Patent Publication Number: US-8989827-B2

Title: Superconducting magnet

Description:
TECHNICAL FIELD 
     The present invention relates to a superconducting magnet. 
     BACKGROUND ART 
     Japanese Patent Laying-Open No. 2-78208 (PTD 1) is a related art document disclosing a configuration of a superconducting magnet. According to the superconducting magnet disclosed in Japanese Patent Laying-Open No. 2-78208 (PTD 1), one side of a flange of a refrigerating machine port is attached to a magnetic shield through a vibration-proof body. Further, the other side of the flange of the refrigerating machine port is coupled to bellows constituting a vacuum chamber. 
     CITATION LIST 
     Patent Document 
     
         
         PTD 1: Japanese Patent Laying-Open No. 2-78208 
       
    
     SUMMARY OF INVENTION 
     Technical Problem 
     According to the superconducting magnet disclosed in Japanese Patent Laying-Open No. 2-78208 (PTD 1), the magnetic shield and the vacuum chamber are assembled to integrate by means of connection parts such as bellows, a bellows flange, a bolt, a nut, and the like, rendering the structure to be complicated, and each constituting part to be an application-specific part, thereby causing lack of versatility. 
     The present invention was achieved in view of the problem described above, and its object is to provide a superconducting magnet having a simple structure. 
     Solution to Problem 
     A superconducting magnet in accordance with the present invention includes a superconducting coil, a heat shield surrounding the superconducting coil, a vacuum chamber accommodating the heat shield, a magnetic shield covering at least a part of the vacuum chamber, and a refrigerating machine fixed to the vacuum chamber to cool the superconducting coil through a heat conducting body. The magnetic shield abuts against the vacuum chamber with an elastic body therebetween to support the vacuum chamber. 
     Advantageous Effects of Invention 
     According to the present invention, the structure of a superconducting magnet can be simplified. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view representing an appearance of a superconducting magnet according to a first embodiment of the present invention. 
         FIG. 2  is a cross-sectional view representing a configuration of the superconducting magnet according to the first embodiment of the present invention. 
         FIG. 3  is a cross-sectional view representing a configuration of a superconducting magnet according to a second embodiment of the present invention. 
         FIG. 4  is a cross-sectional view representing a configuration of a superconducting magnet according to a third embodiment of the present invention. 
         FIG. 5  is a perspective view representing an appearance of a superconducting magnet according to a fourth embodiment of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, a superconducting magnet according to the first embodiment of the present invention will be described with reference to the drawings. In the following description of the embodiments, the same or corresponding parts in the drawings have the same reference numerals allotted, and description thereof will not be repeated. 
     (First Embodiment) 
       FIG. 1  is a perspective view representing appearance of the superconducting magnet according to the first embodiment of the present invention.  FIG. 2  is a cross-sectional view representing a configuration of the superconducting magnet according to the first embodiment of the present invention. 
     As shown in  FIGS. 1 and 2 , a superconducting magnet  100  according to the first embodiment of the present invention includes a superconducting coil  110 , a heat shield  130  surrounding superconducting coil  110 , and a vacuum chamber  140  accommodating heat shield  130 . Heat shield  130  and vacuum chamber  140  constitute a cryostat  150 . Further, superconducting magnet  100  includes a magnetic shield  180  covering at least a part of vacuum chamber  140 , and a refrigerating machine  160  fixed to vacuum chamber  140  to cool the superconducting coil through heat conducting body  170 . Magnetic shield  180  abuts against vacuum chamber  140  with an elastic body  190  therebetween to support vacuum chamber  140 . 
     Superconducting magnet  100  according to the present embodiment is a superconducting magnet of so-called conductive cooling type allowing refrigerating machine  160  and superconducting coil  110  to thermally come in contact with each other to cool superconducting coil  110 . 
     Hereinafter, each element of superconducting magnet  100  according to the present embodiment will be described. Superconducting magnet  100  according to the present embodiment includes two of each superconducting coil  110 , heat shield  130 , vacuum chamber  140 , and refrigerating machine  160 . The configuration of the superconducting magnet is not limited to this, and is arbitrary as long as at least one superconducting coil  110 , heat shield  130 , vacuum chamber  140 , and refrigerating machine  160  are included. 
     Superconducting coil  110  includes a superconducting wire made of niobium-titanium alloy and is wound around a cylindrical bobbin  120 . Material of the superconducting wire is not limited to niobium-titanium alloy, and the material may be, for example, niobium-tin alloy. Bobbin  120  is formed from stainless steel, but the material of bobbin  120  is not limited to this. 
     Heat shield  130  prevents intrusion of heat into superconducting coil  110  due to thermal radiation from outside. Heat shield  130  is formed from aluminum. However, material of heat shield  130  is not limited to this, and any material having superior thermal conductivity may be employed. 
     Vacuum chamber  140  accommodates superconducting coil  110 , bobbin  120 , and heat shield  130 . Vacuum chamber  140  provides vacuum insulation between the inside and outside of vacuum chamber  140 . Both heat shield  130  and vacuum chamber  140  are structures for preventing intrusion of heat into superconducting coil  110 . 
     In the present embodiment, vacuum chamber  140  has a substantially cuboid profile. However, the profile of vacuum chamber  140  is not limited to this, and a substantially cylindrical profile may be employed. Two vacuum chambers  140  are arranged such that respective side surfaces face with each other. 
     Refrigerating machine  160  includes two-stage cooling portions. A first stage cooling portion of refrigerating machine  160  is in contact with heat shield  130 . A second stage cooling portion as a tip portion of refrigerating machine  160  is in contact with superconducting coil  110  through heat conducting body  170  made of, for example, copper. 
     Magnetic shield  180  is formed from a magnetic body such as iron having a thickness greater than or equal to 100 mm to effectively reduce leakage of a magnetic field from superconducting magnet  100  to outer portion. Magnetic shield  180  covers side surfaces excluding the side surfaces facing each other the and bottom surfaces of two vacuum chambers  140 . 
     Elastic body  190  is made of rubber in the present embodiment. However, elastic body  190  is not limited to this, and elements capable of absorbing vibration, such as a spring made of metal, a spring made of resin, or a damper, may be employed. 
     In the present embodiment, elastic bodies  190  are spaced apart at predetermined intervals and arranged between the bottom surface of vacuum chamber  140  and magnetic shield  180 , and between the side surfaces of vacuum chamber  140  and magnetic shield  180 . Elastic bodies  190  are bonded to either vacuum chamber  140  or magnetic shield  180 . 
     Hereinafter, operation performed during generation of a magnetic field in superconducting magnet  100  will be described. 
     Firstly, to bring superconducting coil  110  to a superconducting state, the pressure in vacuum chamber  140  is reduced to attain vacuum. Thereafter, refrigerating machine  160  is operated. Heat shield  130  is cooled down to about 60K by the first stage cooling portion of refrigerating machine  160 . Superconducting coil  110  is eventually cooled down to a temperature less than or equal to 4K by the second stage cooling portion of refrigerating machine  160 . 
     After heat shield  130  and superconducting coil  110  are cooled sufficiently, current is applied to superconducting coil  110  through a lead wire from an unillustrated external power supply device to generate a magnetic field. In the present embodiment, the region between the respective surfaces of two vacuum chambers  140  facing each other is a region of using the generated magnetic field. 
     Since the refrigerating machine is of a reciprocating expansion machine type, driving of the refrigerating machine generates vibration. The vibration propagates to cryostat  150 . Since elastic bodies  190  are arranged between vacuum chamber  140  and magnetic shield  180 , the vibration of refrigerating machine  160  is attenuated by elastic body  190 . Therefore, almost no vibration propagates to magnetic shield  180 . 
     Reducing the propagation of vibration of refrigerating machine  160  through magnetic shield  180  to a floor surface having magnetic shield  180  provided thereon can suppress influence of the vibration to precise measuring equipment arranged around superconducting magnet  100 . 
     Superconducting magnet  100  of the present embodiment can suppress propagation of the vibration of refrigerating machine  160  by employing a simple structure of allowing magnetic shield  180  to abut against vacuum chamber  140  with elastic bodies  190  therebetween to support vacuum chamber  140 . Therefore, elastic bodies  190  are arranged in accordance with the profile of cryostat  150 , in other words, the profile of vacuum chamber  140 , so that the countermeasure to the vibration of superconducting magnet  100  can be taken, and superconducting magnet  100  can have a structure with superior versatility. 
     Hereinafter, a superconducting magnet according to the second embodiment of the present invention will be described. A superconducting magnet  200  of the present embodiment is different from superconducting magnet  100  of the first embodiment in the method of cooling superconducting coil  110 . Therefore, description as to the same configuration as superconducting magnet  100  of the first embodiment will not be repeated. 
     (Second Embodiment) 
       FIG. 3  is a cross-sectional view representing a configuration of a superconducting magnet according to the second embodiment of the present invention. As shown in  FIG. 3 , superconducting magnet  200  according to the second embodiment of the present invention includes superconducting coil  110 , a helium tank  210  accommodating superconducting coil  110  and storing liquid helium  220  inside, heat shield  130  surrounding helium tank  210 , and vacuum chamber  140  accommodating heat shield  130 . Heat shield  130  and vacuum chamber  140  constitute cryostat  150 . Superconducting magnet  200  includes magnetic shield  180  covering at least a part of vacuum chamber  140 , and refrigerating machine  160  fixed to vacuum chamber  140  and liquefying evaporated liquid helium  220  to cool superconducting coil  110 . Magnetic shield  180  abuts against vacuum chamber  140  with elastic bodies  190  therebetween to support vacuum chamber  140 . 
     Superconducting magnet  200  according to the present embodiment is a superconducting magnet employing so-called helium cooling method of cooling superconducting coil  110  by immersing the coil into liquid helium  220 . 
     Hereinafter, each element of superconducting magnet  200  according to the present embodiment will be described. Superconducting magnet  200  of the present embodiment includes two of each superconducting coil  110 , helium tank  210 , heat shield  130 , vacuum chamber  140 , and refrigerating machine  160 . The configuration of the superconducting magnet is not limited to this, and is arbitrary as long as at least one superconducting coil  110 , helium tank  210 , heat shield  130 , vacuum chamber  140 , and refrigerating machine  160  are included. 
     Helium tank  210  has an O-shaped profile. Superconducting coil  110  is wound around a shaft portion of helium tank  210 . A helium pipe  230  is coupled to an upper portion of helium tank  210 . Helium pipe  230  serves to introduce liquid helium  220  and discharge helium gas evaporated from liquid helium  220 . Liquid helium  220  stored in helium tank  210  cools superconducting coil  110 . 
     The first stage cooling portion of refrigerating machine  160  is in contact with heat shield  130 . The second stage cooling portion as a tip of refrigerating machine  160  is in contact with liquid helium evaporated in helium tank  210  and cools the evaporated liquid helium to re-liquefy the helium again. 
     Also in the present embodiment, since elastic bodies  190  are arranged between vacuum chamber  140  and magnetic shield  180 , vibration of refrigerating machine  160  is attenuated by elastic bodies  190 , so that almost no vibration propagates to magnetic shield  180 . 
     Reducing the propagation of vibration of refrigerating machine  160  through magnetic shield  180  to a floor surface having magnetic shield  180  provided thereon can suppress influence of the vibration to precise measuring equipment arranged around superconducting magnet  100 . 
     Superconducting magnet  200  of the present embodiment can suppress propagation of the vibration of refrigerating machine  160  by employing a simple structure of allowing magnetic shield  180  to abut against vacuum chamber  140  with elastic bodies  190  therebetween to support vacuum chamber  140 . Therefore, elastic bodies  190  are arranged in accordance with a profile of cryostat  150 , in other words, a profile of vacuum chamber  140 , so that the countermeasure to the vibration of superconducting magnet  200  can be taken, and superconducting magnet  200  can have a structure with superior versatility. 
     Hereinafter, a superconducting magnet according to the third embodiment of the present invention will be described. Superconducting magnet  300  of the present embodiment is different from superconducting magnet  100  of the first embodiment in the arrangement of the refrigerating machines. Therefore, description as to the same configuration as superconducting magnet  100  of the first embodiment will not be repeated. 
     (Third Embodiment) 
       FIG. 4  is a cross-sectional view representing a configuration of a superconducting magnet according to the third embodiment of the present invention. As shown in  FIG. 4 , superconducting coil  110  is wound around bobbin  120 . Heat shield  130  surrounds superconducting coil  110 . Vacuum chamber  140  accommodates heat shield  130 . Refrigerating machine  160  is thermally connected to superconducting coil  110  through heat conducting body  170  and heat conducting body  310 . 
     In superconducting magnet  300  according to the third embodiment of the present invention, a part  330  of vacuum chamber  140  including a part having refrigerating machine  160  fixed thereon is positioned outside of magnetic shield  180 . Magnetic shield  180  abuts against part  330  of vacuum chamber  140  with elastic bodies  190  therebetween to support vacuum chamber  140 . 
     In particular, part  330  of the vacuum chamber  140  positioned outside of magnetic shield  180  and the other part of vacuum chamber  140  positioned inside magnetic shield  180  are coupled by bellows  350 . Bellows  350  suppress propagation of vibration from part  330  of vacuum chamber  140  positioned outside of magnetic shield  180  to other part of vacuum chamber  140  positioned inside magnetic shield  180 . 
     A part  320  of heat shield  130  is also positioned outside of magnetic shield  180 . Part  320  of heat shield  130  positioned outside of magnetic shield  180  and the other part of heat shield  130  positioned inside of magnetic shield  180  are coupled by coupling pipe heat shield  340 . 
     Part  320  of heat shield  130  incorporates a copper braided wire  321 . Copper braided wire  321  efficiently conducts heat and suppresses propagation of vibration from part  320  of heat shield  130  positioned outside of magnetic shield  180  to the other part of heat shield  130  positioned inside of magnetic shield  180 . 
     Part  320  of heat shield  130  is in contact with the first stage cooling portion of refrigerating machine  160 , so that heat shield  130  is cooled down to about 60K. 
     Heat conducting body  310  also incorporates copper braided wire  311 . Copper braided wire  311  efficiently conducts heat and suppresses propagation of vibration from refrigerating machine  160  to superconducting coil  110 . 
     Heat conducting body  310  is in contact with the second stage heat cooling portion of refrigerating machine  160 , so that superconducting coil  110  is cooled down to about 4K through heat conducting body  170 . 
     Part  330  of vacuum chamber  140  abuts against magnetic shield  180  with elastic bodies  190  therebetween, so that vacuum chamber  140  is supported by magnetic shield  180 . Therefore, propagation of vibration of refrigerating machine  160  to a floor surface and magnetic shield  180  can be suppressed. 
     Also in the present embodiment, reducing the propagation of vibration of refrigerating machine  160  through magnetic shield  180  to a floor surface having magnetic shield  180  provided thereon can suppress influence of the vibration to precise measuring equipment arranged around superconducting magnet  300 . 
     Hereinafter, a superconducting magnet according to the fourth embodiment of the present invention will be described. Superconducting magnet  400  of the present embodiment is different from superconducting magnet  100  of the first embodiment in a profile and the number of cryostat. Therefore, description as to the same configuration as superconducting magnet  100  of the first embodiment will not be repeated. 
     (Fourth Embodiment) 
       FIG. 5  is a perspective view representing an appearance of a superconducting magnet according to the fourth embodiment of the present invention. As shown in  FIG. 5 , in superconducting magnet  400  according to the fourth embodiment of the present invention, a profile of cryostat  410 , in other words, a profile of a vacuum chamber, is substantially cylindrical. In cryostat  410 , a part having refrigerating machine  160  provided thereon has a protruding portion  450  protruding from an outer peripheral surface of cryostat  410 . 
     Magnetic shield  180  is arranged to have a substantially octagonal shape in a side view in an outer periphery of the cylinder of cryostat  410 . However, only the outer side of protruding portion  450  of cryostat  410  does not have magnetic shield  180  positioned thereon. 
     Magnetic shield  180  abuts against cryostat  410  with elastic bodies  190  therebetween to support cryostat  410 . In other words, magnetic shield  180  abuts against the vacuum chamber with elastic bodies  190  therebetween to support the vacuum chamber. 
     In particular, rubber as elastic body  190  is arranged at opposite end portions in the axial direction of cryostat  410  and on the upper, lower, left, and right sides of cryostat  410 . However, the arrangement of elastic bodies  190  is not limited to this, and the elastic bodies  190  is arbitrary as long as it is arranged at a position where cryostat  410  can be supported. 
     Also in the present embodiment, reducing the propagation of vibration of refrigerating machine  160  through magnetic shield  180  to a floor surface having magnetic shield  180  provided thereon can suppress influence of the vibration to precise measuring equipment arranged around superconducting magnet  400 . 
     Combination of embodiments which can be combined in the embodiment described above shall be envisioned. The superconducting magnet can be used for a magnetic resonance imaging diagnosis device, a nuclear magnetic resonance measuring equipment, and a semiconductor production device. 
     It should be understood that the embodiments disclosed herein are only by way of examples, and not to be taken by way of limitation. Therefore, the technical scope of the present invention is not limited by the description above, but rather by the terms of the appended claims. Further, any modifications within the scope and meaning equivalent to the terms of the claims are included. 
     REFERENCE SIGNS LIST 
       100 ,  200 ,  300 ,  400  superconducting magnet;  110  superconducting coil;  120  bobbin;  130  heat shield;  140  vacuum chamber;  150 ,  410  cryostat;  160  refrigerating machine;  170 ,  310  heat conducting body;  180  magnetic shield;  190  elastic body;  210  helium tank;  220  liquid helium;  230  helium pipe;  311 ,  321  copper braiding wire;  320  part of heat shield;  330  part of vacuum chamber;  340  connection pipe heat shield;  350  bellows;  450  protruding portion.