Cryogenic device

Abstract

A cryogenic device (10) comprises: a cryogenic refrigerator (20) which comprises a first cooling stage (25a) and a second cooling stage (25b) arranged along a central axis (C1) of the cryogenic refrigerator (20), and in which the second cooling stage (25b) is cooled to a temperature lower than the first cooling stage (25a); and a heat switch (100) which thermally connects the first cooling stage (25a) and the second cooling stage (25b) or releases the thermal connection between the first cooling stage (25a) and the second cooling stage (25b), and which extends along a direction that is not parallel to the central axis (C1) of the cryogenic refrigerator (20).

Description

cryogenic equipment

[0001] The present invention relates to cryogenic devices.

[0002] For example, in a cryogenic device that operates at extremely low temperatures, such as a superconducting magnet device, initial cooling is performed when the device is started, whereby the device is cooled from an initial temperature, such as room temperature, to a target cooling temperature.

[0003] Japanese Patent Application Laid-Open No. 2005-331180

[0004] The use of cryogenic equipment, such as the provision of a high magnetic field by a superconducting magnet, becomes possible after the initial cooling is complete, so it is desirable that the initial cooling time be as short as possible.

[0005] An exemplary object of certain aspects of the present invention is to reduce the time required for initial cool down in a cryogenic device.

[0006] According to one aspect of the present invention, a cryogenic device includes a cryogenic refrigerator having a first cooling stage and a second cooling stage arranged along a central axis of the cryogenic refrigerator, wherein the second cooling stage is cooled to a lower temperature than the first cooling stage, and a thermal switch that thermally connects the first cooling stage to the second cooling stage or disconnects the thermal connection between the first cooling stage and the second cooling stage, the thermal switch extending along a direction non-parallel to the central axis of the cryogenic refrigerator.

[0007] According to one aspect of the present invention, a cryogenic device includes a cryogenic refrigerator having a first cooling stage and a second cooling stage, with the second cooling stage cooled to a lower temperature than the first cooling stage, and a thermal switch that thermally connects the first cooling stage to the second cooling stage or disconnects the thermal connection between the first cooling stage and the second cooling stage, the thermal switch extending along a direction different from the direction of gravity acting on the cryogenic device.

[0008] According to one aspect of the present invention, a cryogenic device includes a cryogenic refrigerator having a first cooling stage and a second cooling stage, with the second cooling stage cooled to a lower temperature than the first cooling stage, a thermal switch that thermally connects the first cooling stage to the second cooling stage or disconnects the thermal connection between the first cooling stage and the second cooling stage, and a rotatable vacuum vessel in which the cryogenic refrigerator is installed and which houses the first cooling stage, the second cooling stage, and the thermal switch.

[0009] According to the present invention, the time required for initial cooling in a cryogenic device can be reduced.

[0010] FIG. 4( a) is a schematic diagram of a cryogenic device according to an embodiment; FIG. 4( b) is a schematic cross-sectional view showing an exemplary configuration of a thermal switch according to an embodiment in more detail; FIG. 4( a) is a schematic diagram of a thermal switch according to a modified example; FIG. 4( b ...

[0011] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the description and drawings, identical or equivalent components, parts, and processes are designated by the same reference numerals, and redundant explanations will be omitted as appropriate. The scale and shape of each part shown in the drawings are set for convenience to facilitate explanation, and should not be interpreted as limiting unless otherwise specified. The embodiments are merely examples and do not limit the scope of the present invention in any way. All features and combinations thereof described in the embodiments are not necessarily essential to the invention.

[0012] 1 is a diagram schematically illustrating a cryogenic device 10 according to an embodiment. The cryogenic device 10 is configured to cool a superconducting coil 12, which is an example of an object to be cooled, from room temperature to a cryogenic temperature, and to maintain the superconducting coil 12 at a cryogenic temperature while the superconducting coil 12 is in use.

[0013] The superconducting coil 12 is mounted in high magnetic field equipment (not shown) as a magnetic field source for, for example, a single crystal pulling device, an NMR system, an MRI system, an accelerator such as a cyclotron, a high-energy physics system such as a nuclear fusion system, or other high magnetic field equipment, and can generate the high magnetic field required for the equipment. The superconducting coil 12 is configured to generate a strong magnetic field by passing current through the superconducting coil 12 while it is cooled to an extremely low temperature below the superconducting transition temperature.

[0014] The cryogenic device 10 includes a cryogenic refrigerator 20 , a vacuum vessel 30 , a radiation shield 40 , and a thermal switch 100 .

[0015] In this embodiment, the cryogenic refrigerator 20 is a two-stage Gifford-McMahon (GM) refrigerator, and includes a compressor 21 and a two-stage cold head 22.

[0016] The compressor 21 is configured to recover refrigerant gas from the cryogenic refrigerator 20 from the cold head 22, increase the pressure of the recovered refrigerant gas, and supply the refrigerant gas back to the cold head 22. The cold head 22, also referred to as an expander, generates refrigeration by adiabatic expansion of the supplied refrigerant gas in an internal expansion chamber. The circulation of the refrigerant gas between the compressor 21 and the cold head 22 is performed with a combination of appropriate pressure fluctuations and volume fluctuations of the refrigerant gas in the cold head 22, thereby forming a refrigeration cycle (e.g., a GM cycle) of the cryogenic refrigerator 20, thereby cooling each cooling stage of the cold head 22 to a desired cryogenic temperature. The refrigerant gas, also referred to as a working gas, is typically helium gas, but other appropriate gases may be used.

[0017] The cold head 22 includes a cold head flange 23, a first cylinder 24a, a first cooling stage 25a, a second cylinder 24b, and a second cooling stage 25b, which are arranged coaxially along a central axis C1 of the cryogenic refrigerator 20. The central axis C1 can also be referred to as the central axis of the cold head 22.

[0018] The first cylinder 24a connects the cold head flange 23 to the first cooling stage 25a, and the second cylinder 24b connects the first cooling stage 25a to the second cooling stage 25b. The first cooling stage 25a and the second cooling stage 25b are made of a highly thermally conductive metal such as copper (e.g., pure copper) or other thermally conductive material. The first cylinder 24a and the second cylinder 24b are made of a metal such as stainless steel. Generally, the thermal conductivity of the thermally conductive material forming the cooling stage is higher than that of the material forming the cylinder.

[0019] The cold head 22 also includes a cold head drive unit 26. The cold head drive unit 26 is attached to the cold head flange 23. The cold head drive unit 26 includes a motor that axially reciprocates the first displacer and the second displacer housed in the first cylinder 24a and the second cylinder 24b, respectively. The cold head drive unit 26 also includes a pressure switching valve that is driven by the motor in synchronization with the displacers. The pressure switching valve is configured to periodically switch between receiving high-pressure refrigerant gas into the cold head 22 and sending low-pressure refrigerant gas out.

[0020] In the illustrated example, the cold head 22 is installed on the top plate of the vacuum vessel 30. An opening is provided in the top plate of the vacuum vessel 30, through which the cold head 22 is inserted into the vacuum vessel 30. A cold head flange 23 is attached to the vacuum vessel 30 through this opening, and the cold head 22 is fixed to the vacuum vessel 30. The first cylinder 24a, first cooling stage 25a, second cylinder 24b, and second cooling stage 25b of the cold head 22 are disposed inside the vacuum vessel 30. The cold head 22 is installed vertically in the vacuum vessel 30, with the cold head driver 26 facing upward and the first cooling stage 25a and second cooling stage 25b facing downward.

[0021] Therefore, the cold head 22 is installed in the vacuum vessel 30 so that the central axis C1 is aligned with the direction of gravity acting on the cryogenic device 10 (the vertical direction in FIG. 1 ). While this arrangement of the cryogenic refrigerator 20 is typical, other installation positions are also possible. The cryogenic refrigerator 20 may be installed in the vacuum vessel 30 with the central axis C1 oriented horizontally or in other directions.

[0022] The first cooling stage 25a and the second cooling stage 25b are each cooled to a desired cryogenic temperature by operating the cryocooler 20. The first cooling stage 25a is cooled to a first cooling temperature, for example, 30 K to 80 K, and the second cooling stage 25b is cooled to a second cooling temperature lower than the first cooling temperature, for example, 3 K to 20 K. The second cooling temperature is a temperature lower than the superconducting transition temperature of the superconducting coil 12.

[0023] Although Figure 1 shows one cryogenic refrigerator 20 as an example, if necessary, for example, when the superconducting coil 12 is large, the cryogenic device 10 may be equipped with multiple cryogenic refrigerators 20 that cool one and the same object to be cooled.

[0024] The vacuum vessel 30 is configured to separate the vacuum region 32 from the external environment 14 (e.g., a room temperature and atmospheric pressure environment). The vacuum region 32 is defined within the vacuum vessel 30. The vacuum vessel 30 may be, for example, a cryostat. The superconducting coil 12, the first and second cooling stages 25 a and 25 b of the cryocooler 20, the radiation shield 40, and the thermal switch 100 are disposed in the vacuum region 32 and are vacuum-insulated from the external environment 14. The compressor 21, cold head flange 23, and cold head drive unit 26 of the cryocooler 20 are disposed in the external environment 14.

[0025] The cryogenic device 10 is configured as a conduction cooling type in which an object to be cooled (e.g., a radiation shield 40, a superconducting coil 12) is directly cooled by a cryogenic refrigerator 20. The cryogenic refrigerator 20 is thermally coupled to the object to be cooled so as to cool the object by conduction cooling.

[0026] The radiation shield 40 is thermally coupled to the first cooling stage 25a and cooled to a first cooling temperature. The radiation shield 40 is directly attached to the first cooling stage 25a and thermally coupled thereto. Alternatively, the radiation shield 40 may be attached to the first cooling stage 25a via a flexible or rigid heat transfer member. The radiation shield 40 is disposed to surround the superconducting coil 12, which is cooled to a second cooling temperature, the second cooling stage 25b of the cryocooler 20, and other low-temperature parts, and can thermally protect these low-temperature parts from external radiant heat. The radiation shield 40 is formed of a metal material such as copper or another material with high thermal conductivity.

[0027] The superconducting coil 12 is thermally coupled to the second cooling stage 25b via a heat transfer member 50. The heat transfer member 50 is formed of a metal material such as copper or another material with high thermal conductivity, and connects the superconducting coil 12 to the second cooling stage 25b. The heat transfer member 50 may be flexible and connect the superconducting coil 12 and the second cooling stage 25b to allow relative displacement between them, or it may be a rigid member that rigidly connects the superconducting coil 12 and the second cooling stage 25b. The heat transfer member 50 is formed of a metal material such as copper or another material with high thermal conductivity.

[0028] In the illustrated example, the heat transfer member 50 is fixed to the bottom surface of the second cooling stage 25 b, but may be fixed to other locations such as the side surface or top surface of the second cooling stage 25 b. Similarly, the heat transfer member 50 is fixed to the bottom surface of the superconducting coil 12, but may be fixed to other locations such as the side surface or top surface of the superconducting coil 12.

[0029] The thermal switch 100 is configured to thermally connect the first cooling stage 25 a and the second cooling stage 25 b, or to disconnect the thermal connection between the first cooling stage 25 a and the second cooling stage 25 b. In other words, the thermal switch 100 is configured to thermally connect or disconnect a portion of the cryogenic device 10 having a first cooling temperature (e.g., the radiation shield 40) and a portion of the cryogenic device 10 having a second cooling temperature (e.g., the superconducting coil 12).

[0030] In this embodiment, the thermal switch 100 extends in a direction that is not parallel to the central axis C1 of the cryogenic refrigerator 20. That is, the central axis C2 of the thermal switch 100 is not parallel to the central axis C1 of the cryogenic refrigerator 20. As described above, the central axis C1 of the cryogenic refrigerator 20 is parallel to the direction of gravity acting on the cryogenic device 10, and therefore the central axis C2 of the thermal switch 100 extends in a direction that is different from the direction of gravity acting on the cryogenic device 10.

[0031] As an example, as shown in the figure, the thermal switch 100 extends along a direction perpendicular to the central axis C1 of the cryogenic refrigerator 20. When the central axis C1 of the cryogenic refrigerator 20 is parallel to the direction of gravity, the central axis C2 of the thermal switch 100 extends in the horizontal direction.

[0032] The thermal switch 100 is a so-called gas gap type thermal switch. The thermal switch 100 includes a first heat transfer element (hereinafter also referred to as a high-temperature side heat transfer element) 110 and a second heat transfer element (hereinafter also referred to as a low-temperature side heat transfer element) 120, which are arranged opposite each other with a gas gap 130 between them. The high-temperature side heat transfer element 110 has a first heat transfer surface 71 facing the gas gap 130 and extending along the central axis C2 of the thermal switch 100. The low-temperature side heat transfer element 120 has a second heat transfer surface 72 facing the gas gap 130 and extending along the central axis C2 of the thermal switch 100. The high-temperature side heat transfer element 110 is thermally coupled to the first cooling stage 25a, and the low-temperature side heat transfer element 120 is thermally coupled to the second cooling stage 25b.

[0033] The high-temperature side heat transfer element 110 is attached to any location that is cooled to a first cooling temperature, and the low-temperature side heat transfer element 120 is attached to any location that is cooled to a second cooling temperature. As shown in the figure, the high-temperature side heat transfer element 110 may be attached to a first member 61, and the low-temperature side heat transfer element 120 may be attached to a second member 62. The first member 61 is attached to the radiation shield 40 and thermally coupled to the first cooling stage 25a. The second member 62 is attached to the heat transfer member 50 and thermally coupled to the second cooling stage 25b. The first member 61 and the second member 62, like the radiation shield 40 and the heat transfer member 50, are formed of a metal material such as copper or other material with high thermal conductivity. Alternatively, the high-temperature side heat transfer element 110 may be attached to the radiation shield 40, the low-temperature side heat transfer element 120 may be attached to the superconducting coil 12, and the thermal switch 100 may directly connect the superconducting coil 12 and the radiation shield 40.

[0034] The thermal switch 100 includes a connecting tube 140 extending from the high-temperature side heat transfer element 110 to the low-temperature side heat transfer element 120 so as to isolate the gas gap 130 from the ambient environment (i.e., the vacuum region 32) of the thermal switch 100. The connecting tube 140 extends coaxially with the high-temperature side heat transfer element 110 and the low-temperature side heat transfer element 120 along the central axis C2 of the thermal switch 100. The high-temperature side heat transfer element 110, the low-temperature side heat transfer element 120, and the connecting tube 140 form an airtight container that seals the working gas in the gas gap 130.

[0035] When the temperatures of the high-temperature side heat transfer element 110 and the low-temperature side heat transfer element 120 are higher than the switching temperature, the high-temperature side and the low-temperature side of the thermal switch 100 can be thermally connected by heat transfer between the heat transfer elements via the working gas in the gas gap 130. This is the on state of the thermal switch 100. The switching temperature of the thermal switch 100 corresponds to the boiling point of the enclosed working gas.

[0036] The thermal switch 100 disconnects the thermal connection between the high-temperature side and the low-temperature side when the temperature of at least one of the high-temperature side heat transfer element 110 and the low-temperature side heat transfer element 120 (usually the low-temperature side heat transfer element 120) is lower than the switching temperature. This is because the working gas in the gas gap 130 condenses on at least the surface of the low-temperature side heat transfer element 120, creating a vacuum in the gas gap 130, and the high-temperature side heat transfer element 110 and the low-temperature side heat transfer element 120 are vacuum insulated via the gas gap 130. This is the off state of the thermal switch 100.

[0037] An exemplary configuration of the thermal switch 100 that may be installed in the cryogenic device 10 is described in more detail with reference to FIGS.

[0038] The cryogenic device 10 according to the embodiment operates as follows. When the cryogenic refrigerator 20 is started, the first cooling stage 25a of the cryogenic refrigerator 20 is cooled to a first cooling temperature, and the second cooling stage 25b is cooled to a second cooling temperature. The radiation shield 40 is cooled to the first cooling temperature by the first cooling stage 25a, and the superconducting coil 12 is cooled to the second cooling temperature by the second cooling stage 25b. By applying electricity to the superconducting coil 12 from a power source (not shown), the superconducting coil 12 can generate a strong magnetic field. In this manner, the cryogenic device 10 can be operated.

[0039] Connecting a portion of the cryogenic device 10, such as the radiation shield 40, with a portion of the superconducting coil 12, with a first cooling temperature, via the thermal switch 100, is advantageous for initial cooling during startup. During initial cooling, the cryocooler 20 is cooled from an ambient temperature (e.g., room temperature) to a target cryogenic temperature. Therefore, at the beginning of initial cooling, the thermal switch 100 is turned on, thermally connecting the radiation shield 40 and the superconducting coil 12. Generally, the refrigeration capacity of the first cooling stage 25a of the cryocooler 20 is greater than that of the second cooling stage 25b. Typically, the refrigeration capacity of the first stage of the cryocooler 20 can be several tens of times greater than that of the second stage of the cryocooler 20. Through the thermal switch 100, the refrigeration capacity of the first cooling stage 25a can be used to assist the second cooling stage 25b in cooling the superconducting coil 12. This shortens the time required for initial cooling.

[0040] Cooling then continues, and when the superconducting coil 12 is cooled to a temperature lower than the switching temperature of the thermal switch 100, the thermal switch 100 is switched off, and the thermal connection between the radiation shield 40 and the superconducting coil 12 is broken. The radiation shield 40 is maintained at the first cooling temperature by the first cooling stage 25a, while the superconducting coil 12 is further cooled by the second cooling stage 25b, and is finally cooled to the second cooling temperature.

[0041] Existing gas gap thermal switches are designed to rely on natural convection of the internal gas to achieve heat transfer in the on state. Natural convection is generated by temperature differences and gravity. The temperature difference is an environmental factor determined by the application in which the thermal switch is installed. Therefore, existing thermal switches must be installed in the direction of gravity, i.e., vertically, to effectively utilize gravity to generate natural convection.

[0042] Such a placement of a thermal switch is illustrated in Figure 10. As mentioned above, since cryogenic refrigerators are also typically installed along the direction of gravity, existing thermal switches are often installed parallel to the cryogenic refrigerator between the first and second stages.

[0043] If the existing thermal switch is installed in a different orientation without complying with this installation requirement, the heat transfer performance that the existing thermal switch can provide may be reduced compared to the heat transfer performance that it was designed for. If the thermal switch does not operate as designed, the result may be that the thermal switch does not provide the heat transfer performance required for the application.

[0044] When a thermal switch is installed parallel to a cryogenic refrigerator, the longitudinal dimension of the thermal switch is limited by the distance between the first and second stages of the cryogenic refrigerator. Taking the cryogenic refrigerator 20 shown in FIG. 1 as an example, the length of an existing thermal switch that requires parallel installation cannot exceed the distance L1 between the first and second cooling stages 25a and 25b along the central axis C1 of the cryogenic refrigerator 20. The area of ​​the heat transfer surface within the thermal switch should be correlated with the length of the thermal switch. Therefore, the heat transfer performance of the thermal switch is limited by the distance between the first and second stages of the cryogenic refrigerator.

[0045] The present inventors have found through their own research that it is possible to design a gas gap type thermal switch suitable for practical use in cryogenic devices, even if it deviates from the existing design concept based on heat transfer by natural convection of internal gas. The thermal switch 100 according to the embodiment can provide sufficient heat transfer performance by utilizing heat conduction between heat transfer surfaces via gas, rather than relying on natural convection of gas.

[0046] The thermal switch 100 according to the embodiment does not require natural gas convection for heat transfer, and is therefore not subject to the installation posture restrictions described above. Therefore, unlike existing thermal switches, the thermal switch 100 can be installed with its central axis C2 oriented in a direction different from the direction of gravity acting on the cryogenic device 10. When the cryogenic refrigerator 20 is installed in the cryogenic device 10 along the direction of gravity, the thermal switch 100 can be installed with its central axis C2 oriented in a direction non-parallel to the central axis C1 of the cryogenic refrigerator 20. The thermal switch 100 can provide the designed heat transfer performance regardless of the installation posture. The inventors have experimentally confirmed that when the thermal switch 100 is installed with its central axis C2 oriented horizontally, as illustrated in FIG. 1 , the initial cooling time of the cryogenic device 10 can be shortened by the effect of the thermal switch 100.

[0047] In existing thermal switches, a relatively wide gas gap, such as 10 mm or more, is set to promote natural convection. In contrast, the thermal switch 100 according to the embodiment utilizes the thermal conduction of the gas present in the gas gap 130 and does not require natural convection, so the gas gap 130 may be narrower than that of existing thermal switches. The distance between the first heat transfer surface 71 and the second heat transfer surface 72 in the gas gap 130 may be, for example, 1 mm or less, and more preferably 0.5 mm or less. This arrangement can suppress natural convection in the gas gap 130, which is expected to stabilize the performance of the thermal switch 100.

[0048] The length L2 of the thermal switch 100 along the central axis C2 of the thermal switch 100 may be longer than the distance L1 between the first cooling stage 25a and the second cooling stage 25b along the central axis C1 of the cryogenic refrigerator 20. As described above, the installation orientation of the thermal switch 100 does not need to be aligned with the cryogenic refrigerator 20. Therefore, the length L2 of the thermal switch 100 can be longer than the axial distance L1 between the two cooling stages of the cryogenic refrigerator 20. By lengthening the thermal switch 100 in this manner, the areas of the first heat transfer surface 71 and the second heat transfer surface 72 inside the thermal switch can be increased. This enables efficient heat transfer between the first heat transfer surface 71 and the second heat transfer surface 72 via the gas gap 130 when the thermal switch 100 is in the on state, improving the heat transfer performance of the thermal switch 100.

[0049] Furthermore, the longer the thermal switch 100, the less heat can be input from the first cooling stage 25a to the second cooling stage 25b through the structural material of the thermal switch 100, such as the connecting tube 140. This also improves the thermal insulation performance of the thermal switch 100 in the OFF state.

[0050] Fig. 2 is a schematic cross-sectional view showing in more detail an exemplary configuration of the thermal switch 100 shown in Fig. 1. Fig. 2 shows a longitudinal cross section including the central axis of the thermal switch 100. As described above, the thermal switch 100 includes the high-temperature side heat transfer element 110 and the low-temperature side heat transfer element 120 arranged opposite the high-temperature side heat transfer element 110 with a gas gap 130 sandwiched therebetween. For example, the thermal switch 100 may have a generally cylindrical shape extending along its central axis.

[0051] The high-temperature side heat transfer element 110 includes a first base 111 and a column 112 extending from the first base 111. The first base 111 is thermally coupled to a first member 61 (e.g., the radiation shield 40 or the first cooling stage 25a shown in FIG. 1 ) that is cooled to a first cooling temperature. The first base 111 may have, for example, a generally disk-like shape and is fixed to the first member 61 with its circular end face in contact with the surface of the first member 61. The column 112 is disposed inside the thermal switch 100. The column 112 has, for example, a cylindrical shape. The column 112 extends coaxially with the first base 111 from the first base 111 along the central axis of the thermal switch 100 on the side opposite to the first member 61. The pillar portion 112 may be formed integrally with the first base portion 111, or may be prepared separately from the first base portion 111 and joined to the first base portion 111.

[0052] The low-temperature-side heat transfer element 120 includes a second base 121 and a tubular portion 122 extending from the second base 121. The second base 121 is thermally coupled to a second member 62 (e.g., the superconducting coil 12 or the second cooling stage 25b shown in FIG. 1 ) that is cooled to a second cooling temperature. The second base 121 may have, for example, a generally disk-like shape and is fixed to the second member 62 with its circular end face in contact with the surface of the second member 62. The tubular portion 122 has, for example, a cylindrical shape. The tubular portion 122 extends coaxially with the second base 121 along the central axis of the thermal switch 100 from the second base 121 on the side opposite the second member 62. The tubular portion 122 may be integrally formed with the second base 121, or may be prepared separately from the second base 121 and joined to the second base 121.

[0053] The low-temperature side heat transfer element 120 is configured to receive the high-temperature side heat transfer element 110 therein. The columnar portion 112 of the high-temperature side heat transfer element 110 is inserted into a cavity in the cylindrical portion 122 of the low-temperature side heat transfer element 120. The second base portion 121 of the low-temperature side heat transfer element 120 faces the columnar portion 112 of the high-temperature side heat transfer element 110, and the cylindrical portion 122 of the low-temperature side heat transfer element 120 surrounds the columnar portion 112 of the high-temperature side heat transfer element 110. The columnar portion 112 of the high-temperature side heat transfer element 110 and the second base portion 121 and cylindrical portion 122 of the low-temperature side heat transfer element 120 are separated by a gas gap 130 and are not in physical contact with each other. The cylindrical portion 122 of the low-temperature side heat transfer element 120 is disposed adjacent to the first base portion 111 of the high-temperature side heat transfer element 110 on the opposite side from the second base portion 121.

[0054] In this manner, when the high-temperature side heat transfer element 110 has the columnar portion 112 and the low-temperature side heat transfer element 120 has the cylindrical portion 122, the volume of the low-temperature side heat transfer element 120 can be smaller than that of the high-temperature side heat transfer element 110. Having a relatively small volume for the low-temperature side heat transfer element 120 can be advantageous (for example, compared to the example in FIG. 3 ) because it leads to a smaller heat load on the second cooling stage 25b of the cryogenic refrigerator 20.

[0055] The thermal switch 100 also includes a connecting cylinder 140 that, together with the high-temperature side heat transfer element 110 and the low-temperature side heat transfer element 120, forms an airtight container for sealing the working gas of the thermal switch 100 therein. The connecting cylinder 140 connects the high-temperature side heat transfer element 110 and the low-temperature side heat transfer element 120, and more specifically, connects the cylinder portion 122 to the first base portion 111 so as to isolate the gas gap 130 from the ambient environment (e.g., the vacuum region 32 shown in FIG. 1 ). The connecting cylinder 140 has, for example, a cylindrical shape and extends coaxially with the first base portion 111 and the cylinder portion 122 along the central axis of the thermal switch 100. The connecting cylinder 140 may be joined to the high-temperature side heat transfer element 110 and the low-temperature side heat transfer element 120 by, for example, brazing, adhesive bonding, or any other appropriate joining method.

[0056] The axial length of the connecting tube 140 may be significantly shorter than the overall axial length of the thermal switch 100, for example, less than half or less than one-third of the overall axial length of the thermal switch 100. As an example, rather than being a tube, the connecting tube 140 may have a ring shape (e.g., an annular shape) whose axial length is shorter than its diameter.

[0057] In some existing thermal switch designs, a cylindrical shell of the thermal switch extends over almost the entire axial length of the thermal switch, connecting two spaced-apart heat transfer bodies. Therefore, in these existing thermal switches, a radial gap (e.g., radial gap 162 shown in FIG. 5 ) is formed between the cylindrical shell and the heat transfer body inside. Due to this radial gap, the diameter of the heat transfer body is smaller than the diameter of the cylindrical shell. As a result, the surface area of ​​the heat transfer body is also reduced accordingly, which can lead to a reduction in the heat transfer performance of the thermal switch.

[0058] In contrast, in this embodiment, the connecting tube 140 is connected in axial series to the tube portion 122 of the low-temperature side heat transfer element 120. There is no radial gap between the connecting tube 140 and the tube portion 122. The diameter of the tube portion 122 is equal to the diameter of the thermal switch 100, allowing the surface area of ​​the tube portion 122 to be relatively large. This can improve the heat transfer performance of the thermal switch 100 compared to existing designs.

[0059] The high-temperature side heat transfer element 110 and the low-temperature side heat transfer element 120 are made of a metal material such as copper or other material having high thermal conductivity, similar to the other heat transfer members in the cryogenic device 10. Although the high-temperature side heat transfer element 110 and the low-temperature side heat transfer element 120 are typically made of the same material, they may also be made of different materials.

[0060] The connecting tube 140 is formed of a material with a lower thermal conductivity than the high-temperature side heat transfer element 110 and the low-temperature side heat transfer element 120, such as an insulating material. Here, the insulating material may be a material with a thermal conductivity that is, for example, 1 / 10 or less of the thermal conductivity of the high-temperature side heat transfer element 110 (or the low-temperature side heat transfer element 120). The connecting tube 140 may be formed of, for example, stainless steel, glass fiber reinforced plastic (GFRP), or other plastic materials. This prevents or minimizes heat leakage from the high-temperature side heat transfer element 110 to the low-temperature side heat transfer element 120 through the connecting tube 140 when the thermal switch 100 is off.

[0061] Since the material forming the connecting tube 140 is generally stronger than the highly thermally conductive material forming the heat transfer elements, the wall thickness of the connecting tube 140 may be thinner than the wall thickness of the tubular portion 122 of the heat transfer element, as shown in the figure. Making the connecting tube 140 thinner in this way helps to suppress heat penetration from the high-temperature side heat transfer element 110 to the low-temperature side heat transfer element 120 through the connecting tube 140.

[0062] The working gas sealed in the thermal switch 100 is selected so that the switching temperature of the thermal switch 100 is lower than the first cooling temperature and higher than the second cooling temperature of the cryogenic refrigerator 20. As described above, the switching temperature of the thermal switch 100 corresponds to the boiling point of the sealed working gas. Therefore, the working gas sealed in the thermal switch 100 may be, for example, neon (approximately 27.1 K). Alternatively, the working gas may be hydrogen (approximately 20.4 K) or helium (approximately 4.2 K). Here, the boiling points of each gas species at atmospheric pressure are indicated in parentheses next to the gas species. For example, if neon is sealed in the thermal switch 100 at atmospheric pressure, the switching temperature of the thermal switch 100 can be approximately 27.1 K. The working gas may be sealed in the thermal switch 100 at a pressure higher than atmospheric pressure (for example, within 5 atmospheres or within 10 atmospheres). The switching temperature of the thermal switch 100 may be adjusted by adjusting the sealing pressure of the working gas.

[0063] The working gas may be a mixture of gases, such as a mixture of gases containing at least one of neon, hydrogen, and helium. The mixture may also contain a diluent gas, such as nitrogen, argon, or air. The switching temperature of the thermal switch 100 may be adjusted by adjusting the composition of the mixture of gases.

[0064] Optionally, the thermal switch 100 may include a getter material 150 thermally coupled to the cold-side heat transport element 120 and capable of adsorbing gas from the gas gap 130. The getter material 150 may be, for example, activated carbon, or other porous material or other adsorbent material capable of adsorbing the operating gas of the thermal switch 100 at cryogenic temperatures (i.e., temperatures below the switching temperature of the thermal switch 100, e.g., the second cooling temperature). The getter material 150 is disposed on the surface of the cold-side heat transport element 120 in an appropriate manner so that it can be cooled by the cold-side heat transport element 120.

[0065] Ideally, when the thermal switch 100 is cooled to a temperature lower than its switching temperature, the working gas condenses within the thermal switch 100 as described above, the gas gap 130 becomes a vacuum, and the thermal switch 100 turns off. However, in reality, some working gas may remain in the gas gap 130. Such residual gas may cause heat transfer between the high-temperature side heat transfer element 110 and the low-temperature side heat transfer element 120. Unfortunately, there is a possibility that heat leakage from the high-temperature side heat transfer element 110 to the low-temperature side heat transfer element 120 through the thermal switch 100, which should be off, may become significant.

[0066] In contrast, by providing the getter material 150 in the thermal switch 100, the residual gas can be adsorbed and the degree of vacuum in the gas gap 130 can be further increased. Therefore, the thermal connection can be more reliably cut off when the thermal switch 100 is in the OFF state.

[0067] The getter material 150 is disposed on the low-temperature-side heat transfer element 120 so as to face the gas gap 130. This exposes the getter material 150 to residual gas that may be present in the gas gap 130, allowing the getter material 150 to efficiently adsorb the residual gas. Furthermore, by directly cooling the getter material 150 with the low-temperature-side heat transfer element 120, the temperature of the getter material 150 can be quickly lowered. This allows the thermal switch 100 to be quickly switched off, providing a thermal switch 100 with excellent responsiveness.

[0068] In the illustrated example, the getter material 150 is provided on a surface of the second base portion 121 of the low-temperature-side heat transfer element 120 that faces the column portion 112 of the high-temperature-side heat transfer element 110. Alternatively or in addition to this, the getter material 150 can be arranged in other ways on the low-temperature-side heat transfer element 120. For example, the getter material 150 may be provided on the inner surface of the cylindrical portion 122 that faces the circumferential surface of the column portion 112.

[0069] The thermal switch 100 is a so-called one-gap (1-gap) type thermal switch, and the gas gap 130 is the only gas gap in the thermal switch 100. The one-gap type thermal switch has the advantage of being easier to manufacture and assemble than the multi-gap type described below.

[0070] In the exemplary thermal switch 100 described with reference to Figure 2, the hot-side heat transport element 110 has a convex shape and the cold-side heat transport element 120 has a concave shape that receives the hot-side heat transport element 110. However, in any of the embodiments described herein, the hot-side heat transport element 110 may alternatively have a concave shape and the cold-side heat transport element 120 may have a corresponding convex shape, as will be described below with reference to Figure 3.

[0071] 3 is a schematic diagram showing a thermal switch 100 according to a modified example. The thermal switch 100 includes a high-temperature side heat transfer element 110 and a low-temperature side heat transfer element 120 arranged opposite the high-temperature side heat transfer element 110 with a gas gap 130 sandwiched therebetween. The high-temperature side heat transfer element 110 and the low-temperature side heat transfer element 120 are connected by a connecting tube 140.

[0072] 3, the low-temperature side heat transfer element 120 may include a first base 123 and a column 124 extending from the first base 123. The high-temperature side heat transfer element 110 may include a second base 113 facing the column 124 and a tubular portion 114 extending from the second base 113 so as to surround the column 124. The tubular portion 114 is connected to the first base 123 by a connecting tubular portion 140. This configuration also provides a one-gap type thermal switch.

[0073] Optionally, a getter material 150 may be provided in the thermal switch 100. The getter material 150 may be provided, for example, on the tip surface of the column portion 124 of the low-temperature side heat transfer element 120. The getter material 150 may also be provided on the circumferential surface of the column portion 124 of the low-temperature side heat transfer element 120.

[0074] 4(a) and 4(b) are schematic diagrams showing a thermal switch 100 according to a modified example. The thermal switch 100 includes a high-temperature side heat transfer element 110 and a low-temperature side heat transfer element 120 arranged opposite the high-temperature side heat transfer element 110 with a gas gap 130 sandwiched therebetween. The high-temperature side heat transfer element 110 has a convex shape, and the low-temperature side heat transfer element 120 has a concave shape that receives the high-temperature side heat transfer element 110. The high-temperature side heat transfer element 110 and the low-temperature side heat transfer element 120 are connected by a connecting tube 140. The thermal switch 100 is a one-gap type thermal switch.

[0075] 4A, the thermal switch 100 includes a getter chamber 152 having a getter material 150 therein. The getter chamber 152 is housed within the low-temperature side heat transfer element 120, for example, within the second base 121 of the low-temperature side heat transfer element 120. The second base 121 has a recess in its end surface facing the outside of the thermal switch 100, which is opposite to the high-temperature side heat transfer element 110, and the getter chamber 152 is disposed within this recess. Advantageously, the getter chamber 152 does not interfere with the second member 62 when the low-temperature side heat transfer element 120 is attached to the second member 62.

[0076] The getter chamber 152 is connected to the gas gap 130 through an internal passage 154 in the thermal switch 100. The internal passage 154 is formed in the low-temperature side heat transfer element 120. As an example, the internal passage 154 may be a through-hole that penetrates the second base 121 on the central axis of the thermal switch 100. Therefore, residual gas in the gas gap 130 can enter the getter chamber 152 through the internal passage 154 and be adsorbed by the getter material 150.

[0077] 4B, the thermal switch 100 includes a getter chamber 152 having a getter material 150 therein. The getter chamber 152 is disposed outside the thermal switch 100 and is connected to the gas gap 130 through an external passage 156. Because the getter chamber 152 is contained within the axial range of the thermal switch 100, when the thermal switch 100 is attached to the first member 61 and the second member 62, the getter chamber 152 is prevented from interfering with these members.

[0078] The getter chamber 152 is a container that contains the getter material 150, and the external passage 156 may be a pipe that connects the getter chamber 152 to the thermal switch 100. The getter chamber 152 is thermally coupled to the low-temperature-side heat transfer element 120 via the external passage 156. To efficiently cool the getter material 150, the getter chamber 152 and the external passage 156 are formed of a metal material, such as copper, or other material with high thermal conductivity. For example, one end of the external passage 156 is attached to the getter chamber 152, and the other end is attached to the cylindrical portion 122 of the low-temperature-side heat transfer element 120. Residual gas in the gas gap 130 can enter the getter chamber 152 through the external passage 156 and be adsorbed by the getter material 150.

[0079] A heater or other temperature regulator 158 may be attached to the getter chamber 152. In this case, by operating the temperature regulator 158 to heat the getter material 150, the adsorbed working gas can be released from the getter material 150 into the gas gap 130. In order to efficiently heat the getter material 150 using the temperature regulator 158, the getter chamber 152 and the external passage 156 may be formed of a metal material with relatively low thermal conductivity, such as stainless steel. Furthermore, by stopping the temperature regulator 158 and cooling the getter material 150 using the low-temperature-side heat transfer element 120, the working gas can be adsorbed onto the getter material 150 again. In this way, the thermal switch 100 can be switched on and off independently of the cooling operation of the cryogenic refrigerator 20.

[0080] When the thermal switch 100 is installed in the cryogenic device 10, various other devices may actually be installed around the thermal switch 100. Therefore, as schematically shown by the dashed line in FIG. 4B , a predetermined installable area 160 may be set for the thermal switch 100.

[0081] The thermal switch 100 incorporating the getter material 150 according to the embodiments of FIGS. 2 and 4(a) can have larger diameters for the high-temperature side heat transfer element 110 and the low-temperature side heat transfer element 120 than the thermal switch 100 having the external getter chamber 152 according to the embodiment of FIG. 4(b). In other words, in the embodiment of FIG. 4(b), in order to fit the thermal switch 100 within the installation area 160, the diameters of the high-temperature side heat transfer element 110 and the low-temperature side heat transfer element 120 must be reduced by the amount of the external getter chamber 152. The heat transfer areas of the high-temperature side heat transfer element 110 and the low-temperature side heat transfer element 120 of the thermal switch 100 increase or decrease depending on the diameters. Therefore, the thermal switch 100 incorporating the getter material 150 has the advantage that a relatively large area of ​​the heat transfer element can be secured within the high-temperature side heat transfer element 110 for a given size (volume) of the installation area 160.

[0082] 5 is a schematic diagram showing a thermal switch 100 according to a modified example. The thermal switch 100 includes a high-temperature side heat transfer element 110 and a low-temperature side heat transfer element 120 arranged opposite the high-temperature side heat transfer element 110 with a gas gap 130 sandwiched therebetween. The high-temperature side heat transfer element 110 has a convex shape, and the low-temperature side heat transfer element 120 has a concave shape that receives the high-temperature side heat transfer element 110. The high-temperature side heat transfer element 110 and the low-temperature side heat transfer element 120 are connected by a connecting tube 140. The thermal switch 100 is a one-gap type thermal switch.

[0083] 5, the connecting tube 140 is relatively long and extends over almost the entire axial length of the thermal switch. The connecting tube 140 connects the first base 111 of the high-temperature side heat transfer element 110 to the second base 121 of the low-temperature side heat transfer element 120. The tube portion 122 of the low-temperature side heat transfer element 120 is disposed radially inward of the connecting tube 140, forming a radial gap 162 between the connecting tube 140 and the tube portion 122. The column portion 112 of the high-temperature side heat transfer element 110 is inserted into the tube portion 122 of the low-temperature side heat transfer element 120, forming a gas gap 130 between the column portion 112 and the tube portion 122.

[0084] Similar to the above-described embodiment, the thermal switch 100 may include a getter material 150 that is thermally coupled to the low-temperature-side heat transfer element 120 and is capable of adsorbing gas from the gas gap 130. The getter material 150 is disposed on the low-temperature-side heat transfer element 120 facing the gas gap 130. For example, the getter material 150 may be provided on a surface of the second base portion 121 of the low-temperature-side heat transfer element 120 that faces the column portion 112 of the high-temperature-side heat transfer element 110. Alternatively, or in addition to this, the getter material 150 may be provided on another surface of the low-temperature-side heat transfer element 120, for example, on the tip end of the cylindrical portion 122 of the low-temperature-side heat transfer element 120.

[0085] Fig. 6 is a schematic diagram showing a thermal switch 100 according to a modified example. The thermal switch 100 includes a high-temperature side heat transfer element 110 and a low-temperature side heat transfer element 120 arranged opposite the high-temperature side heat transfer element 110 with a gas gap 130 interposed therebetween. The thermal switch 100 shown in Fig. 6 is a multi-gap type thermal switch having multiple gas gaps 130. A multi-gap type thermal switch has the advantage that it is easier to ensure a wider heat transfer area than a one-gap type thermal switch.

[0086] The high-temperature side heat transfer element 110 includes a first base 111 and a column portion 112 extending from the first base 111. However, unlike the embodiment shown in Fig. 2, the column portion 112 is hollow. The low-temperature side heat transfer element 120 includes a second base 121 and a tubular portion 122 extending from the second base 121. However, unlike the embodiment shown in Fig. 2, a shaft portion 126 extending from the second base 121 coaxially with the tubular portion 122 is formed inside the tubular portion 122. The connecting tube 140 connects the tubular portion 122 to the first base 111.

[0087] The low-temperature side heat transfer element 120 is configured to receive the high-temperature side heat transfer element 110 therein. The column portion 112 of the high-temperature side heat transfer element 110 is inserted into a cavity in the cylindrical portion 122 of the low-temperature side heat transfer element 120. At this time, the shaft portion 126 of the low-temperature side heat transfer element 120 is inserted into the hollow portion of the column portion 112. In this manner, one gas gap 130 is formed inside the column portion 112 of the high-temperature side heat transfer element 110, and another gas gap 130 is formed outside the column portion 112. The high-temperature side heat transfer element 110 and the low-temperature side heat transfer element 120 are separated by these gas gaps 130 and are not in physical contact with each other.

[0088] Similar to the above-described embodiment, the thermal switch 100 may include a getter material 150 thermally coupled to the cold-side heat transfer element 120 and capable of adsorbing gas from the gas gap 130. The getter material 150 is disposed on the cold-side heat transfer element 120 facing the gas gap 130. For example, the getter material 150 may be provided on a surface of the stem 126 of the cold-side heat transfer element 120 facing the first base 111 of the hot-side heat transfer element 110. Alternatively or in addition, the getter material 150 may be provided on a surface of the second base 121 of the cold-side heat transfer element 120 facing the column 112 of the hot-side heat transfer element 110. Alternatively or in addition, the getter material 150 may be provided on another surface of the cold-side heat transfer element 120.

[0089] 6, the pillars 112 of the high-temperature-side heat transfer element 110 can also be considered as cylindrical heat transfer fins. Thus, the high-temperature-side heat transfer element 110 may have a cylindrical heat transfer fin extending toward the low-temperature-side heat transfer element 120. The high-temperature-side heat transfer element 110 may also have multiple cylindrical fins arranged coaxially. The low-temperature-side heat transfer element 120 may have at least one cylindrical fin arranged so as to alternate with the multiple cylindrical fins of the high-temperature-side heat transfer element 110. In this manner, a multi-gap type thermal switch having more gas gaps 130 may be configured.

[0090] Alternatively, the hot-side heat transfer element 110 may include at least one heat transfer fin of a flat plate or other shape extending toward the cold-side heat transfer element 120, and the cold-side heat transfer element 120 may include at least one heat transfer fin extending toward the hot-side heat transfer element 110. The at least one heat transfer fin of the hot-side heat transfer element 110 and the at least one heat transfer fin of the cold-side heat transfer element 120 may be staggered to form multiple gas gaps 130 within the thermal switch 100.

[0091] 7 is a schematic diagram showing a thermal switch 100 according to a modified example. The thermal switch 100 includes a high-temperature side heat transfer element 110 and a low-temperature side heat transfer element 120 arranged opposite the high-temperature side heat transfer element 110 with a gas gap 130 sandwiched therebetween. The high-temperature side heat transfer element 110 has a convex shape, and the low-temperature side heat transfer element 120 has a concave shape that receives the high-temperature side heat transfer element 110. The high-temperature side heat transfer element 110 and the low-temperature side heat transfer element 120 are connected by a connecting tube 140. The thermal switch 100 is a one-gap type thermal switch.

[0092] As shown in FIG. 7 , the thermal switch 100 includes a coating material 170 that coats its outer circumferential surface. The coating material 170 coats the outer circumferential surfaces of the tubular portion 122 of the low-temperature-side heat transfer element 120 and the connecting tube 140. Thermal contraction caused by cryogenic cooling can cause relative displacement between the first member 61 and the second member 62, potentially resulting in a load (e.g., a lateral load) acting on the thermal switch 100. The coating material 170 can help reinforce the thermal switch 100 against such loads. To reduce heat penetration from the high-temperature-side heat transfer element 110 to the low-temperature-side heat transfer element 120 through the coating material 170, the coating material 170 may be made of a thermal insulating material.

[0093] 8 is a schematic diagram showing a thermal switch device 200 according to one embodiment. The thermal switch device 200 includes a plurality of thermal switches (two thermal switches 100a and 100b in this example) connected in series. Each of the plurality of thermal switches includes a high-temperature side heat transfer element 110 and a low-temperature side heat transfer element 120 arranged opposite the high-temperature side heat transfer element 110 with a gas gap 130 sandwiched therebetween. The high-temperature side heat transfer element 110 has a convex shape, and the low-temperature side heat transfer element 120 has a concave shape that accommodates the high-temperature side heat transfer element 110. The high-temperature side heat transfer element 110 and the low-temperature side heat transfer element 120 are connected by a connecting tube 140.

[0094] 8, the high-temperature side heat transfer element 110 of one thermal switch 100a of two adjacent thermal switches is thermally coupled to the first member 61. The low-temperature side heat transfer element 120 of the other thermal switch 100b of the two adjacent thermal switches is thermally coupled to the second member 62.

[0095] The cold-side heat transfer element 120 of the hot-side thermal switch 100a and the hot-side heat transfer element 110 of the cold-side thermal switch 100b may be integrated together. This integrated heat transfer element is thermally coupled to the second member 62 via, for example, a heat transfer member 180.

[0096] Alternatively, the cold-side heat transfer element 120 of the hot-side thermal switch 100a and the hot-side heat transfer element 110 of the cold-side thermal switch 100b may be thermally coupled to each other. In other words, each of the multiple thermal switches may be the thermal switch 100 according to any of the above-described embodiments, and such thermal switches 100 may simply be stacked in the axial direction. The cold-side heat transfer element 120 of each thermal switch 100, together with the hot-side heat transfer element 110 of the adjacent coupled thermal switch 100, is thermally coupled to the second member 62.

[0097] When the thermal switch device 200 has a plurality of thermal switches connected in series, turning off any one of the thermal switches breaks the thermal connection between the first member 61 and the second member 62. Even if one of the multiple thermal switches does not turn off due to some kind of fault (e.g., physical contact between the high-temperature side heat transfer element 110 and the low-temperature side heat transfer element 120, the presence of excessive residual gas, etc.), the thermal switch device 200 can break the thermal connection between the first member 61 and the second member 62 by successfully turning off any other thermal switch. Thus, the thermal switch device 200 is advantageous over the single thermal switch 100 in that it is more robust against faults.

[0098] Therefore, it is not necessary to provide a getter material 150 for each thermal switch of the thermal switching device 200. However, similar to the above-described embodiment, a getter material 150 may be provided for each thermal switch, as shown by the dashed lines.

[0099] Consider a situation where the thermal switching device 200 is on. Comparing the case where a single thermal switch 100 is installed in an installation area of ​​a certain size with the case where the thermal switching device 200 is installed, each thermal switch constituting the thermal switching device 200 is smaller in size than the single thermal switch 100, but the total heat transfer area is approximately the same. Therefore, the heat transfer performance of the single thermal switch 100 and the thermal switching device 200 is expected to be approximately equal. Furthermore, the total axial length of the connecting tubes 140 of each thermal switch in the thermal switching device 200 is approximately equal to the axial length of the connecting tubes 140 of the single thermal switch 100. Therefore, the heat insulation performance of the single thermal switch 100 and the thermal switching device 200 is expected to be approximately equal.

[0100] FIG. 9 is a schematic diagram illustrating a cryogenic device 10 according to another embodiment. The cryogenic device 10 includes a cryogenic refrigerator 20 and a thermal switch 100 mounted on the cryogenic refrigerator 20 and connecting a first cooling stage 25a and a second cooling stage 25b. As in the above-described embodiment, the central axis C2 of the thermal switch 100 extends in a direction non-parallel to the central axis C1 of the cryogenic refrigerator 20, for example, in a direction perpendicular to the central axis C1. Through the thermal switch 100, the refrigeration capacity of the first cooling stage 25a can be used to assist the second cooling stage 25b in cooling an object to be cooled, such as a superconducting coil. This shortens the time required for initial cooling.

[0101] 10 is a schematic diagram illustrating a cryogenic device 10 according to another embodiment. Similar to the above-described embodiment, the cryogenic device 10 includes an object to be cooled, such as a superconducting coil 12, a cryogenic refrigerator 20, a vacuum vessel 30, a radiation shield 40, and a thermal switch 100. The central axis C2 of the thermal switch 100 is parallel to the central axis C1 of the cryogenic refrigerator 20. Alternatively, similar to the above-described embodiment, the central axis C2 of the thermal switch 100 may extend in a direction non-parallel to the central axis C1 of the cryogenic refrigerator 20, for example, in a direction perpendicular to the central axis C1.

[0102] However, the vacuum vessel 30 includes a rotation mechanism 80 configured to rotate the vacuum vessel 30 around at least one axis, and is rotatable relative to the floor surface 82. The axis of rotation of the vacuum vessel 30 by the rotation mechanism 80 may be parallel to the floor surface 82, for example. The rotation mechanism 80 can change the angular orientation of the vacuum vessel 30 relative to the floor surface 82. The orientation of the central axis C2 of the thermal switch 100 is determined according to the angular orientation of the vacuum vessel 30 adjusted by the rotation mechanism 80.

[0103] As described above, existing gas gap type thermal switches require vertical installation because they utilize natural convection of the internal gas for heat transfer. Therefore, existing thermal switches are not suitable for the rotatable vacuum vessel 30, which does not have a fixed installation position. In contrast, the thermal switch 100 according to the embodiment can exhibit good heat transfer performance regardless of the installation position, and therefore can be mounted on the rotatable vacuum vessel 30.

[0104] 11 is a schematic diagram of a cryogenic device 10 according to another embodiment. Similar to the above-described embodiment, the cryogenic device 10 includes an object to be cooled, such as a superconducting coil 12, a cryogenic refrigerator 20, a vacuum vessel 30, a radiation shield 40, and a thermal switch 100.

[0105] The thermal switch 100 may be applied to a support structure 201 that is disposed within the vacuum vessel 30 and supports an object to be cooled on the vacuum vessel 30. The support structure 201 includes a vertical support 202, and the thermal switch 100 may be incorporated into the vertical support 202.

[0106] The vertical supports 202 are fixed to the vacuum vessel 30, extend vertically through the radiation shield 40, and abut against the object to be cooled, such as the superconducting coil 12. The vertical supports 202 can support a force acting vertically downward on the object to be cooled, such as the weight of the superconducting coil 12. Supports such as the vertical supports 202 are formed of a heat insulating material, such as fiber reinforced plastic (FRP). Alternatively, the supports may be formed of a material, such as stainless steel, having a lower thermal conductivity than the highly thermally conductive material that forms the heat transfer paths in the cryogenic device 10.

[0107] A first heat transfer stage 204 and a second heat transfer stage 206 may be mounted on the vertical support 202. The first heat transfer stage 204 is fixed to the radiation shield 40 (or connected to the radiation shield 40 via an appropriate heat transfer member) and is thermally coupled to the first cooling stage 25 a of the cryocooler 20 via the radiation shield 40. The second heat transfer stage 206 is fixed to the superconducting coil 12 (or connected to the superconducting coil 12 via an appropriate heat transfer member) and is thermally coupled to the second cooling stage 25 b of the cryocooler 20 via the superconducting coil 12. Therefore, the first heat transfer stage 204 is cooled to a first cooling temperature by the first cooling stage 25 a, and the second heat transfer stage 206 is cooled to a second cooling temperature by the second cooling stage 25 b.

[0108] The thermal switch 100 is configured to thermally couple the second heat transfer stage 206 to the first heat transfer stage 204 when the temperature of the second heat transfer stage 206 exceeds a switching temperature of the thermal switch 100, and to thermally decouple the second heat transfer stage 206 from the first heat transfer stage 204 when the temperature of the second heat transfer stage 206 falls below the switching temperature. The thermal switch 100 includes a high-temperature side heat transfer element 110 thermally coupled to the first heat transfer stage 204 and a low-temperature side heat transfer element 120 thermally coupled to the second heat transfer stage 206. The high-temperature side heat transfer element 110 and the low-temperature side heat transfer element 120 are arranged opposite each other across a gas gap 130 for heat exchange via a working gas of the thermal switch 100. The high-temperature side heat transfer element 110 and the low-temperature side heat transfer element 120 are not in contact with each other.

[0109] As described above, the working gas sealed in the thermal switch 100 is selected so that the switching temperature of the thermal switch 100 is lower than the first cooling temperature and higher than the second cooling temperature of the cryogenic refrigerator 20. Optionally, the thermal switch 100 may include a getter material thermally coupled to the second heat transfer stage 206, capable of absorbing gas from the airtight space within the thermal switch 100.

[0110] The support structure 201 may also include lateral supports 210. The lateral supports 210 are fixed to the vacuum vessel 30, extend horizontally through the radiation shield 40, and abut against the object to be cooled. The lateral supports 210 can support forces acting horizontally on the object to be cooled, such as electromagnetic forces acting on the superconducting coil 12. Similar to the vertical supports 202, the thermal switch 100 may be incorporated into the lateral supports 210.

[0111] In this embodiment as well, during the initial cooling of the cryogenic device 10, the refrigeration capacity of the first cooling stage 25a can be used to assist the second cooling stage 25b in cooling the superconducting coil 12 via the thermal switch 100 in the ON state. This allows the time required for the initial cooling to be shortened. Furthermore, since the thermal switch 100 is switched OFF upon completion of the initial cooling, the first cooling stage 25a can maintain the first heat transfer stage 204 and the radiation shield 40 at the first cooling temperature, and the second cooling stage 25b can cool the second heat transfer stage 206 and the superconducting coil 12 to the second cooling temperature.

[0112] Furthermore, in this embodiment, the thermal switch 100 is incorporated into the support structure 201. Regardless of whether the thermal switch 100 is present or not, the amount of heat that leaks from the vacuum vessel 30 to the superconducting coil 12 through the support structure 201 remains the same. Therefore, there is an advantage in that the addition of the thermal switch 100 does not increase the amount of heat that leaks.

[0113] The present invention has been described above based on examples. It will be understood by those skilled in the art that the present invention is not limited to the above-described embodiments, and that various design changes and modifications are possible, and that such modifications are also within the scope of the present invention. Various features described in relation to one embodiment can also be applied to other embodiments. A new embodiment created by combining embodiments will have the combined effects of the respective combined embodiments.

[0114] In the above embodiment, an example has been described in which one thermal switch 100 is installed in the cryogenic device 10, but the present invention is not limited to this. For example, the cryogenic device 10 may include multiple thermal switches 100, and each of these thermal switches 100 may connect a portion of a first cooling temperature, such as the radiation shield 40, to a portion of a second cooling temperature, such as the superconducting coil 12. Furthermore, the cryogenic refrigerator 20 may include multiple thermal switches 100, and each of these thermal switches 100 may connect the first cooling stage 25a to the second cooling stage 25b.

[0115] In the above embodiment, the cryocooler 20 is a multi-stage Gifford-McMahon refrigerator, but the present invention is not limited to this. The cryocooler 20 may be a pulse tube refrigerator, a Stirling refrigerator, or any other type of multi-stage cryocooler.

[0116] In the above embodiment, the cryogenic device 10 is described as a conduction cooling type in which the object to be cooled is directly cooled by the cryogenic refrigerator 20, but the present invention is not limited to this. The cryogenic device 10 may also be an immersion cooling type in which the object to be cooled is immersed in a cryogenic refrigerant such as liquid helium to cool it.

[0117] The present invention has been described using specific terms based on the embodiments, but the embodiments merely illustrate one aspect of the principles and applications of the present invention, and many modifications and changes in arrangement are permitted to the embodiments as long as they do not deviate from the concept of the present invention as defined in the claims.

[0118] The present invention can be used in the field of cryogenic devices.

[0119] 10 Cryogenic device, 20 Cryogenic refrigerator, 25a First cooling stage, 25b Second cooling stage, 30 Vacuum vessel, 71 First heat transfer surface, 72 Second heat transfer surface, 100 Thermal switch, 110 High temperature side heat transfer element, 120 Low temperature side heat transfer element, 130 Gas gap, 140 Connecting tube, 150 Getter material.

Claims

1. A cryogenic device comprising: a cryogenic refrigerator having a first cooling stage and a second cooling stage arranged along a central axis of the cryogenic refrigerator, the second cooling stage being cooled to a lower temperature than the first cooling stage; and a thermal switch that thermally connects the first cooling stage to the second cooling stage or disconnects the thermal connection between the first cooling stage and the second cooling stage, the thermal switch extending along a direction non-parallel to the central axis of the cryogenic refrigerator.

2. The cryogenic device according to claim 1, wherein the thermal switch extends along a direction perpendicular to a central axis of the cryogenic refrigerator.

3. The cryogenic device according to claim 1, wherein the direction non-parallel to the central axis of the cryogenic refrigerator is a direction different from the direction of gravity acting on the cryogenic device.

4. The cryogenic device of claim 1, wherein the length of the thermal switch in the direction non-parallel to the central axis of the cryogenic refrigerator is longer than the distance between the first cooling stage and the second cooling stage along the central axis of the cryogenic refrigerator.

5. The cryogenic device according to claim 1, characterized in that the thermal switch comprises: a first heat transfer element thermally coupled to the first cooling stage; and a second heat transfer element thermally coupled to the second cooling stage and arranged opposite the first heat transfer element across a gas gap; and a connecting tube extending from the first heat transfer element to the second heat transfer element along the direction non-parallel to the central axis of the cryogenic refrigerator so as to isolate the gas gap from the ambient environment of the thermal switch.

6. The cryogenic device according to claim 5, characterized in that the first heat transfer element has a first heat transfer surface facing the gas gap and extending along the direction non-parallel to the central axis of the cryogenic refrigerator, and the second heat transfer element has a second heat transfer surface facing the gas gap and extending along the direction non-parallel to the central axis of the cryogenic refrigerator.

7. The cryogenic device according to claim 6, wherein the distance between said first heat transfer surface and said second heat transfer surface in said gas gap is within 1 mm.

8. The cryogenic device of claim 5, wherein said thermal switch further comprises a getter material thermally coupled to said second heat transfer element and capable of adsorbing gas from said gas gap.

9. The cryogenic device according to any one of claims 1 to 8, further comprising a rotatable vacuum vessel in which the cryogenic refrigerator is installed and which houses the thermal switch together with the first and second cooling stages.

10. A cryogenic device comprising: a cryogenic refrigerator having a first cooling stage and a second cooling stage, the second cooling stage being cooled to a lower temperature than the first cooling stage; and a thermal switch that thermally connects the first cooling stage to the second cooling stage or disconnects the thermal connection between the first cooling stage and the second cooling stage, the thermal switch extending along a direction different from the direction of gravity acting on the cryogenic device.

11. A cryogenic device comprising: a cryogenic refrigerator having a first cooling stage and a second cooling stage, the second cooling stage being cooled to a lower temperature than the first cooling stage; a thermal switch which thermally connects the first cooling stage to the second cooling stage or disconnects the thermal connection between the first cooling stage and the second cooling stage; and a rotatable vacuum container in which the cryogenic refrigerator is installed and which houses the thermal switch together with the first cooling stage and the second cooling stage.

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