Patent Publication Number: US-9431160-B2

Title: Superconducting magnet

Description:
TECHNICAL FIELD 
     The present invention relates to superconducting magnets. 
     BACKGROUND ART 
     Japanese Utility Model Laying-Open No. 63-89212 (PTD 1) is a prior art document which discloses an ice removing device that removes ice attached to connection terminals connected to a power supply lead. In the ice removing device for a superconducting magnet described in PTD 1, ice is melted by inserting the ice removing device through a connection pipe, and fitting an ice melting portion having a high heat capacity to the connection terminals. 
     CITATION LIST 
     Patent Document 
     PTD 1: Japanese Utility Model Laying-Open No. 63-89212 
     SUMMARY OF INVENTION 
     Technical Problem 
     When the lead is attached to and removed from a vacuum vessel, air or the like enters a helium tank within the vacuum vessel. The air that has entered the helium tank solidifies by being cooled with liquid helium within the helium tank. If the solidification occurs at a connection portion between the lead and the connection terminals, the lead cannot be pulled out of the vacuum vessel. Forced pulling of the lead causes breakage of the lead. In this case, the solidified product cannot be removed with the ice removing device. 
     Furthermore, if the solidification occurs at an exhaust port connected to the helium tank, gasified helium cannot be exhausted, and the superconducting coil cannot be cooled stably. 
     The present invention was made in view of the problem described above, and an object of the invention is to provide a superconducting magnet capable of removing a solidified product of air or the like. 
     Solution to Problem 
     A superconducting magnet according to the present invention includes a superconducting coil, a helium tank that accommodates the superconducting coil and stores liquid helium therein, a radiation shield that surrounds a periphery of the helium tank, a vacuum vessel that accommodates the radiation shield, and an exhaust port that is connected to the helium tank and exhausts gasified helium. The superconducting magnet also includes a lead that electrically connects an external power supply and the superconducting coil and is attachable to and removable from the vacuum vessel, and a connector that connects the lead and the superconducting coil. The superconducting magnet also includes a thermal conductive member having one end in contact with at least one of the connector and the exhaust port, and having the other end located outside the vacuum vessel and attachable to and removable from the vacuum vessel. 
     Advantageous Effects of Invention 
     According to the present invention, a solidified product of air or the like can be removed. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a cross-sectional view showing the structure of a superconducting magnet according to a first embodiment of the present invention. 
         FIG. 2  is a cross-sectional view showing the structure of a connector of the superconducting magnet according to the first embodiment. 
         FIG. 3  is a cross-sectional view showing the structure of a superconducting magnet according to a second embodiment of the present invention. 
         FIG. 4  is a cross-sectional view showing the structure of a superconducting magnet according to a third embodiment of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     A superconducting magnet according to a first embodiment of the present invention will be described hereinafter, referring to the drawings. In the description of the following embodiments, the same or corresponding parts in the figures are indicated by the same reference characters, and the description thereof will not be repeated. 
     First Embodiment 
       FIG. 1  is a cross-sectional view showing the structure of the superconducting magnet according to the first embodiment of the present invention.  FIG. 2  is a cross-sectional view showing the structure of a connector of the superconducting magnet according to the first embodiment. 
     As shown in  FIG. 1 , superconducting magnet  100  according to the first embodiment of the present invention includes a superconducting coil  110  formed by winding a superconducting wire, a helium tank  120  that accommodates superconducting coil  110  and stores liquid helium  150  therein, a radiation shield  130  that surrounds a periphery of helium tank  120 , and a vacuum vessel  140  that accommodates radiation shield  130 . Radiation shield  130  is supported by a supporting member not shown here, so as to reduce heat transfer to helium tank  120 . 
     Superconducting coil  110  is wound around a shaft of helium tank  120 . Superconducting coil  110  is cooled with liquid helium  150  stored in helium tank  120 . 
     An exhaust pipe  190 , which is an exhaust port that exhausts gasified helium, is connected to helium tank  120 . Exhaust pipe  190  is fitted with a valve  191  that is designed to open when the pressure in helium tank  120  has become equal to or higher than a prescribed pressure. 
     Superconducting magnet  100  is equipped with a refrigerator not shown here. A cooling portion in a first stage of the refrigerator is in contact with radiation shield  130 . A cooling portion in a second stage, that is, an end portion, of the refrigerator is in contact with gasified helium in helium tank  120 , to cool the gasified helium for re-liquefaction. 
     An external power supply  170  for passing current in superconducting coil  110  is connected to superconducting magnet  100 . Superconducting magnet  100  is equipped with a lead  171  that electrically connects external power supply  170  and superconducting coil  110  and is attachable to and removable from vacuum vessel  140 , and a connector  160  that connects lead  171  and superconducting coil  110 . 
     As shown in  FIG. 2 , connector  160  includes connection terminals  161  that electrically connect lead  171  and superconducting coil  110 , a main body  163  that holds connection terminals  161  and has thermal conductivity, and an electrical insulating portion  162  interposed between connection terminals  161  and main body  163 . 
     Specifically, two connection terminals  161  penetrate rectangular parallelepiped-shaped main body  163  that is made of a metal such as copper. Electrical insulating portion  162  having electrical insulation properties, such as GFRP (Glass Fiber Reinforced Plastic), is disposed between connection terminals  161  and main body  163 . Electrical insulating portion  162  ensures electrical insulation between connection terminals  161  and main body  163 , and between connected lead  171  and main body  163 . It is noted, however, that the shape of connector  160  and the material forming each element are not limited to those described above, and are set as desired. 
     As shown in  FIG. 1 , superconducting magnet  100  includes a thermal conductive member  180  having one end in contact with connector  160 , and having the other end located outside vacuum vessel  140  and attachable to and removable from vacuum vessel  140 . 
     In this embodiment, thermal conductive member  180  is made up of an L-shaped first thermal conductive member  181  fixedly disposed to be in contact with a lower surface of main body  163  of connector  160  in helium tank  120 , and a bar-shaped second thermal conductive member  182  having a lower end surface in contact with an upper end surface of first thermal conductive member  181 . 
     It is noted that first thermal conductive member  181  is fixed in a non-contact manner with connection terminals  161 . Second thermal conductive member  182  is supported to be attachable to and removable from vacuum vessel  140 . First thermal conductive member  181  and second thermal conductive member  182  are formed of copper. More specifically, first thermal conductive member  181  and second thermal conductive member  182  are formed of phosphorous-deoxidized copper. 
     The composition and material of thermal conductive member  180  are not limited to those described above, and thermal conductive member  180  may be integrally formed of a material having thermal conductivity. For example, the bar-shaped thermal conductive member may be disposed to have one end in contact with a side surface of main body  163  of connector  160 , and the other end located outside vacuum vessel  140 . 
     It is noted, however, that as in this embodiment, when first thermal conductive member  181  is brought into contact with a full length of main body  163  in a direction in which two connection terminals  161  are aligned, more uniform heating of main body  163  can be achieved. 
     Operation of superconducting magnet  100  according to this embodiment will be described hereinafter. 
     First, liquid helium  150  is cooled to about 4.2 K with the refrigerator, without lead  171  and second thermal conductive member  182  being mounted. At this time, air containing nitrogen, oxygen, or the like may solidify. If the solidification occurs near upper ends of connection terminals  161  connected to lead  171 , lead  171  cannot be mounted in that condition. 
     Thus, second thermal conductive member  182  is mounted on vacuum vessel  140 , and allows the lower end surface of second thermal conductive member  182  to contact the upper end surface of first thermal conductive member  181 . Since an upper end portion of second thermal conductive member  182  is located outside vacuum vessel  140 , the upper end portion of second thermal conductive member  182  absorbs heat from outside air outside vacuum vessel  140 . 
     The heat absorbed at the upper end portion of second thermal conductive member  182  is transferred from the lower end surface of second thermal conductive member  182  to first thermal conductive member  181 . The heat transferred to first thermal conductive member  181  is transferred to main body  163  of connector  160 . With the heat transferred to main body  163 , a solidified product formed near the upper ends of connection terminals  161  can be melted and removed. Since the solidification temperature of nitrogen, oxygen, or the like is considerably lower than the outside air temperature, the solidified product can be reliably removed by heating connector  160  via thermal conductive member  180 , using the outside air as a heat source. 
     After removing the solidified product, lead  171  is mounted on vacuum vessel  140 . Second thermal conductive member  182  is then removed. In this state, external power supply  170  is operated, thereby passing current in superconducting coil  110  through lead  171  and connector  160 . 
     At the time of pulling out lead  171  because the magnetic field strength of superconducting magnet  100  has increased to a rated magnetic field and the current supply from external power supply  170  is no longer needed, the solidification may have occurred at a connection portion  171   a  between lead  171  and connection terminals  161  and thus, second thermal conductive member  182  is mounted on vacuum vessel  140  first. 
     As described above, main body  163  is heated with thermal conductive member  180  to melt and remove the solidified product formed at connection portion  171   a . Lead  171  is then pulled out. In this way, lead  171  can be prevented from being subjected to a load. Finally, second thermal conductive member  182  is removed from vacuum vessel  140 . 
     By attaching and removing lead  171  according to the method described above, it is possible to prevent lead  171  from becoming unable to be attached and removed due to the solidified product formed at connection terminals  161  and connection portion  171   a.    
     A superconducting magnet according to a second embodiment of the present invention will be described hereinafter, referring to the drawings. It is noted that superconducting magnet  200  according to this embodiment differs from superconducting magnet  100  according to the first embodiment only in that a thermal conductive member  280  in contact with the exhaust port is additionally provided. The description of the rest of the structure will not therefore be repeated. 
     Second Embodiment 
       FIG. 3  is a cross-sectional view showing the structure of the 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 a thermal conductive member  280  having one end in contact with exhaust pipe  190 , and having the other end located outside vacuum vessel  140  and attachable to and removable from vacuum vessel  140 . 
     In this embodiment, bar-shaped thermal conductive member  280  is disposed to have the one end in contact with a portion of an outer periphery of a port  190   a  of exhaust pipe  190 , and the other end located outside vacuum vessel  140 . 
     Thermal conductive member  280  is supported to be attachable to and removable from vacuum vessel  140 . Thermal conductive member  280  is formed of copper. More specifically, thermal conductive member  280  is formed of phosphorous-deoxidized copper. It is noted, however, that the material of thermal conductive member  280  is not limited to this, and may be any material having thermal conductivity. 
     Operation of removing a solidified product formed at the exhaust port by superconducting magnet  200  according to this embodiment will be described hereinafter. 
     Helium tank  120  is equipped with a pressure sensor not shown here to measure the pressure in helium tank  120 . If the solidification occurs at port  190   a  of exhaust pipe  190  connected to helium tank  120 , gasified helium cannot be exhausted, causing the pressure in helium tank  120  to increase. 
     When the pressure in helium tank  120  has become equal to or higher than a prescribed pressure, it is determined that port  190   a  of exhaust pipe  190  is blocked with a solidified product, and thermal conductive member  280  is mounted on vacuum vessel  140 . Since an upper end portion of thermal conductive member  280  is located outside vacuum vessel  140 , the upper end portion of thermal conductive member  280  absorbs heat from outside air outside vacuum vessel  140 . 
     The heat absorbed at the upper end portion of thermal conductive member  280  is transferred from a lower end portion of thermal conductive member  280  to exhaust pipe  190 . With the heat transferred to exhaust pipe  190 , the solidified product formed in the vicinity of port  190   a  of exhaust pipe  190  can be melted and removed. 
     After checking that the removal of the solidified product has allowed the gas to exhaust through exhaust pipe  190  and the pressure in helium tank  120  to decrease, thermal conductive member  280  is removed. 
     By removing the solidified product formed at the exhaust port according to the method described above, superconducting coil  110  can be cooled stably. Consequently, superconducting magnet  200  can be operated stably. 
     A superconducting magnet according to a third embodiment of the present invention will be described hereinafter, referring to the drawings. It is noted that superconducting magnet  300  according to this embodiment differs from superconducting magnet  100  according to the first embodiment only in that a thermal conductive member  380  in contact with both the connector and the exhaust port is additionally provided. The description of the rest of the structure will not therefore be repeated. 
     Third Embodiment 
       FIG. 4  is a cross-sectional view showing the structure of the superconducting magnet according to the third embodiment of the present invention. As shown in  FIG. 4  superconducting magnet  300  according to the third embodiment of the present invention includes thermal conductive member  380  having one end in contact with main body  163  of connector  160  and exhaust pipe  190  in vacuum vessel  140 , and having the other end located outside vacuum vessel  140  and attachable to and removable from vacuum vessel  140 . 
     In this embodiment, thermal conductive member  380  is made up of an L-shaped first thermal conductive member  381  fixedly disposed to be in contact with a lower surface of main body  163  of connector  160  in helium tank  120 , and a bar-shaped second thermal conductive member  382  having a lower end surface in contact with an upper end surface of first thermal conductive member  381 . 
     It is noted that first thermal conductive member  381  is fixed in a non-contact manner with connection terminals  161 . Second thermal conductive member  382  is supported to be attachable to and removable from vacuum vessel  140 . First thermal conductive member  381  and second thermal conductive member  382  are formed of copper. More specifically, first thermal conductive member  381  and second thermal conductive member  382  are formed of phosphorous-deoxidized copper. 
     The composition and material of thermal conductive member  380  are not limited to those described above, and thermal conductive member  180  may be integrally formed of a material having thermal conductivity. For example, the bar-shaped thermal conductive member may be disposed to have one end in contact with a side surface of main body  163  of connector  160  and a portion of the outer periphery of port  190   a  of exhaust pipe  190 , and having the other end located outside vacuum vessel  140 . 
     With this structure, main body  163  can be heated with thermal conductive member  380  to melt and remove a solidified product formed at connection portion  171   a , and also melt and remove a solidified product formed in the vicinity of port  190   a  of exhaust pipe  190 . 
     Consequently, it is possible to prevent lead  171  from becoming unable to be attached and removed due to the solidified product formed at connection terminals  161  and connection portion  171   a , and also cool superconducting coil  110  stably. 
     Furthermore, superconducting magnet  300  according to this embodiment further includes a heating unit  370  that heats the other end of second thermal conductive member  382 . Any of various heaters such as a resistance heater or a warm air heater can be used as heating unit  370 . By heating second thermal conductive member  382  with heating unit  370 , the time needed to melt the solidified product can be shortened. It is noted, however, that superconducting magnet  300  may not necessarily include heating unit  370 . 
     It should be noted that the foregoing embodiments disclosed herein are illustrative in every respect, and do not form a basis of any limitative interpretation. Accordingly, the technical scope of the present invention shall not be interpreted using the foregoing embodiments only, but shall be defined based on the claims. 
     Furthermore, the present invention includes any modifications within the scope and meaning equivalent to the terms of the claims. 
     REFERENCE SIGNS LIST 
       100 ,  200 ,  300 : superconducting magnet;  110 : superconducting coil;  120 : helium tank;  130 : radiation shield;  140 : vacuum vessel;  150 : liquid helium;  160 : connector;  161 : connection terminal;  162 : electrical insulating portion;  163 : main body;  170 : external power supply;  171 : lead;  171   a : connection portion;  180 ,  280 ,  380 : thermal conductive member;  181 ,  381 : first thermal conductive member;  182 ,  382 : second thermal conductive member;  190 : exhaust pipe;  190   a : port;  191 : valve;  370 : heating portion.