Cooling system, magnetic field generating device, and operating method

Abstract

To provide a cooling system, a magnetic field generation device, and an operation method, each enabling reduction of drive energy for a cryogenic refrigerator.SOLUTION: A cooling system comprises a cooling unit RU and a control portion. The cooling unit RU has: a vacuum thermal insulation container 4; a superconducting coil 3 that is a cooling object arranged inside the vacuum thermal insulation container; a cryogenic refrigerator CR that has a cold stage portion CRS for generating coldness; a thermal conduction connection portion TC that connects between the cold stage portion and the cooling object thermally conductively; a temperature sensor TS; and current leads D1 and D2 arranged inside the vacuum thermal insulation container. The temperature sensor detects temperature of any one of the cooling object, the cold stage portion, the thermal conduction connection portion, and the current leads. The control portion performs an operation stop process of stopping the operation of the cryogenic refrigerator and an operation start process of starting the operation of the cryogenic refrigerator during the operation of the cryogenic refrigerator depending on the temperature detected by the temperature sensor.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a cooling system, a magnetic field generating device, and an operating method. [Background technology]

[0002] BACKGROUND ART Conventionally, there are cryogenic refrigerators used to cool an object to be cooled (for example, Patent Document 1). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 5-312425 Summary of the Invention [Problem to be solved by the invention]

[0004] Conventional cryogenic refrigerators are always operated at a substantially constant output, and therefore continue to cool the object at the same output even after the temperature of the object has dropped sufficiently, which can result in wasted drive energy.

[0005] The present invention has been made to solve the above-mentioned problems, and aims to provide a cooling system, a magnetic field generating device, and an operating method that can reduce the driving energy of a cryogenic refrigerator. [Means for solving the problem]

[0006] [1] A vacuum insulated container; an object to be cooled placed in the vacuum insulated container; a cryogenic refrigerator having a cold stage configured to generate cold; a heat conductive connection portion that connects the cold stage portion and the object to be cooled in a heat conductive manner; one or more temperature sensors; a current lead disposed within the vacuum insulated container; A control unit; A cooling system comprising: the one or more temperature sensors are configured to detect the temperature of any one of the object to be cooled, the cold stage portion, the heat conductive connection portion, and the current lead; The control unit an operation stop process for stopping the operation of the cryogenic refrigerator when a temperature detected by any one of the temperature sensors drops to a predetermined target cooling temperature during operation of the cryogenic refrigerator; an operation start process for starting operation of the cryogenic refrigerator when a temperature detected by any one of the temperature sensors rises to a predetermined operation start temperature that is higher than the predetermined target cooling temperature while the cryogenic refrigerator is stopped; a cooling system configured to:

[0007] [2] The cooling system described in [1], wherein the predetermined target cooling temperature is equal to or higher than the temperature of the cold stage section when the cooling load of the cold stage section is 5W.

[0008] [3] The object to be cooled includes a high-temperature superconducting wire, The cooling system according to [1] or [2], wherein the predetermined operation start temperature is equal to or lower than the maximum temperature at which the high-temperature superconducting wire can become superconducting.

[0009] [4] The cooling system according to any one of [1] to [3], wherein the heat conducting connection part has a cold storage body.

[0010] [5] The cooling system according to [4], wherein the cooling storage body has a larger heat capacity than the object to be cooled.

[0011] [6] The heat conducting connection has one or more equalizing members, The cooling system according to [4] or [5], wherein the one or more heat equalizing members are in contact with the outer peripheral surface of the cooling storage body over the entire circumference.

[0012] [7] The heat conducting connection part has one or more cooling conductor members, The cooling system according to [6], wherein the one or more cooling conductor members are in contact with the heat equalization member and the object to be cooled.

[0013] [8] The regenerator is an iron core member, the object to be cooled is a superconducting coil, The cooling system according to any one of [4] to [7], wherein the superconducting coil is wound around the iron core member.

[0014] [9] The cooling system is configured to be used in a magnetic field generating device, The magnetic field generating device is the cooling system; a substantially C-shaped or substantially U-shaped yoke; Equipped with The cooling system includes one or a pair of the vacuum insulated containers, the cooling system includes a pair of superconducting coils, each of which is the object to be cooled; the cooling system includes a pair of split core portions each serving as the regenerator, the pair of split core portions are formed separately from the yoke, are located inside the yoke, and are arranged opposite to each other with a working space interposed therebetween, Each of the superconducting coils is wound around each of the split core portions along a circumferential direction about an axis parallel to the direction in which the pair of split core portions face each other, a split core-coil assembly having 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, The cooling system according to any one of [4] to [8], wherein the yoke is disposed outside the one or pair of vacuum insulated containers.

[0015]

[10] A cooling system according to any one of [4] to [8]; a substantially C-shaped or substantially U-shaped yoke; A magnetic field generating device comprising: The cooling system includes one or a pair of the vacuum insulated containers, the cooling system includes a pair of superconducting coils, each of which is the object to be cooled; the cooling system includes a pair of split core portions each serving as the regenerator, the pair of split core portions are formed separately from the yoke, are located inside the yoke, and are arranged opposite to each other with a working space interposed therebetween, Each of the superconducting coils is wound around each of the split core portions along a circumferential direction about an axis parallel to the direction in which the pair of split core portions face each other, a split core-coil assembly having 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, A magnetic field generating device, wherein the yoke is arranged outside the one or pair of vacuum insulated containers.

[0016]

[11] An operating method for the cooling system according to any one of [1] to [8], an operation stopping step in which, when a temperature detected by any one of the temperature sensors drops to a predetermined target cooling temperature during operation of the cryogenic refrigerator, the control unit stops operation of the cryogenic refrigerator; an operation start step in which, when a temperature detected by any one of the temperature sensors rises to a predetermined operation start temperature that is higher than the predetermined target cooling temperature while the operation of the cryogenic refrigerator is stopped, the control unit starts operation of the cryogenic refrigerator; Including, how to drive. [Effects of the Invention]

[0017] According to the present invention, it is possible to provide a cooling system, a magnetic field generating device, and an operating method that can reduce the driving energy of a cryogenic refrigerator. [Brief explanation of the drawings]

[0018] [Figure 1] 1 is a cross-sectional view that schematically illustrates a magnetic field generating device according to an embodiment of the present invention, including a cooling system according to an embodiment of the present invention; [Figure 2] FIG. 2 is an enlarged cross-sectional view of the cooling unit of FIG. 1. [Figure 3] FIG. 3 is a perspective view schematically illustrating the cooling unit of FIG. 2. [Figure 4] 4 is a perspective view schematically showing a portion of the cooling unit of FIG. 3 excluding the vacuum insulating container and the radiation shield. FIG. [Figure 5] FIG. 4 is an exploded perspective view showing the split core-coil assembly of FIG. 3 in an exploded state. [Figure 6] 2 is an enlarged cross-sectional view showing a part of the magnetic field generating device of FIG. 1. FIG. [Figure 7] FIG. 2 is a diagram showing an example of a capacity curve of a two-stage cryogenic refrigerator. [Figure 8] FIG. 1 is a diagram showing an example of the critical current characteristics of a REBCO wire, which is a type of high-temperature superconducting wire. DETAILED DESCRIPTION OF THE INVENTION

[0019] The cooling system according to the present invention and the operating method according to the present invention can be used to cool any object to be cooled, for example, a superconducting coil, and can also be used in any device, for example, a magnetic field generating device. The magnetic field generating device according to the present invention can be used for any purpose, for example, as a heating device for aluminum billets. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of a cooling system, a magnetic field generating device, and an operating method according to the present invention will be described with reference to the drawings.

[0020] 1 shows a magnetic field generating device 1 according to an embodiment of the present invention, which is equipped with a cooling system RS according to an embodiment of the present invention. The cooling system RS of this embodiment is configured to be used in the magnetic field generating device 1. As shown in FIG. 1 , the magnetic field generator 1 of this embodiment includes a cooling system RS according to one embodiment of the present invention and a yoke 21. The cooling system RS of this embodiment includes a pair of cooling units RU and a control unit PS. Each cooling unit RU includes a vacuum insulation container 4, an object to be cooled 3, a cryogenic refrigerator CR, a heat conductive connection part TC, a temperature sensor TS, and a radiation shield SH. The cooling system RS (and thus the magnetic field generator 1) of this embodiment includes a pair of the vacuum insulation container 4, the object to be cooled 3, the cryogenic refrigerator CR, the heat conductive connection part TC, the temperature sensor TS, and the radiation shield SH. In this embodiment, the heat conductive connection part TC includes one or more (one in this embodiment) heat transfer conductor members TP, one or more (four in this embodiment) temperature equalizing members SK, one or more (two in this embodiment) cooling conductor members PM, and a cooling storage body 22. The cooling system RS (and thus the magnetic field generating device 1) of this embodiment includes a pair of cold storage bodies 22. Each cooling unit RU is configured to cool a respective object 3 to be cooled. In this embodiment, the configurations of each cooling unit RU are similar to each other, so when describing a cooling unit RU or its components below, unless otherwise specified, it will be assumed that each cooling unit RU is being described individually.

[0021] In this embodiment, the object to be cooled 3 is a superconducting coil 3. Hereinafter, the object to be cooled 3 may be referred to as a "superconducting coil 3". In this embodiment, the cold storage body 22 is an iron core member 22 and divided iron core portions 22. Hereinafter, the cold storage body 22 may be referred to as an "iron core member 22" or a "divided iron core portion 22".

[0022] The vacuum insulated container 4 is configured to maintain a vacuum inside, thereby maintaining the temperature of the components inside the vacuum insulated container 4 cooled by the cryogenic refrigerator CR.

[0023] Arranged within the vacuum insulating container 4 are an object to be cooled 3, a part of the cryogenic refrigerator CR, a heat conductive connection part TC, a temperature sensor TS, and a radiation shield SH.

[0024] The iron core 2 is composed of the yoke 21 and a pair of split core portions 22 (that is, the regenerator body 22 or the iron core members 22).

[0025] The yoke 21 contains iron and is configured to allow magnetic flux to pass through. The yoke 21 is generally C-shaped or U-shaped (generally C-shaped in the example of FIG. 1). The yoke 21 has a pair of end portions 21a. In the example of FIG. 1, the yoke 21 is oriented so that the pair of end portions 21a face the working space 6. However, as long as the yoke 21 has a surface that faces the axially outer surface ADO of the split core portion 22 with a narrow gap therebetween, the end portions 21a of the yoke 21 may be oriented in any direction. The yoke 21 is disposed outside the pair of vacuum insulating containers 4 .

[0026] The pair of split core portions 22 contain iron and are configured to allow magnetic flux to pass through. 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 and are arranged opposite each other with a working space 6 interposed therebetween. The working space 6 is an air gap. In this way, the iron core 2 is formed in a substantially C-shape.

[0027] In this specification, the direction parallel to the axis O, which passes through the pair of split core portions 22 and extends in a direction in which the pair of split core portions 22 face each other, is referred to as the "axial direction AD." Furthermore, the side of the axial direction AD closer to the working space 6 is referred to as the "axial inner side ADI," and the side of the axial direction AD farther from the working space 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 OD." The side of the axial direction OD closer to the axis O is referred to as the "axial inner side," and the side of the axial direction OD farther from the axis O is referred to as the "axial outer side." Furthermore, in this specification, the circumferential direction centered on the axis O may sometimes be simply referred to as the "circumferential direction." 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. In this specification, a direction perpendicular to the axial direction AD is referred to as the "longitudinal direction VD," and a direction perpendicular to both the axial direction AD and the longitudinal direction VD is referred to as the "depth direction DD." One side in the longitudinal direction VD is referred to as the "first longitudinal side VD1," and the other side in the longitudinal direction VD is referred to as the "second longitudinal side VD2." In this embodiment, the longitudinal direction VD is oriented in the vertical direction, and the first longitudinal side VD1 is oriented upward, but the longitudinal direction VD may be oriented in any direction.

[0028] The pair of split core portions 22 and the pair of end portions 21a of the yoke 21 face each other in the axial direction AD. The pair of split core portions 22 are located on the axially inner sides ADI of the pair of end portions 21a of the yoke 21. The axially outer surfaces ADO of the pair of split core portions 22 face the axially inner surfaces ADI of the pair of yokes 21 with a narrow gap therebetween.

[0029] As shown in FIGS. 1 to 6, a superconducting coil 3 is wound around each of the split core portions 22. More specifically, the superconducting coil 3 is wound around each of the split core portions 22 in a circumferential direction centered on the axis O (in other words, so as to go around the axis O). The superconducting coil 3 is located on the outer circumferential side of the outer peripheral surface 221 of the split core portion 22 (specifically, an axial surface 2211b of a stepped portion 2211, described later, of the outer peripheral surface 221; FIGS. 5 to 6) and faces the outer peripheral surface 221 (specifically, the axial surface 2211b) in the radial direction. However, the superconducting coil 3 may be in contact with the outer peripheral surface 221 of the split core portion 22 (for example, the axial surface 2211b). The superconducting coil 3 is configured to include a superconductor, in other words, it is configured to include a coil body (superconducting wire) including a superconductor. The coil body (superconducting wire) of the superconducting coil 3 is preferably a high-temperature superconducting wire. 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 configured, for example, from resin or the like. As shown in Figure 5, in this example, the superconducting coil 3 has an approximately rectangular ring shape that goes around the axis O in the cross section taken along the axis-perpendicular direction OD. However, the superconducting coil 3 may have any ring shape, such as an approximately circular ring shape or an approximately elliptical ring shape, as long as it has a ring shape that goes around the axis O in the cross section taken along the axis-perpendicular direction OD. 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. The superconducting coil 3 is cooled by the cryogenic refrigerator CR until the superconducting wire constituting the superconducting coil 3, and thus the superconductor, becomes superconducting (and thus until the electrical resistance becomes substantially zero).

[0030] 1 and 2, the split core portions 22 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 has the split core portions 22 and the superconducting coil 3 wound around the split core portions 22. In this embodiment, the cooling system RS (and thus the magnetic field generating device 1) has a pair of split core coil assemblies 5. In this embodiment, the split core coil assembly 5 has, in addition to the split core portion 22 and the superconducting coil 3, one or more (four in this embodiment) heat equalizing members SK and one or more (two in this embodiment) cooling conductor members PM.

[0031] Each split core-coil assembly 5 is housed in a respective vacuum insulating container 4. 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. 6, a wall 42 of the axially inner side ADI in the vacuum insulating container 4 is located between the split iron-core coil assembly 5 and the working space 6. Also, a wall 43 of the axially outer side ADO in the vacuum insulating container 4 is located between the split iron-core coil assembly 5 and the end 21a of the yoke 21.

[0032] In the magnetic field generating device 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 (the yoke 21 and the pair of split core portions 22), generating a strong magnetic field in the working space 6. The strong magnetic field generated in the workspace 6 may be used for any purpose.

[0033] For example, the magnetic field generator 1 may be used in a heating device for an aluminum billet. In this case, the heating device includes, in addition to the magnetic field generator 1, a motor for rotating the aluminum billet. A direct current is passed through the superconducting coil 3, thereby generating a strong direct current magnetic field in the working space 6. The aluminum billet is placed in the working space 6 so that the central axis of the aluminum billet extends in the depth direction DD, and is rotated around the central axis of the aluminum billet by the motor. This is equivalent to applying an alternating current magnetic field to the aluminum billet, causing an induced current to flow in the aluminum billet and heating the aluminum billet.

[0034] The cryogenic refrigerator CR may have any conventionally known configuration. The cryogenic refrigerator CR is preferably a regenerative cryogenic refrigerator, and more specifically, is preferably a Gifford-McMahon (GM) refrigerator, for example. As shown in FIG. 2, the cryogenic refrigerator CR has one or more (two in this embodiment) cold stage units CRS configured to generate cold. More specifically, in this embodiment, the cryogenic refrigerator CR is configured as a two-stage GM refrigerator. As shown in FIG. 2, in this embodiment, the cryogenic refrigerator CR has a cold head CRH and a motor CRM. In this embodiment, the cold head CRH has two refrigeration units CRU (a first-stage refrigeration unit CRU1 and a second-stage refrigeration unit CRU2), each configured to generate cold. Each refrigeration unit CRU includes a cylinder CRC, a displacer CRD configured to be reciprocable within the cylinder CRC along the extension direction of the cylinder CRC, a regenerator material CRL disposed within the displacer CRD, a sealing member CRF provided between the cylinder CRC and the displacer CRD, and a sleeve CRV. Here, the "extension direction of the cylinder CRC" refers to a direction parallel to the central axis of the cylinder CRC. An expansion chamber CRR is defined between the cylinder CRC and the tip end surface of the displacer CRD. The sleeve CRV is made of metal and externally covers the portion of the cylinder CRC that defines the expansion chamber CRR. However, the sleeve CRV is not necessarily provided. The refrigeration unit CRU has a cold stage portion CRS near the expansion chamber CRR. The cold stage portion CRS is configured to generate cold, more specifically, to have a temperature equivalent to that of the cold generated in the expansion chamber CRR. The cold stage portion CRS is composed of, for example, a portion of the cylinder CRC that defines the expansion chamber CRR and the sleeve CRV. The two refrigeration units CRU are connected in series; specifically, the cylinders CRC of each refrigeration unit CRU and the displacers CRD of each refrigeration unit CRU are connected in series. The second-stage refrigeration unit CRU2 is located closer to the tip of the cold head CRH than the first-stage refrigeration unit CRU1. The motor CRM is configured to drive (reciprocate) a displacer CRD housed in the cold head CRH, for example. A compressor (not shown) is connected to the cryogenic refrigerator CR. The compressor is connected to the cold head CRH and configured to compress a refrigerant gas. The refrigerant gas may be, for example, helium gas. An inverter (not shown) may be connected to the cryogenic refrigerator CR. In this case, the inverter is connected, for example, between the power supply of the cryogenic refrigerator CR and the compressor, and is configured to set the power supply frequency of the cryogenic refrigerator CR to a predetermined power supply frequency.

[0035] During operation of the cryogenic refrigerator CR configured as described above, high-pressure refrigerant gas compressed by a compressor (not shown) passes through the cold storage material CRL in each cold storage unit CRU and is cooled by the cold stored in the cold storage material CRL. The refrigerant gas is then guided to the expansion chamber CRR, where it is further cooled by adiabatic expansion. The cooled refrigerant gas then passes through the cold storage material CRL and returns, leaving the cold of the refrigerant gas in the cold storage material CRL. This cycle is repeated, gradually lowering the temperature of the expansion chamber CRR and the cold stage CRS. During this cycle, the temperature of the cold generated in the cold stage CRS becomes lower the further downstream (closer to the tip) the cold unit CRU is. That is, in this embodiment, the temperature of the cold generated in the cold stage section CRS of the second stage refrigeration unit CRU2 (hereinafter also referred to as the "second stage cold stage section CRS2") is set to be lower than the temperature of the cold generated in the cold stage section CRS of the first stage refrigeration unit CRU1 (hereinafter also referred to as the "first stage cold stage section CRS1"). The cryogenic refrigerator CR may be configured as a single-stage cryogenic refrigerator having only one refrigeration unit CRU, or may be configured as a multi-stage cryogenic refrigerator having any number of cold stage sections CRS.

[0036] In this embodiment, the cold head CRH of the cryogenic refrigerator CR is disposed inside the vacuum insulating container 4, and the parts of the cryogenic refrigerator CR other than the cold head CRH (motor CRM, power supply, etc.), a compressor (not shown), an inverter, etc. are disposed outside the vacuum insulating container 4. This makes it possible to prevent excess heat from entering the vacuum insulating container 4 from the parts of the cryogenic refrigerator CR other than the cold head CRH.

[0037] 1 to 5, the heat conductive connection part TC thermally conductively connects the rearmost (foremost) cold stage part CRS (in this embodiment, the second-stage cold stage part CRS2) in the cryocooler CR to the object to be cooled 3. As a result, the heat of the object to be cooled 3 is absorbed (and thus cooled) by the rearmost cold stage part CRS (in this embodiment, the second-stage cold stage part CRS2) in the cryocooler CR via the heat conductive connection part TC. The thermally conductive connection part TC may be made up of any one or more members each made of a thermal conductor such as metal. In this embodiment, the heat conduction connection part TC has one or more (in this embodiment, one) heat transfer conductor members TP, one or more (in this embodiment, four) heat equalization members SK, one or more (in this embodiment, two) cooling conductor members PM, and a cold storage body 22 (i.e., split core parts 22 or iron core members 22), each made of a heat conductor such as metal.

[0038] As shown by the broken lines in FIG. 2, in this embodiment, a first current lead D1 and a second current lead D2, which are current leads, are arranged inside the vacuum insulating container 4. One end of the first current lead D1 is connected to the first bus bar BB1. The first bus bar BB1 is in contact with the first cold stage CRS1. The other end of the first current lead D1 is connected to a hermetic feed-through terminal E. The hermetic feed-through terminal E is attached to the wall of the vacuum insulation container 4. The second current lead D2 has a high-temperature end D2a at one end and a low-temperature end D2b at the other end. The high-temperature end D2a of the second current lead D2 is connected to the first bus bar BB1. The low-temperature end D2b of the second current lead D2 is connected to the second bus bar BB2. The second bus bar BB2 is connected to the superconducting coil 3. The low-temperature end D2b of the second current lead D2 is cooled by a terminal portion of the superconducting coil 3 that is cooled by the second-stage cold stage section CRS2. The high-temperature end D2a of the second current lead D2 is cooled by the first-stage cold stage section CRS1.

[0039] The temperature sensor TS is configured to detect the temperature of any one of the object to be cooled 3, the cold stage section CRS of the cryogenic refrigerator CR (preferably the rearmost (foremost) cold stage section CRS (in this embodiment, the second-stage cold stage section CRS2)), the heat conductive connection TC, and the current leads D1 and D2 (preferably the second current lead D2). Note that the temperature of the rearmost (foremost) cold stage section CRS (in this embodiment, the second-stage cold stage section CRS2) in the cryogenic refrigerator CR is quickly transferred to the object to be cooled 3 via the heat conductive connection TC, so the temperatures of the object to be cooled 3, the cold stage section CRS (in this embodiment, the second-stage cold stage section CRS2), and the heat conductive connection TC tend to be approximately equal to each other. The temperature sensor TS detects the above temperatures periodically (at predetermined time intervals) or continuously. The temperature detection result by the temperature sensor TS is output to the control unit PS via wired communication and / or wireless communication. The temperature sensor TS is preferably placed inside the vacuum insulated container 4, and more preferably in contact with the component whose temperature is to be detected (the object to be cooled 3, the cold stage part CRS, the heat conductive connection part TC, or the current leads D1, D2). In this embodiment, as shown in FIG. 1, the temperature sensor TS is in contact with the heat conducting connection part TC (more specifically, the heat conducting conductor member TP) and is configured to detect the temperature of the heat conducting connection part TC (more specifically, the heat conducting conductor member TP).

[0040] The control unit PS includes a processing device such as a CPU, and is configured to perform an operating method described below by executing a program stored in a storage unit (not shown). Specifically, the control unit PS executes the program to perform various processes described below, thereby controlling the cryogenic refrigerator CR based on the detection results of the temperature sensor TS. The control unit PS may further be configured to control a compressor and / or an inverter connected to the cryogenic refrigerator CR. The storage unit (not shown) is composed of, for example, a ROM and / or RAM, and stores various information such as programs to be executed by the control unit PS. The storage unit may be located outside the control unit PS or inside the control unit PS. In this embodiment, as shown in FIG. 1, only one control unit PS is provided for a pair of cooling units RU, that is, one control unit PS is configured to perform the operating method described below in each cooling unit RU. However, one control unit PS may be provided for each cooling unit RU, that is, each control unit PS may be configured to perform the operation method described below in the corresponding cooling unit RU.

[0041] An operating method according to one embodiment of the present invention will now be described, which is an operating method for a cooling system RS and can be used for any embodiment of the cooling system RS described herein. First, the power supply of the cryogenic refrigerator CR is turned on. The temperature sensor TS periodically (at predetermined time intervals) or continuously detects the temperature of any one of the object to be cooled 3, the cold stage section CRS (in this embodiment, the second cold stage section CRS2) of the cryogenic refrigerator CR, the heat conductive connection section TC, and the current leads D1 and D2, and outputs the detection result to the control section PS. During operation of the cryogenic refrigerator CR, if the temperature detected by the temperature sensor TS drops to a predetermined target cooling temperature THL, the control unit PS performs an operation stop process to stop the operation of the cryogenic refrigerator CR (operation stop step). When the operation of the cryogenic refrigerator CR is stopped, if the temperature detected by the temperature sensor TS rises to a predetermined operation start temperature THH that is higher than the predetermined target cooling temperature THL, the control unit PS performs an operation start process to start the operation of the cryogenic refrigerator CR (operation start step). In this manner, in this operating method, after the power supply of the cryogenic refrigerator CR is turned on, the operation stop processing (operation stop step) and the operation start processing (operation start step) are alternately repeated. The control unit PS may stop / start operation of the cryogenic refrigerator CR, for example, by turning the power supply to the compressor and the cryogenic refrigerator CR OFF / ON. More specifically, the control unit PS may turn the power supply to the compressor OFF / ON, and the compressor may automatically control the stop / start of operation of the cryogenic refrigerator CR accordingly, thereby stopping / starting operation of the cryogenic refrigerator CR. Alternatively, if the compressor and the cryogenic refrigerator CR are configured to be controlled by signals, the control unit PS may output control signals to the compressor and the cryogenic refrigerator CR to stop / start operation, thereby stopping / starting operation of the cryogenic refrigerator CR. During operation of the cryogenic refrigerator CR, the driving capacity of the cryogenic refrigerator CR (such as the power supply frequency and the input power to the compressor) is maintained constant. From the viewpoint of improving the driving efficiency of the cryogenic refrigerator CR, it is preferable that the power supply frequency of the cryogenic refrigerator CR during operation be 50 Hz or 60 Hz, and 60 Hz is more preferable. Generally, in commercially available cryogenic refrigerators CR, the compressor and motor CRM connected to the cryogenic refrigerator CR are operated at a common power supply frequency of 50 Hz or 60 Hz. Generally, refrigeration efficiency is better when the power supply frequency is 60 Hz. It is also possible to use an inverter to change the power input to the compressor and motor CRM to 50 Hz or 60 Hz.

[0042] Note that, in addition to radiation and heat transfer from the wall surface of the vacuum insulated container 4, heat may be introduced into the components inside the vacuum insulated container 4 from the outside of the vacuum insulated container 4 via members (current leads D1, D2, etc.) extending into the inside of the vacuum insulated container 4. The temperature of the object to be cooled 3 may rise due to such heat introduced from the outside while the cryogenic refrigerator CR is not operating.

[0043] According to the operating method of this embodiment, the cryogenic refrigerator CR is not operated continuously, but is stopped once the temperature of the object to be cooled 3 has dropped sufficiently during operation, and is restarted when the temperature of the object to be cooled 3 rises again, repeating this process. This prevents the object to be cooled 3 from being continuously cooled more than necessary, and ultimately effectively reduces the driving energy of the cryogenic refrigerator CR when viewed in total. Instead of temporarily stopping the operation of the cryogenic refrigerator CR, it is also possible to temporarily reduce the capacity of the cryogenic refrigerator CR by, for example, temporarily reducing the power supply frequency of the cryogenic refrigerator CR (and thus the rotation speed of the compressor drive motor) or temporarily reducing the input power to the compressor using inverter control. However, in general, the drive efficiency (cooling efficiency) of a cryogenic refrigerator CR tends to decrease the lower the power supply frequency or the input power to the compressor (and thus the lower the capacity of the cryogenic refrigerator CR). Therefore, the method of temporarily reducing the capacity of the cryogenic refrigerator CR as described above does not significantly reduce the drive energy of the cryogenic refrigerator CR when viewed overall. On the other hand, in the operating method of this embodiment, the capacity and operating efficiency of the cryogenic refrigerator CR during operation are not reduced, and by alternately operating and stopping the operation, the driving energy (cooling energy) of the cryogenic refrigerator CR can be effectively reduced overall.

[0044] The cooling system RS is not limited to always repeatedly stopping and starting the operation of the cryogenic refrigerator CR using the above-mentioned operating method, but may be configured to be able to switch between repeatedly stopping and starting the operation of the cryogenic refrigerator CR using the above-mentioned operating method and continuously operating the cryogenic refrigerator CR as in the conventional method, as needed.

[0045] The predetermined target cooling temperature THL is preferably equal to or higher than the temperature (e.g., 10 K in the example of FIG. 7) of the cold stage section CRS (in this embodiment, the second-stage cold stage section CRS2) at the rearmost (most forward) stage in the cryocooler CR when the cooling load of that cold stage section CRS is 5 W, and more preferably equal to or higher than the temperature (e.g., 12 K in the example of FIG. 7) of the cold stage section CRS (in this embodiment, the second-stage cold stage section CRS2) at the rearmost (most forward) stage when the cooling load of that cold stage section CRS is 8 W. As can be seen from the example of the capacity curve of the cryogenic refrigerator CR shown in FIG. 7, generally, the lower the temperature (and thus the cooling temperature) of the cold stage CRS of the cryogenic refrigerator CR, the lower the cooling load (W) (and thus the cooling efficiency) of the cold stage CRS of the cryogenic refrigerator CR. When the cooling load of the cold stage CRS is 0 W, it means that no further cooling will occur under any conditions. Note that FIG. 7 shows an example of the capacity curve of a two-stage cryogenic refrigerator CR when the power frequency is 50 Hz. The horizontal axis represents the temperature (K) of the first-stage cold stage CRS1, and the vertical axis represents the temperature (K) of the second-stage cold stage CRS2. Each curve extending approximately vertically represents the cooling load (W) of the first-stage cold stage CRS1, and each curve extending approximately horizontally represents the cooling load (W) of the second-stage cold stage CRS2. Therefore, by setting the predetermined target cooling temperature THL as described above, the driving efficiency (cooling efficiency) of the cryogenic refrigerator CR during operation can be maintained relatively high, and when viewed in total, the driving energy (cooling energy) of the cryogenic refrigerator CR can be further effectively reduced. From the same viewpoint, the predetermined target cooling temperature THL is preferably 10K or higher, and more preferably 12K or higher. The predetermined target cooling temperature THL is lower than the predetermined operation start temperature THH. The temperature difference between the predetermined operation start temperature THH and the predetermined target cooling temperature THL is preferably 20 K or higher, and more preferably 25 K or higher.

[0046] In the case where the object to be cooled 3 includes a superconducting wire as in this embodiment (i.e., for example, when the object to be cooled 3 is a superconducting coil 3), from the viewpoint of maintaining the superconducting wire constituting the object to be cooled 3 in a superconducting state, the predetermined operation start temperature THH is preferably equal to or lower than the maximum temperature at which the superconducting wire constituting the object to be cooled 3 can become superconducting, and more preferably lower than this maximum temperature. Furthermore, the predetermined operation start temperature THH is preferably equal to or lower than the temperature at which the critical current of the superconducting wire constituting the object to be cooled 3 in a perpendicular magnetic field becomes approximately twice the current passing therethrough, and more preferably lower than this temperature. As described above, the superconducting wire constituting the object to be cooled 3 is preferably a high-temperature superconducting wire. In this case, the predetermined operation start temperature THH is preferably equal to or lower than the maximum temperature at which the high-temperature superconducting wire constituting the object to be cooled 3 can become superconducting, and more preferably lower than this maximum temperature. In general, the maximum temperature at which high-temperature superconducting wire can become superconducting varies depending on the material constituting the high-temperature superconducting wire, but is, for example, about 77 K. On the other hand, the maximum temperature at which general superconducting wire (low-temperature superconducting wire) can become superconducting varies depending on the material constituting the low-temperature superconducting wire, but is, for example, about 4 K. Because the superconducting wire constituting the object to be cooled 3 is a high-temperature superconducting wire, it is possible to maintain the cooling temperature of the cryogenic refrigerator CR during operation at a higher temperature while keeping the superconducting wire constituting the object to be cooled 3 superconductive, compared to when the superconducting wire constituting the object to be cooled 3 is a low-temperature superconducting wire.As a result, the driving efficiency (cooling efficiency) of the cryogenic refrigerator CR during operation can be maintained at a higher level, the operating time can be shortened, and the driving energy (cooling energy) of the cryogenic refrigerator CR can be further effectively reduced.

[0047] As described above, in this embodiment, the heat conductive connection part TC, which thermally conductively connects the rearmost (foremost) cold stage part CRS (in this embodiment, the second-stage cold stage part CRS2) in the cryocooler CR to the object to be cooled 3, has the cold storage body 22 (FIG. 2). That is, the cold storage body 22 is thermally conductively connected to the cold stage part CRS and the object to be cooled 3. The cold storage body 22 is made of a thermal conductor such as metal, and is configured to store a portion of the cold (sensible heat) generated in the rearmost (foremost) cold stage section CRS (in this embodiment, the second cold stage section CRS2) of the cryocooler CR. As described above, in this embodiment, the cold storage body 22 is a divided iron core section 22 or an iron core member 22, and is configured to contain iron. The cold storage body 22 stores a portion of the cold generated from the rearmost (foremost) cold stage section CRS (in this embodiment, the second-stage cold stage section CRS2) during operation of the cryogenic refrigerator CR, and can continue to cool the object to be cooled 3 using the cold stored therein while the operation of the cryogenic refrigerator CR is stopped. This makes it possible to suppress a rise in the temperature of the object to be cooled 3 while the operation of the cryogenic refrigerator CR is stopped, thereby increasing the operation stop time of the cryogenic refrigerator CR and reducing the number of times the cryogenic refrigerator CR is started and stopped (on and off). This reduces the burden that may be placed on electrical components of the cooling system RS due to repeated operation and stop (on and off) of the cryogenic refrigerator CR, and improves the life of the cooling system RS. However, the cold storage body 22 does not necessarily have to be provided.

[0048] It is preferable that the cold storage body 22 has a larger heat capacity (sensible heat capacity) than the object to be cooled 3. Generally, the larger the heat capacity, the higher the ability to store cold (cold storage performance). Therefore, by having the cold storage body 22 have a larger heat capacity (sensible heat capacity) than the object to be cooled 3, the cold storage performance of the cold storage body 22 can be improved, and further, the temperature rise of the object to be cooled 3 while the cryogenic refrigerator CR is not operating can be further suppressed, and further, the operation stop time of the cryogenic refrigerator CR can be increased, and the number of operations and stoppages (starts and stops) of the cryogenic refrigerator CR can be further reduced. From the same viewpoint, it is preferable that the cooling storage body 22 has a larger volume than the object 3 to be cooled.

[0049] As described above, in this embodiment, the heat conductive connection part TC, which thermally conductively connects the rearmost (foremost) cold stage part CRS (in this embodiment, the second-stage cold stage part CRS2) in the cryocooler CR to the object to be cooled 3, has one or more (four in this embodiment) heat equalizing members SK (FIGS. 2, 4, and 5). That is, one or more (four in this embodiment) heat equalizing members SK are thermally conductively connected to the cold stage part CRS and the object to be cooled 3. The heat equalizing member SK has the function of quickly and evenly transferring cold to the cold storage body 22. The heat equalizing member SK is made of a thermal conductor such as metal, and is preferably made of copper (e.g., pure copper (oxygen-free copper)) from the viewpoints of thermal conductivity, availability, workability, cost, etc. The heat equalizing member SK is preferably formed in a plate shape as in this embodiment, as this makes it easier to transfer cold evenly. As shown in Figures 4 and 5, in this embodiment, one or more (four in this embodiment) heat equalizing members SK surround the cold storage body 22 in an annular shape, and specifically, are in contact with the outer peripheral surface of the cold storage body 22 over the entire circumference. More specifically, in this embodiment, as shown in FIG. 5, the cold storage body 22 has a substantially rectangular parallelepiped shape with the axis O as the central axis, and four side surfaces 224 of the cold storage body 22 are located on the outer periphery side of the axis O. Of the four side surfaces 224 of the cold storage body 22, a first side surface 224a and a fourth side surface 224d are parallel to the axial direction AD and the depth direction DD. The first side surface 224a is located closer to the second vertical side VD2 than the fourth side surface 224d. The first side surface 224a faces the second vertical side VD2 (the lower side in this embodiment), and the fourth side surface 224d faces the first vertical side VD1 (the upper side in this embodiment). Of the four side surfaces 224 of the cold storage body 22, the second side surface 224b and the third side surface 224c are parallel to the axial direction AD and the vertical direction VD and are spaced apart from each other in the depth direction DD. The second side surface 224b and the third side surface 224c each face the opposite side to the axis O in the depth direction DD. In this embodiment, the four temperature equalizing members SK are each plate-shaped and are in contact with the four side surfaces 224 of the cold storage body 22 from the outer periphery. Of the four temperature equalizing members SK, the first temperature equalizing member SKa and the fourth temperature equalizing member SKd are oriented parallel to the first side surface 224a and the fourth side surface 224d of the cold storage body 22, respectively, and are in contact (surface contact) with the first side surface 224a and the fourth side surface 224d of the cold storage body 22. Of the four temperature equalizing members SK, the second temperature equalizing member SKb and the third temperature equalizing member SKc are oriented parallel to the second side surface 224b and the third side surface 224c of the cold storage body 22, respectively, and are in contact (surface contact) with the second side surface 224b and the third side surface 224c of the cold storage body 22. The four temperature equalizing members SK are in contact with each other at their respective ends, thereby forming a ring shape. In this embodiment, one or more (four in this embodiment) heat equalizing members SK are in contact with the outer peripheral surface of the cold storage body 22 over the entire circumference, and these heat equalizing members SK can quickly and evenly transfer the cold transferred from the cryogenic refrigerator CR side to the cold storage body 22 over the entire circumference (in other words, it becomes easier to equalize the temperature of the cold storage body 22), and can also suppress sudden temperature changes, allowing stable cold storage by the cold storage body 22. This allows cold storage by the cold storage body 22 to be performed more effectively and stably during operation of the cryogenic refrigerator CR.

[0050] However, the cold storage body 22 and the temperature equalizing member SK may have any shape. Furthermore, one or more heat equalizing members SK may be in contact with any part of the regenerator 22.

[0051] 1 and 2, in this embodiment, the cold head CRH of the cryogenic refrigerator CR extends in the axial direction AD, and the tip of the cold head CRH faces inward in the axial direction ADI. However, the cold head CRH of the cryogenic refrigerator CR may be oriented in any direction.

[0052] 1 and 2, in this embodiment, the split core-coil assembly 5 is located on a first longitudinal side VD1 of the cold head CRH. Also, in this embodiment, the split core-coil assembly 5 is located on an axially inner side ADI of the cold head CRH. However, the positional relationship between the cold head CRH of the cryogenic refrigerator CR and the split core-coil assembly 5 may be arbitrary.

[0053] As described above, in this embodiment, the heat conductive connection part TC that thermally conductively connects the rearmost (foremost) cold stage part CRS (in this embodiment, the second-stage cold stage part CRS2) in the cryocooler CR to the object to be cooled 3 has one or more (in this embodiment, one) heat transfer conductor members TP. That is, one or more (in this embodiment, one) heat transfer conductor members TP are thermally conductively connected to the cold stage part CRS and the object to be cooled 3. The heat transfer conductor member TP is made of a heat conductor such as a metal, and is preferably made of copper (for example, pure copper (oxygen-free copper)) from the viewpoints of thermal conductivity, availability, workability, price, etc. The heat transfer conductor member TP is preferably made in a plate shape as in this embodiment, since this makes it easier to transfer heat evenly. More specifically, the heat transfer conductor member TP is in contact with the rearmost (frontmost) cold stage member CRS (in this embodiment, the second-stage cold stage member CRS2) in the cryocooler CR and at least one (in this embodiment, the first heat spreader SKa) of one or more (in this embodiment, four) heat spreaders SK (FIG. 2), thereby connecting them in a heat conductive manner. This allows the cold generated from the cold stage member CRS to be transferred via the heat transfer conductor member TP to at least one (in this embodiment, the first heat spreader SKa) of one or more (in this embodiment, four) heat spreaders SK. In this embodiment, the heat transfer conductor member TP extends approximately along the vertical direction VD, and the lower end of the heat transfer conductor member TP is in contact (surface contact) with the tip surface of the rearmost (most forward) cold stage section CRS in the cryogenic refrigerator CR (in this embodiment, the second cold stage section CRS2), and the upper end of the heat transfer conductor member TP is in contact (surface contact) with at least one of one or more (in this embodiment, four) heat equalizing members SK (in this embodiment, the first heat equalizing member SKa) (Figure 2). However, the shape and extending direction of the heat transfer conductor member TP may be arbitrary. In addition, the heat transfer conductor member TP does not have to be provided, and for example, the rearmost (most forward) cold stage section CRS (in this embodiment, the second cold stage section CRS2) in the cryogenic refrigerator CR may be in direct contact with at least one of one or more (in this embodiment, four) heat equalization members SK.

[0054] As described above, in this embodiment, the heat conductive connection TC that thermally conductively connects the rearmost (foremost) cold stage section CRS (in this embodiment, the second-stage cold stage section CRS2) in the cryocooler CR to the object to be cooled 3 has one or more (two in this embodiment) cooling conductor members PM ( FIG. 2 ). That is, one or more (two in this embodiment) cooling conductor members PM are thermally conductively connected to the cold stage section CRS and the object to be cooled 3. More specifically, each of the one or more (two in this embodiment) cooling conductor members PM is in contact with at least one of the one or more (four in this embodiment) heat equalizing members SK and the object to be cooled 3. The cooling conductor member PM is made of a thermal conductor such as a metal, and is preferably made of copper (e.g., pure copper (oxygen-free copper)) from the viewpoints of thermal conductivity, availability, workability, cost, etc. The cooling conductor member PM is preferably made in a plate shape as in this embodiment, since this makes it easier to transmit cold evenly. More specifically, each of the heat conducting connections TC has a first cooling conductor member PMa and a second cooling conductor member PMb as the cooling conductor members PM.

[0055] The first cooling conductor member PMa is disposed between the cold storage body 22 and the object to be cooled 3 in the axial direction AD, and is in contact (surface contact) with the cold storage body 22 and the object to be cooled 3. More specifically, in this embodiment, as shown in FIGS. 1, 2, and 5, the outer peripheral surface 221 of the cooling storage body 22 has an annular stepped portion 2211. The stepped portion 2211 extends over the entire circumference in the circumferential direction centered on the axis O. The stepped portion 2211 faces the axially inner side ADI. The stepped portion 2211 is recessed inward in the axially perpendicular direction. Specifically, the stepped portion 2211 includes an axially perpendicular surface 2211a that is substantially parallel to the axially perpendicular direction OD 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 surface 223 of the axially inner side ADI of the cooling storage body 22. The object to be cooled 3 has an annular shape that extends over the entire circumference in the circumferential direction centered on the axis O, and is disposed within the stepped portion 2211. Specifically, the object to be cooled 3 is wound around the step portion 2211 in the circumferential direction with the axis O as the center. On the other hand, the first cooling conductor member PMa is configured in an annular shape extending over the entire circumference in the circumferential direction centered on the axis O. The axially outer surface ADO of the first cooling conductor member PMa is in contact with the axially perpendicular surface 2211a of the stepped portion 2211 of the cold storage body 22, and the axially inner surface ADI of the first cooling conductor member PMa is in contact with the axially outer surface ADO of the object to be cooled 3. The axial surface 2211b of the stepped portion 2211 is located on the inner circumferential side of the first cooling conductor member PMa and the object to be cooled 3. Furthermore, at least one of the temperature equalizing members SK (in this embodiment, the second, third, and fourth temperature equalizing members SKb, SKc, and SKd) extends beyond the axially perpendicular surface 2211a of the stepped portion 2211 of the cold storage body 22 toward the axially inner surface ADI. At least one of the temperature equalizing members SK (in this embodiment, the first temperature equalizing member SKa, the second temperature equalizing member SKb, and the third temperature equalizing member SKc) is in contact with the first cooling conductor member PMa. 6, the first cooling conductor member PMa and at least one of the heat spreader members SK in contact with the first cooling conductor member PMa (in this embodiment, the first heat spreader member SKa) may be fixed to each other with fixing members F such as screws. In this embodiment, the end face of the axially inner side ADI of the first heat spreader member SKa is located in approximately the same position in the axial direction AD as the axis-perpendicular surface 2211a of the step portion 2211 of the regenerator 22. The first cooling conductor member PMa is in contact with the end face of the axially inner side ADI of the first heat spreader member SKa on the second vertical side VD2 from the object to be cooled 3, and is fixed to the first heat spreader member SKa at this position by the fixing members F.

[0056] The second cooling conductor member PMb is disposed on the inside ADI of the object to be cooled 3 in the axial direction, and is in contact (surface contact) with the object to be cooled 3. More specifically, in this embodiment, as shown in Figures 1, 2, and 5, the second cooling conductor member PMb consists of an axial plate-shaped portion PMba that is approximately parallel to the axial direction OD, and an axial plate-shaped portion PMbb that extends from the end of the axial plate-shaped portion PMba on the second vertical side VD2 to the axial outside ADO. The surface of the axially inner side ADI of the object to be cooled 3 and the end surface 223 of the axially inner side ADI of the cooling storage body 22 are flush with each other. The surface of the axially outer side ADO of the axially perpendicular plate-shaped part PMba of the second cooling conductor member PMb is in contact with the surface of the axially inner side ADI of the object to be cooled 3 and the end surface 223 of the axially inner side ADI of the cooling storage body 22. The axial plate portion PMbb of the second cooling conductor member PMb is located on the second vertical side VD2 of the first temperature equalizing member SKa, and the surface of the axial plate portion PMbb of the second cooling conductor member PMb on the first vertical side VD1 is in contact with the surface of the first temperature equalizing member SKa on the second vertical side VD2. The axial plate portion PMbb of the second cooling conductor member PMb is located axially inward ADI of the heat transfer conductor member TP. In this embodiment, the axial plate portion PMbb of the second cooling conductor member PMb is spaced apart from the heat transfer conductor member TP, but the axial plate portion PMbb of the second cooling conductor member PMb may also be in contact with the heat transfer conductor member TP. Furthermore, the second cooling conductor member PMb does not necessarily have to have the axial plate-shaped portion PMbb.

[0057] In this way, one or more (two in this embodiment) cooling conductor members PM are in contact with at least one of one or more (four in this embodiment) temperature equalizing members SK and the object to be cooled 3, so that during operation of the cryogenic refrigerator CR, cold transferred from the cryogenic refrigerator CR side via the temperature equalizing members SK can be transferred to the object to be cooled 3 via each cooling conductor member PM. This allows the object to be cooled 3 to be cooled more evenly and efficiently. Furthermore, when the cryogenic refrigerator CR is not operating, the cold stored in the cold storage body 22 is transferred to the object to be cooled 3 via the first cooling conductor member PMa.

[0058] However, as long as each cooling conductor member PM is in contact with the temperature equalizing member SK and the object 3 to be cooled, its shape, position, etc. may be arbitrary. From the viewpoint of efficiently transmitting cold from the temperature equalizer SK to the object to be cooled 3 via the cooling conductor members PM, it is preferable that each cooling conductor member PM be in contact with at least one temperature equalizer SK and in contact (surface contact) with an end face on either side in the axial direction AD of the object to be cooled 3, as in this embodiment. This increases the contact area between the cooling conductor member PM and the object to be cooled 3, thereby enabling more efficient transmission of cold from the temperature equalizer SK to the object to be cooled 3 via the cooling conductor member PM.

[0059] The radiation shield SH defines a radiation shield space SHR therein. The object to be cooled 3, a portion of the cryogenic refrigerator CR, a heat conduction connection TC, and a temperature sensor TS are arranged within the radiation shield space SHR. In this embodiment, the radiation shield SH is connected (contacted) to a first-stage cold stage CRS1 of the cryogenic refrigerator CR, thereby allowing cold generated in the first-stage cold stage CRS1 to be transmitted to the radiation shield SH. The radiation shield SH is configured to prevent radiant heat from outside the radiation shield SH from penetrating into the radiation shield space SHR. A portion of the cold head CRH of the cryogenic refrigerator CR that is downstream (toward the tip) of the first-stage cold stage CRS1 (in this embodiment, the second-stage cold unit CRU) is arranged within the radiation shield space SHR. It is preferable that the radiation shield SH has laminated insulation material on part or all of its wall (e.g., its outer surface). 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 radiation shield SH does not necessarily have to be provided.

[0060] In the cooling system RS and magnetic field generating device 1 of this embodiment, the magnetic field generating device 1 is equipped with a superconducting coil 3, so a stronger magnetic field can be generated in the working space 6 compared to when the magnetic field generating device 1 is equipped with a normal copper coil instead of the superconducting coil 3. Furthermore, according to the magnetic field generator 1 of 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, ultimately, 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, according to 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. Furthermore, according to this embodiment, as described above, the iron core 2 is divided into the yoke 21 and a pair of split core portions 22, 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 and the pair of superconducting coils wound around a pair of ends of the iron core were housed entirely in the vacuum insulated container. This reduces heat penetration from the outside, thereby enabling energy savings. In addition, if an undivided, roughly C-shaped iron core is used, a possible way to miniaturize the vacuum insulated container is to configure the vacuum insulated container in a doughnut shape so that the vacuum insulated container houses only a pair of superconducting coils that wrap around a pair of ends of the iron core. However, in that case, the wall of the vacuum insulated container is interposed between the iron core and the superconducting coil, which means that the iron core and the superconducting coil are spaced apart, thereby increasing the perimeter of the superconducting coil and increasing the amount of superconducting coil used, leading to increased costs. Furthermore, the increased space between the iron core and the superconducting coil increases leakage flux, which increases the amount of superconductor required and leads 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) without using the wall of the vacuum insulated container, and therefore the iron core 2 (specifically, the split iron core portions 22) 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 is made to be doughnut-shaped as described above. Furthermore, since the iron core 2 (specifically, the split iron core portions 22) 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 is made to be doughnut-shaped as described above. Furthermore, since the iron core 2 (specifically, the split iron core portion 22) and the superconducting coil 3 are in contact (via the cooling conductor member PM), 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) compared to when the vacuum insulated container is doughnut-shaped as described above. This not only reduces the cooling burden on the cryogenic refrigerator CR, but also makes it possible to effectively utilize the capabilities of the superconductor by being able to sufficiently cool the superconducting coil. Furthermore, according to this embodiment, as shown in Fig. 6, in each split core-coil assembly 5, when current is applied, the Lorentz force (black arrow in Fig. 6) acting on the superconducting coil 3 toward the axially outer side ADO and the electromagnetic force (white arrow in Fig. 6) acting on the split core portion 22 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 cryogenic refrigerator CR and enabling the superconducting coil to be sufficiently cooled, thereby making effective use of the capabilities of the superconductor.

[0061] In this embodiment, as shown in FIGS. 1, 2, and 6, the cooling system RS and the magnetic field generator 1 have a support member 7 as a support structure for supporting the split iron-core coil assembly 5 relative to the vacuum insulated container 4. The support member 7 is configured to suspend the split iron-core coil assembly 5 from the vacuum insulated container 4. More specifically, in this example, the support member 7 is configured, for example, in the shape of a rod with low thermal conductivity, and is configured to suspend the split iron-core coil assembly 5 from the upper wall 41 (first vertical side VD1) of the vacuum insulated container 4 while providing thermal insulation. In this way, the support member 7 is configured to support the weight of the split iron-core coil assembly 5, but is not configured to restrict horizontal movement of the split iron-core coil assembly 5. In this way, in this embodiment, the support structure (support member 7) for supporting the split iron-core coil assembly 5 relative to the vacuum insulated container 4 is simply configured. The support structure for supporting the split core coil assembly 5 on the vacuum insulating container 4 is not limited to this, and any structure may be used.

[0062] 1, 2, and 6, the cooling system RS and the magnetic field generator 1 have spacer members 8 between the split iron-core coil assembly 5 and the walls 42, 43 (FIG. 6) on both sides of the axial direction AD of the vacuum insulated container 4. This more effectively prevents the split iron-core coil assembly 5 from moving excessively in the axial direction AD when current is applied. In addition, the spacer members 8 maintain a gap between the split iron-core coil assembly 5 and the vacuum insulated container 4 when current is not applied, thereby reducing the amount of heat entering when current is not applied. The spacer members 8 may be, for example, fixed to the split core portions 22 of the split core-coil assembly 5 or configured integrally with the split core portions 22, and may be separate from and unfixed to the walls 42, 43 on both sides in the axial direction AD of the vacuum insulated container 4. Alternatively, the spacer members 8 may be separate from and unfixed to the split core-coil assembly 5, and may be fixed to or configured integrally with the walls 42, 43 on both sides in the axial direction AD of the vacuum insulated container 4. The spacer member 8 does not necessarily have to be provided.

[0063] As described above, in this embodiment, as shown in FIGS. 1, 2, 5, and 6, in each of a pair of split core-coil assemblies 5, the outer peripheral surface 221 of the split core portion 22 has an annular stepped portion 2211. The stepped portion 2211 extends over the entire circumference in a circumferential direction centered on the axis O. The stepped portion 2211 faces the working space 6 (through the wall 42 of the vacuum insulated container 4). The stepped portion 2211 is recessed inward in the axial direction. Specifically, the stepped portion 2211 includes an axially perpendicular surface 2211a that is substantially parallel to the axial direction OD 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 face 223 of the axially inner side ADI of 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 split core portions 22 face each other in the axial direction AD, so that the Lorentz force (black arrow in FIG. 6 ) acting on the superconducting coil 3 toward the axially outer side ADO and the electromagnetic force (white arrow in FIG. 6 ) acting on the split core portions 22 toward the axially inner side ADI are more effectively canceled out, and the force in the axial direction AD acting on the split core coil assembly 5 is reduced. 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 (black arrow in FIG. 6 ) acting on the superconducting coil 3 toward the axially 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 axially outer side ADO. In other words, the step portion 2211 has the function of restricting the superconducting coil 3 from moving 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 outward side ADO. This reduces the heat penetration from the outside into the superconducting coil 3 via the restricting structure, thereby suppressing the temperature rise of the superconducting coil 3. This reduces the cooling burden on the cryocooler CR and effectively utilizes the superconductor's capabilities by sufficiently cooling the superconducting coil. Furthermore, since the axially inward side ADI of the superconducting coil 3 is not covered by the split core portion 22 but faces the working space 6 (through the wall 42 of the vacuum insulated vessel 4), a stronger magnetic field can be generated in the working space 6. Furthermore, since the superconducting coil 3 is in contact with not only the axial surface 2211b of the step portion 2211 but also the transverse-axial surface 2211a of the step portion 2211, the contact area with the split core portion 22 increases accordingly, thereby improving the cooling effect of the superconducting coil 3 via the split core portion 22. It is preferable that the above-mentioned step portions 2211 are provided on both of the pair of split core coil assemblies 5, but they may be provided on only one of the pair of split core coil assemblies 5.

[0064] In each example described in this specification, in at least one of a pair of split core coil assemblies 5, the outer surface 31 of the superconducting coil 3 may be located at the same axial OD position as the outer surface 221 of the split core portion 22, as in the example of Figure 6, or may be located closer to the inner periphery than the outer surface 221 of the split core portion 22, or may be located closer to the outer periphery than the outer surface 221 of the split core portion 22, although not shown.

[0065] In each example described in this specification, although not shown, in at least one of the pair of split core coil assemblies 5, the outer circumferential surface 221 of the split core portion 22 may have a protrusion protruding outward, and this protrusion may have a step portion 2211. In this case, the outer circumferential surface 31 of the superconducting coil 3 may be located at the same OD position as the outer circumferential surface of the protrusion, or may be located on the inner circumferential side of the outer periphery of the protrusion, or may be located on the outer circumferential side of the outer circumferential surface of the protrusion.

[0066] Although not shown, the outer peripheral surface 221 of the split core portion 22 in at least one of the pair of split core-coil assemblies 5 may have an annular groove. The groove extends around the entire circumference in a 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 OD, and a groove bottom surface that faces the outer peripheral side and is approximately parallel to the axial direction AD. In this case, the superconducting coil 3 is wound around the groove in the circumferential direction and is ultimately housed in the groove.

[0067] However, in at least one of the pair of split core coil assemblies 5, the superconducting coil 3 may be wound on the outer peripheral surface 221 of the split core portion 22 that does not have unevenness such as steps 2211 or grooves. In this case, too, 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 toward the axially inner side ADI cancel each other out, so the force in the axial direction AD acting on the split core coil assembly 5 is reduced. This makes it possible to simplify the support structure for supporting the split core coil assembly 5 relative to the vacuum insulated container 4. However, this effect is greater when the superconducting coil 3 is wound on the steps 2211 or grooves on the outer peripheral surface 221 of the split core portion 22, as in the above-mentioned examples. In addition, when the superconducting coil 3 is wound around the outer peripheral surface 221 of the split core portion 22, which has no unevenness such as steps 2211 or grooves, it is preferable to provide a separate restricting structure to restrict the movement of the superconducting coil 3 outward in the axial direction ADO.

[0068] In each example described in this specification, in at least one of a pair of split core coil assemblies 5, the superconducting coil 3 may have a single-stage structure consisting of only one layer along the axial direction AD, as in the examples of Figures 1 to 6, or may have a multi-stage structure in which multiple superconducting coil layers are arranged along the axial direction AD, although not shown.

[0069] In each example described in this specification, the end 21a of the yoke 21 and the wall 43 of the axially outer ADO of the vacuum insulated container 4 are preferably spaced apart from each other as shown in Figure 6, but may also be in contact with each other.

[0070] In each example described in this specification, it is preferable that the configuration of the vacuum insulated container 4 and the split iron core coil assembly 5 be symmetrical with respect to the center of the axial direction AD of the cooling system RS and the magnetic field generating device 1, but they may also be asymmetrical with respect to the center of the axial direction AD of the cooling system RS and the magnetic field generating device 1.

[0071] In each example described in this specification, the cooling system RS and the magnetic field generator 1 may include only one vacuum insulated container 4. In this case, the pair of split core coil assemblies 5 are housed in the vacuum insulated container 4, and the yoke 21 is disposed outside the vacuum insulated container 4. In this case, the vacuum insulated container 4 can be made smaller than if the undivided, approximately C-shaped iron core and the pair of superconducting coils wound around a pair of ends of the iron core were housed entirely in the vacuum insulated container. In this case, the vacuum insulating container 4 may have a configuration in which, for example, a pair of vacuum insulating containers 4 in the example of FIG. 1 are connected together by a connecting pipe or the like to form an integrated unit.

[0072] In the above-described embodiment, each cooling unit RU includes only one temperature sensor TS. However, the cooling unit RU may include multiple temperature sensors TS. In this case, each temperature sensor TS of the cooling unit RU is configured to detect the temperature of one of the object to be cooled 3, the cold stage portion CRS of one of the cryogenic refrigerators CR, the heat conduction connection portion TC, and the current leads D1 and D2. In this case, it is preferable that each temperature sensor TS is configured to detect the temperature of a different portion. Then, when the temperature detected by any one predetermined temperature sensor TS during operation of the cryogenic refrigerator CR drops to a predetermined target cooling temperature THL, the control unit PS performs an operation shutdown process to stop the operation of the cryogenic refrigerator CR (operation shutdown step). Furthermore, when the temperature detected by any one of the predetermined temperature sensors TS rises to a predetermined operation start temperature THH that is higher than the predetermined target cooling temperature THL while the cryogenic refrigerator CR is stopped, the control unit PS performs an operation start process to start the operation of the cryogenic refrigerator CR (operation start step). The predetermined temperature sensor TS used in the operation stop step and the operation start step may be the same or different between the operation stop step and the operation start step.

[0073] Here, a supplementary explanation will be given regarding the predetermined operation start temperature THH. High-temperature superconducting wire is a general term used to refer to wires that can achieve a superconducting state at liquid nitrogen temperatures. However, there are also materials such as magnesium diboride (MgB2) that exhibit superconductivity at temperatures intermediate between those of liquid helium and liquid nitrogen, and these materials are classified as high-temperature superconducting wires. The minimum cooling temperature (Tc critical temperature) of a high-temperature superconducting wire varies depending on the following conditions. (1) Material manufacturing method and its variation (2) Magnetic field strength in the environment (3) Current Generally, once the above (1) is determined, the mutually linked (2) and (3) are determined, and the required cooling temperature is determined based on the results of these three. However, it is difficult to intentionally determine the cooling temperature, and conventionally, when it was necessary to set the cooling temperature, the cryogenic refrigerator CR was used to cool the material below the set temperature, and then electricity was applied to the heater wrapped around the cold head CRH to raise the temperature and obtain the desired temperature (controlled by a thermostat). The predetermined operation start temperature THH is preferably set to a temperature lower than the critical temperature determined by the above (1), (2), and (3), taking into consideration the start-up time of the refrigerator and temperature errors. Fig. 8 shows an example of the critical current characteristics of a REBCO wire, which is a type of high-temperature superconducting wire. In the example of Fig. 8, for example, when the current of the superconducting coil 3 is 300 A and the critical temperature is 50 K, it is preferable to set the predetermined operation start temperature THH to about 45 K. In addition, when the cryocooler CR is a two-stage type as in the embodiment of Fig. 1, the first-stage cold stage CRS1 cools the high-temperature end D2a of the second current lead D2, and it is preferable that the temperature rise due to heat entering the first-stage cold stage CRS1 reaches its limit later than the temperature rise on the superconducting coil 3 side. If it does, it is preferable to start operation of the cryocooler CR under the temperature conditions of the first-stage cold stage CRS1. Therefore, for example, one temperature sensor TS may be configured to detect the temperature of the first-stage cold stage CRS1, and operation of the cryocooler CR may be started when the temperature detected by the temperature sensor TS reaches a predetermined operation start temperature THH.

[0074] Next, a supplementary explanation will be given regarding the predetermined target cooling temperature THL. Since the temperature of the superconducting coil 3 after the cryogenic refrigerator CR starts operating always becomes a temperature that satisfies the superconducting conditions, the predetermined target cooling temperature THL can be determined under conditions completely separate from maintaining the superconducting conditions. After the cryogenic refrigerator CR starts operating, it cools the sensible heat of the superconducting coil 3 itself and its accessories, as well as a few watts of external heat due to radiation, conduction, etc., which is approximately a fixed value, and the cooling temperature gradually decreases.As the cooling temperature decreases, the efficiency of the refrigerator decreases, and the cooling capacity stabilizes at a temperature balanced with the external heat, and it may not be possible to cool to a temperature below that. If only maintaining the superconducting state is considered, it is possible to stop the operation of the cryocooler CR at any temperature between this balance temperature and the predetermined operation start temperature THH. However, if the predetermined target cooling temperature THL is increased, the time from stopping to starting operation and from starting to stopping operation will be shorter, resulting in an increase in the frequency of starting and stopping the cryocooler CR. Since an increase in the number of starts and stops of the cryocooler CR is thought to have a negative impact on the mechanical life of the cryocooler CR and related equipment, it is possible to lower the predetermined target cooling temperature THL. However, as the efficiency of the cryocooler CR decreases, it will take longer to accumulate cooling energy using the sensible heat of the cryocooler 22, which is thought to be longer than the cooling time using the sensible heat of the cryocooler 22 after the cryocooler CR is stopped. The predetermined target cooling temperature THL is preferably set at a balance point or higher between the operation time based on the amount of cold stored and the time required for the amount of cold stored. Since operation by cold storage is considered to be cooling the heat that has entered from the outside by storing cold, the reference point of the predetermined target cooling temperature THL is considered to be, for example, the point where the cooling capacity is twice the heat that has entered from the outside. At this reference temperature, a significant amount of cooling heat is required, so the temperature becomes higher than the lowest temperature that the cryogenic refrigerator CR can reach under no-load cooling conditions. For example, when the external heat intrusion is 4 W, it is preferable to set the reference point of the predetermined target cooling temperature THL at about 15 K, where the capacity of the second cold stage CRS2 of the cryogenic refrigerator CR is 8 W. In this case, it is considered possible to maximize the start-up and shutdown times of the cryogenic refrigerator CR while saving power consumption of the cryogenic refrigerator CR. At temperatures above the reference point, the capacity of the cryogenic refrigerator CR improves, shortening the time required to reach the specified operation start temperature THH. However, the amount of cold stored per unit time increases, which increases the ratio of the cryogenic refrigerator CR's stopped time to its operating time, resulting in greater energy savings.

[0075] To summarise the above, we can say the following: (a) The predetermined operation start temperature THH is preferably set to a value below which has a necessary margin with respect to the critical temperature standard depending on the characteristics of the wire used, the current conditions, and the cross magnetic field strength. (a) The predetermined target cooling temperature THL is preferably set based on the cooling capacity of the cryogenic refrigerator CR, which is twice the amount of heat entering from the outside, and the cooling temperature at that time. (c) If the predetermined target cooling temperature THL is set higher than the standard, the utilization rate of the cryogenic refrigerator CR will improve, but the frequency of start-stops will increase, which should be taken into consideration as it will have a negative effect on the life of the mechanical parts. (e) In the case of a two-stage cryogenic refrigerator CR, it is preferable that the cooling temperature conditions of the first cold stage CRS1, particularly the temperature of the high temperature end D2a of the second current lead D2, do not exceed the allowable range. If they do exceed the allowable range, it is preferable to operate the cryogenic refrigerator CR under these conditions. [Industrial Applicability]

[0076] The cooling system according to the present invention and the operating method according to the present invention can be used to cool any object to be cooled, for example, a superconducting coil, and can also be used in any device, for example, a magnetic field generating device. The magnetic field generating device according to the present invention can be used for any purpose, for example, as a heating device for aluminum billets. [Explanation of symbols]

[0077] RS Cooling System RU Cooling Unit CR cryogenic refrigerator CRM motor CRH Cold Head CRU Refrigeration Unit CRU1 First Stage Cryogenic Unit CRU2 Second Stage Cryogenic Unit CRC Cylinder CRD Displacer CRL cold storage material CRF sealing material CRR expansion chamber CRV Sleeve CRS cold stage CRS1 First Cold Stage CRS2 Second Cold Stage TS Temperature Sensor PS control unit TC Thermal Conduction Joint SK Heat-equalizing Material SKa First Heat-Soaking Element SKb Second heat equalizing member SKc 3rd heat equalizing member SKd 4th heat equalizing member PM cooling conductor material PMa first cooling conductor member PMb Second cooling conductor member PMba Plate-shaped part in the direction perpendicular to the axis PMbb Axial plate part TP Heat Transfer Conductor SH Radiation Shield SHR radiation shield space F Fixing member D1 First current lead (current lead) D2 Second current lead (current lead) D2a high temperature end D2b Low temperature end E Hermetic feed-through terminal BB1 No. 1 bus bar BB2 Second bus bar 1. Magnetic field generator 2 Iron core 21 York 21a End 22 Divided core section (cold storage body, core material) 221 Outer surface 2211 Step 2211a Axis-perpendicular surface 2211b Axial plane 223 Axial inner end face 224 Side 224a 1st side 224b Second side 224c 3rd side 224d 4th side 3 Superconducting coil (object to be cooled) 31 Outer surface 4. Vacuum insulated container 41 Upper Wall 42 Axial inner wall 43 Axial outer wall 5. Segmented core coil assembly 6. Workspace 7 Support member 8 Spacer member O axis AD Axial direction (opposing direction) ADI Axial inside ADO axially outward OD Direction perpendicular to axis VD Vertical VD1 Vertical first side VD2 Second vertical side DD Depth direction

Claims

1. A vacuum insulated container; an object to be cooled placed in the vacuum insulated container; a cryogenic refrigerator having a cold stage configured to generate cold; a heat conductive connection portion that connects the cold stage portion and the object to be cooled in a heat conductive manner; one or more temperature sensors; a current lead disposed within the vacuum insulated container; A control unit; A cooling system comprising: the one or more temperature sensors are configured to detect a temperature of any one of the object to be cooled, the cold stage portion, the heat conductive connection portion, and the current lead; The control unit an operation stop process for stopping the operation of the cryogenic refrigerator when a temperature detected by any one of the temperature sensors drops to a predetermined target cooling temperature during operation of the cryogenic refrigerator; an operation start process for starting operation of the cryogenic refrigerator when a temperature detected by any one of the temperature sensors rises to a predetermined operation start temperature that is higher than the predetermined target cooling temperature while the cryogenic refrigerator is stopped; and The heat conducting connection part has a heat storage body, the cooling system is configured for use in a magnetic field generating device; The magnetic field generating device is the cooling system; a substantially C-shaped or substantially U-shaped yoke; Equipped with The cooling system includes one or a pair of the vacuum insulated containers, the cooling system includes a pair of superconducting coils, each of which is the object to be cooled; the cooling system includes a pair of split core portions each serving as the regenerator, the pair of split core portions are formed separately from the yoke, are located inside the yoke, and are arranged opposite to each other with a working space interposed therebetween, Each of the superconducting coils is wound around each of the split core portions along a circumferential direction about an axis parallel to the direction in which the pair of split core portions face each other, a split core-coil assembly having 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, A cooling system, wherein the yoke is disposed outside the one or pair of vacuum insulated vessels.

2. The cooling system according to claim 1 , wherein the predetermined target cooling temperature is equal to or higher than a temperature of the cold stage section when a cooling load of the cold stage section is 5 W.

3. the object to be cooled includes a high-temperature superconducting wire, 2. The cooling system according to claim 1, wherein the predetermined operation start temperature is equal to or lower than a maximum temperature at which the high-temperature superconducting wire can become superconducting.

4. The cooling system according to claim 1 , wherein the regenerator has a larger heat capacity than the object to be cooled.

5. the thermally conductive connection includes one or more heat equalizing members; The cooling system according to claim 1 , wherein the one or more heat equalizing members are in contact with the outer circumferential surface of the regenerator over the entire periphery.

6. the thermally conductive connection includes one or more cooling conductor members; The cooling system of claim 5 , wherein the one or more cooling conductor members are in contact with the heat spreader and the object to be cooled.

7. A cooling system according to any one of claims 1 to 6; The yoke has a substantially C-shape or a substantially U-shape; A magnetic field generating device comprising: the pair of split core portions are formed separately from the yoke, are located inside the yoke, and are arranged opposite to each other with a working space interposed therebetween, Each of the superconducting coils is wound around each of the split core portions along a circumferential direction about an axis parallel to the direction in which the pair of split core portions face each other, the split core-coil assembly having 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, A magnetic field generating device, wherein the yoke is arranged outside the one or pair of vacuum insulated containers.

8. A method of operating a cooling system according to any one of claims 1 to 6, comprising the steps of: an operation stopping step in which, when a temperature detected by any one of the temperature sensors drops to a predetermined target cooling temperature during operation of the cryogenic refrigerator, the control unit stops operation of the cryogenic refrigerator; an operation start step in which, when a temperature detected by any one of the temperature sensors rises to a predetermined operation start temperature that is higher than the predetermined target cooling temperature while the operation of the cryogenic refrigerator is stopped, the control unit starts operation of the cryogenic refrigerator; Including, how to drive.

Images