Patent Publication Number: US-2022230792-A1

Title: Superconducting magnet device

Description:
RELATED APPLICATIONS 
     The content of Japanese Patent Application No. 2021-005646, on the basis of which priority benefits are claimed in an accompanying application data sheet, is in its entirety incorporated herein by reference. 
     BACKGROUND 
     Technical Field 
     Certain embodiments relate to a superconducting magnet device. 
     Description of Related Art 
     Superconducting magnet devices are used as magnetic field generation sources of single crystal pulling devices by the magnetic field applied Czochralski (MCZ) method. A strong magnetic field generated by a superconducting magnet can suppress heat convection in the melt of a semiconductor material. A magnetic field distribution to be applied affects the degree of suppression of heat convection, and as a result, the oxygen concentration in the single crystal to be pulled changes. The desired oxygen concentration varies depending on the applications of semiconductor devices that are ultimately manufactured. Thus, in the related art, a single crystal pulling device is known in which the directions of currents flowing through some superconducting coils are switched in order to switch between two types of different magnetic field distributions. 
     SUMMARY 
     According to an embodiment of the present invention, there is provided a superconducting magnet device including a tubular cryostat that defines a central cavity therein, a first superconducting coil set and a second superconducting coil set that are disposed outside the central cavity and inside the tubular cryostat, and a power supply system that is capable of controlling a magnitude of a first exciting current to the first superconducting coil set and a magnitude of a second exciting current to the second superconducting coil set independently of each other. When a center axis of the tubular cryostat is defined as a Z axis and two axes perpendicular to the Z axis and perpendicular to each other are defined as an X axis and a Y axis, respectively, the first superconducting coil set generates a magnetic field distribution, which is convex downward on the X axis and convex upward on the Y axis when the first exciting current is supplied, in the central cavity, and the second superconducting coil set generates a magnetic field distribution, which is convex upward on the X axis and convex downward on the Y axis when the second exciting current is supplied, in the central cavity. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a sectional view schematically showing main parts of a superconducting magnet device according to an embodiment. 
         FIG. 2  is a perspective view schematically showing the disposition of a superconducting coil provided in the superconducting magnet device shown in  FIG. 1 . 
         FIG. 3A  to  FIG. 3C  are diagrams schematically showing magnetic field distributions generated by the superconducting magnet device according to the embodiment. 
         FIG. 4A  and  FIG. 4B  are graphs illustrating a magnetic field distribution in which the magnetic fields generated by a first superconducting coil set and a second superconducting coil set overlap each other. 
         FIG. 5  is a diagram schematically showing an example of a coil power supply circuit of the superconducting magnet device shown in  FIG. 1 . 
         FIG. 6  is a graph showing an example of a contour diagram of a magnetic field generated by the superconducting magnet device according to the embodiment, with a first exciting current and a second exciting current as the horizontal axis and the vertical axis, respectively. 
         FIG. 7  is a perspective view schematically showing the appearance of the superconducting magnet device. 
         FIG. 8A  to  FIG. 8C  are schematic views illustrating the disposition location of a cryocooler in the superconducting magnet device shown in  FIG. 7 . 
         FIG. 9  is a sectional view schematically showing a coil supporting structure of the superconducting magnet device. 
         FIG. 10  is a perspective view schematically showing another example of the superconducting coil disposition in the superconducting magnet device according to the embodiment. 
     
    
    
     DETAILED DESCRIPTION 
     It is desirable to provide a superconducting magnet device capable of more finely controlling a magnetic field distribution to be generated. 
     In addition, optional combinations of the above constituent elements and those obtained by substituting the constituent elements or expressions of the present invention with each other among methods, devices, systems, and the like are also effective as embodiments of the present invention. 
     Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings. In the description and drawings, the same or equivalent components, members, and processing are designated by the same reference numerals, and redundant descriptions will be appropriately omitted. The scales and shapes of the respective parts shown in the figures are set for convenience in order to facilitate the description, and should not be interpreted as limiting unless otherwise specified. The embodiments are merely examples and do not limit the scope of the present invention. All the features and combinations described in the embodiments are not necessarily essential to the invention. 
       FIG. 1  is a sectional view schematically showing main parts of a superconducting magnet device  10  according to an embodiment. Additionally,  FIG. 2  is a perspective view schematically showing the disposition of a superconducting coil provided in the superconducting magnet device  10  shown in  FIG. 1 . 
     The superconducting magnet device  10  can be used as a magnetic field generation source for a single crystal pulling device by the horizontal magnetic field type MCZ (HMCZ; Horizontal-MCZ) method. The single crystal pulling device is, for example, a silicon single crystal pulling device. 
     As shown in  FIG. 1 , the superconducting magnet device  10  includes a tubular cryostat  20 , a first superconducting coil set  30 , a second superconducting coil set  40 , and a power supply system  50 . 
     The tubular cryostat  20  has an internal space isolated from a surrounding environment  22  surrounding the tubular cryostat  20 , and the first superconducting coil set  30  and the second superconducting coil set  40  are disposed in the internal space. The internal space has, for example, a donut shape or cylindrical shape. The tubular cryostat  20  is an adiabatic vacuum vessel, and during the operation of the superconducting magnet device  10 , a cryogenic vacuum environment suitable for bringing the first superconducting coil set  30  and the second superconducting coil set  40  into a superconductive state is provided in the internal space of the tubular cryostat  20 . The tubular cryostat  20  is formed of a metallic material such as stainless steel or other suitable high-strength material to withstand ambient pressure (for example, atmospheric pressure). 
     The tubular cryostat  20  defines a central cavity  24  inside. The first superconducting coil set  30  and the second superconducting coil set  40  are disposed to surround the central cavity  24  outside the central cavity  24 . When the superconducting magnet device  10  is mounted on the single crystal pulling device, a crucible for accommodating the melt of a single crystal material is disposed in the central cavity  24 . The central cavity  24  is a part of the surrounding environment  22  surrounding the tubular cryostat  20  (that is, outside the tubular cryostat  20 ), and is, for example, a columnar space surrounded by the tubular cryostat  20 . 
     In the following, for convenience of explanation, a Cartesian coordinate system will be considered in which a center axis of the tubular cryostat  20  is the Z axis and two axes perpendicular to the Z axis and perpendicular to each other are defined as an X axis and a Y axis, respectively. In the case of the single crystal pulling device, a crystal pulling axis corresponds to the Z axis, and the X axis and the Y axis can be defined on a melt surface perpendicular to the crystal pulling axis. In this case, a direction parallel to the magnetic field generated by the superconducting magnet device  10  at the center of the melt surface can be the X axis, and a direction perpendicular to the X axis can be the Y axis.  FIG. 1  shows a section of the superconducting magnet device  10  on an XY plane, and the Z axis extends in a direction perpendicular to the paper plane. 
     Although the details will be described below, the first superconducting coil set  30  generates a magnetic field distribution, which becomes convex downward on the X axis and convex upward on the Y axis when a first exciting current I 1  is supplied from the power supply system  50 , in the central cavity  24 . When a second exciting current I 2  is supplied from the power supply system  50 , the second superconducting coil set  40  generates a magnetic field distribution, which becomes convex upward on the X axis and convex downward on the Y axis, in the central cavity  24 . 
     The power supply system  50  is provided as a power supply for the first superconducting coil set  30  and the second superconducting coil set  40  and is disposed outside the tubular cryostat  20 . The power supply system  50  is configured so that a magnitude of the first exciting current I 1  to the first superconducting coil set  30  and a magnitude of the second exciting current I 2  to the second superconducting coil set  40  can be controlled independently of each other. 
       FIG. 3A  to  FIG. 3C  are diagrams schematically showing magnetic field distributions generated by the superconducting magnet device  10  according to the embodiment.  FIG. 3A  shows the lines of magnetic forces passing through the centers of the respective superconducting coils, which are indicated by arrows and represent the magnetic field distributions generated in the central cavity  24  by the first superconducting coil set  30  and the second superconducting coil set  40 , respectively.  FIG. 3B  shows magnetic flux densities on the X axis for the first superconducting coil set  30  and the second superconducting coil set  40 , respectively, and  FIG. 3C  shows magnetic flux densities on the Y axis for the first superconducting coil set  30  and the second superconducting coil set  40 , respectively. The horizontal axes of  FIG. 3B  and  FIG. 3C  indicate the distance from the origin of the XYZ coordinate system (in the case of the single crystal pulling device, the distance from the center of the melt surface). 
     The coil disposition of the first superconducting coil set  30  and the second superconducting coil set  40  and the magnetic field distributions to be generated will be described with reference to  FIG. 1 ,  FIG. 2 , and  FIG. 3A  to  FIG. 3C . 
     The superconducting magnet device  10  is provided with six superconducting coils, two of which form the first superconducting coil set  30  and the other four of which form the second superconducting coil set  40 . As shown in the figure, the respective superconducting coils of the first superconducting coil set  30  and the second superconducting coil set  40  have the same shape and the same size, and in this example, the superconducting coils are circular coils having the same diameter. Thus, the six superconducting coils are disposed in a regular hexagonal shape when viewed from above. 
     The first superconducting coil set  30  includes a pair of first superconducting coils  30   a  and  30   b  disposed to face each other on the X axis with the central cavity  24  interposed therebetween. The pair of first superconducting coils  30   a  and  30   b  are disposed such that each coil center axis coincides with the X axis. The direction of the first exciting current I 1  supplied to one first superconducting coil ( 30   a  in this example) is determined such that this superconducting coil generates a radially outward magnetic field (a magnetic field in the direction of exiting the central cavity  24  through the coil). The direction of the first exciting current I 1  supplied to the other first superconducting coil ( 30   b  in this example) is determined such that the superconducting coil generates a radially inward magnetic field (a magnetic field in the direction of entering the central cavity  24  through the coil). Thus, as shown in  FIG. 3A , the lines of magnetic forces passing through the centers of the first superconducting coils  30   a  and  30   b  extend linearly along the X axis. 
     A first magnetic field generated by the first superconducting coil set  30  is the strongest at the centers of the first superconducting coils  30   a  and  30   b  and becomes weaker toward the center of the central cavity  24  along the X axis from the centers (that is, moving away from the coil centers). Thus, as shown in  FIG. 3B , the first magnetic field generated by the first superconducting coil set  30  is convex downward on the X axis. 
     Additionally, as shown in  FIG. 3C , the first magnetic field generated by the first superconducting coil set  30  is convex upward on the Y axis. This is because the distances from the centers of the first superconducting coils  30   a  and  30   b  increase when the center of the central cavity  24  is outward along the Y axis, so that the first magnetic field generated by the first superconducting coil set  30  is strongest at the center of the central cavity  24  and becomes weaker moving outward from the center. 
     The second superconducting coil set  40  includes a pair of second superconducting coils  40   a  and  40   b  disposed to face each other with the central cavity  24  interposed therebetween and disposed adjacent to the pair of first superconducting coils  30   a  and  30   b  in a clockwise direction around the Z axis, and another pair of second superconducting coils  40   c  and  40   d  disposed to face each other with the central cavity  24  interposed therebetween and disposed adjacent to the pair of first superconducting coils  30   a  and  30   b  in a counterclockwise direction around the Z axis. In this embodiment, as shown in  FIG. 1 , the first pair of second superconducting coils  40   a  and  40   b  are disposed such that each coil center axis coincides with a line  42  forming 60 degrees from the X axis clockwise around the Z axis, and the second pair of second superconducting coils  40   c  and  40   d  are disposed such that each coil center axis coincides with a line  44  forming 60 degrees from the X axis counterclockwise around the Z axis. 
     The direction of the second exciting current I 2  supplied to the second superconducting coils ( 40   a  and  40   d  in this example) adjacent to both sides of the one first superconducting coil ( 30   a  in this example) that generates the radially outward magnetic field is determined such that these two second superconducting coils also generate the radially outward magnetic field. The direction of the second exciting current I 2  supplied to the second superconducting coils ( 40   b  and  40   c  in this example) adjacent to both sides of the other first superconducting coil ( 30   b  in this example) that generates the radially inward magnetic field is determined such that these two second superconducting coils also generate the radially inward magnetic field. For that reason, as shown in  FIG. 3A , the lines of magnetic forces passing through the centers of the two second superconducting coils ( 40   a  and  40   c , or  40   b  and  40   d ) adjacent to each other are curved to enter the central cavity  24  through one of the two second superconducting coils and to exit the central cavity  24  through the other second superconducting coil. 
     A second magnetic field generated by the second superconducting coil set  40  is the strongest in a curved magnetic field line passing through the coil center and becomes weaker moving outward from the coil center. Thus, the second magnetic field is relatively strong at the center of the central cavity  24  on the X axis and becomes weaker moving outward along the X axis from the center. That is, as shown in  FIG. 3B , the second magnetic field is convex upward on the X axis. Additionally, the second magnetic field is relatively weak at the center of the central cavity  24  on the Y axis and becomes stronger moving outward along the Y axis from the center. That is, as shown in  FIG. 3C , the second magnetic field is convex downward on the Y axis. 
       FIG. 4A  and  FIG. 4B  are graphs illustrating a magnetic field distribution in which the magnetic fields generated by the first superconducting coil set  30  and the second superconducting coil set  40  overlap each other.  FIG. 4A  shows a magnetic flux density on the X axis, and  FIG. 4B  shows a magnetic flux density on the Y axis. All of the densities are calculation results by the inventor. The vertical axis of the graph represents the magnetic flux density standardized with the magnetic flux density at the center of the central cavity  24  as  1 , and the horizontal axis represents the distance from the center of the central cavity  24 . 
       FIG. 4A  and  FIG. 4B  show three cases where the ratios of the first exciting current I 1  to the first superconducting coil set  30  and of the second exciting current I 2  to the second superconducting coil set  40  are made different. Case A is a case where the ratio of the first exciting current I 1  to the second exciting current I 2  is set to 1:0, that is, a case where a current flows only through the first superconducting coil set  30  and no current flows through the second superconducting coil set  40 . In this case, since only the first superconducting coil set  30  generates a magnetic field, the magnetic field distribution that is convex downward on the X axis and convex upward on the Y axis can be obtained as described above. Case B is a case where the ratio of the first exciting current I 1  to the second exciting current I 2  is set to 0:1, that is, no current flows through the first superconducting coil set  30  and a current flows only through the second superconducting coil set  40 . In this case, only the second superconducting coil set  40  generates a magnetic field, and as described above, the magnetic field distribution that is convex upward on the X axis and convex downward on the Y axis is obtained. 
     Case C is a case where the ratio of the first exciting current I 1  to the second exciting current I 2  is set to 1:1, that is, a case where currents of the same magnitude flow through the first superconducting coil set  30  and the second superconducting coil set  40 . In Case C, as shown in  FIGS. 4A and 4B , a magnetic field distribution having a convex shape obtained by averaging Case A and Case B is obtained. Similarly, in a case where the ratio of the first exciting current I 1  to the second exciting current I 2  is set to another value, it is considered that a magnetic field distribution having a convex shape between Cases A and B can be obtained depending on the ratio. 
     In this way, the convex shape of the magnetic field distribution generated by the first superconducting coil set  30  in the central cavity  24  can be changed by changing the magnitude of the first exciting current I 1 , and the convex shape of the magnetic field distribution generated by the second superconducting coil set  40  in the central cavity  24  can be changed by changing the size of the second exciting current I 2 . 
     It is known that the magnetic field distribution of the first superconducting coil set  30  (the magnetic field distribution that is convex downward on the X axis and convex upward on the Y axis) is suitable for producing a single crystal having a relatively high oxygen concentration and that the magnetic field distribution of the second superconducting coil set  40  (the magnetic field distribution that is convex upward on the X axis and convex downward on the Y axis) is suitable for producing a single crystal having a relatively low oxygen concentration. The desired oxygen concentration varies depending on the applications of semiconductor devices that are ultimately manufactured. For example, so-called horizontal devices such as CPUs and memories and vertical devices such as power devices require different oxygen concentrations. 
     According to the superconducting magnet device  10  according to the embodiment, by controlling the first exciting current I 1  and the second exciting current I 2  independently of each other, it is possible to control the convex shape of the magnetic field distribution of the central cavity  24 , which is the overlap of the magnetic fields generated by the first superconducting coil set  30  and the second superconducting coil set  40 , respectively. 
     In the related-art device, only a single magnetic field distribution can be generated, or it is only possible to switch between two types of magnetic field distributions, and there is a limit to the improvement of crystal quality. In contrast, the superconducting magnet device  10  according to the embodiment can more finely control the magnetic field distribution to be generated. Accordingly, the degree of suppression of heat convection in the melt can be finely adjusted, the oxygen concentration in the single crystal can be more finely adjusted, and the crystal quality can be improved. 
     The single crystal pulling device mounted with the superconducting magnet device  10  according to the embodiment can be used to manufacture single crystals having various oxygen concentrations desired depending on final products. The single crystal pulling device according to the embodiment has an improved operation rate at a manufacturing site as compared to the related-art device and enables more economical factory management. 
       FIG. 5  is a diagram schematically showing an example of a coil power supply circuit of the superconducting magnet device  10  shown in  FIG. 1 . The power supply system  50  includes a first power supply  52  that supplies the first exciting current I 1  to the first superconducting coil set  30 , a second power supply  54  that supplies the second exciting current I 2  to the second superconducting coil set  40 , and a power supply controller  56  that controls the first power supply  52  and the second power supply  54 . 
     As described above, the first superconducting coil set  30  is disposed inside the tubular cryostat  20 , and the power supply system  50  is disposed outside the tubular cryostat  20 . For that reason, a first circuit  53  that connects the first power supply  52  to the first superconducting coil set  30  has feedthrough portions  58  on a positive electrode side and a negative electrode side, respectively. Each feedthrough portion  58  is an airtight terminal for introducing a current into the tubular cryostat  20  and is provided so as to penetrate a wall surface of the tubular cryostat  20 . The two feedthrough portions  58  are connected to corresponding current lead portions  60 , respectively. The pair of first superconducting coils  30   a  and  30   b  are connected in series in the tubular cryostat  20 . A positive electrode of the first power supply  52  is connected to one first superconducting coil  30   a  via one feedthrough portion  58  and one current lead portion  60 , and the other first superconducting coil  30   b  is connected to a negative electrode of the first power supply  52  via the other feedthrough portion  58  and the other current lead portion  60  to form the first circuit  53 . 
     In a second circuit  55  connecting the second power supply  54  to the second superconducting coil set  40 , a positive electrode of the second power supply  54  is connected to the first pair of second superconducting coils  40   a  and  40   b  via the feedthrough portion  58  and the current lead portion  60 . The first pair of second superconducting coils  40   a  and  40   b  are connected in series in the tubular cryostat  20 . The first pair of second superconducting coils  40   a  and  40   b  and the second pair of second superconducting coils  40   c  and  40   d  are connected to each other via the current lead portion  60  and the feedthrough portion  58  on a first pair side, an external wiring line  62  that connects the two feedthrough portions  58  outside the tubular cryostat  20 , and the current lead portion  60  and the feedthrough portion  58  on a second pair side. The second pair of second superconducting coils  40   c  and  40   d  are connected in series in the tubular cryostat  20 . The second pair of second superconducting coil  40   c  and  40   d  are connected to a negative electrode of the second power supply  54  via the feedthrough portion  58  and the current lead portion  60 . 
     Accordingly, the first power supply  52  can supply the first exciting current I 1  to the first superconducting coil set  30  via the first circuit  53 , and the second power supply  54  can supply the second exciting current I 2  to the second superconducting coil set  40  via the second circuit  55 . The first circuit  53  and the second circuit  55  are not connected to each other. 
     The power supply controller  56  can determine the first exciting current I 1  and the second exciting current I 2  so as to realize a desired magnetic field distribution. Here, the power supply controller  56  may control the magnitude of the first exciting current I 1  and the magnitude of the second exciting current I 2  such that the total value of the magnetic fields generated at a predetermined position (for example, the center) in the central cavity  24  by the first superconducting coil set  30  and the second superconducting coil set  40  does not exceed an upper limit value. 
       FIG. 6  is a graph showing an example of a contour diagram of a magnetic field generated by the superconducting magnet device  10  according to the embodiment, with the first exciting current I 1  and the second exciting current I 2  as the horizontal axis and the vertical axis, respectively. A magnetic field value shown in the graph indicates the total value of the magnetic fields generated at a predetermined position (for example, the center) in the central cavity  24  by the first superconducting coil set  30  and the second superconducting coil set  40 . In this example, an upper right contour line has a larger magnetic field value, and a lower left contour line has a smaller magnetic field value. 
     The power supply controller  56  may select a contour line  64  (indicated by a thick line) from a plurality of contour lines and may determine the combination of the first exciting current I 1  and the second exciting current I 2  from a region  66  that gives a magnetic field value of the selected contour line  64  or a magnetic field value lower than that. That is, determining the first exciting current I 1  and the second exciting current I 2  from a region  68  that gives a magnetic field value higher than the selected contour line  64  is prohibited. The magnetic field value of the contour line  64  to be selected may be appropriately defined as a specification of the superconducting magnet device  10  or of the single crystal pulling device and may be input to or stored in the power supply controller  56 . 
     In this way, it is possible to avoid that the excessive magnitudes of first exciting current I 1  and second exciting current I 2 , which generate a magnetic field exceeding the magnetic field value corresponding to the selected contour line  64 , are supplied to the first superconducting coil set  30  and the second superconducting coil set  40 . By avoiding excessive current supply to the superconducting coil, the electromagnetic force and heat load acting on the coil can be suppressed, and the risk of breaking the superconductivity can be reduced. The superconducting magnet device  10  can be more safely operated. 
       FIG. 7  is a perspective view schematically showing the appearance of the superconducting magnet device  10 .  FIG. 8A  to  FIG. 8C  are schematic views illustrating the disposition location of a cryocooler in the superconducting magnet device  10  shown in  FIG. 7 . 
     As shown in  FIG. 7 , the superconducting magnet device  10  includes at least one cryocooler  70 , and the first superconducting coil set  30  and the second superconducting coil set  40  disposed in the tubular cryostat  20  are thermally coupled to the cryocooler  70 . The cryocooler  70  may be, for example, a two-stage Gifford-McMahon (GM) cryocooler or another type of cryocooler. Each superconducting coil is used in a state of being cooled to a cryogenic temperature equal to or lower than the superconducting transition temperature by the cryocooler  70 . In this embodiment, the superconducting magnet device  10  is configured as a so-called conduction cooling type in which the superconducting coil is directly cooled by the cryocooler  70  instead of being immersed in a cryogenic liquid refrigerant such as liquid helium. 
     In the example shown in  FIG. 7 , four cryocoolers  70  are installed on an upper surface of the tubular cryostat  20 . The cryocooler  70  may be disposed between two superconducting coils adjacent to each other around the Z axis when viewed from the Z axis. By installing the cryocooler  70  using an empty space between the coils, the tubular cryostat  20  can be more compactly designed, and the superconducting magnet device  10  can be downsized. 
     As shown in  FIG. 8A , the first cryocooler  70  may be disposed between the first superconducting coil  30   a  and the second superconducting coil  40   a , the second cryocooler  70  may be disposed between the first superconducting coil  30   a  and the second superconducting coil  40   d , the third cryocooler  70  may be disposed between the first superconducting coil  30   b  and the second superconducting coil  40   b , and the fourth cryocooler  70  may be disposed between the first superconducting coil  30   b  and the second superconducting coil  40   c . In this way, each superconducting coil may be directly cooled by any cryocooler  70 . 
     The cryocooler  70  to be installed in the tubular cryostat  20  may be smaller. For example, as shown in  FIG. 8B , three cryocoolers  70  may be installed in the tubular cryostat  20 , and each cryocooler  70  may be disposed between two superconducting coils adjacent to each other around the Z axis. In this case, as shown in the figure, the cryocoolers  70  may be disposed at equal angular intervals around the Z axis. 
     Alternatively, as shown in  FIG. 8C , two cryocoolers  70  may be installed in the tubular cryostat  20  and may be disposed at intervals of 180 degrees around the Z axis. In the shown example, the first cryocooler  70  is disposed between the first superconducting coil  30   a  and the second superconducting coil  40   d , and the second cryocooler  70  is disposed between the first superconducting coil  30   b  and the second superconducting coil  40   c . In this case, some superconducting coils (for example, the second superconducting coils  40   a  and  40   b ) are disposed farther from the cryocooler  70  than other superconducting coils adjacent to the cryocooler  70 . The superconducting coils ( 40   a  and  40   b ) may be connected to the cryocooler  70  (or the superconducting coils adjacent to the cryocooler  70 ) via an appropriate heat transfer member and may be cooled. 
     Alternatively, more cryocoolers  70  may be installed in the tubular cryostat  20  as necessary. For example, a cryocooler  70  may be provided for each superconducting coil. One superconducting coil may be cooled by a plurality of cryocoolers  70 . 
       FIG. 9  is a sectional view schematically showing a coil supporting structure  72  of the superconducting magnet device  10 .  FIG. 9  shows a section taken along line A-A of  FIG. 7 . The coil supporting structure  72  connects a superconducting coil (the first superconducting coil  30   a  in the illustrated example) belonging to the first superconducting coil set  30  or the second superconducting coil set  40  to the tubular cryostat  20  and supports the weight acting on the superconducting coil and the electromagnetic force generated during operation. As shown in  FIG. 9 , the coil supporting structure  72  includes a coil supporting plate  74  and a coil supporting body  76 . The coil supporting plate  74  is provided for connecting the superconducting coil and the coil supporting body  76  to each other and is attached to one side (for example, an inner peripheral side of the tubular cryostat  20 ) of the superconducting coil. 
     The coil supporting body  76  supports the superconducting coil on a peripheral surface (for example, an outer peripheral surface) of the tubular cryostat  20  and is disposed inside the superconducting coil. One end of the coil supporting body  76  is attached to the coil supporting plate  74  inside the superconducting coil, and the other end thereof is attached to the outer peripheral surface of the tubular cryostat  20 . The coil supporting body  76  has a rod shape and extends in a horizontal direction.  FIG. 7  shows an end portion of the coil supporting body  76  provided on the outer peripheral surface of the tubular cryostat  20 . One superconducting coil may be supported on the tubular cryostat  20  by a plurality of (for example, two) coil supporting bodies  76 . 
       FIG. 10  is a perspective view schematically showing another example of the superconducting coil disposition in the superconducting magnet device  10  according to the embodiment. As shown in the figure, two types of saddle-shaped coils having different sizes may be used in the superconducting magnet device  10 . 
     The first superconducting coil set  30  includes a pair of first superconducting coils disposed to face each other on the X axis with the central cavity  24  interposed therebetween. The second superconducting coil set  40  includes a pair of second superconducting coils disposed to face each other on the X axis with the central cavity  24  interposed therebetween. The pair of first superconducting coils are disposed inside the pair of second superconducting coils. 
     Even in a case where such a double saddle-shaped coil disposition is used, similar to the above-described 6-coil type, the first superconducting coil set  30  generates a magnetic field distribution, which is convex downward on the X axis and convex upward on the Y axis when the first exciting current I 1  is supplied, in the central cavity  24 , and the second superconducting coil set  40  generates a magnetic field distribution, which is convex upward on the X axis and convex downward on the Y axis when the second exciting current I 2  is supplied, in the central cavity  24 . By controlling the first exciting current I 1  and the second exciting current I 2  independently of each other, it is possible to control the convex shape of the magnetic field distribution of the central cavity  24 , which is the overlap of the magnetic fields generated by the first superconducting coil set  30  and the second superconducting coil set  40 , respectively. 
     The present invention has been described above on the basis of the embodiment. It should be understood by those skilled in the art that the present invention is not limited to the above embodiment, that various design changes are possible and various modification examples are possible, and that such modification examples are also within the scope of the present invention. Various features described in relation to a certain embodiment can also be applied to other embodiments. New embodiments created by combination have the effects of respective combined embodiments in combination. 
     In the above-described 6-coil type embodiment, all superconducting coils have the same shape and size, but this is not indispensable. For example, in the first superconducting coil set  30  and the second superconducting coil set  40 , the superconducting coils may have different shapes and/or different sizes. 
     The power supply system  50  may change the direction of the first exciting current I 1  and/or the second exciting current I 2  in addition to or instead of changing the magnitude of the first exciting current I 1  and/or the second exciting current I 2 . 
     The single crystal pulling device on which the superconducting magnet device  10  according to the embodiment is mounted may be a single crystal pulling device for producing a single crystal of a semiconductor material other than silicon or of other materials. 
     If applicable, the superconducting magnet device  10  may be mounted on a device other than the single crystal pulling device. The superconducting magnet device  10  may be mounted on a high-magnetic-field utilization device as a magnetic field source of the high-magnetic-field utilization device and can generate a high magnetic field required for the device. 
     The present invention has been described using specific terms and phrases based on the embodiments, but the embodiments show only one aspect of the principles and applications of the present invention. In the embodiments, many modification examples and disposition changes are permitted within a range not departing from the concept of the present invention defined in the claims. 
     It should be understood that the invention is not limited to the above-described embodiment, but may be modified into various forms on the basis of the spirit of the invention. Additionally, the modifications are included in the scope of the invention.