Cryogenic device

Abstract

To shorten time required for initial cooling in a cryogenic device.SOLUTION: A cryogenic device 10 comprises: a cryogenic freezer 20 comprising a first cooling stage 25a and a second cooling stage 25b arranged along a central axis C1 of the cryogenic freezer 20, the second cooling stage 25b being cooled to a lower temperature than the first cooling stage 25a; and a thermal switch 100 that thermally connects the first cooling stage 25a and the second cooling stage 25b or disconnects the thermal connection between the first cooling stage 25a and the second cooling stage 25b, the thermal switch 100 extending along a direction non-parallel to the central axis C1 of the cryogenic freezer 20.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to cryogenic apparatuses.

Background Art

[0002] For example, in a cryogenic apparatus that operates at cryogenic temperatures such as a superconducting magnet apparatus, initial cooling is performed to cool from an initial temperature such as room temperature to a target cooling temperature when starting up the apparatus.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The use of a cryogenic apparatus, such as providing a high magnetic field by a superconducting magnet, becomes possible after completion of the initial cooling. Therefore, it is desirable that the required time for the initial cooling be as short as possible.

[0005] One exemplary object of an aspect of the present invention is to shorten the time required for initial cooling in a cryogenic apparatus.

Means for Solving the Problems

[0006] According to an aspect of the present invention, a cryogenic apparatus includes a cryogenic refrigerator including 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 and 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 an aspect of the present invention, a cryogenic device includes 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 and 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 an aspect of the present invention, a cryogenic device includes 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 that thermally connects the first cooling stage and 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 that houses the thermal switch together with the first cooling stage and the second cooling stage.

Advantages of the Invention

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

Brief Description of the Drawings

[0010]

Figure 1

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Figure 10

Figure 11

Embodiments for Carrying Out the Invention

[0011] Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings. In the description and the drawings, the same or equivalent components, members, and processes are denoted by the same reference numerals, and redundant descriptions will be omitted as appropriate. The scales and shapes of the respective parts shown are set for convenience in order to facilitate the description, and are not to be construed in a limited manner unless otherwise specified. The embodiments are 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] FIG. 1 is a diagram schematically showing 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 cryogenic temperature, and to maintain the superconducting coil 12 at cryogenic temperature during use of the superconducting coil 12.

[0013] The superconducting coil 12 is mounted on a high magnetic field utilization device as a magnetic field source of, 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 fusion system, or other high magnetic field utilization devices (not shown), and can generate a high magnetic field required for the device. The superconducting coil 12 is configured to generate a strong magnetic field by energizing the superconducting coil 12 in a state cooled to cryogenic 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. The cryogenic refrigerator 20 includes a compressor 21 and a two-stage cold head 22.

[0016] The compressor 21 is configured to recover the refrigerant gas of the cryogenic refrigerator 20 from the cold head 22, boost the recovered refrigerant gas in pressure, and supply the refrigerant gas to the cold head 22 again. The cold head 22, also referred to as an expander, can generate cold by adiabatically expanding 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 an appropriate combination of pressure fluctuations and volume fluctuations of the refrigerant gas in the cold head 22, thereby constituting a refrigeration cycle (e.g., a GM cycle) of the cryogenic refrigerator 20, whereby each cooling stage of the cold head 22 is cooled to a desired cryogenic temperature. The refrigerant gas, also referred to as a working gas, is usually 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 coaxially arranged along the 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 formed of a high thermal conductivity metal such as copper (e.g., pure copper) or other thermal conductive materials. The first cylinder 24a and the second cylinder 24b are formed of a metal such as stainless steel. Generally, the thermal conductivity of the thermal conductive material forming the cooling stage is higher than the thermal conductivity of the material forming the cylinder.

[0019] Further, the cold head 22 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 reciprocates a first displacer and a second displacer housed in the first cylinder 24a and the second cylinder 24b, respectively, in the axial direction. The cold head drive unit 26 also houses a pressure switching valve that is driven in synchronization with the displacer by this motor. The pressure switching valve is configured to periodically switch between receiving high-pressure refrigerant gas into the cold head 22 and discharging low-pressure refrigerant gas.

[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, and the cold head 22 is inserted into the vacuum vessel 30 through the opening. The cold head flange 23 is attached to the vacuum vessel 30 at this opening, and the cold head 22 is fixed to the vacuum vessel 30. The first cylinder 24a, the first cooling stage 25a, the second cylinder 24b, and the second cooling stage 25b of the cold head 22 are arranged inside the vacuum vessel 30. The cold head 22 is installed vertically in the vacuum vessel 30 with the cold head drive unit 26 facing upward and the first cooling stage 25a and the second cooling stage 25b facing downward.

[0021] Therefore, the cold head 22 is installed in the vacuum vessel 30 with its central axis C1 aligned with the direction of gravity acting on the cryogenic apparatus 10 (the vertical direction in FIG. 1). Such an arrangement of the cryogenic refrigerator 20 is typical, but other mounting postures are also possible. The cryogenic refrigerator 20 may be installed in the vacuum vessel 30 with its central axis C1 in the horizontal direction or in other directions.

[0022] By operating the cryogenic refrigerator 20, the first cooling stage 25a and the second cooling stage 25b are each cooled to a desired cryogenic temperature. 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 lower than the superconducting transition temperature of the superconducting coil 12.

[0023] In FIG. 1, one cryogenic refrigerator 20 is shown as an example. However, for example, when the superconducting coil 12 is large, the cryogenic apparatus 10 may include a plurality of cryogenic refrigerators 20 that cool one and the same object to be cooled, if necessary.

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

[0025] The cryogenic apparatus 10 is configured as a conduction cooling type that directly cools the object to be cooled (for example, the radiation shield 40, the superconducting coil 12) with the cryogenic refrigerator 20. The cryogenic refrigerator 20 is thermally coupled to the object to be cooled so as to cool the object to be cooled by conduction cooling.

[0026] The radiation shield 40 is thermally coupled to the first cooling stage 25a and is cooled to the first cooling temperature. The radiation shield 40 is directly attached to the first cooling stage 25a and is thermally coupled to the first cooling stage 25a. Alternatively, the radiation shield 40 may be attached to the first cooling stage 25a via a heat transfer member having flexibility or rigidity. The radiation shield 40 is disposed so as to surround the superconducting coil 12 cooled to the second cooling temperature, the second cooling stage 25b of the cryogenic refrigerator 20, and other cryogenic parts, and can thermally protect these cryogenic parts from external radiant heat. The radiation shield 40 is formed of a metal material such as copper or other material having a 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 other material having a high thermal conductivity, and connects the superconducting coil 12 to the second cooling stage 25b. The heat transfer member 50 may have flexibility and connect these so as to allow relative displacement between the superconducting coil 12 and the second cooling stage 25b, or 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 other material having a high thermal conductivity.

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

[0029] The heat switch 100 is configured to thermally connect the first cooling stage 25a and the second cooling stage 25b, or to disconnect the thermal connection between the first cooling stage 25a and the second cooling stage 25b. In other words, the heat switch 100 is configured to thermally connect or disconnect the thermal connection between the part at the first cooling temperature (for example, the radiation shield 40) and the part at the second cooling temperature (for example, the superconducting coil 12) in the cryogenic device 10.

[0030] In this embodiment, the thermal switch 100 extends along a direction non-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. Since the central axis C1 of the cryogenic refrigerator 20 is parallel to the direction of the gravity acting on the cryogenic device 10 as described above, the central axis C2 of the thermal switch 100 extends along a direction different from the direction of the gravity acting on the cryogenic device 10.

[0031] As an example, as shown in the drawing, 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 gravity direction, 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 that are disposed opposite to each other with the gas gap 130 interposed therebetween. The high-temperature-side heat transfer element 110 has a first heat transfer surface 71 that faces the gas gap 130 and extends 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 that faces the gas gap 130 and extends 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 an arbitrary part cooled to the first cooling temperature, and the low-temperature-side heat transfer element 120 is attached to an arbitrary part cooled to the second cooling temperature. As shown in the figure, the high-temperature-side heat transfer element 110 may be attached to the first member 61, and the low-temperature-side heat transfer element 120 may be attached to the second member 62. The first member 61 is attached to the radiation shield 40 and is thermally coupled to the first cooling stage 25a. The second member 62 is attached to the heat transfer member 50 and is thermally coupled to the second cooling stage 25b. The first member 61 and the second member 62 are formed of a metal material such as copper or other material having a high thermal conductivity, similar to the radiation shield 40 and the heat transfer member 50. 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 heat switch 100 may directly connect the superconducting coil 12 and the radiation shield 40.

[0034] The heat switch 100 includes a connection cylinder 140 that extends 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 surrounding environment of the heat switch 100 (i.e., the vacuum region 32). The connection cylinder 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 heat switch 100. The heat switch 100 constitutes an airtight container that encloses the working gas in the gas gap 130 by the high-temperature-side heat transfer element 110, the low-temperature-side heat transfer element 120, and the connection cylinder 140.

[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 heat switch 100 can thermally connect the high-temperature side and the low-temperature side by heat transfer between the heat transfer elements through the working gas in the gas gap 130. This is the on state of the heat switch 100. The switching temperature of the heat switch 100 corresponds to the boiling point of the enclosed working gas.

[0036] 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) of the thermal switch 100 is lower than the switching temperature, the thermal connection between the high-temperature side and the low-temperature side is released. This is because the working gas in the gas gap 130 condenses at least on the surface of the low-temperature side heat transfer element 120, the gas gap 130 becomes a vacuum, and the high-temperature side heat transfer element 110 and the low-temperature side heat transfer element 120 are thermally insulated from each other through the gas gap 130. This is the off state of the thermal switch 100.

[0037] An exemplary configuration of the thermal switch 100 that can be mounted on the cryogenic device 10 will be described in more detail with reference to FIGS. 2 to 8.

[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 the first cooling temperature, and the second cooling stage 25b is cooled to the 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 energizing the superconducting coil 12 from a power source (not shown), the superconducting coil 12 can generate a strong magnetic field. In this way, the cryogenic device 10 can be operated.

[0039] Connecting a part at a first cooling temperature, such as the radiation shield 40, and a part at a second cooling temperature, such as the superconducting coil 12, with the thermal switch 100 is advantageous for the initial cooling at the start-up of the cryogenic apparatus 10. In the initial cooling, the cryogenic refrigerator 20 is cooled from the ambient temperature (e.g., room temperature) to the target cryogenic temperature. Therefore, at the beginning of the initial cooling, the thermal switch 100 is turned on, and the radiation shield 40 and the superconducting coil 12 are thermally connected. Generally, the refrigeration capacity at the first cooling stage 25a of the cryogenic refrigerator 20 is larger than the refrigeration capacity at the second cooling stage 25b. Typically, the refrigeration capacity of the first stage of the cryogenic refrigerator 20 can reach several tens of times the refrigeration capacity of the second stage of the cryogenic refrigerator 20. Through the thermal switch 100, the refrigeration capacity of the first cooling stage 25a can be utilized to assist in the cooling of the superconducting coil 12 by the second cooling stage 25b. Thereby, the required time for the initial cooling can be shortened.

[0040] After that, as the cooling progresses and the superconducting coil 12 is cooled to a temperature lower than the switching temperature of the thermal switch 100, the thermal switch 100 switches to the off state, 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 finally cooled to the second cooling temperature.

[0041] By the way, existing gas-gap type thermal switches are based on the design concept of realizing heat transfer in the on state depending on the natural convection of the internal gas. Natural convection is caused by the temperature difference and gravity. The temperature difference is an environmental factor determined according to the application where the thermal switch is installed. Therefore, in order to effectively utilize gravity for the generation of natural convection, it is necessary to install the existing thermal switch along the direction of the gravity acting on the thermal switch, that is, the vertical direction.

[0042] Such an arrangement of the thermal switch is illustrated in FIG. 10. As described above, since cryogenic refrigerators are also typically installed along the direction of gravity, existing thermal switches are often installed in parallel with this refrigerator between the first and second stages of the cryogenic refrigerator.

[0043]

[0044]

[0045]

[0046] The heat switch 100 according to the embodiment does not require natural convection of gas for heat transfer, so it is not subject to the above-described installation posture constraints. Therefore, unlike existing heat switches, the heat switch 100 is allowed to be installed with its central axis C2 in a direction different from the direction of gravity acting on the cryogenic apparatus 10. When the cryogenic refrigerator 20 is installed in the cryogenic apparatus 10 along the direction of gravity, the heat switch 100 is allowed to be installed with its central axis C2 in a direction non-parallel to the central axis C1 of the cryogenic refrigerator 20. The heat switch 100 can provide heat transfer performance as designed regardless of the installation posture. The inventor has confirmed by experiments that, as illustrated in FIG. 1, when the heat switch 100 is installed with its central axis C2 in the horizontal direction, the initial cooling time of the cryogenic apparatus 10 can be shortened due to the effect of the heat switch 100.

[0047] In existing heat switches, a relatively wide gas gap, such as 10 mm or more, is set to promote natural convection. In contrast, the heat switch 100 according to the embodiment utilizes the heat conduction of the gas present in the gas gap 130 and does not need to utilize natural convection. Therefore, the gas gap 130 may be narrower than existing heat 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, within 1 mm, and more preferably within 0.5 mm. In this way, natural convection in the gas gap 130 can be rather suppressed, which is expected to lead to the stabilization of the performance of the heat switch 100.

[0048] The length L2 of the thermal switch 100 in the direction of 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 posture 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 made longer than the axial distance L1 between the two cooling stages of the cryogenic refrigerator 20. By making the thermal switch 100 longer in this way, the areas of the first heat transfer surface 71 and the second heat transfer surface 72 inside the thermal switch can be increased. Efficient heat transfer between the first heat transfer surface 71 and the second heat transfer surface 72 through the gas gap 130 in the on state of the thermal switch 100 becomes possible, and the heat transfer performance of the thermal switch 100 is improved.

[0049] Moreover, the longer the thermal switch 100 is, the smaller the heat 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 connection cylinder 140, can be. The heat insulation performance of the thermal switch 100 in the off state is also improved.

[0050] FIG. 2 is a schematic cross-sectional view showing more details of the 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 a high-temperature-side heat transfer element 110 and a low-temperature-side heat transfer element 120 disposed opposite to the high-temperature-side heat transfer element 110 with the gas gap 130 interposed 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 portion 111 and a column portion 112 extending from the first base portion 111. The first base portion 111 is thermally coupled to a first member 61 (for example, 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 portion 111 may have, for example, a generally disc-shaped configuration, and its circular end face is brought into contact with the surface of the first member 61 and fixed to the first member 61. The column portion 112 is disposed inside the thermal switch 100. The column portion 112 has, for example, a cylindrical shape. The column portion 112 extends coaxially with the first base portion 111 along the central axis of the thermal switch 100 from the first base portion 111 on the side opposite to the first member 61. The column portion 112 may be integrally formed with the first base portion 111, or may be provided 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 portion 121 and a cylindrical portion 122 extending from the second base portion 121. The second base portion 121 is thermally coupled to a second member 62 (for example, 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 portion 121 may have, for example, a generally disc-shaped configuration, and its circular end face is brought into contact with the surface of the second member 62 and fixed to the second member 62. The cylindrical portion 122 has, for example, a cylindrical shape. The cylindrical portion 122 extends coaxially with the second base portion 121 along the central axis of the thermal switch 100 from the second base portion 121 on the side opposite to the second member 62. The cylindrical portion 122 may be integrally formed with the second base portion 121, or may be provided separately from the second base portion 121 and joined to the second base portion 121.

[0053] The low-temperature side heat transfer element 120 is configured to receive the high-temperature side heat transfer element 110 inside thereof. The column portion 112 of the high-temperature side heat transfer element 110 is inserted into the cavity within 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 column 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 column portion 112 of the high-temperature side heat transfer element 110. The column portion 112 of the high-temperature side heat transfer element 110, the second base portion 121 of the low-temperature side heat transfer element 120, and the cylindrical portion 122 are separated by a gas gap 130 and are not in physical contact. The cylindrical portion 122 of the low-temperature side heat transfer element 120 is disposed close to the first base portion 111 of the high-temperature side heat transfer element 110 on the side opposite to the second base portion 121.

[0054] Thus, when the high-temperature side heat transfer element 110 has the column 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. The fact that the low-temperature side heat transfer element 120 has a relatively small volume can lead to a reduction in the heat load on the second cooling stage 25b of the cryogenic refrigerator 20, and thus can be advantageous (for example, compared to the example of FIG. 3).

[0055] Further, the heat switch 100 includes a connection cylinder 140 that forms an airtight container for enclosing the working gas of the heat switch 100 together with the high-temperature side heat transfer element 110 and the low-temperature side heat transfer element 120. The connection 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 cylindrical portion 122 to the first base portion 111 so as to isolate the gas gap 130 from the ambient environment (for example, the vacuum region 32 shown in FIG. 1). The connection cylinder 140 has, for example, a cylindrical shape and extends coaxially with the first base portion 111 and the cylindrical portion 122 along the central axis of the heat switch 100. The connection 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, adhesion, or other suitable joining methods.

[0056] The axial length of the connection cylinder 140 may be considerably shorter than the total axial length of the thermal switch 100. For example, it may be less than half or 1 / 3 or less of the total axial length of the thermal switch 100. As an example, the connection cylinder 140 may have a ring shape (e.g., an annular shape) whose axial length is shorter than the diameter rather than a cylinder shape.

[0057] In a design of an existing thermal switch, a cylindrical member serving as the outer shell of the thermal switch extends over substantially the entire axial length of the thermal switch, and two spaced-apart heat transfer bodies are connected by this cylindrical member. Therefore, in such an existing thermal switch, a radial gap is formed between the cylindrical member and the heat transfer body inside it (e.g., like the radial gap 162 shown in FIG. 5). Due to this radial gap, the diameter of the heat transfer body becomes smaller than the diameter of the cylindrical member, and as a result, the surface area of the heat transfer body also becomes smaller according to the diameter, which may lead to a decrease in the heat transfer performance of the thermal switch.

[0058] In contrast, in this embodiment, the connection cylinder 140 is axially connected in series with the cylindrical portion 122 of the low-temperature side heat transfer element 120. There is no radial gap between the connection cylinder 140 and the cylindrical portion 122. The diameter of the cylindrical portion 122 is equal to the diameter of the thermal switch 100, and the surface area of the cylindrical portion 122 can be made relatively large. This can result in an improvement in the heat transfer performance of the thermal switch 100 compared to the existing design.

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

[0060] The connection cylinder 140 is formed of a material having a lower thermal conductivity than the high-temperature-side heat transfer element 110 and the low-temperature-side heat transfer element 120, for example, a heat insulating material. Here, the heat insulating material may be a material having a thermal conductivity of, for example, 1 / 10 or less of the thermal conductivity of the high-thermal conductivity material forming the high-temperature-side heat transfer element 110 (or the low-temperature-side heat transfer element 120). The connection cylinder 140 may be formed of, for example, stainless steel, or glass fiber reinforced plastic (GFRP) or other plastic materials. Thereby, when the heat switch 100 is off, heat intrusion from the high-temperature-side heat transfer element 110 to the low-temperature-side heat transfer element 120 through the connection cylinder 140 can be prevented or minimized.

[0061] Compared with the high-thermal conductivity material forming the heat transfer element, the material forming the connection cylinder 140 is usually of high strength. Therefore, the wall thickness of the connection cylinder 140 may be thinner than the wall thickness of the cylindrical portion 122 of the heat transfer element as shown in the figure. Making the connection cylinder 140 thin in this way helps to suppress heat intrusion from the high-temperature-side heat transfer element 110 to the low-temperature-side heat transfer element 120 through the connection cylinder 140.

[0062] The working gas enclosed in the heat switch 100 is selected such that the switching temperature of the heat switch 100 is lower than the first cooling temperature of the cryogenic refrigerator 20 and higher than the second cooling temperature. As described above, the switching temperature of the heat switch 100 corresponds to the boiling point of the enclosed working gas. Therefore, the working gas enclosed in the heat switch 100 may be, for example, neon (about 27.1K). Alternatively, the working gas may be hydrogen (about 20.4K) or helium (about 4.2K). Here, the values in parentheses for each gas species are the boiling points of the respective gas species at atmospheric pressure. For example, when neon is enclosed in the heat switch 100 as the working gas at atmospheric pressure, the switching temperature of the heat switch 100 can be set to about 27.1K. The working gas may be enclosed in the heat switch 100 at a pressure higher than atmospheric pressure (for example, within 5 atmospheres, or within 10 atmospheres). The switching temperature of the heat switch 100 may be adjusted by adjusting the enclosure pressure of the working gas.

[0063] The working gas may be a mixed gas, for example, a mixed gas containing at least one of neon, hydrogen, and helium. This mixed gas may contain a dilution gas such as nitrogen, argon, or air, for example. By adjusting the composition of the mixed gas, the switching temperature of the thermal switch 100 may be adjusted.

[0064] Optionally, the thermal switch 100 may be thermally coupled to the low-temperature side heat transfer element 120 and include a getter material 150 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 adsorption material having the ability to adsorb the working gas of the thermal switch 100 at an extremely low temperature (i.e., a temperature equal to or lower than the switching temperature of the thermal switch 100, for example, the second cooling temperature). The getter material 150 is installed on the surface of the low-temperature side heat transfer element 120 by an appropriate method so as to be cooled by the low-temperature side heat transfer element 120.

[0065] Ideally, when the thermal switch 100 is cooled to a temperature lower than its switching temperature, as described above, the working gas condenses within the thermal switch 100, the gas gap 130 becomes a vacuum, and the thermal switch 100 turns off. However, in practice, 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, the heat intrusion from the high-temperature side heat transfer element 110 to the low-temperature side heat transfer element 120 through the thermal switch 100 that should be off may become non-negligible.

[0066] On the other hand, by providing the getter material 150 in the thermal switch 100, the residual gas can be adsorbed, and the vacuum degree of the gas gap 130 can be further increased. Therefore, the disconnection of the thermal connection in the off state of the thermal switch 100 can be realized more reliably.

[0067] The getter material 150 is disposed facing the gas gap 130 on the low-temperature side heat transfer element 120. As a result, the getter material 150 is exposed to the residual gas that may be present in the gas gap 130, and can efficiently adsorb the residual gas. Further, 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 rapidly decreased. Thereby, the heat switch 100 can be quickly switched off, and a heat switch 100 with excellent responsiveness can be provided.

[0068] In the illustrated example, the getter material 150 is provided on the surface of the second base portion 121 of the low-temperature side heat transfer element 120 facing the column portion 112 of the high-temperature side heat transfer element 110. Instead of this, or together with this, the getter material 150 can be otherwise arranged on the low-temperature side heat transfer element 120. For example, the getter material 150 may be installed on the inner surface of the cylindrical portion 122 facing the circumferential surface of the column portion 112.

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

[0070] In the exemplary heat switch 100 described with reference to FIG. 2, 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. However, as an alternative, in any of the embodiments described in this document, as described later with reference to FIG. 3, the high-temperature side heat transfer element 110 may have a concave shape and the low-temperature side heat transfer element 120 may have a corresponding convex shape.

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

[0072] As shown in FIG. 3, the low-temperature-side heat transfer element 120 may include a first base portion 123 and a column portion 124 extending from the first base portion 123. The high-temperature-side heat transfer element 110 may include a second base portion 113 facing the column portion 124 and a cylindrical portion 114 extending from the second base portion 113 so as to surround the column portion 124. The cylindrical portion 114 is connected to the first base portion 123 by a connection cylinder 140. Even in this way, a one-gap type heat switch can be provided.

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

[0074] FIGS. 4(a) and 4(b) are schematic views showing a heat switch 100 according to a modified example. The heat switch 100 includes a high-temperature-side heat transfer element 110 and a low-temperature-side heat transfer element 120 disposed opposite to the high-temperature-side heat transfer element 110 with a gas gap 130 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 for receiving 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 connection cylinder 140. The heat switch 100 is a one-gap type heat switch.

[0075] As shown in FIG. 4(a), the heat switch 100 includes a getter chamber 152 having a getter material 150 therein. The getter chamber 152 is housed inside the low-temperature-side heat transfer element 120, for example, inside the second base portion 121 of the low-temperature-side heat transfer element 120. The second base portion 121 has a recess in the end face facing the outside of the heat switch 100 on the side opposite to the high-temperature-side heat transfer element 110, and the getter chamber 152 is disposed in this recess. When the low-temperature-side heat transfer element 120 is attached to the second member 62, the getter chamber 152 does not interfere with the second member 62, which is advantageous.

[0076] The getter chamber 152 is connected to the gas gap 130 through an internal passage 154 within 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. Thus, the 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] As shown in FIG. 4(b), 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. Since the getter chamber 152 is 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 can avoid interference with these members.

[0078] The getter chamber 152 is a container that houses 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 materials having high thermal conductivity. As an 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. The 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 to the gas gap 130. In order to efficiently heat the getter material 150 by the temperature regulator 158, the getter chamber 152 and the external passage 156 may be formed of a metal material having a relatively low thermal conductivity, such as stainless steel. Also, by stopping the temperature regulator 158 and cooling the getter material 150 by the low-temperature side heat transfer element 120, the working gas can be adsorbed to the getter material 150 again. In this way, the on / off of the heat switch 100 can be switched independently of the cooling operation of the cryogenic refrigerator 20.

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

[0081] The heat switch 100 incorporating the getter material 150 according to the embodiments of FIGS. 2 and 4(a) can have larger diameters of the high-temperature side heat transfer element 110 and the low-temperature side heat transfer element 120 than the heat 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 accommodate the heat switch 100 in the installable area 160, the diameters of the high-temperature side heat transfer element 110 and the low-temperature side heat transfer element 120 have to 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 heat switch 100 increase or decrease according to the diameter. Therefore, the heat switch 100 incorporating the getter material 150 has the advantage that it can relatively widely secure the area of the heat transfer element that can be ensured in the high-temperature side heat transfer element 110 with respect to the size (volume) of a certain determined installable area 160.

[0082] FIG. 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 that is disposed opposite to the high-temperature-side heat transfer element 110 with a gas gap 130 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 connection cylinder 140. The thermal switch 100 is a one-gap type thermal switch.

[0083] In the thermal switch 100 shown in FIG. 5, the connection cylinder 140 is relatively long and extends over substantially the entire axial length of the thermal switch. The connection cylinder 140 connects a first base portion 111 of the high-temperature-side heat transfer element 110 to a second base portion 121 of the low-temperature-side heat transfer element 120. A cylindrical portion 122 of the low-temperature-side heat transfer element 120 is disposed radially inward of the connection cylinder 140, and a radial gap 162 is formed between the connection cylinder 140 and the cylindrical portion 122. A column portion 112 of the high-temperature-side heat transfer element 110 is inserted into the cylindrical portion 122 of the low-temperature-side heat transfer element 120, and a gas gap 130 is formed between the column portion 112 and the cylindrical 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 facing 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, at a tip portion 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 disposed opposite to the high-temperature-side heat transfer element 110 with a gas gap 130 therebetween. The thermal switch 100 shown in FIG. 6 is a multi-gap type thermal switch having a plurality of gas gaps 130. The multi-gap type thermal switch is advantageous in that it is easier to increase the heat transfer area compared to a one-gap type thermal switch.

[0086] The high-temperature-side heat transfer element 110 includes a first base portion 111 and a column portion 112 extending from the first base portion 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 portion 121 and a cylindrical portion 122 extending from the second base portion 121. However, unlike the embodiment shown in FIG. 2, a shaft portion 126 extending coaxially from the second base portion 121 is formed inside the cylindrical portion 122. The connection cylinder 140 connects the cylindrical portion 122 to the first base portion 111.

[0087] The low-temperature-side heat transfer element 120 is configured to receive the high-temperature-side heat transfer element 110 inside thereof. The column portion 112 of the high-temperature-side heat transfer element 110 is inserted into a cavity inside 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 way, 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 physically in contact.

[0088] Similar to the above-described embodiments, the thermal switch 100 may be thermally coupled to the low-temperature-side heat transfer element 120 and include a getter material 150 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, it may be provided on the surface of the shaft portion 126 of the low-temperature-side heat transfer element 120 facing the first base portion 111 of the high-temperature-side heat transfer element 110. Alternatively, or in addition to this, the getter material 150 may be provided on the surface of the second base portion 121 of the low-temperature-side heat transfer element 120 facing 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 other surfaces of the low-temperature-side heat transfer element 120.

[0089] In the embodiment of FIG. 6, the column portion 112 of the high-temperature-side heat transfer element 110 can also be regarded as a cylindrical heat transfer fin. Therefore, 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. Further, the high-temperature-side heat transfer element 110 may have a plurality of coaxially provided cylindrical fins. The low-temperature-side heat transfer element 120 may have at least one cylindrical fin provided alternately with the plurality of cylindrical fins of the high-temperature-side heat transfer element 110. In this way, a multi-gap type thermal switch having more gas gaps 130 may be configured.

[0090] Alternatively, the high-temperature-side heat transfer element 110 may include at least one heat transfer fin in a flat plate shape or other shape extending toward the low-temperature-side heat transfer element 120, and the low-temperature-side heat transfer element 120 may include at least one heat transfer fin extending toward the high-temperature-side heat transfer element 110. At least one heat transfer fin of the high-temperature-side heat transfer element 110 and at least one heat transfer fin of the low-temperature-side heat transfer element 120 may be alternately arranged so as to form a plurality of gas gaps 130 in the thermal switch 100.

[0091] FIG. 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 disposed opposite to the high-temperature-side heat transfer element 110 with a gas gap 130 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 for receiving 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 cylinder 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 covers its outer peripheral surface. The coating material 170 covers the cylindrical portion 122 of the low-temperature-side heat transfer element 120 and the outer peripheral surface of the connecting cylinder 140. Due to thermal contraction associated with cryogenic cooling, relative displacement may occur between the first member 61 and the second member 62, and as a result, there is a concern that a load (e.g., a lateral load) may act on the thermal switch 100. The coating material 170 can help reinforce the thermal switch 100 against such loads. In order to reduce heat intrusion 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 formed of a heat insulating material.

[0093] FIG. 8 is a schematic diagram showing a thermal switch device 200 according to an embodiment. The thermal switch device 200 includes a plurality of thermally switches (in this example, two thermal switches 100a and 100b) 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 disposed opposite to the high-temperature-side heat transfer element 110 with a gas gap 130 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 for receiving 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 cylinder 140.

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

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

[0096] Alternatively, the low-temperature-side heat transfer element 120 of the high-temperature-side heat switch 100a and the high-temperature-side heat transfer element 110 of the low-temperature-side heat switch 100b may be thermally coupled to each other. In other words, each of the plurality of heat switches may be the heat switch 100 according to any of the above-described embodiments, and such heat switches 100 may be simply stacked axially. The low-temperature-side heat transfer element 120 of each heat switch 100 is thermally coupled to the second member 62 together with the high-temperature-side heat transfer element 110 of the adjacent coupled heat switch 100.

[0097] When the heat switch device 200 has a plurality of heat switches connected in series, the thermal connection between the first member 61 and the second member 62 is disconnected by any one of the heat switches being turned off. Even if, for some reason (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.), one of the plurality of heat switches fails to switch off, the heat switch device 200 can disconnect the thermal connection between the first member 61 and the second member 62 by any other one of the heat switches switching off normally. Therefore, the heat switch device 200 is advantageous in that it is more robust against failures compared to a single heat switch 100.

[0098] Therefore, it is not necessary to provide a getter material 150 for each heat switch of the heat switch device 200. However, as in the above-described embodiments, a getter material 150 may be provided for each heat switch as indicated by the dashed line.

[0099] Consider the situation where the thermal switch device 200 is on. Comparing the case where a single thermal switch 100 is installed in an installable area of a certain size with the case where the thermal switch device 200 is installed, each thermal switch constituting the thermal switch device 200 is smaller in size than the single thermal switch 100, but the total heat transfer area is approximately the same. Therefore, it is expected that the heat transfer performance of the single thermal switch 100 and the thermal switch device 200 will be approximately equal. Also, the total axial length of the connection cylinders 140 of each thermal switch in the thermal switch device 200 is approximately equal to the axial length of the connection cylinder 140 of the single thermal switch 100. Therefore, it is expected that the heat insulation performance of the single thermal switch 100 and the thermal switch device 200 will be approximately equal.

[0100] FIG. 9 is a diagram schematically showing 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. Similar to 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 in cooling an object to be cooled such as a superconducting coil by the second cooling stage 25b. Thereby, the required time for initial cooling can be shortened.

[0101] FIG. 10 is a diagram schematically showing a cryogenic device 10 according to another 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, similar to the above-described embodiment. 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 is provided with a rotation mechanism 80 configured to rotate the vacuum vessel 30 around at least one axis and is rotatable with respect to the floor surface 82. The rotation axis 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 with respect to the floor surface 82. The direction 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, since an existing gas-gap type thermal switch utilizes natural convection of internal gas for heat transfer, it is required to be installed along the vertical direction. Therefore, the existing thermal switch is not suitable for a rotatable vacuum vessel 30 whose installation posture is not fixed. On the other hand, since the thermal switch 100 according to the embodiment can exhibit good heat transfer performance regardless of the installation posture, it can be mounted on the rotatable vacuum vessel 30.

[0104] FIG. 11 is a diagram schematically showing a cryogenic apparatus 10 according to another embodiment. The cryogenic apparatus 10 includes a cooled object such as a superconducting coil 12, a cryogenic refrigerator 20, a vacuum vessel 30, a radiation shield 40, and a thermal switch 100, similar to the above-described embodiment.

[0105] The thermal switch 100 may be disposed in the vacuum vessel 30 and applied to a support structure 201 that supports the cooled object in 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 support 202 is fixed to the vacuum vessel 30, extends through the radiation shield 40 along the vertical direction, and abuts against the object to be cooled such as the superconducting coil 12. The vertical support 202 can support a force acting vertically downward on the object to be cooled, such as the self-weight of the superconducting coil 12. The support such as the vertical support 202 is formed of a heat insulating material such as fiber reinforced plastic (FRP). Alternatively, the support may be formed of a material having a lower thermal conductivity than a high thermal conductivity material that forms a heat transfer path in the cryogenic apparatus 10, such as stainless steel.

[0107] The first heat transfer stage 204 and the second heat transfer stage 206 may be installed 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 25a of the cryogenic refrigerator 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 25b of the cryogenic refrigerator 20 via the superconducting coil 12. Therefore, the first heat transfer stage 204 is cooled to the first cooling temperature by the first cooling stage 25a, and the second heat transfer stage 206 is cooled to the second cooling temperature by the second cooling stage 25b.

[0108] The heat 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 the switching temperature of the heat switch 100, and to thermally disconnect the second heat transfer stage 206 from the first heat transfer stage 204 when the temperature of the second heat transfer stage 206 is below the switching temperature. The heat 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 to face each other with a gas gap 130 for heat exchange via the working gas of the heat switch 100 interposed therebetween. 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 enclosed in the thermal switch 100 is selected such that the switching temperature of the thermal switch 100 is lower than the first cooling temperature of the cryogenic refrigerator 20 and higher than the second cooling temperature. Optionally, the thermal switch 100 may be thermally coupled to the second heat transfer stage 206 and include a getter material capable of adsorbing gas from the hermetic space within the thermal switch 100.

[0110] Further, the support structure 201 may include a lateral support 210. The lateral support 210 is fixed to the vacuum vessel 30, extends through the radiation shield 40 along the horizontal direction, and abuts against the object to be cooled. The lateral support 210 can support a force acting on the object to be cooled in the horizontal direction, such as the electromagnetic force acting on the superconducting coil 12. Similar to the vertical support 202, the thermal switch 100 may be incorporated into the lateral support 210.

[0111] Also in this embodiment, during the initial cooling of the cryogenic apparatus 10, the refrigeration capacity of the first cooling stage 25a can be utilized via the on-state thermal switch 100 to assist in cooling the superconducting coil 12 by the second cooling stage 25b. Thereby, the required time for initial cooling can be shortened. Further, since the thermal switch 100 switches off with the completion of the initial cooling, the first heat transfer stage 204 and the radiation shield 40 can be maintained at the first cooling temperature by the first cooling stage 25a, and the second heat transfer stage 206 and the superconducting coil 12 can be cooled to the second cooling temperature by the second cooling stage 25b.

[0112] Also, in this embodiment, the thermal switch 100 is incorporated into the support structure 201. Regardless of the presence or absence of the thermal switch 100, the heat intrusion through the support structure 201 from the vacuum vessel 30 to the superconducting coil 12 remains unchanged. Therefore, it is advantageous in that there is no increase in heat intrusion due to the addition of the thermal switch 100.

[0113] As described above, the present invention has been explained based on examples. It is understood by those skilled in the art that the present invention is not limited to the above-described embodiments, that various design changes are possible, that various modifications are possible, and that such modifications are also within the scope of the present invention. The various features described in connection with one embodiment are also applicable to other embodiments. New embodiments resulting from combinations have the combined effects of the respective embodiments being combined.

[0114] In the above-described embodiment, the case where one thermal switch 100 is installed in the cryogenic apparatus 10 has been described as an example, but the present invention is not limited thereto. For example, the cryogenic apparatus 10 may include a plurality of thermal switches 100, and each of these thermal switches 100 may connect a part at a first cooling temperature such as the radiation shield 40 and a part at a second cooling temperature such as the superconducting coil 12. Further, the cryogenic refrigerator 20 may include a plurality of thermal switches 100, and each of these thermal switches 100 may connect the first cooling stage 25a and the second cooling stage 25b.

[0115] In the above-described embodiment, the case where the cryogenic refrigerator 20 is a multi-stage Gifford-McMahon refrigerator has been described as an example, but the present invention is not limited thereto. The cryogenic refrigerator 20 may be a pulse tube refrigerator, a Stirling refrigerator, or another type of multi-stage cryogenic refrigerator.

[0116] In the above-described embodiment, the case where the cryogenic apparatus 10 is a conduction cooling type in which the object to be cooled is directly cooled by the cryogenic refrigerator 20 has been described as an example, but the present invention is not limited thereto. The cryogenic apparatus 10 may be an immersion cooling type in which the object to be cooled is immersed in a cryogenic refrigerant such as liquid helium for cooling.

[0117] Based on the embodiments, the present invention has been described using specific terms, but the embodiments merely show one aspect of the principle and application of the present invention, and many modifications and arrangement changes are permitted within the scope of not departing from the idea of the present invention defined in the claims.

Explanation of Reference Numerals

[0118] 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 Connection cylinder, 150 Getter material.

Claims

1. A cryogenic refrigerator comprising a first cooling stage and a second cooling stage arranged along the 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 for thermally connecting the first cooling stage and the second cooling stage or disconnecting 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. The cryogenic device is characterized by comprising the above.

2. The cryogenic device according to claim 1, wherein the thermal switch extends along a direction perpendicular to the 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 according to 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 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 to the first heat transfer element with a gas gap therebetween. The cryogenic device is characterized by further comprising a connecting cylinder extending along the direction non-parallel to the central axis of the cryogenic refrigerator from the first heat transfer element to the second heat transfer element so as to isolate the gas gap from the surrounding environment of the thermal switch. The cryogenic device according to claim 1, wherein 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,

6. 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, and the distance between the first heat transfer surface and the second heat transfer surface in the gas gap is within 1 mm. The cryogenic device according to claim 5 is characterized by this.

7. The cryogenic device according to claim 5, wherein the thermal switch is further provided with a getter material thermally coupled to the second heat transfer element and capable of adsorbing gas from the gas gap.

8. ​ The cryogenic apparatus according to any one of claims 1 to 7, further comprising a rotatable vacuum vessel in which the cryogenic refrigerator is installed and which houses the heat switch together with the first cooling stage and the second cooling stage.

9. A cryogenic refrigerator comprising a first cooling stage and a second cooling stage, wherein the second cooling stage is cooled to a lower temperature than the first cooling stage, a heat switch that thermally connects the first cooling stage and the second cooling stage or disconnects the thermal connection between the first cooling stage and the second cooling stage, the heat switch extending along a direction different from the direction of gravity acting on the cryogenic apparatus.

10. A cryogenic refrigerator comprising a first cooling stage and a second cooling stage, wherein the second cooling stage is cooled to a lower temperature than the first cooling stage, a heat switch that thermally connects the first cooling stage and the second cooling stage or disconnects the thermal connection between the first cooling stage and the second cooling stage, a rotatable vacuum vessel in which the cryogenic refrigerator is installed and which houses the heat switch together with the first cooling stage and the second cooling stage.

Images