Magnetic field generating device

Abstract

A magnetic field generation device 1 comprising an iron core 2 and a pair of superconducting coils 3, wherein the iron core is substantially C-shaped in a cross section parallel to an axial direction AD parallel to a predetermined axis O and a vertical direction OD perpendicular to the axial direction, the iron core having a pair of opposing iron core parts 23, each of which is wound with a respective superconducting coil in the circumferential direction around the axis, each superconducting coil comprising a first curved part 31, a second curved part 32, and a pair of coupling parts 33, and wherein at least the superconducting coil on the first side in the axial direction of the pair of superconducting coils has, in a plan view in the axial direction, an inner peripheral surface radius of curvature Ra of the first curved part that is larger than the inner peripheral surface radius of curvature Rb of the second curved part.

Description

magnetic field generator

[0001] This application claims priority to Japanese Patent Application No. 2024-073123, filed on April 26, 2024, the entire contents of which are incorporated herein by reference. This invention relates to a magnetic field generating device.

[0002] Conventionally, there has been a magnetic field generating device that includes an iron core that is approximately 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).

[0003] Japanese Patent Application Publication No. 2005-123084

[0004] In conventional magnetic field generating devices, 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 of the depth direction higher than the magnetic flux density on the other side of the depth direction in relation to the magnetic field generated in the work space.

[0006] [1] A magnetic field generating device comprising an iron core and a pair of superconducting coils, wherein 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 each extending on the axis and arranged opposite each other in the axial direction with a working space interposed therebetween, each of the superconducting coils being wound around each of the opposing core portions in a circumferential direction centered on the axis, and when a direction perpendicular to the axial direction and the vertical direction is referred to as a depth direction, each of the superconducting coils has, 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, and a second curved linear portion located on a second side in the depth direction relative to the first curved linear portion and extending in a curved linear shape that is convex toward the second side in the depth direction, a pair of connecting portions that connect the first curved linear portion and the second curved linear portion together, wherein at least one of the pair of superconducting coils on a first axial side has a radius of curvature of the inner circumferential surface of the first curved linear portion that is larger than the radius of curvature of the inner circumferential surface of the second curved linear portion when viewed in a plane in the axial direction.

[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 side of the superconducting coil.

[0008] [3] A magnetic field generating device according to [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 according to any one of [1] to [5], further comprising one or a pair of vacuum insulated containers, wherein the core has: a substantially C-shaped or substantially U-shaped yoke; and a pair of split core sections that are configured separately from the yoke, are located inside the yoke, and constitute at least a part of the pair of opposing core sections; each of the superconducting coils is wound around each of the split core sections along the circumferential direction; a split core-coil assembly consisting of the split core sections and the superconducting coils wound around the split core sections is housed in the one or a pair of vacuum insulated containers; and the yoke is arranged outside the one or a pair of vacuum insulated containers.

[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.

[0013] 5 is a perspective view showing a schematic representation of a magnetic field generating device according to an embodiment of the present invention. FIG. 5 is an A-A cross-sectional view showing the magnetic field generating device of FIG. 1 taken along line A-A in FIG. 1. FIG. 6 is a B-B cross-sectional view showing the magnetic field generating device of FIG. 2 taken along line B-B in FIG. 2. FIG. 7 is a C-C cross-sectional perspective view showing a part of the magnetic field generating device of FIG. 2 together with a cross-section taken along line C-C in FIG. 2. FIG. 8 is a plan view showing the split core coil assembly of FIG. 4 as seen in a plan view in the axial direction. FIG. 9 is a graph showing an example of the magnetic field distribution of the magnetic field generated in the working space by the magnetic field generating devices of FIGS. 1 to 5.

[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 (e.g., an aluminum billet). Hereinafter, an embodiment of the magnetic field generating device according to the present invention will be described with reference to the drawings.

[0015] FIGS. 1 to 6 are diagrams illustrating a magnetic field generator 1 according to one embodiment of the present invention. First, the schematic configuration of the magnetic field generator 1 of this embodiment will be described with reference to FIGS. 1 to 5. FIG. 1 is a perspective view schematically illustrating the magnetic field generator 1 according to one embodiment of the present invention. FIG. 2 is an A-A cross-sectional view of the magnetic field generator 1 of FIG. 1 taken along line A-A in FIG. 1. Line A-A 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 B-B cross-sectional view of the magnetic field generator 1 of FIG. 2 taken along line B-B in FIG. 2. Line B-B 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 C-C cross-sectional perspective view showing a portion of the magnetic field generator 1 of FIG. 2 together with a cross section taken along line C-C in FIG. 2. The line CC in Fig. 2 is perpendicular to the axial direction AD, and the cross section in Fig. 4 is parallel to the longitudinal direction OD and the depth direction DD (and therefore parallel to the direction perpendicular to the axis). Fig. 5 is a plan view showing the split core coil assembly 5 in Fig. 4 as seen in the axial direction AD. The magnetic field generating device 1 is configured to generate a magnetic field in a working space 6. The working space 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 in the axial direction AD is referred to as the "axial first side AD1," and the other side in the axial direction AD is referred to as the "axial second side AD2." Furthermore, the side in the axial direction AD closer to the workspace 6 is referred to as the "axial inner side ADI," and the side in the axial direction AD farther from the workspace 6 is referred to as the "axial outer side ADO." Furthermore, the direction perpendicular to the axial direction AD is referred to as the "axial direction." Furthermore, 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 in the vertical direction OD is referred to as the "longitudinal first side OD1," and the other side in the vertical direction OD is referred to as the "longitudinal second side OD2." One side in the depth direction DD is referred to as the "first depth side DD1," and the other side in the depth direction DD is referred to as the "second depth side DD2." In each figure, the above directions are indicated by arrows. In this specification, the circumferential direction and radial direction centered on the axis O may be simply referred to as the "circumferential direction" and the "radial direction," respectively. Unless otherwise specified, the "outer peripheral side" and the "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 generator 1 may be oriented so 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 generator 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 insulated containers 4. In this embodiment, the pair of superconducting coils 3 are disposed inside the pair of vacuum insulated 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 composed of multiple (three in this embodiment) separate members, as in this embodiment, or the entire iron core 2 may be composed of only one member by being integrally configured. The iron core 2 (and therefore each member constituting the iron core 2) is composed of a member containing a magnetic material and is configured to allow magnetic flux to pass through. In this embodiment, the iron core 2 is composed of iron.

[0019] In this embodiment, the core 2 is composed 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 is generally U-shaped or C-shaped (generally U-shaped in this embodiment). More specifically, in this embodiment, the yoke 21 is composed of a pair of legs 21a each extending in the longitudinal direction OD and an intermediate portion 21b connecting the ends of the pair of legs 21a on the 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 giving the yoke 21 a generally U-shaped. However, the pair of legs 21a may also extend from the intermediate portion 21b to the second longitudinal side OD2 and then to the axially inward side ADI, thereby giving the yoke 21 a generally C-shaped.

[0021] The pair of split core portions 22 are configured separately from the yoke 21. The pair of split core portions 22 are located inside the yoke 21 (specifically, on the axially inner side ADI of the pair of legs 21a of the yoke 21) and are arranged opposite each other across the working space 6. The pair of split core portions 22 and the pair of legs 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 extend on the axis O and are arranged opposite each other in the axial direction AD with the work space 6 interposed therebetween. The pair of opposing core portions 23 are composed of both end portions of the approximately C-shape of the core 2. In this embodiment, the pair of opposing core portions 23 are composed 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 approximately C-shaped, the pair of opposing core portions 23 may be composed of a pair of split core portions 22 as well as a portion of a pair of legs 21 a of the yoke 21. Unless otherwise specified, matters described in this specification regarding the split core portions 22 can also apply to each of the pair of split core portions 22. Furthermore, unless otherwise specified, the matters described in this specification regarding the opposing core portions 23 can be applied to each of the pair of opposing core portions 23.

[0023] As shown in FIGS. 1 to 5 , each superconducting coil 3 is wound around each opposing core portion 23 (in this embodiment, the split core portions 22) in the circumferential direction centered on the axis O (in other words, so as to circle around the axis O). The superconducting coil 3 is located on the outer peripheral side of an outer circumferential surface 221 of the opposing core portion 23 (specifically, in this embodiment, a stepped portion 2211 of the outer circumferential surface 221, which will be described later), and faces the outer circumferential surface 221 while being spaced apart radially, or is in contact with the outer circumferential surface 221. Unless otherwise specified, matters described in this specification regarding the superconducting coil 3 can apply to each of the pair of superconducting coils 3. 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. The superconducting coil 3 may further include, in addition to the coil body, a coil case that houses the coil body. The coil case is made of, for example, resin. 5, the superconducting coil 3 has a ring shape that goes around the axis O when viewed in a plan view in the axial direction AD. The shape of the superconducting coil 3 in a cross section perpendicular to the axial direction AD is almost constant along the 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 generator 1 has a pair of split core coil assemblies 5. Unless otherwise specified, matters described in this specification regarding the split core coil assembly 5 can apply to each of the pair of split core coil assemblies 5.

[0026] As shown in Fig. 2, in this embodiment, a pair of split core coil assemblies 5 are housed in a pair of vacuum insulated containers 4, respectively. The yoke 21 is disposed outside the pair of vacuum insulated containers 4. The pair of vacuum insulated containers 4 face each other in the axial direction AD with the work space 6 interposed therebetween. Unless otherwise specified, matters described in this specification regarding the vacuum insulated container 4 can apply to each of the pair of vacuum insulated containers 4. As shown in Fig. 2, the vacuum insulated container 4 includes a wall 42 located between the split core coil assembly 5 and the work space 6, and a wall 43 located between the split core coil assembly 5 and the leg portion 21a of the yoke 21.

[0027] The magnetic field generator 1 includes 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. Thus, the vacuum insulated container 4, together with the refrigerator, cools the segmented core coil assembly 5 and thus the superconducting coil 3, maintaining 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 a laminated insulation material on part or all of its walls. The laminated insulation material is preferably formed, for example, by laminating multiple layers 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 in this manner, when a current is passed through 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 working space 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, such as 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 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. During this time, the billet W is rotated around the billet central axis WC by the motor, which is equivalent to applying an AC 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 generator 1 includes the superconducting coil 3, which allows a stronger magnetic field to be generated in the working space 6 than if the magnetic field generator 1 included a normal copper coil instead of the superconducting coil 3. Furthermore, in this embodiment, the magnetic field generator 1 includes the iron core 2. This allows a stronger magnetic field to be generated while reducing the amount of superconductor used in manufacturing the superconducting coil 3 compared to if the magnetic field generator 1 did not include the iron core 2. This reduces the amount of superconductor used and ultimately reduces costs. Since superconductors are generally expensive, reducing the amount of superconductor used significantly reduces costs. Furthermore, in this embodiment, the iron core 2 of the magnetic field generator 1 includes the yoke 21. This reduces magnetic circuit resistance and increases magnetic flux compared to if the iron core 2 did not include the yoke 21.

[0031] Furthermore, in this embodiment, as described above, the 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 core 2 and the pair of superconducting coils 3 wound around the pair of opposing core portions 23 of the 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 insulated container 4. In that case, the magnetic field generator 1 may be provided with only one vacuum insulated container 4.

[0033] Alternatively, each of the pair of vacuum insulated containers 4 may be configured in a doughnut shape, and the pair of vacuum insulated containers 4 may house only the pair of superconducting coils 3 that wrap around the pair of opposing core portions 23 of the iron core 2, with the iron core 2 being disposed 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, i.e., 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. In addition, 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 core portions 22 and therefore the opposing core portions 23), and therefore the iron core 2 (specifically, the split 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 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 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 portions 22 and therefore the opposing iron core portions 23) and the superconducting coil 3 are in contact with each other, the cold storage effect of the iron core 2 (specifically, the split iron core portions 22 and therefore the opposing iron core portions 23) can be utilized to suppress the temperature rise of the superconducting coil 3 compared to when the vacuum insulated container 4 is doughnut-shaped as described above. As a result, the superconducting coil can be cooled sufficiently, and the capabilities of the superconductor can be utilized effectively.

[0034] In this embodiment, the split core coil assembly 5 may be supported relative to the vacuum insulated container 4 via any support structure so as to maintain the split core coil assembly 5 at a desired position within the vacuum insulated 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 relative to 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 effectively utilizing the capabilities 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 an end face 223 of the axially inner side ADI of the opposing core portion 23 (in this embodiment, the split core portions 22). The superconducting coil 3 is wound around the step portion 2211 in the circumferential direction centered on the axis O. As a result, the superconducting coil 3 and the opposing core portion 23 (the split core portion 22 in this embodiment) face each other in the axial direction AD. This more effectively cancels out 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, 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, movement of the superconducting coil 3 toward the axial outer side ADO is restricted by the step portion 2211 (particularly the surface 2211a perpendicular to the axis). That is, the step portion 2211 has the function of restricting the movement of the superconducting coil 3 toward the axially 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 and enabling the superconducting coil to be sufficiently cooled, thereby enabling effective utilization of the superconductor's capabilities. 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), so a stronger magnetic field can be generated in the working space 6.Furthermore, since the superconducting coil 3 is in contact not only with the axial surface 2211b of the step portion 2211 but also with the axial surface 2211a of the step portion 2211, the contact area with the opposing core portion 23 increases accordingly, 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, the outer peripheral surface 221 of the opposing core portion 23 may have an annular groove. The groove extends over the entire circumference in the circumferential direction centered on the 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, the 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 of the opposing core portion 23 that does not have any unevenness such as steps 2211 or grooves. 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 necessarily have to be provided.

[0042] The leg 21a of the yoke 21 and the wall 43 of the vacuum insulated 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 disposed 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, in a plan view in the axial direction AD ( FIG. 5 ), comprises a first curved linear portion 31, a second curved linear portion 32, and a pair of connecting portions 33. 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 over approximately half the circumference, thereby extending 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 over approximately half the circumference, thereby extending 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 the 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 the 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 overlap with the center DDC).

[0046] In the plan view ( FIG. 5 ) in the axial direction AD, at least the superconducting coil 3 on the first axial side AD1 (preferably both) of the pair of superconducting coils 3 has a radius of curvature Ra of the inner circumferential surface 3i of the first curved linear portion 31 (i.e., a portion of the inner circumferential surface 3i of the superconducting coil 3 that follows the first curved linear portion 31) that is larger than a radius of curvature Rb of the inner circumferential surface 3i of the second curved linear portion 32 (i.e., a portion of the inner circumferential 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 coil 3 on the first axial side AD1 (preferably both) of the pair of superconducting coils 3 has 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 illustrating 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 (FIGS. 1 to 5) of this embodiment. 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. As can be seen from the magnetic field distribution f of the example of FIG. 6, the magnetic field generated in the work space 6 by the magnetic field generating device 1 of this embodiment has a higher maximum value of magnetic flux density (T) on a first depth direction side DD1 relative to the center DDC of the superconducting coil 3 in the depth direction DD than a higher maximum value of magnetic flux density (T) on a second depth direction side DD2 relative to the center DDC of the superconducting coil 3 in the depth direction DD. That is, roughly speaking, the magnetic flux density on one side in the depth direction DD (first depth direction side DD1) is higher than the magnetic flux density on the other side in the depth direction DD (second depth direction 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 the magnetic flux density on both sides of the center DDC in the depth direction DD, the magnetic flux density on the first depth direction side DD1, where the first curved linear portion 31 having a larger diameter (specifically, the radius of curvature of the inner circumferential surface 3 i is larger) of the first curved linear portion 31 and the second curved linear portion 32 of the superconducting coil 3 is located, is higher than the magnetic flux density on the second depth direction side DD2, where the second curved linear portion 32 having a smaller diameter (specifically, the radius of curvature of the inner circumferential surface 3 i) of the first curved linear portion 31 and the second curved linear 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 ( FIG. 6 ), 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 is 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. 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, during extrusion molding of a billet W, the billet W inserted into the extruder is compressed in the direction of the billet central axis WC while being extruded. During this process, the temperature of the billet W in the extruder increases as the billet W is compressed. However, the portion of the billet W on the extruder's extrusion outlet side is extruded before its temperature rises significantly, so its temperature does not rise significantly. Meanwhile, the portion of the billet W on the opposite side (the side pushed by the extruder's extrusion rod) gradually rises in temperature before being extruded, so that the billet W is ultimately extruded in a significantly elevated temperature state. However, from the viewpoint of extrusion processing accuracy, it is desirable for the temperature of the billet W to be as constant as possible when being extruded. 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, 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 keep the temperature of the billet W as it is extruded more constant during extrusion, thereby improving the processing accuracy of the extrusion process.

[0049] From the same viewpoint as above, as in the example of Fig. 5 , it is preferable that, in a plan view (Fig. 5) in the axial direction AD, the radius of curvature Rc of the outer circumferential surface 3o of the first curved linear portion 31 of at least (preferably both) of the pair of superconducting coils 3 (i.e., the portion of the outer circumferential surface 3o of the superconducting coil 3 that follows the first curved linear portion 31) is larger than the radius of curvature Rd of the outer circumferential surface 3o of the second curved linear portion 32 (i.e., the portion of the outer circumferential surface 3o of the superconducting coil 3 that follows the second curved linear portion 32). This makes it possible to make 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 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. Furthermore, it is possible to reduce the amount of superconducting coil 3 used, and thus the cost. Note that the 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 3o of the first curved linear portion 31 is larger than the radius of curvature Rd of the outer peripheral surface 3o of the second curved linear portion 32" means that the minimum value of the radius of curvature Rc of the outer peripheral surface 3o 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 3o 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 3o 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 3o of the second curved linear portion 32 is smallest).

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

[0051] In plan view in the axial direction AD ( FIG. 5 ), the inner circumferential surfaces 3i of the pair of coupling portions 33 of the superconducting coil 3 may extend linearly as in the example of FIG. 5 , or may extend in another form, for example, they may extend along curved lines that are convexly curved away from each other in the longitudinal direction OD. Similarly, in plan view in the axial direction AD ( FIG. 5 ), the outer circumferential surfaces 3o of the pair of coupling portions 33 of the superconducting coil 3 may extend linearly as in the example of FIG. 5 , or may extend in another form, for example, they may extend along curved lines that are convexly curved away from each other in the longitudinal direction OD.

[0052] As shown in FIGS. 3 to 5 , it is preferable that at least one of the pair of opposing core portions 23 on the first axial side AD1 (preferably both) has a recess 24 on the end surface 223 of the axial inner side ADI recessed toward the axial outer side ADO, on the inner circumferential side of the superconducting coil 3. Adjusting the configuration (dimensions and shape) of the recess 24 facilitates fine adjustment of the shape of the magnetic field distribution f in the magnetic field generated in the workspace 6 by the magnetic field generating device 1. For example, adjusting the configuration of the recess 24 facilitates adjustment so that the magnetic field distribution f has a sloped waveform portion fk, as shown in the example of FIG. 6 . The sloped 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 side DD1. In this embodiment, the magnetic field generating device 1 is configured so that the magnetic field distribution f has a sloped waveform portion fk. As shown in the example of Figure 6, it is preferable that the inclined waveform portion fk passes through the center DDC in the depth direction DD of the superconducting coil 3 (i.e., it exists on both sides of the center DDC across the center DDC), and it is more preferable that the approximate center of the inclined waveform portion fk is located on the center DDC in the depth direction DD of the superconducting coil 3. When the magnetic field distribution f has the inclined waveform portion fk, for example, when the billet W is heated by a billet heating device including the magnetic field generating device 1, the billet W can be heated so that the temperature of the billet W increases uniformly as a linear function toward the first depth direction side DD1. As a result, when the billet W is subsequently extruded by an extruder, the billet W can be inserted into the extruder with the first depth direction side DD1, which has a higher temperature, facing the extrusion outlet side. This makes it possible to make the temperature of the billet W when extruded even more constant during extrusion, and ultimately to further improve the processing accuracy of the extrusion processing. On the other hand, if the magnetic field distribution f does not have an inclined waveform portion fk (for example, if the magnetic field distribution f is as shown by the dashed line in Figure 6), the temperature of the billet W does not increase uniformly as a linear function as it moves toward the first depth side DD1, and therefore the temperature of the billet W when extruded during extrusion molding cannot be made very constant.Another advantage is that the recess 24 allows for a reduction in the weight of the opposing core portion 23 (and thus the core 2). However, the recess 24 does not have to be provided. In this example, the end face 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. Providing such a protrusion instead of or in addition to the recess 24 is one method of fine-tuning the shape of the magnetic field distribution f. However, in this case, it is necessary to ensure a longer distance between the end face 223 of the axially inner ADI of the opposing core portion 23 and the wall 42 of the vacuum insulated container 4 facing it. Since the end face 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, as in this example, an increase in the distance between the end face 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] 3 , it is preferable that the recess 24 is located on the center DDC in the depth direction DD of the superconducting coil 3 (i.e., 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 in the depth direction DD of the superconducting coil 3, or may be located at a position shifted from the center DDC in the depth direction DD of the superconducting coil 3.

[0054] In the example of Fig. 5, the recess 24 has a rectangular shape when viewed in a plan view in the axial direction AD (Fig. 5), 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 a plan view 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 workspace 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 facilitating the adjustment of the magnetic field distribution f as described above, it is preferable that, in at least one of the pair of opposing core portions 23 on the first axial side AD1 (preferably both), the maximum value of the depth d24 of the recess 24 in the axial direction AD 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 on 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 the same viewpoint, it is preferable that, in at least one of the pair of opposing core portions 23 on the first axial side AD1 (preferably both), 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 becomes gradually smaller the closer to the first depth side DD1 the divided section is located. From a similar viewpoint, it is preferable that the volume of the recess 24 on at least the opposing core portions 23 on the first axial side AD1 (preferably both) of the pair of opposing core portions 23 be smaller on the first depth side DD1 of the center DDC in the depth direction DD of the superconducting coil 3 than 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 on at least the opposing core portions 23 on the first axial side AD1 (preferably both) of the pair of opposing core portions 23 be smaller in each of the four divided sections when the recess 24 is divided into four sections in the depth direction DD, the closer the divided section is to the first depth side DD1. Note that the shape of the recess 24 may be any shape in a cross section ( FIG. 3 ) parallel to the axial direction AD and the depth direction DD. 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 shown 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 is 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, approximately 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 on the first depth side DD1 of the inclined waveform portion fk 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 on the second depth side DD2 of the inclined waveform portion fk toward the second depth side DD2.

[0058] When the magnetic field distribution f ( FIG. 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 equal to, shorter than, or longer than the entire length of the billet W. The shorter the length in the depth direction DD of the region in the working space 6 corresponding to the inclined waveform portion fk relative to the entire length of the billet W, the higher the magnetic flux density of the inclined waveform portion fk becomes locally. Therefore, during the extrusion molding of the billet W, the temperature of the billet W as it is extruded cannot be made more constant. Therefore, from the viewpoint of heating the billet W so that its temperature increases as uniformly as possible in a linear function toward 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 entire length of the billet W.

[0059] 5, the recess 24 may be spaced away from the superconducting coil 3 toward the inner peripheral side. An uneven portion such as a hole for fixing a component may be present on the end surface 223 of the axially inner ADI of the opposing core portion 23 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 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 recesses 24, which is parallel to the axial direction.

[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).

[0062] REFERENCE SIGNS LIST 1 magnetic field generator 2 iron core 21 yoke 21a leg portion 21b middle portion 22 split core portion 221 outer peripheral surface 2211 step portion 2211a axially perpendicular surface 2211b axial surface 223 axially inner end surface 23 opposing core portion 24 recess 3 superconducting coil 31 first curved wire portion 32 second curved wire portion 33 connecting portion 3o outer peripheral surface 3i inner peripheral surface Ra, Rb, Rc, Rd curvature radius DDC center of superconducting coil in depth direction 4 vacuum insulated container 42, 43 wall 5 split core coil assembly 6 working space O axis AD axial direction (opposing direction) ADI axially inner side ADO axially outer side OD longitudinal direction OD1 First longitudinal side OD2 Second longitudinal side DD Depth direction DD1 First depth side DD2 Second depth side W Billet WC Central axis of billet f Magnetic field distribution fk Slanted waveform portion fka End of the slanted waveform portion on the first depth side fkb End of the slanted waveform portion on the second depth side

Claims

1. A magnetic field generating device comprising an iron core and a pair of superconducting coils, wherein the iron core is substantially C-shaped 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 each extending on the axis and arranged opposite each other in the axial direction with a working space interposed therebetween, each of the superconducting coils being wound around each opposing core portion in a circumferential direction centered on the axis, and when the direction perpendicular to the axial direction and the vertical direction is referred to as the depth direction, each of the superconducting coils has, 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, and a second curved linear portion located on a second side in the depth direction relative to the first curved linear portion and extending in a curved linear shape that is convex toward the second side in the depth direction, a pair of connecting portions that connect the first curved linear portion and the second curved linear portion together, wherein at least one of the pair of superconducting coils on a first axial side has a radius of curvature of the inner circumferential surface of the first curved linear portion that is larger than the radius of curvature of the inner circumferential surface of the second curved linear portion when viewed in a plane in the axial direction.

2. A magnetic field generating device as described in 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 the inner side of the superconducting coil.

3. A magnetic field generating device according to claim 2, wherein the depth of the recess in the axial direction is non-uniform along the depth direction.

4. The magnetic field generating device of claim 1, wherein the magnetic field generating device is configured so that, in the magnetic field distribution, when 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. The magnetic field generating device of claim 1, wherein the magnetic field generating device is configured so that when 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 magnetic field distribution has an inclined waveform portion that passes through the depth center of the superconducting coil and extends linearly so that the magnetic flux density increases as it moves toward the first depth side.

6. The magnetic field generating device according to any one of claims 1 to 5, further comprising one or a pair of vacuum insulated containers, wherein the core has a substantially C-shaped or substantially U-shaped yoke and a pair of split core sections that are configured separately from the yoke, are located inside the yoke, and constitute at least a part of the pair of opposing core sections, wherein each of the superconducting coils is wound around each of the split core sections along the circumferential direction, and a split core coil assembly consisting of the split core sections and the superconducting coils wound around the split core sections is housed in the one or a pair of vacuum insulated containers, and the yoke is arranged outside the one or a pair of vacuum insulated containers.

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