Abstract:
A superconducting magnet assembly is described wherein the magnet cartridge is suspended within the vacuum chamber by a single support member extending from a wall of the vacuum chamber to the magnet cartridge. In one aspect, the support member includes a support tube and a joint attached to an end of the support tube. The joint is attached to the wall of the outer vacuum chamber, and provides at least one degree of freedom to the support tube relative to the wall. In another aspect, a joint is attached to an opposite end of the support tube, and is attached to the magnet cartridge for providing at least one degree of freedom to the support tube relative to the magnet cartridge. In another aspect, the support is constructed from one or more sections and the material choice is governed by the requirements for strength, stiffness, and thermal conductivity.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
         [0001]    This application claims the benefit of a priority under 35 U.S.C. 119 to Great Britain Patent Application No. 0228780.3 filed Dec. 10, 2002, the entire contents of which are hereby incorporated by reference.  
         BACKGROUND OF INVENTION  
         [0002]    This invention relates to support members for super-conducting magnet assemblies. More particularly, the invention relates to a support member for suspending a magnet cartridge within a vacuum chamber in a superconductor magnet assembly.  
           [0003]    Superconducting magnets typically include a magnet cartridge suspended within an outer vacuum chamber by a plurality of support members, which extend from the outer vacuum chamber to the magnet cartridge. Disposed between the magnet cartridge and the outer vacuum chamber is a radiation shield, through which the support members extend.  
           [0004]    To facilitate the superconductivity of the electrical wiring within the magnet cartridge, the magnet cartridge is maintained at a temperature that approaches absolute zero. However, the walls of the outer vacuum chamber are subject to ambient (room) temperature. To maintain this large temperature gradient, the magnet assembly is designed to reduce convection, radiation, and conduction heat transfer between the magnet cartridge and the walls of the outer vacuum chamber.  
           [0005]    A reduction in convection heat transfer is accomplished by maintaining a vacuum within the outer vacuum chamber. A reduction in radiation heat transfer is accomplished by the radiation shield, and a reduction of conductive heat transfer is accomplished through the design of the support members.  
           [0006]    The support members are subjected to the large temperature gradient—with the end of the support member at the magnet cartridge subjected to temperatures approaching absolute zero, and the end of the support member at the outer vacuum chamber subjected to room temperature. The support members are designed to have very low thermal conductivity and to cater for the effects of differences in the coefficient of thermal expansion of the different materials used in the construction of the magnet and the suspension system. In addition to the thermal stresses, the support members must be designed to withstand forces applied by the magnet. These forces include the weight mass of the magnet, which can be many tons, and the forces induced by the magnet, which can be even greater. The support members must have sufficient stiffness to prevent motion of the magnet when these forces are applied.  
           [0007]    Typically, the support members are long, thin rods. Because the rods are long and thin, the heat transfer area is small, which is an advantage in preventing conductive heat transfer. However, these rods provide support in tension only and would buckle if exposed to a compressive load while the forces applied to the support members by the magnet are not constant in direction. Thus, to ensure that the magnet cartridge is supported under the varying forces, the rods are arranged in a matrix surrounding the magnet cartridge.  
           [0008]    While such support members are effective in supporting the magnet cartridge, the use of such support members has drawbacks. First, as the number of rods used in the array increases, the conductive heat transfer area also increases. In addition, the number of penetrations through the radiation shield also increases, which decreases the effectiveness of the radiation shield, and increases the labor necessary to seal each of the penetrations from radiation leakage. Second, the rods must be accurately positioned (e.g., in diametrically opposed fashion) and are typically pre-tensioned. The accurate positioning of the rods and the pre-tensioning of the rods add to the cost of manufacturing the magnet assembly.  
         SUMMARY OF INVENTION  
         [0009]    The above-described drawbacks and deficiencies are overcome or alleviated by a superconducting magnet assembly wherein the magnet cartridge is suspended within the vacuum chamber by a single support member extending from a wall of the vacuum chamber to the magnet cartridge. In one aspect, the support member includes a support tube and a joint attached to an end of the support tube. The joint is attached to the wall of the outer vacuum chamber, and provides at least one degree of freedom to the support tube relative to the wall. In another aspect, a joint is attached to an opposite end of the support tube, and is attached to the magnet cartridge for providing at least one degree of freedom to the support tube relative to the magnet cartridge. In another aspect, the support is constructed from one or more sections and the material choice is governed by the requirements for strength, stiffness, and thermal conductivity.  
           [0010]    The above discussed and other features and advantages of the present invention will be appreciated and understood by those skilled in the art from the following detailed description and drawings. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0011]    Referring to the exemplary drawings wherein like elements are numbered alike in the several Figures:  
         [0012]    [0012]FIG. 1 is a schematic diagram of a superconducting magnet assembly;  
         [0013]    [0013]FIG. 2 is an isometric view of a support member for the superconducting magnet assembly of FIG. 1;  
         [0014]    [0014]FIG. 3 is a cross-sectional view of the support member of FIG. 2;  
         [0015]    [0015]FIG. 4 is an isometric view of an end joint on the outer vacuum chamber side of the support member of FIG. 2; and  
         [0016]    [0016]FIG. 5 is an isometric view of an end joint on the magnet cartridge side of the support member of FIG. 2.  
     
    
     DETAILED DESCRIPTION  
       [0017]    Referring to FIG. 1, a superconducting magnet assembly  10  is shown. Superconducting magnet assembly includes a magnet cartridge  12  suspended within an outer vacuum chamber  14  by a single support member  16 . Disposed between magnet cartridge  12  and a wall  18  of outer vacuum chamber  14  is a radiation shield  20 , through which support member  16  extends. A thermal coupling  22  extends between support member  16  and radiation shield  20 . Support member  16  is fixedly secured to wall  18  and magnet cartridge  12  such that support member  16  transmits axially compressive and tensile loads from magnet cartridge  12  to wall  18 .  
         [0018]    During operation, magnet cartridge  12  is maintained at a low temperature (e.g., near absolute zero), while the wall  18  of outer vacuum chamber is subject to the temperature of the room in which superconducting magnet assembly  10  is placed. Thus, during operation a temperature differential exists along support member  16 .  
         [0019]    Referring to FIG. 2, an isometric view of support member  16  is shown. Support member  16  has an outer vacuum chamber end  50  and a magnet cartridge end  52 . Disposed on ends  50  and  52  are joints  54  and  56  and tube couplings  58  and  60 . Extending between tube couplings  58  and  60  is a support tube  62 . Attached to a central portion of support tube  62  is thermal coupling  22 .  
         [0020]    When support member  16  is installed, ends  50  and  52  are secured against wall  18  and magnet cartridge  12 , respectively. Tensile and compressive forces are transmitted from magnet cartridge  12 , through joint  56  and tube coupling  58  to support tube  62 , and from support tube  62  through tube coupling  56  and joint  54  to wall  18 . As will be discussed in further detail hereinafter, each of joints  54  and  56  are very stiff axially, but allow support tube  62  to pivot through small angles. The joints  54  and  56  compensate for manufacturing tolerances, build errors, and the effect of differential thermal expansion, and translate pure axial tension and compression forces on the support tube  62 .  
         [0021]    Referring to FIG. 3, a cross-sectional view of support member  16  is shown. End  50  of support member is secured against wall  18  by a flange  100 , which captures a circumferential ridge  102  formed on joint  54 . Flange  100  is secured to wall  18  by welding, bolting, or the like. Joint  54  is secured to tube coupling  58  by a plurality of bolts  103 , which are recessed in joint  54  by way of through holes  104  in joint  54 . Bolts  103  engage a collar  106 , which is disposed around the periphery of support tube  62 . While an exemplary embodiment is described herein, it will be appreciated that end  50  and  52  may be secured against wall  18  and magnet cartridge  12 , respectively, using any suitable means.  
         [0022]    In the embodiment shown, support tube  62  is an elongated cylinder of generally uniform thickness having regions of increased thickness. A first region of increased thickness  108  is formed near end  50 , where the outside diameter of support tube  62  is increased abruptly such that a diametrical ridge  110  is formed. From the ridge  110  to the end of the tube  62 , the outside diameter is increased gradually to create taper. A second region of increased thickness  112  is formed near the center of support tube  62 , where the outside diameter of the support tube is increased. The second region of increased thickness  112  provides support for the thermal coupling  22 . The third region of increased thickness  114  is formed near end  52 , where the inside diameter is decreased abruptly such that a diametrical ridge  116  is formed. From the ridge  116  to the end of the tube  62 , the inside diameter is decreased gradually to create taper.  
         [0023]    Support tube  62  may be constructed of any thermally insulative material such as, for example, fiberglass, carbon (graphite) fiber, plastic, or the like. Support tube  62  may also be a composite structure, including more than one material. Where a support tube  62  is a composite structure, the materials are selected based on the performance of the material at the temperatures applied to the different portions of the support tube  62 . For example, the portion of support tube  62  extending from the second region of increased thickness  112  toward end  50  may be constructed of a fiberglass material, which has good strength properties at temperatures around room temperature, and the portion of support tube  62  extending from the second region of increased thickness  112  toward the end  52  may be constructed of a carbon fiber material, which has good strength properties at temperatures approaching absolute zero.  
         [0024]    Disposed within the support tube  62  at the first region of increased thickness  108  is a cylindrical plug  118 . Cylindrical plug  118  and collar  106  form the tube coupling  58 , which secures the support tube  62  to the joint  54 . An inside diameter of collar  106  is tapered to match the taper at the first region of increased thickness  108 . The taper of the collar acts to provide a compressive force onto the first region of increased thickness  108  as the collar  106  is drawn towards the joint  54  by the tightening of screws  103 . The plug  118  acts to support the inside of the support tube  62  against the compressive force of the collar  106 . The inside diameter of the collar  106  includes a ridge, which interacts with the diametrical ridge  110  on the support tube  62 . Together, the collar  106  and plug  118  secure the end of the support tube  62  against the joint  54  when the support tube  62  is under an axially tensile load. Plug  118  and collar  106  may be manufactured from a rigid material such as, for example, stainless steel or titanium.  
         [0025]    Disposed within support tube  62  is a thermal baffle assembly  120 . The thermal baffle assembly  120  includes a support rod  122  that is secured at one end to plug  118 , and extends along the longitudinal axis of the tube  62 . Secured to support rod  122  is a series of spaced-apart disks  124 . The disks  124  act as baffles to intercept heat radiation through the tube  62 . The disks  124  and support rod  122  may be constructed of a thermally insulative material such as, for example, plastic, fiberglass, aluminized Mylar or carbon fiber.  
         [0026]    Attached to the support tube  62  at the second region of increased thickness  112  is the thermal coupling  22 . A cylindrical portion of thermal coupling  130  is disposed around support tube  62  and attached thereto by fasteners, adhesive, or the like. Extending from cylindrical portion  130  towards end  50  is a conical portion  132 . A plurality of thermally conductive braids  134  extend from an end of conical portion  132  towards end  50 , and a second cylindrical portion  136  is, in turn, coupled to the ends of the braids  134 . Extending radially from an end of second cylindrical portion  136  distal from the braids  134  is a flange  138 . Flange  138  is coupled to the radiation shield  20  using, for example, fasteners, adhesive, welding, or the like. Thermal coupling  22  may be constructed of a thermally conductive material, such as copper.  
         [0027]    Thermal coupling  22  acts to shunt the conduction of heat from the outer vacuum chamber wall  18  to the radiation shield  20 , and thereby prevent the conduction of heat to the magnet cartridge  12  via the support member  16 . Braids  134  prevent vibration of the radiation shield  20  from traveling to the magnet cartridge  12  via the support member  16 , and also prevent the forces applied to the support member  16  from being transmitted to the radiation shield  20 .  
         [0028]    The third region of increased thickness  114  on the support tube  62  is captured by the tube coupling  60 . Tube coupling  60  comprises a bolt  140 , a washer  142 , a plug  144 , and a sleeve  146 . The bolt  140  extends along the longitudinal axis of the support member  16 , through the washer  142 , plug  144 , and joint  56 , and threadably engages an end cap  148 . An outside diameter of the plug  144  is tapered to match the taper at the third region of increased thickness  144 . The taper of the plug  144  acts to provide a compressive force onto the inside diameter of the third region of increased thickness  114  as the plug  144  is drawn towards the joint  56  by the tightening of bolt  140 . The collar  146  acts to support the outside of the support tube  62  against the compressive force of the plug  144 . The outside diameter of the plug  144  includes a ridge  148 , which interacts with the diametrical ridge on the inside diameter of the support tube  62 . Together, the collar  146  and plug  144  secure the end of the support tube  62  against the joint  56  when the support tube  62  is under an axially tensile load. Plug  144 , bolt  140 , washer  142 , and collar  146  may be manufactured from a rigid, non-magnetic material such as, for example, titanium.  
         [0029]    End cap  148  is secured to the magnet cartridge  12  by way of fastener, welding, adhesive, or the like. Joint  56  is captured between tube coupling  60  and end cap  148  when bolt  140 , which is threaded into end cap  148 , is tightened.  
         [0030]    Referring now to FIGS. 4 and 5, the construction of joints  54  and  56  will be described. Each joint  54  and  56  includes first, second, and third disks  200 ,  202  and  204 . The first disk  200  is coupled to the second disk  202  by a beam  208 , which extends along a diameter of the first disk  200 . The first disk  200  includes wedges  210  extending therefrom along either side of the beam  208 . The wedges  210  are received within recesses  212  formed in the second disk  202 . Similarly, the second disk  202  is coupled to the third disk  204  by a beam  214 , which extends along the diameter of the second disk  202 . The second disk  202  includes wedges  216  extending therefrom along either side of the beam  214 . The wedges  216  are received within recesses  218  formed in the third disk  204 . In the embodiment shown, each joint  54  and  56  is machined from a solid cylinder of rigid, non-magnetic metal, such as titanium or Inconnel. Two diametrically opposed slots  220  and  222  disposed in the cylinder form the space between each disk  200  and  202 , each beam  208 , two wedges  210 , and two recesses  212 .  
         [0031]    Similarly, two diametrically opposed slots  224  and  226  disposed in the cylinder form the space between each disk  202  and  204 , each beam  214 , two wedges  216 , and two recesses  218 .  
         [0032]    The bending of beams  208  and  214  provides two degrees of freedom to each joint  54  and  56 . Thus, while each joint  54  and  56  is very stiff axially, they allow support tube  62  to pivot through small angles about the y and z axes indicated in FIG. 4 and FIG. 5. The y and z axes may be situated at 90 degrees to each other and at 90 degrees to the centroidal axis x of the support member  16 . The joints  54  and  56  compensate for manufacturing tolerances, build errors and the effect of differential thermal expansion and translate the forces applied by magnet cartridge  12  into pure axial tension and compression forces on the support tube  62 . The wedges  210  and  216  provide lateral support to beams  208  and  214  thereby preventing the buckling of beams  208  and  214 . In addition, the wedges  210  and  216  help to stiffen the disk between the two beams.  
         [0033]    The single support member  16  takes all loads in tension and compression that a typical design would handle with a combination of tension straps. Thus, the support member  16  reduces the number of rods typically used in supporting the magnet cartridge  12 , and, thereby reduces the conductive heat transfer area from that previously possible. In addition, the number of penetrations through the radiation shield  20  also decreases from designs that use a combination of tension straps. This, in turn, increases the effectiveness of the radiation shield  20  and requires less labor to seal penetrations in the radiation shield  20  from that previously possible. The high stiffness joints  54  and  56  take up build errors and the effect of differential thermal expansion and translate them into pure axial tension and compression forces on the support tube  62 .  
         [0034]    While the invention has been described with reference to a preferred embodiment, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiment disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims. Moreover, the use of the terms first, second, etc. do not denote any order or importance, but rather the terms first, second, etc. are used to distinguish one element from another.