Patent Publication Number: US-2022215993-A1

Title: Superconducting coil and method of manufacturing the same

Description:
TECHNICAL FIELD 
     The present invention relates to a superconducting coil and a method of manufacturing the superconducting coil. 
     BACKGROUND ART 
     Japanese Patent Laying-Open No. 02-211608 (PTL 1) discloses a support structure for a superconducting coil. The support structure for a superconducting coil disclosed in PTL 1 is configured as a magnetic support structure for a set of magnet coils made of a solenoid magnet. The support structure includes a set of support rings, attachment means, and a plurality of sets of support pillars. The set of support rings include at least two support rings that are spaced apart from each other along an axis of a through hole of a magnet. Each of the support rings is disposed coaxially with the axis of the through hole of the magnet. Through the attachment means, at least one magnet coil of the set of magnet coils is attached to the inside of each support ring of the set of support rings to be coaxial with the axis of the through hole of the magnet. 
     The above-mentioned support structure for a superconducting coil receives each magnet coil on a radially inner surface of a support ring located at one end. The radially inner surface has a diameter sized such that a magnet coil can be readily inserted into the support ring at one end when this support ring at one end and the magnet coil are at a room temperature. When the magnet coil and the support ring at one end are cooled to a superconducting temperature, the expansion coefficient of aluminum in the support ring at one end is greater than the expansion coefficients of epoxy and the wire of the magnet coil, so that the magnet coil is compressed and securely held by the support ring at one end. The compressive stress generated by the support ring at one end helps the coil to withstand large hoop stress caused by the self-repulsive force occurring inside the magnet coil when it is excited. 
     CITATION LIST 
     Patent Literature 
     PTL 1: Japanese Patent Laying-Open No. 02-211608 
     SUMMARY OF INVENTION 
     Technical Problem 
     According to the superconducting coil disclosed in PTL 1, when the superconducting coil is cooled, an outer frame portion having a coefficient of thermal expansion higher than that of a disk-shaped winding is greatly contracted, so that the outer frame portion holds the disk-shaped winding. When the superconducting coil is cooled, however, the pressure from the contracted outer frame portion causes thermal stress in the disk-shaped winding. This thermal stress may deform the disk-shaped winding, thereby damaging the superconducting coil. 
     The present invention has been made in light of the above-described problems, and aims to provide a method of manufacturing a superconducting coil, by which damage caused by deformation of a disk-shaped winding can be suppressed. 
     Solution to Problem 
     A method of manufacturing a superconducting coil according to the present invention includes: winding a superconducting wire around a rod-shaped jig to form a plurality of disk-shaped windings to be coaxially arranged; removing the rod-shaped jig from the disk-shaped windings; measuring a distance from a winding central axis to an outer circumferential surface of each of the disk-shaped windings, the winding central axis being a central axis of an inner circumferential surface of each of the disk-shaped windings; forming an outer frame portion including a plurality of ring-shaped fixing portions that each have a recessed groove portion extending in a circumferential direction on an inner circumferential side, the ring-shaped fixing portions being coaxially arranged; measuring a shape of a bottom surface of the recessed groove portion of each of the ring-shaped fixing portions; aligning a central axis of an entirety of the ring-shaped fixing portions based on measurement of the shape of the bottom surface; inserting each of the disk-shaped windings into the recessed groove portion of a corresponding one of the ring-shaped fixing portions; fixing the disk-shaped windings in a direction along the winding central axis; and bringing the outer circumferential surface of each of the disk-shaped windings into direct or indirect contact with the bottom surface of the recessed groove portion of the corresponding one of the ring-shaped fixing portions. In inserting each of the disk-shaped windings into the recessed groove portion of a corresponding one of the ring-shaped fixing portions, each of the disk-shaped windings is inserted in a state where the outer circumferential surface of each of the disk-shaped windings is spaced apart from the bottom surface of the recessed groove portion of the corresponding one of the ring-shaped fixing portions, based on: a result of measurement of a distance from the winding central axis to the outer circumferential surface of each of the disk-shaped windings; and a result of alignment of the central axis of the entirety of the ring-shaped fixing portions. In fixing the disk-shaped windings in a direction along the winding central axis, the disk-shaped windings are fixed by disposing a first adjustment member between one side surface of the recessed groove portion of each of the ring-shaped fixing portions and a corresponding one of the disk-shaped windings. In bringing the outer circumferential surface of each of the disk-shaped windings into direct or indirect contact with the bottom surface of the recessed groove portion of the corresponding one of the ring-shaped fixing portions, contact is made by cooling and contracting each of the disk-shaped windings and the outer frame portion. 
     Advantageous Effects of Invention 
     The present invention can reduce the thermal stress generated in each of the plurality of disk-shaped windings by pressure received from each of the plurality of ring-shaped fixing portions when the outer frame portion including the plurality of ring-shaped fixing portions is cooled and contracted. This can suppress damage to the superconducting coil caused by deformation of the plurality of disk-shaped windings. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a perspective view showing a configuration of a superconducting coil according to a first embodiment of the present invention. 
         FIG. 2  is a partial cross-sectional view showing a plurality of disk-shaped windings during measurement of a distance from a winding central axis to an outer circumferential surface, in the method of manufacturing a superconducting coil according to the first embodiment of the present invention. 
         FIG. 3  is a partial cross-sectional view showing an outer frame portion during alignment of a central axis of the entirety of a plurality of ring-shaped fixing portions of the outer frame portion, in the method of manufacturing a superconducting coil according to the first embodiment of the present invention. 
         FIG. 4  is a cross-sectional view of the outer frame portion shown in  FIG. 3  as viewed in a direction of an arrow along a line IV-IV. 
         FIG. 5  is a partial cross-sectional view showing a state where one of the plurality of disk-shaped windings is inserted into a recessed groove portion of a corresponding one of the plurality of ring-shaped fixing portions, in the method of manufacturing a superconducting coil according to the first embodiment of the present invention. 
         FIG. 6  is a partial cross-sectional view showing a configuration of a superconducting coil according to a second embodiment of the present invention. 
         FIG. 7  is a partial cross-sectional view showing a state where one of a plurality of disk-shaped windings is inserted into a recessed groove portion of a corresponding one of a plurality of ring-shaped fixing portions, in a method of manufacturing a superconducting coil according to the second embodiment of the present invention. 
         FIG. 8  is a partial cross-sectional view showing a configuration of a superconducting coil according to a first modification of the second embodiment of the present invention. 
         FIG. 9  is a partial cross-sectional view showing a state where one of a plurality of disk-shaped windings is inserted into a recessed groove portion of a corresponding one of a plurality of ring-shaped fixing portions, in a method of manufacturing a superconducting coil according to the first modification of the second embodiment of the present invention. 
         FIG. 10  is a partial cross-sectional view showing a configuration of a superconducting coil according to a third embodiment of the present invention. 
         FIG. 11  is a partial cross-sectional view showing a state where one of a plurality of disk-shaped windings is inserted into a recessed groove portion of a corresponding one of a plurality of ring-shaped fixing portions, in a method of manufacturing a superconducting coil according to the third embodiment of the present invention. 
         FIG. 12  is a diagram showing a relative positional relation between: a plurality of disk-shaped windings during measurement of a distance from a winding central axis to an outer circumferential surface; and an outer frame portion during alignment of a central axis of the entirety of a plurality of ring-shaped fixing portions, in a method of manufacturing a superconducting coil according to a fourth embodiment of the present invention. 
         FIG. 13  is a diagram showing a state immediately before the plurality of disk-shaped windings are inserted into respective recessed groove portions, in the method of manufacturing a superconducting coil according to the fourth embodiment of the present invention. 
         FIG. 14  is a diagram showing a state immediately after the plurality of disk-shaped windings are inserted into respective recessed groove portions, in the method of manufacturing a superconducting coil according to the fourth embodiment of the present invention. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     In the following, a superconducting coil according to each of embodiments of the present invention will be described with reference to the accompanying drawings. In the following description of each of the embodiments, the same or corresponding components in the accompanying drawings will be denoted by the same reference characters, and the description thereof will not be repeated. 
     First Embodiment 
       FIG. 1  is a perspective view showing a configuration of a superconducting coil according to a first embodiment of the present invention.  FIG. 1  schematically shows the superconducting coil that is partially cut away. 
     As shown in  FIG. 1 , a superconducting coil  100  according to the first embodiment of the present invention includes a plurality of disk-shaped windings  110 , an outer frame portion  120 , and refrigerant (not shown). 
     In the present embodiment, each of the plurality of disk-shaped windings  110  and outer frame portion  120  are accommodated in a refrigerant container (not shown) while being immersed in refrigerant. In other words, the refrigerant cools the plurality of disk-shaped windings  110  and outer frame portion  120 . In the present embodiment, the type of refrigerant is not particularly limited. The refrigerant is liquid helium or liquid nitrogen, for example. 
     Each of the plurality of disk-shaped windings  110  is configured, for example, by winding a superconducting wire formed by embedding a niobium titanium alloy in a central portion of a matrix made of copper. In the present embodiment, a winding frame is not located on the inner circumferential surface of each of the plurality of disk-shaped windings  110 . 
     The plurality of disk-shaped windings  110  are coaxially arranged. Specifically, the central axis of the inner circumferential surface of each of the plurality of disk-shaped windings  110  is located on a winding central axis Cc. The plurality of disk-shaped windings  110  are spaced apart from each other in the direction along winding central axis Cc. The plurality of disk-shaped windings  110  are electrically connected to each other. 
     Superconducting coil  100  according to the first embodiment of the present invention further includes two outermost disk-shaped windings  111 . Each of these two outermost disk-shaped windings  111  is configured by winding a superconducting wire similar to the superconducting wire that forms each of the plurality of disk-shaped windings  110 . Each of two outermost disk-shaped windings  111  is arranged coaxially with each of the plurality of disk-shaped windings  110 . These two outermost disk-shaped windings  111  are located so as to sandwich the plurality of disk-shaped windings  110  in the direction along winding central axis Cc. Each of two outermost disk-shaped windings  111  is electrically connected to the plurality of disk-shaped windings  110 . Each of two outermost disk-shaped windings  111  is also accommodated in the refrigerant container while being immersed in the refrigerant. 
     Outer frame portion  120  fixes each of the plurality of disk-shaped windings  110 . Outer frame portion  120  includes a plurality of ring-shaped fixing portions  121 . Specifically, each of the plurality of ring-shaped fixing portions  121  fixes a corresponding one of the plurality of disk-shaped windings  110 . 
     Each of the plurality of ring-shaped fixing portions  121  has a recessed groove portion  122  extending in the circumferential direction on the inner circumferential side. Also, the plurality of ring-shaped fixing portions  121  are arranged coaxially with each other. In the present embodiment, the plurality of ring-shaped fixing portions  121  are formed of a single piece member. In other words, the plurality of ring-shaped fixing portions  121  are contiguous to each other in the direction along a central axis Cf of the entirety of the plurality of ring-shaped fixing portions  121 . The plurality of ring-shaped fixing portions  121  may be spaced apart from each other in the direction along central axis Cf. 
     Each of the plurality of disk-shaped windings  110  is inserted into recessed groove portion  122  of a corresponding one of the plurality of ring-shaped fixing portions  121 . An outer circumferential surface  112  of each of the plurality of disk-shaped windings  110  is in direct or indirect contact with a bottom surface  124  of recessed groove portion  122  of a corresponding one of the plurality of ring-shaped fixing portions  121 . In the present embodiment, outer circumferential surface  112  of each of the plurality of disk-shaped windings  110  is in direct contact with bottom surface  124  of recessed groove portion  122  of a corresponding one of the plurality of ring-shaped fixing portions  121 . 
     Outer frame portion  120  further includes two outermost ring-shaped fixing portions  123 . These two outermost ring-shaped fixing portions are located so as to sandwich the plurality of ring-shaped fixing portions  121  in the direction along central axis Cf. Each of two outermost ring-shaped fixing portions  123  supports a corresponding one of two outermost disk-shaped windings  111  on the inner circumferential surface side. 
     Outer frame portion  120  is formed by joining a plurality of members to each other in a circumferential direction around central axis Cf when viewed in the direction along central axis Cf of the entirety of the plurality of ring-shaped fixing portions  121 . Thus, outer frame portion  120  has a plurality of joint surfaces  127  extending in the direction along central axis Cf. In the present embodiment, outer frame portion  120  is formed by joining four members, which have substantially the same shape, to each other in the circumferential direction around central axis Cf. In the embodiment of the present invention, the members constituting outer frame portion  120  are joined to each other with fastening members such as bolts. 
     In the present embodiment, outer frame portion  120  is made of aluminum for the purpose of reducing the weight of superconducting coil  100 . Aluminum is higher in coefficient of thermal expansion than copper that is a main component of the material forming the plurality of disk-shaped windings  110  in the present embodiment. In the present embodiment, the material forming outer frame portion  120  is not limited to aluminum as long as it is higher in coefficient of thermal expansion than copper that is a main component of the material forming outer frame portion  120 . 
     A first adjustment member  130  is located between one side surface  125  of recessed groove portion  122  of each of the plurality of ring-shaped fixing portions  121  and a corresponding one of the plurality of disk-shaped windings  110 . In other words, superconducting coil  100  further includes a plurality of first adjustment members  130 . 
     Each of the plurality of first adjustment members  130  is a plate-like member having an annular outer shape when viewed in the direction along winding central axis Cc. Each of the plurality of first adjustment members  130  is located coaxially with the plurality of disk-shaped windings  110  in the direction along winding central axis Cc. 
     In the present embodiment, each of the plurality of first adjustment members  130  is formed by joining a plurality of members in the circumferential direction around winding central axis Cc. Each of the plurality of first adjustment members  130  may be formed of a single member. 
     In the present embodiment, first adjustment member  130  is made of metal, for example. From the viewpoint of the coefficient of thermal expansion, first adjustment member  130  may be made of aluminum similar to the material forming outer frame portion  120 , or may be made of copper that is a main component of the material forming a superconducting wire. 
     In the present embodiment, the other side surface  126  of recessed groove portion  122  of each of the plurality of ring-shaped fixing portions  121  is in direct contact with a corresponding one of the plurality of disk-shaped windings  110 . The other side surface  126  is located opposite to one side surface  125 . 
     The following describes a method of manufacturing superconducting coil  100  according to the first embodiment of the present invention. In the method of manufacturing superconducting coil  100  according to the first embodiment of the present invention, first, a superconducting wire is wound around a rod-shaped jig. After winding the superconducting wire around the rod-shaped jig, the superconducting wire is subjected to finishing. Thereby, the plurality of disk-shaped windings  110  as shown in  FIG. 1  are formed. Then, the rod-shaped jig is removed from the plurality of disk-shaped windings  110 . The rod-shaped jig is a mandrel, for example. 
       FIG. 2  is a partial cross-sectional view showing a plurality of disk-shaped windings during measurement of a distance from the winding central axis to the outer circumferential surface, in the method of manufacturing a superconducting coil according to the first embodiment of the present invention.  FIG. 2  shows a partial cross section of the plurality of disk-shaped windings  110 , which is taken along a plane including a winding central axis as will be described later. 
     As shown in  FIG. 2 , a distance Ro from winding central axis Cc as a central axis of the inner circumferential surface of each of the plurality of disk-shaped windings  110  to outer circumferential surface  112  of a corresponding one of the plurality of disk-shaped windings  110  is measured. In other words, the outer shape of each of the plurality of disk-shaped windings  110  viewed in the direction along winding central axis Cc is measured. It should be noted that the length of a distance Ri from winding central axis Cc to the inner circumferential surface of each of the plurality of disk-shaped windings  110  is the same as the length of the outer diameter of the rod-shaped jig. Thus, distances Ri from winding central axis Cc to the inner circumferential surfaces of the plurality of disk-shaped windings  110  are substantially the same among the plurality of disk-shaped windings  110 . 
     In the method of manufacturing superconducting coil  100  according to the present embodiment, the plurality of disk-shaped windings  110  are formed, and outer frame portion  120  is formed. In the present embodiment, outer frame portion  120  may be formed before the plurality of disk-shaped windings  110  are formed, or outer frame portion  120  may be formed after the plurality of disk-shaped windings  110  are formed. 
       FIG. 3  is a partial cross-sectional view showing an outer frame portion during alignment of a central axis of the entirety of a plurality of ring-shaped fixing portions of the outer frame portion, in the method of manufacturing a superconducting coil according to the first embodiment of the present invention.  FIG. 4  is a cross-sectional view of the outer frame portion shown in  FIG. 3  as viewed in a direction of an arrow along a line IV-IV.  FIG. 3  illustrates a part of joint surface  127  of outer frame portion  120 . 
     As shown in  FIGS. 3 and 4 , after outer frame portion  120  is formed, the shape of bottom surface  124  of recessed groove portion  122  of each of the plurality of ring-shaped fixing portions  121  is measured. Then, based on measurement of the shape of bottom surface  124 , central axis Cf of the entirety of the plurality of ring-shaped fixing portions  121  is aligned. Specifically, alignment is performed such that the length of distance Rf from bottom surface  124  of recessed groove portion  122  of each of the plurality of ring-shaped fixing portions  121  to central axis Cf of the entirety of the plurality of ring-shaped fixing portions  121  is close to a fixed value at any point in one ring-shaped fixing portion  121 . At the same time, central axis Cf of the entirety of the plurality of ring-shaped fixing portions  121  is aligned such that the lengths of distances Rf are close to each other among the plurality of ring-shaped fixing portions  121 . Such alignment eliminates a need for high dimensional accuracy in formation of outer frame portion  120 . 
       FIG. 5  is a partial cross-sectional view showing a state where one of the plurality of disk-shaped windings is inserted into a recessed groove portion of a corresponding one of the plurality of ring-shaped fixing portions, in the method of manufacturing a superconducting coil according to the first embodiment of the present invention.  FIG. 5  partially shows the plurality of disk-shaped windings  110  and outer frame portion  120  on a plane including a joint surface of outer frame portion  120 . 
     As shown in  FIG. 5 , each of the plurality of disk-shaped windings  110  is then inserted into recessed groove portion  122  of a corresponding one of the plurality of ring-shaped fixing portions  121 . In this case, each of the plurality of disk-shaped windings  110  is inserted in the state where outer circumferential surface  112  of each of the plurality of disk-shaped windings  110  is spaced apart from bottom surface  124  of recessed groove portion  122  of a corresponding one of the plurality of ring-shaped fixing portions  121  as shown in  FIG. 5 , based on: the result of measurement of distance Ro from winding central axis Cc to outer circumferential surface  112  of each of the plurality of disk-shaped windings  110  as shown in  FIG. 2 ; and the result of alignment of central axis Cf of the entirety of the plurality of ring-shaped fixing portions  121  as shown in  FIG. 3 . 
     The step of inserting each of the plurality of disk-shaped windings  110  is performed at a room temperature. Further, in the step of inserting each of the plurality of disk-shaped windings  110 , each of the plurality of disk-shaped windings  110  is inserted in the state where outer frame portion  120  is divided into a plurality of constituting members. After each of the plurality of disk-shaped windings  110  is inserted, the plurality of members for constituting outer frame portion  120  are joined to each other. 
     As shown in  FIG. 5 , when each of the plurality of disk-shaped windings  110  is inserted into recessed groove portion  122  of a corresponding one of the plurality of ring-shaped fixing portions  121 , a gap S exists between outer circumferential surface  112  of disk-shaped winding  110  and bottom surface  124  of recessed groove portion  122 . The size of gap S will be described later. 
     Before the plurality of disk-shaped windings  110  are inserted into respective recessed groove portions  122 , the relative position of central axis Cf of the entirety of the plurality of ring-shaped fixing portions  121  with respect to winding central axis Cc is determined based on: the result of measurement of distance Ro from winding central axis Cc to outer circumferential surface  112  of each of the plurality of disk-shaped windings  110  as shown in  FIG. 2 ; and the result of alignment of central axis Cf of the entirety of the plurality of ring-shaped fixing portions  121  as shown in  FIG. 3 . In this case, from the viewpoint of simplification of the method of manufacturing superconducting coil  100 , it is preferable to insert the plurality of disk-shaped windings  110  into respective recessed groove portions  122  such that winding central axis Cc is aligned with central axis Cf of the entirety of the plurality of ring-shaped fixing portions  121 . 
     In the present embodiment, as shown in  FIGS. 2 and 5 , the plurality of disk-shaped windings  110  are fixed at a room temperature in the direction along winding central axis Cc. In this case, the plurality of disk-shaped windings  110  are fixed by disposing first adjustment member  130  between one side surface  125  of recessed groove portion  122  of each of the plurality of ring-shaped fixing portions  121  and a corresponding one of the plurality of disk-shaped windings  110 . 
     Then, each of the plurality of disk-shaped windings  110  and outer frame portion  120  are cooled and contracted, to thereby bring outer circumferential surface  112  of each of the plurality of disk-shaped windings  110  into direct or indirect contact with bottom surface  124  of recessed groove portion  122  of a corresponding one of the plurality of ring-shaped fixing portions  121 . Specifically, after the plurality of disk-shaped windings  110  and outer frame portion  120  are accommodated in the refrigerant container, the refrigerant container is filled with refrigerant. Thereby, the plurality of disk-shaped windings  110  and outer frame portion  120  are immersed in the refrigerant. 
     In the present embodiment, outer frame portion  120  is higher in coefficient of thermal expansion than the plurality of disk-shaped windings  110 . Thus, during the above-mentioned cooling, the contraction rate of distance Rf between bottom surface  124  and central axis Cf of the entirety of the plurality of ring-shaped fixing portions  121  as shown in  FIGS. 3 and 4  is greater than the contraction rate of distance Ro from winding central axis Cc to outer circumferential surface  112  of each of the plurality of disk-shaped windings  110  as shown in  FIG. 2 . Thereby, as shown in  FIG. 1 , outer circumferential surface  112  of each of the plurality of disk-shaped windings  110  can be brought into direct or indirect contact with bottom surface  124  of recessed groove portion  122  of a corresponding one of the plurality of ring-shaped fixing portions  121 . Consequently, each of the plurality of disk-shaped windings  110  can be fixed in the radial direction. 
     Further, in the present embodiment, the size of gap S shown in  FIG. 5  is adjusted in consideration of the coefficient of thermal expansion of each of disk-shaped windings  110  and the coefficient of thermal expansion of outer frame portion  120 , so as to allow suppression of thermal stress generated in each disk-shaped winding  110  by tightening of the plurality of disk-shaped windings  110  from the outer circumferential side with outer frame portion  120  when the plurality of disk-shaped windings  110  and outer frame portion  120  are cooled. Specifically, the size of gap S is adjusted such that the length of distance Ro shown in  FIG. 2  and the length of distance Rf shown in  FIG. 3  become substantially equal to each other due to the above-mentioned cooling. By adjusting the size of gap S in this way, outer circumferential surface  112  of each of the plurality of disk-shaped windings  110  can be brought into contact with bottom surface  124  of recessed groove portion  122  of a corresponding one of the plurality of ring-shaped fixing portions  121 , and also, the pressure applied to the plurality of disk-shaped windings by outer frame portion  120  can be reduced. In other words, the above-mentioned thermal stress can be reduced. 
     Through the above-described steps, superconducting coil  100  according to the first embodiment of the present invention shown in  FIG. 1  is manufactured. 
     As described above, the method of manufacturing superconducting coil  100  according to the first embodiment of the present invention includes: the step of measuring distance Ro from winding central axis Cc as the central axis of the inner circumferential surface of each of the plurality of disk-shaped windings  110  to outer circumferential surface  112  of a corresponding one of the plurality of disk-shaped windings  110 ; the step of measuring the shape of bottom surface  124  of recessed groove portion  122  of each of the plurality of ring-shaped fixing portions  121 ; the step of aligning central axis Cf of the entirety of the plurality of ring-shaped fixing portions  121  based on measurement of the shape of bottom surface  124 ; the step of inserting each of the plurality of disk-shaped windings  110  into recessed groove portion  122  of a corresponding one of the plurality of ring-shaped fixing portions  121 ; the step of fixing the plurality of disk-shaped windings  110  in the direction along winding central axis Cc; and the step of bringing outer circumferential surface  112  of each of the plurality of disk-shaped windings  110  into direct or indirect contact with bottom surface  124  of recessed groove portion  122  of a corresponding one of the plurality of ring-shaped fixing portions  121 . In the step of inserting each of the plurality of disk-shaped windings  110  into recessed groove portion  122  of a corresponding one of the plurality of ring-shaped fixing portions  121 , each of the plurality of disk-shaped windings  110  is inserted in the state where outer circumferential surface  112  of each of the plurality of disk-shaped windings  110  is spaced apart from bottom surface  124  of recessed groove portion  122  of a corresponding one of the plurality of ring-shaped fixing portions  121 , based on: the result of measurement of distance Ro from winding central axis Cc to outer circumferential surface  112  of each of the plurality of disk-shaped windings  110 ; and the result of alignment of central axis Cf of the entirety of the plurality of ring-shaped fixing portions  121 . In the step of fixing the plurality of disk-shaped windings  110  in the direction along winding central axis Cc, the plurality of disk-shaped windings  110  are fixed by disposing first adjustment member  130  between one side surface  125  of recessed groove portion  122  of each of the plurality of ring-shaped fixing portions  121  and a corresponding one of the plurality of disk-shaped windings  110 . In the step of bringing outer circumferential surface  112  of each of the plurality of disk-shaped windings  110  into direct or indirect contact with bottom surface  124  of recessed groove portion  122  of a corresponding one of the plurality of ring-shaped fixing portions  121 , each of the plurality of disk-shaped windings  110  and outer frame portion  120  are cooled and contracted for contact. 
     Thereby, the thermal stress can be reduced that occurs in each of the plurality of disk-shaped windings  110  due to the pressure received from each of the plurality of ring-shaped fixing portions  121  when outer frame portion  120  including the plurality of ring-shaped fixing portions  121  is cooled and contracted. Thereby, damage to superconducting coil  100  caused by deformation of the plurality of disk-shaped windings  110  can be suppressed. 
     Further, in superconducting coil  100  according to the first embodiment of the present invention, first adjustment member  130  is located between one side surface  125  of recessed groove portion  122  of each of the plurality of ring-shaped fixing portions  121  and a corresponding one of the plurality of disk-shaped windings  110 . 
     Thus, when superconducting coil  100  is manufactured, outer circumferential surface  112  of each of the plurality of disk-shaped windings  110  can be kept at a distance from bottom surface  124  of recessed groove portion  122  of a corresponding one of the plurality of ring-shaped fixing portions  121 . Therefore, superconducting coil  100  can be manufactured by the above-described manufacturing method, and damage to superconducting coil  100  caused by deformation of disk-shaped windings  110  can also be suppressed. 
     Second Embodiment 
     The following describes a superconducting coil according to the second embodiment of the present invention. The superconducting coil according to the second embodiment of the present invention is different from superconducting coil  100  according to the first embodiment of the present invention shown in  FIG. 1  only in the configuration between bottom surface  124  of each of the plurality of ring-shaped fixing portions  121  and outer circumferential surface  112  of a corresponding one of the plurality of disk-shaped windings  110 . Thus, the description of the same configurations as those of superconducting coil  100  according to the first embodiment of the present invention will not be repeated. 
       FIG. 6  is a partial cross-sectional view showing a configuration of a superconducting coil according to the second embodiment of the present invention.  FIG. 7  is a partial cross-sectional view showing a state where one of a plurality of disk-shaped windings is inserted into a recessed groove portion of a corresponding one of a plurality of ring-shaped fixing portions, in a method of manufacturing a superconducting coil according to the second embodiment of the present invention.  FIGS. 6 and 7  each are shown in the same cross-sectional view as in  FIG. 5 . 
     As shown in  FIG. 6 , in a superconducting coil  200  according to the second embodiment of the present invention, a second adjustment member  240  is located between bottom surface  124  of at least one of the plurality of ring-shaped fixing portions  121  and outer circumferential surface  112  of at least one of the plurality of corresponding disk-shaped windings  110 . In other words, as shown in  FIG. 7 , the method of manufacturing superconducting coil  200  according to the second embodiment of the present invention further includes the step of disposing second adjustment member  240  at a room temperature between bottom surface  124  of at least one of the plurality of ring-shaped fixing portions  121  and outer circumferential surface  112  of at least one of the plurality of corresponding disk-shaped windings  110 . 
     Due to the above-described configuration, outer circumferential surface  112  can be brought into indirect contact with bottom surface  124  of recessed groove portion  122  by second adjustment member  240 , when outer circumferential surface  112  cannot be brought into direct contact with bottom surface  124  even by cooling the plurality of disk-shaped windings  110  and outer frame portion  120 . 
     In the present embodiment, second adjustment member  240  may be located between entire outer circumferential surface  112  of each of the plurality of disk-shaped windings  110  and bottom surface  124  of a corresponding one of recessed groove portions  122 . 
     The thickness of second adjustment member  240  is adjusted as appropriate based on: the result of measurement of distance Ro from winding central axis Cc to outer circumferential surface  112  of each of the plurality of disk-shaped windings  110  as shown in  FIG. 2 ; and the result of alignment of central axis Cf of the entirety of the plurality of ring-shaped fixing portions  121  as shown in  FIGS. 3 and 4 . As shown in  FIG. 7 , a gap S is formed between bottom surface  124  and outer circumferential surface  112  in the state where second adjustment member  240  is located therebetween. In this way, even when the length of distance Ro shown in  FIG. 2  is relatively short or the difference in length between distances Rf shown in  FIG. 3  is relatively long, the thickness of second adjustment member  240  shown in  FIG. 7  is adjusted as appropriate, and thereby, outer circumferential surface  112  and bottom surface  124  can be brought into indirect contact with each other as shown in  FIG. 6 . Further, even when there is a difference in distance Rf among the plurality of outer frame portions  120  after completion of these outer frame portions  120 , outer circumferential surface  112  and bottom surface  124  can be brought into indirect contact with each other by second adjustment member  240 . 
     Second adjustment member  240  is made of metal, for example. Second adjustment member  240  may be made of stainless steel. In light of the coefficient of thermal expansion, second adjustment member  240  may be made of aluminum similar to the material forming outer frame portion  120  or made of copper as a main component of the material forming the superconducting wire. 
     In the second embodiment of the present invention, second adjustment member  240  may be located along the entire surface in the circumferential direction on outer circumferential surface  112  of each of the plurality of disk-shaped windings  110 , or may be located along a partial surface in the circumferential direction on outer circumferential surface  112  of each of the plurality of disk-shaped windings  110 . 
     In the second embodiment of the present invention, the length of second adjustment member  240  in the direction along winding central axis Cc is the same as the length of recessed groove portion  122 . In the second embodiment of the present invention, the length of second adjustment member  240  in the direction along winding central axis Cc does not have to be the same as the length of recessed groove portion  122 . The following describes a modification in the case where the length of second adjustment member  240  in the direction along winding central axis Cc is not the same as the length of recessed groove portion  122 . 
       FIG. 8  is a partial cross-sectional view showing a configuration of a superconducting coil according to a first modification of the second embodiment of the present invention.  FIG. 9  is a partial cross-sectional view showing a state where one of a plurality of disk-shaped windings is inserted into a recessed groove portion of a corresponding one of a plurality of ring-shaped fixing portions, in a method of manufacturing a superconducting coil according to the first modification of the second embodiment of the present invention.  FIGS. 8 and 9  are shown in the same cross-sectional views as in  FIGS. 6 and 7 , respectively. 
     As shown in  FIG. 8 , in a superconducting coil  200   a  according to the second embodiment of the present invention, the length of a second adjustment member  240   a  in the direction along winding central axis Cc is shorter than the length of recessed groove portion  122 . As shown in  FIG. 9 , in the method of manufacturing superconducting coil  200   a  according to the second embodiment of the present invention, the length of second adjustment member  240   a  in the direction along winding central axis Cc is shorter than the length of recessed groove portion  122  when second adjustment member  240  is disposed at a room temperature. 
     Third Embodiment 
     The following describes a superconducting coil according to the third embodiment of the present invention. The superconducting coil according to the third embodiment of the present invention is different from superconducting coil  100  according to the first embodiment of the present invention shown in  FIG. 1  only in that a winding protection member is disposed in recessed groove portion  122  of each of the plurality of ring-shaped fixing portions  121 . Thus, the description of the same configurations as those of superconducting coil  100  according to the first embodiment of the present invention will not be repeated. 
       FIG. 10  is a partial cross-sectional view showing a configuration of a superconducting coil according to the third embodiment of the present invention.  FIG. 11  is a partial cross-sectional view showing a state where one of a plurality of disk-shaped windings is inserted into a recessed groove portion of a corresponding one of a plurality of ring-shaped fixing portions, in a method of manufacturing a superconducting coil according to the third embodiment of the present invention.  FIGS. 10 and 11  each are shown in the same cross-sectional view as in  FIG. 5 . 
     As shown in  FIG. 10 , in a superconducting coil  300  according to the third embodiment of the present invention, a first winding protection member  350  is located between first adjustment member  130  and each of the plurality of disk-shaped windings  110 . Further, a second winding protection member  360  is located between each of the plurality of disk-shaped windings  110  and the other side surface  126  of recessed groove portion  122  of a corresponding one of the plurality of ring-shaped fixing portions  121 . The other side surface  126  is located opposite to one side surface  125 . In other words, as shown in  FIG. 11 , in the method of manufacturing superconducting coil  300  according to the third embodiment of the present invention, first winding protection member  350  is disposed at a room temperature between first adjustment member  130  and each of the plurality of disk-shaped windings  110 . Also, second winding protection member  360  is disposed between each of the plurality of disk-shaped windings  110  and the other side surface  126  of recessed groove portion  122  of a corresponding one of the plurality of ring-shaped fixing portions  121 , the other side surface  126  being located opposite to one side surface  125 . 
     In the third embodiment of the present invention, disposing first winding protection member  350  and second winding protection member  360  as described above can suppress damage to each of the plurality of disk-shaped windings  110  caused by friction against other members when outer frame portion  120  is contracted by cooling more greatly than the plurality of disk-shaped windings  110 . 
     As shown in  FIG. 10 , each of first winding protection member  350  and second winding protection member  360  is made, for example, of an insulating material, and specifically made of glass epoxy. Further, each of first winding protection member  350  and second winding protection member  360  has an annular outer shape along the plurality of disk-shaped windings  110  when viewed in the direction along winding central axis Cc. 
     As shown in  FIG. 11 , when first winding protection member  350  and second winding protection member  360  are disposed, first winding protection member  350  and second winding protection member  360  each are spaced apart from bottom surface  124  of recessed groove portion  122  in a corresponding one of the plurality of ring-shaped fixing portions  121 . Specifically, first winding protection member  350  and second winding protection member  360  are disposed such that their outer circumferential surfaces are located flush with outer circumferential surface  112  of a corresponding disk-shaped winding  110  among the plurality of disk-shaped windings  110 . 
     Fourth Embodiment 
     The following describes a method of manufacturing a superconducting coil according to the fourth embodiment of the present invention. The method of manufacturing a superconducting coil according to the fourth embodiment of the present invention is different from the method of manufacturing superconducting coil  100  according to the first embodiment of the present invention mainly in the order of steps. Thus, the description of the same configurations as those of the method of manufacturing superconducting coil  100  according to the first embodiment of the present invention will not be repeated. The superconducting coil manufactured by the method of manufacturing a superconducting coil according to the fourth embodiment of the present invention has the same configuration as that of superconducting coil  100  according to the first embodiment of the present invention. 
       FIG. 12  is a diagram showing a relative positional relation between: a plurality of disk-shaped windings during measurement of a distance from a winding central axis to an outer circumferential surface; and an outer frame portion during alignment of a central axis of the entirety of a plurality of ring-shaped fixing portions, in a method of manufacturing a superconducting coil according to a fourth embodiment of the present invention.  FIG. 12  is shown in the same cross-sectional view as in  FIGS. 2 and 3 . 
     As shown in  FIG. 12 , in the fourth embodiment of the present invention, the plurality of disk-shaped windings  110  are configured in the state where a superconducting wire is wound around a rod-shaped jig  10  when the distance from winding central axis Cc to outer circumferential surface  112  is measured. 
     In the present embodiment, rod-shaped jig  10  has a circular outer shape through which winding central axis Cc extends as a central axis when viewed in the direction along winding central axis Cc. The length of an outer diameter Rm when viewing rod-shaped jig  10  in the direction along winding central axis Cc can be changed as appropriate. 
     Rod-shaped jig  10  is configured to be conveyable such that central axis Cf of the entirety of the plurality of ring-shaped fixing portions  121  is located on a trajectory drawn by the central axis of rod-shaped jig  10  during conveyance of rod-shaped jig  10 . In other words, in the fourth embodiment of the present invention, central axis Cf of the entirety of the plurality of ring-shaped fixing portions  121  is located on the trajectory along which winding central axis Cc can move. In the fourth embodiment of the present invention, central axis Cf is aligned by adjusting the relative position of outer frame portion  120  with respect to central axis Cf of the entirety of the plurality of ring-shaped fixing portions  121  that are fixed. 
     As shown in  FIG. 12 , when distance Ro from winding central axis Cc to outer circumferential surface  112  is measured, outer diameter Rm of rod-shaped jig  10  is the same as distance Ri from winding central axis Cc to the inner circumferential surface of each of the plurality of disk-shaped windings  110 . 
       FIG. 13  is a diagram showing a state immediately before the plurality of disk-shaped windings are inserted into respective recessed groove portions, in the method of manufacturing a superconducting coil according to the fourth embodiment of the present invention. 
     As shown in  FIG. 13 , immediately before the plurality of disk-shaped windings  110  are inserted into respective recessed groove portions  122  after measurement of distance Ro and alignment of central axis Cf, outer frame portion  120  is divided into a plurality of members, which constitute outer frame portion  120 , in the state where the position of central axis Cf of the entirety of the plurality of ring-shaped fixing portions  121  is defined. On the other hand, the plurality of disk-shaped windings  110  are conveyed together with rod-shaped jig  10  in the state where a superconducting wire is wound around rod-shaped jig  10 . Specifically, the plurality of disk-shaped windings  110  and rod-shaped jig  10  are conveyed to a region surrounded by a plurality of members constituting outer frame portion  120  that is in a divided state. 
       FIG. 14  is a diagram showing a state immediately after the plurality of disk-shaped windings are inserted into respective recessed groove portions, in the method of manufacturing a superconducting coil according to the fourth embodiment of the present invention. 
     As shown in  FIG. 14 , after conveyance of the plurality of disk-shaped windings  110  and rod-shaped jig  10 , each of the plurality of disk-shaped windings  110  is inserted into recessed groove portion  122  of a corresponding one of the plurality of ring-shaped fixing portions  121 . Then, rod-shaped jig  10  is removed from the plurality of disk-shaped windings  110 . 
     When each of the plurality of disk-shaped windings  110  is inserted into recessed groove portion  122  of a corresponding one of the plurality of ring-shaped fixing portions  121 , rod-shaped jig  10  is reduced in outer diameter Rm so as not to contact outer frame portion  120  or while contacting outer frame portion  120 . 
     As described above, in the method of manufacturing a superconducting coil according to the fourth embodiment of the present invention, the step of inserting each of the plurality of disk-shaped windings  110  into recessed groove portion  122  of a corresponding one of the plurality of ring-shaped fixing portions  121  is followed by the step of removing rod-shaped jig  10  from the plurality of disk-shaped windings  110 . Thereby, winding central axis Cc of disk-shaped windings  110  can be readily aligned with central axis Cf of the entirety of the plurality of ring-shaped fixing portions  121 . 
     In the description of the embodiments described above, configurations that can be combined may be combined with each other. 
     The above embodiments disclosed herein are illustrative in any respects and should not be construed as being restrictive. Therefore, the technical scope of the present invention is not interpreted only in view of the above-described embodiments, but is defined by the terms of the claims, and also, is intended to include any modifications within the meaning and scope equivalent to the terms of the claims. 
     REFERENCE SIGNS LIST 
       10  rod-shaped jig,  100 ,  200 ,  200   a ,  300  superconducting coil,  110  disk-shaped winding,  111  outermost disk-shaped winding,  112  outer circumferential surface,  120  outer frame portion,  121  ring-shaped fixing portion,  122  recessed groove portion,  123  outermost ring-shaped fixing portion,  124  bottom surface,  125  one side surface,  126  the other side surface,  127  joint surface,  130  first adjustment member,  240 ,  240   a  second adjustment member,  350  first winding protection member,  360  second winding protection member.