. Denoted at 907a-907d are light blocking plates for defining the exposure region 902. Each of these light blocking plates 907a-907d is made of a material having a sufficient thickness such that, while the laser light projected from the pickup can path therethrough, almost all the X-rays (exposure light) are blocked thereby. Denoted at 908a-908d are first stages for carrying thereon the pickups 906a-906d, respectively, each of which comprises a single-axis stage movable in a plane parallel to the exposure plane (X-Y plane) and in a direction parallel to corresponding one of the sides 902a-902d of the exposure region 902. The first movable stages 908a and 908c are movable in the Y direction, while the first movable stages 908b and 908d are movable in the X direction. Denoted at 909a-909d are second movable stages for carrying thereon the first movable stages 908a-908d, respectively, each of which comprises a single-axis stage movable in a plane parallel to the X-Y plane and in a direction perpendicular to corresponding one of the sides 902a-902d of the exposure region 2. The second movable stages 909a-909c are movable in the X direction, while the second movable stages 909b and 909d are movable in the Y direction. The first movable stage 908a and the second movable stage 909a cooperate and constitute a dual-axis stage for moving the pickup 906a in the X and Y directions. Similarly, the pair of single-axis stages 908b and 909b, the pair of the single-axis stages 908c and 909c and the pair of single-axis stages 908d and 909d, provide dual-axis stages, respectively, for moving the pickups 906b, 906c and 906d, respectively. The light blocking plates 907a-907d are mounted on the second movable stages 909a-909d, respectively, and they are set at those positions defining the aperture 910 corresponding to the exposure region 902, prior to the X-ray exposure. Alignment marks are formed at such positions that, when the blocking plates 907a-907d are aligned with respect to the exposure region 902, the alignment marks can be detected by the pickups 906a-906d, respectively. In this X-ray aligner, each dual-axis stage for moving corresponding one of the pickups 906a-906d, is provided by a combination of corresponding one of the single-axis stages 908a-908d each being movable in a direction (lateral direction) parallel to corresponding one of the four sides 902a-902d of the exposure region 902, with corresponding one of the single-axis stages 909a-909d each being movable in a direction (longitudinal direction) perpendicular to the corresponding one of the sides 902a-902d of the exposure region 902. Each of the single-axis stages 908a-908d is mounted on corresponding one of the single-axis stages 909a-909d, with the moving direction of each of the single-axis stages 909a-909d being confined only to the longitudinal direction. Additionally, the light blocking plates 907a-907d for defining the exposure region are mounted on the single-axis stages 909a-909d, respectively. In this manner, the stages for moving the pickups 906a-906d, respectively, are used also as the stages for moving the light blocking plates 907a-907d, respectively. This makes it possible to eliminate the necessity of using specific stage means exclusively for changing the aperture size. Also, the light blocking plates 907a-907d are mounted on the stages 909a-909d each being movable only in the longitudinal direction. This avoids the necessity of moving the stages 909a-909d and the blocking plates 907a-907d in their lateral directions even in such a case where, as shown in FIG. 12, each alignment mark is formed at an end portion of corresponding one of the sides 902a-902d of the exposure region 902 and thus the pickups 906a-906d have to be moved laterally to the end portions. Therefore, as compared with a structure wherein each light blocking plate moves laterally, the aperture device comprising the light blocking plates 907a-907d and the like can be made compact. Further, by using, as the light blocking plates 907a-907d, such a material effective to block X-rays for the exposure but effective to transmit alignment laser light, it is possible to dispose the aperture member (blocking plates 907a-907d) between the mask 901 and the pickups 906a-906d, since the alignment light can pass through the light blocking plate. By disposing the aperture member close to the mask 901, as above, it is possible to prevent deterioration of the precision of controlling the exposure region limitation attributable to a change in the angle of incidence of the exposure X-rays or diffraction at the edges of the light blocking plates 907a-907d. Further, when the exposure X-rays are projected, the light blocking plates 907a-907d can serve to prevent impingement of scattered X-rays from the mask 901 upon the pickups 906a-906d. Therefore, it is possible to protect the alignment system against the scattered X-rays. As a matter of course, each light blocking plate has a sufficient size so as to prevent impingement of the scattered X-rays from the mask 901 upon the pickup. As described hereinbefore, an important feature of this embodiment resides in that the light blocking member for blocking the illumination light for the exposure, itself, dose allow passage of the illumination light for the positional deviation detection. Where the illumination light for the exposure comprises X-rays and the illumination light for the positional deviation detection comprises light such as a laser light, for example, having a wavelength longer than near-ultraviolet light, the light blocking member may be made of a material such as light transmissive ceramics such as PLZT or MgO, Y.sub.2 O.sub.3, Gd.sub.2 O.sub.3, etc. While in the foregoing the invention has been described with reference to examples where the invention is applied to an X-ray exposure apparatus, the invention is applicable also to a case where ultraviolet light or any other exposure illumination light is used. While the invention has been described with reference to the structures disclosed herein, it is not confined to the details set forth and this application is intended to cover such modifications or changes as may come within the purposes of the improvements or the scope of the following claims. |
description | A toroidal vessel system 1 containing a magnetically confined DT fusion plasma and a liquid metal first wall is depicted in FIG. 1. The system 1 is axisymmetric about centerline 5, whereas the complete structure of system 1 is obtained by rotating the cross-section shown 360xc2x0 about centerline 5. The toroidal field coils 8 are spaced around the toroid 10 so as to magnetically contain the plasma 6 within the toroidal chamber 9. The toroidal field coils 8 are positioned external to the toroidal vessel 10. Liquid metal, preferably lithium, enters the toroidal vessel chamber 9 as a continuous stream through apertures 14 and 15 located at the top of the toroidal vessel 10 forming two axisymmetric streams of liquid metal 12 and 13. The thick liquid metal streams 12 and 13 continuously flow down each side of the inner wall 7 of the toroidal vessel 10 and exit through a common exit aperture 16 at the base of the toroidal vessel 10. A pump 18 pumps the hot liquid lithium 20 from the base of the toroid 10 to a heat extraction and power conversation unit 22. As the cooled liquid lithium 24 flows back to the top of the toroid for reuse, it is divided into two streams 42 and 43. Two electrodes 26 and 27 separated by an insulator 28 are positioned at the top interior of the toroid 10. The electrodes 26 and 27 are positioned at the edge of the openings 14 and 15 allowing the liquid lithium stream to enter the toroid 10 and to establish electrical contact between the respective liquid lithium stream and its respective electrode. When energized by a direct current source 11 the electrodes 26 and 27 provide a poloidal current which flows in the lithium layers 12 and 13. The current source 11 is connected to the electrodes 26 and 27 so that the poloidal current flows in the same direction as the current in the toroidal field coils 8 which surround the toroid 10. An alternate embodiment is depicted in FIG. 2. were instead of the heat extraction and power conversion unit 22 being outside of the toroidal field coil 8 the unit is placed inside the field coil 8. FIG. 3A depicts a top view of the toroid along section line axe2x80x94a of FIG. 1. In this view the toroidal field coils 8 are missing. The figure illustrates the symmetry and continuity of the entrance apertures or ducts 14 and 15, the electrodes 26 and 27 and the insulator 28. The axis of symmetry is the toroidal axis 5. FIG. 3B depicts a bottom view of the toroid along section line bxe2x80x94b of FIG. 1. Also, in this view the toroidal field magnets 8 are missing. The symmetry and continuity of the exit aperture or duct 16 about the toroidal axis 5 is shown. FIG. 4 depicts a portion of the liquid metal stream and a force diagram resulting from the interaction of the poloidal current in the liquid lithium layer, first wall, and the magnetic field generated in the toroid by the toroidal field coil. This interaction results in electromagnetic xe2x80x9cJxc3x97Bxe2x80x9d forces which push the liquid lithium stream 12 against the toroidal chamber wall, thus, keeping the stream away from the plasma. Under the combined influence of gravity and electromagnetic forces, the stream moves along the chamber wall to the base of the chamber where it exits through exit apertures 16. FIG. 5 depicts an alternate embodiment 40 where the first stream 42 and the second stream 44 enter the toroid at the upper end of the toroid Each stream is electrically coupled to a specific electrode 46 and 48 respectively. The electrodes 46 and 48 are insulated from each other by an insulator 50. At the base of the toroid, each stream is electrically coupled to another electrode 52 and 54. As at the top of the toroid, the two electrodes 52 and 54 are electrically insulated from each other by an insulator 56. The paired electrodes, 48 and 52, and, 46 and 54, are each connected to individual current sources 58 and 60 respectively. Electrodes 48 and 52 which are in contact with the liquid lithium conduct the current supplied by the external direct-current power sources 58 and 60 to produce the lithium-confining poloidal currents. As in the prior embodiment, when each liquid lithium stream 44 or 46 reaches the base of the toroid it flows through orifices 61 and 62 respectively into a common pipe 63 and is pumped by a pump 64 to a heat extraction and power conversion unit 66. The insulating structure 50, also, serves as a site for external access to the plasma for diagnostics, for DT fueling and exhaust, and for plasma current profile control. This invention can also incorporate passive electrical conducting solid structures 30 and 32 mounted on the chamber walls and immersed in the flowing liquid lithium layers 12 and 13 FIG. 1 and FIG. 4. The structures produce eddy currents in the flowing liquid metal causing the poloidal currents within the liquid metal to interact with the applied magnetic to produce xe2x80x9cJxc3x97Bxe2x80x9d forces which limit the flow velocity of the descending liquid lithium to the desired design values. These structures are only optional and are not a required item. In an alternate embodiment to reduce neutron streaming, FIG. 6, the electrodes and insulator 70, 72, and 74 are skewed to that they are no longer approximately perpendicular to the inner surface 9 of the toroid 10. A further embodiment provides for a lower surface vapor pressure of the plasma-facing liquid lithium layer. This is achieved by providing for a liquid lithium sublayer relative to the outer layer which is exposed to the plasma, FIG. 7. To achieve this dual layer approach, relatively cool inner layers 82 are injected axially symmetrically at the top of the toroid 10 (only one side of the symmetrical toroid liquid lithium system is shown). The inner layer 82 rides on the hotter outer layer 84 (only one side shown). The two layers 82 and 84 will not mix or interchange because liquid metal flowing in a strongly magnetic field is laminar not turbulent. The relatively cool inner layer 82 will descend more rapidly than the hot outer layer 84. When the inner layer reaches the base of the toroid 86, it is pumped, by pump 87, via the return pipe 88 back to the top of the toroid and reinjected, through port 90 as the warm outer layer 84. The outer liquid lithium layer 84 descends along the inner wall of the toroid 10 and exits at the base of the toroid through port 94 as hot liquid lithium. The hot liquid lithium 96 is pumped, by pump 95, to a heat extraction and power conversion device 98 which cools the liquid lithium. This cooled liquid lithium 100 is then injected as the inner layer 82 at the top of the toroid through port 102. When the hot layer 96 is cooled to just above the lithium melting point, 181xc2x0 C., the vapor pressure is in the neighborhood of 10xe2x88x9210 torr. If the inner layer 82 exits the toroid at a temperature of 271xc2x0 C. after absorbing about 16% of the fusion heating from alpha heating, this corresponds to a surface vapor pressure of 10xe2x88x927 torr. After reinjection as the outer sublayer 84, the lithium leaves the base of the toroid at approximately 745xc2x0 C. which is then used to generate power. The outer sublayer 84 is more closely coupled to the wall of the toroid and descends more slowly than the inner layer 82. Laminar flow ensures that the hot exiting liquid lithium (with 1 torr vapor pressure) will never directly face the plasma. In order to both moderate i.e., slow down, the 14 Mev neutrons and adequately breed tritium, natural liquid lithium blanket designs for pure DT fusion reactors must be typically on the order of 1 meter in thickness. Furthermore the need to be of low atomic number (low-Z) walls for magnetic fusion so that if any impurities enter the hydrogenic Z=1 DT plasma from the wall, such impurities would not greatly increase radiative losses. Pure lithium is good in this respect as it has a low atomic number Z=3. On the other hand, the salt of liquid lithium and beryllium, known as xe2x80x9cFLIBExe2x80x9d, should not be used as a first wall for magnetic fusion since it contains fluorine, which is expected to greatly increase plasma radiative losses and thus degrade energy confinement Liquid Lithium""s vapor pressure is extremely low, which is a requirement for using liquid walls with magnetic fusion. Examined references state lithium""s 10xe2x88x9210 Torr vapor pressure at selected temperatures and vapor pressure formulae accurate for temperatures above 700xc2x0 C. These formulae have been used to calculate the following table: Note for comparison that typical vacuum xe2x80x9cbase pressuresxe2x80x9d on the TFTR varied from sightly below 10xe2x88x928 Torr to several times 10xe2x88x928 Torr, and when the xe2x80x9cbase pressurexe2x80x9d was 10xe2x88x927 Torr or higher, some type of surface xe2x80x9ccleanupxe2x80x9d operation was usually attempted. Based on this TFTR experience, one might expect that a tokamak reactor plasma would tolerate a liquid lithium first wall whose surface vapor pressure does not exceed 10xe2x88x928 Torr. However, it is conceivable that a fusion reactor plasma might tolerate a much higher lithium surface vapor pressure after the plasma is initially establish. Moreover, rather than degrade performance, it was found that deliberately introduced lithium impurities in the plasma edge region actually seemed to improve plasma performance in TFTR experiments. Studies of lithium/helium LMMHD Power conversion have identified 800xc2x0 C. as a maximum design temperature above which systems performance does not significantly improve. Materials such as vanadium are compatible with liquid lithium up to this maximum temperature, but not significantly beyond. However, most fusion design studies considering liquid lithium in blankets have chosen a lower maximum design temperature. Liquid Lithium density varies linearly from 515 kg/m3 at 200xc2x0 C. to 454 kg/m3 at 800xc2x0 C. with a very high heat capacity, making it useful in heat transfer applications. It""s heat capacity is 1.01xc2x10.04 cal/(gmxc2x0 C.) over the temperature range 181xc2x0 C.-800xc2x0 C. Thus, 1.23 Gigajoules/m3 heat raises the temperature from 200xc2x0 C. to 800xc2x0 C. Furthermore, lithium melts at about 180.54xc2x0 C. and requires 103.2 cal/gm xe2x80x9cheat of fusionxe2x80x9d to melt. Thus, melting lithium requires about 0.22 Gigajoules/m of heat. Indeed, if the heat needed to raise the temperature from room temperature is included, i.e., from 25xc2x0 C. to 185xc2x0 C.00, a total of about 0.57 Gigajoules/m3 of heat to completely melt the lithium is needed. Furthermore, liquid lithium""s thermal conductivity varies linearly from 43 w/(m xc2x0 K) at 200xc2x0 C. to 55 w/(m xc2x0 0K) at 800xc2x0 C. Combining this with lithium""s density and heat capacity results in a heat diffusion constant ranging from 0.2 cm2/sec at 200xc2x0 C. to 0.3 cm2/sec at 800xc2x0 C. It has been determined that liquid lithium has the following electrical resistivity: Note that in order to electromagnetically hold a liquid lithium layer against the wall (or the ceiling) of a chamber, it is necessary that the component of the Jxc3x97B product directed towards that chamber wall must exceed the component of the lithium""s weight density directed away from the chamber wall, i.e., xcfx81gcosxcex8, where xcex8 is the angle between the downward vertical and the local inward normal to the wall, xcfx81 is the lithium density, and g is the gravitational acceleration, 9.8 m/sec2. Using the maximum possible magnitude of xcfx81gcosxcex8 shows that J greater than 5047/B, where B is in Tesla, is always adequate. Thus, for example, if a toroidal field within the liquid lithium layers obeys B greater than 5.1 Tesla then a liquid lithium current density of J greater than 1 kA/m2 guarantees the liquid lithium will be forced against the chamber ceiling and walls, thus keeping it away from the plasma. Electrical power dissipation by this confining current within the liquid lithium will be negligible compared to the fusion power, i.e., xcex7J2 greater than 0.35 watts/m3. For example, an ITER-size DT reactor is contemplated with a plasma having a major radius R=8, a minor radius a=3 meters, a plasma half-height b=5 meters and the plasma is surrounded with a close-fitting liquid lithium blanket with a thickness 1 meter. Then the total volume of liquid lithium is approximately 1300 m3, the total mass of the liquid lithium is about 650,000kg, the total current driven through the lithium must exceed 50 kA, and so the associated dc voltage needed to drive this current exceeds 8.8 millivolts. The foregoing description of a preferred embodiment of the invention has been presented for purposes of illustration and description. It is not intended to be exhaustive or to limit the invention to the precise form disclosed, and obviously many modifications and variations are possible in light of the above teaching. The embodiments described explain the principles of the invention and practical applications and should enable others skilled in the art to utilize the invention in various embodiments and with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims appended hereto. |
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047388218 | description | DETAILED DESCRIPTION OF THE INVENTION Reference will now be made in detail to several present preferred embodiments of the invention, some examples of which are illustrated in the accompanying drawings. In the drawings, like reference characters designate like or corresponding parts throughout the several views. In FIG. 1, a (typically 13.5 foot long) nuclear fuel assembly 10 is shown in vertically foreshortened form. The fuel assembly 10 is the type used in a pressurized water reactor (PWR) and basically includes a bottom nozzle 12 for supporting the assembly on the lower core plate (not shown) in the core region of a nuclear reactor (not shown), and a number (typically 24) of longitudinally extending (typically 12 foot long) guide thimbles 14 which project upwardly from the bottom nozzle 12. The fuel assembly 10 further includes a plurality of transverse grids 16 axially spaced along the guide thimbles 14 and an organized array of elongated fuel rods 18 transversely spaced and supported by the grids 16. The fuel assembly 10 also has a top nozzle 20 whose adaptor plate 22 is attached to the upper ends of the guide thimbles 14. The lower ends of the guide thimbles 14 are attached to the bottom nozzle 12. With such an arrangement of parts, the fuel assembly 10 forms an integral unit capable of being conventionally handled without damaging the assembly parts. As mentioned above, the fuel rods 18 in the fuel assembly 10 are held in spaced relationship with one another by the grids 16 spaced along the fuel assembly length. Typically each fuel rod 18 contains nuclear fuel pellets of uranium dioxide (not shown). A liquid moderator/coolant, such as water or water containing boron, is pumped upwardly through the guide thimbles 14 and along the fuel rods 18 of the fuel assembly 10 in order to extract heat generated therein for the production of useful work. To control the fission process, a number of control rods (not shown) are reciprocally movable in the guide thimbles 14 located at predetermined positions in the fuel assembly 10. The reconstitutable nuclear reactor fuel assembly top-nozzle-to-control-rod-guide-thimble attachment system of the invention, which is shown unassembled in FIG. 2 and assembled in FIG. 3, includes a removable top nozzle 20, a control rod guide thimble 14, and a locking tube 24. FIGS. 2 and 3 show only one guide thimble for clarity, it being understood that the attachment shown therein is repeated for all the guide thimbles shown in FIG. 1 to define the attachment system. The top nozzle's adaptor plate 22 has a control rod passageway 26 which includes a smaller diameter upper portion 28, a larger diameter lower portion 30, and a ledge portion 32 which joins the upper and lower portions. The lower portion 30 has a circumferential groove 34. The guide thimble 14, as best seen in FIGS. 2 and 4, has a top portion 36 with a plurality of longitudinal, open-ended slots 38 defining fingers 40 therebetween. The top portion 36 may be integral with, or an insert bulge-fitted to, the guide thimble 14. Preferably, there are four slots 38 and hence four fingers 40. Each finger 40 has an end 42 and a radially outwardly projecting preformed bulge or rim portion 44. As seen more clearly in FIGS. 3 and 5, each finger rim portion 44 includes an inside surface 46 defining a recess 48. The bottom edge 52 of the recess is taken as the location farthest from the finger's end 42 where the inside diameter of the guide thimble 14 first begins to increase to create the finger rim recess 48. When the top nozzle 20 is attached to the guide thimble 14, the top portion 36 of the guide thimble 14 is coaxially placed in the passageway 26 such that the ends 42 of the fingers 40 are longitudinally positioned proximate the ledge portion 32 with the rim portions 44 of the fingers 40 transversely positioned in the groove 34. This is accomplished by inserting the adaptor plate 22 on top of the preferably outwardly biased flexible fingers 40 where a lead-in chamfer 54 on the adaptor plate 22 compresses the fingers 40 to allow entry of the guide thimble 14 into the passageway 26, with the fingers 40 radially opening up to their outwardly biased position when they reach and engage the groove 34 of the passageway 26. The locking tube 24, as seen alone in FIGS. 6, 7, and 8, includes an annular flexible cylinder 56 which has at least one upper embossed dimple 58 with an apex 60 and at least two-angularly-spaced-apart lower embossed dimples 62 each with a tip 64. When the top nozzle 20 is attached to the guide thimble 14, the cylinder 56 is coaxially placed in the top portion 36 of the guide thimble 14. For an installed cylinder 56, the apex 60 of the upper embossed dimple 58 is located at an elevation below and proximate the ledge portion 32 of the passageway 26 and the tips 64 of the lower embossed dimples 62 are located at an elevation above and proximate the elevation of the bottom edge 52 of the recess 48 of the fingers 40. Also, for the installed cylinder 56, the apex 60 of the upper dimple 58 projects radially outward into the lower portion 30 of the passageway 26 at a distance, from the centerline of the cylinder 56, which is greater than half the diameter of the upper portion 28 of the passageway 26. This projection is made possible by creating a space, either by choosing dimensions, with respect to the rim/groove engagement, such that the finger end 42 is spaced apart from the ledge portion 32 or by making the finger thickness less than the ledge portion width. Furthermore, for the installed cylinder 56, the tips 64 of the lower dimples 62 project radially outward into the recess 48 at a distance, from the centerline of the cylinder 56, which is greater than the difference between the thickness of a finger 40 and half the diameter of the lower portion 30 of the passageway 26 (i.e., lower portion radius minus finger thickness). Finally, for the installed cylinder 56, the lower dimples 62 are angularly spaced apart such that when at least one of the lower dimples 62 is angularly rotated to be placed in a slot 38, at least one other of the lower dimples 62 is angularly oriented to be aligned with the inside surface 46 of the rim portion 44 of one of the fingers 40 of the guide thimble 14. The installation of the locking tube 24 is accomplished by inserting it with sufficient force into the top of the guide thimble 14 after the removable top nozzle 20 has been installed on the guide thimble. Entry is assisted by a lead-in taper 66 on the locking tube 24. As the locking tube 24 enters the passageway 26, the cylinder 56 itself flexibly deforms to allow passage of the upper and lower embossed dimples 58 and 62. It is noted that the locking tube's flexibility is such that while it will allow intended installation and removal by flexing under such predetermined forces, it will not flex under any frictional forces encountered by withdrawal of a control rod, thimble plug, etc. from the guide thimble. When the cylinder 56 reaches its proper seating depth in the passageway 26, the upper dimple 58 will radially outwardly project beneath the ledge portion 32, and at least one of the lower dimples 62 will radially outwardly project into a recess 48. This condition is readily determined at installation by noting the increased force necessary to longitudinally move the locking tube 24 up or down when it is at its properly seated location. The previously described apex and tip projecting distances are such that the upper dipmle 58 will longitudinally engage the ledge portion 32 of the passageway 28 with sufficient force to prevent any unintentional raising of the locking tube 24, and at least one of the lower dimples 62 will longitudinally engage a finger 40 which transversely engages the bottom of the groove 34 all with sufficient force to prevent any unintentional lowering of the locking tube 24 with respect to the adaptor plate 22 (even though the finger 40, through its rim/groove engagement, may experience some longitudinal movement with respect to the adaptor plate due to fuel assembly 10 handling). The presence of the locking tube 24 prevents the unintentional removal of the top nozzle 20 from the guide thimble 14 by preventing the fingers 40 from moving radially inward under a longitudinal force which would otherwise cause the rim (bulge) portions 44 to disengage from the groove 34 resulting in top nozzle 20 removal. To remove the installed locking tube 24, sufficient force is exerted to overcome the dimple engagement to flexibly deform the reusable locking tube 24 to allow its withdrawal from the passageway 26, as is known to those skilled in the art. The dimples 58 and 62 may be formed by an inner/outer die operation, as is within the purview of those skilled in the art. Preferably, the locking tube 24 has two upper dimples 58 and four lower dimples 62. To assist the cylinder 56 to flexibly deform during locking tube 24 installation/removal, an exemplary design has lower dimples 62 consisting of a first generally-diametrically-opposed pair and a second generally-diametrically-opposed pair, wherein the second pair of lower dimples 62 is oriented between ten and forty-five degrees, inclusive, (and preferably generally thirty degrees) from the first pair of lower dimples 62 (see FIG. 8). Also, in this design, the upper dimples 58 consist of a generally-diametrically-opposed pair (see FIG. 7), and this pair of upper dimples 58 is generally angularly aligned with the first or second pair of lower dimples 62 (see FIG. 6). A typical locking tube 24 is made of stainless steel and has a length of 1.25 inches, an inside diameter of 0.45 inch, and a thickness of 15 thousandths of an inch. The dimples (raised dots) 58 and 62 typically are diamond shaped having a square base with a side having a length of 25 thousandths of an inch and having an apex 60 or tip 64 having a height of 5 thousandths of an inch. The upper dimples 58 typically are longitudinally spaced 0.13 inch from the top of the locking tube 24 and 0.11 inch from the lower dimples 62. A locking tube 24 recessed more than 0.03 inch from the top of the adaptor plate 22 typically is considered to be seated too low. It will be apparent that many modifications and variations are possible in light of the above teachings. For example, although outwardly biased fingers 40 are preferred, the locking tube 24 may be used with non-outwardly-biased fingers whereby locking tube insertion forces the fingers apart through the action of suitably tapered surfaces, as can be appreciated by those skilled in the art. Also, though preformed dimples 58 and 62 are favored, the attachment system could be used for a particular application wherein the dimples are formed after the locking tube is inserted into the guide thimble. It, therefore, is to be understood that within the scope of the appended claims, the invention may be practiced other than as specifically described. |
abstract | A system and method for controlling particles using projected light are provided. In some aspects, the method includes generating a beam of light using an optical source, and directing the beam of light to a beam filter comprising a first mask, a first lens, a second mask, and a second lens. The method also includes forming an optical pattern using the beam filter, and projecting the optical pattern on a plurality of particles to control their locations in space. |
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043893694 | claims | 1. An assembled grid for holding fuel rods and control rod guide tubes in spaced relationship with each other in a nuclear reactor fuel assembly comprising: a first set of straps interleaved at right angles to each other to form multiple openings of square configuration; a second set of straps interleaved at right angles to each other to form multiple openings of square configuration and of a size the same as the openings formed by the first set of straps; said second set of straps being mounted on top the first set of straps in a manner wherein the openings in each of said sets are in axial alignment with each other to form multiple cells; a pair of dimples projecting inwardly into a predetermined number of said cells adapted to receive nuclear fuel rods therein from the cell walls formed by two adjacent straps in the first and second strap sets, thus providing two sets of vertically aligned dimples in each cell; the other two walls of said predetermined number of cells other than those cells on the periphery of said grid each having a slot therein at a location spaced from the corners of each said cell; a peripheral strap surrounding said top and bottom sets of straps, the ends of said interleaved straps being bonded to the peripheral strap to thus hold the top and bottom strap sets in immovable relationship with respect to each other; multiple spring means extending across said cells from one side of the assembled grid to the other, each of said spring means being unitary and extending through a plurality of generally diagonally aligned contiguous cells through said slots in said other two walls and having a segment which biases a fuel rod adapted to extend through each of said predetermined number of cells into engagement with said dimples to provide at least five points of support to said fuel rod. an elongated tab on both ends of each of said strip springs and of a size greater than the size of said slots; whereby any of said springs is precluded from escaping into the reactor coolant in the event of spring breakage. the constant for each of said springs being chosen such that after the straps and springs have been exposed to irradiation and the temperatures of an operating reactor, the springs relax to provide a single biasing point which urges the fuel rod into engagement with the dimples located on the other side thereof. 2. The assembled grid according to claim 1 wherein said multiple spring means include individual elongated strip springs extending diagonally across the assembled grid and positioned intermediate the dimples of said upper and said lower straps of said grid; 3. The assembled grid according to claim 2 wherein the segment of each of said springs which is located in each said cell include two or more portions arranged to contact the fuel rod at the time it is first pulled into the grid to thereby provide support thereto during the time the fuel assembly is transferred from one area to another; and 4. The assembled grid according to claim 1 wherein said peripheral strap surrounding the top and bottom grids is of a height sufficient to cover the straps of both grids, said peripheral strap being bonded to tabs extending longitudinally outward from the end of the interleaved straps. 5. The assembled grid according to claim 2 wherein said strip springs each have each of their ends terminating freely in the peripheral openings in said grid. |
description | An embodiment of a process in accordance with the present invention will now be described with reference to the accompanying drawing which is a flow chart showing processes for the treatment of a solvent comprising tributyl phosphate and adourless kerosene in which the amount of tributyl phosphate is about 30% by volume. The first stage in the process is the distillation, under reduced pressure, of solvent which has become too degraded for further use. The distillation is carried out to remove substantially al the diluent and a major proportion of the phosphate ester, for example, 90% of the total volume of organic material. This distillate is returned to the reprocessing or ore purification process. The residual volume consists essentially of organophosphate plus some phosphatic and diluent degradation products. This material is treated to convert the organophosphate to inorganic phosphate salts, such as a calcium salt. Preferred processes are high temperature processes or chemical oxidation processes. A high temperature process may be carried out by mixing the residue solvent with a metal salt hydroxide in aqueous solution or suspension for instance, calcium hydroxide, and then feeding the mixture to a stirred pebble ball reactor at about 550xc2x0 C., thereby producing a metal phosphate ash. This ash may be fed to a vitrification plant and the organics volatilised from the reactor and combusted. An alternative process is chemical oxidation, typically using a metallic catalyst such as sodium dichromate and hydrogen peroxide at a temperature of between ambient and boiling point (around 100xc2x0 C.) in an aqueous medium. This reaction produces an aqueous phosphoric acid, which is then reacted with an aqueous solution or suspension of a metal hydroxide such as calcium hydroxide. A metal phosphate salt solution is produced which is fed to vitrification or an alternative encapsulation method, such as encapsulation in cement. Prior to encapsulation, the material may be mixed with other radioactive waste. A process in accordance with the present invention is applicable to the treatment of a variety of solvents comprising an organophosphate ester and a hydrocarbon diluent. Mention has been made above to a number of hydrocarbon diluents. Two further examples of such diluents are Exxsol D80 and Isopar L. Exxsol D80 is a kerosene type material which can be used as a direct replacement for OK in reprocessing plants and has a narrower boiling point (202xc2x0-240xc2x0 C.) than OK (180xc2x0-280xc2x0 C.). Isopar L is a highly branched chain material with a very narrow boiling point range (190xc2x0-210xc2x0 C.). |
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046684689 | description | DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings and to FIGS. 1 and 2 in particular there is shown fuel pellet 10 constructed according to the teachings of the invention. Fuel pellet 10 includes an inner part 12 and an outer, annular, part 14 surrounding part 12 and being of substantially the same length as the latter. The typical length of the pellet is 1/2 inch to 1 inch; a typical range for the outer diameter of part 14 is 0.30 inch to 0.50 inch and a typical diameter is 0.48 inch. A typical range for the diameter of part 12 is such that the volume of outer annulus 14 is 25 to 50 percent of the volume of interior part 12. Parts 12 and 14 are of integral construction containing fuel of different physical characteristics. In forming fuel pellet 10, blending and mixing of the nuclear fuel and burnable poison materials is done in a manner to promote maximum homogenous dispersal of the different types of starting powders. The starting powder mixture will therefore be as homogeneous as possible prior to pellet pressing. Typically, after mechanically mixing and blending the appropriate physical powders for each of parts 12 and 14, the fuel pellet is compacted by cold pressing and then is sintered at an elevated temperature to form the final shape of the pellet. During this pressing and sintering, the separate powders will not substantially migrate into each other and thus part 12 and part 14 will be substantially composed of the materials set forth in the above examples. The teachings of the invention are that by repositioning the nuclear fissile material, the nuclear fertile material, and the nuclear poison material within the pellet in two regions, and by adjusting the volume fractions of the inner and outer regions, it is possible to control the nuclear reactivity (K) of the fuel pellet throughout life. The precise disposition of the nuclear materials allows a minimum of burnable poison to be used for maintaining (K) below a predetermined value at a predetermined time in the life of the fuel. Further, the new fuel pellet designs may be placed at the periphery of the fuel assembly which allows improvements in the power distribution throughout the assembly (e.g. a more uniform power distribution). As will be explained later, the present invention is not limited to any one or several physical arrangements or fuel mixtures or even any particular mixture of fuel and burnable poison. However, three preferred embodiment mixtures and arrangements have been determined to be of particular usefulness and will be set forth in the following three examples relative to the structure of fuel pellet 10 in FIGS. 1 and 2: EXAMPLE A The fuel content of part 12 is a mixture of natural or depleted nuclear fuel material and the fuel content or part 14 is a homogeneous mixture of gadolinium oxide and enriched nuclear fuel material. The diameter of part 12 for example A will generally range from 40 to 75 percent of the diameter of part 14. EXAMPLE B The fuel content of part 12 includes a homogeneous mixture of gadolinium oxide and enriched nuclear fuel material which may again be a mixture of both uranium oxide and plutonium oxide, and the fuel content of part 14 contains a homogeneous mixture of gadolinium oxide and enriched nuclear fuel material. The concentrations of gadolinium and fissile material in the inner part differs (for example substantially lower) from that in the outer part. The diameter of part 12 for example B may range from 40 to 75 percent of part 14. EXAMPLE C The fuel content of part 12 includes a homogeneous mixture of enriched nuclear fuel, such as for example a mixture of uranium oxide and plutonium oxide, and the fuel content of part 14 includes a homogeneous mixture of either natural or depleted nuclear fuel material. The diameter of part 12 in example C may range from 40 to 85 percent of the diameter of part 14. After formation, the fuel pellets 10 can be arranged in the manner shown in FIG. 2 in a fuel rod cladding 16 so as to provide fuel rod 18 which may then be combined with a multiplicity of other fuel rods to provide a nuclear fuel assembly. Referring now to FIG. 3 there is shown a schematic view of a typical nuclear fuel assembly 20 of the prior art. Fuel assembly 20 includes enriched UO.sub.2 fuel rods 22 and a water rod 24. Fuel rods containing fuel pellets having a homogeneous mixture of nuclear fuel materials such as, for example, enriched UO.sub.2 and a burnable poison such as, for example, Gd.sub.2 O.sub.3 are dispersed more or less uniformly throughout the nuclear fuel assembly as shown by fuel rods 26. Referring now to FIG. 4, if fuel rods 26, constructed according to the teachings of the prior art, were removed and replaced with fuel rods containing fuel pellets constructed according to the teachings of the invention, there would be nuclear fuel assembly 30 having enriched UO.sub.2 fuel rods 32, a water rod 34 and fuel rods 36 constructed according to the teachings of the invention. Fuel rods 36 now contain fuel pellets 10, constructed according to the teachings of the invention, according to the physical constituent selection of example A. When all the fissile U.sub.235 (enriched UO.sub.2) and Gd atoms are redistributed into part 14 of fuel pellets 10 of fuel assembly 30, it is found that by changing the volume fraction of part 14 the K value of the assembly can be controlled. The smaller the volume fraction of part 14 is, the higher the absorbing strength of fuel rod 36 is early in life. In addition, as the absorbing strength increases, the Gd depletion rate decreases early in life and increases later in life for fuel rod 36. Because of the increased reactivity control capabilities, the volume fraction of part 14 in pellets 10 for fuel rod 36 can be selected to minimize the requirements for gadolinium atoms in fuel assembly 30, based on a given margin to shutdown in the cold condition. The preferred embodiment is for part 14 of pellets 10 in fuel rod 36 to occupy 25 to 50 percent of fuel pellet volume. As mentioned earlier when the fuel rods containing fuel pellets having a homogeneous mixture of nuclear fuels and burnable poison are disposed such as in FIG. 3, a substantial amount of burnable poison must be used so as to provide enough control of the reactivity of the nuclear fuel assembly during the beginning of a cycle of the fuel assembly. The gadolinia burnable poison is a strong absorber of thermal neutrons. The gadolinium isotopes which have very high neutron absorption cross sections are the odd numbered isotopes (Gadolinium 155 and 157). Even numbered isotopes have much lower, though not negligible, absorption cross sections. Therefore, early in life it is the concentration of odd numbered Gadolinium isotopes which is primarily responsible for controlling the reactivity of the burnable poison rod and therefore the fuel assembly. Later in life, the even numbered gadolinium isotopes will be more controlling. Early in life the gadolinium atoms in the interior of the fuel pellet are shielded by those at the periphery. The rate of absorption is therefore controlled to a certain extent by the outer surface area and gadolinium concentration in the proximity of the outer surface. As the gadolinium is depleted, the absorbing surface will move from the periphery of the pellet to the interior. Since, as stated previously, reactivity control is necessary only early in the life of the fuel assembly, the gadolinia poison at the center of the pellet is an unnecessary burden to the reactivity of the assembly later in life. This burden is compensated for in prior art fuel assembly designs by increasing the enrichment of the fissile material of the assembly. In this present invention, it is found that by repositioning the burnable poison material within the pellet, less total amount of burnable poison atoms are required to control the reactivity by a given amount. Therefore, the fissile enrichment requirements of the assembly can be lowered and still produce the same amount of energy. For example, if in a 3.0% average U.sub.235 enrichment 8.times.8 fuel assembly designed to include six fuel rods to which 5% Gd.sub.2 O.sub.3 have been uniformly admixed to the UO.sub.2, the burnable poison rods of the prior art are exchanged (according to the teachings of the present invention) for rods containing pellets of design A above, comprising a natural uranium core occupying 50% of the volume of the pellet and an outer annulus occupying the remaining 50% of the volume and which outer annulus includes enriched U.sub.235 such that the total number of U.sub.235 atoms is not changed from the burnable poison rods of the prior art, and Gd.sub.2 O.sub.3 uniformly admixed so that the same number of gadolinium atoms is used relative to the burnable poison rods of the prior art, then it is found that during the first irradiation cycle of the assembly, and up to a burnup of 7 MWd/KgU, the reactivity of the new fuel assembly is less than that of the reference assembly containing the burnable poison rods of the prior art, and beyond 7 MWd/KgU it is more. This is shown in FIG. 5 wherein there is shown a graph of the assembly reactivities (K.sub..infin.) of a fuel assembly of the prior art and a fuel assembly constructed according to the teachings of the invention. It is clear that all the odd numbered gadolinium isotopes in the assembly containing pellets of design A deplete approximately 1 MWd/KgU earlier than for the assembly of the prior art. Therefore end of cycle residual poison penalties are reduced. Further, since in a typical application the most limiting condition from a shutdown margin point of view is between 3-5 MWd/KgU, and since, as shown in FIG. 5, the reactivity of the assembly with pellets A is less than the prior art assembly in this range, the concentration of gadolinia in pellet A could be reduced to match the K of the prior art assembly. The reduction would further decrease end of cycle residual poison penalties, and increase the K of the assembly later in life (beyond 10 MWd/KgU) since fewer even numbered gadolinium isotopes are present. By use of pellet design A it is also found that because the surface concentration of gadolinia in the outer shell is higher than for a homogeneous pellet, the fuel is less sensitive to changes in thermal neutron flux. This is very advantageous since the most limiting condition for reactor control is is the cold (shutdown) condition, where the thermal neutron flux is higher. This means that a reduction in the gadolinia concentration of pellet A has a smaller impact on the K of the fuel in the cold condition than reference assembly 20. Therefore it is estimated that with approximately 20% less gadolinium atoms, assembly with pellets A will have equivalent shutdown margin to the reference assembly. That is to say that the concentration of gadolinia in the outer annulus which occupies 50% of the volume need be only about 8%. The reduced number of gadolinium atoms employed reduces the reactivity burden of the assembly later in life such that simply by substituting pellets 10 having the constituency of example A of this invention for the pellets of the prior art, the enrichment of the assembly can be reduced to about 2.9% U.sub.235 while still generating the same amount of energy as the current assembly. Shown in FIG. 6 is nuclear fuel assembly 40 having enriched UO.sub.2 fuel rods 42, a water rod 44 and fuel rods 46 containing fuel pellets 10 constructed according to the teachings of the invention and having the consistency of example B. If fuel pellet B (fuel pellet 10 having the consistency of example B) is constructed as pellet A (fuel pellet 10 having the consistency of example A), but with a small amount of fissile and gadolinium atoms in the center part of the pellet, than for equivalent volume fractions of part 14 of pellets A and B and for equivalent number of fissile and gadolinium atoms, the reactivity of fuel assembly 40 will be similar to that of fuel assembly 30 early in life, and less later in life. Alternatively, if more gadolinium and fissile atoms are placed in center part 12 than in part 14 of pellet 10 in fuel rod 46, than the reactivity of fuel assembly 40 can be made to be more than that of fuel assembly 30 early in life and less later in life. From the above discussion, it is clear that with pellet design A the reactivity of the fuel assembly can be controlled by changing the volume fraction of part 14 in pellet 10 and accordingly adjusting the concentration of fissile and gadolinium atoms in part 14 so that the average pellet concentration is unchanged. It is also clear that with this method reactivity control is accomplished without changing the number of fuel rods in the assembly containing burnable poison atoms. As described in the example, the properties of pellet A can be used to minimize the amount of burnable poison atoms necessary to maintain K value of the assembly below a given value at a given time in the life of the assembly. The invention further teaches that additional control, if needed, can be obtained with pellets of design B. However, more burnable poison atoms are required for pellet B than for pellet A, but less than for the fully homogeneous pellets of the prior art. Referring now to FIG. 7, there is shown nuclear fuel assembly 50 having enriched UO.sub.2 fuel rods 52, a water rod 54 and fuel rods 56 containing fuel pellets 10 constructed according to the teachings of the invention and having the constituency of example C. Fuel rods 56 may be located at the periphery of the fuel assembly. For application in a BWR fuel assembly they are especially beneficial if located adjacent to or diametrically opposite from a neighboring control blade of the nuclear reactor. This is because the fertile material in part 14 of fuel pellet 10 dampens the number of fissions in part 12 which are due to increases in the number of thermal neutrons in the vicinity of fuel rod 56. The amount of dampening is controlled by changing the thickness of the annulus 14. In a BWR, this feature is particularly useful if rods 56 are located at the periphery of the fuel assembly next to a control blade. The power level of these fuel rods will respond less quickly to control blade movements and therefore improve the safety design of the fuel assembly. At peripheral locations in the assembly, fertile material in region 14 of fuel pellets in rod 56 will be converted to fissile material more rapidly than if the same rods were in the interior of the assembly, due to the higher density of thermal neutrons at the periphery. In this fuel assembly 50 the natural uranium oxide in outer part 14 becomes enriched in plutonium during irradiation therefore provides a reactivity dampening affect at the beginning of the lifetime of the fuel assembly which decreases during use. That is to say, relative to a standard, fully homogeneous pellet, pellet C has a lower nuclear reactivity early in life and a much higher one later in life. The rate of fissioning in pellet C can be controlled by changing the thickness of the outer annulus. When the volume fraction part 14 is properly adjusted and the number and locations of such pellets within the assembly properly determined, than it will be seen that less burnable poison atoms will be necessary in the fuel assembly for a given shutdown margin requirement. Fuel rods containing burnable poison pellet design A or B or other constituency may be located within the interior of fuel assembly 50 as shown in FIG. 7 at 58. The location, nuclear materials and amount of rods 58 are discretionary. Fuel assembly 30, may be designed with combinations of fuel rods and the individual fuel rods may contain combinations of fuel pellets according to the teachings of the invention. For all of the above preferred embodiments and examples of nuclear fuel material and burnable poison material constituencies, it can be appreciated that the various nuclear fuel assemblies according to the teachings of the present invention can use less enriched nuclear fuel material or can operate for a longer time having a greater lifetime power output with the same amount of enriched materials. It also can be appreciated that the teachings of the invention are not limited to any particular pellet construction or material selection or combination, but rather are broadly applicable to minimizing burnable poison material for controlling the reactivity of a nuclear fuel assembly by predetermining radial disposition of the fissile, fertile and burnable poison material within the fuel pellet. The present invention presents a novel way of controlling the rate of fissions and neutron absorption through adjustments of the chemical and fissile element composition as a function of radial position in a nuclear fuel pellet. The present invention further teaches how, by means of fuel pellets A, B and C the reactivity of the assembly can be controlled more precisely and with a reduced amount of burnable poison atoms than would be necessary with current design (fully homogeneous) pellets. With pellet design A, by decreasing the fraction of the volume of the outer part (which includes, for example, enriched UO.sub.2 and Gd.sub.2 O.sub.3) the concentration of fissile material (for example U.sub.235) and burnable poison material is increased in this region since atoms of both types are being redistributed from throughout the pellet to a smaller volume. It is found that because of this redistribution, the strength of the absorber is increased early in life and the rate of depletion of the absorber is decreased early in life and increased later in life. The smaller the volume of the outer part, the more pronounced the effect. This means that less burnable poison atoms need be used to maintain the reactivity of the assembly below a given value at at point in time in the life of the fuel. This, in combination with the faster poison depletion rate later in life, results in reduced end of cycle residual poison penalties. Accordingly, by means of pellet design A, the enrichment of the assembly can be reduced for a given energy generation requirement. Pellet design B, allows control of the reactivity of the fuel over a wider range of time than pellet design A, should this be required. For example, if a small amount (i.e. low concentration) of burnable poison and fissile atoms are added to the interior part of pellet A to produce a new pellet B, early in life the reactivity characteristics will be similar to those of pellet A; but later in life the reactivity will be slightly less due to the neutron absorbing contribution of the inner part. Pellet design B, allows less of a reduction in end of cycle residual poison penalties than pellet design A, but it is still an advantage over the standard, fully homogeneous, pellets of current use. There may be instances of practical application in which use of pellet design B provides a significant advantage. Pellet design C, exhibits a lower reactivity at the beginning of the fuel cycle and higher reactivity later in the fuel cycle relative to a standard pellet of equivalent enrichment. Early in life, the fertile material in the outer part shields partially from thermal neutrons the fissile material in the inner part, thereby depressing the reactivity of the fuel. During irradiation, the fertile material is converted to fissile material which contributes to power generation both directly and indirectly. The rate of relative reactivity increase over the lifetime of the fuel can be controlled by increasing or decreasing the pellet volume fraction of the outer part (and correspondingly increasing or decreasing the concentration of fissile material in the inner part so that the pellet average fissile enrichment is unchanged) and by placing the pellets in low or high thermal nuetron flux locations within the assembly. Pellet design C provides a very desirable effect when used at selected locations of the fuel assembly since the decreased reactivity of the pellet early in life decreases the reactivity and therefore the burnable poison requirements of the fuel assembly. The decreased reactivity early in life is recovered later in life as pellets of design C increase power generation, so as a net result the assembly operates with a more constant reactivity throughout life with reduced burnable poison. Pellet C can provide for significant economic, safety, nuclear, and assembly thermal hydraulic benefits when used at selected locations within standard design fuel assembly or assemblies which include advanced features such as pellet design A or B. The invention teaches that if in an assembly of standard design all the fuel pellets which include a homogeneously distributed burnable poison are substituted by pellets of design A or B above and all the fissile atoms and the burnable poison atoms are conserved in the substitution, than it will be found that: (1) the reactivity of the assembly can be controlled during the first cycle of irradiation by changing the volume fraction distribution of pellets A or B without increasing or decreasing the number of fuel rods in the assembly which include a burnable poison material, (2) due to the higher burnable poison depletion rate later in life, end of first residual poison penalties are decreased, (3) the improved control of reactivity with pellets A or B can be used to decrease the number of burnable poison atoms necessary and this in turn also reduces the end of cycle residual poison penalties which allows a reduction of the enrichment requirement of the fuel assembly. The increased reactivity control capabilities with pellets A or B affords increased flexibility of assembly design which can yield increased benefits since more locations within the assembly lattice are available for placement of burnable poison fuel rods. The invention further teaches that use of pellet design C in selected assembly lattice locations (for example at the periphery of a BWR fuel assembly) provides a very desirable effect of controlling the reactivity of the assembly throughout life and with reduced burnable poison. |
description | A star pinch photon source in accordance with a feature of the invention operates in two stages to produce X-ray or extreme ultraviolet radiation. In a first stage, a central plasma is formed using multiple ion beams directed at a central plasma discharge region as described below. In a second stage, a heating current pulse is passed through the central plasma in order to heat and compress the plasma, raising its temperature and density. The astron source is a source of photons comprising a discharge chamber, a plurality of ion beam sources in the discharge chamber, each electrostatically accelerating a beam of ions of a working gas toward a plasma discharge region, and a neutralizing mechanism for at least partially neutralizing the ion beams before they enter the plasma discharge region. The neutralized beams enter the plasma discharge region and form a hot plasma that radiates photons. The astron principle that operates in the first stage of the photon source described above is illustrated in FIGS. 1A and 1B. The embodiment of the source shown in FIGS. 1A and 1B has a two-gap ion acceleration structure 100. Acceleration structure 100 includes concentric spherical electrode shells 112, 113 and 114. The electrode shells 112, 113 and 114 have a plurality of sets of holes aligned along axes which pass through a central plasma discharge region 120. Thus, for example, holes 122, 123 and 124 in electrode shells 112, 113 and 114, respectively, are aligned along an axis 126 that passes through plasma discharge region 120. Each set of holes, such as holes 122, 123 and 124, defines an acceleration column 128. The spaces between electrode shells 112, 113 and 114 constitute acceleration gaps for electrostatic acceleration of ion beams. Thus, each acceleration column has two gaps in the embodiment of FIGS. 1A and 1B. The embodiment of FIGS. 1A and 1B includes 36 acceleration columns 128, arrayed in three sets of 12. Thus, the acceleration structure directs 36 ion beams toward plasma discharge region 120. However, different numbers of ion beams may be utilized within the scope of the invention. The electrode shells 112, 113 and 114 may be supported by insulating spacers 130. A plenum 132 having ports 134 encloses acceleration structure 100. A working gas is introduced, either in a pulsed mode or continuously, through ports 134 into a space 144 behind the outermost electrode shell 114. Some of the working gas flows down the acceleration columns 128. When the appropriate gas density is present in the acceleration columns, a pulsed voltage may be applied between electrode shells 112 and 114, with the polarity of electrode shell 114 being positive with respect to electrode shell 112. In the configuration of FIGS. 1A and 1B, provided the appropriate gas density is present and provided that sufficient voltage is applied, a pseudospark discharge develops simultaneously in each of the acceleration columns 128. The pseudospark discharge is characterized by the development of oppositely directed electron and ion beams that can have extremely high intensity. The ion beam exits from the negative polarity end of the acceleration column 128 at electrode shell 112 and progresses toward the central plasma discharge region 120. By correct adjustment of the working gas density at an exit region 146 of each of acceleration columns 128, most of the ions can be neutralized by resonant charge exchange, so as to form a neutral beam that propagates without deflection to the plasma in plasma discharge region 120. Those ions that are not neutralized contribute excess positive charge to each of the ion beams, causing electrons to be attracted from the nearby surface of electrode shell 112, which is already primed as a cathode due to the breakdown into a pseudospark discharge. Thus, the neutral atoms are accompanied by a nearly charge-balanced beam plasma, including the remaining unneutralized ions and electrons. The slow ions resulting from resonant charge exchange define tracks that are favored for conduction of a high current heating pulse in the second stage of device operation, as described below. Additional details and embodiments of the astron photon source are described in the aforementioned application Ser. No. 09/815,633, which is hereby incorporated by reference. In the second stage of device operation, the newly-formed plasma is heated and compressed, or pinched, by passage through the plasma of a pulse of electric current. A first embodiment of a star pinch photon source which incorporates both the first stage of operation, wherein beams of ions are electrostatically accelerated toward a plasma discharge region and are at least partially neutralized, and the second stage, wherein an electric current is passed through the plasma discharge region, is shown in FIGS. 2A and 2B. FIG. 2A is a simplified cross-sectional side view of the photon source, and FIG. 2B is a cross-section defined by revolution of line Axe2x80x94A in FIG. 2A around axis 200. In FIGS. 2A and 2B, a central cathode shell, corresponding to electrode shell 112 in FIG. 1A, is divided into two half shells 202 and 204 that are electrically connected to a pulse voltage source 205. The anode shell of the photon source is divided into two half shells 212 and 214 which are electrically connected by a conductor 216. The working gas is introduced at low pressure through ports 218 and flows through passages 220 to enter hollow anode volumes 222 within anode half shells 212 and 214. Cathode half shells 202 and 204 are electrically isolated by insulator 225. The cathode half shells are electrically isolated from the respective anode half shells by insulators 227 and 229. A pulse voltage source 215 has one terminal connected to cathode half shells 202 and 204 (through the low impedance of voltage source 205) and the other terminal connected to anode half shells 212 and 214. During the first phase of operation of the photon source shown in FIGS. 2A and 2B, a pulsed voltage V1 from pulse voltage source 215 is applied between anode half shells 212, 214 and cathode half shells 202, 204. In the absence of any applied voltage V2 from pulse source 205, the potential difference between cathode half shells 202 and 204 remains at zero. The combined cathode half shells are therefore pulsed negatively by voltage V1 relative to the combined anode half shells, and a discharge develops as described above in connection with FIGS. 1A and 1B. Neutralized beams from this discharge pass through a plasma discharge region 224 to form a small spherical plasma. At the same time, the passage of ions and energetic neutral atoms forms ionized tracks 230 between cathode half shell 202 and plasma discharge region 224, and ionized tracks 232 between cathode half shell 204 and plasma discharge region 224. The ionized tracks 230 and 232 lie on the surfaces of two cones that have their vertices located at plasma discharge region 224 and provide conducting paths between cathode half shells 202 and 204. During the second phase of operation, a pulsed voltage V2 from pulse voltage source 205 is applied between cathode half shells 202 and 204. The circuit is completed by conduction through the conical configuration of ionized tracks connecting cathode half shells 202 and 204. Thus, cathode half shells 202 and 204 constitute first and second electrodes, respectively, for application of a heating current to the plasma in plasma discharge region 224. The current flows through the plasma in plasma discharge region 224, heating and compressing it via the magnetic pinch effect. The plasma temperature and density rise to the point where the desired X-ray or extreme ultraviolet radiation is emitted copiously. The radiation is emitted from the photon source in conical beams 234 that are relayed to the point of use by collecting optical surfaces (not shown in FIGS. 2A and 2B). The working gas pressure in the central part of the acceleration structure may be maintained in a range of about 1.0 to 100 millitorr to provide the appropriate gas density. As noted above, one suitable working gas is xenon. Other suitable working gases include, but are not limited to, hydrogen, lithium, helium, nitrogen, oxygen, neon, argon and krypton. The ion beams may be pulsed or continuous, and the ion acceleration voltage V1 may be from 2 kV to 20 kV, but is not limited to this range. Voltage V1 may have a typical pulse duration of 0.1 to 10 microseconds, but may also be applied continuously. The heating voltage V2 is applied typically within 100 nanoseconds to 10 microseconds of the initial application of voltage V1. The amplitude of voltage V2 is typically in the range of 100 volts to 10 kV, and the width of this pulse typically ranges from 10 nanoseconds to 1 microsecond. A second embodiment of a photon source in accordance with the invention is shown in FIGS. 3 and 4. FIG. 3 is a simplified cross-sectional side view of the photon source, and FIG. 4 is a cross-section defined by revolution of line Axe2x80x94A in FIG. 3 around axis 200. Like elements in FIGS. 2A, 2B, 3 and 4 have the same reference numerals. The embodiment of FIGS. 3 and 4 differs from the embodiment of FIGS. 2A and 2B by the addition of a transformer 211 for coupling pulsed electrical current from pulse voltage source 205 to cathode half shells 202 and 204. Transformer 211 includes multiple primary windings 208, a toroidal core 210, which may be of non-magnetic or magnetic material, and an armature or secondary 206, also having a toroidal configuration. Primary windings 208 are connected to pulse voltage source 205, and secondary 206, which may have a single turn, is connected between cathode half shells 202 and 204. During the first phase of operation, a pulsed voltage V1 is applied by pulse source 215 between the anode half shells 212, 214 and secondary winding 206 that is connected to cathode half shells 202 and 204. In the absence of any applied voltage V2 from pulse voltage source 205 to primary windings 208, the electric potential between the cathode half shells 202 and 204 remains at zero. The combined cathode half shells are therefore pulsed negatively by voltage V1I relative to the combined anode half shells 212 and 214, and a discharge develops as described above. The neutralized beams of this discharge pass through plasma discharge region 224 to form a small spherical plasma. At the same time, the passage of ions and energetic neutral atoms forms ionized tracks 230 and 232 as described above. During the second phase of operation, a pulsed voltage V2 is applied simultaneously and in parallel across all the primary windings 208, with the result that a voltage is induced between cathode half shells 202 and 204 that are connected to opposite ends of transformer secondary 206. The transformer secondary circuit is completed by a conduction through the ionized tracks 230 and 232 connecting cathode half shells 202 and 204. As in the embodiment of FIGS. 2A and 2B, cathode half shells 202 and 204 constitute first and second electrodes, respectively, for application of a heating current to the plasma in plasma discharge region 224. The secondary current flows through the plasma in plasma discharge region 224, heating and compressing it via the magnetic pinch effect. As described above, the plasma temperature and density rise to the point where the desired X-ray or extreme ultraviolet radiation is emitted. An embodiment of a system for generating photons in accordance with the invention is shown schematically in FIG. 5. An acceleration structure 500 may correspond to the acceleration structure shown in FIGS. 2A and 2B, the acceleration structure shown in FIGS. 3 and 4, or any other acceleration structure within the scope of the present invention. In the system of FIG. 5, acceleration structure 500 is a modification of acceleration structure 100 shown in FIGS. 1A and 1B and described above. Like elements in FIGS. 1A, 1B and 5 have the same reference numerals. Acceleration structure 500 includes concentric spherical electrode shells 112, 113 and 114, each of which is divided by an insulator 503 into electrode half shells. A pulse voltage source 540 is connected between inner electrode half shells 112a and 112b. A pulse voltage source 530 is connected between outer electrode half shells 114a, 114b and inner electrode half shells 112a, 112b. Acceleration structure 500 is enclosed within a housing 502 that defines a discharge chamber 504. A top aperture 140 of acceleration structure 500 is coupled through a screen 510 to a collection region 514 that is defined by an enclosure 516. Enclosure 516 contains collection optics 518 for relaying a photon beam 150 to a remote point of use. Screen 510 constitutes a beam exit aperture which allows propagation of photons from discharge chamber 504 to collection region 514 but impedes flow of gas from discharge chamber 504 to collection region 514. A gas source 520 coupled to housing 502 supplies a working gas through inlets 522 and ports 134 in plenum 132 to acceleration structure 500. A bottom aperture 142 of acceleration structure 500 is coupled to a vacuum pump 524. An outlet 526 of vacuum pump 524 is connected to gas source 520 to form a gas recirculation system. The gas source 520 and the vacuum pump 524 are connected to housing 502 in a closed loop configuration that permits recirculation of the working gas through discharge chamber 504. Gas source 520 may include elements for removing impurities and particulates from the working gas. The system may include a detector 550 located in collection region 514, a control circuit 552 and a flow controller 554 for a feedback control of the rate of flow of the working gas into the discharge chamber 504 in response to a measured spectrum of the radiated photons. In another embodiment of the vacuum pumping system (not shown), the vacuum pump is connected to enclosure 516 rather than to housing 502. In this embodiment, gas is pumped from the central part of acceleration structure 500 through screen 510 or other beam exit aperture and then through enclosure 516. The system of FIG. 5 operates with first and second phases as described above in connection with FIGS. 2A and 2B. In the first phase, pulse source 530 applies a pulsed voltage between inner electrode half shells 112a, 112b and outer electrode half shells 114a, 114b, causing neutralized beams to be directed toward plasma discharge region 120. In the second stage, the plasma in discharge region 120 is heated and compressed by passage of a pulse of electric current. The neutralized beams form ionized tracks between cathode half shells 112a, 112b and plasma discharge region 120. Application of a pulse to cathode half shells 112a and 112b by pulse source 540 causes electrical current to flow along the ionized tracks through plasma discharge region 120. Thus, cathode half shells 112a and 112b constitute first and second electrodes, respectively, for application of a heating current to the plasma in plasma discharge region 120. The current flows through the plasma in plasma discharge region 120, heating and compressing it. The plasma temperature and density rise to the point where the desired X-ray or extreme ultraviolet radiation is emitted. The radiation is emitted from the acceleration structure 500 as conical photon beam 150. A third embodiment of a photon source in accordance with the invention is shown in FIGS. 6A and 6B. Like elements in FIGS. 1A, 1B, 6A and 6B have the same reference numerals. The embodiment of FIGS. 6A and 6B differs from the structure of FIGS. 1A and 1B by the addition of an external electrode 600 for supplying an electrical heating current to plasma discharge region 120. A pulse voltage source 601 is connected between inner electrode shell 112 and outer electrode shell 114. A pulse voltage source 602 is connected between inner electrode shell 112 and external electrode 600. Insulators 603 and 604 electrically isolate the connections to electrode shells 112 and 114, respectively. External electrode 600 may have a cylindrical configuration and may be positioned in the bottom aperture of the acceleration structure in spaced relationship to plasma discharge region 120. During the first phase of operation, a pulse voltage V3 from voltage source 601 is applied between electrode shells 112 and 114. A discharge develops as described above, and the neutralized beams of the discharge pass through plasma discharge region 120 to form a plasma. At the same time, the passage of ions and energetic neutral atoms forms ionized tracks as described above. During the second phase of operation, a pulse voltage V4 from voltage source 602 is applied between external electrode 600 and electrode shell 112. The circuit is completed by conduction through the ionized tracks connecting electrode shell 112 and plasma discharge region 120 and through a glow region 605 between plasma discharge region 120 and external electrode 600. Thus, inner electrode shell 112 constitutes a first electrode and external electrode 600 constitutes a second electrode for application of a heating current to the plasma in plasma discharge region 120. The current flows through the plasma in plasma discharge region 120, heating and compressing it. The plasma temperature and density rise to the point where the desired X-ray or extreme ultraviolet radiation is emitted. The plasma tends to be elongated in the direction of external electrode 600. The working gas extends to electrode 600 at approximately the same pressure as inside electrode shell 112. A fourth embodiment of a photon source in accordance with the invention is shown in FIG. 7. FIG. 7 is a simplified cross-sectional side view of the photon source. A chamber, or inner shell 700, which may be spherical, has an electrically conducting wall and a hollow interior. Inner shell 700 may include an annular flange 702 for electrical connection and mechanical support. The photon source further includes ring electrodes 710 and 712 disposed around a source axis 714 outside inner shell 700. Ring electrodes 710 and 712 may include flanges 716 and 718, respectively, for electrical connection and mechanical support. Ring electrodes 710 and 712 are supported by insulators 720 and 722, respectively. Each of ring electrodes 710 and 712 may comprise a hollow ring or toroid. Each of ring electrode 710 and ring electrode 712 has a plurality of holes 730, and inner shell 700 has a hole 732 corresponding to each hole 730 to form hole pairs 730, 732. The holes 730 and 732 of each hole pair are aligned and define a plasma channel 734 that intersects a central plasma discharge region 740. In one embodiment, each of ring electrodes 710 and 712 has 24 holes 730 spaced around axis 714. The spaces between each of ring electrodes 710 and 712 and inner shell 700 constitute acceleration gaps for electrostatic acceleration of ion beams. Each hole pair 730, 732 defines an ion beam source, thus providing 48 ion beam sources having plasma channels 734 intersecting plasma discharge region 740. The photon source shown in FIG. 7 may be mounted in a housing, as described above in connection with FIG. 5. The housing is filled with a working gas, for example xenon for 10-15 nanometer extreme ultraviolet emission, at low pressure, typically 1-100 millitorr. Inner shell 700 may be provided with a beam exit aperture, such as a honeycomb structure 742 comprising multiple, aligned, small bore holes having high optical transmission for a photon beam and low conductance for the working gas in order to provide near vacuum conditions for photon propagation. The honeycomb structure 742 may correspond to the screen 510 shown in FIG. 5 and described above. A photon beam 744 of extreme ultraviolet or soft X-ray radiation is emitted from inner shell 700 through honeycomb structure 742. A power supply 750 is connected between ring electrode 710 and inner shell 700, and a power supply 752 is connected between ring electrode 710 and ring electrode 712. Each of power supplies 750 and 752 is capable of providing high voltage pulses having pulse widths of 0.1-10 microseconds. In a first phase of operation, power supply 750 applies a negative DC potential to inner shell 700 relative to ring electrodes 710 and 712. Ring electrodes 710 and 712 remain at the same electrical potential during this phase of operation, connected through low impedance power supply 752. Power supply 750 supplies a DC current, typically 1-100 milliamps, to maintain a discharge in all hole pairs 730, 732. The plasma channels 734 defined by hole pairs 730, 732 intersect at plasma discharge region 740. Power supply 750 is then pulsed, typically a 1-10 microsecond pulse, to a negative voltage, typically 1-20 kV, and drives an increased current, typically 1-100 amps, through the plasma channels 734. Ions of the working gas are accelerated toward plasma discharge region 740. During passage along plasma channels 734, the ions experience neutralizing collisions in a resonant charge exchange process, so that the ion beams are at least partially neutralized before they enter plasma discharge region 740 to form a dense plasma. During a second phase of operation, power supply 752 applies a high current pulse, typically 0.1-10 microseconds and 1-100 kiloamps, to ring electrodes 710 and 712. The pulse from power supply 752 may be initiated during the pulse from power supply 750 or at most slightly after the end of the pulse from power supply 750. Thus, power supply 752 is typically triggered about 0.1-10 microseconds after power supply 750 is triggered. The circuit is completed through plasma channels 734. In particular, ring electrode 710 defines an upper conical array of plasma channels 734, and ring electrode 712 defines a lower conical array of plasma channels 734. In this embodiment, ring electrode 710 constitutes a first electrode and ring electrode 712 constitutes a second electrode for application of a heating current to the plasma in plasma discharge region 740. The high current from power supply 752 compresses and heats the plasma in plasma discharge region 740 so that it emits extreme ultraviolet or soft X-ray photons which propagate from inner shell 700 through honeycomb structure 742 as photon beam 744 to be used in an application. A fifth embodiment of a photon source in accordance with the invention is shown in FIG. 8. FIG. 8 is a simplified cross-sectional side view of the photon source. Like elements in FIGS. 7 and 8 have the same reference numerals. In the embodiment of FIG. 8, an electrode 800 replaces ring electrode 712 used in the embodiment of FIG. 7. Electrode 800 may be cup-shaped and may have a single hole 802 and a rod 804 for electrical connection and mechanical support. Cup electrode 800 functions as a hollow electrode and is supported by an insulator 810. A hole 812 in inner shell 700 is aligned with hole 802 in cup electrode 800 to define a plasma channel 820. Power supply 750 is connected between ring electrode 710 and inner shell 700, and power supply 752 is connected between ring electrode 710 and cup electrode 800. In a first phase of operation, power supply 750 applies a negative DC potential to inner shell 700 relative to electrodes 710 and 800. Electrode 800 and ring electrode 710 remain at the same potential during this phase of operation, connected through low impedance power supply 752. Power supply 750 supplies a DC current, typically 1-100 milliamps, to maintain a discharge in all hole pairs 730, 732. Plasma channels 734 intersect at plasma discharge region 740. Power supply 750 is pulsed, typically 1-10 microseconds, to a negative voltage, typically 1-20 kV, and drives an increased current, typically 1-100 amps, through hole pairs 730, 732 and 802, 812. Ions of the working gas are accelerated toward plasma discharge region 740. In passage along plasma channel 734, the ions experience neutralizing collisions in a resonant charge exchange process, so that the ion beams are at least partially neutralized before they enter plasma discharge region 740 to form a dense plasma. During a second phase of operation, power supply 752 applies a high current pulse, typically 0.1-10 microseconds and 1-100 kiloamps, to electrodes 710 and 800. The circuit is completed through plasma channels 734 and 820. In this embodiment, ring electrode 710 constitutes a first electrode and electrode 800 constitutes a second electrode for application of a heating current to the plasma in plasma discharge region 740. This high current compresses and heats the plasma in plasma discharge region 740 so that it emits extreme ultraviolet or soft X-ray photons which propagate from inner shell 700 through honeycomb structure 742 as photon beam 744 to be used in an application. A sixth embodiment of a photon source in accordance with the invention is shown in FIG. 9. FIG. 9 is a simplified cross-sectional side view of the photon source. Like elements in FIGS. 7-9 have the same reference numerals. The embodiment of FIG. 9 differs from the embodiment of FIG. 8 by the addition of a ring electrode 900 within cup electrode 800 and a power supply 910 connected between ring electrode 900 and cup electrode 800. The connection to ring electrode 900 is electrically isolated from chamber 700 and cup electrode 800 by an insulator 912. The DC discharge between cup electrode 800 and inner shell 700 can be modulated to have greater or lesser current by the application of a voltage from power supply 910 between ring electrode 900 and cup electrode 800. When ring electrode 900 is positive with respect to cup electrode 800, electrons are removed from the discharge and the cup electrode current is decreased or inhibited completely. When ring electrode 900 is made negative with respect to cup electrode 800, the discharge is enhanced. In this way, the discharge from the cup electrode 800 may be balanced with the combined discharges from ring electrode 710 to inner shell 700 in spite of their different geometries. This configuration facilitates rapid electrical breakdown between external electrode 800 and ring electrode 710 during the high current phase when power supply 752 is energized. A rapid negative pulse to ring electrode 900 can assist in the initiation of the high current discharge when power supply 752 is energized. Operation of the sixth embodiment is otherwise similar to the operation of the fifth embodiment described above. Any of the DC discharges can be controlled using electrodes, similar to ring electrode 900, within the anode enclosures adjacent to holes 730. This may apply, for example, in FIG. 7 to balance the DC discharges from ring electrode 710 to inner shell 700 with respect to the DC discharges from ring electrode 712 to inner shell 700. A seventh embodiment of a photon source in accordance with the invention is shown in FIGS. 10A and 10B. FIG. 10A is a simplified cross-sectional side view of the photon source, and FIG. 10B is a cross-sectional top view of the photon source shown in FIG. 10A. Like elements in FIGS. 7-10B have the same reference numerals. The embodiment of FIGS. 10A and 10B differs from the embodiment of FIG. 8 with respect to the coupling between cup electrode 800 and inner shell 700. Referring again to FIG. 8, cup electrode 800 is coupled to inner shell 700 through a relatively small diameter hole 812. In the embodiment of FIGS. 10A and 10B, inner shell 700 has a relatively large diameter opening 1010 to cup electrode 800. Opening 1010 may be in a range of about 40% to 100% of the diameter of inner shell 700. Operation of the seventh embodiment is otherwise similar to the operation of the fifth embodiment described above. As noted above, the working gas is ionized within hollow ring electrode 710. In a preferred embodiment, the working gas is supplied to the interior of ring electrode 710 through a plurality of conduits 1020 in flange 716 to ensure relatively uniform distribution of the working gas within ring electrode 710. It will be understood that similar conduits may be utilized in ring electrode 712 of FIG. 7 and in the cup electrode 800 of FIGS. 8, 9 and 10A and 10B. It will be further understood that different configurations may be utilized for supplying the working gas to the interior regions of the ion beam sources within the scope of the present invention. An eighth embodiment of a photon source in accordance with the invention is shown in FIGS. 11A and 11B. FIG. 11A is a simplified cross-sectional side view of the photon source, and FIG. 11B is a cross-sectional top view of the photon source shown in FIG. 11A. Like elements in FIGS. 7-11B have the same reference numerals. The embodiment of FIGS. 11A and 11B differs from the embodiment of FIG. 8 with respect to the configuration of the second electrode and the inner shell. In the embodiment of FIGS. 11A and 11B, an inner shell 1100 may be generally spherical in shape and has an opening 1102 for emission of photon beam 744. Hollow ring electrode 710 has an annular configuration and is located outside inner shell 1100 in a plane perpendicular to source axis 714. A second electrode 1110 having honeycomb structure 742 or other beam exit aperture is positioned over opening 1102 in inner shell 1100. Second electrode 1110 is electrically isolated from inner shell 1100 by an insulator 1112. First power supply 750 is connected between inner shell 1100 and ring electrode 710, and second power supply 752 is connected between ring electrode 710 and second electrode 1110. Photon beam 744 is emitted in a beam direction 1120 along source axis 714. In a first phase of operation, power supply 750 applies a negative DC potential to inner shell 1100 relative to ring electrode 710. Power supply 750 supplies a DC current, typically 1-100 milliamps, to maintain a discharge in all hole pairs 730, 732. The plasma channels 734 defined by hole pairs 730, 732 intersect at plasma discharge region 740. Power supply 750 is then pulsed, typically a 1-10 microsecond pulse, to a negative voltage, typically 1-20 kV, and drives an increased current, typically 1-100 amps, through the plasma channels 734. Ions of the working gas are accelerated toward plasma discharge region 740. During passage along plasma channel 734, the ions experience neutralizing collisions in a resonant charge exchange process and impinge on plasma discharge region 740 to form a dense plasma. During a second phase of operation, power supply 752 applies a high current pulse, typically 0.1-10 microseconds and 1-100 kiloamps, between ring electrode 710 and second electrode 1110. The pulse from power supply 752 may be initiated during the pulse from power supply 750 or at most slightly after the end of the pulse from power supply 750. Thus, power supply 752 is typically triggered about 0.1-10 microseconds after power supply 750 is triggered. The circuit is completed through plasma channels 734. In the embodiment of FIGS. 11A and 11B, hollow ring electrode 710 constitutes a first electrode and electrode 1110 constitutes a second electrode for application of a heating current to the plasma in plasma discharge region 740. The high current from power supply 752 compresses and heats the plasma in plasma discharge region 740 so that it emits extreme ultraviolet or soft X-ray photons which propagate from inner shell 1100 through honeycomb structure 742 as photon beam 744 to be used in an application. In the embodiment of FIGS. 11A and 11B, the anode and cathode are reversed during high current discharge relative to the embodiment of FIGS. 10A and 10B. This configuration keeps the output photon beam 744 pointing away from the cathode. This avoids a jet of ions that otherwise would accompany the photon beam. The anode is now the honeycomb structure 742 that the photon beam 744 passes through. An electron column 1130 may extend from plasma discharge region 740 to electrode 1110. A ninth embodiment of a photon source in accordance with the invention is shown in FIG. 12. FIG. 12 is a simplified cross-sectional side view of the photon source. Like elements in FIGS. 7-12 have the same reference numerals. The embodiment of FIG. 12 differs from the embodiment of FIGS. 11A and 11B by the addition of a receptacle 1230 at the lower end of inner shell 1100 for the accumulation of ions from plasma discharge region 40. Receptacle 1230 may have any desired size and shape and may be coupled to a vacuum system, as shown in FIG. 5 and described above. A tenth embodiment of a photon source in accordance with the invention is shown in FIG. 13. FIG. 13 is a simplified cross-sectional side view of the photon source. Like elements in FIGS. 7-13 have the same reference numerals. The embodiment of FIG. 13 differs from the embodiment of FIG. 7 with respect to the configuration of the inner shell and the addition of a resistor. The photon source of FIG. 13 includes a first inner shell portion 1300 associated with ring electrode 710 and a second inner shell portion 1302 associated with ring electrode 712. Inner shell portions 1300 and 1302 are electrically isolated from each other by an insulator 1310. Each of the shell portions 1300 and 1302 may include a hemispherical portion and a flange portion. Shell portion 1300 may be provided with honeycomb structure 742 or other beam exit aperture. The hemispherical portions may be mounted together and spaced apart by insulator 1310 to form a spherical inner shell. A resistor 1320 may be connected between shell portions 1300 and 1302. The value of resistor 1320 is selected to be high compared to the impedance of the plasma load on power supply 752 during the high current heating pulse. The purpose of resistor 1320 is to allow the shell portions 1300 and 1302 to float electrically with respect to each other during the high current pulse, but to prevent significant current from power supply 752 from bypassing the plasma through the inner shell walls. An eleventh embodiment of a photon source in accordance with the invention is shown in FIG. 14. FIG. 14 is a simplified cross-sectional side view of the photon source. Like elements in FIGS. 7-14 have the same reference numerals. The embodiment of FIG. 14 differs from the embodiment of FIG. 13 with respect to the configuration of the inner shell. The photon source of FIG. 14 includes first inner shell portion 1300 associated with ring electrode 710, second inner shell portion 1302 associated with ring electrode 712 and a third inner shell portion 1400. The third inner shell portion 1400 includes honeycomb structure 742 or other beam exit aperture and is connected to a reference potential, such as ground. The hot and dense plasma that is created in the star pinch apparatus described herein can also be used for the production of neutrons. Neutrons may be emitted with an energy of 2.45 MeV upon the collision of two energetic deuterium ions. The ion density within the heated plasma may exceed 1020 ions cmxe2x88x923 for a period of the order of 10xe2x88x926 seconds. Although existing experimental data with xenon in the star pinch apparatus indicates that a plasma temperature of only 50 eV has been achieved, future improvements to the density and temperature using the same principle should allow the deuterium plasma temperature to be raised to more than 1 keV, at which level Dxe2x80x94D fusion reactions producing 2.45 MeV neutrons begin to become very plentiful. The production of net fusion energy requires even higher plasma temperature, in the range of 10 keV, and the use of fusion reactants such as deuterium plus tritium, D+T, which have the highest fusion reaction cross section. The Dxe2x88x92T reaction produces 14MeV neutrons plus an energetic charged particle. Many different plasma configurations have been studied intensively in the quest for fusion energy, including several types of plasma pinch. To date it has been difficult to approach fusion densities and temperatures in any type of plasma pinch, and that is expected to also be true of the star pinch apparatus. However, the advantages that the star pinch apparatus would have relative to other types of pinch in the economical generation of fusion power are the large distance between the heated plasma and the nearest solid surface, to absorb the plasma blast wave after a pulsed fusion reaction, and the capability for long duration repetitive operation because of low erosion rates on the distributed electrode. While there have been shown and described what are at present considered the preferred embodiments of the present invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the scope of the invention as defined by the appended claims. |
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045308144 | summary | This invention relates to apparatus for superheating steam. In a conventional nuclear or non-nuclear steam power plant, heat supplied by a reactor core, combustion of fuel, or other means is used to raise the temperature of water until steam at saturation temperature is provided. This saturated steam is then superheated to a desired number of degrees of superheat by means of heat from the same source so that it is at a condition suitable for delivery to a steam turbine. After the steam has performed work as it is expanded through a high pressure turbine, it is generally desirable to deliver it to a low pressure turbine to further expand it as it performs additional work. However, in many such power plants, the steam leaving the high pressure turbine may be at a condition less suitable for delivery to the low pressure turbine without first removing moisture therefrom and reheating it. A moisture separator-reheater is commonly provided between a high pressure and a low pressure turbine to increase the plant efficiency and also protect the turbine blades of the low pressure turbine by reducing moisture in the steam which is to be expanded in the low pressure turbine. The reheater for a fossil power plant may be located within the steam generator and heat supplied by combustion of fuel in the steam generator is thus utilized to reheat the steam to a desired degree of superheat. Throttle steam or steam extracted from the high pressure turbine may also be used to reheat the main steam after it has been exhausted from the high pressure turbine. Likewise in a nuclear power plant, heat supplied by the reactor core may be used to reheat the steam before it is provided to a lower pressure turbine. Current pressurized water reactor steam cycles utilize modest amounts of superheat such as about 30.degree. to 60.degree. F. (17.degree. to 33.degree. C.) for steam delivered to the high pressure turbine and modest amounts of reheat such as about 100.degree. F. (56.degree. C.) of superheat for steam delivered to the low pressure turbine in order to improve heat rate for greater power output and reduced turbine blade maintenance which would otherwise be required of a greater amount of moisture in the steam. It is considered desirable to increase the number of degrees of superheat of steam delivered to the high pressure and low pressure turbines to further reduce moisture therein and to increase plant efficiency. Operators of nuclear power plants may sometimes find that use of electricity has increased over the years such that the power output thereof is less than the power required. Rather than constructing a new power plant, they have increasingly asked whether there is a way to increase the output of the plant in such situations especially when excess turbine generator capacity exists. Moisture separator-reheaters for steam power generation typically employ large cylindrical shells containing moisture separators and heat transfer tubes extending therethrough. The separators are typically of an inertial type and separate water from wet steam exhausted from the high pressure turbine. This steam is then directed to the heat exchange portion of the unit. The heat transfer tubes of the heat exchange portion may employ throttle steam and/or extraction steam to reheat the main steam flow. The water separated from the main steam is then drained at the bottom of the unit while the dried and reheated main steam is directed to the low pressure turbine. A common problem with horizontally disposed moisture separator-reheaters is unequal heat transfer and flow oscillations. The lowermost tubes of a tube bundle are subjected to a high temperature differential while tubes high in a tube bundle receive shell side flow which has already been partially heated by the lower tubes. As a result, the lower tubes may tend to accumulate water until they no longer carry steam along their entire length. Subcooling of the water in the lower tubes may then occur while steam may pass through the entire length of the tubes higher up in the bundle. Such occurrences may create an unstable condition which results in reduced overall heat transfer and potentially damaging cyclical thermal stresses on the tubes and tube sheets. One proposal for solving this problem has involved employing larger diameter tubes at the bottom of a tube bundle and smaller diameter tubes at the top thereof. Design of individual tubes sizes for such an arrangement is difficult and some tubes may be designed too large and other tubes may be designed too small resulting in perhaps even less flow stability. In addition, such an arrangement results in greater expenses for design and construction since varying tubes sizes are required. Another proposal directed to this problem provides in a water separator-superheater structure a plurality of horizontally disposed netting mattresses arranged in superposed stepped relation through which the main steam passes to be dried after which it passes through a single bank of heat exchange tubes which are disposed at an inclined angle in order to promote self-draining. An inlet header is provided at the upper end of the tubes and an outlet header is provided at the lower end of these tubes. Such an arrangement does not utilize the available space to provide heat transfer surface as effectively as may be desired. It is therefore desirable to more effectively utilize the available space within the shell of a moisture separator-reheater to provide a greater heat transfer area therein while also providing adequate means for separating moisture from the steam. Other proposals for solving this problem have included the use of inlet flow control orifices in each tube and the deliberate passage of excess steam through each tube. Although these methods are in some instances reasonably successful in controlling the tendency for tube flow oscillation, the flow orifices reduce steam pressure in the tubes and thus result in less efficient operation. In addition, the flow orifices cannot adjust to the effects of shell side flow changes caused by tube bowing, bundle bowing, or side baffle misalignment. On the other hand, the use of excess steam passage through each tube constitutes a power loss which is also undesirable. It is, therefore, an object of an aspect of the present invention to provide increased output for a nuclear power plant which has excess turbine-generator capacity. It is another object of an aspect of the present invention to provide a peak load or power upgrade device for nuclear power plants. It is a further object of an aspect of the present invention to increase the thermal efficiency of a nuclear power plant. It is still another object of an aspect of the present invention to provide a moisture separator-superheater which more efficiently utilized the heat provided in the reheating steam for more efficient operation thereof. It is yet another object of an aspect of the present invention to reduce the possibility of radiation contamination of such a superheater and of a separately fired vapor generator supplying vapor thereto. It is yet another object of an aspect of the present invention to provide such a superheater which more effectively utilizes the available space within the superheater for providing heat transfer surface. It is still another object of an aspect of the present invention to simplify and reduce the expense of fabrication of such a moisture separator-superheater. It is another object of an aspect of the present invention to reduce the power loss which would otherwise result from a large pressure drop of the main steam as it passes through a moisture separator-superheater. The above and other objects, features, and advantages of this invention will be apparent in the following detailed description of the preferred embodiments thereof which is to be read in connection with the accompanying drawings. |
abstract | Disclosed herein is an approach that validates the sensitivity of a working fluid parameter indicator in a system using centrifugal machines. In one aspect, a lead centrifugal machine and a lag centrifugal machine supply a working fluid to a distribution conduit. A working fluid parameter indicator measures a process parameter associated with the working fluid supplied to the distribution conduit by the lead centrifugal machine and the lag centrifugal machine. A controller validates the sensitivity of the working fluid parameter indicator to measure the process parameter associated with the working fluid as a function of operation of the lag centrifugal machine relative to the lead centrifugal machine during an operational test performed on the centrifugal machines. |
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description | The present invention relates to a mechanical decladder for spent nuclear rod-cuts, and more particularly, to a mechanical decladder which can perform a continuous slitting and decladding for a large amount of spent nuclear fuel rod-cuts. A nuclear fuel used for a nuclear power generation is supplied to a nuclear power plant in the form of nuclear fuel rods. The nuclear fuel rod is formed by linearly arranging a plurality of pellets in a cladding tube having a receiving space formed therein. These fuel rods are supplied to the nuclear power plant in the form of a bundle, and the spent nuclear fuel rod assemblies that have been gone through a fission reaction stored in a water tank. As a cumulative amount of these spent fuel rods is enormous, it grows a need to deal with them. Thus, a technology has been developed to cut away and dislodge the cladding tubes and separate the nuclear fuel accommodated in the cladding tube to permanently dispose of or recycle it. To this end, a mechanical decladder for a spent nuclear fuel rod-cut has been proposed to recover the nuclear fuel materials by slitting the cladding tube of the spent nuclear fuel rod-cut (see, e.g., Korean Patent Registration No. 10-1778580). In the types of the mechanical decladder for the spent nuclear fuel rod-cut, there are a vertical type mechanical decladder which slits the spent nuclear fuel rod-cut in a vertical direction by vertically feeding the spent nuclear fuel rod-cut, a horizontal type mechanical decladder which slits the spent nuclear fuel rod-cut in a horizontal direction by horizontally feeding the spent nuclear fuel rod-cut, and a slant type mechanical decladder which slits the spent nuclear fuel rod-cut in an inclined direction by obliquely feeding the spent nuclear fuel rod-cut. Recently, there has been a need for the mechanical decladder having a structure capable of preventing debris generated during slitting the cladding tube from being accumulated in a cutting module while avoiding scattering of the debris, while continuously feeding the spent nuclear fuel rod-cuts. Embodiments of the present disclosure are to provide a mechanical decladder for a spent nuclear fuel rod-cut having a structure capable of preventing scattering of debris generated during cutting a cladding tube, protecting durability of a blade, and avoiding the debris from accumulating in a cutting module, when continuously supplying the spent nuclear fuel rod-cuts. In accordance with an aspect of the present invention, there is provided, a mechanical decladder for a spent nuclear fuel rod-cut, including: an opening and closing unit configured to open and close an outlet of a basket into which the nuclear fuel rod-cut is loaded; a supporter on which the nuclear fuel rod-cut discharged from the outlet of the basket is seated; a hydraulic cylinder module configured to move the nuclear fuel rod-cut seated on the supporter; and a cutting module for slitting the nuclear fuel rod-cut while the nuclear fuel rod-cut is being moved by the hydraulic cylinder module, wherein the opening and closing unit opens and closes the outlet of the basket in conjunction with a movement of the hydraulic cylinder module. The mechanical decladder for the spent nuclear fuel rod-cut according to embodiments of the present disclosure has effects capable of protecting durability of a blade during cutting a cladding tube, preventing scattering of generated debris, and also avoiding the debris from accumulating in the cutting module, when continuously supplying the spent nuclear fuel rod-cuts. Hereinafter, configurations and operations of embodiments will be described in detail with reference to the accompanying drawings. In describing the embodiments of the present disclosure, the detailed descriptions of well-known functions or configurations will be omitted if it is determined that the detailed descriptions of well-known functions or configurations may unnecessarily make obscure the spirit of the present disclosure. When it is said that a component is “transferred” “connected”, “contacted” or “pressurized” to another component, it should be understood that the former component may be directly transferred, connected, contacted or pressurized to the latter component or a third component may be interposed between the two components. Specific terms used in the present application are used simply to describe specific embodiments without limiting the disclosure. An expression used in the singular encompasses the expression of the plural, unless it has a clearly different meaning in the context. Hereinafter, a mechanical decladder for a spent nuclear fuel rod-cut according to an embodiment of the present disclosure will be described with reference to FIGS. 1 to 3. Further, a moving direction of a hydraulic cylinder module described later is defined as a front and rear direction, and embodiments of the present disclosure will be described with reference to front and rear, left and right, and up and down directions indicated in FIG. 1. A mechanical decladder 1 for the spent nuclear fuel rod-cut includes a basket 5 into which a plurality of spent nuclear fuel rod-cuts (hereinafter, simply referred to as “fuel rod-cut”) are loaded, an opening and closing unit 10 configured to open and close a lower end outlet of the basket 5, a supporter 20 on which the fuel rod-cut discharged from the outlet of the basket is seated, a hydraulic cylinder module 30 configured to push and move the fuel rod-cut seated on the supporter 20, a cutting module 40 for cutting a cladding tube of the fuel rod-cut that is moved forward by the hydraulic cylinder module 30 to separate it into hull pieces and pellets, a rotatable housing module 50 which accommodates a plurality of the cutting modules 40 so that the cutting modules 40 can be alternately used, a support frame 300 for supporting the above components, and a control unit 500 for controlling each of the components. The hydraulic cylinder module 30 is reciprocated between a pressing position and a standby position in the front and rear direction of the mechanical decladder 1. When the hydraulic cylinder module 30 is in the pressing position, an extrusion pin of the hydraulic cylinder module 30 is operated to protrude in one direction to push and move the fuel rod-cut seated on the supporter 20 to pass it through the cutting module 40. Herein, the direction in which the hydraulic cylinder module 30 moves from the standby position to the pressing position to push the spent nuclear fuel rod-cut may be defined as a front direction, and the direction in which the hydraulic cylinder module 30 moves from the pressing position to the standby position after pushing the spent nuclear fuel rod-cut may be defined as a rear direction. During the movement of the hydraulic cylinder module toward the standby position, the supporter 20 and the opening and closing unit 10 are operated in conjunction with the movement of the hydraulic cylinder module 30. When the hydraulic cylinder module 30 is in the standby position, a fuel rod-cut seating unit 21 of the supporter 20 is lifted, and the fuel rod-cut disposed at the bottom of the basket 5 is discharged through the outlet of the basket 5 and seated on the supporter 20. The opening and closing unit 10 is configured to automatically discharge the fuel rod-cut disposed at the bottom of the basket 5 by opening the outlet of the basket 5 in conjunction with a backward movement of the hydraulic cylinder module 30. Hereinafter, the configuration of the opening and closing unit 10 will be described in detail with reference to FIG. 2. The opening and closing unit 10 includes a first gear unit 11 coupled to the hydraulic cylinder module 30 and driven in conjunction with the movement of the hydraulic cylinder module 30, a second gear unit 12 driven in conjunction with driving of the first gear unit 11, a third gear unit 13 provided on a side of the basket 5 and driven in conjunction with driving of the second gear unit 12, and an operating member 60 coupled to the third gear unit 13 and operated to open and close the outlet of the basket 5. The first gear unit 11 has a first rack gear 11a and a first pinion gear 11b meshed with the first rack gear 11a. The second gear unit 12 has a second rack gear 12a and a second pinion gear 12b meshed with one side surface of the second rack gear 12a (for example, a surface facing the rear of the mechanical decladder). The third gear unit 13 has a third pinion gear 13a meshed with the other side surface of the second rack gear 12a (for example, a surface facing the left side of the mechanical decladder). The first pinion gear 11b and the second pinion gear 12b are connected by a belt 14 so that the rotation of the first pinion gear 11b is delivered to the second pinion gear 12b. The first pinion gear 11b and the second pinion gear 12b are mounted on the support frame 300 to rotate about a rotation axis orthogonal to the moving direction of the hydraulic cylinder module 30. The second rack gear 12a is mounted on the support frame 300 to move in the up and down direction in accordance with the rotation of the second pinion gear 12b. The third pinion gear 13a is mounted on a side of the lower end portion of the basket 5 to rotate about a rotation axis extending in a direction parallel to a longitudinal direction of the fuel rod-cut loaded in the basket 5. As the second rack gear 12a moves in the up and down direction, the third pinion gear 13a rotates about a rotation axis extending in a direction parallel to the front and rear direction of the mechanical decladder, and the operating member 60 provided to open and close the outlet of the basket 5 is operated to open and close the outlet of the basket 5. Hereinafter, with reference to FIG. 2, the operation of the opening and closing unit 10 will be described in more detail. When the hydraulic cylinder module 30 moves backward to the standby position, the first rack gear 11a coupled to the hydraulic cylinder module 30 is also moved backward in a horizontal direction. When the first rack gear 11a is moved backward in the horizontal direction, the first pinion gear 11b meshed with the first rack gear 11a is rotated about a rotation axis thereof (counterclockwise direction when viewed from the right side of the mechanical decladder). When the first pinion gear 11b is rotated, the second pinion gear 12b connected to the first pinion gear 11b by the belt is rotated about a rotation axis thereof in the same direction, whereby the second rack gear 12a meshed with the second pinion gear 12b is moved downward. In this case, the third pinion gear 13a meshed with the other side surface of the second rack gear 12a is rotated about the rotation axis thereof (counterclockwise direction when viewed from the rear direction of the mechanical decladder), and the operating member 60 which blocks the outlet of the basket 5 is driven with the rotation of the third pinion gear 13a to open the outlet of the basket 5, so that the fuel rod-cut disposed at bottom of the basket 5 is discharged through the outlet, while fuel rod-cuts having been disposed just above the discharged fuel rod-cut are prevented from being discharged. The fuel rod-cut discharged through the outlet of the basket 5 is seated on the fuel rod-cut seating unit 21 of the supporter 20 in a lifted position as described later. Hereinafter, the configurations of the supporter 20, the hydraulic cylinder module 30 and the rotatable housing module 50 will be described with reference to FIGS. 2 and 3. The supporter 20 includes a fuel rod-cut seating unit 21 on which one of the fuel rod-cuts loaded on the basket 5 is seated, a support member 23 provided at a lower side of the fuel rod-cut seating unit 21 and fixed to the support frame 300, a movable member 24 provided at a lower side of the support member 23 and coupled to the fuel rod-cut seating unit 21, a movable plate 22 coupled to the movable member 24, and a plurality of elastic members 25 (for example, springs) provided between the fuel rod-cut seating unit 21 and the support member 23. The movable plate 22 has an inclined surface 22a. The fuel rod-cut seating unit 21 and the movable member 24 may be coupled to each other via a plurality of connection portions 26 (for example, two) extending through the support member 23. The fuel rod-cut seating unit 21 is pressed upward by the elastic member 25 provided between the fuel rod-cut seating unit 21 and the support member 23. As described later, when a roller 31 of the hydraulic cylinder module 30 moves forward and contacts the inclined surface 22a of the movable plate 22 and then moves forward along the inclined surface 22a, the movable plate 22 is moved downward. Accordingly, the fuel rod-cut seating unit 21 is moved downward against a spring force of the elastic member 25, so that the fuel rod-cut seated on the fuel rod-cut seating unit 21 is placed at a position corresponding to an inlet of the cutting module 40. The hydraulic cylinder module 30 includes an extrusion pin (not shown). A front end of the extrusion pin is configured to be coupled to the first rack gear 11a to press the fuel rod-cut loaded in the fuel rod-cut seating unit 21 of the supporter 20 into the cutting module 40. Since the configuration of the extrusion pin for pressing the fuel rod-cut is a known technique, a detailed description thereof will be omitted. The rotatable housing module 50 is arranged at a front side of the supporter 20. In the embodiment, the rotatable housing module 50 is configured to accommodate four cutting modules 40, but the present disclosure is not limited thereto and may be configured to accommodate two, three or five or more cutting modules 40. In the embodiment, the basket 5, the supporter 20, the opening and closing unit 10, and the hydraulic cylinder module 30 are provided in the left and right sides of the mechanical decladder 1. The rotatable housing module 50 may be installed on the support frame 300 to be rotatable about a rotation axis thereof. In addition, the rotatable housing module 50 may accommodate a plurality of cutting modules 40 (for example, four) arranged along the rotation direction about the rotation axis. Further, by rotating the rotatable housing module 50, it is possible to replace the cutting module 40 used in cutting the fuel rod-cut from the plurality of cutting modules 40. For example, the rotatable housing module 50 may be configured to place two cutting modules 40 among the plurality of cutting modules 40 to correspond to the respective supporters 20 in the front and rear direction of the mechanical decladder (that is, in a slitting direction of the fuel rod-cut). When the replacement of the cutting module 40 is required, the rotatable housing module 50 is rotated by, e.g., 90 degrees so that the unused cutting module 40 can be placed at a position (operating position) corresponding to the supporter 20 in the front and rear direction of the mechanical decladder (i.e., in the slitting direction of the fuel rod-cut). With such configuration, it is possible to easily replace the cutting module 40, thereby the durability of the cutting module 40 can be improved. That is, when a temperature of a blade 41, which is described later, inside the cutting module 40 is increased by the use of the cutting module 40 for a long periods, the housing module 50 rotates so that the unused cutting module is placed in the operating position. By alternately using the cutting modules 40 in this way, it is possible to prevent the temperature of the blade 41 from being excessively increased, thereby the durability life of the blade 41 can be increased. The front side of the rotatable housing module 50 is provided with a collecting box 400 for collecting hull pieces and pellets of the cladding tube cut by the cutting module 40. Hereinafter, the configuration of the cutting module 40 will be described with reference to FIGS. 4A and 4B. The cutting module 40 can separate the fuel rod-cut moved forward by the hydraulic cylinder module 30 into hull pieces and pellets by cutting the cladding tube of the fuel rod-cut. The cutting module 40 includes a plurality of blade sets 41s and each of which has a plurality of blades (e.g., four in the embodiment). The blade sets 41s are arranged at a predetermined interval in a circumferential direction to cut the cladding tube of the fuel rod-cut which passes through the cutting module 40. For example, the plurality of blade sets 41s may be three and arranged at intervals of 120 degrees. Since the configuration of such a cutting module 40 is a known technique, a detailed description thereof will be omitted. According to the embodiment of the present disclosure, an opening 42a is formed in a casing 42 of the cutting module 40 so that debris accumulated in the cutting module 40 is discharged downward through the opening 42a and collected in the collecting box 400 by a guide member 51 provided in a lower side of the opening 42a. Hereinafter, the operation of the supporter 20 on which the fuel rod-cuts are seated and the hydraulic cylinder module 30 that presses the fuel rod-cuts seated on the supporter 20 into the cutting module 40 will be described with reference to FIGS. 1 to 3. The basket 5 containing the spent nuclear fuel rod-cuts is mounted to the mechanical decladder 1 by a crane and a master slave manipulator (MSM). As the hydraulic cylinder module 30 is moved backward to the standby position, the fuel rod-cut seating unit 21 of the supporter 20 is lifted by a spring force of the elastic member 25 and positioned close to a fuel rod-cut feeding opening 13b. In this case, as described above, as the hydraulic cylinder module 30 is moved backward to the standby position, the opening and closing unit 10 is operated so that the fuel rod-cut disposed at the bottom of the basket 5 is seated on the fuel rod-cut seating unit 21 of the supporter 20 via the fuel rod-cut feeding opening 13b. As such, since the fuel rod-cut is loaded on the fuel rod-cut seating unit 21 of the supporter 20 while the fuel rod-cut seating unit 21 of the supporter 20 is lifted and positioned close to the fuel rod-cut feeding opening 13b, the impact on the fuel rod-cut during the loading can be alleviated. When the fuel rod is loaded on the fuel rod-cut seating unit 21 of the supporter 20, the hydraulic cylinder module 30 moves forward to the pressing position. At this time, the roller 31 provided in a lower portion of the hydraulic cylinder module 30 contacts the inclined surface 22a of the movable plate 22 of the supporter 20, and then, when the hydraulic cylinder module 30 continues to move forward in a horizontal direction, the movable plate 22 moves downward while the roller 31 moves along the inclined surface 22a of the movable plate 22. In this state, the fuel rod-cut seating unit 21 of the supporter 20 along with the movable plate 22 descends to a position where the fuel rod-cut is aligned with the inlet of the cutting module 40 against the spring force of the spring. In this state, the extrusion pin of the hydraulic cylinder module 30, the fuel rod-cut, and the inlet of the cutting module 40 are aligned in the horizontal direction. Then, the extrusion pin of the hydraulic cylinder module 30 is advanced to press the fuel rod-cut seated on the fuel rod-cut seating unit 21 to push it into the cutting module 40. The pressed fuel rod-cut is separated into hull pieces and pellets of the cladding tube while passing through the cutting module 40. The separated hull pieces and pellets are collected in the collecting box 400. Since the collecting box 400 is configured to have three stages consisting of the mesh of 7 mm size, the mesh of 5 mm size and the mesh of 1 mm size in order from the top, the hull pieces and pellets are separated by size of the mesh as the collecting box 400 vibrates. The hull pieces and pellets that pass through the bottom mesh of 1 mm size are put into a container and delivered to a recovering process. Pursuant to the mechanical decladder 1 for the spent nuclear fuel rod-cut according to the embodiment of the present disclosure, the fuel rod-cuts in the basket 5 can be continuously loaded on the supporter 20 in conjunction with the operation of the hydraulic cylinder module 30. Further, since the cutting module 40 can be used alternately by rotating the rotatable housing module 50, it is possible to improve the durability of the blades 41 inside the cutting module 40. In addition, the opening 42a may be provided in the casing 42 of the cutting module 40 to prevent debris from accumulating in the cutting module 40. The control unit 500 can control the operation and the driving of the opening and closing unit 10, the hydraulic cylinder module 30, the cutting module 40, and the rotatable housing module 50. The control unit 500 may be implemented by a processing device including a microprocessor. The implementation manner is obvious to those skilled in the art, and thus a detailed description thereof will be omitted. While the present disclosure has been shown and described with respect to the embodiments, it will be understood by those skilled in the art that various changes and modifications may be made without departing from the scope of the present disclosure as defined in the following claims. This application claims priority to Korean Patent Application No. 10-2019-0047985, filed on Apr. 24, 2019, the entire contents of which are hereby incorporated herein by reference. |
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claims | 1. A fast reactor controlled with a reflector comprising:a reactor vessel accommodating therein a coolant;a reactor core disposed in the reactor vessel and immersed in the coolant; anda reflector that vertically moves for adjusting leakage of neutrons generated from the reactor core to control a reactivity of the reactor core, the reflector including a neutron reflecting part disposed on an outside of the reactor core in a vertically movable manner, and a cavity part positioned above the neutron reflecting part, the cavity part having a neutron reflecting ability lower than that of the coolant, said cavity part includes a frame, and a plurality of sealable containers of a box shape that are held in the frame;wherein the neutron reflecting part is formed of a plurality of metal plates that are stacked on each other,each of the metal plates has a plurality of coolant channels through which the coolant flows,and the number of the coolant channels in each of the metal plates per unit area increases from a side of the reactor vessel to a corresponding side of the reactor core. 2. The fast reactor controlled with the reflector according to claim 1, whereinthe frame is formed of a plurality of frame units, andthe respective frame units are connected to each other by a bolt. 3. The fast reactor controlled with the reflector according to claim 1, whereinthe respective sealable containers are fitted to the adjacent sealable containers to be vertically connected to each other, or are fitted in an intermediate rib of the frame to be vertically connected to each other. 4. The fast reactor controlled with the reflector according to claim 1, whereina resilient member(s) is (are) disposed between an upper end of the uppermost sealable container in the frame and an upper end of the frame, and/or between a lower end of the lowermost sealable container in the frame and a lower end of the frame. 5. The fast reactor controlled with the reflector according to claim 1, whereina reflector drive unit is connected to an upper portion of the cavity part via a universal joint and a drive shaft, andthe neutron reflecting part is connected to the cavity part via a universal joint. 6. The fast reactor controlled with the reflector according to claim 1, whereina gap is formed between the neutron reflecting part and the cavity part. 7. The fast reactor controlled with the reflector according to claim 1, whereina volume of the neutron reflecting part excluding the coolant channels is between 80% and 95% of a total volume of the neutron reflecting part. 8. The fast reactor controlled with the reflector according to claim 1, whereina volume of a structural member constituting the cavity part is not less than 10% of a total volume of the cavity part. |
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description | This application is a continuation of U.S. application Ser. No. 09/786,507, filed May 1, 2001, now abandoned which is the U.S. national phase of international application PCT/GB99/02943 filed 6 Sep. 1999, designating the U.S. and claiming priority from GB 9819504.3, filed 7 Sep. 1998, the entire contents of each of which are hereby incorporated by reference. The present invention relates to the generation of electromagnetic radiation and, more particularly, to an apparatus and method of generating focused pulses of electromagnetic radiation over a wide range of frequencies. More particularly it relates to an apparatus and method for generating pulses of non-spherically decaying electromagnetic radiation. The present apparatus and method are based on the emission of electromagnetic radiation by rapidly varying polarisation or magnetisation current distributions rather than by conduction or convection electric currents. Such currents can have distribution patterns that move with arbitrary speeds (including speeds exceeding the speed of light in vacuo), and so can radiate more intensely over a much wider range of frequencies than their conventional counterparts. The spectrum of the radiation they generate could extend to frequencies that are by many orders of magnitude higher than the characteristic frequency of the fluctuations of the source itself. Furthermore, intensities of normal emissions decay at a rate of R−2, where R is the distance from the source. It has been noted, however, that the intensities of certain pulses of electromagnetic radiation can decay spatially at a lower rate than that predicted by this inverse square law (see Myers et al., Phys. World, November 1990, p. 39). The new solution of Maxwell's equations set out below, for example, predicts that the electromagnetic radiation emitted from superluminally, circularly moving charged patterns decays at a rate of R−1. Another example is the electromagnetic radiation emitted from superluminally, rectilinearly moving charged patterns which decays at a rate of R - 2 3 . This emission process can be exploited, moreover, to generate waves which do not form themselves into a focused pulse until they arrive at their intended destination and which subsequently remain in focus only for an adjustable interval of time. It will be widely appreciated that being able to employ such emissions for signal transmission, amongst other applications, would have significant commercial value, given that it would enable the employment of lower power transmitters and/or larger transmission ranges, the use of signals that cannot be intercepted by third parties, and the exploitation of higher bandwidth. The near-field component of the radiation in question has many features in common with, and so can be used as an alternative to, synchrotron radiation. The present invention provides a method and apparatus for generating such emissions. According to the present invention there is provided an apparatus for generating electromagnetic radiation comprising: a polarizable or magnetizable medium; and means of generating, in a controlled manner, a polarisation or magnetisation current with a rapidly moving, accelerating distribution pattern such that the moving source in question generates electromagnetic radiation. The speed of the moving distribution pattern may be superluminal so that the apparatus generates both a non-spherically decaying component and an intense spherically decaying component of electromagnetic radiation. The apparatus may comprise a dielectric substrate, a plurality of tightly packed electrodes positioned adjacent to the substrate, and the means for applying a voltage to the electrodes sequentially at a rate sufficient to induce a polarised region in the substrate whose distribution pattern moves along the substrate with a speed exceeding the speed of light. The dielectric substrate may have either a rectilinear or a circular shape. The wavelength of the generated electromagnetic radiation may be in any range from the radio to a minimum determined only by the lower limit to the acceleration of the source (potentially optical, ultraviolet or even x-ray). Prior to description of the invention, it is appropriate to discuss the principles underlying it. Bolotovskii and Ginzburg (Soviet Phys. Usp. 15, 184, 1972) and Bolotovskii and Bykov (Sovet Phys. Usp. 33, 477, 1990) have shown that the coordinated motion of aggregates of charged particles can give rise to extended electric charges and currents whose distribution patterns propagate with a phase speed exceeding the speed of light in vacuo and that, once created, such propagating charged patterns act as sources of the electromagnetic fields in precisely the same way as any other moving sources of these fields. That distribution patterns of these sources travel faster than light is not, of course, in any way incompatible with the requirements of special relativity. The superluminally moving pattern is created by the coordinated motion of aggregates of subluminally moving particles. We have solved Maxwell's equations for the electromagnetic field that is generated by an extended source distribution pattern of this type in the case where the charged pattern rotates about a fixed axis with a constant angular frequency. There are solutions of the homogeneous wave equation referred to, inter alia, as non-diffracting radiation beams, focus wave modes or electromagnetic missiles, which describe signals that propagate through space with unexpectedly slow rates of decay or spreading. The potential practical significance of such signals is clearly enormous. The search for physically realizable sources of them, however, has so far remained unsuccessful. Our calculation pinpoints a concrete example of the sources that are currently looked for in this field by establishing a physically tenable inhomogeneous solution of Maxwell's equations with the same characteristics. Investigation of the present emission process was originally motivated by the observational data on pulsars. The radiation received from these celestial sources of radio waves consists of highly coherent pulses (with as high a brightness temperature as 1030° K) which recur periodically (with stable periods of the order of 1 sec). The intense magnetic field (˜1012 G) of the central neutron star in a pulsar affects a coupling between the rotation of this star and that of the distribution pattern of the plasma surrounding it, so that the magnetospheric charges and currents in these objects are of the same type as those described above. The effect responsible for the extreme degree of coherence of the observed emission from pulsars, therefore, may well be the violation of the inverse square law that is here predicted by our calculation. The present analysis is relevant also to the mathematically similar problem of the generation of acoustic radiation by supersonic propellers and helicopter rotors, although this is not discussed in detail here. We begin by considering the waves that are emitted by an element of the distribution pattern of the superluminally rotating source from the standpoint of geometrical optics. Next, we calculate the amplitudes of these waves, i.e. the Green's function for the problem, from the retarded potential. We then specify the bifurcation surface of the observer and proceed to calculate the electromanetic radiation arising from an extended source with a superluminally moving distribution pattern. The singularities of the integrands of the radiation integrals that occur on the bifurcation surface are here handled by means of the theory of generalised functions: the electric and magnetic fields are given by the Hadamard's finite parts of the divergent integrals that result from differentiating the retarded potential under the integral sign. The theory is then concluded with a descriptive account of the analysed emission process in more physical terms, the description of examples of the apparatus, and an outline of the applications of the invention. Consider a point source (an element of the propagating distribution pattern of a volume source) which moves on a circle of radius r with the constant angular velocity ωêz, i.e. whose path x(t) is given, in terms of the cylindrical polar coordinates (r, φ, z), byr=const., z=const., φ={circumflex over (φ)}+ωt, (1)where êz is the basis vector associated with z, and {circumflex over (φ)} the initial value of φ. The wave fronts that are emitted by this point source in an empty and unbounded space are described by|xP−x(t)|=c(tP−t), (2)where the constant c denotes the wave speed, and the coordinates (xP, tP)=(rP, φP, zP, tP) mark the spacetime of observation points. The distance R between the observation point xp and a source point x is given by x P - x ≡ R ( φ ) = [ ( z P - z ) 2 + r P 2 + r 2 - 2 r P r cos ( φ P - φ ) ] 1 2 , ( 3 ) so that inserting (1) in (2) we obtain R ( t ) ≡ [ ( z P - z ) 2 + r P 2 + r 2 - 2 r P r cos ( φ P - φ ^ - ω t ) ] 1 2 = c ( t P - t ) . ( 4 ) These wave fronts are expanding spheres of radii c(tP−t) whose fixed centres (rP=r, φP={circumflex over (φ)}+ωt, zP=z) depend on their emission times t (see FIG. 1). Introducing the natural length scale of the problem, c/ω, and using t=(φ−{circumflex over (φ)})/ω to eliminate t in favour of φ, we can express (4) in terms of dimensionless variables asg≡φ−φP+{circumflex over (R)}(φ)=Φ, (5)in which {circumflex over (R)}≡Rω/c, andΦ≡{circumflex over (φ)}−{circumflex over (φ)}P (6)stands for the difference between the positions {circumflex over (φ)}=φ−ωt of the source point and {circumflex over (φ)}P≡φP−ωtP of the observation point in the (r, {circumflex over (φ)}, z)-space. The Lagrangian coordinate {circumflex over (φ)}in (5) lies within an interval of length 2π (e.g. −π<{circumflex over (φ)}≦π), while the angle φ, which denotes the azimuthal position of the source point at the retarded time t, ranges over (−∞, ∞). FIG. 1 depicts the wave fronts described by (5) for fixed values of (r, {circumflex over (φ)}, z) and of Φ (or tP), and a discrete set of values of φ (or t). [In this figure, the heavier curves show the cross section of the envelope with the plane of the orbit of the source distribution pattern. The larger of the two dotted circles designates the orbit (at r=3c/ω) and the smaller the light cylinder (rP=c/ω).] These wave fronts possess an envelope because when r>c/ω, and so the speed of the source distribution pattern exceeds the wave speed, several wave fronts with differing emission times can pass through a single observation point simultaneously. Or stated mathematically, for certain values of the coordinates (rP, {circumflex over (φ)}P, zP; r, z) the function g(φ) shown in FIG. 2 is oscillatory and so can equal Φ at more than one value of the retarded position φ: a horizontal line Φ=constant intersects the curve (a) in FIG. 2 at either one or three points. [FIG. 2 is drawn for φP=0, {circumflex over (r)}P=3, {circumflex over (r)}=2 and (a) {circumflex over (z)}={circumflex over (z)}P, inside the envelope, (b) {circumflex over (z)}={circumflex over (z)}c, on the cusp curve of the envelope, (c) {circumflex over (z)}=2{circumflex over (z)}P, outside the envelope. The marked adjacent turning points of curve (a) have the coordinates (φ±, Φ±), and φout represents the solution of g(φ)=φ0 for a φ0 that tends to Φ− from below.] Wave fronts become tangent to one another and so form an envelope at those points (rP, {circumflex over (φ)}P, zP) for which two roots of g(φ)=Φ coincide. The equation describing this envelope can therefore be obtained by eliminating φ between g=φ and ∂g/∂φ=0. Thus, the values of φ on the envelope of the wave fronts are given by∂g/∂φ=1−{circumflex over (r)}{circumflex over (r)}P sin(φP−φ)/{circumflex over (R)}(φ)=0. (7)When the curve representing g(φ) is as in FIG. 2(a) (i.e. {circumflex over (r)}>1 and Δ>0), this equation has the doubly infinite set of solutions φ=φ±+2nπ, where φ ± = φ P + 2 π - arc cos [ ( 1 ∓ Δ 1 2 ) / ( r ^ r ^ P ) ] , ( 8 ) Δ ≡ ( r ^ P 2 - 1 ) ( r ^ 2 - 1 ) - ( z ^ - z ^ P ) 2 , ( 9 ) n is an integer, and ({circumflex over (r)}, {circumflex over (z)}; {circumflex over (r)}P, {circumflex over (z)}P) stand for the dimensionless coordinates rω/c, zω/c, rPω/c and zPω/c, respectively. The function g(φ) is locally maximum at φ++2nπ and minimum at φ−+2nπ. Inserting φ=φ± in (5) and solving the resulting equation for Φas a function of ({circumflex over (r)}P, {circumflex over (z)}P), we find that the envelope of the wave fronts is composed of two sheets: ϕ = ϕ ± ≡ g ( φ ± ) = 2 π - arc cos [ ( 1 ∓ Δ 1 2 ) / ( r ^ r ^ P ) ] + R ^ ± , in which ( 10 ) R ^ ± ≡ [ ( z ^ - z ^ P ) 2 + r ^ 2 + r ^ P 2 - 2 ( 1 ∓ Δ 1 2 ) ] 1 2 ( 11 ) in whichare the values of {circumflex over (R)}at φ=φ±. For a fixed source point (r, {circumflex over (φ)}, z), equation (10) describes a tube-like spiralling surface in the (rP, {circumflex over (φ)}P, zP)-space of observation points that extends from the speed-of-light cylinder {circumflex over (r)}P=1 to infinity. [A three-dimensional view of the light cylinder and the envelope of the wave fronts for the same source point (S) as that in FIG. 1 is presented in FIG. 3(a) (only those parts of these surfaces are shown which lie within the cylindrical volume {circumflex over (r)}P≦9 , −2.25≦{circumflex over (z)}P−{circumflex over (z)}≦2.25).] The two sheets Φ=Φ± of this envelope meet at a cusp. The cusp occurs along the curve ϕ = 2 π - arc cos [ 1 / ( r ^ r ^ P ) ] + ( r ^ P 2 r ^ 2 - 1 ) 1 2 ≡ ϕ c , ( 12 a ) z ^ = z ^ P ± ( r ^ P 2 - 1 ) 1 2 ( r ^ 2 - 1 ) 1 2 ≡ z ^ c , ( 12 b ) shown in FIG. 4 and constitutues the locus of points at which three different wave fronts intersect tangentially. [FIG. 4 depicts the segment −15≦{circumflex over (z)}P−{circumflex over (z)}≦15 of the cusp curve of the envelope shown in FIG. 3(a). This curve touches—and is tangent to—the light cylinder at the point ({circumflex over (r)}P=1, {circumflex over (z)}P={circumflex over (z)}, Φ=Φc|{circumflex over (r)}P=1) on the plane of the orbit.] On the cusp curve Φ=Φc, z=zc, the function g(φ) has a point of inflection [FIG. 2(b)] and ∂2g/∂φ2, as well as ∂g/∂φ and g, vanish atφ=φP+2π−arc cos[1/({circumflex over (r)}{circumflex over (r)}P)]≡φc. (12c)This, in conjunction with t=(φ−{circumflex over (φ)})/ω, represents the common emission time of the three wave fronts that are mutually tangential at the cusp curve of the envelope. In the highly superluminal regime, where {circumflex over (r)}>>1, the separation of the ordinates Φ+ and Φ− of adjacent maxima and minima in FIG. 2(a) can be greater than 2π. A horizontal line Φ=constant will then intersect the curve representing g(φ) at more than three points, and so give rise to simultaneously received contributions that are made at 5, 7, . . . , distinct values of the retarded time. In such cases, the sheet Φ− of the envelope (issuing from the conical apex of this surface) undergoes a number of intersections with the sheet Φ+ before reaching the cusp curve. We shall be concerned in this paper, however, mainly with source elements whose distances from the rotation axis do not appreciably exceed the radius c/ω of the speed-of-light cylinder and so for which the equation g(φ)=Φ has at most three solutions. At points of tangency of their fronts, the waves which interfere constructively to form the envelope propagate normal to the sheets Φ=Φ±(rP, zP) of this surface, in the directions n ^ ± ≡ ( c / ω ) ∇ P ( ϕ ± - ϕ ) = e ^ r P [ r ^ P - r ^ P - 1 ( 1 ∓ Δ 1 2 ) ] / R ^ ± + e ^ φ P / r ^ P + e ^ z P ( z ^ P - z ^ ) / R ^ ± , ( 13 ) with the speed c. (êrP, ê100 P and êzP are the unit vectors associated with the cylindrical coordinates rP, φP and zP of the observation point, respectively.) Nevertheless, the resulting envelope is a rigidly rotating surface whose shape does not change with time: in the (rP, {circumflex over (φ)}P, zP)-space, its conical apex is stationary at (r, {circumflex over (φ)}, z), and its form and dimensions only depend on the constant parameter {circumflex over (r)}. The set of waves that superpose coherently to form a particular section of the envelope or its cusp, therefore, cannot be the same (i.e. cannot have the same emission times) at different observation times. The packet of focused waves constituting any given segment of the cusp curve of the envelope, for instance, is constantly dispersed and reconstructed out of other waves. This one-dimensional caustic would not be unlimited in its extent, as shown in FIG. 4, unless the source distribution pattern is infinitely long-lived: only then would the duration of the source distribution pattern encompass the required intervals of emission time for every one of its constituent segments. Our discussion has been restricted so far to the geometrical features of the emitted wave fronts. In this section we proceed to find the Lienard-Wiechert potential for these waves. The scalar potential arising from a volume element of the moving distribution pattern of the source we have been considering is given by the retarded solution of the wave equation∇′2G0−∂2G0/∂(ct′)2=−4πρ0, (14a)in whichρ0(r′, φ′, z′, t′)=δ(r′−r)δ(φ′−ωt′−{circumflex over (φ)})δ(z′−z)/r′ (14b)is the density of a point source of unit strength with the trajectory (1). In the absence of boundaries, therefore, this potential has the value G 0 ( x P , t P ) = ∫ ⅆ 3 x ′ ⅆ t ′ ρ 0 ( x ′ , t ′ ) δ ( 15 a ) ( t P - t ′ - x P - x ′ / c ) / x P - x ′ = ∫ - ∞ + ∞ ⅆ t ′ δ [ t P - t ′ - R ( t ′ ) / c ] R ( t ′ ) , ( 15 b ) where R(t′) is the function defined in (4) (see e.g. Jackson, Classical Electrodynamics, Wiley, New York 1975). If we use (1) to change the integration variable t′ in (15b) to φ, and express the resulting integrand in terms of the quantities introduced in (3), (5) and (6), we arrive atG0(r, rP, {circumflex over (φ)}−{circumflex over (φ)}P, z−zP)=∫−∞+∞dφδ[g(φ)−Φ]/R(φ). (16)This can then be rewritten, by formally evaluating the integral, as G 0 = ∑ φ = φ j 1 R ∂ g ∂ φ , ( 17 ) where the angles φj are the solutions of the transcendental equation g(φ)=Φ in −∞<φ<+∞ and correspond, in conjunction with (1), to the retarded times at which the source point (r, {circumflex over (φ)}, z) makes its contribution towards the value of G0 at the observation point (rP, {circumflex over (φ)}P, zP). Equation (17) shows, in the light of FIG. 2, that the potential G0 of a point source is discontinuous on the envelope of the wave fronts: if we approach the envelope from outside, the sum in (17) has only a single term and yields a finite value for G0, but if we approach this surface from inside, two of the Φjs coalesce at an extremum of g and (17) yields a divergent value for G0. Approaching the sheet Φ=Φ+ or Φ=Φ− of the envelope from inside this surface corresponds, in FIG. 2, to raising or lowering a horizontal line Φ=Φ0=const., with Φ−≦Φ0≦Φ+, until it intersects the curve (a) of this figure at its maximum or minimum tangentially. At an observation point thus approached, the sum in (17) has three terms, two of which tend to infinity. On the other hand, approaching a neighbouring observation point just outside the sheet Φ=Φ− (say) of the envelope corresponds, in FIG. 2, to raising a horizontal line Φ=Φ0=const., with Φ0≦Φ−, towards a limiting position in which it tends to touch curve (a) at its minimum. So long as it has not yet reached the limit, such a line intersects curve (a) at one point only. The equation g(φ)=Φ therefore has only a single solution φ=φout in this case which is different from both φ+ and φ− and so at which ∂g/∂φ is non-zero (see FIG. 2). The contribution that the source distribution pattern makes when located at φ=φout is received by both observers, but the constructively interfering waves that are emitted at the two retarded positions approaching φ− only reach the observer inside the envelope. The function G0 has an even stronger singularity at the cusp curve of the envelope. On this curve, all three of the φjs coalesce [FIG. 2(b)] and each denominator in the expression in (17) both vanishes and has a vanishing derivative (∂g/∂φ=∂2g/∂φ2=0). There is a standard asymptotic technique for evaluating radiation integrals with coalescing critical points that describe caustics. By applying this technique—which we have outlined in Appendix A—to the integral in (16), we can obtain a uniform asymptotic approximation to G0 for small |Φ+−Φ−|, i.e. for points close to the cusp curve of the envelope where G0 is most singular. The result is G 0 in ∼ 2 c 1 - 2 ( 1 - χ 2 ) - 1 2 [ p 0 cos ( 1 3 arc sin χ ) - c 1 q 0 sin ( 2 3 arc sin χ ) ] , χ < 1 , and ( 18 ) G 0 out ∼ c 1 - 2 ( χ 2 - 1 ) - 1 2 [ p 0 sinh ( 1 3 arc cosh χ ) + c 1 q 0 sgn ( χ ) sinh ( 2 3 arc cosh χ ) ] , χ > 1 , ( 19 ) where c1, p0, q0 and χ are the functions of (r, z) defined in (A2), (A5), (A6) and (A10), and approximated in (A23)-(A30). The superscripts ‘in’ and ‘out’ designate the values of G0 inside and outside the envelope, and the variable χ equals +1 and −1 on the sheets Φ=Φ+ and Φ=Φ− of this surface, respectively. The function G0out is indeterminate but finite on the envelope [cf. (A39)], whereas G0in diverges like 3 c 1 - 2 ( p 0 ∓ c 1 q 0 ) / ( 1 - χ 2 ) 1 2 as χ → ± 1. The singularity structure of G0in close to the cusp curve is explicitly exhibited by G 0 in ∼ 2 3 1 6 ( ω / c ) ( r ^ 2 r ^ P 2 - 1 ) - 1 2 c 0 1 2 ( z ^ c - z ^ ) 1 2 / [ c 0 3 ( z ^ c - z ^ ) 3 - ( ϕ c - ϕ ) 2 ] 1 2 , in which 0 ≤ z ^ c - z ^ ⪡ 1 , ϕ c - ϕ ⪡ 1 and ( 20 ) c 0 ≡ 2 3 2 3 ( r ^ 2 r ^ P 2 - 1 ) - 1 ( r ^ P 2 - 1 ) 1 2 ( r ^ 2 - 1 ) 1 2 ( 21 ) [see (18) and (A22)-(A26)]. It can be seen from this expression that both the singularity on the envelope (at which the quantity inside the square brackets vanishes) and the singularity at the cusp curve (at which {circumflex over (z)}c−{circumflex over (z)} and Φc−Φ vanish) are integrable singularities. The potential of a volume source, which is given by the superposition of the potentials G0 of its constituent volume elements, and so involves integrations with respect to (r, {circumflex over (φ)}, z), is therefore finite. Since they are created by the coordinated motion of aggregates of particles, the types of source distribution patterns we have been considering cannot, of course, be point-like. It is only in the physically unrealizable case where the distribution pattern of a superluminal source is point-like that its potential has the extended singularities described above. In fact, not only is the potential of an extended source with a superluminally moving distribution pattern singularity free, but it decays in the far zone like the potential of any other source. The following alternative form of the retarded solution to the wave equation ∇2A0−∂2A0/∂(ct)2=−4πρ [which may be obtained from (15a) by performing the integration with respect to time]:A0=∫d3xρ(x, tP−|x−xP|/c)/|x−xP| (22)shows that if the density ρ of the source is finite and vanishes outside a finite volume, then the potential A0 decays like |xP|−1 as the distance |xP−x|≃|xP| of the observer from the source tends to infinity. Let us now consider an extended source distribution pattern which rotates about the z-axis with the constant angular frequency ω. The density of such a source—when it has a distribution with an unchanging pattern—is given byρ(r, φ, z, t)=ρ(r, {circumflex over (φ)}, z), (23)where the Lagrangian variable {circumflex over (φ)} is defined by φ−ωt as in (1), and ρ can be any function of (r, {circumflex over (φ)}, z) that vanishes outside a finite volume. If we insert this density in the expression for the retarded scalar potential and change the variables of integration from (r, φ, z, t) to (r, {circumflex over (φ)}, z, t), we obtain A 0 ( x P , t P ) = ∫ ⅆ 3 x ⅆ t ρ ( x , t ) δ ( t P - t - x - x P / c ) / x - x P ( 24 a ) = ∫ r ⅆ r ⅆ φ ^ ⅆ z ρ ( r , φ ^ , z ) G 0 ( r , r P , φ ^ - φ ^ P , z - z P ) , ( 24 b ) where G0 is the function defined in (16) which represents the scalar potential of a corresponding point source. That the potential of the extended source distribution pattern in question is given by the superposition of the potentials of the moving source points that constitute the distribution pattern is an advantage that is gained by marking the space of source points with the natural coordinates (r, {circumflex over (φ)}, z) of the source distribution pattern. This advantage is lost if we use any other coordinates. In Sec. II, where the distribution pattern of the source was point-like, the coordinates (r, {circumflex over (φ)}, z) of the source point in G0(r, rP, {circumflex over (φ)}−{circumflex over (φ)}P, z−zP) were held fixed and we were concerned with the behaviour of this potential as a function of the coordinates (rP, {circumflex over (φ)}P, zP) of the observation point. When we superpose the potentials of the volume elements that constitute an extended source distribution pattern, on the other hand, the coordinates (rP, {circumflex over (φ)}P, zP) are held fixed and we are primarily concerned with the behaviour of G0 as a function of the integration variables (r, {circumflex over (φ)}, z). Because G0 is invariant under the interchange of (r, {circumflex over (φ)}, z) and (rP, {circumflex over (φ)}P, zP) if Φ is at the same time changed to −Φ [see (5) and (16)], the singularity of G0 occurs on a surface in the (r, {circumflex over (φ)}, z)-space of source points which has the same shape as the envelope shown in FIG. 3(a) but issues from the fixed point (rP, {circumflex over (φ)}P, zP) and spirals around the z-axis in the opposite direction to the envelope. [FIG. 5 in which the light cylinder and the bifurcation surface associated with the observation point P are shown for a counterclockwise motion of the source distribution pattern. In this figure P is located at {circumflex over (r)}P=9, and only those parts of these surfaces are shown which lie within the cylindrical volume {circumflex over (r)}≦11, −1.5≦{circumflex over (z)}−{circumflex over (z)}P≦1.5. The two sheets Φ=Φ±(r, z) of the bifurcation surface meet along a cusp (a curve of the same shape as that shown in FIG. 4) that is tangent to the light cylinder. For an observation point in the far zone ({circumflex over (r)}P>>1), the spiralling surface that issues from P undergoes a large number of turns-in which its two sheets intersect one another—before reaching the light cylinder.] In this paper, we refer to this locus of singularities of G0 as the bifurcation surface of the observation point P. Consider an observation point P for which the bifurcation surface intersects the source distribution pattern, as in FIG. 6. [In FIG. 6, the full curves depict the cross section, with the cylinder {circumflex over (r)}=1.5, of the bifurcation surface of an observer located at {circumflex over (r)}P=3. (The motion of the source distribution pattern is counterclockwise.) Projection of the cusp curve of this bifurcation surface onto the cylinder {circumflex over (r)}=1.5 is shown as a dotted curve, and the region occupied by the source distribution pattern as a dotted area. In this figure the observer's position is such that one of the points (Φ=Φc, z=zc) at which the cusp curve in question intersects the cylinder {circumflex over (r)}=1.5—the one with zc>0—is located within the source distribution pattern. As the radial position rP of the observation point tends to infinity, the separation—at a finite distance zc−z from (Φc, zc)—of the shown cross sections decreases like r P - 3 2 . ] The envelope of the wave fronts emanating from a volume element of the part of the source distribution pattern that lies within this bifurcation surface encloses the point P, but P is exterior to the envelope associated with an element of the source distribution pattern that lies outside the bifurcation surface. We have seen that three wave fronts—propagating in different directions—simultaneously pass an observer who is located inside the envelope of the waves emanating from a point source, and only one wavefront passes an observer outside this surface. Hence, in contrast to the elements of the source distribution pattern outside the bifurcation surface which influence the potential at P at only a single value of the retarded time, this potential receives contributions from each of the elements inside the bifurcation surface at three distinct values of the retarded time. The elements of the source distribution pattern inside but adjacent to the bifurcation surface, for which G0 diverges, are sources of the constructively interfering waves that not only arrive at P simultaneously but also are emitted at the same (retarded) time. These elements of the source distribution pattern approach the observer along the radiation direction xP−x with the wave speed at the retarded time, i.e. are located at distances R(t) from the observer for which ⅆ R ⅆ t t = t P - R / c = - c ( 25 ) [see (4), (7) and (8)]. Their accelerations at the retarded time, ⅆ 2 R ⅆ t 2 t = t P - R / c = ∓ c ω Δ 1 2 R ^ ± , ( 26 ) are positive on the sheet Φ=Φ− of the bifurcation surface and negative on Φ=Φ+. The elements of the source distribution pattern on the cusp curve of the bifurcation surface, for which Δ=0 and all three of the contributing retarded times coincide, approach the observer—according to (26)—with zero acceleration as well as with the wave speed. From a radiative point of view, the most effective volume elements of the distribution pattern of the superluminal source in question are those that approach the observer along the radiation direction with the wave speed and zero acceleration at the retarded time, since the ratio of the emission to reception time intervals for the waves that are generated by these particular elements of the source distribution pattern generally exceeds unity by several orders of magnitude. On each constituent ring of the source distribution pattern that lies outside the light cylinder (r=c/ω) in a plane of rotation containing the observation point, there are two volume elements that approach the observer with the wave speed at the retarded time: one whose distance from the observer diminishes with positive acceleration, and another for which this acceleration is negative. These two elements are closer to one another the smaller the radius of the ring. For the smallest of such constituent rings, i.e. for the one that lies on the light cylinder, the two volume elements in question coincide and approach the observer also with zero acceleration. The other constituent rings of the source distribution pattern (those on the planes of rotation which do not pass through the observation point) likewise contain two such elements if their radii are large enough for their velocity rωeφ to have a component along the radiation direction equal to c. On the smallest possible ring in each plane, there is again a single volume element—at the limiting position of the two coalescing volume elements of the neighbouring larger rings—that moves towards the observer not only with the wave speed but also with zero acceleration. For any given observation point P, the efficiently radiating pairs of volume elements on various constituent rings of the source distribution pattern collectively form a surface: the part of the bifurcation surface associated with P which intersects the source distribution pattern. The locus of the coincident pairs of volume elements, which is tangent to the light cylinder at the point where it crosses the plane of rotation containing the observer, constitutes the segment of the cusp curve of this bifurcation surface that lies within the source distribution pattern. Thus the bifurcation surface associated with any given observation point divides the volume of the source distribution pattern into two sets of elements with differing influences on the observed field. As in (18) and (19), the potentials G0in and G0out of the source distribution pattern's elements inside and outside the bifurcation surface have different forms: the boundary |χ(r, rP, {circumflex over (φ)}−{circumflex over (φ)}P, z−zP)|=1 between the domains of validity of (18) and (19) delineates the envelope of wave fronts when the source point (r, {circumflex over (φ)}, z) is fixed and the coordinates (rP, {circumflex over (φ)}P, zP) of the observation point are variable, and describes the bifurcation surface when the observation point (rP, {circumflex over (φ)}P, zP) is fixed and the coordinates (r, {circumflex over (φ)}, z) of the source point sweep a volume. The expression (24b) for the scalar potential correspondingly splits into the following two terms when the observation point is such that the bifurcation surface intersects the source distribution pattern: A 0 = ∫ ⅆ V ρ G 0 ( 27 a ) = ∫ V in ⅆ V ρ G 0 in + ∫ V out ⅆ V ρ G 0 out , ( 27 b ) where dV≡rdrd{circumflex over (φ)}dz, Vin and Vout designate the portions of the source distribution pattern which fall inside and outside the bifurcation surface (see FIG. 6), and G0in and G0out denote the different expressions for G0 in these two regions. Note that the boundaries of the volume Vin depend on the position (rP, {circumflex over (φ)}P, zP) of the observer: the parameter {circumflex over (r)}P fixes the shape and size of the bifurcation surface, and the position (rP, {circumflex over (φ)}P, zP) of the observer specifies the location of the conical apex of this surface. When the observation point is such that the cusp curve of the bifurcation surface intersects the source distribution pattern, the volume Vin is bounded by Φ=Φ−, Φ=Φ+, and the part of the boundary ρ(r, {circumflex over (φ)}, z)=0 of the distribution pattern that falls within the bifurcation surface. The corresponding volume Vout is bounded by the same patches of the two sheets of the bifurcation surface and by the remainder of the boundary of the source distribution pattern. In the vicinity of the cusp curve (12), i.e. for |Φc−Φ|<<1 and 0≦{circumflex over (z)}c−{circumflex over (z)}<<1, the cross section of the bifurcation surface with a cylinder {circumflex over (r)}=constant is described by ϕ ± - ϕ c ≃ ( r ^ 2 - 1 ) 1 2 ( r ^ P 2 - 1 ) 1 2 ( r ^ 2 r ^ P 2 - 1 ) - 1 2 ( z ^ c - z ^ ) ± 2 3 2 3 ( r ^ 2 - 1 ) 3 4 ( r ^ P 2 - 1 ) 3 4 ( r ^ P 2 r ^ 2 - 1 ) - 3 2 ( z ^ c - z ^ ) 3 2 ( 28 ) [see (10)-(12) and (A26)]. This cross section, which is shown in FIG. 6, has two branches meeting at the intersections of the cusp curve with the cylinder {circumflex over (r)}=constant whose separation in Φ—at a given ({circumflex over (z)}c−{circumflex over (z)})—diminishes like r ^ P - 3 2 in the limit {circumflex over (r)}P→∞. Thus, at finite distances {circumflex over (z)}c−{circumflex over (z)} from the cusp curve, the two sheets Φ=Φ− and Φ=Φ+ of the bifurcation surface coalesce and become coincident with the surface ϕ = 1 2 ( ϕ - + ϕ + ) ≡ c 2 as r ^ P → ∞ . That is to say, the volume Vin vanishes like r ^ P - 3 2 . Because the dominant contributions towards the value of the radiation field come from those source distribution pattern's elements that approach the observer—along the radiation direction—with the wave speed and zero acceleration at the retarded time, in what follows, we shall be primarily interested in far-field observers the cusp curves of whose bifurcation surfaces intersect the source distribution pattern. For such observers, the Green's function lim{circumflex over (r)}P→∞ G0 undergoes a jump discontinuity across the coalescing sheets of the bifurcation surface: the values of χ on the sheets Φ=Φ±, and hence the functions G0out|Φ=Φ− and G0out|Φ=Φ+, remain different even in the limit where Φ=Φ− and Φ=Φ+ coincide [cf. (A10) and (A39)]. A. Gradient of the Scalar Potential In this section we begin the calculation of the electric and magnetic fields by finding the gradient of the scalar potential A0, i.e. by calculating the derivatives of the integral in (27a) with respect to the coordinates (rP, φP, zP) of the observation point. If we regard its singular kernel G0 as a classical function, then the integral in (27a) is improper and cannot be differentiated under the integral sign without characterizing and duly handling the singularities of its integrand. On the other hand, if we regard G0 as a generalized function, then it would be mathematically permissible to interchange the orders of differentiation and integration when calculating ∇PA0. This interchange results in a new kernel ∇PG0 whose singularities are non-integrable. However, the theory of generalized functions prescribes a well-defined procedure for obtaining the physically relevant value of the resulting divergent integral, a procedure involving integration by parts which extracts the so-called Hadamard's finite part of this integral (see e.g. Hoskins, Generalised Functions, Ellis Horwood, London 1979). Hadamard's finite part of the divergent integral representing ∇PA0 yields the value that we would have obtained if we had first evaluated the original integral for A0 as an explicit function of (rP, {circumflex over (φ)}P, zP) and then differentiated it. From the standpoint of the theory of generalized functions, therefore, differentiation of (27a) yields∇PA0=∫dVρ∇PG0=(∇PA0)in+(∇PA0)out, (29a)in which(∇PA0)in,out≡∫Vin,outdVρ∇PG0in,out. (29b)Since ρ vanishes outside a finite volume, the integral in (27a) extends over all values of (r, {circumflex over (φ)}, z) and so there is no contribution from the limits of integration towards the derivative of this integral. The kernels ∇PG0in,out of the above integrals may be obtained from (16). Applying ∇P to the right-hand side of (16) and interchanging the orders of differentiation and integration, we obtain an integral representation of ∇PG0 consisting of two terms: one arising from the differentiation of R which decays like rP−2 as rP→∞ and so makes no contribution to the field in the radiation zone, and another that arises from the differentiation of the Dirac delta function and decays less rapidly than rP−2. For an observation point in the radiation zone, we may discard terms of the order of rP−2 and write∇PG0≃(ω/c)∫−∞+∞dφR−1δ′(g−Φ){circumflex over (n)}, {circumflex over (r)}P>>1, (30)in which δ′ is the derivative of the Dirac delta function with respect to its argument and{circumflex over (n)}≡êrP[{circumflex over (r)}P−{circumflex over (r)} cos(φ−φP)]/{circumflex over (R)}+êφP/{circumflex over (r)}P+êzP({circumflex over (z)}P−{circumflex over (z)})/{circumflex over (R)}. (31)Equation (30) yields ∇PG0in or ∇PG0out depending on whether Φ lies within the interval (Φ−, Φ+) or outside it. If we now insert (30) in (29b) and perform the integrations with respect to {circumflex over (φ)} by parts, we find that(∇PA0)in≃(ω/c)∫Srdrdz{−[ρG1in]Φ=Φ−Φ=Φ++∫Φ−Φ+dΦ∂ρ/∂{circumflex over (φ)}G1in}, {circumflex over (r)}P>>1, (32)and(∇PA0)out≃(ω/c)∫Srdrdz{[ρG1out]Φ=Φ−Φ=Φ++(∫−πΦ−+∫Φ++π)dΦ∂ρ/∂{circumflex over (φ)}G1out}, {circumflex over (r)}P>>1, (33)in which S stands for the projection of Vin onto the (r, z)-plane, and G1in and G1out are given by the values of G 1 ≡ ∫ - ∞ + ∞ ⅆ φ R - 1 δ ( g - ϕ ) n ^ = ∑ φ = φ j R - 1 ∂ g / ∂ φ - 1 n ^ ( 34 ) for Φ inside and outside the interval (Φ−, Φ+), respectively. Like G0in, the Green's function G1in diverges on the bifurcation surface Φ=Φ±, where ∂g/∂φ vanishes, but this singularity of G0in is integrable so that the value of the second integral in (32) is finite (see Sec. II and Appendix A). Hadamard's finite part of (∇PA0)in (denoted by the prefix Fp) is obtained by simply discarding those ‘integrated’ or boundary terms in (32) which diverge. Hence, the physically relevant quantity Fp{(∇PA0)in} consists—in the far zone—of the volume integral in (32). Let us choose an observation point for which the cusp curve of the bifurcation surface intersects the source distribution pattern (see FIG. 6). When the dimensions (˜L) of the source are negligibly smaller than those of the bifurcation surface (i.e. when L<<rP and so zc−z<<rP throughout the source distribution pattern) the functions G1in,out in (32) and (33) can be approximated by their asymptotic values (A34) and (A35) in the vicinity of the cusp curve (see Appendix A). According to (A34), (A36) and (A44), G1in decays like p1/c12=O(1) at points interior to the bifurcation surface where limRP→∞χ remains finite. Since the separation of the two sheets of the bifurcation surface diminishes like r ^ P - 3 2 within the source distribution pattern [see (28)], it therefore follows that the volume integral in (32) is of the order of 1 × r ^ P - 3 2 ,a result which can also be inferred from the far-field version of (A34) by explicit integration. Hence, Fp { ( ∇ p A 0 ) i n } = O ( r ^ P - 3 2 ) , r ^ P ⪢ 1 , ( 35 ) decays too rapidly to make any contribution towards the value of the electric field in the radiation zone. Because G1out is, in contrast to G1in, finite on the bifurcation surface, both the surface and the volume integrals on the right-hand side of (33) have finite values. Each component of the second term has the same structure as the expression for the potential itself and so decays like rP−1 (see the ultimate paragraph of Sec. II). But the first term—which would have cancelled the corresponding boundary term in (32) and so would not have survived in the expression for ∇PA0 had the Green's function G1 been continuous—behaves differently from any conventional contribution to a radiation field. Insertion of (A39) in (33) yields the following expression for the asymptotic value of this boundary term in the limit where the observer is located in the far zone and the source distribution pattern is localized about the cusp curve of his (her) bifurcation surface: ∫ r ⅆ r ⅆ z [ ρG 1 out ] ϕ - ϕ + ∼ 1 3 c 1 - 2 ∫ r ⅆ r ⅆ z [ p 1 ( ρ | ϕ + - ρ | ϕ - ) + 2 c 1 q 1 ( ρ | ϕ + + ρ | ϕ - ) ] . ( 36 ) In this limit, the two sheets of the bifurcation surface are essentially coincident throughout the domain of integration in (36) [see (28)]. So the difference between the values of the source density on these two sheets of the bifurcation surface is negligibly small ( ∼ r ^ P - 3 2 )for a smoothly distributed source pattern and the functions ρ|Φ± appearing in the integrand of (36) may correspondingly be approximated by their common limiting value ρbs(r, z) on these coalescing sheets. Once the functions ρ|Φ± are approximated by ρbs(r, z) and q1 by (A41), equation (36) yields an expression which can be written, to within the leading order in the far-field approximation {circumflex over (r)}P>>1 [see (A44) and (A45)], as ∫ S r ⅆ r dz [ ρG 1 out ] ϕ - ϕ + ∼ 2 3 2 ( c / ω ) 2 r ^ P - 3 2 ∫ r ^ < r ^ > ⅆ r ^ ( r ^ 2 - 1 ) - 1 4 n 1 × ∫ z ^ c - L z ^ ω / c z ^ c ⅆ z ^ ( z ^ c - z ^ ) - 1 2 ρ bs ( r , z ) ∼ 2 5 2 ( c / ω ) 2 r ^ P - 3 2 ∫ r ^ < r ^ > ⅆ r ^ ( r ^ 2 - 1 ) - 1 4 n 1 ( L z ^ ω / c ) 1 2 〈 ρ bs 〉 , ( 37 ) with 〈 ρ bs 〉 ( r ) ≡ ∫ 0 1 ⅆ ηρ bs ( r , z ) | z = z c - η 2 L z ^ , ( 38 ) where zc−L{circumflex over (z)}(r)≦z≦zc and r<≦r≦r> are the intervals over which the bifurcation surface intersects the source distribution pattern (see FIG. 6). The quantity (ρbs)(r) may be interpreted, at any given r, as a weighted average—over the intersection of the coalescing sheets of the bifurcation surface with the plane z=zc−η2L{circumflex over (z)}—of the source density ρ. The right-hand side of (37) decays like r P - 3 2 as rP→∞. The second term in (33) thus dominates the first term in this equation, and so the quantity (∇PA0)out itself decays like rP−1 in the far zone. B. Time Derivative of the Vector Potential Inasmuch as the charge density (23) has an unchanging distribution pattern in the (r, {circumflex over (φ)}, z)-frame, the electric current density associated with the moving source distribution pattern we have been considering is given byj(x, t)=rωρ(r, {circumflex over (φ)}, z)êφ, (39)in which rωêφ=rω[−sin(φ−φP)êrP+cos(φ−φP)êφP] is the velocity of the element of the source distribution pattern that is located at (r, φ, z). This current satisfies the continuity equation ∂ρ/∂(ct)+∇·j=0 automatically. In the Lorentz gauge, the retarded vector potential corresponding to (24a) has the formA(xP, tP)=c−1∫d3xdtj(x, t)δ(tP−t−|x−xP|/c)/|x−xP|. (40)If we insert (39) in (40) and change the variables of integration from (r, φ, z, t) to (r, φz, {circumflex over (φ)}), as in (24), we obtainA=∫dV{circumflex over (r)}ρ(r, {circumflex over (φ)}, z)G2(r, rP, {circumflex over (φ)}−{circumflex over (φ)}P, z−zP) (41)in which dV=rdrd{circumflex over (φ)}dz, the vector G2—which plays the role of a Green's function—is given by G 2 ≡ ∫ - ∞ + ∞ ⅆ φ e ^ φ δ [ g ( φ ) - ϕ ] / R ( φ ) = ∑ φ = φ j R - 1 ∂ g / ∂ φ - 1 e ^ φ , ( 42 ) and g and φjs are the same quantities as those appearing in (17) (see also FIG. 2). Because (17), (34) and (42) have the factor |∂g/∂φ|−1 in common, the function G2 has the same singularity structure as those of G0 and G1: it diverges on the bifurcation surface ∂g/∂φ=0 if this surface is approached from inside, and it is most singular on the cusp curve of the bifurcation surface where in addition ∂2g/∂φ2=0. It is, moreover, described by two different expressions, G2in and G2out, inside and outside the bifurcation surface whose asymptotic values in the neighbourhood of the cusp curve have exactly the same functional forms as those found in (18) and (19); the only difference being that p0 and q0 in these expressions are replaced by the p2 and q2 given in (A37) (see Appendix A). As in (29), therefore, the time derivative of the vector potential has the form ∂A/∂tP=(∂A/∂tP)in+(∂A/∂tP)out with(∂A/∂tP)in,out≡−ω∫Vin,outdV{circumflex over (r)}ρ∂G2in,out/∂{circumflex over (φ)}P (43)when the observation point is such that the bifurcation surface intersects the source distribution pattern. The functions G2in,out depend on {circumflex over (φ)}P and {circumflex over (φ)} in the combination {circumflex over (φ)}−{circumflex over (φ)}P only. We can therefore replace ∂/∂{circumflex over (φ)}P in (43) by −∂/∂{circumflex over (φ)} and perform the integration with respect to {circumflex over (φ)} by parts to arrive at(∂A/∂tP)in=c∫Sdrdz{circumflex over (r)}2{[ρG2in]Φ=Φ−Φ=Φ+−∫Φ−Φ+dΦ∂ρ/∂{circumflex over (φ)}G2in}, (44)and(∂A/∂tP)out=−c∫Sdrdz{circumflex over (r)}2{[ρG2out]Φ=Φ−Φ=Φ++(∫−πΦ−+∫Φ++π)dΦ∂ρ/∂{circumflex over (φ)}G2out}. (45)For the same reasons as those given in the paragraphs following (32) and (33), Hadamard's finite part of (∂A/∂tP)in consists of the volume integral in (44) and is of the order of r ^ P - 3 2 [note that according to (A37) and (A42), p2>>c1q2 and p2/c12=O(1)]. The volume integral in (45), moreover, decays like {circumflex over (r)}P−1, as does its counterpart in (33). The part of ∂A/∂tP that decays more slowly than conventional contributions to a radiation field is the boundary term in (45). The asymptotic value of this term is given by an expression similar to that appearing in (36), except that p1 and q1 are replaced by p2 and q2. Once the quantities ρ|Φ± and q2 in the expression in question are approximated by ρbs and by (A42), as before, it follows that ( ∂ A / ∂ t P ) out ∼ - c ∫ S ⅆ r ⅆ z r ^ 2 [ ρG 2 out ] ϕ - ϕ + ∼ - 4 3 c ∫ S ⅆ r ⅆ z r ^ 2 ρ bs c 1 - 1 q 2 ∼ - 2 5 2 3 ( c 2 / ω ) r ^ P - 1 2 e ^ φ P ∫ r ^ < r ^ > ⅆ r ^ r ^ 2 ( r ^ 2 - 1 ) - 1 4 ∫ z c - L z ^ ω / c z ^ c ⅆ z ^ ( z ^ c - z ^ ) - 1 2 ρ bs . ( 46 ) This behaves like τ ^ P - 1 2 as {circumflex over (r)}P→∞ since the {circumflex over (z)}-quadrature in (46) has the finite value 2 ( L z ^ ω / c ) 1 2 〈 ρ bs 〉 in this limit [see (37) et seq.]. Hence, the electric field vector of the radiation E = - ∇ P A 0 - ∂ A / ∂ ( ct P ) ∼ - c - 1 ( ∂ A / ∂ t P ) out ∼ 2 7 2 3 ( c / ω ) τ ^ P - 1 2 e ^ φ P ∫ τ ^ < τ ^ > ⅆ τ ^ τ ^ 2 ( τ ^ 2 - 1 ) - 1 4 ( L z ^ ω / c ) 1 2 〈 ρ bs 〉 ( 47 ) itself decays like τ P - 1 2 in the far zone: as we have already seen in Sec. IV(A), the term ∇PA0 has the conventional rate of decay rP−1 and so is negligible relative to (∂A/∂tP)out. C. Curl of the Vector Potential There are no contributions from the limits of integration towards the curl of the integral in (41) because ρ vanishes outside a finite volume and so the integral in this equation extends over all values of (r, {circumflex over (φ)}, z). Hence, differentiation of (41) yieldsB=∇P×A=Bin+Bout, (48a)in whichBin,out≡∫Vin,outdV{circumflex over (r)}ρ∇P×G2in,out. (48b)Operating with ∇P× on the first member of (42) and ignoring the term that decays like rP−2, as in (30), we find that the kernels ∇P×G2in and ∇P×G2out of (48b) are given—in the radiation zone—by the values of∇P×G2≃(ω/c)∫−∞+∞dφR−1δ′(g−Φ){circumflex over (n)}×êφ, {circumflex over (r)}P>>1, (49)for Φ inside and outside the interval (Φ−, Φ+), respectively. [{circumflex over (n)} is the unit vector defined in (31).] Insertion of (49) in (48) now yields expressions whose {circumflex over (φ)}-quadratures can be evaluated by parts to arrive atBin≃∫Sdrdz{circumflex over (r)}2{−[ρG3in]Φ=Φ−Φ=Φ++∫Φ−Φ+dΦ∂ρ/∂{circumflex over (φ)}G3in}, {circumflex over (r)}P>>1, (50)andBout≃∫Sdrdz{circumflex over (r)}2{[ρG3out]Φ=Φ−Φ=Φ++(∫−πΦ−+∫Φ++π)dΦ∂ρ/∂{circumflex over (φ)}G3out}, {circumflex over (r)}P>>1, (51)where G3in and G3out stand for the values of G 3 ≡ ∫ - ∞ + ∞ ⅆ φ R - 1 δ ( g - ϕ ) n ^ × e ^ φ = ∑ φ = φ j R - 1 ∂ g / ∂ φ - 1 n ^ × e ^ φ ( 52 ) inside and outside the bifurcation surface. Once again, owing to the presence of the factor |∂g/∂φ|−1 in G3in, the first term in (50) is divergent so that the Hadamard's finite part of Bin consists of the volume integral in this equation, an integral whose magnitude is of the order of τ ^ P - 3 2 [see the paragraph containing (35) and note that, according to (A38) and (A44), p3>>c1q3 and p3/c12=O(1)]. The second term in (51) has—like those in (33) and (45)—the conventional rate of decay {circumflex over (r)}P−1. Moreover, the surface integral in (51)—which would have had the same magnitude as the surface integral in (50) and so would have cancelled out of the expression for B had G3in and G3out matched smoothly across the bifurcation surface—decays as slowly as the corresponding term in (45). The asymptotic value of G3 for source points close to the cusp curve of the bifurcation surface has been calculated in Appendix A. It follows from this value of G3 and from (51), (52), (A40), (A44) and (A45) that, in the radiation zone, B ∼ ∫ S ⅆ τ ⅆ z τ ^ 2 [ ρ G 3 out ] ϕ - ϕ + ∼ 4 3 ∫ S ⅆ τ ⅆ z τ ^ 2 ρ bs c 1 - 1 q 3 ∼ 2 3 2 3 ( c / ω ) τ ^ P - 1 2 ∫ τ ^ < τ ^ > ⅆ τ ^ τ ^ 2 ( τ ^ 2 - 1 ) - 1 4 ∫ z ^ c - L z ^ ω / c z ^ c ⅆ z ^ ( z ^ c - z ^ ) - 1 2 ρ bs n 3 ( 53 ) to within the order of the approximation entering (37) and (46). The far-field version of the radial unit vector defined in (31) assumes the form lim τ P → ∞ n ^ | ϕ = ϕ c , z ^ = z ^ c = τ ^ - 1 e ^ τ P - ( 1 - τ ^ - 2 ) 1 2 e ^ z P ( 54 ) on the cusp curve of the bifurcation surface [see (12b), (13) and (A27), and note that the position of the observer is here assumed to be such that the segment of the cusp curve lying within the source distribution pattern is described by the expression with the plus sign in (12b), as in FIG. 6]. So, n3 equals {circumflex over (n)}×êφP in the regime of validity of (53) [see (A45)]. Moreover, {circumflex over (n)} can be replaced by its far-field value{circumflex over (n)}≃(rPêrP+zPêzP)/RP, RP→∞, (55)if it is borne in mind that (53) holds true only for an observer the cusp curve of whose bifurcation surface intersects the source distribution pattern. Once n3 in (53) is approximated by {circumflex over (n)}×êφP and the resulting {circumflex over (z)}-quadrature is expressed in terms of ρbs [see (38)], this equation reduces toB˜{circumflex over (n)}×E, (56)where E is the electric field vector earlier found in (47). Equations (47) and (56) jointly describe a radiation field whose polarization vector lies along the direction of motion of the source distribution pattern, êφP. Note that there has been no contribution toward the values of E and B from inside the bifurcation surface. These quantities have arisen in the above calculation solely from the jump discontinuities in the values of the Green's functions G1out, G2out and G3out across the coalescing sheets of the bifurcation surface. We would have obtained the same results had we simply excised the vanishingly small volume limrP→∞ Vin from the domains of integration in (29), (43) and (48). Note also that the way in which the familiar relation (56) has emerged from the present analysis is altogether different from that in which it appears in conventional radiation theory. Essential though it is to the physical requirement that the directions of propagation of the waves and of their energy should be the same, (56) expresses a relationship between fields that are here given by non-spherically decaying surface integrals rather than by the conventional volume integrals that decay like rP−1. Expressions (47) and (56) for the electric and magnetic fields of the radiation that arises from a charge-current density with the components (23) and (39) imply the following Poynting vector: S ∼ 2 5 3 2 π - 1 c ( c / ω ) 2 τ ^ P - 1 [ ∫ τ ^ < τ ^ > ⅆ τ ^ τ ^ 2 ( τ ^ 2 - 1 ) - 1 4 ( L z ^ ω / c ) 1 2 〈 ρ bs 〉 ] 2 n ^ . ( 57 ) In contrast, the magnitude of the Poynting vector for the coherent cyclotron radiation that would be generated by a macroscopic lump of charge, if it moved subluminally with a centripetal acceleration cω, is of the order of (ρL3)2ω2/(cRP2) according to the Larmor formula, where L3 represents the volume of the source distribution pattern and ρ its average charge density. The intensity of the present emission is therefore greater than that of even a coherent conventional radiation by a factor of the order of (L{circumflex over (z)}/L)(Lω/c)−4(RP/L), a factor that ranges from 1016 to 1030 in the case of pulsars for instance. The reason this ratio has so large a value in the far field (RP/L>>1) is that the radiative characteristics of a volume-distributed source pattern which moves faster than the waves it emits are radically different from those of a corresponding source that moves more slowly than the waves it emits. There are elements of the distribution pattern of the source in the former case that approach the observer along the radiation direction with the wave speed at the retarded time. These lie on the intersection of the source distribution pattern with what we have here called the bifurcation surface of the observer (see FIGS. 5 and 6): a surface issuing from the position of the observer which has the same shape as the envelope of the wave fronts emanating from an element of the source distribution pattern (FIGS. 1 and 3(a)) but which spirals around the rotation axis in the opposite direction to this envelope and resides in the space of source points instead of the space of observation points. The elements of the source distribution pattern inside the bifurcation surface of an observer make their contributions towards the observed field at three distinct instants of the retarded time. The values of two of these retarded times coincide for an interior element of the source distribution pattern that lies next to the bifurcation surface. This limiting value of the coincident retarded times represents the instant at which the component of the velocity of the element in question of the source distribution pattern equals the wave speed c in the direction of the observer. The third retarded time at which an element of the source distribution pattern adjacent to—just inside—the bifurcation surface makes a contribution is the same as the single retarded time at which its neighbouring element of the source distribution pattern just outside the bifurcation surface makes its contribution towards the observed field. (The elements of the source distribution pattern outside the bifurcation surface make their contributions at only a single instant of the retarded time). At the instant marked by this third value of the retarded time, the two neighbouring elements of the source distribution pattern—just interior and just exterior to the bifurcation surface—have the same velocity, but a velocity whose component along the radiation direction is different from c. The velocities of these two neighbouring elements are, of course, equal at any time. However, at the time they approach the observer with the wave speed, the element inside the bifurcation surface makes a contribution towards the observed field while the one outside this surface does not: the observer is located just inside the envelope of the wave fronts that emanate from the interior element of the source distribution pattern but just outside the envelope of the wave fronts that emanate from the exterior one. Thus, the constructive interference of the waves that are emitted by the element of the source distribution pattern just outside the bifurcation surface takes place along a caustic which at no point propagates past the observer at the conical apex of the bifurcation surface in question. On the other hand, the radiation effectiveness of an element of the distribution pattern of the source which approaches the observer with the wave speed at the retarded time is much greater than that of a neighbouring element the component of whose velocity along the radiation direction is subliminal or superluminal at this time. This is because the piling up of the emitted wave fronts along the line joining the source and the observer makes the ratio of emission to reception time intervals for the contributions of the luminally moving elements of the source distribution pattern by many orders of magnitude greater than that for the contributions of any other elements. As a result, the radiation effectiveness of the various constituent elements of the source distribution pattern (i.e. the Green's function for the emission process) undergoes a discontinuity across the boundary set by the bifurcation surface of the observer. The integral representing the superposition of the contributions of the various volume elements of the source distribution pattern to the potential thus entails a discontinuous integrand. When this volume integral is differentiated to obtain the field, the discontinuity in question gives rise to a boundary contribution in the form of a surface integral over its locus. This integral receives contributions from opposite faces of each sheet of the bifurcation surface which do not cancel one another. Moreover, the contributions arising from the exterior faces of the two sheets of the bifurcation surface do not have the same value even in the limit RP→∞ where this surface is infinitely large and so its two sheets are—throughout a localized source distribution pattern that intersects the cusp—coalescent. Thus the resulting expression for the field in the radiation zone entails a surface integral such as that which would arise if the source distribution pattern were two-dimensional, i.e. if the source distribution pattern were concentrated into an infinitely thin sheet that coincided with the intersection of the coalescing sheets of the bifurcation surface with the source distribution pattern. For a two-dimensional source distribution pattern of this type—whether it be real or a virtual one whose field is described by a surface integral—the near zone (the Fresnel regime) of the radiation can extend to infinity, so that the amplitudes of the emitted waves are not necessarily subject to the spherical spreading that normally occurs in the far zone (the Fraunhofer regime). The Fresnel distance which marks the boundary between these two zones is given by RF˜L⊥2/L∥, in which L⊥ and L∥ are the dimensions of the source distribution pattern perpendicular and parallel to the radiation direction. If the distribution pattern of the source is distributed over a surface and so has a dimension L∥ that is vanishingly small, therefore, the Fresnel distance RF tends to infinity. In the present case, the surface integral which arises from the discontinuity in the radiation effectiveness of the source elements across the bifurcation surface has an integrand that is in turn singular on the cusp curve of this surface. This has to do with the fact that the elements the source distribution pattern on the cusp curve of the bifurcation surface approach the observer along the radiation direction not only with the wave speed but also with zero acceleration. The ratio of the emission to reception time intervals for the signals generated by these elements is by several orders of magnitude greater even than that for the elements on the bifurcation surface. When the contributions of these elements are included in the surface integral in question, i.e. when the observation point is such that the cusp curve of the bifurcation surface intersects the source distribution pattern (as shown in FIG. 6), the value of the resulting improper integral turns out to have the dependence RP−1/2, rather than RP−1, on the distance RP of the observer from the source distribution pattern. This non-spherically decaying component of the radiation is in addition to the conventional component that is concurrently generated by the remaining volume elements of the source distribution pattern. It is detectable only at those observation points the cusp curves of whose bifurcation surfaces intersect the source distribution pattern. It appears, therefore, as a spiral-shaped wave packet with the same azimuthal width as the {circumflex over (φ)}-extent of the source distribution pattern. For a source distribution pattern whose superluminal portion extends from {circumflex over (r)}=1 to {circumflex over (r)}={circumflex over (r)}>>1, this wave packet is detectable—by an observer at infinity—within the angles ½π−arc cos {circumflex over (r)}>−1≦θP≦½π+arc cos {circumflex over (r)}>−1 from the rotation axis: projection (12b) of the cusp curve of the bifurcation surface onto the (r, z)-plane reduces to cot θP=({circumflex over (r)}2−1)1/2 in the limit RP→∞, where θP≡arc tan(rP/zP) [also see (54)]. Because it comprises a collection of the spiralling cusps of the envelopes of the wave fronts that are emitted by various elements of the source distribution pattern, this wave packet has a cross section with the plane of rotation whose extent and shape match those of the source distribution pattern. It is a diffraction-free propagating caustic that—when detected by a far-field observer—would appear as a pulse of duration Δ{circumflex over (φ)}/ω, where Δ{circumflex over (φ)} is the azimuthal extent of the source distribution pattern. Note that the waves that interfere constructively to form each cusp, and hence the observed pulse, are different at different observation times: the constituent waves propagate in the radiation direction {circumflex over (n)} with the speed c, whereas the propagating caustic that is observed, i.e. the segment of the cusp curve that passes through the observation point at the observation time, propagates in the azimuthal direction êφP with the phase speed rPω. The fact that the intensity of the pulse decays more slowly than predicted by the inverse square law is not therefore incompatible with the conservation of energy, for it is not the same wave packet that is observed at different distances from the source distribution pattern: the wave packet in question is constantly dispersed and re-constructed out of other waves. The cusp curve of the envelope of the wavefronts emanating from an infinitely long-lived source distribution pattern is detectable in the radiation zone not because any segment of this curve can be identified with a caustic that has formed at the source and has subsequently travelled as an isolated wavepacket to the radiation zone, but because certain set of waves superpose coherently only at infinity. Relative phases of the set of waves that are emitted during a limited time interval is such that these waves do not, in general, interfere constructively to form a cusped envelope until they have propagated some distance away from the source distribution pattern. The period in which this set of waves has a cusped envelope and so is detectable as a periodic train of non-spherically decaying pulses, would of course have a limited duration if the source distribution pattern is short-lived. Thus, pulses of focused waves may be generated by the present emission process which not only are stronger in the far field than any previously studied class of signals, but which can in addition be beamed at only a select set of observers for a limited interval of time. An apparatus can be designed for generating such pulses, in accordance with the above theory, which basically entails the simple components shown in FIGS. 7(a) and 7(b). Referring to the example of FIG. 7(a), a linear dielectric rod 1 of length l is provided with an array of electrodes 2, 3 arranged opposite one another along its length with n/l electrodes per unit length. In use, a voltage potential is applied across the dielectric rod 1 by the electrodes 2, 3, with each pair of electrodes 2, 3, in the array being activated in turn to generate a polarisation region with the fronts 5. By rapid application and removal of a potential voltage to electrodes 2, 3, the distribution pattern of this polarised region can be set in accelerated motion with a superluminal velocity. Creating a voltage across a pair of electrodes polarises the material in the rod between the electrodes. The electrodes can be controlled independently, so that the distribution pattern of polarisation of the rod as a function of length along the rod is controlled. By varying the voltage across the electrode pairs as a function of time, this polarisation pattern is set in motion. For example, neighbouring electrode pairs can be turned on with a time interval of Δt between them, starting from one end of the rod. Thus, at a snapshot in time, part of the rod is polarised (that part lying between electrode pairs with a voltage across them) and part of it is not polarised (that part lying between electrode pairs without a voltage across them). These regions are separated by “polarisation fronts” which move with a speed of l/(nΔt). With suitable choices of n and Δt the polarisation fronts can be made to move at any speed (including speeds faster than the speed of light in vacuo). The polarisation fronts can be accelerated through the speed of light by changing Δt with time. High-frequency radiation may be generated by modulating the amplitude of the resulting polarisation current with a frequency Ω that exceeds a/c, where a is the acceleration of the source distribution pattern. The spectrum of the spherically decaying component of the radiation would then extend to frequencies that would be by a factor of the order of (cΩ/a)2 higher than Ω. The required modulation may be achieved by varying the amplitudes of the voltages that are applied across various electrode pairs all in phase. FIG. 7(b) shows another example of the invention, the one analysed above. In this example, the dielectric rod is formed in the shape of a ring. FIG. 7(b) is a plan view showing electrodes 2, and has electrodes 3 disposed below the rod 1. For a ring of radius r and a polarisation pattern that moves around the ring with an angular frequency ω, the velocity of the charged region is rω. In this example, rω is greater than the speed of light c so that the moving polarisation pattern emits the radiation described with reference to FIGS. 1 to 6. FIGS. 3(b) and 3(c) depict representative three dimensional plots of the radiation pattern of the entire source of FIG. 7(b) at a frequency of 2.4 GHz and a phase difference between adjacent electrodes between 15 degrees and 5 degrees respectively. An azimuthal or radial polarisation current may be produced by displacing the plates of each electrode pair relative to one another. The voltages across neighbouring electrode pairs have the same time dependence (their period is 2π/ω) but, as in the rectilinear case, there is a time difference of Δt between them. The polarisation distribution pattern must move coherently around the ring, i.e. must move rigidly with an unchanging shape; this would be the case if nΔt=2πN/ω, where n is the number of electrodes around the ring and N an integer. Within the confines of this condition, the time dependence of the voltage across each pair of electrodes can be chosen at will. The exact form of the adopted time dependence would allow, for example, the generation of harmonic content and structure in the source distribution pattern. As in the rectilinear case, modulation of the amplitude of this source distribution pattern at a frequency Ω would result in a radiation whose spectrum would contain frequencies of the order of (Ω/ω)2Ω. The electrodes are driven by an array of similar oscillators, an array in which the phase difference between successive oscillators has a fixed value. There are several ways of implementing this: a single oscillator may be used to drive each electrode through progressively longer delay lines; each electrode pair may be driven by an individual oscillator in an array of phase-locked oscillators; or the electrode pairs may be connected to points around a circle of radius r which lies within—and is coplanar with—an annular waveguide, a waveguide whose normal modes include an electromagnetic wave train that propagates longitudinally around the circle with an angular frequency ω>c/r. For a dielectric rod in the shape of a ring of diameter 1 m, oscillators operating at a frequency of 100 MHz would generate a superluminally moving polarisation distribution pattern. The required oscillator frequencies are easily obtainable using standard laboratory equipment, and any material with an appreciable polarizability at MHz frequencies would do for the medium. If the amplitude of the resulting polarisation current is in addition modulated at 1 GHz, then the device would radiate at ˜100 GHz. The efficiency of this emission process is expected to be as high as a few percent. With oscillators operating at frequencies of 1 GHz (also available), the size of the device would be about 10 cm across; applications demanding portability are therefore viable. A. Medical and Biomedical Applications The present invention may be exploited to generate waves which do not form themselves into a focused pulse until they arrive at their intended destination and which subsequently remain in focus only for an adjustable interval of time, a property that allows for applications in various areas of medical practice and biomedical research. Examples of its use in therapeutic medicine are: (i) the selective irradiation of deep tumours whilst sparing surrounding normal tissue, and (ii) the radiation pressure or thermocautery removal of thrombotic and embolic vascular lesions that may result from abnormalities in blood clotting without invasive surgery. Examples of its use in diagnostic medicine are absorption spectroscopy (focusing a broadband pulse within a tissue some frequencies of which would be absorbed) and three-dimensional tomography (mapping specifiable regions of interest within the body to high levels of resolution). In biomedical research, it provides a more powerful alternative to confocal scanning microscopy; with a single aerial being used as an X-ray source for imaging purposes. An example of an apparatus required for generating the pulses in question is that shown in FIG. 7(a). It consists of a linear dielectric rod, an array of electrode pairs positioned opposite to each other along the rod, and the means for applying a voltage to the electrodes sequentially at a rate sufficient to induce a polarization current whose distribution pattern moves along the rod with a constant acceleration at speeds exceeding the speed of light in vacuo. The envelope of the wave fronts emanating from a volume element of the superluminally moving distribution pattern thus produced is shown in FIG. 8. It consists of a two-sheeted closed surface when the duration of the source includes the instant at which the distribution pattern of the source becomes superluminal. The two sheets of this envelope are tangent to one another and form a cusp along an expanding circle. If the source distribution pattern has a limited duration, the envelope in question is correspondingly limited [as in FIG. 9(d)] to only a truncated section of the surface shown in FIG. 8. The snapshots in FIG. 9 trace the evolution in time of the relative positions of a particular set of wave fronts that are emitted during a short time interval. They include times at which the envelope has not yet developed a cusp [(a) and (b)], has a cusp [(c)-(e)], and has already lost its cusp (f). A source distribution pattern with the life span 0<t<T gives rise to a caustic, i.e. to a set of tangential wave fronts with a cusped envelope, only during the following finite interval of observation time:M(M2−1)l/c≦tP≦M[M2(1+aT/u)3−1]l/c, (58)where M≡u/c and l≡c2/a with u, c, and a standing for the speed of the distribution pattern of the source at t=0, the wave speed, and the constant acceleration of the distribution pattern of the source, respectively. For aT/u<<1, therefore, the duration of the caustic, 3M2T, is proportional to that of the source distribution pattern. Moreover, a cusped envelope begins to form in the case of a short-lived source distribution pattern only after the waves have propagated a finite distance away from the source. The distance of the caustic from the position of the source distribution pattern at the retarded time is given by R _ P = β P 1 3 ( β P 2 3 - 1 ) l , ( 59 ) where βP≡(u+atP)/c and tP is the observation time. This distance can be long even when the duration of the source distribution pattern is short because there is no upper limit on the value of the length l(≡c2/a) that enters (58) and (59): l tends to infinity for a→0 and is as large as 1018 cm when a equals the acceleration of gravity. Thus RP can be rendered arbitrarily large, by a suitable choice of the parameter l, without requiring either the duration of the source (T) or the retarded value (βP1/3c) of the speed of the source distribution pattern to be correspondingly large. This means that, when either M or l is large, the waves emitted by a short-lived source do not focus to such an extent as to form a cusped envelope until they have travelled a long distance away from the source. The period during which they then do so can be controlled by adjusting the parameters M and T. The collection of the cusp curves of the envelopes that are associated with various elements of the distribution pattern of the source constitutes a ring-shaped wave packet. This wave packet is intercepted only by those observers who are located, during its life time (58), on its trajectory ξ = ( β P 2 3 - 1 ) 3 2 , ζ = 1 2 β P 2 - 3 2 β P 2 3 + 1 , ( 60 ) where ξ represents the distance (in units of l) of the observer from the rectilinear path of the source, say the z-axis, and ζ stands for the difference between the Lagrangian coordinates z _ = z - ui - 1 2 at 2 of the source point and z _ P = z P - ui P - 1 2 at P 2 of the observation point. It is possible to limit the spatial extent of the wave packet embodying the large-amplitude pulse by enclosing the path of the source distribution pattern within an opaque cylindrical surface which has a narrow slit parallel to its axis, a slit acting as an aperture that would only allow an arc of the ring-shaped wave packet to propagate to the far field. The volume occupied by the resulting wave packet could then be chosen at will by adjusting the width of the aperture and the longitudinal extent of the source distribution pattern. B. Compact Sources of Intense Broadband Radiation In the near zone, the radiation that is generated by the invention can be arranged to have many features in common with synchrotron radiation. Most experiments presently carried out at large-scale synchrotron facilities could potentially be performed by means of a polarization synchrotron, i.e. the compact device described in Sec. VI. This device has applications, as a source of intense broadband radiation, in many scientific and industrial areas, e.g. in spectroscopy, in semiconductor lithography at very fine length scales, and in silicon chip manufacture involving UV techniques. The spectrum of the radiation generated in a polarization synchrotron extends to frequencies that are by a factor of the order of (cΩ/a)2 higher than the characteristic frequency Ω of the fluctuations of the source distribution pattern itself (c and a are the speed of light and the acceleration of the source distribution pattern, respectively). For a polarizable medium consisting of a 1 m arc of a circular rod whose diameter is ˜10 m [see FIG. (7b)], superluminal source distribution pattern motion is achieved by an applied voltage that oscillates with the frequency ˜10 MHz. If the amplitude of the resulting polarization current is in addition modulated at ˜500 MHz, then the device would radiate at ˜1 THz. In the case of the source distribution pattern elements that approach the observer with the wave speed and zero acceleration, the interval of retarded time δt during which a set of waves are emitted is significantly longer than the interval of observation time δtP during which the same set of waves are received. For a rectilinearly moving superluminal source distribution pattern, the ratio δt/δtP is given by 2 1 3 ( u 2 / c 2 - 1 ) 1 3 ( a δ t P / c ) - 2 3 ,where u is the retarded speed of the source distribution pattern and a its constant acceleration. This ratio increases without bound as a approaches zero. Regardless of what the characteristic frequency of the temporal fluctuations of the source may be, therefore, it is possible to push the upper bound to the spectrum of the emitted radiation to arbitrarily high frequencies by making the acceleration a small. [Note that the emission process described here remains different from the {hacek over (C)}erenkov process, in which a exactly equals zero, even in the limit a→0.] The relationship between δt and δtP is δ t P ≃ 1 6 ω 2 ( δ t ) 3 if the source distribution pattern moves circularly with the angular frequency ω. Thus the spectrum of the spherically decaying part of the radiation that is generated by a source with an accelerated superluminal distribution pattern extends to frequencies which are by a factor of the order of (cΩ/a)2 or (Ω/ω)2 higher than the characteristic frequency Ω of the modulations of the amplitude of the source distribution pattern. C. Long-Range and High-Bandwidth Telecommunications There are at present no known antennas in which the emitting electric current is both volume distributed and has the time dependence of a travelling wave with an accelerated superluminal motion. A travelling wave antenna of this type, designed on the basis of the principles underlying the present invention, generates focused pulses that not only are stronger in the far field than any previously studied class of signals, but can in addition be beamed at only a select set of observers for a limited interval of time: the constituent waves whose constructive interference gives rise to the propagating wave packet embodying a given pulse come into focus (develop a cusped envelope or a caustic) only long after they have emanated from the source and then only for a finite period (FIG. 9). The intensity of the waves generated by this novel type of antenna decay much more slowly over distance than that of conventional radio or light signals. In the case of conventional sources, including lasers, if the transmitter (source) to receiver (destination) distance doubles, the power of the signal is reduced by a factor of four. With the present invention, the same doubling of distance only halves the available signal. Thus the power required to send a radio signal from the Earth to the Moon by the present transmitter would be 100 million times smaller than that which is needed in the case of a conventional antenna. The emission mechanism in question can therefore be used to convey telephonic, visual and other electronic data over very long distances without significant attenuation. In the case of ground-to-satellite communications, the power required to beam a signal would be greatly reduced, implying that either far fewer satellites would be required for the same bandwidth or each satellite could handle a much wider range of signals for the same power output. D. Hand-Held Communication Devices A combined effect of the slow decay rate and the beaming of the new radiation is that a network of suitably constructed antennae could expand the useable spectrum of terrestrial electromagnetic broadcasts by a factor of a thousand or more, thus dispensing with the need for cable or optical fibre for high-bandwidth communications. The evolution of the Internet, real-time television conferencing and related information-intense communication media means that there is a growing demand for cheap high-bandwidth aerials. Highly compact aerials for hand-held portable phones and/or television/Internet connections based on the present invention can handle, not only much longer transmitter-to-receiver distances than those currently available in cellular phone systems, but also much higher bandwidth. Far fewer ground based aerial structures are required to obtain the same area coverage. Because there would be no cross-talk between any pairs of transmitter and receiver, the effective bandwidth of free space could be increased many thousand-fold, thus allowing, say, for video transmission between hand-held units. Asymptotic Expansion of the Green's Functions In this Appendix, we calculate the leading terms in the asymptotic expansions of the integrals (16), (34), (42) and (52) for small Φ+−Φ−, i.e. for points close to the cusp curve (12) of the bifurcation surface (or of the envelope of the wavefronts). The method—originally due to Chester et al. (Proc. Camb. Phil. Soc., 54, 599, 1957)—which we use is a standard one that has been specifically developed for the evaluation of radiation integrals involving caustics (see Ludwig, Comm. Pure Appl. Maths, 19, 215, 1966). The integrals evaluated below all have a phase function g(φ) whose extrema (φ=φ±) coalesce at the caustic (12). As long as the observation point does not coincide with the source point, the function g(φ) is analytic and the following transformation of the integration variables in (16) is permissible: g ( φ ) = 1 3 v 3 - c 1 v + c 2 , ( A 1 ) where ν is the new variable of integration and the coefficients c 1 ≡ ( 3 4 ) 1 3 ( ϕ + - ϕ - ) 1 3 and c 2 ≡ 1 2 ( ϕ + + ϕ - ) ( A 2 ) are chosen such that the values of the two functions on opposite sides of (A1) coincide at their extrema. Thus an alternative exact expression for G0 is G 0 = ∫ - ∞ + ∞ ⅆ vf 0 ( v ) δ ( 1 3 v 3 - c 1 2 v + c 2 - ϕ ) , in which ( A 3 ) f 0 ( v ) ≡ R - 1 ⅆ φ / ⅆ v . ( A 4 ) Close to the cusp curve (12), at which c1 vanishes and the extrema ν=35 c1 of the above cubic function are coincident, f0(ν) may be approximated by p0+q0ν, with p 0 = 1 2 ( f 0 | v = c 1 + f 0 | v = - c 1 ) , and ( A 5 ) q 0 = 1 2 c 1 - 1 ( f 0 | v = c 1 - f 0 | v = - c 1 ) . ( A 6 ) The resulting expression G 0 ∼ ∫ - ∞ + ∞ ⅆ v ( p 0 + q 0 v ) δ ( 1 3 v 3 - c 1 2 v + c 2 - ϕ ) ( A 7 ) will then constitute, according to the general theory, the leading term in the asymptotic expansion of G0 for small c1. To evaluate the integral in (A7), we need to know the roots of the cubic equation that follows from the vanishing of the argument of the Dirac delta function in this expression. Depending on whether the observation point is located inside or outside the bifurcation surface (the envelope), the roots of 1 3 v 3 - c 1 2 v + c 2 = 0 are given by ( A8 ) v = 2 c 1 cos ( 2 3 n π + 1 3 arc cos χ ) , χ < 1 , for n = 0 , 1 and 2 , or by ( A9a ) v = 2 c 1 sgn ( χ ) cosh ( 1 3 arc cosh χ ) , χ > 1 , ( A9b ) respectively, where χ ≡ [ ϕ - 1 2 ( ϕ + + ϕ - ) ] / [ 1 2 ( ϕ + - ϕ - ) ] = 3 2 ( ϕ - c 2 ) / c 1 3 . ( A 10 ) Note that equals +1 on the sheet Φ=Φ+ of the bifurcation surface (the envelope) and −1 on Φ=Φ−. The integral in (A7), therefore, has the following value when the observation point lies inside the bifurcation surface (the envelope): ∫ - ∞ + ∞ ⅆ v δ ( 1 3 v 3 - c 1 2 v + c 2 ) = ∑ n = 0 2 c 1 - 2 4 cos 2 ( 2 3 n π + 1 3 arc cos χ ) - 1 - 1 , χ < 1. ( A 11 ) Using the trignometric identity 4 cos2 α−1=sin 3α/sin α, we can write this as ∫ - ∞ + ∞ ⅆ v δ ( 1 3 v 3 - c 1 2 v + c 2 ) = c 1 - 2 ( 1 - χ 2 ) - 1 2 ∑ n = 0 2 sin ( 2 3 n π + 1 3 arc cos χ ) = 2 c 1 - 2 ( 1 - χ 2 ) - 1 2 cos ( 1 3 arc sin χ ) , χ < 1 , ( A 12 ) in which we have evaluated the sum by adding the sine functions two at a time. When the observation point lies outside the bifurcation surface (the envelope), the above integral receives a contribution only from the single value of ν given in (A9b) and we obtain ∫ - ∞ + ∞ ⅆ v δ ( 1 3 v 3 - c 1 2 v + c 2 ) = c 1 - 2 ( χ 2 - 1 ) - 1 2 sinh ( 1 3 arc cosh χ ) , χ > 1 , ( A 13 ) where this time we have used the identity 4 cos h2α−1=sin h 3α/sin h α. The second part of the integral in (A7) can be evaluated in exactly the same way. It has the value ∫ - ∞ + ∞ ⅆ vv δ ( 1 3 v 3 - c 1 2 v + c 2 ) = 2 c 1 - 1 ( 1 - χ 2 ) - 1 2 ∑ n = 0 2 sin ( 2 3 n π + 1 3 arc cos χ ) × cos ( 2 3 n π + 1 3 arc cos χ ) = - 2 c 1 - 1 ( 1 - χ 2 ) - 1 2 sin ( 2 3 arc sin χ ) , χ < 1 , ( A 14 ) when the observation point lies inside the bifurcation surface (the envelope), and the value ∫ - ∞ + ∞ ⅆ vv δ ( 1 3 v 3 - c 1 2 v + c 2 ) = c 1 - 1 ( χ 2 - 1 ) - 1 2 sgn ( χ ) sinh ( 2 3 arc cosh χ ) , χ > 1 , ( A 15 ) when the observation point lies outside the bifurcation surface (the envelope). Inserting (A12)-(A15) in (A7), and denoting the values of G0 inside and outside the bifurcation surface (the envelope) by G0in and G0out, we obtain G 0 in ∼ 2 c 1 - 2 ( 1 - χ 2 ) - 1 2 [ p 0 cos ( 1 3 arc sin χ ) - c 1 q 0 sin ( 2 3 arc sin χ ) ] , χ < 1 , and ( A 16 ) G 0 out ∼ c 1 - 2 ( χ 2 - 1 ) - 1 2 [ p 0 sinh ( 1 3 arc cosh χ ) + c 1 q 0 sgn ( χ ) sinh ( 2 3 arc cosh χ ) ] , χ > 1 , ( A 17 ) for the leading terms in the asymptotic approximation to G0 for small c1. The function f0(ν) in terms of which the coefficients p0 and q0 are defined is indeterminate at ν=c1 and ν=−c1: differentiation of (A1) yields dφ/dν=(ν2−c12)/(∂g/∂φ) the zeros of whose denominator at φ=φ− and φ=φ+ respectively coincide with those of its numerator at ν=+c1 and ν=−c1. This indeterminacy can be removed by means of l'Hopital's rule by noting that ⅆ φ ⅆ v v = ± c 1 = v 2 - c 1 2 ∂ g / ∂ φ v = ± c 1 = 2 v ( ∂ 2 g / ∂ φ 2 ) ( ⅆ φ / ⅆ v ) v = ± c 1 , i . e . that ( A 18 ) ⅆ φ ⅆ v v = ± c 1 = ( ± 2 c 1 ∂ 2 g / ∂ φ 2 ) 1 2 φ = φ ∓ = ( 2 c 1 R ^ ∓ ) 1 2 Δ 1 4 , ( A 19 ) in which we have calculated (∂2g/∂φ2)φ± from (7) and (8). The right-hand side of (A19) is, in turn, indeterminate on the cusp curve of the bifurcation surface (the envelope) where c1=Δ=0. Removing this indeterminacy by expanding the numerator in this expression in powers of Δ1/4, we find that dφ/dν assumes the value 21/3 at the cusp curve. Hence, the coefficients p0 and q0 that appear in the expressions (A8) and (A9) for G0 are explicitly given by p 0 = ( w / c ) ( 1 2 c 1 ) 1 2 ( R ^ - - 1 2 + R ^ + - 1 2 ) Δ - 1 4 , and ( A 20 ) ) q 0 = ( w / c ) ( 2 c 1 ) - 1 2 ( R ^ - - 1 2 - R ^ + - 1 2 ) Δ - 1 4 ( A 21 ) [see (A4)-(A6) and (A19)]. In the regime of validity of (A8) and (A9), where Δ is much smaller than ( r ^ P 2 r ^ 2 - 1 ) 1 2 ,the leading terms in the expressions for {circumflex over (R)}±, c1, p0 and q0 are R ^ ± = ( r ^ P 2 r ^ 2 - 1 ) 1 2 ± ( r ^ P 2 r ^ 2 - 1 ) - 1 2 Δ 1 2 + O ( Δ ) , ( A22 ) c 1 = 2 - 1 3 ( r ^ P 2 r ^ 2 - 1 ) - 1 2 · Δ 1 2 + O ( Δ ) , ( A23 ) p 0 = 2 1 3 ( ω / c ) ( r ^ 2 r ^ P 2 - 1 ) - 1 2 Δ 1 2 + O ( Δ 1 2 ) , ( A24 ) and q 0 = 2 - 1 3 ( ω / c ) ( r ^ 2 r ^ P 2 - 1 ) - 1 + O ( Δ 1 2 ) . ( A25 ) These may be obtained by using (9) to express {circumflex over (z)} everywhere in (10), (11) and (A2) in terms of Δ and {circumflex over (r)}, and expanding the resulting expressions in powers of Δ1/2. The quantity Δ in turn has the following value at points 0 ≤ z ^ c - z ^ ⪡ ( r ^ P 2 - 1 ) 1 2 ( r ^ 2 - 1 ) 1 2 : Δ = 2 ( r ^ P 2 - 1 ) 1 2 ( r ^ 2 - 1 ) 1 2 ( z ^ c - z ^ ) + O [ ( z ^ c - z ^ ) 2 ] , ( A26 ) in which {circumflex over (z)}c is given by the expression with the plus sign in (12b). For an observation point in the far zone ({circumflex over (r)}P>>1), the above expressions reduce to R ^ ± ≃ r ^ r ^ P , c 1 ≃ 2 1 6 ( r ^ r ^ P ) - 1 2 ( 1 - r ^ - 2 ) 1 4 ( z ^ c - z ^ ) 1 2 , ( A27 ) Δ ≃ 2 r ^ p ( r ^ 2 - 1 ) 1 2 ( z ^ c - z ^ ) , ( A28 ) p 0 ≃ 2 1 3 ( ω / c ) ( r ^ P r ^ ) - 1 , q 0 ≃ 2 - 1 3 ( ω / c ) ( r ^ P r ^ ) - 2 , ( A29 ) and χ ≃ 3 ( 1 2 r ^ r ^ P ) 3 2 ( 1 - r ^ - 2 ) - 3 4 ( ϕ - ϕ c ) / ( z ^ c - z ^ ) 3 2 , ( A30 ) in which {circumflex over (z)}c−{circumflex over (z)} has been assumed to be finite. Evaluation of the other Green's functions, G1, G2 and G3, entails calculations which have many steps in common with that of G0. Since the integrals in (34), (42) and (52) differ from that in (16) only in that their integrands respectively contain the extra factors {circumflex over (n)}, êφ and {circumflex over (n)}×êφ, they can be rewritten as integrals of the form (A3) in which the functionsf1(ν)≡{circumflex over (n)}f0, f2(ν)≡êφf0 and f3(ν)≡{circumflex over (n)}×êφf0 (A31)replace the f0(ν) given by (A4). If p0 and q0 are correspondingly replaced, in accordance with (A5) and (A6), by p k = 1 2 ( f k | v = c 1 + f k | v = - c 1 ) , k = 1 , 2 , 3 , ( A32 ) and q k = 1 2 c 1 - 1 ( f k | v = c 1 - f k | v = - c 1 ) , k = 1 , 2 , 3 , ( A33 ) then every step of the analysis that led from (A7) to (A8) and (A9) would be equally applicable to the evaluation of Gk. It follows, therefore, that G k in ∼ 2 c 1 - 2 ( 1 - χ 2 ) - 1 2 [ p k cos ( 1 3 arcsin χ ) - c 1 q k sin ( 2 3 arcsin χ ) ] , χ < 1 , ( A34 ) and G k out ∼ c 1 - 2 ( χ 2 - 1 ) - 1 2 [ p k sinh ( 1 3 arccosh χ ) + c 1 q k sgn ( χ ) sinh ( 2 3 arccosh χ ) ] , χ > 1 , ( A35 ) constitute the uniform asymptotic approximations to the functions Gk inside and outside the bifurcation surface (the envelope) |χ|=1. Explicit expressions for pk and qk as functions of (r, z) may be found from (8), (A19), and (A31)-(A33) jointly. The result is p 1 q 1 = 2 - 1 2 ( ω / c ) c 1 ± 1 2 Δ - 1 4 { [ ( r ^ P - r ^ P - 1 ) ( R ^ - - 3 2 ± R ^ + - 3 2 ) - r ^ P - 1 Δ 1 2 ( R ^ - - 3 2 ∓ R ^ + - 3 2 ) ] e ^ r P + r ^ P - 1 ( R ^ - - 1 2 ± R ^ + - 1 2 ) e ^ φ P + ( z ^ P - z ^ ) ( R ^ - - 3 2 ± R ^ + - 3 2 ) e ^ z P } , ( A36 ) p 2 q 2 = 2 - 1 2 ( ω / c ) ( r ^ r ^ P ) - 1 c 1 ± 1 2 Δ - 1 4 { ( R ^ - 1 2 ± R ^ + 1 2 ) e ^ r P + [ R ^ - - 1 2 ± R ^ + 1 2 + Δ 1 2 ( R ^ - - 1 2 ∓ R ^ + - 1 2 ) ] e ^ φ P } , ( A37 ) and p 3 q 3 = 2 - 1 2 ( ω / c ) ( r ^ r ^ P ) - 1 c 1 ± 1 2 Δ - 1 4 { - ( z ^ P - z ^ ) [ R ^ - - 3 2 ± R ^ + - 3 2 + Δ 1 2 ( R ^ - - 3 2 ∓ R ^ + - 3 2 ) ] e ^ r P + ( z ^ P - z ^ ) ( R ^ - - 1 2 ± R ^ + - 1 2 ) e ^ φ P + r ^ P [ Δ 1 2 ( R ^ - - 3 2 ∓ R ^ + - 3 2 ) - ( r ^ 2 - 1 ) ( R ^ - - 3 2 ± R ^ + - 3 2 ) ] e ^ z P } , ( A38 ) where use has been made of the fact that êφ=−sin(φ−φP)êrP+cos(φ−φP)êφP. Here, the expressions with the upper signs yield the pk and those with the lower signs the qk. The asymptotic value of each Gkout is indeterminate on the bifurcation surface (the envelope). If we expand the numerator of (A35) in powers of its denominator and cancel out the common factor ( χ 2 - 1 ) 1 2 prior to evaluating the ratio in this equation, we obtainGkout|Φ=Φ±=Gkout|χ=±1˜(pk±2c1qk)/(3c12). (A39)This shows that Gkout|Φ=Φ− and Gkout|Φ=Φ+ remain different even in the limit where the surfaces Φ=Φ− and Φ=Φ+ coalesce. The coefficients qk that specify the strengths of the discontinuities G k out | ϕ = ϕ + - G k out | ϕ = ϕ - ∼ 4 3 q k / c 1 ( A40 ) reduce to q 1 ≃ 3 2 1 3 ( ω / c ) ( r ^ r ^ P ) - 3 [ ( 1 - 2 3 r ^ 2 ) r ^ P e ^ r P + ( z ^ P - z ^ ) e ^ z P ] , ( A41 ) q 2 ≃ 2 2 3 ( ω / c ) ( r ^ r ^ P ) - 1 e ^ φ P , ( A42 ) and q 3 ≃ - 2 2 3 ( ω / c ) ( r ^ r ^ P ) - 2 [ ( z ^ P - z ^ ) e ^ ^ r P - r ^ P e ^ z P ] ( A43 ) in the regime of validity of (A27) and (A28). When 0 ≤ z ^ - z ^ P ⪡ ( r ^ 2 - 1 ) 1 2 r ^ P ,the expressions (A41) and (A43) further reduce to q 1 ≃ 3 2 1 3 ( ω / c ) ( r ^ r ^ P ) - 2 n 1 , and q 3 ≃ 2 2 3 ( ω / c ) ( r ^ r ^ P ) - 1 n 3 , with ( A44 ) n 1 ≡ ( r ^ - 1 - 2 3 r ^ ) e ^ r P - ( 1 - r ^ - 2 ) 1 2 e ^ z P and n 3 ≡ ( 1 - r ^ - 2 ) 1 2 e ^ r p + r ^ - 1 e ^ z P , ( A45 ) for in this case (12b)—with the adopted plus sign—can be used to replace z ^ - z ^ P by ( r ^ 2 - 1 ) 1 2 r ^ P . |
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claims | 1. A nuclear fuel pin comprising a linear element defined by a bar or billet in a cylindrical shape of metal nuclear fuel material including uranium and/or plutonium and a cladding comprising Fe and Cr or an alloy comprising at least these two elements, further comprising: a main shell positioned around the linear element of metal nuclear fuel material, said main shell being disposed between an inside surface of the cladding and the linear element of metal nuclear fuel material, said main shell comprising yarns or fibers made of SiC; and a primary shell of silica or quartz fibers inserted between the linear element of metal nuclear fuel material and the main shell, the primary shell being disposed directly onto an outer surface of the cylinder of metal nuclear fuel material. 2. The nuclear fuel pin as claimed in claim 1, further comprising:a plenum to receive said discharge of fission gasses; anda reservoir, wherein the linear element is disposed at a first end of said nuclear fuel pin, the plenum is disposed at a second end of said nuclear fuel pin, and said reservoir is disposed between said plenum and said linear element, the cladding is configured to cover and contain said linear element, said reservoir, and said plenum. 3. The nuclear fuel pin as claimed in claim 2, wherein said reservoir comprises an annulus made of a material which is resistant to a corrosion of molten actinides. 4. The nuclear fuel pin as claimed in claim 3, wherein said annulus is made of tantalum. 5. The nuclear fuel pin as claimed in claim 1, wherein the SiC constituting the fibers is of cubic β allotropic variety. 6. The nuclear fuel pin as claimed in claim 1, wherein the main shell also comprises free Si fillers. 7. The nuclear fuel pin as claimed in claim 1, wherein said main shell comprises strips comprising SiC yarns or fibers. 8. The nuclear fuel pin as claimed in claim 1, wherein the main shell comprises a plurality of wrapped layers of SiC fibers wound around the linear element of metal nuclear fuel material. 9. The nuclear fuel pin as claimed in claim 8, wherein the primary shell comprises a plurality of wrapped layers of silica or quartz fibers wound around the linear element of metal nuclear fuel material. 10. A process for manufacturing a metal nuclear fuel pin as claimed in claim 1, further comprising the production of the main shell around the linear element of metal nuclear fuel material by weaving or braiding SiC fibers. 11. The process for manufacturing a metal nuclear fuel pin as claimed in claim 10, further comprising a prior step of surface oxidation of the linear element of metal nuclear fuel material. 12. The process for manufacturing a metal nuclear fuel pin as claimed in claim 10, further comprising a prior step of coating the linear element of metal nuclear fuel material with a binder comprising a soft brazing powder, the soft brazing powder including a conductive material. 13. The process for manufacturing a metal nuclear fuel pin as claimed in claim 10, further comprising the production of the primary shell between the linear element of metal nuclear fuel material and the main shell, said primary shell comprising silica or quartz fibers. 14. A process for manufacturing a metal nuclear fuel pin as claimed in claim 1, further comprising the production of the main shell with strips of SiC fibers wound around the linear element of metal nuclear fuel material. 15. The nuclear fuel pin as claimed in claim 1, wherein the primary shell comprises a plurality of wrapped layers of silica or quartz fibers wound around the linear element of metal nuclear fuel material. |
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059149981 | summary | BACKGROUND OF THE INVENTION The present invention relates to an X-ray microbeam generating method for various kinds of apparatuses using X-rays, and a device for practicing the same. Apparatuses using X-rays are extensively used today. X-rays for such an application must be condensed to form a microbeam having a small beam size. Various kinds of technologies for condensing X-rays have been proposed in the past. For example, X-rays, issuing from an X-ray generator or X-ray source may be condensed to a focus position or virtual light source by an X-ray Fresnel zone plate playing the role of a condensing element. The Fresnel zone plate may be replaced with a mirror totally reflecting X-rays on the basis of the fact that X-rays having a refractive index smaller than 1 are totally reflected when incident to the surface of an object at an angle less than a critical angle. Japanese Patent Laid-Open Publication Nos. 62-15014 and 4-43998 each teaches an arrangement including an asymmetrical reflection type crystal collimator located on an input X-ray path and a mirror. X-rays from a false emission point defined by the crystal collimator and X-rays from the original emission point are reflected to the same point by asymmetrical X-ray diffraction. Further, an X-ray beam may have its cross-section restricted by a slit or a pin hole so as to produce a spatially restricted X-ray beam. On the other hand, a solar slit or dynamic diffraction using the perfect crystal of X-rays has customarily been used to restrict the angular divergence of an X-ray beam. However, the solar slit scheme can restrict the divergence angle to the order of minutes at most, so that the resulting microbeam is too broad to be called a plane wave. As for the X-ray perfect crystal scheme, X-rays scarcely interacts with a substance, so that a great number of lattice planes join in diffraction. That is, a great number of reflected waves contribute to interference, implementing a noticeable interference effect. This further restricts the angular spread of the diffracted wave and allows, under diffraction conditions, angular divergence in the direction of scattering planes defined by the direction of input X-rays and the direction of diffracted X-rays to the order to seconds. However, the condensation of X-rays and the restriction of the divergence angle of X-rays have customarily been effected independently of each other, failing to produce an X-ray microbeam having a restricted divergence angle. This is because condensation is not achievable without increasing the angular divergence and because the angular divergence cannot be reduced without increasing the spatial spread. Moreover, the spatial spread can be reduced by a condensing element only at the focal position; at the other positions, the beam size increases. Therefore, as the distance from the focal position increases, the microbeam spatially spreads by many figures due to angular divergence. That is, the microbeam cannot be used at positions other than the focal position. SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a method capable of generating an X-ray microbeam with a restricted divergence angle and desirable condensed planeness, and a device for practicing the same. It is another object of the present invention to provide a method capable of generating and X-ray microbeam while maintaining a constant degree of asymmetry and a constant condensing efficiency even when the wavelength of X-rays is changed. In accordance with the present invention, a method of generating a plane wave X-ray microbeam has the steps of condensing X-rays issuing from an X-ray source to a focus, causing diffractions having scattering planes perpendicular to each other to occur simultaneously, and restricting the divergence angle of the condensed X-ray beam to thereby separate a part of the X-ray beam which can be considered to be a plane wave. Also, in accordance with the present invention, a device for generating a plane wave X-ray microbeam has an X-ray source, a condensing element for condensing X-rays issuing from the X-ray source to a focus, and an optical element located at a focus for restricting the divergence angle of a condensed X-ray beam. Further, in accordance with the present invention, in a method of generating an X-ray microbeam by using an asymmetrical reflection X-ray diffraction method using a diffraction plane not parallel to a crystal surface, a crystal is rotated about an axis perpendicular to the diffraction plane so as to vary an input angle to and an output angle from the crystal surface while preserving a Bragg condition. |
claims | 1. A plant abnormality prediction detection system for detectably monitoring an abnormality prediction in a nuclear power plant, comprising:a data storage unit configured to store plant operation data including an instrument parameter measured in the nuclear power plant and an alarm threshold for a warning of abnormality in the nuclear power plant; anda monitoring control unit configured to detect an abnormality prediction in the nuclear power plant on the basis of the plant operation data,wherein the nuclear power plant performs a base-load operation so that the instrument parameter has a predefined target value, andwherein the monitoring control unit is further configured to set a region having a value which is equal to or smaller than the alarm threshold as a normality determination range in which the instrument parameter is normal and a region having a value greater than the alarm threshold as an abnormality determination range in which the instrument parameter is abnormal, and set, in the normality determination range, a normal range which is a range for a transition of the instrument parameter in an operation cycle from operation starting to operation stopping of the nuclear power plant based on the past plant operation data to store the normal range in the data storage unit in advance, and configured to detect an abnormality prediction in a case where the instrument parameter at the current time exceeds the set normal range. 2. The plant abnormality prediction detection system according to claim 1,wherein an alarm threshold for a warning of abnormality in the nuclear power plant is set in advance,wherein the alarm threshold is a threshold value for dividing a region of the instrument parameter into a normality determination range in which the instrument parameter is normal and an abnormality determination range in which the instrument parameter is abnormal, andwherein the normal range is set in the normality determination range. 3. The plant abnormality prediction detection system according to claim 1,wherein a plurality of operation modes corresponding to operation situations of the nuclear power plant are prepared in advance,wherein the normal range is prepared in a plurality on the basis of the plant operation data in the past operation situations corresponding to the plurality of operation modes, andwherein, if the operation mode corresponding to the present operation situation of the nuclear power plant is set, the monitoring control unit is further configured to set the normal range corresponding to the operation mode. 4. The plant abnormality prediction detection system according to claim 1,wherein the monitoring control unit is further configured to change a width of the set normal range. |
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claims | 1. A system for refueling a nuclear reactor, comprising:a lower reactor vessel comprising a plurality of fuel rods and a plurality of control rods disposed therein, the lower reactor vessel further comprising an upper flange;an upper reactor vessel comprising a steam generator and pressurizer disposed therein, the upper reactor vessel further comprising a lower flange that matingly engages the upper flange of the lower reactor vessel; anda transporter surrounding an outer surface of the upper reactor vessel, wherein the transporter includes a collar surrounding the outer surface of the upper reactor vessel, the collar including first and second wheels affixed thereto that are disposed upon respective first and second horizontal tracks, the first and second horizontal tracks being parallel to each other, andone or more of hydraulically-operated and electrically-operated lifts, each lift being secured to the collar and extendable upwardly to engage the upper reactor vessel and translate the upper reactor vessel vertically toward or away from the lower reactor vessel, and the transporter translates the upper reactor vessel horizontally toward or away from vertical alignment with the lower reactor vessel. 2. The system of claim 1, wherein the upper reactor vessel comprises an upper flange disposed concentrically around the outer surface thereof, wherein the upper flange of the upper reactor vessel is disposed below the pressurizer, wherein the one or more lifts are extendable upwardly to engage the upper flange of the upper reactor vessel to urge the upper reactor vessel vertically with respect to the lower reactor vessel when the transporter translates vertically. 3. The system of claim 1, wherein the collar further comprises third and fourth wheels that are disposed upon the first and second tracks, respectively, and with a spacing between the first and third wheels is equal to a spacing between the second and fourth wheels. 4. The system of claim 1, further comprising a plurality of vertical support members fixed to the collar and disposed in a mutually spaced relationship around the outer surface of the upper reactor vessel. 5. The system of claim 4, wherein the plurality of vertical support members collectively support a plurality of platforms arranged in a vertical spaced-apart fashion, each of the plurality of platforms extend around the outer surface of the upper reactor vessel. 6. The system of claim 4, wherein each of the vertical support members are configured to be translated with the collar. 7. The system of claim 1, wherein the transporter comprises horizontal first and second crane members, each of the first and second horizontal crane members are rollably mounted upon respective first and second horizontal tracks on opposite ends of the crane member, wherein the first and second horizontal tracks are aligned on opposite sides of the upper reactor vessel, and the first and second crane members collectively support first and second cross members disposed upon opposite sides of the upper reactor vessel. 8. The system of claim 1, wherein the plurality of control rods are configured to reciprocate axially with respect to the lower reactor vessel. 9. A method, comprising:providing a nuclear reactor primary plant within a stationary lower reactor vessel that encloses a plurality of fuel rods and a plurality of control rods, the lower reactor vessel comprising an open top defined by a first flange,providing a movable upper reactor vessel that encloses a steam generator and a pressurizer, the upper reactor vessel comprising an open bottom defined by a second flange that matingly engages the first flange during normal operation of the nuclear reactor,providing an upper reactor vessel transporter that surrounds the upper reactor vessel, the transporter comprising a collar surrounding an outer surface of the upper reactor vessel, the transporter further comprising at least first and second sets of wheels affixed to the collar that are mounted upon respective first and second horizontal tracks that are both disposed upon opposite sides of the upper reactor vessel and are parallel to each other, andproviding one or more lifts secured to the collar, wherein extension of the plurality of lifts upwardly causes engagement with the upper reactor vessel and urges the reactor vessel upwardly with respect to the lower reactor vessel. 10. The method of claim 9, further comprising providing a plurality of vertical support members fixed to the collar and spaced apart around the upper reactor vessel, wherein the plurality of vertical support members collectively support a plurality of platforms arranged in a vertical spaced-apart fashion, the platforms each extend around the outer surface of the upper reactor vessel. 11. A method of refueling a nuclear reactor, comprising:shutting down and cooling down the nuclear reactor, the nuclear reactor comprising a reactor vessel and steam system and a feedwater system;removing decay heat from the nuclear reactor;isolating the reactor vessel from the steam system and the feedwater system connected to the nuclear reactor during normal operation of the nuclear reactor;disconnecting a lower reactor vessel enclosing nuclear fuel and a plurality of control rods from an upper reactor vessel enclosing a steam generator and pressurizer disposed above the lower reactor vessel; andlifting the upper reactor vessel upwardly from the lower reactor vessel and sliding the upper reactor vessel away from the lower reactor vessel, to allow access to the lower reactor vessel to remove old nuclear fuel and/or add new nuclear fuel, wherein the upper reactor vessel is surrounded by a transporter, the transporter including a collar that surrounds the upper reactor vessel and being rollably connected to first and second parallel rails disposed upon opposite sides of the upper reactor vessel by one or more wheels that are secured to the collar, and the transporter further comprises one or more lifts that secured to the collar are extendable upwardly to engage the upper reactor vessel to upwardly translate the upper reactor vessel upwardly away from the lower reactor vessel. |
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claims | 1. An exposure apparatus for exposing a substrate to an image of a pattern of an original, the apparatus comprising:a projection optical system configured to project the image onto the substrate;a stage configured to hold the substrate;a cover configured to substantially surround an exposure light path between an end portion of the projection optical system and the stage, the end portion facing the stage;a supply port provided inside the cover, via which a purge gas is supplied into a space surrounded by the cover; anda first exhaust port provided in an end portion of the cover, via which the gas is exhausted from the space, the end portion of the cover facing the stage. 2. An apparatus according to claim 1, further comprising a second exhaust port provided in the end portion of the cover and at a position outside the first exhaust port, via which the gas is exhausted from the space. 3. An apparatus according to claim 1, further comprising a third exhaust port provided in the cover, opposed to the supply port, via which the gas is exhausted from the space. 4. An apparatus according to claim 1, further comprising a vacuum pump configured to exhaust the gas via the first exhaust port. 5. A method of manufacturing a device, the method comprising:exposing a substrate to an image of a pattern of an original by use of exposure apparatus defined in claim 1;developing the exposed substrate; andprocessing the developed substrate to manufacture the device. |
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claims | 1. In a pressurized water nuclear power plant having a nuclear reactor core and a multiplicity of control rods arranged for movement through the core for controlling the reactor power by absorbing nuclear particles while exposed to the nuclear reactions in the core, wherein a subset of said multiplicity of control rods is designated for controlling reactor power during normal power production in the plant, said subset including a plurality of groups of control rods, the groups being under the control of a reactor operator who can move each group through the core in staggered sequence, and wherein each said group has imposed thereon an administrative limit of cumulative exposure in the core while each group is situated within a preestablished position range in the core, a method for the operator to monitor compliance with said administrative limit, comprising: continually measuring the core power and generating a power signal commensurate therewith; continually measuring the position of each group in the core; establishing an incremental time base common to measuring the core power and measuring the position of each group; from said measuring of position, continually determining when on said time base, each group is within said prestablished position range; from said measuring of core power, determining the core power when each group is in said prestablished position range; computing an incremental effective exposure for each group, commensurate with core power, for each time increment at which each group is within said prestablished position range; accumulating said incremental effective exposures for each group; comparing the accumulated effective exposure for each group with the administrative limit for each group; and displaying said comparison to the reactor operator. 2. The method of claim 1 , wherein said administration limit is in the form of a limit index W:X, defined by a maximum of W hours of accumulated effective exposure on the sum S of effective exposure occurrences w 1 , w 2 , . . . etc. during any X hour period, with W less than X, and said increments in said time base, are one hour each. claim 1 3. The method of claim 1 , wherein said administration limit is in the form of a limit index Y:Z defined by a maximum of Y effective full power hours of exposure consisting of the sum of effective exposure occurrences y 1 , y 2 , etc. during any Z hour period of effective full power operation of the core, with Y less than Z and said increments in said time base, are one effective full power hour each. claim 1 4. The method of claim 1 , wherein said administration limit is imposed on exposure while a group is positioned between (i) the maximum insertion position which is permitted to be maintained indefinitely (long term steady state insertion limit, LTSSIL) and (ii) the maximum insertion position which is permitted during a normal operational transient (transient insertion limit, TIL). claim 1 5. The method of claim 1 , wherein said administration limit the maximum permitted time interval (T) during which a group can be positioned between (1) the short term steady state insertion limit (STSSIL) and (2) the maximum insertion position which is permitted during a normal operational transient (transient insertion limit, TIL). claim 1 6. The method of claim 5 , wherein the plant has a system (COLSS) for continually computing the available margin of core power relative to a limiting condition of operation (LCO), and the method comprises; claim 5 generating an alarm if (i) the COLSS is out of service and (ii) any group position exceeds its STSSIL; and displaying the time available for the operator to take corrective action, before violating the administrative limit on the permitted time interval (T). 7. The method of claim 2 , wherein the step of displaying comprises claim 2 displaying at least one scale of X uniform intervals, marked with a plurality of numeric values indicative of an initial zero value and a final value X; displaying an indicator configuration for each group, each indicator configuration having a scale associated therewith, and consisting of an indicator for each component w of said sum S, each indicator initially appearing at the zero representation of the scale and growing in size toward the scale value X to span the number of scale intervals corresponding to the ratio of effective exposure of component w to the effective power interval X; independently of but simultaneously with said indicator growth, advancing each indicator along said scale toward the scale value X, at a uniform rate; displaying the sum S of all components w displayed adjacent the scale during the immediately preceding interval X; displaying an instantaneous margin value M=Wxe2x88x92S; whereby at any given moment, the operator can visually recognize the number of and effective exposure for each component w during the immediately preceding core effective power interval X, the total exposure S during the immediately preceding interval X, and the margin M. 8. The method of claim 7 , wherein claim 7 a respective scale is displayed for each group; each scale is displayed as a circle with coincident zero and X values; and each indicator of a component w is displayed as a sector of the circle, which grows by increasing the included angle of the sector and which advances by continually rotating about the center of the circle toward the value X. 9. The method of claim 7 , wherein, claim 7 one scale is displayed as a linear segment with the zero value at one end and the X value at the other end; the indicator configuration for each of at least two groups is associated with said one scale; and each indicator of a component w is displayed as a horizontal bar, which grows by increasing in horizontal length and which advances by continually moving horizontally toward the value X. 10. The method of claim 7 , wherein the method includes, claim 7 selecting a particular indicator for higher resolution display; and in response to said selecting, resealing said scale such that each scale interval represents a shorter duration, and resizing said intervals commensurate with the resealing of the scale. 11. The method of claim 10 , wherein the step of resealing is responsive to a further step of selecting one of at least two rescale ranges, each having a respective different duration represented by each interval. claim 10 |
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054024552 | summary | FIELD OF THE INVENTION The present invention relates to a composite material having use in containment systems and container vessels for storage of waste materials. More specifically, the invention relates to containment systems and container vessels for storage of hazardous, radioactive, or mixed wastes wherein the system or vessel is fabricated with a multilayered structure including a fibrous mat layer. BACKGROUND OF THE INVENTION Containment systems employing various composite structures have been developed to handle waste materials. The waste materials to which this invention is concerned are primarily hazardous, radioactive, and mixed, that is both hazardous and radioactive, wastes. These containment systems must meet rigid governmental safety standards set for structural stability and strength, along with those for its shielding characteristics. Conventionally, these containment systems have been made with composite materials having concrete layers, optionally reinforced with metal bars such as a rebar construction to improve the strength of the container. Examples of such systems are generally shown in U.S. Pat. Nos. 4,950,246 and 4,845,372. These systems have been widely used and accepted by the industry, however improvements upon these designs can be made to improve their strength and shielding capacity. SUMMARY OF THE INVENTION The present invention provides an improved shielding composite material having a multiple layered construction. The composite contains a fibrous mat layer that has a first and a second face. The mat layer contains a mat that is made from interwoven fibers, preferably metallic fibers, and these fibers are encased within a concrete-based material. A first concrete-based layer is located proximate to at least one face, and optionally both faces, of the mat layer. The concrete-based layer preferably contains at least one shielding additive such as barite, magnetite, taconite, depleted uranium, vitrified glass-like materials manufactured from thermal treatment of wastes, and mixtures thereof. An impermeable coating layer is optionally placed on the exposed face of either concrete-based layer to prevent liquids and other fluids from contacting the concrete-based layers. The mat layer, composed of the fibrous mat and solidified in the concrete-based material, improves both the strength of the layered storage composite, but also improves its shielding capacity in comparison to a similar composite made with concrete, or concrete with a rebar construction. The present invention also provides methods for constructing the multi-layered storage structure composite. The fibrous mat containing the interwoven fibers is provided such that a first and second face are exposed. A concrete-based mixture is then poured into and adjacent to the mat to encase the fibers of the mat in the concrete-based mixture and to provide a first concrete-based layer proximate to the first face of the mat. The concrete-based mixture preferably contains at least one shielding additive. |
description | This application claims priority to U.S. Provisional Patent Application Ser. No. 62/036,219, filed on Aug. 12, 2014 and entitled “Nanophotonic Interaction Measurements of Freely Binding Biomolecules,” the entire disclosure of which is incorporated herein by reference. This invention was made with Government support under Grant Number 1R01GM106420-01 awarded by the NIH; Grant Number ECCS-0335765 awarded by the NSF; and Grant Number DMR-1120296 awarded by the NSF MRSEC program. The United States Government has certain rights in the invention. The present disclosure is directed generally to methods and systems for label-free analysis of molecular interactions using near-field optical techniques. Analyzing and understanding molecular interactions is fundamentally important to the life sciences. Exploring these interactions will not only advance the understanding of basic biology, but will provide researchers with the ability design molecules to modify, block, or otherwise affect certain interactions. There are currently numerous methods available to analyze molecular interactions, including both labeled and label-free mechanisms. Labeling methods include fluorescence, radioactivity, phosphorescence, bioluminescence, and chemiluminescence, among others. Label-free methods include surface plasmon resonance, differential scanning calorimetry, various biosensors such as capacitive, conductometric, and impedimetric sensors, among many other methods. However, these common approaches typically require immobilizing one or both of the interacting molecules on a sensing area such as an assay plate or a sensor surface, thereby constraining their binding activity. When analyzing multivalent bindings, for example, this restriction prevents an accurate measurement of affinity and binding capacity. Accordingly, there is a continued need in the art for methods and systems that allow for label-free analysis of free-solution molecular interactions with increased resolution. The present disclosure is directed to inventive methods and systems for detecting unrestricted interactions between molecules. A near-field optical trap is utilized to provide quantitative analysis of the interactions at, for example, the attogram scale. The method exploits the fact that the optical force exerted on a trapped particle is proportional to the particle's volume and polarizability. The spring constant or the trap stiffness can be extracted from the Brownian fluctuation of the trapped particle. Thus, by observing these fluctuations, the binding of a partner biomolecule to the trapped particle can be detected. For example, specific antibody binding to an optically trapped virus is detected by analyzing changes in the confined Brownian motion of the virus observed via evanescent wave light scattering. The method allows the measurement of binding interactions without restricting them by immobilizing or labeling either of the interacting biomolecules. In addition, the developed model for the effective polarizability of the binding complex enables accurate measurements of the affinity and stoichiometry of the interactions. According to one embodiment, the label-free method for analyzing molecular interactions can be used to analyze the potential pathogenicity and virulence of rapidly mutating influenza viruses, in addition to identification. Furthermore, the light-scattering-based detection method can be used to monitor biomolecular interactions in real time, giving new information on the kinetics of the interaction at a single molecule level. The methods and systems described herein have many potential applications, including in drug discovery for screening, developing drug compounds, and in clinical diagnosis as a label-free ultrasensitive biosensor, among many other applications. Generally, in one aspect, a method for characterizing an interaction between a first particle and one or more second particles is provided. The method includes the steps of: (i) providing an optical trap system including a photonics-based trap, a light source, and a camera; (ii) optically trapping, using the photonics-based trap, the first particle; (iii) obtaining a first measurement of a trap stiffness of the photonics-based trap; (iv) introducing the one or more second particles to the optically trapped particle; (v) incubating the first and second particles under conditions suitable for an interaction between the first and second particles; (vi) obtaining a second measurement of the trap stiffness of the photonics-based trap after the incubation; and (vii) determining, using the first measurement of trap stiffness and the second measurement of trap stiffness, a property of the interaction between the first particle and the second particle. According to an embodiment, the photonics-based trap is, for example, a photonic crystal resonator, a photonic waveguide, a plasmonic structure, or an optically-excited nano-structure or micro-structure. According to an embodiment, the step of obtaining a first measurement of a stiffness of the photonics-based trap comprises the step of analyzing reduced Brownian motion of the first particle in the photonics-based trap. According to an embodiment, the trap stiffness of the photonics-based trap is extracted from a positional variance of the particle within the photonics-based trap. According to an embodiment, the positional variance of the particle within the photonics-based trap is determined at least in part using image analysis. According to an embodiment, the image analysis is video tracking. According to an embodiment, the first particle is between 10 nm and 20 μm. According to an embodiment, the method includes the step of determining an affinity between the first particle and the second particle. According to an embodiment, the method includes the step of determining a stoichiometric relationship between the first particle and the second particle. According to an embodiment, the system obtains multiple measurements of the trap stiffness during the incubation, and determines the rate of the interaction between the first particle and the second particle. According to an aspect, a method for characterizing an interaction between a first particle and one or more second particles is provided. The method includes the steps of: (i) optically trapping the first particle; (ii) obtaining a first measurement of a trap stiffness of the trap; (iii) introducing the one or more second particles to the optically trapped particle; (iv) incubating the first and second particles under conditions suitable for an interaction between the first and second particles; (v) obtaining a positional variance of the trapped molecule after incubation with the second particle; and (vi) determining, using the positional variance, a property of the interaction between the first particle and the second particle. According to an embodiment, the positional variance is obtained using a near-field light scattering imaging system. According to an aspect is a system configured to characterize an interaction between a first particle and one or more second particles. The system includes: (i) a first particle; (ii) a second particle; (iii) a photonics-based optical trap; (iv) a camera configured to detect a positional variance of an optically trapped particle in the photonics-based trap; and (v) a processor configured to receive a first measurement of a trap stiffness of the photonics-based trap, receive a second measurement of the trap stiffness of the photonics-based trap after the second particle is incubated with the first particle, and determine, using the first measurement of trap stiffness and the second measurement of trap stiffness, a property of the interaction between the first particle and the second particle. These and other aspects of the invention will become clear in the detailed description set forth below. The present disclosure is directed to embodiments of a method and system for detecting unrestricted interactions between molecules using a near-field optical trap. Since the optical force exerted on a trapped particle is proportional to the particle's volume and polarizability, and the spring constant or the trap stiffness can be extracted from the Brownian fluctuation of the trapped particle, the binding of a partner molecule to the trapped particle can be detected. For example, according to an embodiment, the near-field optical trap method and system can be utilized to analyze many different specific biomolecular interactions, including but not limited to antibody/virus interactions. As described in detail below, the near-field optical trap method and system can detect interactions between single influenza viruses and antibodies at the attogram scale. Specific antibody binding to an optically trapped virus is detected, for example, by analyzing changes in the confined Brownian motion of the virus observed via evanescent wave light scattering. This same technique can be applied to a wide range of molecular interactions because the nanophotonic tweezer can handle molecules from tens to thousands of nanometers in diameter. Referring to FIG. 1, in one embodiment, is a method 100 for analyzing and quantifying interactions between two or more particles. The particles analyzed by this method can be, for example, a biological particle such as a virus, cell, protein, protein aggregate, and many other types of biological particles, or can be a non-biological particle such as a polymeric, glass, or metallic nanoparticle. Many other types of biological and non-biological particles are possible. The interactions analyzed and/or quantified by the methods described or otherwise envisioned herein can be any type of interaction between the two or more particles. For example, the interaction can be binding such as specific or non-specific binding, rate of binding, rate of absorption, unbinding, and desorption, among many others. The interaction analyzed and/or quantified can also be, for example, the lack of an interaction. At step 110 of the method, an optical trap is provided. The optical trap can be any of the devices described herein or otherwise envisioned. For example, the optical trap is a photonic crystal (“PhC”) resonator, as shown in FIGS. 2-3, and/or a photonic waveguide, a plasmonic structure, or any other optically excited nano or micro-structure. According to one embodiment, the silicon nitride PhC resonator comprises a series of holes on both sides of a resonator cavity and a central hole. The holes may be etched in a silicon nitride waveguide lying on a silicon dioxide substrate, although other materials are possible. As shown in FIG. 3, for example, according to an embodiment, the holes are spaced at approximately 352 nm, although the distance is variable. For example, the periodicity of the PhC structure is kept constant, and the hole sizes can be chosen to have a Gaussian-shaped field attenuation inside the Bragg mirror and have a desired resonant wavelength. According to an embodiment the PhC resonator comprises a small hole at the center of the cavity such that the superposition of evanescent fields leads to an increase in the field intensity and thus the trapping stiffness is significantly increased. Many other variations of the optical trap are possible. For example, according to one embodiment, the PhC is a component of a microarray utilized to simultaneously or sequentially analyze multiple interactions. Referring to FIG. 2A, in one embodiment, is a PhC resonator system 200 including a PhC resonator 210, an oxide base 220 such as a silicon dioxide substrate, and a chamber 230. According to an embodiment, chamber 230 allows solutions and/or molecules to be introduced for trapping, binding, washing, and other purposes. The PhC resonator system 200 may also include a light source 240, such as a laser, configured to emit light to trap a molecule on the PhC resonator 210. The system can also include a camera 250 or other visualization device for obtaining images or other data of the system for analysis. At step 120 of the method, a particle is optically trapped. For example, the particle may be introduced into chamber 230 or otherwise introduced to the system. According to one embodiment, the PhC resonator 210 is situated within a chamber comprising multiple copies of the target particle, or just a limited number of copies of the target particle. The light source 240 can be utilized to excite the resonator, causing the particle to be propelled by the optical force to the center of the cavity while it is trapped on the resonator surface. Referring to FIG. 2B, for example, particle 260 is trapped on PhC resonator 210 by light source 240 emitting light 270. At step 130 of the method, one or more initial measurements are obtained. For example, according to an embodiment, an initial measurement of the trap stiffness is conducted. Referring to FIG. 2B, for example, where particle 260 is optically trapped, trap stiffness can be measured. According to an embodiment, in order to determine the stiffness of the optical trap, the reduced Brownian motion of the particle trapped at the center of the cavity is analyzed, including as described in greater detail below. According to another embodiment, the first particle is not optically trapped using the PhC resonator, but the position of the particle is observed using a near-field light scattering technique. Using this method, neither of the interacting biomolecules is immobilized. At step 140 of the method, a second particle is introduced. The second particle can be any particle, including but not limited a binding partner such as a known binding partner, a suspected binding partner, or a possible binding partner, such as in the case of a screen for molecular interactions. The second particle can be one particle, or can be many particles. For example, according to an embodiment, two or more different types of particles are introduced at step 140 of the method. The second particle(s) can be introduced, for example, by introducing a flow to the chamber where the PhC resonator resides. Referring to the right panel in FIG. 2B, for example, where particle 260 is optically trapped, second particle 280 is introduced to chamber 230. If the conditions are suitable for a biomolecular interaction, the first particle 260 and one or more of the second particles 280 will bind. This will increase, for example, the radius of the complex 290, shown in FIG. 2B. According to just one embodiment, for example, the flow in a microchannel is switched from virus solution to antibody dispersed solution at step 140. Antibodies in the following solution bind to the trapped virus. The binding can be saturated for a period of time, such as 30 min, after the flow switching. At step 150 of the method, one or more post-exposure measurements are obtained. For example, according to an embodiment, an measurement of the trap stiffness is conducted. Referring to the right panel in FIG. 2B, for example, where particle 260 is optically trapped, trap stiffness can be measured for the complex 290. According to an embodiment, in order to determine the stiffness of the optical trap, the reduced Brownian motion of the complex 290 trapped at the center of the cavity is analyzed, including as described in greater detail below. According to an embodiment, the relationship between the change in the particle radius between particle 260 and complex 290, and the trap stiffness, is analyzed. The relative trap stiffness of the complex after binding is related to that of the particle before binding, as described in greater detail below. Accordingly, if the refractive indices of the trapped particle and binding antibody are known, specific binding characterized by the change in radius corresponding to the bound layer is detected by measuring the relative trap stiffness. According to an embodiment, the stoichiometry of the binding can also be determined from the obtained measurements. According to an embodiment, as shown by arrow 152 in FIG. 1, step 150 can be repeated two or more times. For example, the system can be utilized to analyze kinetics of the interaction between the two or more particles. Rather than making an initial measurement of the trap stiffness before binding and then a final measurement after binding, the system can be configured to take multiple measurements at step 150. For example, the system can be configured to take measurements in a time-dependent manner. In one embodiment, the system can be configured to take time-dependent measurements depending on the expected or suspected kinetics of the possible interaction(s). Rate of binding or any other interaction can then be extracted from the multiple obtained measurements using known techniques. At step 160 of the method, the trapped particle 260, or complex 290 if a complex formed, is released from the optical trap. This occurs when the light source is deactivated or otherwise adjusted. According to an embodiment, the system comprises a processor which is configured to receive a first measurement of a trap stiffness of the optical trap, receive a second measurement of the trap stiffness of the optical trap after the second particle is incubated with the first particle, and determine, using the first measurement of trap stiffness and the second measurement of trap stiffness, a property of the interaction between the first particle and the second particle. According to an embodiment, the methods and systems described and otherwise envisioned herein are used for multiplexed analysis of multiple interactions. For example, the optical trapping system can comprises multiple optical devices, or multiple optical traps, in an array. The array can then monitor multiple interactions at the same time. According to one embodiment, an array comprises multiple optical traps that each trap a first particle. Each of the traps is isolated within the array such that a different second particle can be introduced individually to different chambers. In this way, interactions between a first particle and multiple different second particles are analyzed. According to another embodiment, an array comprises multiple optical traps that each trap different first particles. A second particle is then added to the array. In this way, interactions between multiple different first particles and a second particle are analyzed. Many other configurations are possible. Accordingly, methods and systems are described herein to directly and accurately detect the binding of unrestricted molecules using near-field optical trapping. The methods and systems also demonstrate the ability to measure the affinity and stoichiometry of molecular interactions at the attogram scale. According to an embodiment, and where comparison is possible, measurements of the affinity and the stoichiometry of a specific antibody to the colloid are in agreement with the manufacturer-quoted binding capacity. Notably, the detection method does not require labeling or immobilizing either of the interacting molecules. As described in detail below, affinity measurements for a single influenza virus and an anti-influenza antibody are obtained, which is found to be 6.8 (±1.1) attogram of anti-influenza antibodies per virus. According to an embodiment, the method can be utilized for studying the potential pathogenicity and virulence of rapidly mutating influenza viruses in addition to identification. Furthermore, the light-scattering-based detection method can be used to monitor biomolecular interactions in real time, giving new information on the kinetics of the interaction at a single molecule level. Because a very high optical intensity is available at the center cavity of the photonic crystal resonator, the methods are able to observe scattered light signals from sub-100 nm particles. This technique has many potential applications, including but not limited to drug discovery for screening and developing drug compounds, clinical diagnosis as a label-free ultrasensitive biosensor, and many other applications. According to an embodiment, the near-field optical trap method and system can be utilized to investigate interactions between, for example, a pathogenic virus and its antibody. Understanding these interactions is vital to pathogen control and prevention. By observing Brownian fluctuations of a trapped particle, the spring constant or the trap stiffness can be extracted, and the binding of a partner biomolecule to the trapped particle can be detected. This allows for analysis of binding interactions without restricting them by immobilizing or labeling either of the interacting biomolecules. In addition, the inventive model for the effective polarizability of the binding complex enables accurate measurements of the affinity and stoichiometry of the interactions. According to an embodiment, therefore, is an antibody binding assay in which one interacting antibody is coupled to the surface of a nanoparticle and the partner antibody freely moving in a solution is allowed to bind to it. The affinities and stoichiometries measured affinities and stoichiometries using the near-field optical trap method and system can then be compared to known values. Further, binding interactions can be analyzed using a system in which neither of the interacting biomolecules is immobilized. For example, the system can detect the binding of antibody to a single human influenza A virus, and can measure the stoichiometry of the specific antibody. According to an embodiment, the result of the molecular binding to the target is described using an effective sphere model of antibody-particle complexes. The effective polarizability of the sphere allows one to describe the interactions with the known applied optical force from the following equation:Ftrap=2π∇Ioαeff/c (Eq. 1)where c and λ are the speed and wavelength of light, Io is the incident intensity, and αeff is the effective polarizability expressed according to the following equations: α eff = 4 πɛ 0 ( ɛ e - ɛ m ɛ e + 2 ɛ m ) R outer 3 where ( Eq . 2 ) ɛ e = ɛ s ( R outer 3 ( ɛ e + 2 ɛ s ) + 2 R inner 3 ( ɛ c - ɛ s ) R outer 3 ( ɛ c + 2 ɛ s ) - R inner 3 ( ɛ c - ɛ s ) ) ( Eq . 3 ) where εc, εs, and εm are dielectric constants of the core (polystyrene or a virus), shell (antibodies), and medium (water) respectively, εe is the effective dielectric constant of the core-shell complex (ε≈n2 assuming non-absorbing materials of refractive indices such as 1.59 for a polystyrene (PS) particle, 1.41 for an antibody, and 1.48 for an influenza virus), Router is the core-shell radius, and Rinner is the core radius. The force is calibrated with its spring constant or the trap stiffness. At a step of the method as described above, a particle is optically trapped. Referring to FIG. 3, according to an embodiment, is a schematic representation of a scanning electron microscope image of a photonic crystal (“PhC”) resonator. A particle is optically trapped using the PhC resonator and the equipartition method is utilized to extract the trap stiffness from the positional variance of the particle within the optical trap using video tracking analysis. According to an embodiment, the silicon nitride PhC resonator was fabricated according to the procedure set forth in Chen et al., Controlled Photonic Manipulation of Proteins and Other Nanomaterials, Nano Lett 12:1633-1647 (2012) (the entire contents of which are hereby incorporated by reference), with several important modifications. NEB-31 electron beam photoresist was spun on a wafer on which a 250-nm stoichiometric silicon nitride layer was deposited on top of a 3.5 gm thermal oxide layer by the low-pressure chemical vapor deposition. To reduce a charging effect during exposure, a 5-10 nm thin gold film was deposited on the resist with a thermal evaporator. It was patterned using a JEOL 9500 electron beam lithography system. According to an embodiment, a 1064 nm fiber coupled diode laser (LU1064M400, Lumics, El Segundo, Calif.) was used as a light source for optical trapping. The laser was coupled to the input waveguide of silicon nitride through a lensed optical fiber. A thermistor in the laser diode was controlled to tune in a resonance wavelength of a photonic crystal resonator with an increase of approximately 0.3 nm per 1 K temperature rise. The power coupled into the resonator was measured by focusing the light emitting from output waveguide onto a detector of a power meter. Power measurements with a power meter were sampled in real time using a Labview program. A polarizer passing a TE-polarized light was placed between the focusing lens and the detector. At a step of the method as described above, the relationship between the change in the particle radius and the trap stiffness is analyzed. The relative trap stiffness of the complex after binding is related to that of the particle before binding with the relative polarizabilities expressed as:(ktrap,ΔR/PΔR)/(ktrap,0/P0)=αeff,ΔR/αeff,0 (Eq. 4)where P is the power, ktrap is the trap stiffness, subscript 0 denotes an initial measurement, and subscript ΔR denotes the measurement at equilibrium. Therefore, if the refractive indices of the trapped particle and binding antibody are known, specific binding characterized by the change in radius corresponding to the bound layer, ΔR, is detected by measuring the relative trap stiffness. This relationship is described by the transcendental equation: R outer , Δ R = R outer + Δ R = [ ( k trap , Δ R P Δ R ) ( k trap , 0 P 0 ) · ( ɛ e , 0 - ɛ m ɛ e , 0 + 2 ɛ m ) ( ɛ e , Δ R - ɛ m ɛ e , Δ R + 2 ɛ m ) ] 1 / 3 · R outer ( Eq . 5 ) where ktrap=2kBT/rrms2, where kB is the Boltzmann constant, T is the temperature in K, and rrms2=(1/n)Σ(x2+y2) is the variance of n instantaneous positions, and all other variables are noted as previously. According to an embodiment, the power-normalized relative trap stiffness for equilibrium binding affinity is determined after an incubation period of approximately 30-min. During this time, the solution of binding antibody is flowed over a trapped particle using a microfluidic channel. Referring to FIG. 4, in one embodiment, is an integrated optofluidic device. According to an embodiment, to make flow channels, three holes of D=500 nm were cut on a glass coverslip using a CO2 laser (VersaLaser VLS3.50). Punched PDMS piece was bonded to the punched cover glass by oxygen plasma bonding. A 100-μm thick parafilm spacer was cut using the CO2 laser to have three inlet channels combining to one channel whose width is approximately 1 mm. The parafilm spacer was laid between the cover glass and a fabricated nitride chip. Next the sandwiched complex was briefly heated on a 100-degree-Celsius hot plate to melt the parafilm spacer and bond firmly for preventing leaking in flowing and switching solutions. Tygon tubings were inserted tightly to the holes through PDMS fixtures to inject solutions into the channels using three syringe pumps (Harvard Apparatus, Holliston, Mass.). Before conducting an experiment, a SuperBlock blocking buffer solution (Sigma-Aldrich, 37580) with 0.05% tween 20 (Sigma-Aldrich, P7949) was filled in the channels and incubated either over 30 min at room temperature or over 12 hours at 2-8 degree Celsius to prevent non-specific binding. According to an embodiment, a specific binding between a fluorescent polystyrene bead coated with goat anti mouse IgG and antibodies in solution was measured. The measured binding capacity of the antibodies was compared to the manufacturer's quoted value (Spherotech Inc.). The position fluctuations were measured using fluorescence microscopy, an example of which is shown in FIG. 5, with typical measurements using this setup shown in FIG. 6. Changes in power-normalized trap stiffness and radius increases of an IgG coated colloid were compared for solutions of mouse IgG, mouse IgM, goat anti-rabbit IgG, and a buffer. As described above, the power-normalized relative trap stiffness was correlated to the radius increase with a known initial diameter for Router (D≈270 nm). From studies on protein sizes, changes in thickness resulting from specific antibody binding were predicted to be 5.79 nm for IgG (MIgG=160.5 kDa) and 10.55 nm for IgM (MIgM=970 kDa). Affinity is indicated by a measured radius increase 7.5±6.5 nm and 14.4±5.6 nm for solutions of mouse IgG and mouse IgM respectively, in agreement with the predictions. It should be noted that theoretical estimates are based on the unhydrated mass of protein while in the experiment there are water molecules bound to the antibody. Electrical measurements indicate an increase of about 4.5 nm for IgG. Specificity is demonstrated by measured negligible radius increases of −1.7±6.6 nm and −2.2±5.7 nm in the solution of an unspecific antibody (goat anti-rabbit IgG) and a buffer respectively. Referring to FIG. 7, in one embodiment, are measurements of the stoichiometry of each binding event. The manufacturer-quoted binding capacity of coated IgG to polystyrene particles (Spherotech, Inc) is ≈117.4 IgGs (≈31.3 ag) per particle. The manufacturer-quoted binding capacity of mouse IgG (FITC-labeled) to coated anti-mouse IgG is ≈107.6 IgGs (≈28.7 ag) per particle. In comparison, the binding capacity measured in the affinity assay for mouse IgG was 124.0±112.7 IgGs (33.0±30.0 ag) per particle, whereas for mouse IgM it was 57.0±23.9 IgMs (91.8±38.5 ag) per particle. Despite the large uncertainties, the results of the binding capacity indicate a 1:1 binding ratio, consistent with the manufacturer-quoted binding capacity. Slightly larger binding capacity of the mouse IgG than the manufacturer-quoted one is likely because of unlabeled antibodies used in these experiments. According to an embodiment, the methods and systems described herein are utilized to analyze the stoichiometry of the interaction between a first particle and two or more second particles. For example, the stoichiometry of an interacting antibody was examined. Specifically, the binding capacity of antibody coated on a polystyrene particle with 2.89 μg/mg of particles was used to determine stoichiometry of binding antibody from a radius change. The number of IgG per mg of particle was calculated as NIgG=MIgG,total/MIgG=1.084>1013 IgG/mg, where molecular weight of IgG is 160.5 kDa (=0.2665 ag). The number of polymer particles per mg are calculated as Nps=Mps,total/Mps=Mps,total/(ρpsπD2)=9.241×1010 particles/mg, where the density of polystyrene is 1.05 g/cm3, and manufacturer-quoted diameter of particles is approximately 270 nm. Therefore the binding capacity of anti-mouse IgGs to a polymer particle is calculated to be 117.4 IgGs per particle. Volume occupied by the number of antibody (NIgG=117.4) to the volume of a IgG-coated layer (t=δIgG=5.794 nm) determines the antibody density in a binding layer. Volume of an individual antibody is determined from dehydrated mass of an antibody as V=dIgG (or IgM)3, where dIgG=5.79 nm and dIgM=10.55 nm. The density was used to determine the volume of antibodies binding to a IgG-coated colloid with a radius increase resulting from the bindings. This allows for the determination of the total mass of bound antibodies, and thus the number of bound antibodies. According to an embodiment, the near-field optical trap method and system can be utilized to investigate interactions between, for example, a pathogenic virus and its antibody. Understanding these interactions is vital to pathogen control and prevention. According to an embodiment, the specific antibody to a human influenza A virus was detected using the near-field light scattering technique. Referring to FIG. 8, in one embodiment, is a schematic representation of a system 800 for analyzing biomolecular interactions using a near-field light scattering method. The technique provides a detection method for pathogen identification without the need of labeling either of a virus or an antibody. Accordingly, the method can accurately measure affinity and stoichiometry of an anti-influenza antibody to the influenza virus. Further, sensitivity of the binding detection can be improved by trapping a smaller target particle like an influenza virus (D≈100 nm) than a 270-nm diameter IgG coated colloid. Changes in power-normalized trap stiffness are compared for different solutions of mouse anti-influenza IgG, goat anti-rabbit IgG, and a buffer. The methods described above are utilized to correlate the power-normalized relative trap stiffness to the radius increase with a known initial diameter for Rinner (Dvirus≈100 nm). Affinity is indicated from a radius increase 7.6±1.1 nm in the solution of mouse anti-influenza IgG. The radius increase is attributed to the specific binding of anti-influenza IgG. Specificity is demonstrated by much smaller radius increases 0.2±1.7 nm and i 0.2±1.5 nm in the solution of an unspecific antibody (goat anti-rabbit IgG) and a buffer respectively. Compared to the previous assay, the sensitivity of binding detection to the unspecific binding was improved, which is attributed to the smaller size of viruses leading to a larger fractional polarizability change for a given bound layer, and to the better signal-to-noise ratio of the light scattering imaging technique. The stoichiometry of the binding antibodies was also determined from the obtained measurements. The binding capacity of anti-influenza IgG to the virus is 6.8±1.1 ag (25.5±4.3 IgGs) per virus. In comparison, specificity is shown by much smaller binding of 0.2±1.4 ag (0.7±5.1 IgGs) and −0.1±1.1 ag (−0.5±4.3 IgGs) per virus in the solution of goat anti-rabbit IgG and a buffer respectively. While other techniques are capable of virus detection, the methods and systems described herein enable quantitative measurements of the binding capacity of an anti-influenza antibody to a single virus. Sample Preparation According to an embodiment, colloids and antibodies were diluted in a buffer solution of 1× phosphate buffered saline (PBS) containing 0.05% bovine serum albumin (BSA), and 0.05% Tween 20. For anti-influenza antibody 5 μl stock solution was diluted in 1 ml of the buffer solution, and concentration of all other antibodies in a diluted solution was 1 μg/ml, which is the typical limit of detection for numerous types of biosensors. Goat anti-mouse IgG coated fluorescent polystyrene particles (FITC, MFP-0252-5, Dmean≈0.27 μm) were purchased from Spherotech Inc. (Lake Forest, Ill.). Mouse IgG (MG300) and mouse IgM (MGM00) antibodies were from Invitrogen Corp. (Camarillo, Calif.). Goat anti-rabbit IgG (A10533) antibody was from Life Technologies (Carlsbad, Calif.). Swine-origin Human influenza A California/4/2009 (H1N1) virus (purified and UV-inactivated) was from Advanced Biotechnologies Inc. (Columbia, Md.). Mouse anti-influenza A H1N1 monoclonal IgG antibody (MAB8256) was purchased from EMD Millipore Corp (Temecular, Calif.). Other chemicals such as Superblock blocking buffer (37580), PBS (10× concentrate, P5493), bovine serum albumin (A9647), Tween 20 (P7949), were purchased from Sigma-Aldrich. Imaging and Data Analysis Image acquisition was performed by a Hamamatsu ORCA-ER CCD camera controlled by a Hamamatsu HCImage software. 40× objective (LUCPlanFL N, 0.60, ∞/0-2/FN22, UIS2) was used for both the fluorescence imaging and the near-field light scattering imaging. Fluorescent particles were imaged with excitation by a mercury arc lamp. Fluorescence imaging was optimized with an 842 nm blocking edge BrightLine short-pass filter for exposure time of 10 ms. Detection of near infrared at 1064 nm from the camera is accounted for manufacturer-quoted quantum efficiency of 0.45% (Hamamatsu Photonics). The light scattering imaging was optimized with a 641/75 nm BrightLine single-band bandpass filter (FF01-641/75-25, Transmission at 1064 nm, 2.6%) for exposure time of 20-100 μs, or a 628/40 nm BrightLine single-band bandpass filter (FF02-628/40-25, Transmission at 1064 nm, 0.2%) for exposure time of 0.7-2 ms. Experimental Measurements According to an embodiment, in measurements, experimental parameters such as power, number of instantaneous positions to determine the trap stiffness, and uncertainty of a measurement were characterized to obtain a reliable measurement of the trap stiffness. The critical power to optically trap a D 270 nm colloid ranged in 1.5-2 mW (PTE) whereas that for D≈100 nm influenza A virus ranged in 3.5-5 mW (PTE). Below this range the optical scattering force or hydrodynamic force exerted on a trapped particle destabilize the optical trap, either transporting the particle in the propagation direction of electromagnetic wave or losing the optical trap. In addition, power above the range caused sticking of a trapped particle on the resonator surface in which the trap stiffness ranged in 1.7<kr<2.5. In order to minimize external noise such as thermal excitation caused by long-time fluorescent excitation, observation time related to the number of instantaneous positions is optimized to be 12-25 sec for each measurement with exposure time 10 μs, resulting in 0.6<kr<0.9 otherwise. According to an embodiment, the detection method is based on fluctuation-based measurements that can involve external noises such as mechanical vibrations, detector noise, and thermal noise. Determination of the uncertainty caused by these factors describes signal-to-noise ratio, providing a more accurate assay analysis. TEM Imaging Transmission electron microscopy (TEM) image of a Human influenza A H1N1 virus was taken with the FEI Tecnai F20 in STEM mode in the Cornell Center for Materials Research Shared Facilities. A staining protocol was performed prior to TEM imaging. Observed size range of the viruses was consistent with the literature that the range is considered to be approximately 90-110 nm in diameter. Average size was estimated approximately 100 nm. The TEM image showed that the viruses retain viral morphology and hemagglutin (HA) in the viral envelope, allowing viable affinity assays with anti-influenza antibodies. While various embodiments have been described and illustrated herein, those of ordinary skill in the art will readily envision a variety of other means and/or structures for performing the function and/or obtaining the results and/or one or more of the advantages described herein, and each of such variations and/or modifications is deemed to be within the scope of the embodiments described herein. More generally, those skilled in the art will readily appreciate that all parameters, dimensions, materials, and configurations described herein are meant to be exemplary and that the actual parameters, dimensions, materials, and/or configurations will depend upon the specific application or applications for which the teachings is/are used. Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments described herein. It is, therefore, to be understood that the foregoing embodiments are presented by way of example only and that, within the scope of the appended claims and equivalents thereto, embodiments may be practiced otherwise than as specifically described and claimed. Embodiments of the present disclosure are directed to each individual feature, system, article, material, kit, and/or method described herein. In addition, any combination of two or more such features, systems, articles, materials, kits, and/or methods, if such features, systems, articles, materials, kits, and/or methods are not mutually inconsistent, is included within the scope of the present disclosure. |
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claims | 1. A luminescence sensor comprising at least a first polarization wire grid and a second polarization wire grid for receiving and polarizing excitation radiation, wherein the first polarization wire grid comprises slits and wires extending in a first direction and the second polarization wire grid comprising slits and wires extending in a second direction, the first direction and the second direction being substantially perpendicular with respect to each other, wherein the excitation radiation is polarized such that it is substantially suppressed by one of the first and second polarization wire grids and substantially passed through by the other of the first and second polarization wire grids. 2. The luminescence sensor according to claim 1, wherein the sensor is irradiated with excitation radiation from an excitation radiation source. 3. The luminescence sensor according to claim 1, wherein the excitation radiation is polarized such that it is substantially suppressed by the second polarization wire grid which is positioned farthest away from the excitation radiation source and substantially not suppressed by the first polarization wire grid which is positioned closest to the excitation radiation source. 4. The luminescence sensor according to claim 1, the second polarization wire grid having a top surface, wherein the first polarization wire grid is positioned on the top surface of the second wire grid. 5. The luminescence sensor according to claim 1, wherein the luminescence sensor furthermore comprises a gap between the first polarization wire grid and the second polarization wire grid, causing a distance d between the first polarization wire grid and the second polarization wire grid. 6. The luminescence sensor according to claim 5, wherein the distance d is between 100 nm and 100 .mu.m. 7. The luminescence sensor according to claim 5, wherein the distance d is variable. 8. The luminescence sensor according to claim 1, wherein the luminescence sensor furthermore comprises a third wire grid between the first and second polarization wire grids and which is aligned such that the wires of the third wire grid are positioned under or above and parallel to the slits of respectively the first or second polarization wire grid. 9. The luminescence sensor according to claim 8, wherein the third wire grid is positioned on the top surface of the second polarization wire grid. 10. The luminescence sensor according to claim 8, wherein the third wire grid has side walls, the luminescence sensor comprising a luminophore attached on the side walls of the third wire grid. 11. The luminescence sensor according to claim 1, the slits having a smallest dimension and the sensor being immersed in an immersion fluid, wherein the smallest dimension of the slits is smaller than the wavelength of the excitation radiation in the immersion fluid. 12. The luminescence sensor according to claim 1, wherein at least one of the at least first and second polarization wire grids is positioned on top of a bearing substrate. 13. The luminescence sensor according to claim 1, wherein the luminescence sensor is a luminescence biosensor. 14. The luminescence biosensor according to claim 13, wherein the luminescence biosensor is a fluorescence biosensor. 15. The luminescence sensor according to claim 1, wherein the first and second polarization wire grids have side walls, the luminescence sensor comprising a luminophore attached on the side walls of one of the first and second polarization wire grids. 16. A method for the detection of luminescence radiation generated by at least one luminophore, the method comprising acts of:irradiating a luminescence sensor with excitation radiation, the luminescence sensor comprising at least a first polarization wire grid having slits and wires extending in a first direction and a second polarization wire grid having slits and wires extending in a second direction, the first direction and the second direction being substantially perpendicular with respect to each other; andpolarizing luminescence radiation in the luminescence sensor,wherein the excitation radiation is polarized such that it is substantially suppressed by one of the at least first polarization wire grid and second polarization wire grid and substantially passed through by the other of the at least first polarization wire grid and second polarization wire grid. 17. The method according to claim 16, wherein the excitation radiation is substantially passed through by the first polarization wire grid but is substantially suppressed by the second polarization wire grid. 18. The method according to claim 16, comprising an act of detecting the generated luminescence radiation. 19. The method according to claim 16, wherein the first and second polarization wire grids have side walls, the method comprising an act of attaching a luminophore to the side walls of one of the first and second polarization wire grids. 20. The luminescence sensor according to claim 16, comprising acts of:providing a third wire grid having side walls, wherein the third wire grid is provided between the first an second wire grids; andattaching a luminophore to the side walls of the third wire grid. |
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abstract | An electronic device (18) is for managing the display of data to control a nuclear power plant. The data comes from a plurality of electronic control units (16A, 16B, 16C). Each control unit is configured to perform at least one action from among acquiring a value measured by a sensor (12A, 12B, 12C) and controlling an actuator (14A, 14B, 14C), the control units, sensor(s) and/or actuator(s) being according to several different nuclear safety classes. This electronic device (18) is able to be connected to the control units, and includes a set (25) of electronic module(s) (26A, 26B, 26C) for creating overlay(s) (28A, 28B, 28C). Each overlay contains information associated with one or several control units and according to a respective safety class; and a module (30) for generating a page (32) to be displayed, by superposition of several separate overlays. |
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description | The present invention relates to detecting leaks in fuel channels of nuclear reactors. More particularly, the invention relates to detecting a leaking fuel channel in a CANDU-type nuclear reactor. The CANDU (“CANada Deuterium Uranium”) reactor is a heavy water or light water cooled, heavy-water moderated, fission reactor capable of using fuels composed of natural uranium, other low-enrichment uranium, recycled uranium, mixed oxides, fissile and fertile actinides, and combinations thereof. In some embodiments, the invention provides methods and systems for identifying an individual leaking fuel channel in a reactor. One system includes a plurality of inlet lines and a plurality of outlet lines. Each of the plurality of inlet lines feeds annulus fluid in parallel to an annulus space of each of a first plurality of fuel channels included in the reactor. Each of the plurality of outlet lines collects, in parallel, annulus fluid exiting an annulus space of each of a second plurality of fuel channels included in the reactor. In some embodiments, the system also includes a detector positioned at an outlet of each of the plurality of outlet lines configured to detect moisture in annulus fluid and to identify a first position of an individual leaking fuel channel, and an isolation valve positioned at an inlet of each of the plurality of inlet lines operable to stop annulus fluid from circulating through one of the plurality of inlet lines and to identify a second position of the individual leaking fuel channel. Another embodiment of the invention provides a method of detecting an individual leaking fuel channel included in a reactor. The method includes supplying annulus fluid to the reactor through a plurality of inlet lines and collecting annulus fluid exiting the reactor in a plurality of outlet lines. Each of the plurality of inlet lines feeds annulus fluid to an annulus space of a plurality of fuel channels included in the reactor, and each of the plurality of outlet lines collects, in parallel, annulus fluid exiting an annulus space of each of a second plurality of fuel channels included in the reactor. In some embodiments, the method also includes detecting moisture in annulus fluid at an outlet of one of the plurality of outlet lines to identify a first position of an individual leaking fuel channel and sequentially stopping annulus fluid from circulating through each of the plurality of inlet lines after detecting moisture in annulus fluid to identify a second position of the individual leaking fuel channel. Other aspects of the invention will become apparent by consideration of the detailed description and accompanying drawings. Before any embodiments of the invention are explained in detail, it is to be understood that the invention is not limited in its application to the details of construction and the arrangement of components set forth in the following description or illustrated in the following drawings. The invention is capable of other embodiments and of being practiced or of being carried out in various ways. FIG. 1 is a perspective view of a reactor core of a CANDU-type reactor 6. The reactor core is typically contained within a vault 8 that is sealed with an air lock for radiation control and shielding. A generally cylindrical vessel, known as a calandria 10, contains a heavy-water moderator. The calandria 10 has an annular shell 14 and a tube sheet 18 at a first end 22 and a second end 24. The tube sheet 18 includes a plurality of bores that each accepts a fuel channel 28. As shown in FIG. 1, a number of fuel channels 28 pass through the tube sheets 18 of the calandria 10 from the first end 22 to the second end 24. For example, as schematically illustrated in FIG. 2, a CANDU-type reactor can include 380 fuel channels 28, and the fuel channels 28 can be positioned within the calandria 10 in a plurality of rows or horizontal positions (e.g., twenty-two rows labeled A through W in FIG. 2) and a plurality of columns or vertical positions (e.g., twenty-two columns labeled 1 through 22 in FIG. 2). FIG. 3 is a cut-away view of the fuel channel 28. As illustrated in FIG. 3, each fuel channel 28 is surrounded by a calandria tube (“CT”) 32. The CT 32 forms a first boundary between the heavy water moderator of the calandria 10 and the fuel channels 28. The CTs 32 are positioned in the bores on the tube sheet 18. A pressure tube (“PT”) 36 forms an inner wall of the fuel channel 28. The PT 36 provides a conduit for reactor coolant and fuel bundles or assemblies 40. The PT 36, for example, generally holds two or more fuel assemblies 40 and acts as a conduit for reactor coolant that passes through each fuel assembly 40. An annulus space 44 is defined by a gap between the PT 36 and the CT 32. The annulus space 44 can be filled with a circulating annulus fluid. The annulus fluid can include a gas or a liquid. For example, the annulus fluid can include dry carbon dioxide, helium, nitrogen, air, or combinations thereof. The annulus space 44 and annulus fluid are part of an annulus fluid system (“AFS”). The annulus fluid system forms a boundary between the CT 32 and PT 36 that provides thermal insulation between the hot reactor coolant and fuel bundles 40 within the PTs 36 and the relatively cool CTs 32. The annulus fluid system can also provide an indication of a leaking PT 36 via the presence of moisture, deuterium, or both in the annulus fluid. An annulus spacer or garter spring 48 can be disposed between the CT 32 and PT 36. The annulus spacer 48 maintains the gap between the PT 36 and the corresponding CT 32, while allowing the passage of the annulus fluid through and around the annulus space 44. FIG. 4 illustrates a portion of an existing annulus fluid system 50. The coolant (e.g., heavy water, D2O) inside the PTs 36 is at high pressure (e.g., approximately 10 MPa or greater), a high temperature (e.g., approximately 260° C. or higher), and is highly radioactive during normal reactor operation. As described above, the PTs 36 are placed inside the CTs 32, which forms the annulus space 44 between each PT 36 and each CT 32. An annulus fluid, such as carbon dioxide (CO2), is then circulated through the annulus spaces 44 within each fuel channel 28 from an inlet tube 52. If any coolant leaks into the annulus space 44 from a PT 36, the coolant vaporizes and the resulting moisture travels along with the annulus fluid to an outlet tube 54. As described below, moisture detectors and dew point analyzers are connected downstream the outlet tubes 54 to detect moisture in the circulated annulus fluid, which indicates a leaking fuel channel 28. As described above with respect to FIG. 1, the calandria 10 is located inside a vault 8. Therefore, installing an inlet tube 52 and an outlet tube 54 for each fuel channel 28 would require 380 inlet penetrations and 380 outlet penetrations through the vault 8 walls. Accordingly, in some embodiments, the annulus space 44 associated with one fuel channels 28 is serially connected to the annulus space 44 associated with one or more other fuel channels 28 to form a “string” or “line.” Therefore, annulus fluid can be circulated through a line to reach multiple fuel channels in series, which reduces the number of inlet tubes 52 and outlet tubes 54. For example, FIG. 5 illustrates a portion of two lines 55a and 55b for a column of fuel channels 28. As shown in FIG. 5, each line 55a and 55b connects alternating rows of fuel channels 28 within a particular column. As an additional example, when the reactor 6 includes 380 fuel channels 28 arranged as illustrated in FIG. 2, the first line for the fuel channels 28 positioned in column 1 connects the annulus spaces 44 associated with the fuel channels 28 positioned at rows J, L, and N. The second line connects the annulus spaces 44 associated with the fuel channels 28 at column 1 and rows K, M, and O. Similarly, the first line for column 11 connects the annulus spaces 44 associated with the fuel channels 28 positioned at rows A, C, E, G, J, L, N, P, R, T, and V of column 11, and the second line connects the annulus spaces 44 associated with the fuel channels 28 positioned at rows B, D, F, H, K, M, O, Q, S, U, and W of column 11. Therefore, when the reactor includes 380 fuel channels arranged as illustrated in FIG. 2, each line connects the annulus space 44 of three to eleven fuel channels 28. Accordingly, as schematically illustrated in FIGS. 6, because the AFS 50 includes forty-four inlet tubes 52 and forty-four outlet tubes 54 (rather than 380 inlet tubes and 380 outlet tubes), only forty-four inlet penetrations and forty-four outlet penetrations are required through the calandria vault 8. Furthermore, in some embodiments, as illustrated in FIG. 6, the outlet tubes 54 are combined into a single line and the single line is passed through the vault 8. Therefore, only a single outlet penetration is required through the calandria vault 8 for the AFS 50. It should be understood that only eight rows and eight columns of fuel channels 28 are illustrated in FIG. 6 to simplify the figure. It should be understood that, in some embodiments, rather than serially connecting alternating rows of fuel channels contained within a particular column, existing annulus fluid systems use a first line that serially connects a first half of the fuel channels 28 in a particular column and a second line that serially connects the second half of the fuel channels 28 in the column. Also, some existing annulus fluid systems use more than two lines per column to serially connect fuel channels 28 contained within the column. FIG. 7 illustrates the existing AFS 50 including a portion of the system 50 outside of the calandria 10. As shown in FIG. 7, the forty-four outlet tubes 54 are connected to two leakage indicators 56. Coolant leaking into the annulus fluid collects in the leakage indicators 56 and can be seen through windows (e.g., glass windows) in the leakage indicators 56. The collected water then flows to beetles 57 that generate an alarm when liquid exists in the collected water. After the leakage indicators 56, the annulus fluid (i.e., vapor and CO2 gas but not water) is combined into a single line 58 that penetrates the wall of the calandria vault 8. The annulus fluid in the combined line 58 passes through a heat exchanger 60, which reduces the temperature of the annulus fluid. The cooled annulus fluid then passes through a flow meter 62 and through one of two or more dew point analyzers 64. The dew point analyzers 64 can detect moisture, deuterium (e.g., in vaporized form), or both within the annulus fluid. The annulus fluid passing through the dew point analyzers 64 is then pressurized by a compressor 66, split back into forty-four branches, and fed into the forty-four inlet tubes 52. In some embodiments, multiple dew point analyzers 64 are used to detect moisture, deuterium, or both in annulus fluid supplied by one or more lines. Isolation valves installed on the outlet lines 54 can also be used to control the flow of annulus fluid to the one or more dew point analyzers 64. Although the lines connecting the annulus spaces 44 of multiple fuel channels 28 and the combined single line 58 reduce the number of penetrations required through the calandria vault 8, using these combined lines prevents the AFS 50 from identifying the individual fuel channel that is leaking (e.g., by row and column position). In particular, when the output tubes 54 are combined into the single outlet line 58 as illustrated in FIGS. 6 and 7, the dew point analyzers 64 can only identify whether or not a leak exists within the calandria 10 but cannot identify the particular individual fuel channel that is leaking. To solve this issue, in some embodiments, a moisture detector 67 is installed on the end of each outlet tube 54 within the vault 8 as illustrated in FIG. 8. Using this configuration, if a leak occurs in a particular fuel channel 28 (e.g., as indicated by the star in FIG. 8), it is detected by the downstream moisture detector 67. Therefore, the particular moisture detector 67 that detects the leak identifies the particular line that includes the leaking fuel channel 28. However, the AFS 50 still cannot identify a particular fuel channel (e.g., by row and column position) within the identified line that is leaking. Alternatively or in addition, the AFS 50 can include an isolation valve 68 associated with each inlet tube 52 (see FIGS. 6 and 8). The isolation valve 68 can be opened to allow the annulus fluid to flow through the line and can be closed to stop the flow of the annulus fluid through the line. After a leak is initially detected, the AFS 50 can sequentially close each isolation valve 68. When the isolation valve 68 associated with the line containing the leaking fuel channel is closed, the AFS 50 will no longer detect a leak because the annulus fluid will not be circulating through the line that contains the leaking fuel channel 28. Therefore, the AFS 50 can use the isolation valves 68 to identify the particular line that includes the leaking fuel channel 28. Again, even with using the isolation valves 68, the existing AFS 50 can only identify a particular line that includes a leaking fuel channel and cannot identify the individual fuel channel 28 (e.g., by row and column position) within the identified line that is leaking. FIGS. 9a-b illustrates a modified AFS 70. In this AFS 70, the portion of the AFS 70 outside of the calandria vault 8 is generally the same as the existing AFS 50 illustrated in FIG. 7. Similar to the AFS 50, the modified AFS 70 can be used with a CANDU-type reactor that includes 380 fuel channels arranged as illustrated in FIG. 2 (i.e., twenty-two columns and twenty-two rows) (however, only eight columns and eight rows are illustrated in FIG. 9a to simplify the figure). Based on this configuration, the AFS 70 includes twenty-two outlet lines 72 and twenty-two inlet lines 74. In some embodiments, the inlet lines 74 are feed horizontally into the reactor 6 through one wall of the vault 8, and the outlet lines 72 exit the reactor 6 vertically through a different wall of the vault 8. The annulus fluid flows through the forty-four inlet lines and forty-four outlet lines in parallel. In particular, each inlet line 74 feeds annulus fluid, in parallel, into the annulus space 44 of each fuel channel 28 having a common horizontal position (i.e., each fuel channel 28 within the same row). Therefore, annulus fluid from the same inlet line 74 flows through each fuel channel 28 within the same row in parallel. As annulus fluid flows through each fuel channel 28, the annulus fluid exits the fuel channel 28 and enters one of the outlet lines 72. In particular, the annulus fluid exiting each fuel channel 28 having a common vertical position (i.e., each fuel channel 28 within the same column) flows in parallel into the same outlet line 72. Accordingly, each outlet line 72 collects, in parallel, the annulus fluid exiting the fuel channels 28 within the same column. As shown in FIG. 9a, a moisture detector 67 is installed at the outlet of vertical outlet line 72 that can detect moisture and/or deuterium within the outlet line 72. An isolation valve 68 is also installed on each inlet line 74. As described above, each isolation valve 68 can be closed to stop the annulus fluid from circulating through a particular inlet line 74. During operation of the AFS 70, if there is a leak in a fuel channel 28 (e.g., indicated by the star in FIG. 9a), the leak is detected by the moisture detector 67 on the outlet line 72 receiving the annulus fluid from the leaking fuel channel 28. Therefore, the vertical position (i.e., the column) of the leaking channel is identified by the moisture detector 67. After the vertical position of the leaking fuel channel 28 is identified, the row of the leaking fuel channel 28 can be determined using the isolation valves 68 installed on the inlet lines 74. In particular, the isolation valves 68 associated with each inlet line 74 can be sequentially closed. When the isolation valve 68 associated with the inlet line 74 that feeds annulus fluid to the leaking fuel channel 28 is closed, the moisture detector 67 that initially detected the leak, will no longer detect a leak. In particular, because annulus fluid is not flowing through the annulus space 44 of the leaking fuel channel 28 (i.e., because the isolation valve 68 is closed), no moisture or deuterium will be carried to and detected by the moisture detector 67. In some embodiments, an isolation valve can also be installed on each outlet line 74 to help identify a leaking fuel channel and prevent cross-bleeding through the grid of fuel channels (e.g., due to a leaking isolation valve). Accordingly, unlike the existing AFS 50, the AFS 70 identifies the individual fuel channel 28 (i.e., by horizontal or row position and by vertical or column position) that is leaking. In addition, the AFS 70 can identify a leaking fuel channel faster than existing systems. For example, when a leak occurs, the moisture resulting from the leaking coolant travels with the annulus fluid to the downstream moisture detector 67, which takes time. For the existing AFS 50, each line includes multiple fuel channels connected in series. Therefore, in the existing AFS 50, the moisture associated with a leak often travels through multiple fuel channels 28 before reaching a moisture detector 67. In the modified AFS 70, however, because the fuel channels 28 are supplied with annulus fluid in parallel, moisture only needs to travel through a single fuel channel 28 before it is detected by a moisture detector 67. Accordingly, the response time of the modified AFS 70 is faster than the existing AFS 50. Furthermore, because the modified AFS 70 only includes twenty-two moisture detectors 67 and twenty-two isolation valves 68 (as compared to the forty-four moisture detectors 67 and forty-four isolation valves 68 included in the AFS 50), the modified AFS 70 is less expensive than the existing AFS 50. Also, it should be understood that the orientations of the inlet and outlet lines illustrated in FIGS. 9a-b can be switched such that the row of the leaking fuel channel 28 is identified first and then the isolation valves 68 are used to identify the column of the leaking fuel channel 28. In this arrangement, the inlet lines 74 can be feed vertically into the vault 8 and the outlet lines 72 can exit the vault 8 horizontally. FIG. 10 illustrates another modified AFS 80. The modified AFS 80 can also be used with a CANDU-type reactor that includes 380 fuel channels arranged as illustrated in FIG. 2 (i.e., twenty-two columns and twenty-two rows) (however, only eight columns and eight rows are illustrated in FIG. 10 to simplify the figure). As shown in FIG. 10, the fuel channels 28 are divided into sections, such as four quadrants 82a, 82b, 82c, and 82d. Each quadrant includes eleven outlet lines 84 and eleven inlet lines 86. The inlet lines 86 can be feed into the reactor 6 through one wall of the vault 8 and the outlet lines 84 can exit the reactor through a different wall of the vault 8. Using the inlet lines 86, annulus fluid flows through the fuel channels 28 included in each quadrant in parallel. Also, the outlet lines 84 of each quadrant are serially connected to the inlet lines 86 of another quadrant, with the exception of the last quadrant (e.g., quadrant 82c) where the annulus fluid exits the vault 8 to be processed as described above with respect to FIG. 7. As shown in FIG. 10, for a first quadrant 82a, each inlet line 86 feeds the annulus fluid, in parallel, into the annulus space 44 of each fuel channel 28 within the same row within the quadrant 82a. As the annulus fluid flows through each fuel channel 28, the annulus fluid exits the fuel channel 28 and enters one of the outlet lines 84. In particular, the annulus fluid exiting each fuel channel 28 within the same column within the quadrant 82a flows, in parallel, into the same outlet line 84. Accordingly, each outlet line 84 collects the annulus fluid exiting the fuel channels 28 within the same column within the same quadrant of the reactor 6. As also shown in FIG. 10, a moisture detector 67 is installed at the end of each outlet line 84 within the quadrant 82a to detect moisture or vapor within the line. An isolation valve 68 is also installed on each inlet line 86 within the quadrant 82a. As described above, each isolation valve 68 can be closed to stop the annulus fluid from circulating through a particular inlet line 86. As shown in FIG. 10, the orientations of the outlet lines 84 and the inlet lines 86 can vary from one quadrant to another. For example, for the quadrant 82a, the inlet lines 86 horizontally feed the annulus fluid into the fuel channels 28 with the same column of quadrant 82a and the outlet lines 84 vertically collect the annulus fluid exiting the fuel channels 28 within the same row of the quadrant 82a. Alternatively, for the quadrant 82b, the inlet lines 86 feed the annulus fluid vertically into the fuel channels 28 within the same column of the quadrant 82b and the outlet lines 84 horizontally collect the annulus fluid exiting the fuel channels 28 within the same row of the quadrant 82b. In operation, each quadrant operates as the AFS 70 system described above. In particular, if a leak takes place in a fuel channel 28 indicated by the star in FIG. 10, it is detected by the downstream moisture detector 67 on the outlet line 84 associated with that quadrant. Therefore, the moisture detector 67 identifies the quadrant of the leaking fuel channel and the column or row of the leaking fuel channel within the quadrant. For example, for the leaking fuel channel 28 illustrated in FIG. 10, the moisture detector 67 detecting the leak identifies the quadrant of the leaking fuel channel 28 (i.e., quadrant 82b) and the row the leaking fuel channel 28. Similarly, after identifying the quadrant and the row of the leaking fuel channel 28, the eleven isolation valves 68 on the upstream end of the quadrant are used to identify the row of the leaking fuel channel as described above for the AFS 70. Therefore, the AFS 80 identifies the individual fuel channel (i.e., by horizontal or row position and by vertical or column position) that is leaking. Similar to the modified AFS 70, in the modified AFS 80, moisture caused by a leaking fuel channel 28 travels through only one fuel channel 28 before reaching a downstream moisture detector 67 as compared to multiple fuel channels 28 in the AFS 50. Therefore, the response time of the modified AFS 80 is faster than the existing AFS 50. In addition, the modified AFS 80 includes 95 parallel lines (380 fuel channels divided into four quadrants) as compared to the 380 parallel lines in the modified AFS 70. As a result, the flow rate of the annulus fluid in a line of the modified AFS 80 is approximately four times greater than the flow rate of the annulus fluid in a line of the modified AFS 70. This means that moisture travels faster in the modified AFS 80 than in modified AFS 70, which increases the response time of the AFS 80. Furthermore, although approximately twenty-two operations are performed to identify an individual leaking fuel channel 28 using the modified AFS 70, only approximately eleven operations are needed to identify an individual leaking fuel channel 28 using the modified AFS 80. Consequently, the response time of the modified AFS 80 is faster than the response time of the modified AFS 70. Accordingly, in the modified annulus fluid systems 70 and 80, the moisture detectors 67 can respond to leaks much faster than the beetles 57 in the existing annulus fluid systems, which increases the margin for detecting a leak before a break occurs. In addition, because both the AFS 70 and the AFS 80 identify the individual fuel channel that is leaking, an identified leak can be addressed faster and more efficiently using the AFS 70 or the AFS 80 than using existing annulus fluid systems. Furthermore, because the modified annulus fluid systems 70 and 80 include the same or fewer moisture detectors 67 and/or isolation valves 68, the cost of the modified annulus fluid systems 70 and 80 is the same or lower than existing annulus fluid systems 50. Thus, embodiments of the invention provide, among other things, methods and systems for detecting an individual leaking fuel channel in a nuclear reactor. It should be understood that although a CANDU-type reactor is illustrated in FIGS. 1-10, the leak detection methods and systems also apply to other types of reactors containing similar components as illustrated in FIGS. 1-10. For example, the methods and systems for detecting an individual leaking fuel channel described in the present application can be used with a reactor that includes various numbers of fuel channels, various numbers of fuel bundles within each fuel channel (e.g., 12 or 13 fuel bundles), and various types of heat transport mechanisms. In particular, the disclosed methods and systems can be used in reactors using light water as a primary heat transport mechanism as compared to heavy water. Also, the details of the methods and systems can be modified according to the specific configuration of the reactor being monitored for leaks (e.g., the specific configuration of fuel channels in the reactor). For example, fuel channels can be divided into more or fewer sections and can include fewer or more inlet and/or outlet lines. In particular, it should be understood that the 44 inlet and outlet lines described above for the AFS 70 are provided as one embodiment of the AFS 70 and different numbers of inlet and outlet lines can be used depending on the reactor core size and the number and arrangement of rows and columns of fuel channels within the reactor. Furthermore, in some embodiments, fuel channels can be connected in different patterns along lines, such as horizontal lines. For example, in general, any pattern of constructing the inlet and outlet lines of the AFS 70 or the AFS 80 can be used where each inlet line is associated with a set of fuel channels that differs from (e.g., by at least one fuel channel) the set of fuel channels associated with each other outlet line. Various features of the invention are set forth in the following claims. |
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040595390 | claims | 1. In a method of operating a nuclear reactor at a temperature at which UN fuel decomposes to free uranium, the improvement which comprises using a (U,Zr)N composition containing at least 2 and up to 10 weight percent Zr at a temperature in the range 1500.degree.-1700.degree. C. as a reactor fuel in said reactor said (U,Zr)N being a solid solution of ZrN in a solvent matrix of UN and having a homogeneous single-phase structure. 2. The method according to claim 1 in which the (U,Zr)N composition contains Th or Pu. |
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description | This invention claims the benefit of U.S. Provisional Application No. 60/651,124 filed Feb. 4, 2005. This invention was made with Government support under United States Department of Energy Contract No. DE-AC05-00OR22725 awarded by the United States Department of Energy. The Government has certain rights in this invention. Since the 1950s, scientists have developed neutron scattering techniques to better utilize neutrons in research areas such as nuclear physics, advanced synthetic materials development, and macroscopic structural analysis. Research facilities such as the Spallation Neutron Source are dedicated to neutron-related science. Such facilities require complex generation, focus, and collection of neutrons. In the interest of time and cost effectiveness, it is essential to develop superior methods to capture and focus neutrons. Neutrons are typically delivered close to a sample by the use of a neutron guide made of supermirrors to direct the source beam of neutrons. The neutron guide moves the source phase space close to the sample to increase the flux on samples. If the sample is small and the guide tube not in direct contact with the sample, however, the divergence of the beam after the guide must be limited to maintain a small beam on the sample. This makes it highly advantageous to use focusing for small samples, and in realistic conditions, it is estimated that a simple Kirkpatrick-Baez (KB) super mirror system can focus about 100 times as many neutrons onto a 100 micron sized spot at the sample than is possible with a guide tube. Much better performance than even this major improvement over common practice will be possible if the convergence angles of the neutrons from the KB mirror system can be increased. A single mirror surface focusing in the meridional direction can collect at most a convergence 2 times its critical angle, and a practical single mirror surface can collect only about its critical angle in convergence. A sagittal focusing or figure of revolution mirror system (e.g., a Wolter Optics system) can collect up to 4 times its critical angle, but there is a hole in the convergence distribution, and it is difficult or impossible to produce a system of this type that can achieve the glancing angles needed to deflect thermal neutrons. Kumakov lenses can collect large divergences, but are very inefficient because they have intrinsically small scattering angles and large absorption in the optics. U.S. Pat. Nos. 5,082,621 and 5,167,912, both to Wood, show a neutron reflecting supermirror structure, however, both are limited to the structure of the supermirror surface and do not address the geometry of how to use the supermirror surface for focusing. In addition, there is no discussion of an array composition of supermirrors nor nondispersive focusing of neutrons via an array composition of supermirrors. U.S. Pat. No. 5,949,840 to Greene teaches a neutron guide, however, the guide as disclosed is limited to fabrication of the guide surface and structure, and does not address the geometry of how to use the guide for focusing neutrons. In addition, there is no discussion of an array composition of supermirrors nor nondispersive focusing of neutrons via an array composition of supermirrors. Accordingly, a need in the art exists for a method to extend the KB mirror focusing geometry to allow nondispersive focusing of neutrons with a convergence on a sample much larger than is possible with existing KB optical schemes. In view of the above need, it is an object of the present invention to provide a method for the extension of the KB mirror focusing geometry to allow focusing of neutrons with a convergence on the sample much larger than is possible with existing KB optical schemes, but with the advantageous small beam producing capabilities and source brilliance conserving properties intact. It is another object of the present invention to provide a method to allow focusing of neutrons utilizing at least three KB supermirrors. It is another object of the present invention to provide a method to allow focusing of neutrons utilizing at least three multilayer mirrors. It is another object of the present invention to provide a method to allow focusing of neutrons utilizing at least three total external reflection mirrors. Briefly, the present invention is a method for nondispersive neutron focusing beyond the critical angle of mirrors by positioning an array of mirrors to deflect neutrons at a preferred angle. One aspect of the present invention comprises the steps of: placing one mirror at an optimal angle to another mirror such that the neutron source beam is directed towards a focused point. In accordance with another aspect of the invention, several mirrors may be placed at optimal angles to one another, creating an array of mirrors such that the neutron source beams are directed towards a focused point. In accordance with another aspect of the invention, numerous mirrors may be placed at optimal angles to one another in at least two dimensions, creating a three-dimensional array of mirrors such that the neutron source beams are directed towards a focused point. Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. For example, the geometrical principles of this invention can be applied to any specularly reflecting focusing system including, but not limited, to nickel-coated mirrors, multilayer mirrors, or total external reflection mirrors. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims. In striving to develop superior methods to capture and focus neutrons, it was realized that no combination of deflections where all the neutron rays bounce off the same mirrors can collect more than about the critical angle in the plane of scatter. However, if some rays bounce off one mirror, and some rays bounce off two or more mirrors, then the total collected divergence can be greatly increased. With up to two deflections, the convergence can be increased by a factor of 3. With up to three deflections, the convergence can be increased by a factor of 5. Since these improvements are in two axes, the total flux can be improved by around a factor of 9 to 25 over conventional systems. Because the KB geometry preserves source brilliance at the sample, this invention provides the highest possible neutron flux into a small sample volume within the convergence limitation of the optics. Because the convergence limitation can now be greatly extended, flux densities up to and even greater than an order of magnitude beyond those previously possible can be realized and is achievable since the technology for producing high-performance flat and elliptical neutron and x-ray mirrors is well established. In view of the above need, a new invention, a nondispersive neutron focusing method beyond the critical angle of mirrors, was developed. One way to extend mirror technology is based on mirrors nested together where some neutron source beam rays strike a vertically deflecting mirror first and some neutron source beam rays strike a horizontally deflecting mirror to produce line focusing. FIG. 1 shows a simple mirror system made with elliptical supermirrors (Osmic Corporation, Auburn Hills, Mich.). Consider the behavior in one axis, in which a single elliptical mirror focuses line-to-line. By duplicating the first KB mirror 11 and arranging it so its lowest angle neutron source beam 13 follows the same path as the highest angle neutron source beam 13 of the second mirror 12 and its focal length is the same to the sample, the divergence on the sample is doubled. The axis of the second mirror 12, however, is not oriented along the nominal beam axis. As shown in FIG. 2, this orientation issue is corrected with a flat mirror 21 set at half the nominal angle of the two elliptical mirrors 22 that aligns the neutron source beam axis 23 for the second elliptical mirror 22 so the neutron source beam 23 is set to focus at the same angle as the first elliptical mirror 22. This process can be extended with other mirrors, with increasing numbers and complexity of mirrors to produce point focusing. See FIG. 2. The mirror lengths can be adjusted to compromise between a more compact design with less demanding optical elements, and a design with fewer optical elements: shorter mirrors are sometimes easier to fabricate and take up less room along the neutron source beam axis. However, shorter mirrors mean that more mirrors must be mounted and aligned. The final focusing-mirror elliptical surfaces are determined by the x-ray critical angle and the demagnification. For example, if F1 is the effective object distance and F2 is the image distance, (magnification=F2/F1), and theta is the nominal glancing angle at the center of the mirror, then the elliptical surface has primary axis A and secondary axis B given by, A=(F1+F2)/2; and B=√{square root over (A2−Z2/4)}. Here Z is the distance between foci on the ellipse; Z2=F12+F22−2F1F2 cos(π−2θ). The following example is given to illustrate the process of the invention and is not to be taken as limiting the scope of the invention which is defined in the appended claims. For one possible configuration of a multiple mirror array, two sets of three mirrors are utilized. For each set of three mirrors, two mirrors must be elliptical and one mirror must be a flat mirror. Thus, in this example of two sets of three mirrors, there are four elliptical mirrors and two flat mirrors. The flat mirrors are set to deflect the neutron source beam first. The neutron source beam deflects off the flat mirrors and is next deflected off the elliptical mirrors. The elliptical surface geometry being determined using the formulas provided above, these elliptical mirrors will deflect the neutron source beam into a preferred focal point. See FIG. 2. The mirrors used in the present invention may also be total external reflection or multilayer mirrors. The described optics allow neutron measurements on much smaller samples. The described optics can replace expensive neutron guides for many applications and provide better initial performance and an easier path to upgrade with evolving technology. Further, because high-energy x-rays behave like neutrons in their absorption and reflectivity rates, this method may be used with x-rays as well as neutrons. Thus, it will be seen that a nondispersive neutron focusing method beyond the critical angle of mirrors has been provided. The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims. |
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description | This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2005-361338 filed on Dec. 15, 2005 in Japan, the entire contents of which are incorporated herein by reference. 1. Field of the Invention The present invention relates to a charged particle beam writing method and a charged particle beam writing apparatus, for example, an electron beam writing apparatus which uses a deflector to deflect an electron beam. 2. Related Art A lithography technique which leads development of micropatterning of a semiconductor device is a very important process which uniquely generates a pattern in semiconductor manufacturing processes. In recent years, with high integration of an LSI, a circuit line width required for semiconductor devices progressively decreases year after year. In order to form a desired circuit pattern on the semiconductor devices, a high-definition original pattern (also called a reticle or a mask) is necessary. In this case, an electron beam writing technique has an essentially excellent resolution and is used in production of a high-definition original pattern. FIG. 13 is a conceptual view for explaining an operation of a conventional variable-shaped electron beam photolithography apparatus. In the variable-shaped electron beam photolithography apparatus (electron beam (EB) writing apparatus), writing is performed as follows. An opening 411 having a rectangular shape, for example, a square shape to shape an electron beam 330 is formed in a first aperture 410. A variable-shaped opening 421 to shape the electron beam 330 having passed through the opening 411 in a desired square shape is formed in a second aperture 420. The electron beam 330 irradiated from a charged particle source 430 and having passed through the opening 411 is deflected by a deflector. The electron beam 330 is irradiated on a target object 340 placed on a stage through a part of the variable-shaped opening 421. At this time, the stage continuously moves in one predetermined direction (for example, defined as an X direction). More specifically, a square shape which can pass through both the opening 411 and the variable-shaped opening 421 is written in a writing region of the target object 340. A scheme which causes an electron beam to pass through both the opening 411 and the variable-shaped opening 421 to form an arbitrary shape is called a variable-shaping scheme. In general, overall control of electron optics of an electron beam writing apparatus is performed every shot which irradiates the electron beam 330 on the target object 340. More specifically, upon completion of irradiation of one shot, the next shot is prepared. The next shot is performed. In the electron beam writing apparatus, the electron beam 330 reaches the target object 340 while being deflected by a plurality of deflectors. In this case, upon completion of one shot, a period for preparing amplification to apply a voltage to the deflectors is necessary as a preparation period (so-called settling time) for the next shot. As a technique related to the settling time, a technique which matches settling time to the longest preparation period of amplification is disclosed in a reference (for example, see JP-A-63-92020). With an increase in degree of integration density of an LSI, time required for writing a mask by an electron beam writing apparatus or direct writing time required when writing is directly performed on a wafer or the like explosively increases. In order to cope with this, a current density of an electron beam used in the writing apparatus must be increased, or a device to shorten settling time between shots is required. In this case, as described above, in a conventional method, preparation for the next shot is performed upon completion of irradiation of one shot. In this method, the system has limitations even though irradiation time is shortened by increasing a current density of an electron beam and settling time is shortened by improving the capabilities of amplifiers for deflectors. For this reason, it is difficult to further shorten the writing time. Therefore, it is an object of the present invention to provide a method and apparatus which further shorten writing time. In accordance with one aspect of the present invention, a pattern writing method with using a charged particle beam includes irradiating a shot of a charged particle beam, and deflecting the charged particle beam of the shot using a plurality of deflectors arranged on an optical path of the charged particle beam to write a pattern on a target object, wherein any one of the plurality of deflectors controls deflection of a charged particle beam of a shot different from a shot which is controlled in deflection by another deflector in the same period. In accordance with another aspect of the present invention, a pattern writing method with using a charged particle beam includes irradiating a shot of a charged particle beam, deflecting a charged particle of the beam to write a pattern on a target object, independently applying voltages to deflectors in accordance with movement of the charged particle, by using the deflectors obtained by dividing a base deflector to cause the charged particle to obtain a predetermined amount of deflection in a plurality of stages, when deflecting the charged particle, being begun to perform preparation for deflection of the next shot by at least another deflector when deflecting by one of the deflectors for a certain shot, and performing control which charges an appropriate voltage as a sum of the deflectors to the charged particle irradiated, when deflecting the charged particle. In accordance with another aspect of the present invention, a charged particle beam writing apparatus includes a first deflector which does not deflect a charged particle beam to set a beam-on state and which deflects the charged particle beam to set a beam-off state, a second deflector which deflects the charged particle beam to shape the beam, and a third deflector which deflects the charged particle beam to a predetermined position on a target object, wherein at least two deflectors of the first, second, and third deflectors control deflection of charged particle beams of different shots in the same period. In accordance with another aspect of the present invention, a charged particle beam writing apparatus includes an irradiation unit which irradiates a charged particle beam, deflectors of a plurality of stages each having a deflector length which is shorter than a deflector length to cause each charged particle in the charged particle beam to obtain a predetermined amount of deflection, and a voltage applying unit which independently applies voltages to the deflectors of the plurality of stages in accordance with movement of the charged particle. In the following embodiments, a configuration using an electron beam will be described as an example of a charged particle beam. However, the charged particle beam is not limited to an electron beam, another beam such as an ion beam using other charged particles may be used. FIG. 1 is a conceptual diagram showing a configuration of a writing apparatus according to a first embodiment. FIG. 1 shows, as an example of a charged particle beam writing apparatus, a writing apparatus 100 serving as a variable-shaped electron beam writing apparatus. The writing apparatus 100 writes, or “draws” a pattern on a target object 101. The writing apparatus 100 includes a pattern writing unit 150 and a control system. The pattern writing unit 150 includes an electron lens barrel 102, a writing chamber 103, an X-Y stage 105, an electron gun assembly 201, an illumination lens 202, a blanking (BLK) deflector 212, a BLK aperture 214, a first shaping aperture 203, a projection lens 204, a shaping deflector 205, a second shaping aperture 206, an objective lens 207, an objective deflector, or “position deflector” 208, and a reflecting mirror 209. The control system includes a control computer (CPU) 120 serving as a computer, a memory 122, a deflection control circuit 112, a laser length measuring system 132, a drive circuit 114, a deflecting amplifier 142, 144 and 146, a digital/analog converter (DAC) 152, 154 and 156, a buffer memory 162, 164 and 166. In the electron lens barrel 102, the electron gun assembly 201, the illumination lens 202, the BLK deflector 212, the BLK aperture 214, the first shaping aperture 203, the projection lens 204, the shaping deflector 205, the second shaping aperture 206, the objective lens 207, and the objective deflector 208 are arranged. In the writing chamber 103, the X-Y stage 105 is arranged. The reflecting mirror 209 for measuring a laser length is arranged on the X-Y stage 105. For example, the electrostatic BLK deflector 212 (an example of a first deflector) causes an electron beam 200 to pass without being deflected to set a beam-on state, and deflects the electron beam 200 to set a beam-off state. For example, the electrostatic shaping deflector 205 (an example of a second deflector) is arranged behind the BLK deflector 212 on the optical path and deflects the electron beam 200 to shape the electron beam 200. For example, the electrostatic objective deflector 208 (an example of a third deflector) is arranged behind the shaping deflector 205 on the optical path and deflects the electron beam 200 to a predetermined position on a target object 101. The target object 101 includes a mask for writing, or “drawing”. The memory 122, the deflection control circuit 112, the laser length measuring system 132, and the drive circuit 114 are connected to the CPU 120 through a bus (not shown). The deflection control circuit 112 and the drive circuit 114 are controlled by the CPU 120. Information, arithmetic operation result, and the like input to the CPU 120 are stored (memorized) in the memory 122. The laser length measuring system 132, the buffer memory 162, the buffer memory 164, and the buffer memory 166 are further connected to the deflection control circuit 112 through a bus (not shown). The DAC 152 is connected to the buffer memory 162, the deflecting amplifier 142 is connected to the DAC 152, and the deflecting amplifier 142 is connected to the BLK deflector 212. Similarly, the DAC 154 is connected to the buffer memory 164 the deflecting amplifier 144 is connected to the DAC 154, and the deflecting amplifier 144 is connected to the shaping deflector 205. Similarly, the DAC 156 is connected to the buffer memory 166, the deflecting amplifier 146 is connected to the DAC 156, and the deflecting amplifier 146 is connected to the objective deflector 208. In FIG. 1, constituent parts required for explaining the first embodiment are described. Other configurations which are generally required for the writing apparatus 100 are included as a matter of course. The electron beam 200 irradiated from the electron gun assembly 201 is converged by the illumination lens 202, forms a crossover by the BLK aperture 214, and passes through the BLK aperture 214. Thereafter, the electron beam 200 entirely illuminates the first shaping aperture 203 having a square, for example, rectangular opening. In this case, the electron beam 200 is shaped into a square shape, for example, a rectangular shape. The electron beam 200 of a first aperture image having passed through the first shaping aperture 203 is projected on the second shaping aperture 206 by the projection lens 204. A position of the first aperture image on the second shaping aperture 206 is controlled by the shaping deflector 205 to make it possible to change a beam shape and a beam size. The electron beam 200 of a second aperture image having passed through the second shaping aperture 206 is focused by the objective lens 207 and deflected by the objective deflector 208. The electron beam 200 is irradiated on a desired position of the target object 101 on or “above” the X-Y stage 105 which is movably arranged. The X-Y stage 105 is driven in X and Y directions by the drive circuit 114. A laser beam irradiated from the laser length measuring system 132 is reflected by the reflecting mirror 209, and the reflected beam is received by the laser length measuring system 132 to measure the position of the X-Y stage 105. The electron lens barrel 102 and the writing chamber in which the X-Y stage 105 is arranged are vacuumed by a vacuum pump (not shown) to have a vacuum atmosphere in which a pressure is lower than the atmospheric pressure. The BLK deflector 212 is controlled by the deflection control circuit 112, the buffer memory 162, the DAC 152, and the deflecting amplifier 142. The shaping deflector 205 is controlled by the deflection control circuit 112, the buffer memory 164, the DAC 154, and the deflecting amplifier 144. The objective deflector 208 is controlled by the deflection control circuit 112, the buffer memory 166, the DAC 156, and the deflecting amplifier 146. When the position of the electron beam 200 on the target object 101 is moved, or when irradiation time has elapsed, the electron beam 200 is deflected by the electrostatic BLK deflector 212 in order to prevent the electron beam 200 from being irradiated on an unnecessary region on the target object 101. The deflected electron beam 200 is cut by the BLK aperture 214. As a result, the electron beam 200 is prevented from reaching a surface of the target object 101. The electron beam 200 is deflected by the BLK deflector 212 and cut by the BLK aperture 214, so that shots of the electron beam 200 having a predetermined electron beam length can be formed. More specifically, in a beam-off (blanking-on) state, the electron beam 200 is deflected by the BLK deflector 212 to cause the BLK aperture 214 to cut the electron beam 200. In a beam-on (blanking-off) state, the electron beam 200 passes through the BLK aperture 214 without being deflected by the BLK deflector 212. In FIG. 1, a shot beam progressing to the target object 101 is obtained as an electron beam 200b or an electron beam 200c. FIGS. 2A to 2D are diagrams for explaining proceedings of an electron beam when preparation for the next shot is performed upon completion of irradiation of one shot. FIGS. 2A to 2D show respective states changing with time. In this specification, it is assumed that an acceleration voltage is set at 50 kV and that a length between the electron gun assembly 201 and the target object 101 is set at about 1 m. In a conventional system in which irradiation time of one shot and waiting time between shots are about 30 to 40 ns, an electron is irradiated on a target object when a deflector for positioning or shaping has a predetermined voltage. After predetermined irradiation time has elapsed, a voltage is applied to a blanking deflector to end beam irradiation. A voltage for the next shot is applied to the deflector for positioning or shaping, the apparatus waits until the voltage of the deflector becomes a predetermined voltage. This waiting time is waiting time between shots. That is, in such a control, entire voltage control of the deflector for positioning and shaping is performed every irradiation of one shot. In order to shorten the writing time, a method which increases a current density of the electron beam 200 to shorten the irradiation time and shortens time required for stabilizing a deflector (speeding up of the deflector) is known. For example, irradiation time of one shot is set at 2 ns, and stabilizing time of the deflector is set at 2 ns. However, in the above conventional “method which performs entire voltage control of the deflector for positioning and shaping every irradiation of one shot”, writing time cannot be sufficiently shortened. More specifically, even though the shot time is changed from 40 ns obtained in the conventional technique to 2 ns, the writing time cannot be made 1/20. This will be described below. A traveling distance of an electron accelerated at 50 kV for 1-shot irradiation time of 2 ns is about 24 cm. In FIGS. 2A to 2D, electron beams of respective shots reaching the target object 101 are shown. More specifically, the electron beam 200 which is deflected by the BLK deflector 212 and cut by the BLK aperture 214 is omitted. When, in a shot having the electron beam length, the electron beam 200 of one shot is irradiated from the electron gun assembly 201 as shown in FIG. 2A, the electron beam 200 of one shot passes through the BLK deflector 212 without being deflected by the BLK deflector 212 as shown in FIG. 2B. Thereafter, as shown in FIG. 2C, the electron beam 200 reaches the target object 101 such as a mask to irradiate the target object 101. When the state shown in FIG. 2C changes into a state shown in FIG. 2D, irradiation of the beam of one shot is ended, and a voltage begins to be applied to the deflector to prepare the next shot therefrom. Thereafter, the apparatus waits for time T required for reaching a predetermined voltage, and irradiation for the next shot beings. Upon completion of the irradiation of the previous shot, time required for the next shot to reach the target object is a sum of the following two times. In other words, (i) time T required for a deflected voltage to be stabilized and (ii) time Tb required for the next electron to reach a target object surface through a lens barrel of an electron optics are used. The latter time Tb is traveling time of an electron (accelerated at 50 kV) for a distance of 1 m between the proximal end of the electron gun assembly to the target object surface, i.e., about 8 ns. Even if the time T for stabilizing a voltage of a deflector is set at 2 ns, the sum T and Tb is 8+2 ns=10 ns. Therefore, a shot cycle (time required for ending the next shot after a certain shot is ended) is 10+2 ns=12 ns. In the conventional technique mentioned in [0024], the shot time is 30 ns, and the stabilizing time of the deflector is 30 ns, so that the shot cycle is 60 ns. In the example mentioned here, shot time and stabilizing time of a deflector are set at 2 ns and 2 ns, respectively, and a total is set at 1/15. However, since the traveling time of the electron is 8 ns, the shot cycle is 12 ns, so that only a shortening effect of ⅕ can be obtained. More specifically, when preparation for the next shot after irradiation of one shot is ended, it is difficult in the system to shorten the waste interval. FIGS. 3A to 3D are diagrams for explaining proceedings of an electron beam when an electron beam writing method according to the first embodiment is performed. In FIGS. 3A to 3D, states changing with time are shown. In the charged particle beam writing method mentioned here, a plurality of deflectors arranged on an optical path of the electron beam 200 are used to irradiate a shot of the electron beam 200 while controlling deflection of the electron beam 200. In this manner, a predetermined pattern is written on the target object 101. In the charged particle beam writing method, as shown in FIGS. 3A to 3D, any one of the plurality of deflectors is designed to control deflection of the electron beam 200 of a shot different from a shot which is controlled in deflection by another deflector in the same period. In other words, at least two deflectors of the BLK deflector 212, the shaping deflector 205, and the objective deflector 208 control deflection of charged particle beams of different shots in the same period. More specifically, as shown in FIG. 3A, an (n+1)th shot is irradiated from the electron gun assembly 201 and partially passes through the BLK deflector 212 in the same period in which an nth shot passes while being deflected by the shaping deflector 205. Furthermore, an (n−1)th shot begins to be irradiated on the target object 101, and the remaining is partially deflected by the objective deflector 208. As shown in FIG. 3B, in the same period in which the (n+1)th shot passes while being deflected by the shaping deflector 205, the (n)th shot passes while being deflected by the objective deflector 208. As shown in FIG. 3C, in the same period in which an (n+2)th shot passes while being deflected by the shaping deflector 205, the (n+1)th shot passes while being deflected by the objective deflector 208. As shown in FIG. 3D, in the same period in which an (n+3)th shot begins to be deflected by the shaping deflector 205, the (n+2)th shot passes while being deflected by the objective deflector 208. The following control is performed to performed the above processes. First, the deflection control circuit 112 inputs positions of the reflecting mirror 209, eventually, position information of the target object 101 from the laser length measuring system 132 at any time or at predetermined intervals. The deflection control circuit 112 distributes deflection signals to the buffer memory 162, the buffer memory 164, and the buffer memory 166. In the distribution mentioned here, on the basis of the position information of the target object 101, signal indicating a time (i.e., time at which a beam-on state is set) at which deflection is turned off is distributed to the BLK deflector 212, and signals (deflection signals) for designating amounts of deflection to be performed are distributed to the shaping deflector 205 and the objective deflector 208 such that a pipeline process can be performed in accordance with movement of the respective shots of the electron beam 200. A signal (data of beam-on time) temporarily stored or “accumulated” in the buffer memory 162 is output to the DAC 152. The DAC 152 adjusts a voltage of the deflecting amplifier 142 such that a beam-on state is kept for time described in the data at a timing (which will be described later). The beam is output to the BLK deflector 212, and the voltage is applied to the BLK deflector 212. Similarly, the signal temporarily stored or “accumulated” in the buffer memory 164 is output to the DAC 154. The DAC 154 digital/analog-converts the data at a timing (which will be described later). The resultant analog voltage signal is output to the deflecting amplifier 144 for only desired time. Then, the analog voltage signal is amplified by the deflecting amplifier 144 and output to the shaping deflector 205 to apply a voltage to the shaping deflector 205. Similarly, the signal temporarily stored or “accumulated” in the buffer memory 166 is output to the DAC 156. The DAC 156 digital/analog-converts the data at a timing (which will be described later). The resultant analog voltage signal is output to the deflecting amplifier 146 for only desired time. The analog voltage signal is amplified by the deflecting amplifier 146 and output to the objective deflector 208 to apply a voltage to the objective deflector 208. FIG. 4 is a diagram for explaining signal distribution in the first embodiment. In FIG. 4, the deflection control circuit 112 has a distribution circuit 180, a timing controller 190, and a plurality of delay circuits 192, 194, and 196 (an example of timing signal generating units). The delay circuits 192, 194, and 196 are controlled by the timing controller 190. In the deflection control circuit 112, the distribution circuit 180 distributes deflection signals of, for example, the nth shot to the buffer memory 162, the buffer memory 164, and the buffer memory 166 on the basis of the position information of the target object 101. The timing controller 190 confirms that the deflection signals are distributed to the buffer memories. A signal of a start of operation is output to the delay circuit 192. At this time, the delay circuit 192 transmits a timing signal to the DAC 152 with reference to the nth shot. Predetermined time T1 after, a timing signal is transmitted to the DAC 154. Furthermore, predetermined time T2 after, a timing signal is transmitted to the DAC 156. In this manner, the delay circuit 192 independently generates timing signals for the DACs 154, and the timing signals are transmitted to the respective DACs. FIG. 5 is a flow chart of timing signals in the first embodiment. In this case, for example, the timing signal transmitted by the delay circuit 192 is indicated by (1). For example, a pulse signal is transmitted. When the DAC 152 receives the timing signal, the DAC 152 outputs an analog voltage signal for setting a beam-on state to the deflecting amplifier 142 for time (beam-on time) of the data received through the buffer memory 162. In this manner, the DAC 152 (an example of a voltage applying unit) applies a voltage to the BLK deflector 212 through the deflecting amplifier 142. A deflection signal which is completely output to the DAC 152 is erased from the buffer memory 162. After the DAC 152 set a beam-on state for designated time, a voltage for setting a beam-off state is automatically generated, and the BLK deflector is controlled through the amplifier to set the beam-off state. When the DAC 154 receives a timing signal time T1 after, the DAC 154 digital/analog-converts the deflection signal received through the buffer memory 164 as described above. The DAC 154 outputs the analog voltage signal to the deflecting amplifier 144. In this manner, the DAC 154 (an example of an voltage applying unit) applies a voltage to the shaping deflector 205 through the deflecting amplifier 144. The deflection signal which is completely output to the DAC 154 is erased from the buffer memory 164. Similarly, when the DAC 156 receives a timing signal time T2 after, the DAC 156 digital/analog-converts the deflection signal received through the buffer memory 166 as described above. The DAC 156 outputs the analog voltage signal to the deflecting amplifier 146. In this manner, the DAC 156 (an example of an voltage applying unit) applies a voltage to the objective deflector 208 through the deflecting amplifier 146. The deflection signal which is completely output to the DAC 156 is erased from the buffer memory 166. Meanwhile, the distribution circuit 180 distributes deflection signals about the (n+1)th shot to the buffer memory 162, the buffer memory 164, and the buffer memory 166. The timing controller 190 confirms that the deflection signals have been distributed to the respective buffer memories. Thereafter, a signal of a start of operation is output to the delay circuit 194. At this time, the delay circuit 194 transmits a timing signal to the DAC 152 with respect to this shot. The predetermined time T1 after, the delay circuit 194 transmits a timing signal to the DAC 154. The predetermined time T2 after, the delay circuit 194 transmits a timing signal to the DAC 154. Furthermore, the predetermined time T2 after, the delay circuit 194 transmits a timing signal to the DAC 156. In FIG. 5, the timing signal transmitted by the delay circuit 194 is indicated by (2). By the same manner as described above, the deflection signals are processed to control deflection of the (n+1)th shot. The distribution circuit 180 distributes deflection signals about an (n+2)th shot to the buffer memory 162, the buffer memory 164, and the buffer memory 166. The timing controller 190 confirms that the deflection signals have been distributed to the respective buffer memories. Thereafter, a signal of a start of operation is output to the delay circuit 196. At this time, the delay circuit 196 transmits a timing signal to the DAC 152 with respect to this shot. The predetermined time T1 after, the delay circuit 196 transmits a timing signal to the DAC 154. The predetermined time T2 after, the delay circuit 196 transmits a timing signal to the DAC 156. In FIG. 5, the timing signal transmitted by the delay circuit 196 is indicated by (3). By the same manner as described above, the deflection signals are processed to control deflection of the (n+2)th shot. In this case, as shown in FIG. 5, it is also supposed that the timing signal to the DAC 156 with respect to the nth shot and the timing signal to the DAC 152 with respect to the (n+1)th shot are simultaneously output. At this time, the electron cannot be controlled by only one delay circuit. In contrast to this, in the first embodiment, the plurality of delay circuits 192, 194, and 196 are arranged to cope with a case in which output timings overlap. In this case, for example, delay time T1 can be calculated as follows. A value obtained by dividing a distance between a blanking deflector and a shaping deflector by a velocity of an electron beam is given by t0. A value obtained by dividing a distance between a delay circuit and the DAC 154 by a signal velocity of a timing signal is given by t1. A value obtained by dividing a distance between the delay circuit and the DAC 152 by a signal velocity of a timing signal is given by t2. Electric circuit delay time on an output side toward the DAC 154 in the delay circuit is given by t3. Dielectric circuit delay time on an output side toward the DAC 152 in the delay circuit is given by t4. Time between signal reception of the DAC 154 and an operation of the deflector is given by t5. Time from signal reception of the DAC 152 and the operation of the deflector is given by t6. Time until voltage of deflector 205 reaches target voltage after start of amplifier operation is given by t7. Time until voltage of deflector 212 reaches target voltage after start of amplifier operation is given by t8. In this conditions, the delay time T1 can be calculated by T1=t0−t1+t2−t3+t4−t5+t6−t7+t8. The time T2 may be similarly calculated such that the DAC 154, the DAC 152, the blanking deflector, and the shaping deflector are replaced with the DAC 156, the DAC 154, the shaping deflector, and the objective deflector or “position deflector”, respectively. FIG. 6 shows control of the deflectors and changes in voltage with respect to one shot. On the blanking deflector side, after reception of a timing signal, delay occurs in a digital circuit. Thereafter, a voltage of the blanking deflector begins to increase and reaches a predetermined voltage, a beam begins to be on. Predetermined time after, a voltage for setting a beam-off state begins to be applied. As time designated by the DAC 152, time calculated in consideration of these delay times and the like is set. Similarly, in the shaping deflector, after reception of a timing signal, delay time in a digital circuit or the like is generated. Thereafter, a voltage of the deflector increases and reaches a predetermined voltage. Thereafter, a beam to be on passes. On the contrary, after the shaping deflector has the predetermined voltage, the timing of the time T1 may be adjusted such that the on-beam passes through the shaping deflector. Unlike in the case of the blanking deflector, the voltage is not automatically changed even after the on-beam passes, the apparatus waits the next timing signal. The deflector related to a position performs the same operation as that of the shaping deflector. The above explanation is made such that rise times of the blanking deflector, the shaping deflector, and the position deflector are almost equal to each other. Depending on systems, the rise times are different from each other, and the rise times of the shaping deflector and the position deflector may be longer than the rise time of the blanking deflector. In such a case, the timing signals are transmitted to the DACs of the shaping deflector and the position deflector first, and the timing signal may be transmitted to the DAC of the blanking deflector. As described above, preparation for the next shot is not performed upon completion of irradiation of one shot, and preparation for the next shot is performed immediately after the electron beam passes through its own deflector. With this operation, preparation for a deflecting amplifier can be rapidly started, and settling time can be shortened. As a result, any one of the plurality of deflectors can control deflection of a charged particle beam of a shot different from a shot which is controlled in deflection by another deflector in the same period. Therefore, deflection of a plurality of shots can be controlled in the same period. The BLK deflector 212, the shaping deflector 205, and the objective deflector 208 perform a pipeline process to make it possible to perform shots in succession. Consequently, in comparison with a conventional method in which preparation for the next step is performed upon completion of irradiation of one shot, irradiation of the next shot can be more rapidly performed. As a result, writing time can be shortened. For example, as described above, the current density of the electron beam 200 is increased to shorten irradiation time, and irradiation time of one shot is set at 2 ns. In this case, an electron beam length can be made short, i.e., about 24 cm. When the pipeline process is performed, an interval (beam-off interval) between the end of the nth shot and the start of the (n+1)th shot can be shortened to about 24 cm. Time until voltage of deflector 205 (and 208) reaches target voltage after starting the amplifier operation depends on the difference between initial voltage and target voltage. So, the value of T1 (and T2) must be controlled shot by shot. There is a case that the time until voltage of deflector 205 (and 208) reaches target voltage after starting the amplifier operation is much larger than the Time until voltage of blanking deflector reaches target voltage after starting the amplifier operation. In such a case, T1 (T2) becomes less than zero. Then the signal should be sent to shaping deflector sub-system before the signal is sent to blanking deflector sub-system. FIG. 7 is a conceptual diagram showing a configuration of a writing apparatus according to a second embodiment. FIG. 7 is the same as FIG. 1 except that a buffer memory 172, 174, and 176 are arranged in a deflection control circuit 112. In FIG. 7, a distribution circuit 180 which is omitted in FIG. 1 is shown. The DAC 152 is connected to the buffer memory 172. Similarly, the DAC 154 is connected to the buffer memory 174. Similarly, the DAC 156 is connected to the buffer memory 176. In the first embodiment, the respective buffer memories are arranged on respective deflector sides serving as receiving sides of output signals from the deflection control circuit 112. However, the second embodiment is the same as the first embodiment except that the buffer memories are arranged in the deflection control circuit 112 and arranged on sending sides to the deflectors. In FIG. 7, constituent elements required for explaining the second embodiment are described. In general, a writing apparatus 100 includes other necessary components as a matter of course. In the second embodiment, the distribution circuit 180 in the deflection control circuit 112 distributes signals to the buffer memory 172, 174, and 176 in the deflection control circuit 112. As in the first embodiment, this distribution is also performed such that signals for designating amounts of deflection to be performed by the deflectors of the BLK deflector 212, the shaping deflector 205, and the objective deflector 208 can be subjected to a pipeline process in accordance with movement of respective shots of the electron beam 200 on the basis of position information of the target object 101. The other configurations, control method, and writing method are the same as those in the first embodiment. Control of the timing signals is also performed by the same method as that in the first embodiment. As described above, even though the buffer memories which accumulate deflection signals to the deflectors are arranged on a sending side, as in the first embodiment, any one of the plurality of deflectors can perform a pipeline process while controlling deflection of the electron beam 200 of a shot different from a shot which is controlled in deflection by another deflector in the same period. Therefore, writing time can be shortened. FIG. 8 is a conceptual diagram showing a configuration of a writing apparatus according to a third embodiment. In FIG. 8, a writing apparatus 100 includes, as an example of a pattern writing unit 150, an electron lens barrel 102, a writing chamber 103, an X-Y stage 105, an electron gun assembly 201, an illumination lens 202, a first BLK deflector 221, a second BLK deflector 222, a BLK aperture 214, a first shaping aperture 203, a projection lens 204, a first shaping deflector 224, a second shaping deflector 225, a second shaping aperture 206, an objective lens 207, a first objective deflector 226, a second objective deflector 228, and a reflecting mirror 209. The writing apparatus 100 includes, as a control system, a CPU 120, a memory 122, a deflection control circuit 112, a laser length measuring system 132, a drive circuit 114, a deflecting amplifier 142, a DAC 152, a buffer memory 162, a deflecting amplifier 143, a DAC 153, a buffer memory 163, a deflecting amplifier 144, a DAC 154, a buffer memory 164, a deflecting amplifier 145, a DAC 155, a buffer memory 165, a deflecting amplifier 146, a DAC 156, a buffer memory 166, a deflecting amplifier 147, a DAC 157, and a buffer memory 167. The electron gun assembly 201, the illumination lens 202, the first BLK deflector 221, the second BLK deflector 222, the BLK aperture 214, the first shaping aperture 203, the projection lens 204, the first shaping deflector 224, the second shaping deflector 225, the second shaping aperture 206, the objective lens 207, the first objective deflector 226, and the second objective deflector 228 are arranged in the electron lens barrel 102. In the writing chamber 103, the X-Y stage 105 is arranged. On the X-Y stage 105, the reflecting mirror 209 for measuring a laser length is arranged. The first BLK deflector 221 and the second BLK deflector 222 transmit the electron beam 200 without deflecting the electron beam 200 to set a beam-on state, and deflect the electron beam 200 to set a beam-off state. The first BLK deflector 221 and the second BLK deflector 222 serve as deflectors having a plurality of stages obtained by dividing the BLK deflector 212 having a deflector length to cause an electron to obtain a predetermined amount of deflection for blanking in a plurality of stages. In this case, as an example, the first BLK deflector 221 and the second BLK deflector 222 obtained by dividing the BLK deflector 212 in two stages are shown. The number of divided stages may be three or more. The divided deflectors are arranged to have shapes separated from one another. The first shaping deflector 224 and the second shaping deflector 225 are respectively arranged behind the first BLK deflector 221 and the first shaping deflector 224 on optical paths to deflect and shape the electron beam 200. The first shaping deflector 224 and the second shaping deflector 225 serve as deflectors of a plurality of stages obtained by dividing the shaping deflector 205 having a deflector length to cause an electron to obtain a predetermined amount of deflection for shaping in a plurality of stages. In this case, as an example, the first shaping deflector 224 and the second shaping deflector 225 obtained by dividing the shaping deflector 205 in two stages are shown. The number of divided stages may be three or more. The divided deflectors are arranged to have shapes separated from one another. The first objective deflector 226 and the second objective deflector 228 are arranged behind the first shaping deflector 224 and the second shaping deflector 225 on optical paths to deflect the electron beam 200 to a predetermined position of the target object 101. The first objective deflector 226 and the second objective deflector 228 serve as deflectors of a plurality of stages obtained by dividing the objective deflector 208 having a deflector length to cause an electron to obtain a predetermined amount of deflection for deflection to the predetermined position of the target object 101 in a plurality of stages. In this case, as an example, the first objective deflector 226 and the second objective deflector 228 obtained by dividing the objective deflector 208 in two stages are shown. The number of divided stages may be three or more. The divided deflectors are arranged to have shapes separated from one another. The memory 122, the deflection control circuit 112, the laser length measuring system 132, and the drive circuit 114 are connected to the CPU 120 through a bus (not shown). The deflection control circuit 112 and the drive circuit 114 are controlled by the CPU 120. Information, an arithmetic operation result, and the like input to the CPU 120 are stored (memorized) in the memory 122. The laser length measuring system 132, the buffer memory 162, the buffer memory 163, the buffer memory 164, the buffer memory 165, the buffer memory 166, and the buffer memory 167 are further connected to the deflection control circuit 112 through a bus (not shown). The DAC 152 is connected to the buffer memory 162, the deflecting amplifier 142 is connected to the DAC 152, and the deflecting amplifier 142 is connected to the first BLK deflector 221. The DAC 153 is connected to the buffer memory 163, the deflecting amplifier 143 is connected to the DAC 153, and the deflecting amplifier 143 is connected to the second BLK deflector 222. Similarly, the DAC 154 is connected to the buffer memory 164, the deflecting amplifier 144 is connected to the DAC 154, and the deflecting amplifier 144 is connected to the first shaping deflector 224. The DAC 155 is connected to the buffer memory 165, the deflecting amplifier 145 is connected to the DAC 155, and the deflecting amplifier 145 is connected to the second shaping deflector 225. Similarly, the DAC 156 is connected to the buffer memory 166, the deflecting amplifier 146 is connected to the DAC 156, and the deflecting amplifier 146 is connected to the first objective deflector 226. The DAC 157 is connected to the buffer memory 167, the deflecting amplifier 147 is connected to the DAC 157, and the deflecting amplifier 147 is connected to the second objective deflector 228. The first BLK deflector 221 is controlled by the deflection control circuit 112 serving as an example of a voltage applying unit, the buffer memory 162, the DAC 152, and the deflecting amplifier 142 and applied with a voltage. The second BLK deflector 222 is controlled by the deflection control circuit 112 serving as an example of the voltage applying unit, the buffer memory 163, the DAC 153, and the deflecting amplifier 143 and applied with a voltage. The first shaping deflector 224 is controlled by the deflection control circuit 112 serving as an example of the voltage applying unit, the buffer memory 164, the DAC 154, and the deflecting amplifier 144 and applied with a voltage. The second shaping deflector 225 is controlled by the deflection control circuit 112 serving as an example of the voltage applying unit, the buffer memory 165, the DAC 155, and the deflecting amplifier 145 and applied with a voltage. The first objective deflector 226 is controlled by the deflection control circuit 112 serving as an example of the voltage applying unit, the buffer memory 166, the DAC 156, and the deflecting amplifier 146 and applied with a voltage. The second objective deflector 228 is controlled by the deflection control circuit 112 serving as an example of the voltage applying unit, the buffer memory 167, the DAC 157, and the deflecting amplifier 147 and applied with a voltage. In FIG. 8, constituent parts required for explaining the third embodiment are described. In general, the writing apparatus 100 includes other necessary components as a matter of course. FIG. 8 is the same as FIG. 1 except that multistage deflectors are used and the deflecting amplifier, the DAC, and the buffer memory which control the multistage deflectors are added. In the deflection control circuit 112, a timing controller for controlling a timing and a plurality of delay circuits are arranged and similarly controlled as in the first embodiment. FIGS. 9A to 9E are diagrams for explaining manners of an electron passing through deflectors which are not multistaged. In FIGS. 9A to 9E show states changing with time. As described above, a current density of a charged particle beam is increased to shorten a beam length of 1 shot, so that a plurality of shots can be traveled in the writing apparatus in the same period. However, when the plurality of shots can travel in the writing apparatus to shorten a shot interval, it is time to prepare deflection of the next shot while an electron is deflected by the deflectors in some cases, and the electron may be uncontrollable during the deflection. This will be concretely described below with reference to drawings. FIG. 9A shows a state in which original voltages “+V′” and “−V′” are applied to opposite electrodes. From this state, voltages are changed such that voltages “+V” and “−V” as shown in FIG. 9B are applied to opposite electrodes of the deflector in order to deflect the next electron. FIG. 9C shows a state in which an electron is injected in a state in which the voltages “+V” and “−V” are applied to opposite electrodes of the deflector. When the electron is passing through the deflector as shown in FIG. 9D, the electron is deflected by the deflection voltages “+V” and “−V”. However, as shown in FIG. 9E, when the electron does not completely pass through the deflector, it is time to perform preparation for deflection of the next shot, and voltage changes from the voltages “+V” and “−V” to the voltages “+V″” and “−V″” are started. For this reason, the electron is not deflected to a desired position, and the electron is uncontrollable. In the embodiment, voltages are independently applied from the deflection control circuit 112, corresponding DACs, corresponding deflecting amplifiers to the deflectors of the plurality of stages in accordance with movement of the electron by using deflectors of a plurality of stages obtained by dividing a deflector to cause an electron to obtain a predetermined amount of deflection in a plurality of stages. This operation will be concretely described below with reference to drawings. FIGS. 10A to 10E are diagrams for explaining a deflecting method according to the third embodiment. FIGS. 10A to 10E show states changing with time. FIG. 10A shows a state in which original voltages “+V′” and “−V′” are applied to opposite electrodes of the first deflector on the upper stage. From this state, voltages are changed such that voltages “+V” and “−V” as shown in FIG. 10B are applied to opposite electrodes of the first deflector on the upper stage in order to deflect an electron beam 200n of the next shot. Voltages are changed such that the original voltages “+V” and “−V” applied to the first deflector on the upper stage are applied to opposite electrodes of the second deflector on the lower stage. FIG. 10C shows a state in which the electron beam 200n is injected into the first deflector on the upper stage in the state the voltages “+V” and “−V” are applied to the opposite electrodes of the first deflector on the upper stage. While the electron beam 200n passes through the first deflector on the upper stage, the voltages “+V′” and “−V” applied to the second deflector on the lower stage are changed into the voltages “+V” and “−V” to deflect the electron beam 200n in deflection by the first deflector on the upper stage. As a result, as shown in FIG. 10D, deflection of a desired amount of deflection can be achieved even through the electron beam 200n is injected into the second deflector on the lower stage. Furthermore, as shown in FIG. 10E, the electron beam 200n completely passes through the first deflector on the upper stage even though the electron beam 200n passes through the second deflector on the lower stage. When it is time to perform preparation for deflection of the next shot, voltage changes from the voltages “+V” and “−V” applied to the first deflector on the upper stage into voltages “+V″” and “−V″” to deflect an electron beam 200n+1 of the next shot are started. In the second deflector on the lower stage, the voltages “+V” and “−V” are maintained since the electron beam 200n passes through the second deflector. In FIGS. 10A to 10E, the deflectors having one certain deflecting function are described. However, as shown in FIG. 8, the first BLK deflector 221 and the second BLK deflector 222 desirably similarly perform deflection control, the first shaping deflector 224 and the second shaping deflector 225 desirably similarly perform deflection control, and the first objective deflector 226 and the second objective deflector 228 desirably similarly perform deflection control. As described above, by using deflectors of a plurality of stages obtained by dividing a deflector to cause an electron to obtain a predetermined amount of deflection in a plurality of stages, voltages are independently applied to the deflectors of the plurality of stages in accordance with movement of the electron to perform a pipeline process, so that a deflector through which the electron has passed can be started to perform preparation for the next deflection. Therefore, uncontrollability during deflection can be avoided, and settling time can be shortened. In this manner, shot time and waiting time between shots can be shortened. As a consequence, writing time can be shortened accordingly. In this case, as deflector lengths of the deflectors of the plurality of stages are obtained by dividing a deflector length to cause electrons in the electron beam 200 to obtain predetermined amounts of deflection into the plurality of stages. However, the present invention is not limited to the deflector lengths. Deflectors having lengths shorter than the deflector length to obtain the predetermined amount of deflection may be preferably combined to each other on many stages. FIG. 11 is a conceptual diagram showing a configuration of a writing apparatus according to a fourth embodiment. In FIG. 11, in place of the buffer memories arranged outside the deflection control circuit 112 in FIG. 8, a buffer memory 172, a buffer memory 173, a buffer memory 174, a buffer memory 175, a buffer memory 176, and a buffer memory 177 are arranged in the deflection control circuit 112. In FIG. 11, a distribution circuit 180 which is omitted in FIG. 8 is described. Other configurations are the same as those in FIG. 8. A DAC 152 is connected to the buffer memory 172, and a DAC 153 is connected to the buffer memory 173. Similarly, a DAC 154 is connected to the buffer memory 174. A DAC 155 is connected to the buffer memory 175. Similarly, a DAC 156 is connected to the buffer memory 176. A DAC 157 is connected to the buffer memory 177. In the third embodiment, the buffer memories are arranged on deflector sides serving as receiving sides of output signals from the deflection control circuit 112. However, in the fourth embodiment, the buffer memories are arranged in the deflection control circuit 112 and arranged on sending sides to the deflectors. Except for this configuration, FIG. 11 is the same as FIG. 8. In FIG. 11, constituent parts required for explaining the fourth embodiment are described. In general, a writing apparatus 100 includes other necessary components as a matter of course. In the fourth embodiment, the distribution circuit 180 in the deflection control circuit 112 distributes signals to the buffer memory 172, the buffer memory 173, the buffer memory 174, the buffer memory 175, the buffer memory 176, and the buffer memory 177 in the deflection control circuit 112. In this distribution, signals (deflection signals) for designating amounts of deflection to be performed by the deflectors of a first BLK deflector 221, a second BLK deflector 222, a first shaping deflector 224, a second shaping deflector 225, a first objective deflector 226, and a second objective deflector 228 on the basis of position information of a target object 101 are distributed such that a pipeline process can be performed in accordance with movement of the shots of the electron beam 200. A signal temporarily accumulated in the buffer memory 172 is output to the DAC 152 at a desired timing. The DAC 152 applies a voltage to the first BLK deflector 221 at a desired timing through a deflecting amplifier 142. A signal temporarily accumulated in the buffer memory 173 is output to the DAC 153 at a desired timing. The DAC 153 applies a voltage to the second BLK deflector 222 at a desired timing through a deflecting amplifier 143. Similarly, a signal temporarily accumulated in the buffer memory 174 is output to the DAC 154 at a desired timing. The DAC 154 applies a voltage to the first shaping deflector 224 at a desired timing through a deflecting amplifier 144. A signal temporarily accumulated in the buffer memory 175 is output to the DAC 155 at a desired timing. The DAC 155 applies a voltage to the second shaping deflector 225 at a desired timing through a deflecting amplifier 145. Similarly, a signal temporarily accumulated in the buffer memory 176 is output to the DAC 156 at a desired timing. The DAC 156 applies a voltage to the first objective deflector 226 at a desired timing through a deflecting amplifier 146. A signal temporarily accumulated in the buffer memory 177 is output to the DAC 157 at a desired timing. The DAC 157 applies a voltage to the second objective deflector 228 at a desired timing through a deflecting amplifier 147. The other configurations, control method, and writing method are the same as those in the third embodiment. As described above, even though the buffer memories which measure timings for applying voltages to deflectors are arranged on sending sides, independent voltages are applied to the deflectors of the plurality of stages in accordance with movement of the electron, so that a pipeline process can be performed, as in the third embodiment, by using deflectors of a plurality of stages obtained by dividing a deflector to cause an electron to obtain a predetermined amount of deflection in a plurality of stages. When the pipeline process is performed, a deflector through which the electron has passed can be started to perform preparation for the next deflection. Therefore, uncontrollability during deflection can be avoided, and settling time can be shortened. FIG. 12 is a conceptual diagram showing a configuration of a writing apparatus according to a fifth embodiment. In the fifth embodiment, description will be given to a configuration obtained by adding one set of blanking deflection mechanism to the configuration of the third embodiment. More specifically, a first BLK deflector 232 and a second BLK deflector 234 are arranged behind the first BLK deflector 221 and the second BLK deflector 222 on the optical path in the configuration in FIG. 8. In addition, a deflecting amplifier 148, a DAC 158, a buffer memory 168, a deflecting amplifier 149, a DAC 159, and a buffer memory 169 are added to control the first BLK deflector 232 and the second BLK deflector 234. Except for this configuration, FIG. 12 is the same as FIG. 8. In FIG. 12, constituent parts required for explaining the fifth embodiment are described. In general, a writing apparatus 100 includes other necessary components as a matter of course. Connected to the deflection control circuit 112 are, in addition to the CPU 120, a laser length measuring system 132, a buffer memory 162, a buffer memory 163, a buffer memory 164, a buffer memory 165, a buffer memory 166, a buffer memory 167, a buffer memory 168, and a buffer memory 169 through a bus (not shown). The DAC 158 is connected to the buffer memory 168, and the deflecting amplifier 148 is connected to the DAC 158. The deflecting amplifier 148 is connected to the first BLK deflector 232. The DAC 159 is connected to the buffer memory 169, and the deflecting amplifier 149 is connected to the DAC 159. The deflecting amplifier 149 is connected to the second BLK deflector 234. The first BLK deflector 232 is controlled by the deflection control circuit 112 serving as an example of a voltage applying unit, the buffer memory 168, the DAC 158, and the deflecting amplifier 148 and applied with a voltage. The second BLK deflector 234 is controlled by the deflection control circuit 112 serving as an example of the voltage applying unit, the buffer memory 169, the DAC 159, and the deflecting amplifier 149 and applied with a voltage. The first BLK deflector 221 and the second BLK deflector 222 on the upper stage and the first BLK deflector 232 and the second BLK deflector 234 on the lower stage are arranged on upstream sides of the first shaping aperture 203 and the second shaping aperture 206. To the electrodes of the first BLK deflector 232 and the second BLK deflector 234 on the lower stage, voltages equal to those applied to the electrodes of the first BLK deflector 221 and the second BLK deflector 222 on the upper stage are applied in a backward direction. For this reason, the electron beam 200 deflected by the first BLK deflector 221 and the second BLK deflector 222 on the upper stage may be preferably swung back by the first BLK deflector 232 and the second BLK deflector 234 on the lower stage. Even though blanking is performed while swinging the electron beam 200 back by using the BLK deflectors on the upper stage and the BLK deflectors on the lower stage, as in the third embodiment, the BLK deflectors on the upper and lower stages are divided in a plurality of stages and independently pipeline-controlled, so that the same effect as in the third embodiment can be obtained. As in the third embodiment, buffer memories for the deflectors are arranged on receiving sides in the fifth embodiment. However, as in the fourth embodiment, the buffer memories may be arranged on sending sides, i.e., on the deflection control circuit 112 side as a matter of course. The embodiments have been described with reference the concrete examples. However, the present invention is not limited to the concrete examples. For example, in the embodiments described above, the BLK aperture 214 is arranged on the upstream side of the first shaping aperture 203 on the optical path. However, the present invention is not limited to the embodiments. For example, the BLK aperture 214 may be preferably arranged on the downstream side of the second shaping aperture 206 on the optical path. In particular, assume that the BLK aperture 214 is arranged on the downstream side of the second shaping aperture 206 on the optical path. In this case, as described in the fifth embodiment, BLK deflectors are more preferably arranged on two stages, i.e., upper and lower stages and applied with equal voltages in a backward direction to swing the electron beam 200 back. With this configuration, amounts of current and irradiation positions on the first shaping aperture 203 and the second shaping aperture 206 can be prevented from being changed. As a result, the numbers of reflected electrons and secondary electrons generated by the first shaping aperture 203 and the second shaping aperture 206 can be prevented from being changed, and a charge-up state in a beam-on (blanking-off) state can be maintained. Consequently, since a degree of optical overlap between the first shaping aperture 203 and the second shaping aperture 206 does not change, a beam size can be prevented from being changed. Furthermore, doses of the electron beam 200 being incident on the first shaping aperture 203 and the second shaping aperture 206 do not change in a blanking-on/off state. For this reason, the first shaping aperture 203 and the second shaping aperture 206 do not change in temperature, so that a beam size can be prevented from being deteriorated by thermal expansion. In the embodiments described above, different shots are deflected by different deflectors, respectively. However, the present invention is not limited to the configuration. For example, when a certain deflector A performs deflection for an nth shot, preparation for deflection of an (n+1)th shot may be performed by another deflector B. Parts such as an apparatus configuration and a control method which are not directly necessary for explanation of the present invention are omitted in the above description. However, a necessary apparatus configuration and a necessary control method can be appropriately selected and used. For example, a configuration of a control unit which controls the writing apparatus 100 is omitted in the description. However, a configuration necessary for the control unit may be appropriately selected and used as a matter of course. In addition, the spirit or scope of the present invention includes all charged particle beam writing apparatuses and all charged particle beam writing methods which include the elements of the invention and can be changed in design by those skilled in the art. Furthermore, although the method of mask writing and the mask writing system were explained in the embodiments, the invention can be applied to direct writing method (that is method to write pattern on resist on silicon wafer) and direct writing system. Additional advantages and modification will readily occur to those skilled in the art. Therefore, the invention in its broader aspects is not limited to the specific details and representative embodiments shown and described herein. Accordingly, various modifications may be made without departing from the spirit or scope of the general invention concept as defined by the appended claims and their equivalents. |
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description | This invention relates to methods and apparatuses for producing very high localised energies. It relates particularly, although not exclusively, to using mechanisms of cavitation in producing a localised compression of gas, which compression generates localised energies which potentially may be high enough to cause nuclear fusion. The development of fusion power has been an area of massive investment of time and money for many years. This investment has been largely centred on developing a large scale fusion reactor, at great cost. However, there are other theories that predict much simpler and cheaper mechanisms for creating fusion. Of interest here is the umbrella concept “inertial confinement fusion”, which uses mechanical forces (such as shock waves) to concentrate and focus energy into very small areas. Much of the confidence in the potential in alternative methods of inertial confinement fusion comes from observations of a phenomenon called sonoluminescence. This occurs when a liquid containing appropriately sized bubbles is driven with a particular frequency of ultrasound. The pressure wave causes bubbles to expand and then collapse very violently; a process usually referred to as inertial cavitation. The rapid collapse of the bubble leads to non-equilibrium compression that causes the contents to heat up to an extent that they emit light [Gaitan, D. F., Crum, L. A., Church, C. C., and Roy, R. A., Journal of the Acoustical Society of America, 91(6), 3166-3183 June (1992)]. There have been various efforts to intensify this process and one group has claimed to observe fusion [Taleyarkhan, R. P., West, C. D., Cho, J. S., Lahey, R. T., Nigmatulin, R. I., and Block, R. C., Science, 295(5561), 1868-1873 March (2002)]. However, the observed results have not yet been validated or replicated, in spite substantial effort [Shapira, D. and Saltmarsh, M., Physical Review Letters, 89(10), 104302 September (2002)]. This is not the only proposed mechanism that has led to luminescence from a collapsing bubble; however it is the most documented. Luminescence has also been observed from a bubble collapsed by a strong shock wave [Bourne, N. K. and Field, J. E., Philosophical Transactions of the Royal Society of London Series A-Mathematical Physical and Engineering Sciences, 357(1751), 295-311 February (1999)]. It has been proposed in U.S. Pat. No. 7,445,319 to fire spherical drops of water moving at very high speed (˜1 km/s) into a rigid target to generate an intense shockwave. This shockwave can be used to collapse bubbles inside the droplet. Another mechanism of using a shockwave to collapse a bubble is described in WO 2011/138622, where the present Applicants have proposed to collapse a bubble within a liquid by applying a high pressure shockwave to the liquid. Although this affords a number of advantages over previous techniques, e.g. not requiring high speed droplet impact, the apparatus needed to generate high enough pressure shockwaves can be complicated and expensive. The present invention aims to provide alternatives to the aforementioned techniques and may also have other applications. When viewed from a first aspect the invention provides a method of using cavitation in producing a localised compression of gas comprising: providing a non-gaseous medium having therein a pocket of gas, wherein the pocket of gas is in contact with a surface comprising a depression shaped so as to at least partially receive the pocket of gas; and applying a static pressure to the non-gaseous medium, wherein the static pressure has an average value greater than atmospheric pressure such that the pocket of gas collapses to form a transverse jet, and wherein the surface depression is arranged to receive the transverse jet impact such that at least some of pocket of gas is trapped between the impacting jet and the surface depression. The invention also extends to an apparatus for using cavitation for producing a localised compression of gas comprising: a non-gaseous medium having therein a pocket of gas, wherein the pocket of gas is in contact with a surface comprising a depression shaped so as to at least partially receive the pocket of gas; and means to apply a static pressure to the non-gaseous medium, wherein the static pressure has an average value greater than atmospheric pressure such that the pocket of gas collapses to form a transverse jet, and wherein the surface depression is arranged to receive the transverse jet impact such that at least some of pocket of gas is trapped between the impacting jet and the surface depression. It will thus be appreciated that the present invention provides for a similar controlled collapse of a gas pocket as obtained in WO 2011/138622, i.e. a transverse jet traversing the gas pocket and trapping part of the gas against the surface, but without having to provide the complicated and expensive apparatus typically required for generating a high pressure shockwave. Instead, a static pressure can be controllably applied to the non-gaseous medium, and it is this elevation in ambient pressure which generates a controllable amount of energy that is delivered into the collapse of the gas pocket and hence into the jet. The level of the static pressure applied can be chosen so as to control the resulting effects and their magnitude, as will be explained further below. As well as the higher ambient pressure which allows more energy to be stored in the non-gaseous medium such that this can be used in the collapse of the gas pocket, it has been found that at high static pressures the collapse of the gas pocket in contact with a surface is highly asymmetric, which generally leads to formation of a transverse jet of the non-gaseous medium that moves across the collapsing gas pocket. In most systems this asymmetric collapse is undesirable as it leads to instability and the formation of multiple gas pockets, e.g. bubbles which are then unusable. In accordance with the present invention, however, the inventors have appreciated that this phenomenon can be appropriately adapted and harnessed to produce a very high localised energy concentration which can be used, e.g. to potentially create nuclear fusion as will be explained later. In the present invention the provision of a surface in contact with the gas pocket breaks the symmetry such that under a static pressure the formation of a transverse jet is in the direction of the surface, i.e. the only way for the gas pocket to collapse is for a transverse jet to be formed which traverses the gas pocket in the direction of the surface and subsequently impacts against the surface. The surface depression is designed to receive the transverse jet impact while trapping a small volume of the original gas pocket between the impacting jet and itself. The trapped portion of gas is strongly heated and this leads to various physical mechanisms that cause very substantial energy focusing in this volume of trapped gas. Preferably the gas pocket contacts the surface in the vicinity of the depression. The pocket of gas does not need to be fully in contact with the surface or fully within the depression, as long as it contacts the surface sufficiently such that when the transverse jet impacts on the leeward side of the gas pocket, this part of the pocket of gas is in contact with the surface, and does not have some of the non-gaseous medium between the gas pocket and the surface of the depression, so that a portion of the gas pocket can be trapped between the tip of the jet and the surface, thus compressing the trapped volume of gas in the depression. For example, the contact could be over a single contact patch or, by appropriate design of the surface texture, at a plurality of discrete contact points/regions. The high speed transverse jet can, purely as an example, reach over 2000 ms−1 for a static pressure of 200 bar applied at atmospheric pressure. When this jet strikes the surface of the depression, thus trapping at least a portion of the pocket of gas between the tip of the jet and the surface, a strong shockwave is generated within the pocket of gas by the force of the impact in a manner analogous to the high speed droplet impact situation described in U.S. Pat. No. 7,445,319. The resultant impacting jet speed can be tailored to a desired application by appropriate selection of the static pressure applied. What is meant by the static pressure applied to the non-gaseous medium, is the long term average pressure experienced by the non-gaseous medium, i.e. contrasting to the scenario in WO 2011/138622 in which a high pressure shockwave is applied momentarily to the non-gaseous medium. It is therefore preferable that the static pressure is applied over a timescale longer than that of a high pressure shockwave applied to the non-gaseous medium, i.e. the applied static pressure is substantially continuous. Preferably the static pressure is applied over a timescale greater than 1 ms, e.g. greater than 1 s, e.g. greater than 100 s. The atmospheric pressure is the pressure to which the non-gaseous medium would relax if the static pressure were to be removed. Generally the atmospheric pressure is around 1 bar. Of course this may vary, e.g. owing to environmental or atmospheric conditions, as well as with altitude. The static pressure that is applied may be constant over time, however this is not necessary and in at least one set of embodiments the static pressure applied to the non-gaseous medium is varied over time. As will be discussed, these variations of the static pressure could be significant, even reaching negative pressures, however what is important is that the average pressure, taken over a timescale longer than these variations, is greater than atmospheric pressure, so that the potential energy stored in the non-gaseous medium through the static pressure can be harnessed in the collapse of the pocket of gas. The static pressure could be generated using any known method, e.g. using a pressure vessel, which is able to maintain the average pressure of the non-gaseous medium at a level above atmospheric pressure. The Applicant has recognised that the speed of the transverse jet obtained upon collapse of the pocket of gas increases with the static pressure applied to the non-gaseous medium, e.g. scaling with the square root of the static pressure. Hence the level of static pressure to be applied may be chosen depending on the desired application of the method, i.e. the level of the static pressure is controlled to form a transverse jet having a desired speed. For some applications preferably the average value of the static pressure is at least 2 bar, further preferably at least 10 bar, e.g. at least 15 bar, e.g. at least 25 bar, e.g. at least 50 bar. For other applications, such as those that potentially may be able to allow for nuclear fusion, preferably the average value of the static pressure is at least 300 bar, e.g. at least 1 kbar, e.g. at least 2 kbar or higher. These high static pressures increase the amount of energy carried by the jet and thus the resulting temperatures and physical effects in the compressed volume of gas. Jet speeds in the realm above 1000 ms−1 potentially may be suitable to achieve nuclear fusion in the gas, though in accordance with the invention jet speeds of greater than 5000 ms−1 or 6000 ms−1 may be obtained which generate very high temperatures and pressures in the compressed volume of gas. Furthermore it will be appreciated that such elevated static pressures represent much larger (and controllable) pressure changes than would be experienced by gas bubbles during cavitation in typical engineering contexts, while the jet speeds achieved are augmented by the trapping of the pocket of gas provided by the depression. Various regimes may be applied to enhance the conditions for the collapse of the pocket of gas and the formation and control of a high speed impacting jet, in addition to the static pressure being applied. For example, the ambient temperature may also be raised. In a set of embodiments in which the static pressure is varied, the variation could be provided by a standing pressure wave (e.g. an acoustic or ultrasonic pressure wave), or a low frequency pressure variation (e.g. applied by a piston with a slowly varying force), applied to the non-gaseous medium, i.e. superimposed on a constant pressure. This is particularly advantageous for the present invention because the constant pressure may provide the potential energy for an intense collapse of the pocket of gas while the peaks of the standing wave or pressure variation can be used to trigger the collapse of the pocket of gas, e.g. if the pressure values are arranged such that the standing wave raises the static pressure above a certain threshold for asymmetric collapse of the gas pocket. As will be explained below, a standing pressure wave or pressure variation has a number of other advantages within the scope of the present invention. As the standing wave or pressure variation will generally be a continuous periodic drive and have a frequency, this can be chosen to collapse pockets of gas with a frequency great enough to provide a significant net energy output. Preferably the frequency of the standing wave or pressure variation is greater than 10 Hz, e.g. greater than 100 Hz, e.g. greater than 1 kHz, e.g. greater than 10 kHz, e.g. 20 kHz. Alternatively, or in addition, a single shot pressure wave, e.g. a shockwave, could be applied to the non-gaseous medium, e.g. as in WO 2011/138622. However, because the static pressure is already applied to the non-gaseous medium, the shockwave need not necessarily be as intense as in WO 2011/138622. For example, as for the standing wave or pressure variation discussed above, the peak pressure of the shockwave could be used to trigger the collapse of the pocket of gas, but because the static pressure is already applied, the pressure on top of this applied by the shockwave does not need to be as intense as if the shockwave is applied to a non-gaseous medium at atmospheric pressure. For these reasons, the complicated and expensive apparatus needed in WO 2011/138622 would not have to be used in the present system and so a much simpler and cheaper device could be used to generate the shockwave, e.g. a piezoelectric actuator. In preferred embodiments such a piezoelectric device may create a shockwave pressure of between 10 bar and 10 kbar. The shockwave could be planar, e.g. produced by a plane wave generator, but in other embodiments the shockwave is shaped to conform to the shape of the pocket of gas. This focuses the shockwave onto the pocket of gas, resulting in a more intense collapse of the pocket of gas. The pocket of gas could already be present within the non-gaseous medium. If a pocket of gas is already present but not in contact with the surface then the method may include moving an/or growing the gas pocket to bring it into contact with the surface (in the vicinity of a depression). However in one set of embodiments the method includes a step of providing the pocket of gas within the non-gaseous medium and the apparatus comprises means for providing a pocket of gas within the non-gaseous medium. This allows the non-gaseous medium to be held at a high static pressure such that a pocket of gas can be introduced within the non-gaseous medium and then collapsed, creating the desired high temperatures and pressures within the compressed volume of gas. It will be recognised that the introduction of a pocket of gas into a non-gaseous medium held at an elevated pressure represents an externally controlled process as compared to the natural formation of bubbles, e.g. owing to low pressures inducing cavitation. The pocket of gas may be provided so as to be in contact with the surface, e.g. nucleated as the surface, or the pocket of gas may be provided near to the surface and then expanded to bring it into contact with the surface. In one set of embodiments the pocket of gas is allowed or caused to expand after it has been provided in the non-gaseous medium, prior to being collapsed, so as to increase the energy available for the formation of a transverse jet. Such embodiments also allow for repeatability of the process, e.g. reintroducing a pocket of gas into the non-gaseous medium after the previous pocket of gas has collapsed, and therefore in one set of embodiments the method comprises the step of repeatedly providing a pocket of gas within the non-gaseous medium. This repeatability enables, in some embodiments, the pockets of gas to collapse at a frequency which is high enough to provide a significant net energy output, i.e. from the accumulation of all the individual reactions. Preferably the frequency at which the pocket of gas is repeatedly provided within the non-gaseous medium is greater than 10 Hz, e.g. greater than 100 Hz, e.g. greater than 1 kHz, e.g. greater than 10 kHz, e.g. 20 kHz. The means for providing the pocket of gas could comprise means for pumping a volume of gas into the non-gaseous medium, e.g. through the surface into the depression. This allows the composition of the gas to be controlled accurately as well as its volume. However this process is invasive and may interfere with the collapse of the pocket of gas and the impact of the jet against the surface. In a set of embodiments where the non-gaseous medium is a gel the gas pocket can be pre-manufactured by punching or otherwise cutting out or moulding the correct shape from the gel block to be used. Additionally or alternatively, the micro-structure or wetting characteristics of the surface can be optimised to naturally maintain a void within the non-gaseous medium. In one set of embodiments the means for providing the pocket of gas comprises means for nucleating a pocket of gas within the non-gaseous medium. Once the pocket of gas has been nucleated it will quickly expand, e.g. over a timescale of approximately 10 μs, to a volume which can then be collapsed by the static pressure. Nucleating the pocket of gas allows it to be provided at an accurate location within the non-gaseous medium in a non-invasive manner, and techniques can be used to control the volume and composition of the pocket of gas. Furthermore, unlike pumping in a volume of gas, nucleating the pocket of gas allows it initially to be positioned away from the surface such that when the pocket of gas expands it contacts the surface before it collapses, i.e. in this embodiment the growing pocket of gas needs to displace the non-gaseous medium between it and the surface. This enables a volume of a pocket of gas to be trapped between the transverse jet and the surface. However the pocket of gas can also be nucleated next to the surface such that when it expands it is always in contact with the surface. Nucleation can also be used to provide pockets of gas within the non-gaseous medium at a high repetition rate, along with multiple pockets of gas within the non-gaseous medium at any one time. In the set of embodiments comprising a plurality of pockets of gas within the non-gaseous medium, preferably these each comprise an associated depression, i.e. the surface comprises a plurality of depressions each shaped so as to at least partially receive a pocket of gas. There are a number of different ways by which the pocket of gas could be nucleated within the non-gaseous medium. The pocket of gas could be nucleated using an unstable emulsion of different liquids, or by using a spark, e.g. an electrical spark. This latter method is relatively inexpensive and simple, and allows precise control over the point of the nucleation. Furthermore it can help to ensure that the pocket of gas is provided in contact with the surface. A couple of electrodes may be provided, e.g. either side of or within the depression, to ignite the electrical spark, which can be small enough not to interfere with the collapse of the bubble. However, in one set of embodiments the pocket of gas is nucleated using a laser. In the set of embodiments comprising a plurality of pockets of gas within the non-gaseous medium these are nucleated using an array of lasers. In a particular set of embodiments the pocket of gas is nucleated using a system similar to that described in U.S. Pat. No. 7,445,319, where a laser is used in conjunction with nano-particles in the liquid to nucleate a pocket of gas. When a laser is used to nucleate the pocket of gas, the energy of the laser, the focussing of the laser and/or the duration of the laser pulse applied to the non-gaseous medium can be controlled to nucleate a pocket of gas of a certain size, e.g. so that it is centred about a particular point and in contact with the surface. In another set of embodiments the pocket of gas is nucleated using a pressure wave applied to the non-gaseous medium to induce the cavitation of a pocket of gas within the non-gaseous medium. The pressure wave could be a standing acoustic or ultrasonic wave, or a low frequency pressure variation, applied to the non-gaseous medium, e.g. as discussed above. The decrease in pressure, which for example could be a negative pressure, in the cycle of the standing wave or pressure variation can be used to induce cavitation of the pocket of gas in the non-gaseous medium, i.e. the standing wave or pressure variation can be used to nucleate the pocket of gas and/or expand an already nucleated pocket of gas. As the standing wave or pressure variation will generally have a frequency, this can be chosen to cavitate pockets of gas such that they form and collapse with a frequency great enough to provide a significant net energy output from the accumulation of all the individual reactions. In some embodiments the non-gaseous medium, or its container, comprises a resonator, e.g. matched to the frequency of the standing wave or pressure variation. As above, preferably the frequency of the standing wave or pressure variation is greater than 10 Hz, e.g. greater than 100 Hz, e.g. greater than 1 kHz, e.g. greater than 10 kHz, e.g. 20 kHz. As will be appreciated, in the set of embodiments in which the pocket of gas is repeatedly provided within the non-gaseous medium this frequency has some relationship to the frequency of the standing wave or pressure variation. For example, these two frequencies could be equal or one could be an integer multiple of the other. Furthermore, the shape of the standing wave or pressure variation can be used to focus the pressure variations in the non-gaseous medium to allow the pocket of gas to be cavitated at the desired position relative to the surface depression. Alternatively a negative pressure shockwave could be applied to the non-gaseous medium to induce cavitation of the gas pocket in the non-gaseous medium, i.e. to nucleate the pocket of gas, and/or to expand an already nucleated pocket of gas. This could be applied by any suitable means to the non-gaseous medium, e.g. using a piezoelectric actuator or an explosive plane wave generator, depending on the magnitude of the pressure desired. The negative pressure wave could also be created by inverting a positive pressure wave using a low acoustic impedance reflector. This could also focus the wave, enhancing its magnitude. The Applicant notes that the scope of the present invention does not extend to usage of a shockwave or a static pressure causing an ultrasound shockwave, nor to usage of a device that generates ultrasound shockwaves (e.g. a lithotripsy device). Nor does the scope of the claimed invention include a pocket of gas being collapsed through a process of sonoluminescence. Nor does the scope of the claimed invention include a nuclear fusion reaction. For both of these methods, i.e. applying a standing wave, pressure variation or a negative pressure wave to the non-gaseous medium, these need not be used to induce cavitation of the pocket of gas directly. In one set of embodiments the pocket of gas is nucleated within the non-gaseous medium and a standing wave, pressure variation or a negative pressure wave is applied to the non-gaseous medium. For example, if a standing wave or pressure variation is used, the pocket of gas could be nucleated or supplied at a particular point on the standing wave or pressure variation's cycle, e.g. the negative gradient part of the cycle, such that the next part of the cycle, e.g. the negative part of the cycle, is used to expand the pocket of gas. In this way the nucleation is used as a trigger to produce the pocket of gas and the pressure wave is used to help it grow to the pocket of gas. This enables control to be exercised over both the location and size of the pocket of gas. It will be appreciated that, in the embodiments in which a pocket of gas is nucleated at a particular point in the cycle of a standing wave, pressure variation and/or a shockwave is applied to the non-gaseous medium to trigger the collapse of the gas pocket, the timings of these events will need to be precise for them to be coordinated, particularly when the system is being operated at a high repetition rate. Therefore in one set of embodiments the apparatus comprises control means to coordinate the nucleation of the gas pocket with the application of the standing wave, pressure variation and/or the shockwave, where provided. This, for example, allows the gas pocket to be nucleated at the optimum point in the standing wave or pressure variation cycle such that it can be expanded to as large as possible a volume and then collapsed by the applied static pressure and/or the shockwave when it reaches its maximum volume. The larger the gas pocket is able to grow to in the non-gaseous medium, the more potential energy it gains, therefore resulting in more energy being able to be harnessed in its collapse, i.e. an increased jet speed, leading to greater temperatures and pressures being obtained in the compressed volume of gas which is trapped between the jet and the surface. In another set of embodiments the gas pocket is formed with the use of a pre-manufactured membrane that defines the boundary between the gas pocket and the non-gaseous medium and hence also defines the gas pockets shape. The use of a thin membrane in this manner allows a decoupling of the liquid and gas materials, allowing any choice of combination of compositions to be made. It also allows the shape and volume of the gas pocket to be controlled with a precision not available to other methods. The membrane could be formed from any suitable material, e.g. glass e.g. plastic e.g. rubber. Having a prefabricated membrane allows a liquid medium to be used more easily as the pocket of gas is trapped against the surface and therefore cannot float away or be otherwise disturbed. In a particular set of embodiments the membrane is frangible and is arranged to break upon a certain pressure being reached within the non-gaseous medium, either from the static pressure or an applied shockwave, such that it has no influence on the resulting dynamics. In one set of embodiments the prefabricated membrane includes a line or region of weakness, so that upon the critical pressure being reached it breaks along the line or in the region of weakness. The line or region of weakness can be arranged so that the position of the breach has an influence on the ensuing flow patterns, for example this could help control the formation and dynamics of the transverse jetting. In another set of embodiments the membrane is designed to deform with the collapsing pocket of gas. When using a membrane to define the pocket of gas, in the set of embodiments in which a pocket of gas is repeatedly provided within the non-gaseous medium, this allows the pocket of gas, or multiple pockets of gas where provided, to easily be inserted into the non-gaseous medium once the previous pocket of gas has collapsed. Multiple pockets of gas could be provided on a single membrane which is then advanced through the non-gaseous medium, e.g. one or more pockets of gas at a time are exposed to the static pressure in order to collapse them. This set of embodiments works particularly well with the set of embodiments in which a standing wave or pressure variation is applied to the non-gaseous medium. For example, the previously broken membrane can be withdrawn from and the next membrane with a new pocket of gas introduced into the non-gaseous medium during a low part of the cycle of the standing wave or pressure variation such that the pressure is below the critical pressure for breaking the membrane. Once the new pocket of gas is in place the pressure can increase so to break the membrane and collapse the pocket of gas. Thus the replacement of the membrane can to be coordinated with the variations in the standing wave or pressure variation, e.g. by the control means as discussed above. Similarly, the frequency at which the membrane is repeatedly provided within the non-gaseous medium has some relationship to the frequency of the standing wave or pressure variation. For example, these two frequencies could be equal or one could be an integer multiple of the other. In one set of embodiments the non-gaseous medium and/or the pocket of gas are heated. Raising the ambient temperature is can help to supply more energy into the collapse of the pocket of gas, further increasing the peak temperatures and pressures obtained. This could be achieved by heating the whole volume of the non-gaseous medium and/or heating the gas introduced into the non-gaseous medium. The shape of the surface in the depression opposite where the pocket of gas collapses could be flat so that the jet contacts the surface at a planar region. In a preferred set of embodiments however the surface depression and gas pocket are arranged such that the initial contact region between the jet and the surface is a curve which forms a closed loop—e.g. a ring. This makes it easier to trap a portion of the gas pocket between the jet tip and the edge of the depression. To achieve this, a section of the surface has a curvature greater than that of the tip of the jet and this part of the surface is placed such that the jet impacts into it. Upon impacting, a toroidal shockwave is generated whose inner edge propagates towards the base of the depression and towards the trapped portion of gas. Combining this with the ‘piston’ effect of the gas halting the motion of the impacting jet yields extremely strong heating of the trapped gas. For example, for a given static pressure the peak temperatures can be increased by over an order of magnitude by these arrangements as compared to a pocket of gas in contact with to a planar surface. The depression could take a number of shapes. In a set of embodiments it tapers in cross-section away from the mouth. The depression could resemble a dish—e.g. being continuously curved. The surface need not be continuously curved however. In a set of embodiments the surface more closely resembles a crack rather than a dish shape. This could be defined by stating that the depth is greater than the width or by the presence of a region of curvature at the tip of the crack greater than the curvature (or maximum curvature) of the portion of the gas pocket received in it. In one set of embodiments the surface comprises a plurality of discrete portions, e.g. with a gradient discontinuity between them. The portions could themselves be partial ellipses, parabolas, and so on, but equally could be straight. A particular set of embodiments of surfaces made from discrete portions could be described as piecewise polynomial. As above, the pocket of gas could be small in comparison to the dimensions of the depression such that it is attached only to one side or it could be of similar size so as to close it off, or indeed the pocket of gas could have a volume greater than that of the depression. It is not essential that there is only one depression which partly receives the gas pocket; a gas pocket could extend across, and be partially received by, a plurality of depressions, as is discussed below. In a particular set of embodiments the high speed jet is arranged to strike an area of surface that has been prepared with a particular roughness or microscopic shape such that many small portions of the pocket of gas are trapped between the jet tip and the surface, i.e. the many small depressions are small in comparison to the size of the transverse jet tip. Furthermore, in the set of embodiments in which a shockwave is additionally applied to the non-gaseous medium, the geometry of the surface can be used to control the reflections of the incident shockwave before it reaches the pocket of gas such that the collapse of the gas pocket is intensified, for example such that the initially incident shockwave is more conforming to the surface of the gas pocket. There are many shapes and configurations which the surface might take to provide suitable regions for the pocket of gas to contact the surface in the vicinity of a depression. The configuration of the surface will determine how the shockwave interacts with it and the shape of the surface relative to the placement and shape of the pocket of gas will determine how the shockwave interacts with the gas pocket, which it may do so before, simultaneously or after it interacts with the surface. This in turn affects the dynamics of the collapse and hence can increase temperatures and densities that are achievable through compression of the gas achieved by the static pressure and augmented by the shockwave. More details on the shape of the surfaces which are suitable for focussing a shockwave onto a pocket of gas are discussed in WO 2011/138622. The surface contacted by the gas pocket is not limited to having a single depression (e.g. to exploit the jetting phenomenon described above) and thus in one set of embodiments, the surface comprises a plurality of depressions. Each individual depression may be shaped to encourage energy focusing by causing multiple jets to form or causing the shockwave, where provided, to converge on one or more pockets of gas. That is to say, the surface may be prepared with more than one site where a pocket of gas is in contact with a depression, thus providing infinite scalability. An advantage of employing a plurality of depressions is that a greater proportion of the energy stored by the static pressure (and optionally augmented by applying a shockwave) may be harnessed. For example, a large pocket of gas could be spread across a plurality of depressions, or smaller individual volumes of gas could be located within each individual depression. For the former case, depending upon the number of such depressions, the size of an individual depression will be significantly smaller than the size of the pocket of gas. For a larger volume of the non-gaseous medium able to accommodate a large number of depressions, this points towards simplicity of manufacturing an apparatus for producing a localised compression of gas, which compression generates localised energies which may potentially be high enough to cause fusion. Such pluralities of depressions could be formed in a number of ways. For example, a solid surface could be drilled or otherwise machined to produce depressions or pits. In one set of embodiments, however, the depressions are created by the surface texture of the surface. For example, the surface could be blasted with an abrasive material, etched or otherwise treated to give a desired degree of surface roughness which provides, at the microscopic level, a large number of pits or depressions. The surface could be constructed from a solid material, as implied in many of the embodiments outlined above, e.g. a metal, stiff plastic or ceramic, but it could equally well be a liquid, e.g. a heavier liquid than the non-gaseous medium such as a liquid metal. In the case of a solid, any of the proposed materials in U.S. Pat. No. 7,445,319 could be suitable. In the case of a liquid the required surface shape could be achieved in a number of ways. For example, the surface of a volume of liquid could be excited with a suitable vibration (e.g. using ultrasound or another method) to generate a wave having the desired shape. Alternatively the desired shape could be achieved through the contact angle between a liquid and a solid surface with appropriately matched wetting properties. Of course, this latter example shows that the surface could comprise a combination of solid and liquid. Where the surface comprises a liquid it will generally be denser than the non-gaseous medium. The surface could comprise part of the wall of the container which holds the non-gaseous medium. Alternatively, or additionally, if a plurality of pockets of gas and depressions in the surface are provided, the surface could be provided by a piece of material positioned within the non-gaseous medium, e.g. suspended or otherwise arranged. By positioned the material providing the surface within the non-gaseous medium, e.g. away from the walls of the container holding the non-gaseous medium, pockets of gas can be provided on multiple surfaces of the material. The aspects of the invention described herein provide alternatives to the techniques described in WO 2011/138622 and U.S. Pat. No. 7,445,319 which may carry their own benefits. The present inventors have recognised that there are significant challenges in the complexity and expense of a high pressure shockwave generator as suggested in WO 2011/138622, and in the nucleation of a bubble in a droplet fired at high speed into a target as suggested in U.S. Pat. No. 7,445,319. The timing will have to be very precise for the bubble to be at a favourable moment of its expand-collapse cycle when the shockwave strikes, in both of these methods. The method by which the high speed droplets are created as required by U.S. Pat. No. 7,445,319 and detailed in U.S. Pat. No. 7,380,918 is also complex and expensive. By contrast such complexity and associated expense can be avoided in accordance with at least preferred embodiments of the present invention. Thus, the various aspects of the present invention provide much simpler techniques for compressing a volume of gas entrapped in a gas pocket as an elevated static pressure simply needs to be applied to the non-gaseous medium in which the gas pocket is formed. Moreover the theoretical and computer modelling of both techniques carried out by the present inventors suggests that the method in accordance with the present invention can give pressure and temperature intensities which are an order of magnitude greater than the method detailed in U.S. Pat. No. 7,445,319. The term “gas” as used herein should be understood generically and thus not as limited to pure atomic or molecular gases but also to include vapours, suspensions or micro-suspensions of liquids or solids in a gas or any mixture of these. The “non-gaseous medium” should be understood generically and thus could include liquids, non-Newtonian liquids, semi-solid gels, materials that are ostensibly solid until the passage of the shockwave changes their properties, suspensions or micro-suspensions and colloids. Examples include but are not limited to water, oils, solvents such as acetone, hydrogels and organogels. It should be understood that the liquid will have a greater density than the gas in the pocket. The non-gaseous medium could be any suitable substance for applying a static pressure to, such as a liquid or a semi-solid gel. The gas pocket can then be provided by a bubble suspended within the liquid or gel medium in the required location, i.e. in contact with the surface. Using a gel or a viscous liquid has the advantage that it is easier to control the location of the bubble within the medium, compared to a lower viscosity liquid in which the buoyancy of the pocket of gas may overcome the viscosity of the liquid. As the pocket of gas is in contact with the surface, the nature of the surface, e.g. the material, and the depression(s) in it, could help to adhere the bubble to the surface. Using a gel or viscous liquid also has the advantage that it will be easier to control the detailed shape of the bubble. Owing to the more static nature of the setup of the device when compared to U.S. Pat. No. 7,445,319, much more control can be exercised over the shape of the pocket of gas. The pocket of gas may be spherical in shape apart from where it is truncated by its attachment to the surface, for example it could be hemi-spherical. In some embodiments the pocket of gas is in contact with the surface normal to it whereas in others a different angle is required. In a superset of these embodiments the pocket of gas itself is not spherical in nature but takes a different shape that includes but is not limited to ellipsoids, cardioids, variations from spherical, cardioid or ellipsoid shape in which the surface has perturbations that could be described, for example, by a Fourier series and pockets of gas with other distinct shapes such as cones or trapezoids. It will be apparent that, for example, a conical pocket of gas would be difficult to achieve in a true liquid medium but that in the case of a gel medium this set of embodiments becomes possible and could be advantageous. In a set of such embodiments the shape of the pocket of gas and the shape of the surface can be appropriately matched, e.g. if the depression is hemispherical, the pocket of gas may be spherical. In a preferred set of embodiments, the methods described herein are employed to produce a localised compression of gas, which compression generates localised energies which may potentially be high enough to cause nuclear fusion reactions. The fuel for the reaction could be provided by the gas in the pocket, the non-gaseous medium, or the fuel could be provided by the surface itself. In the set of embodiments in which the pocket of gas is nucleated within the non-gaseous medium, the fuel could be present initially in the non-gaseous medium and then vaporised by the nucleation to create the pocket of gas containing the fuel. Any of the fuels mentioned in U.S. Pat. No. 7,445,319 is suitable for use in the present invention. The invention extends to a method of producing a localised compression of gas, which compression generates localised energies which may potentially be high enough to cause a nuclear fusion comprising: providing a non-gaseous medium having therein a pocket of gas, wherein the pocket of gas is in contact with a surface comprising a depression shaped so as to at least partially receive the pocket of gas; and applying a static pressure to the non-gaseous medium, wherein the static pressure has an average value greater than atmospheric pressure such that the pocket of gas collapses to form a transverse jet, and wherein the surface depression is arranged to receive the transverse jet impact such that at least some of pocket of gas is trapped between the impacting jet and the surface depression. The invention also extends to a reactor which potentially may be able to allow for nuclear fusion comprising: a non-gaseous medium having therein a pocket of gas, wherein the pocket of gas is in contact with a surface comprising a depression shaped so as to at least partially receive the pocket of gas; and means to apply a static pressure to the non-gaseous medium, wherein the static pressure has an average value greater than atmospheric pressure such that the pocket of gas collapses to form a transverse jet, and wherein the surface depression is arranged to receive the transverse jet impact such that at least some of pocket of gas is trapped between the impacting jet and the surface depression. The device in the present invention is not as restricted, regarding size, as U.S. Pat. No. 7,445,319 where the size of the droplet constrains the maximum size of the pocket of gas. It may be advantageous to have a larger apparatus where a larger volume of gas is heated. The volume of gas in each pocket may be chosen depending on the circumstances but in one set of preferred embodiments it is between 5×10−11 and 5×10−3 liters. The fusion reactions which it may potentially be possible to obtain in accordance with certain embodiments of the invention could be used for net energy production (the long term research aim in this field), but the inventors have appreciated that even if the efficiency of the fusion is below that required for net energy production, the reliable fusion which may potentially be obtainable in accordance with embodiments of the invention is advantageous for example in the production of tritium which can be used as fuel in other fusion projects and is very expensive to produce using currently existing technologies. The potential fusion may also be beneficial in giving a fast and safe neutron source which has many possible applications that will be apparent to those skilled in the art. Moreover, it is not essential in accordance with the invention to produce fusion at all. For example, in some embodiments the techniques and apparatus of the present invention may be advantageously employed as a sonochemistry or chemical reactor which can be used to access extreme and unusual conditions. FIGS. 1a, 1b, 1c and 1d show four successive stages of the nucleation (FIG. 1a), growth (FIG. 1b) and collapses (FIGS. 1c and 1d) of a pocket of gas 2 in accordance with the invention. The apparatus comprises a solid surface 4, for example made from high strength steel, which is placed inside a non-gaseous medium 6 in the form of a hydrogel, for example a mixture of water and gelatine. The non-gaseous medium 6 also contains nanoparticles suitable for helping the nucleation of a pocket of gas 2 within the non-gaseous medium 6, and a fuel suitable for taking part in a nuclear fusion reaction. Defined in the surface 4 is a concave depression 8, which in FIGS. 1a-1d takes the form of a V-shaped tapering depression 4 that could be machined or formed as a result of a naturally occurring crack in the surface 4. Although not shown, the non-gaseous medium 6 is held within a container, e.g. a pressure vessel, which enables a static pressure to be applied to the non-gaseous medium 6. The size of the apparatus is flexible but a typical dimension of this diagram could be between 0.1 and 1×10−5 m. In operation, a static pressure is applied to the non-gaseous medium 6, for instance a static pressure of 1 kbar. Using a laser (not shown), a pocket of gas 2 is nucleated within the non-gaseous medium 6, aided by the presence of nanoparticles, as shown in FIG. 1a. Owing to the energy supplied by the laser, this pocket of gas 2 contains a vaporised form of the non-gaseous medium 6 which therefore includes vaporous fuel suitable for taking part in a nuclear fusion reaction. The energy supplied by the laser also causes the pocket of gas 2 to expand against the static pressure of the non-gaseous medium 6, i.e. the energy from the laser is converted into potential energy stored in the expanded pocket of gas 2 as shown in FIG. 1b. The pocket of gas 2 expands such that it comes into contact with the surface 4, thus filling the depression 8 and displacing the non-gaseous medium 6 that was previously between the pocket of gas 2 and the surface 4, i.e. as shown in FIG. 1a. The maximum volume to which the pocket of gas 2 expands is dictated by the energy supplied by the laser and the static pressure of the non-gaseous medium 6, and in this embodiment is much larger than the volume of the surface depression 8, before it collapses as shown in FIG. 1c. Owing to the high static pressure of the non-gaseous medium 6, the pocket of gas 2 is unstable and collapses. However, owing to the presence of the surface 4 with which the pocket of gas 2 is in contact, this breaks the symmetry of the system and causes the pocket of gas 2 to collapse by forming a transverse jet 10 of the non-gaseous medium 6 which flows into the expanded pocket of gas 2 and traverses the pocket of gas 2. The transverse jet 10 accelerates across the pocket of gas 2 until it impacts in the surface depression 8, trapping a volume 12 of the pocket of gas 2 between the tip of the jet 10 and the tapering depression 8 in the surface 4. The compression of the gaseous fuel inside the trapped volume causes intense local heating which potentially may be sufficient to generate a nuclear fusion reaction. FIGS. 2a and 2b show a variant of the embodiment shown in FIGS. 1a-1d, in which the pocket of gas 102 is nucleated within a V-shaped tapering depression 108 in a surface 104. In this embodiment the volume of the depression 108 is much larger than the volume of the pocket of gas 102, even when the pocket of gas 102 expands to its maximum volume as shown in FIG. 2b. The operation of the embodiment shown in FIGS. 2a and 2b is very similar to the embodiment shown in FIGS. 1a-1d. First the volume of gas 102 is nucleated within the non-gaseous medium 106 as shown in FIG. 2a such that it then expands in volume to come into contact with the surface 104 and displaces the non-gaseous medium 106 at the bottom of the depression 108. Once the pocket of gas 102 has expanded to its maximum volume, as shown in FIG. 2b, it then collapses in the same manner as described for FIGS. 1c and 1d, thus trapping and compressing a portion of the pocket of gas 102 between the transverse jet and the tapering depression 108, creating intense local heating. FIG. 3 shows an alternative embodiment in which the pocket of gas 202 is nucleated within the non-gaseous medium 206 using a different method. In this embodiment a pair of electrodes 214 are provided projecting from the top of the depression 208 in the surface 204. In operation a voltage pulse is applied to the electrodes 214 which creates an electric spark between the electrodes 214. This provides the energy to nucleate the pocket of gas 202, which then expands to contact the surface 204 and collapses in the same manner as has been described for the previous embodiments. Although for simplicity the same shape of depression is shown in this embodiment as is shown in FIGS. 1a-1d, any type of depression could be provided and the electrodes placed in a position to nucleate a pocket of gas at the desired location. FIGS. 4a and 4b show alternative embodiments in which the surface depression has a different geometry to that shown in the previous Figures. In FIG. 4a, the surface 304 comprises a smoothly curved concave depression 308, at the bottom of which is located the pocket of gas 302 within the non-gaseous medium 306. In FIG. 4b, the depression 408 is a trapezium in the surface 404, with the pocket of gas 402 covering more than the entire depression 408. In addition, the depression 408 comprises multiple smaller depressions 416 at the bottom of the larger depression 408. These two embodiments operate in the same manner as has been described for the previous embodiments, apart from in FIG. 4b, the jet formed will trap multiple portions of the pocket of gas 402 in the multiple smaller depressions 416, causing multiple volumes of gas to be compressed and locally heated. Although specific examples have been given, it will be appreciated that there are a large number of parameters that influence the actual results achieved, for example liquid or gel medium density, ambient pressure and temperature, composition of the pocket of gas and of the non-gaseous medium, surface or depression shape and micro-structure of the surface or depression, magnitude of the static pressure, and the application of any standing waves, pressure variations and/or shockwaves to the non-gaseous medium. In each of the embodiments described above, the diagrams shown are a vertical cross-section through a three-dimensional volume of the gaseous medium and surface and hence they depict embodiments that are rotationally symmetric. However, this is not essential to the invention. In particular the surface could comprise discrete surface portions in the rotational direction either instead of, or as well as in the vertical cross-section shown. In the latter case the surface would be multi-facetted. Each facet could give rise to separate but converging shockwaves. In numerical modelling of the experiment, the techniques described herein give rise to a peak pressure of ˜200 kbar which is sufficient to cause temperatures inside the collapsed volume of gas in excess of 1×106 Kelvin which potentially may be sufficient for a nuclear fusion reaction. In some non-limiting examples the resulting neutrons could be used in other processes, or could be absorbed by a neutron absorber for conversion of the kinetic energy of the neutrons to thermal energy and thus conventional thermodynamic energy generation. |
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041728076 | abstract | Disclosed is a method for containing high-level radioactive waste in a body resistant to leaching by water. The method includes the steps of providing a mass containing radioactive substances and either a material which is resistant to leaching by water or a material which when heated forms a material resistant to leaching by water, enclosing the mass in a capsule, and then isostatically pressing the capsule at a temperature and pressure sufficient to form a coherent, dense body from the mass. |
abstract | A method for producing a CT image by applying Z-filtering to axial scan data collected using a multi-row detector, wherein second axial scan data is collected at a second position Z2 to which an X-ray tube and a multi-row detector are rectilinearly moved relative to a subject to be imaged from a first position Z1 toward an end of the multi-row detector, projection data corresponding to a central portion a2 of a reconstruction field P3 near the end of the multi-row detector is extracted from the second axial scan data, and Z-filtering is applied based on the projection data of reconstruction fields P1, P2 and P3 to produce one CT image. |
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050292498 | summary | BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electron microscope e.g, a scanning electron microscope or a transmission electron microscope. 2. Summary of the Prior Art An electron microscope normally comprises a specimen chamber in which the specimen to be analysed is located, and an electron column which generates a beam of electrons which are used to bombard the specimen. That electron column itself normally has two parts, an electron gun chamber containing an electron gun for generating the beam of electrons, and a casing containing an electron lens arrangement. That electron lens arrangement usually includes a plurality of condenser lenses arranged vertically inside the casing with the electron beam passing down a central axis of those condenser lenses. Alignment coils for aligning the electrons into a narrow beam are located between the condenser and the electron gun. Finally, in e.g, a scanning electron microscope, scanning coils (deflection coils) are located between the condenser lenses and the sample, which cause the beam to scan across that sample. Thus, an electron beam path is defined between the electron gun and the sample, passing through the lenses and coils. It is important that electrons following that path are not scattered, and for this reason the interior of the electron column has to be evacuated to a low pressure. The sample chamber must also be evacuated. The standard method of evacuating the interior of the electron column is to connect that column to a vacuum pump via a plurality of ducts which extend from the vacuum pump through the walls of the electron column. Example of such an arrangement is shown in Japanese patent application laid-open number 49-131376, in which there are three ducts extending from the electron column and one from the sample chamber which are interconnected at a diffusion pump. Similarly, in Japanese patent application laid-open number 55-136446, there are again a plurality of ducts leading from the electron column. However, the presence of such ducts causes a number of problems. The first problem is that, if a good vacuum is to be achieved within the electron column, it is necessary that the ducts be relatively large, so that they have satisfactory conductance. The size of the ducts is inconvenient, and limits the positioning of additional devices which may be heeded around the electron column, such as an X-ray system. A further problem associated with the presence of the ducts to the vacuum pump is that their presence means that apertures must be made in any magnetic shielding around the electron column. Stray magnetic fields may cause magnetic disturbance, and if this is allowed to affect the electron beam, the accuracy of the operation of the microscope may be compromised. For example, a magnetic disturbance due to e.g. noise may cause a ripple on the image produced by the electron microscope, thereby blurring that image. Therefore, in order to limit magnetic disturbance. it is known to place a shielding cylinder around the electron column, but it is necessary that apertures be made in that shielding to permit the ducting to the vacuum pump to emerge. Bearing in mind that that ducting needs to be large in order to achieve a good vacuum, there is thus a conflict between the need for a good vacuum and the need for good magnetic shielding. SUMMARY OF THE INVENTION The present invention therefore seeks to overcome, or at least ameliorate, these problems. The present invention proposes that the ducting to the electron column which has been used in the prior art be dispensed with, and that the evacuation path of the electron gun chamber and/or casing containing the electron lens assembly, be defined within the casing itself. At first sight, the beam path may be thought of as a suitable route for that evacuation path, but in fact that beam path will normally include a plurality of restricted apertures whose purpose is to collimate the beam, and therefore those small apertures would restrict the conductance of any evacuation path running along the beam path. Therefore, in the present invention, that evacuation path is off-axis relative to the beam. In the present invention, the casing containing the electron lens assembly may be made from a closed enclosure, together with the electron gun chamber and the sample chamber. Then, by connecting suitable evacuation means in the form of e.g., a vacuum pump to the sample chamber, the whole interior can be evacuated. Furthermore, since the ducting outside the electron column is dispensed with, it becomes possible for the magnetic shielding to be unbroken, except possibly where the electron microscope has an adjustable aperture (which is normally positioned between the condenser lenses and the deflection coils) since the control for that adjustable aperture has to project through the magnetic shielding. The magnetic shielding may simply extend along the casing, and be sealed to the outside of the sample chamber, but preferably there is a further shielding part which encloses the electron gun chamber. Of course, if the evacuation path is defined within the casing, its size needs to be sufficiently large to permit a high conductance. However, in practice it is found that suitable apertures between the electron gun chamber and the casing, adjacent the condenser lenses, and between the casing and the sample chamber permit a sufficiently high conductance to be achieved. Indeed, it is possible with the present invention to achieve a higher conductance than was normally achieved in standard arrangements using external ducting. Japanese patent application laid-open number 59-209045 apparently shows an arrangement in which there is no external ducting. However, the device shown in that disclosure is an electron analysing apparatus which involves the detection of Auger electrons, and therefore must operate under extremely high vacuum, much higher than is normally used in electron microscopes such as scanning electron microscopes or transmission electron microscopes. Therefore, one skilled in the art reading Japanese patent application laid-open number 59-209045 will immediately appreciate that what is illustrated is wholly schematic, and that additional ducting would be necessary in order to achieve the desired level of vacuum. Indeed, this can be seen from the fact that the arrangement is illustrated with the condenser lenses apparently directly contacting the vacuum, which would result in contamination and would not operate satisfactorily. In the present invention, the electron lenses should be sealed from the vacuum. To do this, a development of the present invention proposes that those electron lenses be mounted in sealed modules, and a plurality of such modules be positioned within the casing of the electron. A bore extends through the centre of those modules, to define the electron beam path, but by suitable design of the modules, the evacuation path may be between the outer wall of those modules and the inner wall of the casing. If the electron lens assembly is formed in this way, forming a plurality of modules, the modules may be spaced by suitable spacers. It is desirable that those spacers have apertures therein so that they may thus form part of the evacuation path. If the evacuation path extends around the condenser lenses in the way described above, then the main limit on conductance from the electron gun chamber to the specimen chamber is at the mounting of the electron gun chamber to the casing, and the mounting of the casing to the specimen chamber. At these points, a plurality of apertures are usually necessary, and, particularly between the electron gun chamber and the casing, this may be achieved by providing a tie member in the form of a plate with a plurality of apertures therein. |
062927515 | description | DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An operational flow chart of steps for implementing the methods of the present invention is shown in FIG. 1. Initially, an inertial navigation system (INS), which incorporates a conventional IMU, is at rest, 100. A ZVU is performed prior to commencement of motion of the INS to calibrate the IMU, 100. Motion of the INS then commences and the INS operates in an unaided navigation mode, 102. At some time after the commencement of motion a period of interest begins. At the start of the period of interest, the time and position of the INS is recorded, 104. At a later time, the period of interest ends. At this time, the INS receives a stop notification 106 and comes to rest, 108, and the time and position of the INS is recorded, 100. The velocity along two horizontal axes, say north and east, is then recorded, 112. Because the IMU is at rest, any velocity indicated by the IMU is the result of errors accumulated during the time of motion of the IMU. With the information now obtained, an accurate determination of the position of the INS relative to its position at the start of the period of interest can be made 114. The IMU produces measurements of acceleration over time which may be integrated once to produce a velocity history and twice to produce an indication of position. However, the accelerometer output of the IMU contains errors which are random in nature. Since velocity and position are obtained from integration of the IMU ouput, velocity and position errors accumulate over time. In the present invention, the velocity errors are approximated by a function with parameters that can be determined by evaluating the function at two instances of time: at an initial time when the IMU is at rest and the function is set equal to zero, and at the end of the period of interest when the function is set equal to the velocity recorded after the ZVU is performed when the IMU is at rest. Once the function is determined, it can be integrated over the period of interest to determine the error in position that has accumulated during the period of interest. For example, if the accelerometer bias is constant, the velocity error will grow linearly with time, while position error grows as the square of time. FIG. 2 shows velocity error as a function of time, assuming a constant bias in the accelerometer output: EQU V.sub.e (t)=.intg.a.sub.e dt=a.sub.e t+b where V.sub.e (t) is the velocity error and a.sub.e is the constant acceleration error, and b is some initial velocity error. At time, t=0, V.sub.e (t) is zero because a ZVU was performed with the INS at rest. This yields b=0. At a later time, t.sub.1, when a period of interest begins, the time, t.sub.1, and an indicated position, P.sub.1, is recorded. At a still later time, t.sub.2, the period of interest ends, and the time, t.sub.2, and position P.sub.2, is recorded. The INS is stopped and the velocity V.sub.2, is recorded. Since the actual velocity of the INS is zero, V.sub.2, is equal to the velocity error, V.sub.e (t.sub.2), at time, t.sub.2 : EQU V.sub.e (t.sub.2)=a.sub.e t.sub.2 =V.sub.2 From this equation we can determine the constant acceleration error, a.sub.e =V.sub.2 /t.sub.2. The position error can now be determined by integrating the function for velocity error over the period of interest: ##EQU1## where .DELTA.P.sub.e is the position error that accumulated from the beginning of the period of interest to the end of the period of interest. The indicated position, P.sub.2, at time, t.sub.2, is given by: ##EQU2## where P.sub.a (t.sub.2) is the actual position of the INS at the end of the period of interest relative to its position at time t=0. Since P.sub.2, t.sub.2 and V.sub.2 are known, P.sub.a (t.sub.2) can be calculated directly as: ##EQU3## Similarly, the actual position of the INS at the beginning of the period of interest relative to its position at time t=0 can also be calculated: ##EQU4## Thus, the actual change in position during the period of interest is: ##EQU5## Although the velocity error was approximated by a straight line in this example, a person of ordinary skill in the art will recognize that other suitable functions for approximating velocity error may be employed in accordance with the method of the invention as herein disclosed. The calculation of position errors is performed for each orthogonal direction for which motion may take place. For example, if the motion of the IMU is in a plane, position error is calculated for each of the two orthogonal axes that define the plane of motion. The method of the present invention may be implemented by providing a computer processor for performing the computations and logical decisions required to implement the method for correcting position errors described herein. Programming the processor to implement the method is a relatively simple task for a person of ordinary skill in the art. The method of the present invention described herein may be employed in a mine hunter-killer system. Such a system utilizes a vehicle upon which is mounted an INS comprising an IMU and a processor for deriving errors in position from recorded data obtained in accordance with the method herein described. Initially, the vehicle is at rest and a ZVU is performed on the IMU. The vehicle then commences motion. A period of interest begins when the vehicle detects a mine just in front of the vehicle and records its position relative to the vehicle. At that moment, the time and position of the vehicle is recorded. The vehicle then stops with the mine behind the vehicle and in close proximity thereto, so that the mine may be reached by a robotic arm. At that moment, the time and position is again recorded and a ZVU is performed. From this data the precise position of the mine relative to the vehicle can be accurately determined. Using this accurate position data, a robotic arm places a neutralizer atop the mine for later remote detonation. Although the present invention and its advantages have been described in detail, it should be understood that various changes, substitutions and alterations can be made to the embodiments described herein without departing from the spirit and scope of the invention as defined by the appended claims. Moreover, the scope of the present application is not intended to be limited to the particular embodiments of the process, machine, manufacture, composition of matter, means, methods and steps described in the specification. As one of ordinary skill in the art will readily appreciate from the disclosure of the present invention, processes, machines, manufacture, compositions of matter, means, methods, or steps, presently existing or later to be developed that perform substantially the same function or achieve substantially the same result as the corresponding embodiments described herein may be utilized according to the present invention. Accordingly, the appended claims are intended to include within their scope such processes, machines, manufacture, compositions of matter, means, methods, or steps. |
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050283847 | summary | FIELD OF THE INVENTION This invention relates to water cooled, boiling water nuclear fission reactor plants for producing steam to be used in the generation of electrical power. The invention comprises measures for minimizing the amount of radiation attributable to a unique source and provides improved protection of operating and maintenance personnel performing within the electrical power generating facility. BACKGROUND OF THE INVENTION Corrosion is an inevitable problem in most water containing and operating systems such as steam producing boilers. This detrimental phenomenon is particularly destructive in steam generating nuclear fission reactors which present an environment of radiation as well as high temperatures accentuating the deleterious effects of the water upon many metal components. Moreover, corrosion can constitute an exceedingly complex problem as to its source and effects upon structural materials, and the particular environment. One rather distinctive type of corrosion which has been found to occur in the stainless steel piping and other water containing vessels in nuclear reactor plants has been designated intergranular stress corrosion cracking. This type of corrosion is considered to be attributable to the stainless steel metal having become sensitized by high heat, such as from welding joints, and subsequently subjected to both mechanical stress and a corrosive environment, as well as the high temperatures and radiation encountered within and about a steam generating water cooled nuclear fission reactor plant. The occurrence of such stress corrosion cracking has been found to be more prevalent or aggressive in higher oxidizing environments. High oxygen concentrations in nuclear fission reactor water coolant is a common condition due to the irradiation induced decomposition of some water into its components of oxygen and hydrogen. To counter the corrosive effects of a high oxidizing environment attributable to such radiation disassociation of water, it has been proposed to add hydrogen to reactor water coolant which will reduce free oxygen in the water by combining with it and thereby minimize its corrosive inducing effects. For example, under typical water chemistry conditions, the oxygen concentration is approximately 200 parts per billion and the hydrogen concentration is approximately 10 parts per billion. The concentration of oxygen and hydrogen found to be required for effective prevention of intergranular stress corrosion cracking is in the approximate range of about 2 to 15 parts per billion of oxygen and about 100 parts per billion hydrogen. Corrosion control through manipulation of the free hydrogen and/or oxygen content of reactor water coolant is an established procedure. Although an effective measure for controlling corrosion within the water system of a nuclear fission reactor, the addition of hydrogen to reactor water coolant for the purpose of suppressing the free oxygen content also fosters the conversion of nitrate and nitrite compounds within the water coolant to ammonia. This hydrogen promoted conversion of nitrogen containing compounds to volatile ammonia presents an ancillary problem within the radioactive environment of a nuclear fission reactor due to the radiation induced transmutation of oxygen, by the O.sup.16 (n,p) reaction, into the nitrogen-16 isotope. Although nitrogen-16 is a radioactive nuclide with a half-life of only approximately 7 seconds, about 6 MeV gamma ray is emitted therefrom in its decay. The level of intensity and the relatively high energy of such gamma radiation would require significant shielding to protect personnel from the radiation field. Thus, when this gamma ray emitting nitrogen isotope derived from oxygen is incorporated in a compound which is then converted into volatile ammonia, it becomes a significant source of radiation which can be transported along with steam throughout a steam or vapor system. Boiling water type of nuclear fission reactors, unlike pressure water reactors, produce steam initially within the reactor pressure vessel from the reactor coolant water surrounding at least a major portion of the heat producing core of fissionable nuclear fuel. This steam is conveyed directly from the fissioning fuel core containing reactor pressure vessel to its designated location of work such as a steam turbine for electrical power generation. Thus, differing from the pressure water type reactor where hot pressurized water from the reactor pressure vessel passes through a heat exchanger which in turn produces steam, the steam from a boiling water reactor passes directly to and through the turbine system and generating facility before returning by way of the circuit to the nuclear reactor pressure vessel for repeating the cycle. Accordingly, when treating the coolant water in a boiling water nuclear fission reactor by the addition of hydrogen to control corrosion, there occurs a combination of conditions which may raise the radiation level in a nuclear plant facilities at locations beyond the reactor containment structure, namely, within the steam turbine electrical generating unit. For instance, it appears that an increase in hydrogen concentration of the coolant water will foster oxidation of nitrogen containing compounds in the coolant water to volatile ammonia, including those comprising radioactive nitrogen-16 isotope produced from oxygen. The ammonia, containing gamma ray emitting nitrogen isotopes, being readily volatile, will be carried along with the steam out from the reactor pressure vessel into and through steam conduits and the turbines of the generator, where it decays in the turbine condenser system. Such a potentially adverse condition can significantly increase the reactors construction and operating costs because of a need for added radiation shielding and more stringent limitations on personnel exposure time in carrying out normal facilities operations and maintenance. SUMMARY OF THE INVENTION This invention comprises means for overcoming the transfer of volatile radioactive nitrogen compounds with steam to beyond the containment structure in the operation of a steam producing, water cooled, boiling water nuclear fission reactor plant. The invention provides for the conversion of volatile nitrogen compounds to non-volatile forms within the pressure vessel of the boiling water nuclear fission reactor. OBJECTS OF THE INVENTION It is a primary object of this invention to provide for enhanced personnel safety in the operations of a steam generating, water cooled, boiling water nuclear fission reactor. It is also an object of this invention to provide means for inhibiting the transfer of radiation emitting compounds from a boiling water, nuclear fission reactor through the steam circuit beyond the reactor pressure vessel. It is another object of this invention to provide a method for preventing the escape of volatile, radiation emitting compounds from a boiling water, nuclear fission reactor pressure vessel into the steam turbines of electrical power generators. It is still another object of this invention to provide a method for converting volatile nitrogen compounds to non-volatile compounds within the pressure vessel of a water cooled, boiling water nuclear fission reactor. It is also another object of this invention to provide a steam generating, water cooled, boiling water nuclear fission reactor system having means for converting volatile nitrogen compounds to non-volatile compounds. It is a further object of this invention to provide a steam generating, water cooled, boiling water nuclear fission reactor having a steam separator and/or drying within the reactor pressure vessel which prevents the transfer with steam of radioactive nitrogen compounds from the pressure vessel. |
abstract | The ion acceleration system or complex (T) for medical and/or other applications is composed in essence by an ion source (1), a pre-accelerator (3) and one or more linear accelerators or linacs (6, 8, 10, 13), at least one of which is mounted on a rotating mechanical gantry-like structure (17). The isocentrical gantry (17) is equipped with a beam delivery system, which can be either ‘active’ or ‘passive’, for medical and/or other applications. The ion source (1) and the pre-accelerator (3) can be either installed on the floor, which is connected with the gantry basement, or mounted, fully or partially, on the rotating mechanical structure (17). The output beam can vary in energy and intensity pulse-by-pulse by adjusting the radio-frequency field in the accelerating modules of the linac(s) and the beam parameters at the input of the linear accelerators. |
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description | 1. Field Example embodiments generally relate to jet pump sensing line support clamp assemblies usable in nuclear reactors for jet pump sensing line component repair and replacement. Additionally, example embodiments relate to method of using jet pump sensing line repair apparatuses in a Boiling Water Reactor (BWR). 2. Description of Related Art Generally, BWRs include jet pumps as part of a recirculation system to effectively move coolant and moderator through a nuclear core. In order to evaluate operating conditions within the nuclear core, it may be desirable to monitor the flow rate through the core, including flow rate of coolant from the jet pumps. Typically, a jet pump sensing line is used to measure flow rate from the jet pumps by measuring a pressure differential between the inlet and nozzle of the jet pumps. FIGS. 1 and 2 are illustrations of a related art jet pump sensing lines 100 coupled to a lower diffuser shell 110 at the base of the jet pumps by a sensing line support 120 welded to both the diffuser shell 110 and the jet pump sensing lines 100. The sensing lines 100 are typically welded to the support 120 in support grooves 125, and, as such, are subject to flow-induced vibration in the jet pump. The jet pump sensing lines 100 shown in FIGS. 1 and 2 are typically installed within a BWR core and are accessible only during scheduled plant outages for refueling and repair. These outages occur at several month intervals, and thus components within the core, including the jet pumps and jet pump sensing lines 100, must operate for lengthy periods before they can be inspected or repaired. Further, BWR core operating conditions include high levels of radioactivity due to fission occurring in the fuel rods. Radioactivity, particularly neutron flux commonly encountered in operating nuclear cores, degrades many materials' strength and elasticity over time. Components within the core, including jet pump sensing lines 100 and sensing line supports 120, are subject to premature brittling and cracking due to radiation exposure. The combination of flow-induced vibration, lengthy operating cycles, and radiation degrading may cause jet pump sensing line welds to fail, allowing the jet pump sensing lines 100 to become unseated from their support 120 and become damaged and/or damage other core components. Related art repair means typically include re-welding broken supports during plant outages. Example embodiments are directed to a clamp for use as a BWR jet pump sensing line support clamp or a repair method of the jet pump sensing line. The clamp includes a housing that secures the jet pump sensing lines within the jet pump sensing line support through a non-welded clamping action. The housing may have holes to accommodate a pad that seats against the individual sensing lines. The pads may be installed and tightened with a jack screw and associated ratchet lock spring to permit specific degrees of seating against the jet pump sensing lines. FIG. 3 is an isometric view of a housing 200 used in a jet pump sensing line support clamp in accordance with an example embodiment. As shown in FIG. 7, the housing 200 is clamped to the jet pump sensing line support 120 in order to prevent jet pump sensing lines 100 from becoming unseated or otherwise damaged during operation of a BWR. The housing 200 of may be clamped to the sensing line support 120 without welding by several methods of attachment. For example, as shown in FIG. 7, an upper plate 300 and a lower plate 310 may be attached to both the housing 200 and the sensing line support 120 to clamp the housing 200 onto the sensing line support 120 and provide the securing and confining to the jet pump sensing lines 100 in support grooves 125. A bolt 350 may attach each of the upper plate 300, housing 200, and lower plate 310 through a clearance hole 250 in the housing (shown in FIG. 3). Alternatively, several bolts 350 may be used with multiple clearance holes 250 to provide the desired clamping with the sensing line support 120. As a further example, bolts 350 may have a ratcheting edge that interacts with ratchet lock springs (not shown) in the upper plate 300 to provide incremental tightening of the bolts 350. Alternatively, the housing 200 may be secured in a notch in the upper plate 300 and lower plate 310 to prevent radial displacement or uneven contact between the support clamp components. Each component of example jet pump sensing line support clamp is fabricated from materials that will substantially maintain their physical properties in a nuclear reactor environment. For example, the housing 200, upper and lower plates 300 and 310, and bolts 350 may be fabricated from an austenitic stainless steel and/or similar material. It may be desirable to vary the materials used for components to reduce corrosion and/or galling. For example, the housing 200 and upper and lower plates 300 and 310 may be fabricated from Type 316 austenitic stainless steel, whereas bolts 350 may be fabricated from Type XM-19 stainless steel to prevent galling with the Type 316 stainless steel. As shown in FIG. 7, at least one groove 360 may be machined, for example, by electric discharge machining, or otherwise made into the top or bottom of the sensing line support 120, and either upper or lower plate 300 and 310 may have at least one tongue 365 that is configured to mate with the groove 360. When the plates 300 and 310 are secured to the housing 200 and support 120, the tongue 365 and groove 360 may provide further securing and alignment of the housing 200 and support 120. As shown in FIG. 3, the housing 200 may have a series of access holes 210 that align with individual jet pump sensing lines, transverse from and not overlapping any bore hole 250. The access holes 210 may be of any size and may permit access through the housing 200 to the sensing lines 100 in the support 120 without allowing the sensing lines 100 to pass through the housing 200 and become unseated. As shown in FIGS. 4-6, access holes 210 may permit other components to pass through the housing 200 and interact with the sensing lines 100. For example, jack screws 400 may pass through the access holes 210 and mate with pads 450. The pads 450 may be seated against the individual jet pump sensing lines 100 by a dowel pin 420 in order to further secure the lines 100 in the support 120, dampen vibration in the lines 100, and prevent or reduce other damage to the lines 100. The pads 450 may be secured in the access holes 210 in several different ways, and the use of jack screws 400 is disclosed only as an example of one such way. Pads 450 may be tightened to a desired force against the sensing lines 100 using a variety of fastening and tightening devices. For example, FIGS. 4-6 show a jack screw-ratchet lock spring configuration to allow incremental tightening of the pads 450 against the lines 100. A series of ratchet lock springs 410 may be placed in grooves in the housing 200 in order to provide a ratcheting securing of the jack screws 400 or otherwise inserted into the housing 200 to interact with the jack screws 400. In this example, the jack screws 400 may be incrementally tightened as their serrated edges pass over and lock against the corresponding ratchet lock spring edge. Pads 450 may be tightened against the sensing lines 100 in a variety of ways and not necessarily by a ratcheting device. For example, no access holes 210 may be provided, and pads 450 may instead be fastened directly to the housing 200 so as to secure the sensing lines 100 as the housing is clamped to the support 120. Further, any number of access holes 210 and corresponding components may be included in example embodiments, depending on the number of sensing lines to be secured, the amount of room available, or any other engineering consideration. Each tightening component that is present in an example embodiment is fabricated from a material designed to maintain its physical characteristics in an operating nuclear reactor. For example, jack screws 400 and pads 450 may be fabricated from austenitic stainless steel. As a further example, in order to prevent corrosion, jack screws 400 and pads 450 may be fabricated from different types of austenitic stainless steel, for example, Type XM-19 for the jack screws 400 and Type 316 for pads 450. Ratchet lock springs may be fabricated from a different material, for example, Inconel X-750, a nickel-chromium-iron alloy. The specific materials described for components of a jet pump sensing line support clamp are mere examples. Any material may be used depending on core chemistry and sensing line condition, so long as the material will substantially maintain its physical characteristics in an operating nuclear reactor environment over an operating cycle. Example methods of securing a jet pump sensing line to a support may include attaching a support clamp assembly to a jet pump sensing line support and tightening the support clamp assembly. Structural components described above with regard to example jet pump sensing line support clamps are useable with example methods of securing a jet pump sensing line to a support. For example, as shown in FIG. 8, a support clamp may be attached to a jet pump sensing line support in step S100. This may include affixing an upper and lower plate onto both a housing and jet pump support line so as to confine the jet pump sensing lines into particular grooves blocked by the housing. Step S100 may further include machining appropriate tongue and grooves into jet pump sensing line supports in order to further mate and align the housing and jet pump sensing line support. In step S200, the support clamp may then be tightened against the jet pump sensing lines in order to provide further seating, protection, and/or vibration damping. For example, tightening may include ratcheting a jack screw and ratchet lock spring in a hole in the housing so as to incrementally tighten a pad attached to the jack screw against the jet pump sensing line in the support. The above and other features of the invention including various and novel details of construction and combinations of parts will now be more particularly described with reference to the accompanying drawings. It will be understood that the details of the example embodiments are shown by way of illustration only and not as limitations of the invention. The principles and features of this invention may be employed in varied and numerous embodiments without departing from the spirit and scope of the following claims. |
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046413359 | abstract | A primary-beam collimator for a stereo radiographic x-ray diagnostic installation has an x-ray tube with dual focal points (F1, F2) arranged at a distance from each other. Shutter leaves (1a, 1b, 2a, 2b, 3a, 3b, 4a, 4b) are provided, and adjustable so that two beam pyramids (I from focal point F1, and II from focal point F2) can be individually controlled. Two internal shutter leaves (4a, 4b) are provided for restricting the beam in planes perpendicular to the stereo base F1-F2. These are adjustable between two external shutter leaves--each in the direction of its corresponding external shutter leaf. The internal shutter leaves (4a, 4b) are constructed so that, when adjusted to their external positions, they permit the emission of a central beam-pyramid from a central focal point (FN) and, together with the external shutter leaves (2a, 2b), they close the external shutter openings. |
description | The invention relates in general to the field of equipment allowing for the circulation of a liquid in a circuit. More precisely, the invention relates to a system intended to be integrated into a circuit of which the direction of circulation can be alternated. It applies particularly advantageously to industrial circuits wherein it is desirable to vary the load and the direction of circulation. An application relates for example to the cleaning of equipment of the circuit, such as filters, by reversing the direction of circulation. Another application related to test circuits which make it possible to test or characterise equipment such as pumps. A privileged field of application is the nuclear industry with the characterisation of equipment integrated into the reactors for which the heat carrying fluid is a liquid metal. As such, the invention is particularly suited in the development of 4th generation sodium cooled reactors such as the ASTRID reactor (Advanced Sodium Technological Reactor for Industrial Demonstration). In certain types of circuits, it is necessary to be able to reverse the direction of circulation of the liquid. For this, there are pumps able to deliver a reversible flow. This is the case with electromagnetic pumps (EMP). Reversing the direction of circulation of the fluid in a circuit inevitably modifies the distribution of the pressure along the latter. This change in the distribution of pressure is not compatible with a circuit that is not provided for this such as shall be explained in more detail hereinbelow in reference to FIG. 1 which describes a conventional circuit. The circuit shown in FIG. 1 comprises a pump 2 and a throttle valve 9, making it possible for example to interrupt the circulation or to vary the load loss as is the case in circuits for testing and characterising pumps. In the example shown in FIG. 1, the circuit furthermore has an exchanger 6, for example to evacuate the heat that the pump supplies to the circuit. Pump 2, throttle valve 9 and exchanger 6 are placed in series. The circuit also comprises an expansion reservoir 7, also designated as a pressurisation reservoir, placed upstream of the pump 2 and as a bypass with respect to the circuit and being connected to a pipe. In a known manner, and as shown in FIG. 1, an expansion reservoir 7 comprises an expansion chamber in free and permanent communication with the liquid of the circuit and comprises a gas 72 applying a pressure on the free surface 73 of the liquid 71 of the expansion reservoir 7. No flow circulated in the expansion reservoir 7. There is only a displacement of the liquid 71 of the expansion reservoir 7 that makes it possible to offset the variations in volume of the liquid present in the circuit. This variation in volume is due to the variations in the temperature of the liquid. In the framework of the heat carrying fluid circuit, these variations in volume can be substantial. As such, the expansion reservoir 7 makes it possible to limit the variations in pressure upstream of a pump 2. The expansion reservoir 7 is associated with a device for controlling the pressure of the pressurisation gas Pc, which through injecting or removing gas makes it possible to vary the pressure of the gas 72 and therefore the pressure. It is also provided with a protective device 8 that limits the pressure in the circuit in order to prevent the destruction of it and the associated consequences. In the event of excess pressure in the circuit, the protective device 8 activates and the excess pressure (of gas and/or of liquid) is directed to an outlet 81. There is then an opening of the circuit. In the test circuits, by measuring the pressure PC of the expansion reservoir 7, and the pressures upstream Pe and downstream Ps of the pump 2 as well as by varying parameters such as the direction of circulation of the liquid and the load loss by actuating the throttle valve 9, the behaviour of the pump 2 can be characterised. In FIG. 1, the direction of circulation is shown by the arrows. The distribution of the pressure is then such that: Ps>Pe. Through simplification, it is considered here that Pc Pe. Indeed Pc is fixed by the value of the pressure Pe and the difference between these two pressures is equal to the pressure exerted by the height of the liquid between the altitude of the free surface 73 in the expansion reservoir 7 and the altitude of the inlet of the pump 2. This altimeter pressure is most often negligible. The pressure Pc is generally fixed at a value close to atmospheric pressure (from 1 to 2 bars abs), therefore clearly less than the values that Ps can take (from a few bars to several ten of bars and even more). The protective device 8 is provided to trigger if the pressure Pc reaches a limit value beyond which the installation is no longer safe. In the case of the preceding diagram, this device could be adjusted to a pressure that is just slightly greater than Pc, i.e. 2.5 bars for example. If the direction of circulation is that of FIG. 1, i.e. from the pump 2 to the throttle valve 9, the unit is operating correctly. FIG. 2 shows the circuit of FIG. 1 wherein the direction of circulation is reversed. This inversion in the direction of circulation, even voluntary, causes the pump 2 to deliver at pressure Ps in the portion of the circuit that is connected to the expansion reservoir 7. This therefore risks triggering the protective device 8 and opening the circuit although there is no failure of the circuit. Moreover, the pressure Pe at the inlet of the pump 2 can potentially fall under the saturation vapour pressure of the fluid contained in the circuit and result in its vaporisation in the portion of the circuit between the throttle valve 9 and the pump 2. The pump 2 can then be damaged and substantial turbulence can be generated. As such, the relative position of the pump 2 and of the expansion reservoir 7 depends on the direction of the circulation of the liquid in the circuit. This therefore gives rise to a problem in circuits with a reversible direction of circulation. In order to allow for the reversibility of the direction of circulation, a solution consists in providing the circuit with two throttle valves 9, 91 and with two expansion reservoirs 7, 7′, each provided with a safety device 8, 8′ and with a pressure control device. Such a system is shown in FIGS. 3 and 4. Furthermore, it is necessary to provide an isolation valve 74, 74′ between each expansion reservoir and the circuit. According to the direction of circulation, an expansion reservoir 7, 7′ is disconnected from the circuit by closing the isolation valve 74, 74′ that connects it to the circuit. In these figures the valves in dotted lines are fully open and the valves in solid lines are fully closed. This solution has for disadvantage to require a substantial amount of equipment and increased complexity which tends to reduce the reliability of the unit and increase the manufacturing and maintenance cost. In addition, this requires either frequent human intervention for opening and closing of valves, or the setting up of an automatic pilot system, with the risks of failure. Another solution shown in FIGS. 5 and 6, consists in providing a circuit provided with two throttle valves 9, 91 and with a single expansion reservoir 7 provided with a protective device 8 and with a pressure control device. The throttle valve 9 arranged at the inlet of pump 2 is always fully open. This valve is shown as a dotted line in the two directions of circulation. When the expansion reservoir is arranged at the inlet of the pump (FIG. 5), the circuit operates normally, since the pressure at the outlet of the pump is not directly transferred to the expansion reservoir 7. When the expansion reservoir 7 is arranged at the outlet of the pump (FIG. 6), the load loss provoked by the exchanger risks lowering the pressure excessively at the pump inlet and conveying it under a cavitation threshold. This solution is therefore limited to applications wherein the pressure is sufficiently high to avoid cavitation. The range of useful flow is therefore necessarily reduced. There is therefore a need consisting in offering a solution that allows for a circulation of liquid that is reversible and which does not have at least some of the disadvantages mentioned hereinabove of existing solutions. This invention aims to achieve this objective for circuits in which the valve is a plug valve. More precisely, it has for purpose to propose a circuit that integrates a plug valve and that makes it possible to alternate the direction of circulation while limiting the complexity of the circuit and by allowing for an unrestricted operating range, and this preferably for several types of plug valves. In order to achieve this objective, an embodiment of this invention relates to a system for regulating a liquid in a circuit preferably able to reverse the direction of the circulation, with the system comprising: a plug valve comprising at least one inlet and one outlet, with the plug comprising an internal passage through which is intended to pass the liquid flowing from the inlet to the outlet of the valve when the valve is open at least partially, with the position of the plug with respect to a body of the valve making it possible to adjust the rate of the flow of the liquid through the valve, an expansion reservoir in communication with the liquid flowing in the circuit and intended to contain liquid and a compensating gas,The plug comprises at least partially an expansion channel which has at least one lateral opening located on a lateral face of the plug and which is conformed to provide a communication between said lateral opening and the expansion reservoir, the valve being conformed in such a way that: at least when the valve is closed: the lateral opening is in direct communication with the liquid coming from the inlet or from the outlet of the valve, i.e. when the internal passage does not communicate directly with the inlet or the outlet of the valve; the liquid present in the inlet or the outlet of the valve can therefore communicate with the expansion reservoir by entering the expansion channel through the lateral opening, when the valve is open at least partially, i.e. when the internal passage communicates directly with the inlet and/or the outlet of the valve, the lateral opening cooperates with an inner wall of a body of the valve in such a way as to form a conduit in communication on the one hand with the expansion reservoir and on the other hand with the internal passage. As such, the expansion reservoir is connected to the circuit by the intermediary of the valve, preferably between the inlet and the outlet of the valve, and in such a way that the expansion reservoir communicates with at least one from among the inlet and the outlet of the valve regardless of the position of the plug. The position of the plug is also independent of the pressure of the liquid in the circuit and in the expansion reservoir. The channel of the plug allows permanent communication between the expansion reservoir and at least one of the branches of the circuit. As such, the invention makes it possible to design a reversible circuit wherein the expansion reservoir is permanently in communication with the liquid of the circuit. Furthermore, the invention makes it possible to considerably improve the reliability of the system since it does not require controlling the isolation valves of one or more reservoirs with precision as in a solution of prior art. With the solution shown in FIGS. 3 and 4, incorrect controlling of the isolation valves can indeed result in a simultaneous deactivation of the two expansion reservoirs which can have serious consequences. Moreover, it is possible to have only one throttle valve formed by the valve. This makes it possible to reduce the load loss that is inevitable induced by the presence of additional valves as is the case in other solutions of prior art. The invention as such makes it possible to widen the range of admissible flows. In addition to simplifying the control of the expansion reservoir, the invention makes it possible to significantly reduce the number of components required and in particular the number of control components, which makes it possible to improve the reliability of the circuit and to reduce the cost of it. Moreover, the system according to the invention makes it possible to precisely and reliably control the lowest pressure of the circuit, as such preventing the pressure in the circuit from falling below a minimum desired pressure. Particularly advantageously, the system according to the invention applies to straight valves, also designated as in-line valves, as well as to elbow valves. It can therefore be integrated into all of the portions of the circuit, into the straight sections as well as curvatures or angles. One of the advantages of the invention is to reduce the risks of jets of liquid appearing inside the expansion reservoir. The level of the free surface of the liquid in the expansion reservoir is therefore stabilised which increases the reliability of the control of the level and of the pressure of the liquid in the circuit. Optionally, the invention can furthermore have at least one of any one of the following characteristics separately or in combination: Advantageously, the system is configured in such a way that the expansion reservoir is, during operation, in permanent communication with the liquid flowing in the circuit Preferably, the conduit opens on the one hand into the expansion reservoir an opens on the other hand into a space formed by a lower face of the plug and a bottom of the body of the valve, with this space being in communication with the internal passage by a channel made in the plug. Preferably, the lateral opening is a recess, with the cooperation of the recess and the inner wall integral with the body of the valve forming the conduit when the valve is open at least partially. The body comprises a seat configured to receive a plug. The inner wall integral with the body is a wall of the seat. Alternatively, the body of the valve does not include a seat and the wall integral with the body of the valve with which the plug cooperates and an inner wall opposite an outer wall of the body of the valve. Preferably, the recess extends from the expansion reservoir to the lower face of the plug. More precisely, the recess extends from an upper face of the body of the plug to the lower face of the plug. Preferably, the recess forms a groove. According to an advantageous embodiment, the plug is a spherical plug. This type of plug has for advantage to improve the seal. The invention makes it possible to be applied in a particular simple manner to this type of valve. Alternatively, the plug is a cylindrical plug. Advantageously, the system is conformed in such a way that when the valve is open, the expansion reservoir communicates with the liquid passing through the valve solely through the recess, of said space and of the lower channel. Advantageously, the valve is of the “full-flow” type. It makes it possible, when it is fully open to create a load loss of the same degree as the portion of a pipe, elbow or straight section, of the same length. Preferably, all of the liquid flowing from the circuit to the expansion reservoir passes through the expansion channel or channels. Preferably, the system is conformed in such a way that when the valve is open, the expansion reservoir communicates with the liquid passing through the valve solely through the recess, of said space and of the lower channel. As such, when the valve is open and the speed of circulation of the liquid is substantial, the liquid penetrating into the expansion reservoir does not pass directly from the internal passage to the expansion reservoir, which as such limits the jets in the latter. Advantageously, the valve is a straight valve. More generally, the inlet and the outlet of the valve form an angle between 130° and 180°. Alternatively, the valve is an elbow valve, with the inlet and the outlet of the valve forming an angle less than 130°. Advantageously, the valve comprises a body and a cover forming an enclosure, with the expansion reservoir being housed in the enclosure. As such, the expansion reservoir and the valve are grouped together within the same component. This makes it possible in particular to simplify the mounting of the circuit and to limit the encumbrance. Furthermore, the number of components is limited and the reliability of the circuit is improved. In particular, the seal of the system is made particularly safe. The obturator is movable inside the body of the valve. The movable obturator is movable with respect to the expansion reservoir. The valve body is fixed with respect to a frame of the system. Typically, the valve body is fixed with respect to the conduits connected at the inlet and at the outlet of the valve. The expansion reservoir is fixed with respect to the valve body during the displacement of the movable obturator. Advantageously, the expansion reservoir is formed at least partially by an inner wall of the valve body. More precisely, the expansion reservoir is formed by the inner walls of the valve body, by the inner wall of the cover and by an upper face of the body of the movable obturator. Preferably, the expansion reservoir is defined only by the inner walls of the valve body, by the inner wall of the cover and by an upper face of the body of the movable obturator. The expansion reservoir is housed at least partially in the cover. Preferably, at least 20% and preferably at least 30% and preferably at least 50% of the internal volume of the expansion reservoir is housed in the internal volume of the cover. The obturator is separated from the cover. It is not present in the cover. According to an advantageous embodiment, the expansion reservoir is vertically arranged higher than the movable obturator. The liquid present in the expansion reservoir can therefore flow via gravity to the movable obturator. Preferably, the expansion reservoir can be arranged vertically and above the movable obturator or not be arranged vertically to the movable obturator. According to an advantageous embodiment, the expansion reservoir surmounts the movable obturator. According to an embodiment, the movable obturator is separated from at least a portion of the expansion reservoir. As such, in at least a portion of the expansion reservoir, the movable obturator is absent. According to an embodiment, the expansion reservoir is separated from the obturator. According to an embodiment, the expansion reservoir is connected to the valve by being arranged at a distance from the latter. The expansion reservoir is separate from the obturator. This makes it possible in particular to not drive the expansion reservoir in displacement during the displacement of the movable obturator, improving as such the reliability and the robustness of the system. The independence between the expansion reservoir and obturator also makes it possible to independently dimension the expansion reservoir and the movable obturator. In particular, the expansion reservoir can be adapted, in particular in terms of volume, to the characteristics of the circuit (flow, pressure), while still retaining a movable obturator of small size in order to reduce the encumbrance of the system and carry out a movable obturator with dimensions and surface states that are perfectly controlled. The expansion reservoir is configured in such a way as to contain a compressed gas Advantageously, in closed position, the body of the plug prevents any communication of the liquid between the inlet and the outlet i.e. from one flange to the other. Advantageously, the system is configured in such a way as to orient the direction of closing of the plug according to the direction of the circulation of the liquid in the circuit. Advantageously, in closed position of the valve, the internal passage of the plug remains in communication with a portion of the circuit separating the valve from an inlet of the pump. Advantageously, the plug is actuated by a control device comprising a reduction gear housed inside the expansion reservoir. As such it is located in the enclosure. Advantageously, the reduction gear is immersed in the compensating gas, reducing as such the sealing constraints. Advantageously, the system comprises an overflow in order to limit the level of liquid in the expansion reservoir and wherein the reduction gear is arranged above the overflow. The system is configured in such a way that the level of liquid in the expansion reservoir is less than a given level, and wherein, the reduction gear is arranged above this given level. Advantageously, the system comprises a device arranged in the expansion reservoir, under the overflow and configured to break the jets of liquid coming from the expansion channel. Advantageously, the system comprises a thermal protection device housed inside the expansion reservoir and conformed to thermally insulate the reduction gear from the heat of the liquid. Advantageously, the system comprises a rotational guiding bearing of the plug and wherein the bearing is housed inside the expansion reservoir. As such, the bearing is located in the enclosure. Advantageously, the system is configured in such a way that in operation the bearing is immersed in the fluid. Alternatively it is immersed in the compensating gas and is located outside of the fluid. Advantageously, the bearing comprises a passage allowing the free circulation of the fluid through the bearing. Advantageously, the valve is a throttle valve. Advantageously, the inlet and/or the outlet is formed by a flange configured to be connected to a pipe of the circuit. Another aspect of this invention relates to a circuit comprising a system according to any of the preceding characteristics and a pump able to deliver in two opposite directions. Optionally and advantageously: the plug comprises at least one expansion channel for the passing of the liquid opening into an internal passage of the plug in order to place in communication the expansion reservoir and the circuit, the circuit being configured in such a way as to orient the direction of closing of the plug according to the direction of the circulation of the liquid in the circuit. the circuit is configured in such a way that, during the closing of the valve, the plug is turned in such a way that the internal passage remains in communication with a portion of the circuit separating the valve from an inlet of the pump. the circuit comprises a single valve. As such the load loss is limited with respect to circuits comprising two valves in order to ensure the reversible operation of the circuit. The range of admissible flow is therefore more substantial. Another aspect of this invention relates to the usage of a system according to the invention to adjust the circulation of a liquid having a temperature greater than or equal to 350° C. and preferably greater than or equal to 400° C. Preferably, the invention is used to adjust the circulation of liquid sodium intended to provide for the heat transfer in a circuit of a sodium cooled nuclear reactor. The other objects, characteristics and advantages of this invention shall appear when examining the following description and the accompanying drawings. It is understood that other advantages can be incorporated therein. The drawings are provided as examples and do not limit the invention. They form diagrammatical representations intended to facilitate the understanding of the invention and are not necessarily at the scale of practical applications. In particular the relative dimensions and thicknesses of the various parts, walls and members do not represent reality. An example of a circuit integrating a system according to the invention shall now be described in reference to FIG. 7. In this example, the circuit 1 comprises a pump 2, preferably reversible, an exchanger 6 and a system 10 according to the invention comprising a valve 200. These three elements are arranged in series. They form a closed circuit and are fluidly connected together by sections 3, 4 5 of pipes. The section 3 connects the pump 2 to the exchanger 6, the section 4 connects the exchanger 6 to the valve 200 of the system 10 and the section 5 connects the valve 200 of the system 10 to the pump. In the framework of this invention, circuit 1 is qualified as the closed circuit comprising the pump 2 and comprising preferably the exchanger 6 or any other member(s) as well as the valve 200 of the system 10. Other elements can naturally be incorporated into the system 10. Moreover, the exchanger 6 can be replaced with another component or several other components. The pump 2 is reversible which allows it to have for inlet and for outlet, respectively the sections 5 and 3 or inversely for inlet and for outlet respectively the sections 3 and 5. The valve 200 comprises an outlet and an inlet that are inverted according to the direction of the circulation of the liquid. Particularly advantageously, the system 10 comprises an expansion reservoir 100 that makes it possible to offset the variations in the volume of the liquid present in the circuit and which are due to the variations in the temperature of the liquid. The expansion reservoir 100 is connected to the valve 200 mounted in series on circuit 1. As such, the expansion reservoir 100 is not connected in series on the circuit 1 comprising the pump 2 and the valve 200. It is connected as a bypass by the intermediary of valve 200. Valve 200 is configured to allow for permanent communication between the circuit 1 and the expansion reservoir 100. As such, regardless of the position of the plug 210 of the valve 200, the expansion reservoir 100 communicates with at least one of the sections 4 or 5 of the circuit. Particularly advantageously, this makes it possible to considerably improve the reliability of the system 10 since it is no longer required to control the isolation valves of one or more reservoirs with precision as in the solution shown in FIGS. 3 and 4. Moreover, it is possible to have only one throttle valve formed by the valve 200. This makes it possible to reduce the load loss that is inevitable induced by the presence of additional valves as is the case in the solutions shown in FIGS. 5 and 6. In particular, the invention does not require the presence of a throttle valve 91 on the section 3 between the exchanger 6 and the pump 2. The invention as such makes it possible to widen the range of admissible flows. In addition to simplifying the control of the expansion reservoir 100, the invention makes it possible to significantly reduce the number of components required and in particular the number of control components, which makes it possible to improve the reliability of the circuit 1 and to reduce the cost of it. The expansion reservoir 100 can be connected on the valve 200 by being arranged at a distance from the latter. In a preferred embodiment, the expansion reservoir 100 and the valve 200 are on the contrary grouped together within the same component. This makes it possible in particular to simplify the mounting of the circuit and to limit the encumbrance. More advantageously, this makes it possible to approach the expansion reservoir 100 of the circuit 1 and as such improve the reactivity of the expansion reservoir 100 and a protective device 8 against excessive pressure associated with the expansion reservoir 100. Advantageously, the portions of the expansion reservoir comprising the liquid 112 and the pressurisation gas 103 have substantially identical diameters. Preferentially, the expansion reservoir 100 surmounts the valve 200 and communicates with the liquid of the circuit by a channel, designated as expansion channel 213, carried at least partially by the plug 210. Also advantageously, the valve 200 comprises a body 201 and a cover 101 forming together an enclosure 102, with the expansion reservoir 100 being housed inside this enclosure 102. As such, the movable obturator is separate from the expansion reservoir 100, with the latter fixed with respect to the body 201 of valve 200. The movable obturator is movable with respect to the expansion reservoir. In non-restricted embodiments shown in the figures which are described hereinbelow, the expansion reservoir 100 is vertically arranged above the movable obturator. More precisely, the expansion reservoir 100 surmounts the movable obturator. The expansion reservoir is formed by the inner walls 201 of the valve 200, by the inner wall of the cover 101 and by an upper face 214 of the body of the movable obturator. As such, the expansion reservoir is housed at least partially in the cover. Preferably, at least 20% and preferably at least 30% and preferably at least 50% of the internal volume of the expansion reservoir 100 is housed in the internal volume of the cover 101. A first example of the system 10 according to the invention shall now be described in detail in reference to FIGS. 8 to 17. In the following example, the valve 200 is a throttle valve or a valve that makes it possible to circulate or interrupt the circulation of the liquid inside the circuit 1. FIGS. 8 and 9 show the body 201 of the valve inside of which the plug 210 for example cylindrical, is movable in order to adjust the passage of the liquid from one flange to another of the valve 200. For a direction of circulation of the fluid, the flange 202 forms the inlet of the valve and the flange 203 forms the outlet of the valve. The inlet and outlet are naturally inverted in case of an inversion in the direction of circulation. In the example shown, the flanges 202, 203 are intended to be connected to a pipe by bolting without this being restrictive. Indeed, a fastening via welding can be considered, in particular for applications wherein the liquid is a liquid metal such as sodium as is the case in sodium cooled nuclear reactors. In the following example, the valve is an in-line valve, with the inlet and the outlet substantially coaxial. Sections 4 and 5 are then arranged in the extension of one another. Moreover, the plug is spherical. As shall be shown in what follows in reference to FIGS. 18 to 27, the invention also covers the plug valves 200 that have an elbow. It also covers cylindrical plugs. As shown in FIGS. 10, 11 and 12, the plug 210 has a body 211 that comprises an internal passage 212 for the liquid. This internal passage 212 makes it possible to place the inlet and the outlet of the liquid into communication for certain angular positions at least of the plug 210 with respect to the body 201 of the valve. As with all plug valves, the shape and the size of the inside of the body 201 of the valve and of the body 211 of the plug are chosen in such a way that the liquid can flow from one flange to the other only through the internal passage 212 carried by the body 211 of the plug 210. Preferably, the valve body comprises a seat 209 conformed to receive the spherical plug. The seat 209 is integral with the body 201 of the valve 200. The angular position of the plug with respect to the body 201 of the valve therefore with respect to the inlet 202 and outlet 203 flanges, is controlled by a control device which typically comprises an actuator, for example a reduction gear 120. The body 201 of the valve and the cover 101 form an enclosure 102 inside of which the expansion reservoir 100 is housed. This enclosure 102 is sealed except for a channel 213 for communication between the expansion reservoir 100 and one of the flanges, such as shall be described hereinafter, and possibly except for an overflow 107, an orifice 104 for the management of the pressurisation gas which will also be described in more detail in what follows. Particularly advantageously, the body 211 of the plug comprises at least partially a channel 213 that allows the liquid circulating inside the circuit and coming from one of the two flanges 202, 203, to penetrate inside the expansion reservoir 100 formed by the enclosure 102. It is as such qualified as an expansion channel 213. The body 211 of the plug 210 comprises at least one lateral opening located on a lateral face 219 of the plug. Valve 200 is conformed to ensure permanent communication between said lateral opening and the expansion reservoir 100. In the example shown, the lateral opening forms a recess 218 which extends from the inside of the circuit to the expansion reservoir 100. Preferably, the recess 218 extends from an upper face of the body 211 of the plug to the lower face 220 of the plug 210. Advantageously, the recess 218 forms a groove. The valve is conformed in such a way that at least when the valve is closed the recess 218 is in direct communication with the liquid coming from the inlet or from the outlet of the valve 200. In FIG. 10, the recess 218 communicates with the liquid passing through the flange 203. As such, when the internal passage 212 no longer communicates directly with the inlet or the outlet of the valve, the liquid present in the inlet or the outlet of the valve can therefore communicate with the expansion reservoir 100 by entering into the expansion channel 213 via the recess 218. Moreover, the valve is conformed in such a way that at least when the valve 200 is open at least partially, i.e. when the internal passage 212 communicates directly with the inlet and/or the outlet of the valve, the recess 218 cooperates with the inner wall 207 of the seat 209 in such a way as to form a conduit of which the section, taken perpendicularly to the flow of the liquid in the conduit forms a closed perimeter. This conduit is in communication on the one hand with the expansion reservoir 100 and on the other hand with the internal passage 212. Preferably, this conduit opens on the one hand into the expansion reservoir 100 and opens on the other hand into a space 221 formed by the lower face 220 of the plug 210 and the bottom 208 of the body 201. In the embodiment shown and wherein the body 201 comprises a seat 209, the bottom 208 delimiting with the lower face 220 of the spherical plug the space 221 is the bottom of the seat 209. This space 221 is in communication with the internal passage 212 via a channel 217, typically a hole, made in the plug 210. In the non-restricted example shown, this space 221 is formed by a groove 222 made on the lower face 220 of the body 211 of the plug 210 and which cooperates with the bottom 208 of the seat 209 in order to define a passage for the liquid. An expansion channel forming a recess 218 or a groove on the lateral face of the body 211 of the plug 210 advantageously makes it possible to simplify the carrying out of the plug. This example is not however restrictive. The invention extends to embodiments wherein the expansion channel forms a conduit that has a lateral opening that does not form a groove. Moreover, the invention extends to embodiments wherein the expansion channel forms a conduit, typically a hole, which communicates directly between the lateral opening and the internal passage 212. As such, the valve 200 is conformed in such a way that, regardless of the position of the plug 210, the expansion channel 213 is always in communication with the inlet or the outlet of the valve 200. Either the lateral opening communicates directly with the inlet or the outlet of the valve, or it communicates with the internal passage 212, preferably via the space 211, when the internal passage 212 communicates with the inlet or the outlet of the valve. Liquid can therefore permanently reached the expansion reservoir 100 formed by the enclosure 102. This shall be described in more detail in reference to FIGS. 13 to 17. The expansion volume is the volume of liquid 112 located between the upper face 214 of the plug 210 and the free surface 105 of the liquid. The plug 210 represents a variable load loss. The communication between the circuit and the expansion reservoir 100 is carried out via a path which is always outside of the pump-load loss section induced by the plug 210. As such, regardless of the expansion reservoir 100 in the circuit, the expansion reservoir 100 never sees the pressure delivered by the pump contrary to the expansion reservoir of the circuit shown in FIG. 2 which is in direct communication with the outlet of the pump. Moreover, in the circuit of FIG. 2 the expansion reservoir 100 imposes the pressure between the valve and a component such as the exchanger. Preferably, and as shown in FIG. 10, a bearing 108 provided with rollers 109 is provided in order to ensure the guiding in rotation of the plug 210. Preferably, the bearing 108 guides the plug 210 on an axis 216 of the plug 210 integral with the body 211 of the plug and which extends according to the direction of rotation of the latter. Preferably, the bearing 108 is situated in the immediate vicinity of the upper face 214 of the plug 200 forming a cylinder in its upper portion. A passage 110 is provided in the bearing 108 for the liquid coming from the internal passage 212 carried by the body 211 of the plug. According to an alternative embodiment not shown, if the bearing 108 is housed in the body 201 of the valve, a passage can be made in the thickness of the wall of the body 201 of the valve in order to allow the liquid to pass from the upper face 214 of the body 211 of the plug to a space located above the bearing. As such in operation, the bearing 108 is immersed in the liquid 112 present in the expansion reservoir 100. Advantageously, an aerator device 111 is provided to prevent projections of liquid coming from the expansion channel 213 with a substantial speed. In this example, an aerator device 111 is placed above the bearing 108. In normal operation, the aerator device 111 is immersed and the free surface 105 of the liquid 112 is located above the aerator device 111. An overflow 107 is also provided to evacuate any overflow of liquid. In normal operation, the free surface 105 of the liquid 112 is therefore located underneath the overflow 107. In the enclosure 102 formed by the body 201 of the valve 200 and the cover 101, and above the free surface 105 of the liquid 112, is located the pressurisation gas 103 also designated as sky gas, of which the function is to offset the variations in volume of the liquid in the circuit and to ensure that the pressure of the circuit remains within an acceptable operating interval. An orifice 104 is also provided for the management of the pressure of the pressurisation gas 103. This orifice 104 is preferably located in the upper portion of the cover 101. Advantageously but optionally, the system also comprises a protective device 8, preferably connected to the orifice 104 for the management of gases, and configured to adjust and to limit the pressure of the gas in the expansion reservoir 100 and therefore the pressure of the liquid in the circuit when the latter exceeds a threshold value that could damage the circuit. When the protective device 8 is activated, the excess gas pressure is directed to an outlet 81 which prevents exceeding an admissible pressure limit for the expansion reservoir and the circuit. As indicated hereinabove, a control device is provided in order to control the angular position of the plug 210 with respect to the body 201 of the valve. Note here that the angular position of the plug 210 is perfectly independent of the pressure inside the circuit and of the pressure inside the expansion reservoir 100. According to a particular advantageous embodiment, it is placed that this control device be housed inside the enclosure 102 and that, also preferably, the coupling between the plug 210 and the control device also be housed inside the enclosure 102. As such, the invention makes it possible to substantially reduce the constraints for sealing, as such improving the reliability of the system 10. More precisely, the control device comprises a motor, typically a reduction gear 120, preferably housed in the enclosure 102 above the overflow 107. It is therefore immersed in the pressurisation gas by being advantageously separated from the liquid 112. A coupling device 125 between the outlet of the reduction gear 120 and the plug 210 is also located above the overflow 107 and therefore immersed in the pressurisation gas 103 while still being separated from the liquid 112. The axis 216 of the plug 210 connects the coupling device 125 to the body 211 of the plug. Preferably, the reduction gear 120 is arranged in such a way that its output axis is coaxial with the axis 216 of rotation of the plug 210. Advantageously, a thermal protection device 124 is arranged between the liquid 112 and the reduction gear 120 in such a way as to preserve the latter from the heat of the liquid 112. This is even more advantageous when the liquid is a liquid metal such as sodium. The thermal protection device 124 can be for example a stack of thin disks and spaced apart or any other volume or association of subsets having low thermal conductivity. Preferably, the thermal protection device 124 is arranged around the coupling device 125 as is shown in FIG. 10. Preferably, the motor is fixed onto a support 121 conformed to be fixed into an upper portion of the body 201 of the valve, for example on the opening of the body 201 of the valve. Once the motor is fixed on the body 201 of the valve, the cover 101 can then be positioned on the body 201 of the valve in order to cover the motor and form the sealed enclosure 102. The mounting of the system 10 is therefore particularly simple. For example, the attaching between the body 201 of the valve and the cover 101 is carried out by bolting of two flanges 204, 207 carried respectively by the body 201 of the valve and the cover 101. When the liquid is brought to a high temperature, typically between 300 and 500° C. as in the case with liquid sodium, the system 10 advantageously comprises a cooling system 123 of the motor. A heat carrying fluid then circulates in the pipes passing through the enclosure 102 and penetrates into the motor. Preferably, holes for the passage of these pipes are made in the cover 101. The enclosure 102, preferably the wall of the cover, also comprises a hole for the passage of a power supply line or lines 122 of the motor. The system 10 can also comprise one or more level sensors 106 to measure and control the level of liquid in the expansion reservoir 100. A hole can be made in the enclosure 102, typically in the wall of the cover 101, for the passage of the sensors 106. Preferably, the body of the valve has an emptying hole 206 made in the bottom 209 of the body 201 and which makes it possible to facilitate the emptying of the system 10 incorporating the valve 200 and the expansion reservoir 100. The invention as such proposes a system 10 integrating within the same component a valve 200, in particular an in-line valve, and an expansion reservoir 100 in permanent communication with the liquid of the circuit and for which the design offers improved operating reliability, a particularly simple and effective seal, as well as easy assembly. The operation of the invention shall now be described in detail in reference to FIGS. 13 to 17. FIGS. 13 to 15 show the valve 200 in fully open position. In this position, the plug 210 is equivalent to the pipe portion that the valve 200 replaces in circuit 1. The load loss in the valve 200 is very low and even zero, which is an advantage with respect to the other valves with a transfer obturator. In this position the circulation of the liquid is possible in both directions. Moreover, as can be seen clearly in FIG. 15, the internal passage 212 is in communication with the liquid of the circuit. The liquid can therefore pass through the lower channel 217, reach the space 221 in order to reach the conduit formed by the recess 218 and the inner wall integral with the body. From this conduit, the liquid can reach the expansion reservoir 100. As such, the expansion channel 213 then formed by the lower channel 217, the space 221 and the recess 218 allows for the communication of the liquid circulating in the circuit 1 with the liquid 112 contained in the expansion reservoir 100. When the valve 200 is closed, as shown in FIGS. 16 and 17, the circulation of the liquid in the circuit 1 is interrupted. The internal passage 212 is no longer in communication with the section of the circuit connected to the flange 202 or even with the circuit connected to the flange 203. The recess 218 forms an opening that opens into the circuit. The liquid can therefore directly reach the recess 218 from the inlet or the outlet of the valve. In the example shown, the recess 218 is arranged directly facing the flange 202. As the recess opens into the expansion reservoir 100, the latter is therefore in communication with the liquid. Such will be the case for all of the angular positions of the plug wherein the recess 218 is directly accessible by the liquid present in a section between the plug 210 and a flange 202, 203. By the intermediary of the expansion channel 213, the expansion reservoir 100 therefore remains in communication with the liquid present in the section connected to this flange 202 as is shown in FIG. 15. This position if the valve 200 will be favoured when the flange 202 is connected to a section forming the inlet of the pump 2 or in the vicinity of the inlet of the pump 2. As such, in the event of a drop in pressure at the inlet of the pump 2, the expansion reservoir 100 allows for an offsetting of the volume and as such prevent a cavitation at the pump inlet. As such, it is preferable to ensure to adapt the angular orientation of the plug 210 according to the direction of circulation of the liquid. Generally, the position of the plug 210 will be controlled in such a way as to place in communication the expansion reservoir 100 with a portion of the circuit 1 that separates the expansion reservoir 100 from the inlet of the pump 2. In addition to allowing for permanent communication between the expansion reservoir 100 and the liquid of the circuit, the invention makes it possible to limit the speed of the liquid reaching the expansion reservoir 100, in particular when the valve is open and the liquid passes through with a high speed. However, due to the speed of displacement of the liquid in the circuit 1, liquid could arrive at a relatively high speed in the expansion reservoir 100 if the communication were direct. The invention as such makes it possible to limit and even prevent the appearance in the expansion reservoir 100 of jets of liquid coming from the liquid in movement in the circuit 1. However, these jets can be a source of mechanical fatigue and control difficulties. Indeed, these projections of liquid induce significant fluctuations at the level of the free surface 105 of the liquid 112 and in the expansion reservoir 100. These jets of liquid can also be the source of the generation of aerosols for which the formation is sought to be avoided as much as possible in order to reinforce the reliability of the mechanism. The limitation of aerosols is very advantageous. Without this, aerosols can be found in the pressurisation gas 103 (sky gas) and come from the reduction gear 120. This reduces the reliability of it. The limitation of the aerosols significantly improves the reliability of the mechanism. Moreover, aerosols can impregnate the thermal protection 124 and therefore significantly increase its thermal conductivity. This would have the consequence of increasing the temperature of all of the mechanical parts that are above the thermal protection 124, of which the reduction gear 120, and would therefore reduce the reliability of it. A second example of the system 10 according to the invention shall now be described in detail in reference to FIGS. 18 to 27. The system according to this second example differs from the system according to the first example described in reference to FIGS. 8 to 17 in that the plug is cylindrical and in that the valve is an elbow. The other characteristics described in terms of the first example all apply to the second example. In this second example, the expansion channel 213 is also configured to limit the appearance in the expansion reservoir 100 of jets of liquid coming from the liquid in movement in the circuit 1. Indeed, the expansion channel 213 of this second embodiment does not offer a straight path for the liquid, generates load losses and reduces the speed of the liquid when it enters the expansion reservoir 100. As in the preceding example, the expansion channel 213 comprises at least: a lower channel 217 opening on the one hand into the internal passage 212 and on the other hand under a lower face 220 of the body 211 of the plug. More precisely, the lower channel 217 opens into a space 221 defined by the lower face 220 of the body 211 of the plug and by the bottom 208 of the body 201 of the valve. As the valve is cylindrical, it is preferable to avoid a seat 209 to receive the plug 210; a recess 218 is made on a lateral face 219 of the body 211 of the plug, with this recess opening on the one hand under the lower face 220 and on the other hand in the expansion reservoir 100. This recess 218 preferably forms a groove. In the case where the plug 210 is cylindrical, and as shown in FIGS. 20 and 21, this groove is preferably linear and extends along a direction parallel to the axis of rotation of the plug 210. The recess 218 made on the lateral face 219 of the body 211 of the plug as such forms an open channel. When this recess 218 is arranged facing the body 201 of the valve, more precisely facing its inner wall 207, it cooperates with the latter in such a way as to form a channel. Preferably, the section of this channel forms a perimeter. The section is taken according to a plane perpendicular to the direction of flow of the liquid in this channel. This channel then has two openings, one opening under the lower face 220 of the body 211 of the plug, the other opening into the expansion reservoir 100. FIG. 19 clearly shows the opening on the expansion reservoir 100 of this closed channel formed by the recess 218 and the inner wall 207 of the body 201 of the valve. The valve 200 is configured so that the liquid present in the internal passage 212 can pass into the lower passage 217 then into the recess 218 in order to reach the expansion reservoir 100. Between the lower channel 217 and the recess 218, the liquid transits by the space 221. In FIG. 22, the expansion channel 213 appears between the bottom of the recess 218 and the inner wall of the body 201 of the valve. The other characteristics of the system are identical to those described in particular in reference to FIG. 10. The operation of the system according to this embodiment shall now be described in detail in reference to FIGS. 23 to 27. FIG. 23 shows the valve 200 in fully open position. In this position, the plug 210 is equivalent to the elbow portion that the valve 200 replaces in circuit 1. The load loss in the valve 200 is very low and even zero. More generally, it is identical to the elbow that this valve replaces. In this position, the circulation of the liquid is possible in both directions. The liquid present in the internal passage 212 communicates with the lower channel 217 in order to reach the space formed between the lower face 208 of the body 211 of the plug and the bottom 220 of the body 201 of the valve. The liquid then reaches the closed channel defined by the cooperation between the recess 218 and the inner wall 207 of the body 201 of the valve. It can as such enter the expansion reservoir 100. The conveying of the liquid in the expansion channel 213, formed by the lower channel 217, the space 221 and the recess 218, makes it possible to limit the speed of the liquid at the inlet of the reservoir 100 and to limit the formation of jets of liquid in the latter. This is all the more so advantageous that in this angular position of the body 211 of the plug, the speed of the liquid passing through the valve 200 is normally substantial. When the valve 200 is closed on the right, as shown in FIGS. 24 and 25, the circulation of the liquid in the circuit 1 is interrupted. On the other hand, the internal passage 212 remains in communication with the section of the circuit connected to the flange 202. By the intermediary of the expansion channel 213, the expansion reservoir 100 therefore remains in communication with the liquid present in the section connected to this flange 202 as is shown in FIG. 25. In the case where the valve 200 is closed and where the recess 218 is not in direct communication with the inlet or the outlet of the valve 200 but cooperates with the inner wall 207 of the body 201 of the valve in order to form a closed channel, the liquid reaches the expansion reservoir 100 by passing through the internal passage 212, the lower channel 217, the space 221 then the recess 218, as is the case when the valve is open (as shown in FIG. 23). In this position of the plug, the risks of jets of liquid appearing in the reservoir are limited and even suppressed. When the valve 200 is closed on the left, as shown in FIGS. 26 and 27, the circulation of the liquid in the circuit 1 is interrupted. On the other hand, the internal passage 212 remains in communication with the section of the circuit connected to the flange 203. By the intermediary of the expansion channel 213, the expansion reservoir 100 therefore remains in communication with the liquid present in the section connected to this flange 203 as is shown in FIG. 27. In the case where the valve 200 is closed and where the recess 218 is in direct communication with the inlet or the outlet of the valve 200 (the outlet in the example of FIGS. 26 and 27) the liquid reaches the expansion reservoir 100 by penetrating from the inlet/the outlet of the valve directly into the recess 218. Of course liquid can penetrate into the internal passage 212 through the recess 218, the space 221 and the lower channel 217, but this liquid remains in the internal passage 212 without being able to pass through the valve 200. This position if the valve 200 will be favoured when the flange 203 is connected to a section forming the inlet of the pump 2 or in the vicinity of the inlet of the pump 2. In this section, the speed of the liquid is generally low and the risks of jets in the expansion reservoir 100 are limited. In each of the embodiments considered in the description hereinabove, the obturator is movable inside the body 201 of the valve 200 which is fixed with respect to the conduits connected to the inlet and to the outlet of the valve 200. The expansion reservoir 100 is fixed with respect to the body 201 of the valve 200. The movable obturator is movable with respect to the expansion reservoir 100. Advantageously, the movable obturator is separated from at least a portion of the expansion reservoir 100. As such, in at least a portion of the expansion reservoir 100, the movable obturator is absent. As such, the expansion reservoir 100 is separate from the movable obturator. This makes it possible in particular to not drive in displacement, typically in rotation, the expansion reservoir 100 during the displacement of the movable obturator, with the expansion reservoir 100 possibly comprising a significant volume of liquid and gas. The system is therefore made more robust, more reliable and less complex. Moreover, the independence between the expansion reservoir 100 and the movable obturator makes it possible to independently size these two elements. In particular, the expansion reservoir 100 can be adapted, in particular in terms of volume, to the characteristics of the circuit (flow, pressure), while still retaining a movable obturator of small size. A movable obturator of small size makes it possible in particular to reduce the encumbrance of the system and to facilitate the carrying out of a movable obturator with dimensions and surface states that are perfectly controlled in such a way as to guarantee a good seal of the valve in closed position. In light of the preceding description, it clearly results that the invention offers an effective system for improving the reliability and the simplicity of reversible circuits, particularly those in which circulate a liquid at high temperature and/or chemically reactive. The invention as such offers a particularly advantageous solution for test circuits for electromagnetic pumps for liquid metals such as those used in the sodium circuits of certain nuclear reactors. Moreover, the invention is advantageous, regardless of the liquid, in the circuits where it is necessary to proceed with an inversion in the direction of circulation, for example to clean in-line filters. The invention is not limited to the embodiments described hereinabove and extends to all the embodiments covered by the claims. In particular, the invention covers the systems wherein the motor is arranged outside of the enclosure formed by the valve body and by the cover. In this case, a coupling device passes through the enclosure. 1. Circuit 2. Pump 3. Section 4. Section 5. Section 6. Exchanger 7. Expansion reservoir 71. Liquid 72. Pressurisation gas 73. Free level 74. Isolation valve 7′. Expansion reservoir 74′. Isolation valve 8. Protection device 81. Outlet 9. Throttle valve 91. Second throttle valve 10. System 100. Expansion reservoir 101. Valve cover 102. Sealed enclosure 103. Pressurisation gas 104. Orifice for pressurisation gas 105. Free surface of the liquid 106. Level sensor 107. Overflow 108. Bearing 109. Roller 110. Bearing passage 111. Aerator device 112. Liquid 120. Reduction gear 121. Motor support 122. Power supply/control lines 123. Cooling circuit 124. Thermal protection device 125. Coupling device 200. Valve 201. Valve body 202. Inlet flange 203. Outlet flange 204. Cover flange 205. Edge 206. Emptying hole 207. Inner wall 208. Bottom of the valve body 209. Seat 210. Plug 211. Plug body 212. Internal passage 213. Expansion channel 214. Upper face 215. Upper hole 216. Axis 217. Lower orifice 218. Recess 219. Lateral face 220. Lower face 221. Space |
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claims | 1. A method of intervention by at least one operator in a radioactive zone, the method comprising the following steps:obtaining a digital model representing the three-dimensional topography of the radioactive zone;intervention of at least one operator in the radioactive zone, the intervention step comprising at least the following sub-steps:repeatedly, measuring an intensity of the radioactive radiation by a portable detector carried by the at least one operator, and determining the spatial coordinates of the portable detector at the time of measurement;recording in the digital model of a plurality of said measurements and the corresponding spatial coordinates;materialisation of the recorded measurements in an augmented reality device carried by the at least one operator, by a plurality of discrete holographic symbols, using the digital model, each holographic symbol indicating the intensity of the radioactive radiation of one of the recorded measurements, said symbol being materialized so as to appear to the at least one operator standing at a current position at the corresponding spatial coordinates where the at least one operator was standing when measuring the intensity of said recorded measurement at the sub-step of measuring the intensity of the radioactive radiation. 2. The method according to claim 1, wherein the augmented reality device comprises at least one helmet worn by the at least one operator, with a translucent display surface placed in front of the eyes of the at least one operator, wherein the holographic symbols are displayed on the display surface in such a way that the holographic symbols appear visible to the at least one operator at the corresponding determined spatial coordinates. 3. The method according to claim 1, wherein the obtaining step comprises a sub-step of recording images of the radioactive zone with at least one camera, and a sub-step of determining the digital model using the recorded images. 4. The method according to claim 3, wherein the obtaining step is carried out simultaneously with the intervention step, the digital model being progressively determined or enriched with the images recorded during the intervention step. 5. The method according to claim 1, wherein the recording of one of the measurements and the materialisation of said recorded measurement are triggered by the at least one operator, the said discrete holographic symbol materialising the intensity of the radioactive radiation measured by the portable detector at the moment of triggering. 6. The method according to claim 1, wherein the addition of a discrete holographic symbol to the augmented reality device is triggered when the intensity of the radioactive radiation measured by the portable detector is greater than a predetermined value. 7. The method according to claim 1, further comprising a step of recording in the digital model at least one of the elements associated with corresponding spatial coordinates selected from the group consisting of ALARA fallback zone and conventional non-nuclear risk;the intervention step comprising a sub-step of materialisation of the at least one element in the augmented reality device by a specific holographic symbol appearing visibly to the operator at the corresponding spatial coordinates. 8. The method according to claim 1, wherein the digital model is shared by several operators, each operator being equipped with an augmented reality device materialising the recorded measurements by a plurality of discrete holographic symbols using the digital model, each holographic symbol indicating the intensity of the radioactive radiation of one of the recorded measurements and being placed so as to appear visible to said operator at the corresponding spatial coordinates. 9. The method according to claim 8, wherein the operators all intervene in the radioactive zone during the intervention step, the intervention step comprising at least the following sub-steps:repeatedly, measuring an intensity of the radioactive radiation by the portable detector carried by each operator, and determining the spatial coordinates of the portable detector at the time of the measurement; andrecording in the shared digital model of a plurality of said measurements and the corresponding spatial coordinates. 10. The method according to claim 1, wherein at the sub-step of recording images of the radioactive area, the at least one camera is carried by the at least one operator. 11. A method of intervention by at least one operator in a radioactive zone, the method comprising the following steps:obtaining a digital model representing the three-dimensional topography of the radioactive zone;intervention of at least one operator in the radioactive zone, the intervention step comprising at least the following sub-steps:repeatedly, measuring an intensity of the radioactive radiation by a portable detector, and determining the spatial coordinates of the portable detector at the time of measurement;recording in the digital model of a plurality of said measurements and the corresponding spatial coordinates;materialisation of the recorded measurements in an augmented reality device carried by the at least one operator, by a plurality of discrete holographic symbols, using the digital model, each holographic symbol indicating the intensity of the radioactive radiation of one of the recorded measurements and being placed so as to appear visible to the at least one operator at the corresponding spatial coordinates; andrecording in the digital model at least one of the elements associated with corresponding spatial coordinates selected from the group consisting of ALARA fallback zone and conventional non-nuclear risk;the intervention step comprising a sub-step of materialisation of the at least one element in the augmented reality device by a specific holographic symbol appearing visibly to the operator at the corresponding spatial coordinates. |
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description | This application is a divisional application of U.S. application Ser. No. 11/564,046 filed on Nov. 28, 2006, the entire contents of which are incorporated herein by reference. 1. Field of the Invention The present invention relates to an accumulator incorporating a flow damper which is capable of statically switching flow rates from large to small. The present invention is useful when applied to an accumulator of an emergency injection system for a reactor in a pressurized water reactor (PWR) power plant, for example. 2. Description of the Related Art An emergency core cooling system is installed in the PWR power plant. The emergency core cooling system includes an accumulator and so forth on the assumption that the PWR might cause a loss of primary coolant accident. Water (coolant) is stored in the accumulator, and the water stored therein is pressurized by a pressurizing gas (nitrogen gas) which is filled in an upper part in the accumulator. Moreover, a flow damper is provided in the accumulator. The flow damper can switch a water injection flow rate in a reactor from a large flow to a small flow statically (without moving any part thereof). The flow damper includes a vortex chamber, a large flow pipe, a small flow pipe, an outlet pipe and the like, and is disposed at the bottom in the accumulator (see FIG. 1). A tip end of the outlet pipe is connected to a low temperature pipeline of a reactor primary coolant loop with a check valve interposed in between. The check valve is used for avoiding a back flow from a rector primary cooling system to the accumulator. If the pipeline or the like in the reactor primary cooling system of the PWR power plant is broken and the coolant flows out of a crack to the outside (i.e. upon occurrence of a loss of primary coolant accident), the amount of the coolant in a reactor vessel may be reduced, and thereby a reactor core may become exposed. In this situation, however, if a pressure of the primary cooling system drops below a pressure in the accumulator, the water stored in the accumulator is injected from the primary cooling system pipeline into the reactor vessel through the check valve, and thereby refloods the reactor core. In this case, the reactor vessel is refilled quickly by injecting water at a large flow rate at an initial stage thereof. Then, it is necessary to switch the water injection flow rate from the large flow to a small flow at a later stage when the reactor core is reflooded, because excessively injected water may spill out of the crack. In order to ensure this water injection flow rate switching operation, a reliable flow damper without a moving part is used for the accumulator. The principles of the water injection flow rate switching by use of such a flow damper will be explained on the basis of FIGS. 10A and 10B (horizontal sectional views). As shown in FIGS. 10A and 10B, a flow damper 10 has a structure in which a large flow pipe 2 and a small flow pipe 3 are connected to a peripheral portion (a circumferential portion) of a cylindrical vortex chamber 1, while an outlet 4 is formed in the center of the vortex chamber 1. The large flow pipe 2 and the small flow pipe 3 extend in mutually different directions from the outlet 4. Specifically, the small flow pipe 3 extends in the left direction along a tangential direction to the peripheral portion (the circumferential portion) of the vortex chamber 1. Meanwhile, the large flow pipe 2 extends in the right direction while forming a predetermined angle θ with the small flow pipe 3. Moreover, although illustration is omitted, an inlet of the small flow pipe 3 is located at the same level as the vortex chamber 1. Meanwhile, the large flow pipe 2 is connected to a standpipe which extends upward. An inlet of this standpipe is located higher than the vortex chamber 1 and the inlet of the small flow pipe 3. Furthermore, an outlet pipe is connected to the outlet 4 of the vortex chamber 1. Moreover, since the water level in the accumulator is higher than the inlet of the large flow pipe 2 at the initial stage of water injection, the water in the accumulator flows into the vortex chamber 1 from both of the large flow pipe 2 and the small flow pipe 3 as indicated with arrows A and B in FIG. 10A. As a result, the injected water (a jet) from the large flow pipe 2 collides with the injected water (a jet) from the small flow pipe 3, and angular momenta of the jets are offset. In this way, the water flows directly toward the outlet 4 as indicated with an arrow C in FIG. 10A. Specifically, no vortex is formed in the vortex chamber at this time. Accordingly, a flow resistance is reduced at this time, and thus a large amount of water flows out of the outlet 4 and is injected into the reactor vessel. By contrast, at the later stage of water injection, the water level in the accumulator drops below the inlet of the standpipe connected to the large flow pipe 2. Accordingly, there is no water flow from the large flow pipe 2 into the vortex chamber 1, and the water flows into the vortex chamber 1 only through the small flow pipe 3 as indicated with an arrow B in FIG. 10B. As a result, the injected water from this small flow pipe 3 proceeds to the outlet 4 while forming a vortex (a swirling flow) as indicated with an arrow D in FIG. 10B. Accordingly, the flow resistance is increased by the centrifugal force at this time, and an outflow (the water injected to the reactor vessel) from the outlet 4 becomes a small flow. This device is called a flow damper because it has the function to damp the flow rate as described above. As described above, the accumulator currently in development is the advanced accumulator which is capable of switching from a large flow to a small flow statically and securely by including the flow damper 10. Moreover, the flow damper 10 of this advanced accumulator is required to define a proportion between the large flow and the small flow as high as possible in order to achieve a reasonable tank volume. For this reason, it is essential not to form a vortex in the vortex chamber by surely offsetting the angular momenta between the jet from the large flow pipe 2 and the jet from the small flow pipe 3 at the time of the large flow injection. In addition, it is necessary to generate a high flow resistance by forming a strong vortex in the vortex chamber 1 when switching from the large flow to the small flow. For this reason, in the case of a large flow, it is necessary to control an angle θ defined between the large flow pipe 2 and the small flow pipe 3 (a collision angle of the two jets) and the flows (the flow rates) of the large flow pipe 2 and the small flow pipe 3 so that the jet from the large flow pipe 2 and the jet from the small flow pipe 3 mutually offset the angular momenta. Moreover, in the case of a small flow, a strong vortex is formed in the vortex chamber 1 by connecting the small flow pipe 3 to the peripheral portion (the circumferential portion) of the vortex chamber 1 along the tangential direction. However, in an attempt not to form a vortex in the vortex chamber at the time of the large flow injection by fine-tuning the values of the angle θ between the large flow pipe 2 and the small flow pipe 3 and the flows (the flow rates) of the large flow pipe 2 and the small flow pipe 3, it is necessary to rebuild the entire flow damper many times in order to adjust these values. Such an attempt may bring about numerous prototype flow dampers that would involve huge labors and fabrication costs. In view of the aforementioned circumstances, it is an object of the present invention to provide an accumulator including a flow damper which is capable of suppressing formation of a vortex in a vortex chamber at the time of a large flow injection without requiring huge labors and fabrication costs. To attain the object, an accumulator according to a first aspect of the present invention is an accumulator provided with a flow damper inside, the flow damper including a cylindrical vortex chamber, a small flow pipe connected to a peripheral portion of the vortex chamber along a tangential direction thereto, a large flow pipe connected to the peripheral portion while forming a predetermined angle with the small flow pipe, and an outlet pipe connected to an outlet formed at a central part of the vortex chamber. Here, the accumulator is characterized in that the flow damper includes a colliding jet controller for controlling a colliding jet composed of a jet from the large flow pipe and a jet from the small flow pipe flowing into the vortex chamber at the time of a large flow injection so that the colliding jet may proceed directly to the outlet without forming a vortex in the vortex chamber, the colliding jet controller being provided at a junction of the small flow pipe and the vortex chamber. Moreover, an accumulator according to a second aspect of the present invention, in the case of the accumulator of the first aspect, is characterized in that the colliding jet controller is a bevel formed at the junction of the small flow pipe and the vortex chamber. Furthermore, an accumulator according to a third aspect of the present invention, in the case of the accumulator of the first aspect, is characterized in that the colliding jet controller is a projection formed at the junction of the small flow pipe and the vortex chamber. The accumulator of the first aspect of the present invention is characterized in that the flow damper includes a colliding jet controller for controlling a colliding jet composed of a jet from the large flow pipe and a jet from the small flow pipe flowing into the vortex chamber at the time of a large flow injection so that the colliding jet may proceed directly to the outlet without forming a vortex in the vortex chamber, the colliding jet controller being provided at a junction of the small flow pipe and the vortex chamber. Accordingly, it is possible to cause the jet from the large flow pipe and the jet from the small flow pipe to offset the mutual angular momenta easily and securely so as not to generate a vortex in the vortex chamber at the rime of a large flow only by adjusting a control amount of the colliding jet by use of the colliding jet controller (i.e. only by rebuilding the colliding jet controller) instead of rebuilding the entire flow damper. Hence is it possible to drastically reduce labors and fabrication costs for adjusting the colliding jet. In particular, according to the accumulator of the second or the third aspect of the present invention, either the bevel or the projection is formed as the colliding jet controller, and the colliding jet is controlled by use of the bevel or the projection. Hence, it is possible to obtain a significant effect as similar to the first aspect merely by an extremely simple adjustment work for adjusting either the size of the bevel or a projecting amount of the projection. Hereinafter, a preferred embodiment of the present invention will be described below in detail with reference to the accompanying drawings. (Configuration) An accumulator 21 shown in FIG. 1 is an apparatus constituting part of an emergency core cooling system, which is installed in a pressurized water reactor (PWR) power plant on the assumption that a loss of primary coolant accident might occur in the PWR power plant. As shown in FIG. 1, water (a coolant) 22 is stored in the accumulator 21, and the water 22 stored therein is pressurized by a pressurizing gas (nitrogen gas) 23 which is filled in an upper part in the accumulator 21. Moreover, a flow damper 24, which can switch a water injection flow rate in a reactor from a large flow to a small flow statically, is provided in the accumulator 21. The flow damper 24 includes a vortex chamber 25, a large flow pipe 26, a small flow pipe 27, an outlet pipe 28 and the like, and is disposed at the bottom in the accumulator 21. Although illustration is omitted, a tip end of the outlet pipe 28 is connected to a low temperature pipeline of a reactor primary coolant loop with a check valve interposed in between. The check valve is used for avoiding a back flow from a rector primary cooling system to the accumulator 21. As shown in FIG. 1 to FIG. 5B, the flow damper 24 has a structure in which the large flow pipe 26 and the small flow pipe 27 are connected to a peripheral portion (a circumferential portion) of the cylindrical vortex chamber 25, while an outlet 29 is formed in the center of an upper surface 25b of the vortex chamber 25. Alternatively, the outlet 29 may be provided in the center of a lower surface 25c of the vortex chamber 25. In view of horizontal surfaces as illustrated in FIG. 3 and FIG. 4, the large flow pipe 26 and the small flow pipe 27 extend in mutually different directions from the outlet 29. Specifically, the small flow pipe 27 extends in a direction (which is the left direction in the drawings) along a tangential direction to the peripheral portion (the circumferential portion) of the vortex chamber 25. Meanwhile, the large flow pipe 26 extends in another direction (which is the right direction in the drawings) while forming a predetermined angle θ (in a range from 90°<θ<180°; such as 95°, 100° or 110°) with the small flow pipe 27. Cross sections of flow passages of the large flow pipe 26 and the small flow pipe 27 are formed into rectangular shapes. Specifically, as shown in FIGS. 5A and 5b, for example, the large flow pipe 26 (a horizontal portion 26a) has a parallel pair of inner surfaces (vertical surfaces) 26d and 26e which face each other in the horizontal direction, and a parallel pair of inner surfaces (horizontal surfaces) 26f and 26g which face each other in the vertical direction. Meanwhile, the small flow pipe 27 has a parallel pair of inner surfaces (vertical surfaces) 27b and 27e which face each other in the horizontal direction, and a parallel pair of inner surfaces (horizontal surfaces) 27d and 27e which face each other in the vertical direction. The heights of the flow-passage cross sections of the large flow pipe 26 and the small flow pipe 27 (the heights of the inner surfaces 26d and 26e and of the inner surfaces 27b and 27c) are the same as the height of an inner peripheral surface 25a of the vortex chamber 25. On the other hand, the widths of the flow-passage cross sections of the large flow pipe 26 (the widths of the inner surfaces 26f and 26g) are greater than the widths of the flow-passage cross sections of the small flow pipe 27 (the widths of the inner surfaces 27d and 27e). Moreover, an inlet 27a of the small flow pipe 27 is located at the same height as that of the inner peripheral surface 25a of the vortex chamber 25. On the other hand, the large flow pipe 26 includes a standpipe 26b connected to the horizontal portion 26a, and an inlet 26c thereof is located higher than the vortex chamber 25 and the inlet 27a of the small flow pipe 27. It is to be noted, however, that a water level 22a of the stored water 22 is usually located higher than this inlet 26c of the large flow pipe 26. The outlet pipe 28 is connected to the outlet 29 of the vortex chamber 25. Anti-vortex plates 30 and 31 are respectively provided to the inlets 26c and 27a of the large flow pipe 26 and the small flow pipe 27. As shown in FIG. 4 and FIG. 6, the inner surface 27b, at the side of the large flow pipe 26, of the small flow pipe 27 is connected to the inner surface 26e, at the side of the small flow pipe 27, of the large flow pipe 26. Moreover, in consideration of a spread of a jet from the small flow pipe 27 (a free-jet-spread proportion), a junction 32 of the inner surface 26d, at the opposite side of the small flow pipe 27, of the large flow pipe 26 and an extended surface portion (a flat surface portion) 25a-1 of the inner peripheral surface 25a of the vortex chamber 25 is located outside an extension line of the inner surface 27b, at the side of the large flow pipe 26, of the small flow pipe 27 (the line extending from the junction 33 in the tangential direction). It is to be noted, however, that the present invention is not limited to the foregoing configuration. It is also serves the purpose to adopt a structure in which the junction of the inner surface 26d and the inner peripheral surface 25a does not include the extended surface portion (the flat surface portion) 25a-1 as indicated with a dashed line K in the drawing. Moreover, the inner surface 27c, at the opposite side of the large flow pipe 26, of the small flow pipe 27 is connected to the inner peripheral surface 25a of the vortex chamber 25 at a junction 34. This junction 34 is located upstream of the junction 33 in terms of the direction of the flow (the direction of the jet: see an arrow B) from the small flow pipe 27. Moreover, in this embodiment, as shown in FIG. 4 and FIG. 6, the flow damper 24 includes a bevel 41 functioning as a colliding jet controller which is provided at the junction 34 of the small flow pipe 27 (the inner surface 27c) and the vortex chamber 25 (the inner peripheral surface 25a). Specifically, by forming the bevel 41 in an appropriate size at the junction 34, it is possible to control a colliding jet composed of a jet from the large flow pipe 26 and a jet from the small flow pipe 27 flowing into the vortex chamber 25 at the time of a large flow injection so that the colliding jet may proceed directly to the outlet 29 securely without forming a vortex in the vortex chamber 25. For example, a decrease in the size of the bevel 41 as indicated with a dashed line L in FIG. 6 causes an increase in the amount of the jet from the large flow pipe 26, which flows along the direction of the jet from the small flow pipe 27 while bypassing the bevel 41 as indicated with an arrow N. As a result, the colliding jet composed of the jet from the large flow pipe 26 and the jet from the small flow pipe 27 tends to form a clockwise vortex as indicated with an arrow P. On the other hand, an increase in the size of the bevel 41 as indicated with a dashed line M in FIG. 6 causes a decrease in the amount of the jet from the large flow pipe 26, which flows along the direction of the jet from the small flow pipe 27 while bypassing the bevel 41. As a result, the colliding jet composed of the jet from the large flow pipe 26 and the jet from the small flow pipe 27 tends to form a counterclockwise vortex as indicated with an arrow O. In other words, it is possible to control the colliding jet by the size of the bevel 41. Accordingly, it is possible to cause the colliding jet to proceed directly toward the outlet 29 as indicated with an arrow C by adjusting the bevel 41 into an appropriate size. Incidentally, the bevel formed at the junction 34 is not limited to the bevel 41 which is cut away in an orthogonal direction to the direction of the jet from the small flow pipe 27 (the tangential direction). For example, the bevel may be formed in an oblique direction relative to the direction of the jet from the small flow pipe 27. Moreover, the bevel may be a bent bevel or a curved bevel. Furthermore, the flow damper 24 shown in FIG. 7 and FIG. 8 includes a projection 51 functioning as the colliding jet controller which is provided at the junction 34 of the small flow pipe 27 (the inner surface 27c) and the vortex chamber 25 (the inner peripheral surface 25a). The projection 51 in the illustrated example has a plate shape. By forming the projection 51 in an appropriate projecting amount at the junction 34, it is possible to control the colliding jet composed of the jet from the large flow pipe 26 and the jet from the small flow pipe 27 flowing into the vortex chamber 25 at the time of a large flow injection so that the colliding jet may proceed directly to the outlet 29 securely without forming a vortex in the vortex chamber 25. For example, an increase in the projecting amount of the projection 51 causes an increase in the amount of the jet from the large flow pipe 26, which flows along the direction of the jet from the small flow pipe 27 while bypassing the projection 51 as indicated with an arrow Q. As a result, the colliding jet composed of the jet from the large flow pipe 26 and the jet from the small flow pipe 27 tends to form a clockwise vortex as indicated with the arrow P. On the other hand, a decrease in the projecting amount of the projection 51 causes a decrease in the amount of the jet from the large flow pipe 26, which flows along the direction of the jet from the small flow pipe 27 while bypassing the projection 51. As a result, the colliding jet composed of the jet from the large flow pipe 26 and the jet from the small flow pipe 27 tends to form a counterclockwise vortex as indicated with the arrow O. In other words, it is possible to control the colliding jet by the projecting amount of the projection 51. Accordingly, it is possible to cause the colliding jet to proceed directly toward the outlet 29 as indicated with the arrow C by adjusting the projecting amount of the projection 51 into an appropriate size. Incidentally, the projection formed at the junction 34 is not limited to the projection 51 which is projected straight in the direction of the jet from the small flow pipe 27 (the tangential direction). For example, the projection may be formed into a plate in an oblique direction relative to the direction of the jet. Moreover, the projection may be a bent projection or a curved projection. Furthermore, the projection may be formed into a shape other than the plate shape (one having a triangular horizontal cross section is also applicable, for example). (Operation and Effects) The accumulator 21 having the above-described configuration exerts the following operation and effects. If a pipeline or the like in a reactor primary cooling system of a PWR power plant is broken, and the coolant flows out of a crack to the outside (i.e. upon occurrence of a loss of primary coolant accident), thereby reducing a pressure of the primary cooling system below a pressure in the accumulator 21, the stored water 22 in the accumulator 21 is injected from the primary cooling system pipeline into a reactor vessel through a check valve, and thereby refloods a reactor core. At this time, the water injection flow rate to the reactor vessel is switched from a large flow to a small flow statically by way of the flow damper 24. Specifically, since the water level in the accumulator 21 is higher than the inlet 26c of the large flow pipe 26 at an initial stage of water injection, the water 22 in the accumulator 21 flows into the vortex chamber 25 from both of the large flow pipe 26 and the small flow pipe 27 as indicated with arrows A and B in FIG. 9A. As a result, the injected water (a jet) from the large flow pipe 26 collides with the injected water (a jet) from the small flow pipe 27, and angular momenta of the jets are offset. In this way, the water 22 flows directly toward the outlet 29 as indicated with an arrow C in FIG. 9A. Specifically, no vortex is formed in the vortex chamber 25 at this time. Accordingly, a flow resistance is reduced at this time, and a large amount of water flows out of the outlet 29 and is injected into the reactor vessel. By contrast, at a later stage of water injection, the water level in the accumulator 21 drops below the inlet 26c of the standpipe connected to the large flow pipe 26. Accordingly, there is no water 22 flowing from the large flow pipe 26 into the vortex chamber 25, and the water 22 flows into the vortex chamber 25 only through the small flow pipe 27 as indicated with an arrow B in FIG. 9B. As a result, the injected water from this small flow pipe 27 proceeds to the outlet 29 while forming a vortex (a swirling flow) as indicated with an arrow D in FIG. 7B. Accordingly, the flow resistance is increased by the centrifugal force at this time, and an outflow (the water injected to the reactor vessel) from the outlet 29 becomes a small flow. Although FIG. 9 illustrates the example of providing the bevel 41, similar water injection flow rate switching is achieved in the case of providing the projection 51 as well. Moreover, according to the accumulator 21 of this embodiment, the flow damper 24 includes the colliding jet controller (the bevel 41 or the projection 51), which is configured to control the colliding jet composed of the jet from the large flow pipe 26 and the jet from the small flow pipe 27 flowing into the vortex chamber 25 at the time of a large flow injection so that the colliding jet may proceed directly to the outlet 29 without forming a vortex in the vortex chamber 25, the colliding jet controller being provided at the junction 34 of the small flow pipe 27 and the vortex chamber 25. Accordingly, it is possible to cause the jet from the large flow pipe 26 and the jet from the small flow pipe 27 to offset the mutual angular momenta easily and securely so as not to generate a vortex in the vortex chamber 25 at the rime of a large flow, only by adjusting a control amount of the colliding jet by use of the colliding jet controller (i.e., only by rebuilding the colliding jet controller in the vortex chamber 25) instead of rebuilding the entire flow damper 24. Hence is it possible to drastically reduce labors and fabrication costs for adjusting the colliding jet. In particular, according to the flow damper 24 of this accumulator 21, either the bevel 41 or the projection 51 is formed as the colliding jet controller, and the colliding jet is controlled by use of the bevel 41 or the projection 51. Hence, it is possible to obtain a significant effect as described above merely by an extremely simple adjustment work for adjusting either the size of the bevel 41 or the projecting amount of the projection 51. Incidentally, application of the bevel or the projection for controlling the colliding jet may be selected as appropriate depending on the angle θ between the large flow pipe 26 and the small flow pipe 27 or on the proportion of the flows (the flow rates) between the large flow pipe 26 and the small flow pipe 27 (i.e. a balance in the angular momenta between the jet from the large flow pipe 26 and the jet from the small flow pipe 27), for example. The invention thus described, it will be obvious that the same way may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended to be included within the scope of the following claims. |
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claims | 1. A method of retrofitting a nuclear reactor comprising the steps of:providing a nuclear reactor including radioactive fuel installed in a reactor core, said reactor designed to generate heat by controlling a neutron fission process;subsequent to operating the neutron fission process in said nuclear reactor, installing a plurality of emitter devices each configured to generate an energy beam impinging on the reactor core to induce a photo-fission reaction in the fuel. 2. The method of claim 1, further comprising the step of installing additional shielding in said nuclear reactor to absorb portions of the energy beam not absorbed by the reactor core or the fuel. 3. The method of claim 1, further comprising the step of extracting heat from said nuclear reactor during said photo-fission process to perform useful work. 4. The method of claim 1, further comprising the step of, after at least partially depleting said fuel using neutron fission, at least partially decontaminating said fuel using the photo-fission process over a period of time. 5. The method of claim 1, wherein said emitter device comprises:a source of charged particles;a conduit;a plurality of capacitor elements stacked to form a capacitor array configured to accelerate the charged particles through the conduit which is formed through the capacitor array, each one of said capacitor elements utilizing a pair of electrodes having a layer including diamond or diamond-like carbon, and a plurality of photo switches each including a diamond crystal and being uniformly arranged around the capacitor element for activation during a discharge of the capacitor element; anda cooling system for circulating a coolant in the device for cooling the device, whereinsaid device is adapted to emit an energy beam including gamma rays as a result of accelerating the charged particles. 6. The method of claim 5, wherein each emitter device comprises a plurality of capacitor elements each including a pair of electrodes having a layer including diamond or diamond-like carbon. 7. The method of claim 6, wherein each emitter device comprises a plurality of photo switches each including a diamond crystal and being uniformly arranged around the capacitor element for activation during a discharge of the capacitor element. 8. The method of claim 5, further comprising the step of installing additional shielding in said nuclear reactor to absorb portions of the energy beam not absorbed by the reactor core or the fuel. 9. The method of claim 5, further comprising the step of, after at least partially depleting said fuel using neutron fission, at least partially decontaminating said fuel using the photo-fission process over a period of time. 10. A method of retrofitting a nuclear reactor comprising the steps of:providing a nuclear reactor including radioactive fuel installed in a reactor core, said reactor designed to generate heat by controlling a neutron fission process;subsequent to operating the neutron fission process in said nuclear reactor, installing a plurality of emitter devices each arranged to focus an energy beam to impinge on the reactor core to induce a photo-fission reaction in the fuel, said emitter device comprising:a conduit, anda plurality of capacitor elements stacked to form a capacitor array configured to accelerate the charged particles through the conduit which is formed through the capacitor array, whereinsaid emitter device is adapted to emit the energy beam including gamma rays as a result of accelerating the charged particles. 11. The method of claim 10, wherein each one of said capacitor elements utilizes a pair of electrodes having a layer including diamond or diamond-like carbon. 12. The method of claim 10, wherein each emitter device comprises a plurality of photo switches each including a diamond crystal. 13. The method of claim 12, wherein said photo switches are uniformly arranged around the capacitor elements for activation during a discharge of the capacitor elements. 14. The method of claim 10, further comprising the step of installing additional shielding in said nuclear reactor to absorb portions of the energy beam not absorbed by the reactor core or the fuel. 15. The method of claim 10, further comprising the step of, after at least partially depleting said fuel using neutron fission, at least partially decontaminating said fuel using the photo-fission process over a period of time. 16. A method of retrofitting a nuclear reactor comprising the steps of:providing a nuclear reactor including radioactive fuel installed in a reactor core, said reactor designed to generate heat by controlling a neutron fission process;subsequent to operating the neutron fission process in said nuclear reactor, performing the steps of:installing a plurality of emitter devices each configured to generate an energy beam impinging on the reactor core to induce a photo-fission reaction in the fuel,installing additional shielding in said nuclear reactor to absorb portions of the energy beam not absorbed by the reactor core or the fuel, andafter at least partially depleting said fuel using neutron fission, at least partially decontaminating said fuel using the photo-fission process over a period of time;wherein said emitter device comprises:a conduit;a plurality of capacitor elements stacked to form a capacitor array configured to accelerate charged particles through the conduit which is formed through the capacitor array, each one of said capacitor elements utilizing a pair of electrodes having a layer including diamond or diamond-like carbon, and a plurality of photo switches each including a diamond crystal and being uniformly arranged around the capacitor element for activation during a discharge of the capacitor element; anda cooling system for circulating a coolant in the device for cooling the device, whereinsaid emitter device is adapted to emit the energy beam including gamma rays as a result of accelerating the charged particles. |
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063209365 | summary | FIELD OF THE INVENTION The present invention relates to x-ray tube assemblies, and more particularly, to x-ray tube assemblies including beam limiting devices for reducing off-focus radiation and for collimating or pre-collimating x-ray beams, and further relates to x-ray tube housings formed of moldable, radiation absorbing materials, such as filled epoxy resins, and other thermoset and thermoplastic polymers. BACKGROUND OF THE INVENTION A typical x-ray tube comprises an evacuated glass tube with an anode and cathode spaced relative to each other within the tube. The anode and cathode are maintained at a high differential voltage relative to each other, typically on the order of about 150 kV or less for medical applications. The anode may be maintained at ground, and the cathode may be maintained at a relatively high negative potential, e.g., -150 kV. Alternatively, the anode may be maintained at a positive potential, e.g., +75 kV, and the cathode may be maintained at a negative potential, e.g., -75 kV. The cathode thermionically emits electrons which are electrostatically directed onto a target surface of the anode with sufficient energy to generate x-rays which emerge from the target in a diffuse pattern. A considerable amount of heat is generated at the anode during operation of an x-ray tube. Thus, in x-ray tubes having stationary anodes, a cooling fluid, such as oil, typically flows through a base portion of the anode to cool the anode to permit a higher x-ray output and prevent overheating and deformation of the target surface. In rotating anode x-ray tubes, on the other hand, the target surface is typically defined by a rotating disc so that the region of electron incidence is distributed over an annular target surface area. Thus, in rotating anode x-ray tubes, the energy of the incident electrons is typically distributed over a larger surface area than in stationary anode tubes, thereby allowing for higher peak energies operating for short times. The cathode comprises one or more filaments for generating the electron beam, and the filaments project a focal spot area onto the target surface of the anode. Typically, the focal spot area is rectangular; however, the cathode filaments may take any of various different shapes, and thus the focal spots likewise may correspondingly vary in shape. The x-ray tube is mounted within a hermetically-sealed housing, and the housing defines an x-ray port radially aligned with the focal spot on the target surface. The housing is filled with oil to electrically insulate the tube, and frequently, a heat exchanger is either mounted to the housing, or remotely connected to the housing to cool the oil and thereby cool the x-ray tube. The housing is typically formed of aluminum, and the interior surfaces of the housing are lined with a radiation absorbing material, typically lead. An x-ray window made of an x-ray transmissive material is mounted over the x-ray port to allow the diffuse radiation beam to pass out of the housing through the x-ray window only. Frequently, the transmissive window is made of a transparent, polymeric material, such as polycarbonate, and defines a frusto-conical or cup-like shape. The cup-like window projects into the housing, such that the base of the window is spaced closely adjacent to the exterior surface of the glass x-ray tube. Alternatively, the x-ray windows have been made of non-transparent, metallic materials, such as aluminum and beryllium, which are also radiation transmissive. However, the polymeric windows may be made transparent, and thereby allow an operator to view the interior of the housing. In addition, the polymeric windows are non-conductive, and therefore may be mounted in close proximity to the glass x-ray tube. The metallic windows, on the other hand, must be spaced a sufficient distance from the glass x-ray tube to avoid high voltage arcing between the metallic window and tube. The oil within the housing may include gas bubbles, particulate matter, or other non-homogeneous materials, and if any such bubbles or particulates pass between the tube and x-ray window during operation, they may show up as artifacts on the x-ray image. Accordingly, one advantage of the polymeric x-ray windows is that they may be mounted in close proximity to the tube in order reduce the thickness of oil between the tube and window and thereby minimize the possibility of any gas bubbles negatively effecting the x-ray images. One of the drawbacks of the polymeric windows, however, is that the high energy x-rays tend to destroy the molecular bonds of the polymeric material, and if such windows are not replaced, they can eventually craze and/or crack. This condition not only may negatively affect the x-ray images, but may destroy the hermetic seal of the housing and, in some cases, allow oil to leak from the housing. It is well understood in the prior art, and particularly in connection with computerized tomography ("CT"), that the x-rays emanating from the focal spot should be precisely collimated into a fan or other preselected shaped beam, in order to cover the image detector surface. One phenomena that can have a significantly negative effect on the image quality of x-ray images is "off-focus" radiation (also referred to as "off-focal" radiation). Off-focus radiation is primarily produced by energetic back-scattered electrons that produce x-radiation outside of the focal spot. These secondary electrons tend to cause x-rays to be generated from broad areas of the anode and possibly surrounding material that may be at a positive potential relative to the cathode. In addition, high field emission electrons from portions of the cathode other than the filament may impinge on the target and possibly other surrounding material outside of the focal spot and, in turn, create additional off-focus radiation. Both standard radiographic and CT apparatus typically require a well-defined x-ray source. Accordingly, off-focus radiation reduces the image resolution of both conventional x-ray and CT imaging apparatus, and increases the radiation exposure level to patients and technicians. In order to reduce off-focus radiation, and control the size and shape of the x-ray beam, conventional x-ray tube assemblies have incorporated a beam limiting device in the form of a lead plate mounted on the outer side of the x-ray window. The lead plate has formed therein a beam-defining aperture corresponding in size and shape to the desired beam. Thus, the lead plate operates as a first stage of control to define the size and shape of the beam and block any off-focus radiation outside the periphery of the aperture. One drawback associated with these types of prior art beam limiting devices, is that the lead is conductive, and therefore the beam limiting device cannot be located in close proximity to the high voltage x-ray tube. As a result, substantial off-focus radiation may be allowed to pass through the aperture and, in turn, degrade the resolution of the x-ray image. Other prior art x-ray tube assemblies have included beam limiting devices mounted directly onto the glass x-ray tubes. For example, one such prior art beam limiting device is an elongated, arcuate-shaped device having a rectangular beam slot formed therethrough. The device is made of a radiation absorbing, non-conductive, thermoset material sold under the trademark LITHARGE.TM.. This beam limiting device is mounted directly onto the glass x-ray tube between the focal spot and the x-ray window, and is attached to the tube with a silicone ("RTV") adhesive. Thus, the rectangular slot is designed to control the size and shape of the x-ray beam, and the surrounding LITHARGE.TM. material is designed to filter out any off-focus radiation impinging thereon. One of the drawbacks associated with these types of prior art beam limiting devices is that they must be adhesively or mechanically attached to the glass tubes. The silicone adhesives, such as the RTV adhesives, tend to degrade over time, particularly as a result of radiation exposure. Accordingly, these types of beam limiting devices can become detached from the x-ray tubes and/or the silicone or other adhesives can break off or dissolve into the oil, which, in turn, negatively affects the dielectric and/or other properties of the oil. Another drawback of these types of beam limiting devices is that the thermoset materials require relatively expensive tooling, and do not lend themselves to allowing easy and inexpensive manufacture of complex parts. Another drawback of the above-described prior art x-ray tube assemblies is that the use of lead to line the interior of the housings involves relatively time-consuming, labor-intensive, and expensive manufacturing procedures. Typically, the lead lining consists of a plurality of lead pre-forms, each of which must be cut and shaped with special dies and tooling to conform to a respective portion of the housing. Then, the pre-forms must be pressed into the housing, and fixedly secured to the housing. The lead is hazardous to handle, and therefore requires either expensive automated assembly equipment, and/or sophisticated procedures and handling equipment to prevent assembly workers from improper exposure to the lead. In addition, the lead presents significant problems and costs in connection with its disposal. Accordingly, it is an object of the present invention to overcome one or more of the above-described drawbacks and disadvantages of prior art x-ray tube assemblies. SUMMARY OF THE INVENTION The present invention is directed to a beam limiting apparatus for reducing the emission of off-focus radiation from an x-ray tube assembly and for containing the x-rays generated other than from the focal spot. The x-ray tube assembly comprises a housing including an x-ray port allowing the throughput of x-rays, and a mounting surface formed adjacent to the x-ray port. An x-ray tube is mounted within the housing and includes an evacuated envelope, an anode mounted within the envelope, and a cathode spaced relative to the anode within the envelope. The anode defines a target surface, the cathode projects onto the target surface a focal spot defining a focal spot size and shape, the x-ray port is spaced relative to the focal spot for receiving x-radiation emitted therefrom, and the x-ray port and envelope define a first predetermined depth therebetween. The beam limiting apparatus comprises a peripheral flange defining a second mounting surface locatable over the first mounting surface of the housing for fixedly securing the beam limiting apparatus to the housing. A radiation-absorbing body of the beam limiting apparatus projects downwardly from the peripheral flange and is receivable through the x-ray port. The radiation-absorbing body defines a base surface, an x-ray entrance aperture formed through the base surface, an x-ray exit aperture formed through an approximately opposite side of the body relative to the x-ray entrance aperture, and an x-ray transmissive beam conduit formed between the entrance and exit apertures. The base surface of the radiation-absorbing body extends into the housing a second depth less than the first depth, with the base surface spaced closely adjacent to the evacuated envelope of the x-ray tube to define a predetermined gap therebetween. The radiation-absorbing body is formed of a substantially electrically nonconductive, filled polymeric radiopaque material to prevent the passage of x-radiation therethrough. In addition, the x-ray entrance aperture defines a second size and shape, the x-ray exit aperture defines a third size and shape, and the second and third sizes and shapes are selected to define an x-ray beam of predetermined corresponding size and shape. In accordance with a preferred embodiment of the present invention, the x-ray tube housing also is formed of the filled polymeric, electrically non-conductive, radiopaque material. Preferably, the housing is formed of two castings, wherein a first casting defines the beam limiting apparatus integral with the x-ray port, a hermetically-sealed, radiopaque enclosure for receiving the x-ray tube, anode and cathode plug cavities for receiving high-voltage plugs, and an oil pump cavity for pumping oil through the hermetically-sealed enclosure to electrically insulate and cool the x-ray tube. The second casting preferably defines a cover which is attachable to the first casting to enclose the x-ray tube, and forms a hermetic seal with the first casting to seal the x-ray tube and oil within the housing. A conductive layer, preferably in the form of a conductive paint or like coating, is applied to the exterior surface of at least one of the first and second castings. One advantage of the beam limiting apparatus of the present invention is that it is made of a non-conductive, radiopaque material, and therefore may be mounted in close proximity to the x-ray tube to more effectively reduce the transmission of off-focus radiation. Another advantage of the beam limiting apparatus of the present invention is that an x-ray transmissive window may be molded into the radiation-absorbing body, and the window may be made of an opaque metal, a transparent polymeric elastomer, or other desired material. Yet another advantage of the present invention is that the x-ray tube housing may be made of a filled polymeric material, which is electrically non-conductive, and radiopaque, and therefore the drawbacks and disadvantages associated with prior art, lead-lined housings may be entirely avoided. Other objects and advantages of the present invention will become apparent in view of the following detailed description and accompanying drawings. |
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