Magnetic field generation device

Abstract

To provide a magnetic field generation device capable of making a magnetic flux density on one side in a depth direction higher than a magnetic flux density on the other side in the depth direction, with respect to a magnetic field generated in a working space.SOLUTION: A magnetic field generation device includes an iron core and a pair of superconducting coils 3. A divided-iron core coil assembly 5 includes a pair of opposing iron core portions arranged to face each other with a working space interposed therebetween in a central axis direction. Each of the opposing iron core portions has a respective superconducting coil wound along a circumferential direction around an axis O. At least the superconducting coil on a first side of the axial direction among the pair of superconducting coils has a curvature radius Ra of an inner circumferential surface of a first curved-line portion 31 that is larger than a curvature radius Rb of an inner circumferential surface of a second curved-line portion 32 in a plan view of an axial direction.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to a magnetic field generating device. [Background technology]

[0002] Conventionally, there has been a magnetic field generating device that includes an iron core that is substantially C-shaped in cross section perpendicular to the depth direction, and a pair of coils wound around a pair of ends of the iron core (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-123084 Summary of the Invention [Problem to be solved by the invention]

[0004] In conventional magnetic field generators, the magnetic field generated in the working space between the pair of coils is generally uniform along the depth direction. However, in recent years, there has been a demand for the magnetic field generated in the working space to have a higher magnetic flux density on one side of the depth direction than on the other side of the depth direction.

[0005] The present invention is intended to solve the above-mentioned problems, and aims to provide a magnetic field generating device that can make the magnetic flux density on one side in the depth direction higher than the magnetic flux density on the other side in the depth direction with respect to the magnetic field generated in the working space. [Means for solving the problem]

[0006] [1] Iron core and a pair of superconducting coils; A magnetic field generating device comprising: The iron core has a substantially C-shape in a cross section parallel to an axial direction parallel to a predetermined axis and a vertical direction perpendicular to the axial direction, The iron core has a pair of opposing core portions that extend on the axis and are arranged opposite each other in the axial direction with a working space interposed therebetween, Each of the superconducting coils is wound around each of the opposing core portions in a circumferential direction centered on the axis, When a direction perpendicular to the axial direction and the longitudinal direction is referred to as a depth direction, each of the superconducting coils has a depth as follows when viewed in a plan view in the axial direction: a first curved linear portion extending in a curved linear shape that is convex toward a first side in the depth direction; a second curved linear portion located on a second depth direction side relative to the first curved linear portion and extending in a curved linear shape that is convex toward the second depth direction side; a pair of connecting portions that connect the first curved linear portion and the second curved linear portion to each other; It consists of A magnetic field generating device in which, when viewed in a plane in the axial direction, the radius of curvature of the inner surface of the first curved linear portion of at least the superconducting coil on the first axial side of the pair of superconducting coils is larger than the radius of curvature of the inner surface of the second curved linear portion.

[0007] [2] A magnetic field generating device as described in [1], wherein at least one of the pair of opposing core portions on the first axial side has an inner end face in the axial direction that is recessed outward in the axial direction, on the inner peripheral side of the superconducting coil.

[0008] [3] A magnetic field generating device as described in [2], wherein the depth of the recess in the axial direction is non-uniform along the depth direction.

[0009] [4] The magnetic field generating device described in any one of [1] to [3], wherein the magnetic field generating device is configured so that, in the magnetic field distribution, when the horizontal axis is the depth position and the vertical axis is the magnetic flux density of the magnetic field generated in the working space by the magnetic field generating device, the maximum value of the magnetic flux density on the first depth side relative to the depth center of the superconducting coil is higher than the maximum value of the magnetic flux density on the second depth side relative to the depth center of the superconducting coil.

[0010] [5] The magnetic field generating device described in any one of [1] to [4], wherein the magnetic field generating device is configured so that when the horizontal axis is the position in the depth direction and the vertical axis is the magnetic flux density of the magnetic field generated in the working space by the magnetic field generating device, the magnetic field distribution has an inclined waveform portion that passes through the center of the superconducting coil in the depth direction and extends linearly so that the magnetic flux density increases as it moves toward the first side in the depth direction.

[0011] [6] The magnetic field generating device further comprises one or a pair of vacuum insulated containers; The iron core is a substantially C-shaped or substantially U-shaped yoke; a pair of split core portions that are configured separately from the yoke, are located inside the yoke, and constitute at least a part of the pair of opposing core portions; and the superconducting coils are wound around the respective split core portions along the circumferential direction, a split core-coil assembly consisting of the split core portion and the superconducting coil wound around the split core portion is housed in one or a pair of vacuum insulated containers, The magnetic field generating device according to any one of [1] to [5], wherein the yoke is disposed outside the one or pair of vacuum insulating containers. [Effects of the Invention]

[0012] According to this invention, it is possible to provide a magnetic field generating device that can make the magnetic flux density on one side in the depth direction higher than the magnetic flux density on the other side in the depth direction with respect to the magnetic field generated in the working space. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a perspective view schematically illustrating a magnetic field generating device according to an embodiment of the present invention; [Figure 2] 2 is a cross-sectional view of the magnetic field generating device of FIG. 1 taken along the line AA of FIG. 1. FIG. [Figure 3] 3 is a cross-sectional view of the magnetic field generating device of FIG. 2 taken along the line BB in FIG. 2. FIG. [Figure 4] 3 is a cross-sectional perspective view showing a part of the magnetic field generating device of FIG. 2 together with a cross section taken along line CC of FIG. 2. FIG. [Figure 5] 5 is a plan view showing the split core-coil assembly of FIG. 4 as viewed in the axial direction. FIG. [Figure 6] 6 is a graph schematically showing an example of a magnetic field distribution of a magnetic field generated in a working space by the magnetic field generating device of FIGS. 1 to 5. DETAILED DESCRIPTION OF THE INVENTION

[0014] The magnetic field generating device according to the present invention can be used for any purpose, for example, as a billet heating device for heating a billet (for example, an aluminum billet). DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the magnetic field generating device according to the present invention will be described with reference to the drawings.

[0015] 1 to 6 are diagrams for explaining a magnetic field generating device 1 according to one embodiment of the present invention. First, a schematic configuration of a magnetic field generator 1 according to this embodiment will be described with reference to FIGS. 1 to 5. FIG. 1 is a perspective view schematically illustrating a magnetic field generator 1 according to one embodiment of the present invention. FIG. 2 is an AA cross-sectional view of the magnetic field generator 1 of FIG. 1 taken along line AA in FIG. 1. Line AA in FIG. 1 is parallel to the axial direction AD, and the cross section of FIG. 2 is parallel to the axial direction AD and the longitudinal direction OD. FIG. 3 is a BB cross-sectional view of the magnetic field generator 1 of FIG. 2 taken along line BB in FIG. 2. Line BB in FIG. 2 is parallel to the axial direction AD, and the cross section of FIG. 3 is parallel to the axial direction AD and the depth direction DD. FIG. 4 is a CC cross-sectional perspective view of a portion of the magnetic field generator 1 of FIG. 2 together with a cross section taken along line CC in FIG. 2. Line CC in FIG. 2 is perpendicular to the axial direction AD, and the cross section of FIG. 4 is parallel to the longitudinal direction OD and the depth direction DD (and thus parallel to the axial direction). FIG. 5 is a plan view showing the split core-coil assembly 5 of FIG. 4 as viewed in the axial direction AD. The magnetic field generating device 1 is configured to generate a magnetic field in a workspace 6. The workspace 6 is an air gap.

[0016] In this specification, the direction parallel to a predetermined axis O fixed to the magnetic field generating device 1 is referred to as the "axial direction AD." One side of the axial direction AD is referred to as the "first axial side AD1," and the other side of the axial direction AD is referred to as the "second axial side AD2." The side of the axial direction AD closer to the workspace 6 is referred to as the "inner axial side ADI," and the side of the axial direction AD farther from the workspace 6 is referred to as the "outer axial side ADO." The direction perpendicular to the axial direction AD is referred to as the "perpendicular-to-axial direction." Two directions that are perpendicular to the axial direction AD and perpendicular to each other are referred to as the "longitudinal direction OD" and the "depth direction DD." One side of the longitudinal direction OD is referred to as the "first longitudinal side OD1," and the other side of the longitudinal direction OD is referred to as the "second longitudinal side OD2." One side of the depth direction DD is referred to as the "first depth side DD1," and the other side of the depth direction DD is referred to as the "second depth side DD2." In each drawing, the above directions are indicated by arrows. In this specification, the circumferential direction and radial direction about the axis O are sometimes simply referred to as the "circumferential direction" and the "radial direction," respectively. Furthermore, unless otherwise specified, the terms "outer peripheral side" and "inner peripheral side" refer to the outer peripheral side and the inner peripheral side, respectively, when the axis O is the center. For example, the magnetic field generating device 1 may be oriented such that the axial direction AD is horizontal, the longitudinal direction OD is vertical, and the first longitudinal side OD1 is above the vertical direction. However, the magnetic field generating device 1 may be oriented in any direction.

[0017] 1 and 2, a magnetic field generator 1 of this embodiment includes an iron core 2, a pair of superconducting coils 3, and a pair of vacuum insulating containers 4. In this embodiment, the pair of superconducting coils 3 are disposed inside the pair of vacuum insulating containers 4 (FIG. 2), and are not shown in FIG.

[0018] The iron core 2 has a substantially C-shape in a cross section (FIG. 2) parallel to the axial direction AD and the longitudinal direction OD (i.e., perpendicular to the depth direction DD). The iron core 2 may be made up of multiple (three in this embodiment) separate members, as in this embodiment, or the entire iron core 2 may be made up of only one member, with the entire iron core 2 being integrally constructed. The iron core 2 (and therefore each member that constitutes the iron core 2) is made up of a member that contains a magnetic material and is configured to allow magnetic flux to pass through. In this embodiment, the iron core 2 is made up of iron.

[0019] In this embodiment, the core 2 is made up of a yoke 21 and a pair of split core portions 22, which are formed separately from each other.

[0020] In this embodiment, the yoke 21 has a substantially U-shape or a substantially C-shape (a substantially U-shape in this embodiment). More specifically, in this embodiment, the yoke 21 includes a pair of legs 21a each extending in the longitudinal direction OD and an intermediate portion 21b connecting ends of the pair of legs 21a on a first longitudinal side OD1 and extending in the axial direction AD. In this embodiment, each of the pair of legs 21a extends substantially parallel to the longitudinal direction OD over substantially the entire length of the leg 21a in the longitudinal direction OD, thereby forming a substantially U-shape as a whole. However, the pair of legs 21a may extend from the intermediate portion 21b to a second longitudinal side OD2 and then extend to an inner axial direction ADI, thereby forming a substantially C-shape as a whole.

[0021] The pair of split core portions 22 are configured as separate bodies from the yoke 21. The pair of split core portions 22 are located inside the yoke 21 (specifically, on the axially inner sides ADI of the pair of legs 21a of the yoke 21), and are arranged opposite each other with the working space 6 interposed therebetween. The pair of split core portions 22 and the pair of leg portions 21a of the yoke 21 are spaced apart and face each other in the axial direction AD.

[0022] The core 2 has a pair of opposing core portions 23 that each extend on the axis O and are arranged opposite each other in the axial direction AD with a working space 6 interposed therebetween. The pair of opposing core portions 23 are made up of both end portions of the approximate C-shape of the core 2. In this embodiment, the pair of opposing core portions 23 are made up of a pair of split core portions 22 in the core 2. Therefore, matters described in this specification regarding the split core portions 22 also apply to the opposing core portions 23. Conversely, matters described in this specification regarding the opposing core portions 23 can also apply to the split core portions 22. However, for example, when the yoke 21 is substantially C-shaped, the pair of opposing core portions 23 may be made up of a pair of split core portions 22 as well as parts of the pair of legs 21 a of the yoke 21 . Unless otherwise specified, the matters described in this specification regarding the split core portion 22 can be applied to each of the pair of split core portions 22. Furthermore, the matters described in this specification regarding the opposing core portion 23 can be applied to each of the pair of opposing core portions 23, unless otherwise specified.

[0023] 1 to 5, each superconducting coil 3 is wound around each opposing core portion 23 (in this embodiment, split core portion 22) in the circumferential direction centered on axis O (in other words, so as to go around axis O). Superconducting coil 3 is located on the outer circumferential side of outer circumferential surface 221 of opposing core portion 23 (specifically, in this embodiment, step portion 2211 of outer circumferential surface 221, which will be described later), and faces outer circumferential surface 221 in the radial direction or is in contact with outer circumferential surface 221. In this specification, the matters described regarding the superconducting coil 3 can be applied to each of the pair of superconducting coils 3 unless otherwise specified. The superconducting coil 3 includes at least a coil body containing a superconductor. The coil body of the superconducting coil 3 is configured, for example, in a strip shape. In addition to the coil body, the superconducting coil 3 may further include a coil case that houses the coil body inside. The coil case is made of, for example, resin. 5, superconducting coil 3 has a ring shape going around axis O in plan view in axial direction AD. The shape of superconducting coil 3 in a cross section perpendicular to axial direction AD is almost constant along axial direction AD.

[0024] Although not shown, the magnetic field generating device 1 includes a current supply unit for supplying a current (for example, a direct current) to the superconducting coil 3.

[0025] In this embodiment, the split core portions 22 (opposing core portions 23 in this embodiment) and the superconducting coil 3 wound around the split core portions 22 constitute a split core coil assembly 5. That is, the split core coil assembly 5 is made up of the split core portions 22 and the superconducting coil 3 wound around the split core portions 22. In this embodiment, the magnetic field generating device 1 has a pair of split core coil assemblies 5. In this specification, the matters described regarding the split core-coil assembly 5 can be applied to each of the pair of split core-coil assemblies 5 unless otherwise specified.

[0026] 2, in this embodiment, a pair of split core-coil assemblies 5 are housed in a pair of vacuum insulating containers 4, respectively. The yoke 21 is disposed outside the pair of vacuum insulating containers 4. The pair of vacuum insulating containers 4 face each other in the axial direction AD with a working space 6 interposed therebetween. In this specification, the matters described regarding the vacuum insulated container 4 can be applied to each of the pair of vacuum insulated containers 4 unless otherwise specified. As shown in Figure 2, the vacuum insulated container 4 has a wall 42 located between the split iron core coil assembly 5 and the working space 6, and a wall 43 located between the split iron core coil assembly 5 and the leg 21a of the yoke 21.

[0027] The magnetic field generating device 1 is equipped with a refrigerator (not shown), which cools the equipment inside the vacuum insulated container 4. The vacuum insulated container 4 is configured to maintain the temperature of the internal equipment cooled by the refrigerator. As a result, the vacuum insulated container 4, together with the refrigerator, is configured to cool the split core coil assembly 5 and thus the superconducting coil 3, and maintain them at extremely low temperatures. Specifically, the superconducting coil 3 is cooled until the superconductor becomes superconducting (and thus until the electrical resistance becomes substantially zero). The vacuum insulated container 4 is preferably evacuated and has laminated insulation material on part or all of its walls. The laminated insulation material is formed, for example, by laminating multiple sheets of metal-deposited resin film and resin mesh. Examples of materials that can be used to form the body of the vacuum insulated container 4 include austenitic stainless steel and composite glass fiber reinforced plastic (GFRP). However, the vacuum insulating container 4 may be configured to cool the superconducting coil 3 by any other method as long as the superconducting coil 3 is accommodated therein.

[0028] In the magnetic field generator 1 configured as above, when a current is applied to the superconducting coil 3 by a current supply unit (not shown), a magnetic flux passes through the iron core 2, generating a magnetic field (strong magnetic field) in the working space 6. The strong magnetic field generated in the workspace 6 may be used for any purpose.

[0029] For example, the magnetic field generator 1 may be used in a billet heating device for heating a billet W (FIGS. 1 to 3). The billet W is preferably made of metal, for example, aluminum. The billet W has a columnar (e.g., cylindrical) shape. In addition to the magnetic field generator 1, the billet heating device includes a motor for rotating (spinning) the billet W about a billet central axis WC (FIGS. 2 to 3). The billet central axis WC passes through the working space 6 and is oriented parallel to the depth direction DD. The billet central axis WC is preferably positioned equidistant from the end faces 223 of the axially inner sides ADI of the pair of opposing core portions 23 in the axial direction AD. The depth direction DD may be parallel to the horizontal direction. A direct current is passed through the superconducting coil 3, thereby generating a strong direct-current magnetic field in the working space 6. Meanwhile, the billet W is rotated about the billet central axis WC by the motor. This is equivalent to applying an alternating magnetic field to the billet W, causing an induced current to flow within the billet W, which heats the billet W.

[0030] In this embodiment, the magnetic field generating device 1 is equipped with a superconducting coil 3, and therefore a stronger magnetic field can be generated in the working space 6 compared to a case in which the magnetic field generating device 1 is equipped with a normal copper coil instead of the superconducting coil 3. Furthermore, in this embodiment, since the magnetic field generator 1 includes the iron core 2, it is possible to generate a strong magnetic field while reducing the amount of superconductor used in manufacturing the superconducting coil 3 compared to a case in which the magnetic field generator 1 does not include the iron core 2, and therefore it is possible to reduce the amount of superconductor and, in turn, reduce costs. Since superconductors are generally expensive, it can be said that the effect of reducing costs by reducing the amount of superconductor is significant. Furthermore, in this embodiment, the iron core 2 of the magnetic field generator 1 has the yoke 21, so that the magnetic circuit resistance can be reduced and the magnetic flux can be increased compared to when the iron core 2 does not have the yoke 21.

[0031] Furthermore, in this embodiment, as described above, the iron core 2 is divided into the yoke 21 and a pair of split core portions 22 (opposing core portions 23), each split core coil assembly 5 is housed in a respective vacuum insulated container 4, and the yoke 21 is disposed outside the pair of vacuum insulated containers 4. Therefore, the vacuum insulated container 4 can be made smaller than if the undivided, approximately C-shaped iron core 2 and the pair of superconducting coils 3 wound around the pair of opposing core portions 23 of the iron core 2 were housed entirely in the vacuum insulated container 4. This makes it possible to reduce heat penetration from the outside, thereby enabling energy savings.

[0032] However, without being limited to the configuration of this embodiment, the undivided, substantially C-shaped iron core 2 and the pair of superconducting coils 3 wound around the pair of opposing core portions 23 of the iron core 2 may be housed entirely in one vacuum insulating container 4. In that case, the magnetic field generating device 1 may be provided with only one vacuum insulating container 4.

[0033] Alternatively, each of the pair of vacuum insulated containers 4 may be configured in a donut shape, so that the pair of vacuum insulated containers 4 only accommodates a pair of superconducting coils 3 that orbit around a pair of opposing core portions 23 of the iron core 2, and the iron core 2 is arranged outside the pair of vacuum insulated containers 4. In that case, however, the wall of the vacuum insulated container 4 is interposed between the iron core 2 and the superconducting coil 3, meaning that the iron core 2 and the superconducting coil 3 are spaced apart, which increases the circumferential length of the superconducting coil 3 and increases the amount of superconducting coil 3 used, leading to increased costs. Also, the increased space between the iron core 2 and the superconducting coil 3 increases leakage flux, which increases the amount of superconductor required, leading to increased costs. In this regard, according to this embodiment, the superconducting coil 3 is wound directly around the iron core 2 (specifically, the split iron core portions 22 and therefore the opposing core portions 23), and therefore the iron core 2 (specifically, the split iron core portions 22 and therefore the opposing core portions 23) and the superconducting coil 3 are in contact with each other, eliminating the distance between them. This allows the circumferential length of the superconducting coil 3 to be shorter, thereby reducing the amount of superconductor and costs, compared to when the vacuum insulated container 4 is doughnut-shaped as described above. Furthermore, since the iron core 2 (specifically, the split iron core portions 22 and therefore the opposing core portions 23) and the superconducting coil 3 are in contact with each other, eliminating the distance between them, this allows the leakage magnetic flux to be reduced, thereby reducing the amount of superconductor and costs, compared to when the vacuum insulated container 4 is doughnut-shaped as described above. Furthermore, since the iron core 2 (specifically, the split iron core portion 22 and thus the opposing iron core portion 23) is in contact with the superconducting coil 3, the temperature rise of the superconducting coil 3 can be suppressed by utilizing the cold storage effect of the iron core 2 (specifically, the split iron core portion 22 and thus the opposing iron core portion 23) compared to when the vacuum insulated container 4 is doughnut-shaped as described above. Therefore, the superconducting coil can be cooled sufficiently, and the capacity of the superconductor can be effectively utilized.

[0034] In this embodiment, the split core-coil assembly 5 may be supported relative to the vacuum insulating container 4 via any support structure so that it is maintained at a desired position within the vacuum insulating container 4. In this embodiment, in each split core coil assembly 5, when current is applied, the Lorentz force acting on the superconducting coil 3 toward the axially outer side ADO and the electromagnetic force acting on the split core portion 22 and, in turn, the opposing core portion 23 toward the axially inner side ADI cancel each other out, thereby reducing the force in the axial direction AD acting on the split core coil assembly 5. This makes it possible to simplify the support structure for supporting the split core coil assembly 5 on the vacuum insulated container 4. This in turn makes it possible to reduce heat penetration from the outside into the superconducting coil 3 via the support structure, thereby reducing the cooling burden on the refrigerator and enabling the superconducting coil 3 to be sufficiently cooled, thereby making effective use of the capacity of the superconductor.

[0035] In this embodiment, as shown in FIGS. 2 to 5, the outer peripheral surface 221 of the opposing core portion 23 (in this embodiment, the split core portions 22) has an annular step portion 2211. The step portion 2211 extends over the entire circumference in the circumferential direction centered on the axis O. The step portion 2211 faces the working space 6 (through the wall 42 of the vacuum insulated container 4). The step portion 2211 is recessed toward the inner peripheral side. Specifically, the step portion 2211 is made up of an axially perpendicular surface 2211a that is substantially parallel to the axial direction and faces the axially inner side ADI, and an axial surface 2211b that extends substantially parallel to the axial direction AD from the axially perpendicular surface 2211a to the end surface 223 of the axially inner side ADI of the opposing core portion 23 (in this embodiment, the split core portion 22). The superconducting coil 3 is wound around the stepped portion 2211 in the circumferential direction around the axis O. As a result, the superconducting coil 3 and the opposing core portion 23 (the split core portion 22 in this embodiment) are arranged to face each other in the axial direction AD, so that the Lorentz force acting on the superconducting coil 3 toward the axial outer side ADO and the electromagnetic force acting on the opposing core portion 23 toward the axial inner side ADI more effectively cancel each other out, thereby reducing the force in the axial direction AD acting on the split core coil assembly 5. This makes it possible to further simplify the support structure for supporting the split core coil assembly 5 relative to the vacuum insulated container 4. Furthermore, although the Lorentz force acting toward the axial outer side ADO acts on the superconducting coil 3, the step portion 2211 (particularly the surface 2211a perpendicular to the axis) restricts the superconducting coil 3 from moving toward the axial outer side ADO. In other words, the step portion 2211 has the function of restricting the superconducting coil 3 from moving toward the axial outer side ADO. Therefore, there is no need to provide a separate restricting structure for restricting the movement of the superconducting coil 3 toward the axially outer side ADO. This reduces the heat penetration from the outside into the superconducting coil 3 through the restricting structure, thereby reducing the cooling burden on the refrigerator. Furthermore, the superconducting coil can be sufficiently cooled, allowing the superconductor's capabilities to be effectively utilized. Furthermore, the axially inner side ADI of the superconducting coil 3 is not covered by the opposing core portion 23 but faces the working space 6 (through the wall 42 of the vacuum insulated container 4). Therefore, a stronger magnetic field can be generated in the working space 6. Furthermore, the superconducting coil 3 is in contact with not only the axial surface 2211b of the step portion 2211 but also the transverse-axis surface 2211a of the step portion 2211. This increases the contact area with the opposing core portion 23, thereby improving the cooling effect of the superconducting coil 3 via the opposing core portion 23.

[0036] However, the present invention is not limited to this embodiment, and the outer circumferential surface 221 of the opposing core portion 23 may have any shape.

[0037] For example, although not shown, the outer peripheral surface 221 of the opposing core portion 23 may have a protrusion that protrudes outward, and this protrusion may have the step portion 2211 as described above.

[0038] Alternatively, outer peripheral surface 221 of opposing core portion 23 may have an annular groove. The groove extends over the entire circumference in the circumferential direction centered on axis O. The groove is open on the outer peripheral side. The groove has a pair of groove wall surfaces that face each other and are each approximately parallel to the axial direction, and a groove bottom surface that faces the outer peripheral side, is approximately parallel to the axial direction AD, and connects the pair of groove wall surfaces. In this case, superconducting coil 3 is wound around the groove in the circumferential direction, and is ultimately housed in the groove.

[0039] Alternatively, the superconducting coil 3 may be wound around the outer circumferential surface 221 that does not have unevenness such as steps 2211 or grooves in the opposing core portion 23. In this case, it is preferable to separately provide a restricting structure for restricting the movement of the superconducting coil 3 outward in the axial direction ADO.

[0040] The superconducting coil 3 may have a single-stage structure consisting of only one layer along the axial direction AD, or may have a multi-stage structure in which multiple superconducting coil layers are arranged along the axial direction AD.

[0041] Although not shown, a cooling plate may be applied to the surface of the axially inner ADI of the split core coil assembly 5 inside the vacuum insulated container 4 (specifically, the end surface 223 of the axially inner ADI of the split core portion 22 and / or the end surface of the axially inner ADI of the superconducting coil 3). In this case, it is more preferable that the superconducting coil 3 and the cooling plate are in contact with each other. This allows the superconducting coil 3 to be cooled more effectively. However, the cooling plate does not have to be provided.

[0042] The leg 21a of the yoke 21 and the wall 43 of the vacuum insulating container 4 may be in contact with each other as shown in FIG. 2, or may be spaced apart from each other.

[0043] The configuration of the magnetic field generating device 1 is preferably symmetrical with respect to the center of the axial direction AD of the magnetic field generating device 1, but may be asymmetrical with respect to the center of the axial direction AD of the magnetic field generating device 1.

[0044] The magnetic field generating device 1 may include only one vacuum insulated container 4. In this case, the pair of split core coil assemblies 5 may be housed in the vacuum insulated container 4, and the yoke 21 may be arranged outside the vacuum insulated container 4. In this case, the vacuum insulated container 4 may have a configuration in which the pair of vacuum insulated containers 4 shown in the example of FIG. 2 are connected to each other by a connecting pipe or the like to form an integrated unit.

[0045] Each superconducting coil 3 is made up of a first curved wire portion 31, a second curved wire portion 32, and a pair of connecting portions 33 when viewed in a plan view in the axial direction AD (FIG. 5). The first curved linear portion 31 extends in a curved linear shape that is convex toward the first side DD1 in the depth direction. The first curved linear portion 31 extends approximately halfway around the circumference, and thereby extends in a substantially semicircular arc shape. The first curved linear portion 31 constitutes the portion of the superconducting coil 3 that is closest to the first side DD1 in the depth direction. The second curved linear portion 32 extends in a curved linear shape that is convex toward the second side DD2 in the depth direction. The second curved linear portion 32 extends approximately halfway around the circumference, and thereby extends in a substantially semicircular arc shape. The second curved linear portion 32 constitutes the portion of the superconducting coil 3 that is closest to the second side DD2 in the depth direction. The pair of connecting portions 33 connect the first curved linear portion 31 and the second curved linear portion 32 to each other. One of the pair of connecting portions 33 connects the ends of the first curved linear portion 31 and the second curved linear portion 32 on a first longitudinal side OD1, and extends substantially along the depth direction DD. The other of the pair of connecting portions 33 connects the ends of the first curved linear portion 31 and the second curved linear portion 32 on a second longitudinal side OD2, and extends substantially along the depth direction DD. The pair of connecting portions 33 are located on a center DDC of the superconducting coil 3 in the depth direction DD (i.e., the pair of connecting portions 33 and the center DDC overlap).

[0046] In at least one of the pair of superconducting coils 3 on the first axial side AD1 (preferably both), when viewed in a plane in the axial direction AD (Figure 5), the radius of curvature Ra of the inner surface 3i of the first curved linear portion 31 (i.e., the portion of the inner surface 3i of the superconducting coil 3 that follows the first curved linear portion 31) is larger than the radius of curvature Rb of the inner surface 3i of the second curved linear portion 32 (i.e., the portion of the inner surface 3i of the superconducting coil 3 that follows the second curved linear portion 32). As described above, in this embodiment, at least the superconducting coils 3 on the first axial side AD1 (preferably both) of the pair of superconducting coils 3 have an asymmetric shape with respect to the center DDC of the superconducting coil 3 in the depth direction DD. In addition, the above-mentioned radii of curvature Ra and Rb may be uniform along the extension direction of the first curved linear portion 31 and the second curved linear portion 32 over the entire length of the first curved linear portion 31 and the second curved linear portion 32, respectively, or may be non-uniform along the extension direction of the first curved linear portion 31 and the second curved linear portion 32. In the latter case, the above-mentioned "the radius of curvature Ra of the inner surface 3i of the first curved linear portion 31 is larger than the radius of curvature Rb of the inner surface 3i of the second curved linear portion 32" means that the minimum value of the radius of curvature Ra of the inner surface 3i of the first curved linear portion 31 (i.e., the radius of curvature Ra at the point where the radius of curvature Ra of the inner surface 3i of the first curved linear portion 31 is smallest) is larger than the minimum value of the radius of curvature Rb of the inner surface 3i of the second curved linear portion 32 (i.e., the radius of curvature Rb at the point where the radius of curvature Rb of the inner surface 3i of the second curved linear portion 32 is smallest).

[0047] Fig. 6 is a graph schematically showing an example of a magnetic field distribution f of the magnetic field generated in the work space 6 by the magnetic field generating device 1 of this embodiment (Figs. 1 to 5). In the graph of Fig. 6, the horizontal axis represents the position in the depth direction DD, and the vertical axis represents the magnetic flux density (absolute value) (T) of the magnetic field generated in the work space 6 by the magnetic field generating device 1 of this embodiment. 6, the magnetic field generated in the working space 6 by the magnetic field generating device 1 of this embodiment has a higher maximum value (T) of magnetic flux density on a first depth-direction side DD1 relative to the center DDC in the depth direction DD of the superconducting coil 3 than a maximum value (T) of magnetic flux density on a second depth-direction side DD2 relative to the center DDC in the depth direction DD of the superconducting coil 3. That is, roughly speaking, the magnetic flux density on one side in the depth direction DD (first depth side DD1) is higher than the magnetic flux density on the other side in the depth direction DD (second depth side DD2). Such a magnetic field distribution asymmetric with respect to the center DDC in the depth direction DD can be easily realized by forming the superconducting coil 3 asymmetric with respect to the center DDC in the depth direction DD as described above. That is, in this embodiment, when comparing both sides of the center DDC in the depth direction DD, the magnetic flux density on a first depth direction side DD1 where the first curved wire-shaped portion 31 having a larger diameter (specifically, a larger radius of curvature of the inner circumferential surface 3i) of the first curved wire-shaped portion 31 and the second curved wire-shaped portion 32 of the superconducting coil 3 is located is higher than the magnetic flux density on a second depth direction side DD2 where the second curved wire-shaped portion 32 having a smaller diameter (specifically, a smaller radius of curvature of the inner circumferential surface 3i) of the first curved wire-shaped portion 31 and the second curved wire-shaped portion 32 of the superconducting coil 3 is located. In this way, the magnetic field generating device 1 of this embodiment is configured so that, in the magnetic field distribution (Figure 6), the maximum value (T) of the magnetic flux density on the first depth side DD1 relative to the center DDC of the depth direction DD of the superconducting coil 3 is higher than the maximum value (T) of the magnetic flux density on the second depth side DD2 relative to the center DDC of the depth direction DD of the superconducting coil 3. As described above, according to this embodiment, with regard to the magnetic field generated in the working space 6, it is possible to make the magnetic flux density on one side in the depth direction DD higher than the magnetic flux density on the other side in the depth direction DD.

[0048] Incidentally, making the magnetic flux density higher on one side of the depth direction DD than on the other side of the depth direction DD as described above is particularly advantageous, for example, when the billet W is heated by a billet heating device equipped with the magnetic field generating device 1 and then extruded by an extruder. Generally, in extrusion molding of a billet W, the billet W inserted into the extruder is extruded while being compressed in the direction of the billet central axis WC. During this extrusion molding of the billet W, the temperature of the billet W in the extruder increases as the billet W is compressed. However, the portion of the billet W in the extruder on the extrusion outlet side is extruded before the temperature rises significantly, so the temperature does not rise significantly. However, the temperature of the portion of the billet W on the opposite side (the side pushed by the extrusion rod of the extruder) gradually rises before being extruded, so that the portion is ultimately extruded in a significantly increased state. However, from the viewpoint of extrusion processing accuracy, it is desirable for the temperature of the billet W when extruded to be as constant as possible. In this regard, according to the present embodiment, the magnetic flux density on the first depth side DD1 can be made higher than the magnetic flux density on the second depth side DD2, so that, for example, when the billet W is heated by a billet heating device equipped with the magnetic field generating device 1, the billet W can be heated so that the temperature on the first depth side DD1 is higher than the temperature on the second depth side DD2. Therefore, when the billet W is subsequently extruded using an extruder, by inserting the billet W into the extruder with the first depth side DD1, which has a higher temperature, facing the extrusion outlet, the temperature of the billet W when extruded during extrusion can be made more constant, which in turn makes it possible to improve the processing accuracy of the extrusion process.

[0049] From the same viewpoint as above, as in the example of Figure 5, it is preferable that, in a plan view in the axial direction AD, at least one of the pair of superconducting coils 3 on the first axial side AD1 (preferably both) has a radius of curvature Rc of the outer peripheral surface 3о of the first curved linear portion 31 (i.e., the portion of the outer peripheral surface 3о of the superconducting coil 3 that follows the first curved linear portion 31) that is larger than the radius of curvature Rd of the outer peripheral surface 3о of the second curved linear portion 32 (i.e., the portion of the outer peripheral surface 3о of the superconducting coil 3 that follows the second curved linear portion 32). This allows the maximum value (T) of the magnetic flux density on the first depth-direction side DD1 relative to the center DDC in the depth direction DD of the superconducting coil 3 to be higher than the maximum value (T) of the magnetic flux density on the second depth-direction side DD2 relative to the center DDC in the depth direction DD of the superconducting coil 3 in the magnetic field distribution f (FIG. 6). Furthermore, the amount of superconducting coil 3 used can be reduced, which in turn reduces costs. In addition, the above-mentioned radii of curvature Rc and Rd may be uniform along the extension direction of the first curved linear portion 31 and the second curved linear portion 32 over the entire length of the first curved linear portion 31 and the second curved linear portion 32, respectively, or may be non-uniform along the extension direction of the first curved linear portion 31 and the second curved linear portion 32. In the latter case, the above-mentioned "the radius of curvature Rc of the outer peripheral surface 3о of the first curved linear portion 31 is larger than the radius of curvature Rd of the outer peripheral surface 3о of the second curved linear portion 32" means that the minimum value of the radius of curvature Rc of the outer peripheral surface 3о of the first curved linear portion 31 (i.e., the radius of curvature Rc at the point where the radius of curvature Rc of the outer peripheral surface 3о of the first curved linear portion 31 is smallest) is larger than the minimum value of the radius of curvature Rd of the outer peripheral surface 3о of the second curved linear portion 32 (i.e., the radius of curvature Rd at the point where the radius of curvature Rd of the outer peripheral surface 3о of the second curved linear portion 32 is smallest).

[0050] As in the example of Figure 5, it is preferable that, in a plan view in the axial direction AD (Figure 5), the superconducting coils 3 on at least the first axial side AD1 (preferably both) of the pair of superconducting coils 3 have a vertical OD distance between the ends on the first depth side DD1 of the inner surfaces 3i of each of the pair of connecting portions 33 (i.e., the portions of the inner surfaces 3i of the superconducting coils 3 that are aligned with each of the pair of connecting portions 33) that is longer than the vertical OD distance between the ends on the second depth side DD2 of the inner surfaces 3i of each of the pair of connecting portions 33. As a result, in the magnetic field distribution f (Figure 6), the maximum value (T) of the magnetic flux density on the first depth side DD1 relative to the center DDC of the depth direction DD of the superconducting coil 3 can be made higher than the maximum value (T) of the magnetic flux density on the second depth side DD2 relative to the center DDC of the depth direction DD of the superconducting coil 3. From a similar viewpoint, as in the example of Figure 5, it is preferable that the average value of the vertical OD distance between the respective inner circumferential surfaces 3i of the pair of connecting portions 33 on at least the first axial side AD1 (preferably both) of the pair of superconducting coils 3 at the first depth side DD1 of the center DDC in the depth direction DD of the superconducting coil 3 is longer than the average value of the vertical OD distance between the respective inner circumferential surfaces 3i of the pair of connecting portions 33 at the second depth side DD2 of the center DDC in the depth direction DD of the superconducting coil 3.

[0051] In addition, in a plan view in the axial direction AD (Figure 5), the inner surfaces 3i of each of the pair of connecting portions 33 of the superconducting coil 3 may extend in a straight line, as in the example of Figure 5, or may extend in some other form, for example, they may extend along curved lines that are convexly curved away from each other in the longitudinal direction OD. Similarly, in a plan view in the axial direction AD (Figure 5), the outer peripheral surfaces 3o of each of the pair of connecting portions 33 of the superconducting coil 3 may extend in a straight line, as in the example of Figure 5, or may extend in some other form, for example, each may extend along a curved line that is convexly curved away from each other in the longitudinal direction OD.

[0052] As shown in Figures 3 to 5, it is preferable that the end face 223 of at least the opposing core portions 23 on the first axial side AD1 (preferably both) of the pair of opposing core portions 23 has a recess 24 recessed toward the outer axial side ADO on the inner axial side ADI, more inward than the superconducting coil 3. By adjusting the configuration (dimensions, shape) etc. of the recess 24, it becomes easier to finely adjust the shape of the magnetic field distribution f in the magnetic field generated in the working space 6 by the magnetic field generating device 1. For example, by adjusting the configuration of the recess 24, it becomes easy to adjust the magnetic field distribution f to have a gradient waveform portion fk, as in the example of Figure 6. The gradient waveform portion fk is a waveform portion of the magnetic field distribution f that extends linearly so that the magnetic flux density (absolute value) (T) increases toward the first depth direction side DD1. In this embodiment, the magnetic field generating device 1 is configured so that the magnetic field distribution f has the gradient waveform portion fk. As shown in the example of Figure 6, it is preferable that the inclined waveform section fk passes through the center DDC of the depth direction DD of the superconducting coil 3 (i.e., it is present on both sides of the center DDC, straddling the center DDC), and it is even more preferable that the approximate center of the inclined waveform section fk is located on the center DDC of the depth direction DD of the superconducting coil 3. By having the inclined waveform portion fk, when the billet W is heated using a billet heating device equipped with the magnetic field generator 1, the billet W can be heated so that the temperature of the billet W increases linearly and uniformly toward the first depth side DD1. Therefore, when the billet W is subsequently extruded using an extruder, the billet W can be inserted into the extruder with the first depth side DD1, which has a higher temperature, facing the extrusion outlet. This makes it possible to further stabilize the temperature of the billet W as it is extruded during extrusion, thereby further improving the processing accuracy of the extrusion process. On the other hand, if the magnetic field distribution f does not have the inclined waveform portion fk (for example, if the magnetic field distribution f is as shown by the dashed line in FIG. 6 ), the temperature of the billet W does not increase linearly and uniformly toward the first depth side DD1, and therefore the temperature of the billet W as it is extruded during extrusion cannot be stabilized as much. Another advantage is that the recess 24 allows the opposing core portion 23 (and thus the iron core 2) to be lighter in weight. However, the recess 24 does not necessarily have to be provided. In this example, the end surface 223 of the axially inner ADI of the opposing core portion 23 does not have a protrusion protruding toward the axially inner ADI on the inner side of the superconducting coil 3. As a method for fine-tuning the shape of the magnetic field distribution f, it is possible to provide such a protrusion instead of or in addition to the recess 24. In that case, however, it is necessary to ensure a longer distance between the end surface 223 of the axially inner ADI of the opposing core portion 23 and the opposing wall 42 of the vacuum insulated container 4. As in this example, the end surface 223 of the axially inner ADI of the opposing core portion 23 does not have a protrusion on the inner side of the superconducting coil 3, so that an increase in the distance between the end surface 223 of the axially inner ADI of the opposing core portion 23 and the wall 42 of the vacuum insulated container 4 can be avoided.

[0053] As shown in FIG. 3, it is preferable that the recess 24 is located on the center DDC of the superconducting coil 3 in the depth direction DD (that is, the recess 24 and the center DDC overlap). The center of the recess 24 in the depth direction DD may be located on the center DDC of the superconducting coil 3 in the depth direction DD, or may be located at a position offset from the center DDC of the superconducting coil 3 in the depth direction DD.

[0054] In the example of FIG. 5, the recess 24 has a rectangular shape in a plan view (FIG. 5) in the axial direction AD, and the length of the recess 24 in the longitudinal direction OD is constant along the depth direction DD. However, the recess 24 may have any shape when viewed in plan in the axial direction AD (FIG. 5), and the length of the recess 24 in the longitudinal direction OD does not have to be constant along the depth direction DD.

[0055] 3, it is preferable that the depth d24 of the recess 24 in the axial direction AD is non-uniform along the depth direction DD. In this case, it becomes easier to finely adjust the shape of the magnetic field distribution f in the magnetic field generated in the working space 6 by the magnetic field generating device 1, and therefore it becomes easier to make the magnetic field distribution f have an inclined waveform portion fk.

[0056] From the viewpoint of making it easier to adjust the magnetic field distribution f as described above, it is preferable that the maximum value of the depth d24 of the recess 24 in the axial direction AD at least on the first axial side AD1 (preferably both) of the pair of opposing core portions 23, on the first depth side DD1 of the center DDC in the depth direction DD of the superconducting coil 3, is smaller than the maximum value of the depth d24 of the recess 24 in the axial direction AD at the second depth side DD2 of the center DDC in the depth direction DD of the superconducting coil 3, as illustrated in Figures 3 and 4. From a similar viewpoint, it is preferable that the maximum value of the depth d24 of the recess 24 in the axial direction AD in each of the four divided sections when the recess 24 is divided into four in the depth direction DD of at least the opposing core sections 23 on the axial first side AD1 (preferably both) of the pair of opposing core sections 23 becomes gradually smaller the closer the divided section is located to the depth direction first side DD1. From a similar viewpoint, it is preferable that the volume of the recess 24 of at least the opposing core portions 23 on the first axial side AD1 (preferably both) of the pair of opposing core portions 23 is smaller on the first depth side DD1 of the center DDC in the depth direction DD of the superconducting coil 3 than the volume of the recess 24 on the second depth side DD2 of the center DDC in the depth direction DD of the superconducting coil 3. From a similar viewpoint, it is preferable that the volume of the recess 24 in each of the four divided sections when the recess 24 is divided into four sections in the depth direction DD of at least the opposing core sections 23 on the axial first side AD1 (preferably both) of the pair of opposing core sections 23 is gradually smaller the closer the divided section is to the depth direction first side DD1. Note that the shape of the recess 24 may be any shape in a cross section parallel to the axial direction AD and the depth direction DD (FIG. 3). For example, in a cross section parallel to the axial direction AD and the depth direction DD, the shape of the recess 24 may be a curved line shape without any angular edges, as in the example of FIG. 3. Alternatively, in a cross section parallel to the axial direction AD and the depth direction DD, the shape of the recess 24 may be a broken line shape bent at one or more points. In this case, it becomes easier to design the shape of the recess 24. In this case, for example, in a cross section parallel to the axial direction AD and the depth direction DD, the shape of the recess 24 may be a broken line shape formed by connecting multiple points arranged at a predetermined pitch (for example, about 30 mm to 60 mm) along the depth direction DD with straight lines.

[0057] When the magnetic field distribution f (Figure 6) has an inclined waveform portion fk, it is preferable that the magnetic flux density (absolute value) (T) gradually decreases from the end fka of the inclined waveform portion fk on the first depth side DD1 toward the first depth side DD1, as in the example of Figure 6, and that the magnetic flux density (absolute value) (T) gradually decreases from the end fkb of the inclined waveform portion fk on the second depth side DD2 toward the second depth side DD2.

[0058] When the magnetic field distribution f (Figure 6) has an inclined waveform portion fk, the length in the depth direction DD of the region in the working space 6 corresponding to the inclined waveform portion fk may be the same as the total length of the billet W, or it may be shorter or longer. The shorter the length in the depth direction DD of the region in the working space 6 corresponding to the inclined waveform portion fk is relative to the overall length of the billet W, the higher the magnetic flux density in the inclined waveform portion fk becomes locally, and therefore the temperature of the billet W as it is extruded cannot be made more constant during extrusion molding of the billet W. Therefore, from the viewpoint of heating the billet W so that its temperature increases as uniformly as possible in a linear function as it approaches the first depth direction side DD1, it is preferable that the length in the depth direction DD of the region in the working space 6 corresponding to the inclined waveform portion fk be 100% or more of the overall length of the billet W.

[0059] 5, the recess 24 may be spaced from the superconducting coil 3 toward the inner peripheral side. The end surface 223 of the axially inner side ADI of the opposing core portion 23 may have an uneven portion such as a hole for fixing a component in the region between the superconducting coil 3 and the recess 24.

[0060] As illustrated in Figures 2 and 3, it is preferable that the end face 223 of the axially inner side ADI of the opposing core portion 23, on the inner side of the superconducting coil 3, has a flat surface portion excluding uneven portions such as depressions 24, which is parallel to the axial direction. [Industrial Applicability]

[0061] The magnetic field generating device according to the present invention can be used for any purpose, for example, as a billet heating device for heating a billet (for example, an aluminum billet). [Explanation of symbols]

[0062] 1. Magnetic field generator 2 Iron core 21 York 21a Legs 21b Middle part 22 Split core 221 Outer surface 2211 Step 2211a Axis-perpendicular surface 2211b Axial plane 223 Axial inner end face 23 opposing core section 24 depression 3 Superconducting coil 31 First curved part 32 Second curved part 33 Connecting part 3о Outer surface 3i Inner surface Ra, Rb, Rc, Rd Radius of curvature DDC Superconducting coil depth center 4. Vacuum insulated container 42, 43 Wall 5. Segmented core coil assembly 6. Workspace O axis AD Axial direction (opposing direction) ADI Axial inside ADO axially outward OD longitudinal direction OD1 Vertical first side OD2 Second vertical side DD Depth direction DD1 Depth direction 1st side DD2 Depth direction second side W Billet WC billet center axis f magnetic field distribution fk slope waveform section fka End of the inclined waveform section on the first side in the depth direction fkb End of the second side in the depth direction of the inclined waveform section

Claims

1. Iron core and a pair of superconducting coils; A magnetic field generating device comprising: the iron core has a substantially C-shape in a cross section parallel to an axial direction parallel to a predetermined axis and a vertical direction perpendicular to the axial direction, The iron core has a pair of opposing core portions that extend on the axis and are arranged opposite each other in the axial direction with a working space interposed therebetween, Each of the superconducting coils is wound around each of the opposing core portions in a circumferential direction centered on the axis, When a direction perpendicular to the axial direction and the longitudinal direction is referred to as a depth direction, each of the superconducting coils has a depth as follows when viewed in a plan view in the axial direction: a first curved linear portion extending in a curved linear shape that is convex toward the first side in the depth direction; a second curved linear portion located on a second depth direction side relative to the first curved linear portion and extending in a curved linear shape that is convex toward the second depth direction side; a pair of connecting portions that connect the first curved linear portion and the second curved linear portion to each other; It consists of A magnetic field generating device, wherein at least one of the pair of superconducting coils on the first axial side has a radius of curvature of the inner surface of the first curved linear portion that is larger than the radius of curvature of the inner surface of the second curved linear portion when viewed in a plane in the axial direction.

2. 2. The magnetic field generating device according to claim 1, wherein at least one of the pair of opposing core portions on the first axial side has an inner end face in the axial direction that is recessed outward in the axial direction, on an inner side of the superconducting coil.

3. The magnetic field generating device according to claim 2 , wherein the recess has a depth in the axial direction that is non-uniform along the depth direction.

4. 2. The magnetic field generating device according to claim 1, wherein the magnetic field generating device is configured such that, in a magnetic field distribution where the horizontal axis represents the depth position and the vertical axis represents the magnetic flux density of the magnetic field generated in the working space by the magnetic field generating device, the maximum value of the magnetic flux density on the first depth side relative to the depth center of the superconducting coil is higher than the maximum value of the magnetic flux density on the second depth side relative to the depth center of the superconducting coil.

5. 2. The magnetic field generating device according to claim 1, wherein the magnetic field distribution has an inclined waveform portion that extends linearly so that the magnetic flux density increases as it passes through the center of the superconducting coil in the depth direction and moves toward the first side in the depth direction, when the horizontal axis represents the position in the depth direction and the vertical axis represents the magnetic flux density of the magnetic field generated in the working space by the magnetic field generating device.

6. The magnetic field generating device further includes one or a pair of vacuum insulated containers, The iron core is a substantially C-shaped or substantially U-shaped yoke; a pair of split core portions that are configured separately from the yoke, are located inside the yoke, and constitute at least a part of the pair of opposing core portions; and the superconducting coils are wound around the respective split core portions along the circumferential direction, a split core-coil assembly including the split core portions and the superconducting coil wound around the split core portions is housed in one or a pair of vacuum insulated containers, 6. The magnetic field generating device according to claim 1, wherein the yoke is disposed outside the one or pair of vacuum insulating containers.

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