Thermal switches and cryogenic devices

Abstract

To improve the heat transfer efficiency of thermal switches. [Solution] The thermal switch 100 comprises a first heat transfer element 110 having a first heat transfer surface 111, a second heat transfer element 120 having a second heat transfer surface 121, and a connecting container 130 extending along the main axis 102 so as to surround the first heat transfer element 110 and the second heat transfer element 120. The connecting container 130 connects the first heat transfer element 110 and the second heat transfer element 120 such that the first heat transfer surface 111 and the second heat transfer surface 121 are in contact when the first heat transfer element 110 and the second heat transfer element 120 are at a first temperature. The total amount of thermal contraction of the first heat transfer element 110 and the second heat transfer element 120 along the main axis 102 due to cooling from the first temperature to the second temperature is greater than the amount of thermal contraction of the connecting container 130 along the main axis 102 due to cooling such that the first heat transfer surface 111 and the second heat transfer surface 121 are separated by the cooling. The first heat transfer surface 111 and the second heat transfer surface 121 are inclined with respect to the main shaft 102.

Description

Technical Field

[0001] The present invention relates to a thermal switch and a cryogenic device using the same.

Background Art

[0002] For example, in a cryogenic device that operates at cryogenic temperatures such as a superconducting magnet device, initial cooling is performed to cool from an initial temperature such as room temperature to a target cooling temperature when the device is started up. The use of a cryogenic device, such as providing a high magnetic field by a superconducting magnet, becomes possible after the completion of the initial cooling. Therefore, it is desirable that the required time for the initial cooling be as short as possible.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In a cryogenic device, for cryogenic cooling, a two-stage cryogenic refrigerator such as a Gifford-McMahon (GM) refrigerator is often used. The second stage of the cryogenic refrigerator that is cooled to a lower temperature cools the object to be cooled of the cryogenic device such as a superconducting coil, and the first stage of the cryogenic refrigerator that is cooled to a higher temperature cools the object to be cooled of the first stage such as a radiation shield for reducing the heat input to the object to be cooled of the second stage. Since the refrigeration capacity of the first stage is relatively large, the initial cooling of the object to be cooled of the first stage can be performed in a relatively short time. However, since the refrigeration capacity of the second stage is generally much smaller than that of the first stage, the initial cooling of the object to be cooled of the second stage often requires a longer time than that of the first stage. In particular, in a cryogenic device having a large superconducting coil, for example, the required time for the initial cooling may become quite long.

[0005] To accelerate the cooling rate and complete the initial cooling in a short time, it has been proposed to interpose a thermal switch between the objects being cooled in the first and second stages. An example of a thermal switch is known in which two heat transfer surfaces are placed non-contacting with each other inside a gas-filled container. When the temperature of the heat transfer surfaces is higher than the boiling point of the gas, the two heat transfer surfaces are thermally connected through heat exchange via the gas, and the thermal switch is turned on. When the heat transfer surfaces cool and their temperature falls below the boiling point of the gas, the gap between the two heat transfer surfaces becomes a vacuum due to gas condensation, the thermal connection is released by vacuum insulation, and the thermal switch is turned off.

[0006] By installing a thermal switch between the first and second stages of objects to be cooled, at high temperatures such as room temperature, the first and second stages of objects to be cooled are thermally connected by the thermal switch, allowing the second stage object to be cooled rapidly using not only the second stage but also the first stage of the cryogenic refrigerator. In this way, the initial cooling time can be shortened. At cryogenic temperatures, the thermal switch is switched off, the thermal connection between the first and second stages is disconnected, and the first and second stages of objects to be cooled can be cooled to their respective target cooling temperatures.

[0007] One exemplary objective of a certain aspect of the present invention is to improve the heat transfer efficiency of a thermal switch, thereby shortening the initial cooling time of a cryogenic device. [Means for solving the problem]

[0008] According to one aspect of the present invention, a thermal switch comprises a first heat transfer element having a first heat transfer surface, a second heat transfer element having a second heat transfer surface, and a connecting container extending along the main axis so as to surround the first and second heat transfer elements. The connecting container connects the first and second heat transfer elements such that when the first and second heat transfer elements are at a first temperature, the first and second heat transfer surfaces are in contact or a first gas gap is formed between the first and second heat transfer surfaces. The sum of the thermal contraction of the first and second heat transfer elements along the main axis due to cooling from a first temperature to a second temperature lower than the first temperature is greater than the thermal contraction of the connecting container along the main axis due to cooling such that the first and second heat transfer surfaces are separated or a second gas gap wider than the first gas gap is formed between the first and second heat transfer surfaces. The first and second heat transfer surfaces are inclined with respect to the main axis.

[0009] According to one aspect of the present invention, a thermal switch comprises a first heat transfer element having a first heat transfer surface, a second heat transfer element having a second heat transfer surface, and a connecting container extending along the main axis so as to surround the first and second heat transfer elements. The connecting container connects the first and second heat transfer elements such that when the first and second heat transfer elements are at a first temperature, the first and second heat transfer surfaces are in contact or a first gas gap is formed between the first and second heat transfer surfaces. The total amount of thermal contraction along the main axis of the first and second heat transfer elements due to cooling from a first temperature to a second temperature lower than the first temperature is greater than the amount of thermal contraction along the main axis of the connecting container due to cooling such that the first and second heat transfer surfaces are separated or a second gas gap wider than the first gas gap is formed between the first and second heat transfer surfaces. The connecting container comprises an airtight partition that connects the first heat transfer element and the second heat transfer element so as to house the first heat transfer surface and the second heat transfer surface inside, and is flexible along the main axis, and a support that connects the first heat transfer element and the second heat transfer element and has higher rigidity along the main axis than the airtight partition.

[0010] According to one aspect of the present invention, the cryogenic apparatus comprises a cryogenic refrigerator having a first cooling stage that is cooled to a first cooling temperature and a second cooling stage that is cooled to a second cooling temperature lower than the first cooling temperature, and a thermal switch according to any of the above-described aspects. A first heat transfer element is thermally coupled to the first cooling stage, and a second heat transfer element is thermally coupled to the second cooling stage. [Effects of the Invention]

[0011] According to the present invention, the heat transfer efficiency of the thermal switch can be increased, thereby shortening the initial cooling time of the cryogenic device. [Brief explanation of the drawing]

[0012] [Figure 1] Figure 1(a) is a schematic diagram showing a cryogenic apparatus according to one embodiment, and Figure 1(b) is a schematic diagram showing a cryogenic refrigerator according to one embodiment. [Figure 2] This is a schematic cross-sectional view showing in more detail an exemplary configuration of a thermal switch according to an embodiment. [Figure 3] This figure schematically shows another example of a thermal switch according to the embodiment. [Figure 4] This figure schematically shows another example of a thermal switch according to the embodiment. [Figure 5] This figure schematically shows another example of a thermal switch according to the embodiment. [Figure 6] This figure schematically shows another example of a thermal switch according to the embodiment. [Figure 7] This figure schematically shows another example of a thermal switch according to the embodiment. [Modes for carrying out the invention]

[0013] The embodiments for carrying out the present invention will be described in detail below with reference to the drawings. In the description and drawings, identical or equivalent components, members, and processes are denoted by the same reference numerals, and redundant descriptions will be omitted as appropriate. The scale and shape of the illustrated parts are set for convenience to facilitate the explanation and are not to be interpreted restrictively unless otherwise specified. The embodiments are illustrative and do not limit the scope of the present invention in any way. Not all features or combinations thereof described in the embodiments are necessarily essential to the invention.

[0014] Figure 1(a) is a schematic diagram showing a cryogenic apparatus 10 according to an embodiment. The cryogenic apparatus 10 is configured to cool a superconducting coil 12, which is an example of an object to be cooled, from room temperature to an extremely low temperature, and to maintain the superconducting coil 12 at an extremely low temperature while it is in use.

[0015] The superconducting coil 12 can be mounted on high-magnetic-field equipment (not shown) as a magnetic field source, for example, in accelerators such as single crystal pulling devices, NMR systems, MRI systems, and cyclotrons, high-energy physical systems such as nuclear fusion systems, or other high-magnetic-field equipment, and can generate the high magnetic field required for such equipment. The superconducting coil 12 is configured to generate a strong magnetic field by energizing it while it is cooled to an extremely low temperature below its superconducting transition temperature.

[0016] The cryogenic apparatus 10 comprises a cryogenic refrigerator 20, a vacuum vessel 30, and a radiation shield 40. In this embodiment, the cryogenic apparatus 10 is configured as a conduction cooling type in which the superconducting coil 12 is directly cooled by the cryogenic refrigerator 20, rather than an immersion cooling type in which the superconducting coil 12 is cooled by immersion in a cryogenic liquid coolant such as liquid helium. The cryogenic refrigerator 20 is thermally coupled to the superconducting coil 12 so as to cool the superconducting coil 12 by conduction cooling.

[0017] In FIG. 1(a), 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, as needed.

[0018] The cryogenic refrigerator 20 includes a cooling stage 22 that cools an object by conduction cooling, more specifically, a first cooling stage 22a and a second cooling stage 22b. The cryogenic refrigerator 20 is installed in a vacuum vessel 30, and the first cooling stage 22a and the second cooling stage 22b are arranged inside the vacuum vessel 30. As an example, the cryogenic refrigerator 20 is a two-stage Gifford-McMahon refrigerator.

[0019] The cryogenic refrigerator 20 includes a compressor (not shown) for an operating gas (e.g., helium gas) and an expansion machine also called a cold head. The compressor and the expansion machine constitute the refrigeration cycle of the cryogenic refrigerator 20, whereby the first cooling stage 22a and the second cooling stage 22b are each cooled to a desired cryogenic temperature. The first cooling stage 22a is cooled to a first cooling temperature, for example, 30 K to 80 K, and the second cooling stage 22b 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. The first cooling stage 22a and the second cooling stage 22b are formed of a metal material such as copper (e.g., pure copper, the same hereinafter) or other materials having high thermal conductivity.

[0020] The vacuum vessel 30 is configured to separate the vacuum region 32 from the external 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 cooling stage 22 of the cryogenic refrigerator 20, and the radiation shield 40 are arranged in the vacuum region 32 and are thermally insulated from the external environment 14.

[0021] The radiant shield 40 is thermally coupled to the first cooling stage 22a and cooled to a first cooling temperature. The radiant shield 40 is directly attached to the first cooling stage 22a and thermally coupled to it. Alternatively, the radiant shield 40 may be attached to the first cooling stage 22a via a flexible or rigid heat transfer member. The radiant shield 40 is positioned to surround the superconducting coil 12, the second cooling stage 22b of the cryogenic refrigerator 20, and other low-temperature parts that are cooled to a second cooling temperature, and can thermally protect these low-temperature parts from radiant heat from the outside. The radiant shield 40 is formed of a metallic material such as copper or other material with high thermal conductivity.

[0022] The superconducting coil 12 is thermally coupled to the second cooling stage 22b via a heat transfer member 50. The heat transfer member 50 is made of a metallic material such as copper or other material with high thermal conductivity and connects the superconducting coil 12 to the second cooling stage 22b. The heat transfer member 50 may be flexible and connect the superconducting coil 12 and the second cooling stage 22b in a way that allows for relative displacement between them, or it may be a rigid member that rigidly connects the superconducting coil 12 and the second cooling stage 22b. The heat transfer member 50 is made of a metallic material such as copper or other material with high thermal conductivity.

[0023] In the illustrated example, the heat transfer member 50 is fixed to the bottom surface of the second cooling stage 22b, but it may also be fixed to other parts such as the side or top surface of the second cooling stage 22b. Similarly, the heat transfer member 50 is fixed to the bottom surface of the superconducting coil 12, for example, but it may also be fixed to other parts such as the side or top surface of the superconducting coil 12.

[0024] In this embodiment, the cryogenic device 10 includes a thermal switch 100 for thermally connecting or disconnecting the superconducting coil 12 and the radiation shield 40. As will be described in detail later, the thermal switch 100 includes a first heat transfer element 110 and a second heat transfer element 120 that are arranged opposite each other across a gas gap. The thermal switch 100 constitutes an airtight container that seals the working gas in the gas gap.

[0025] As an example, as shown in the figure, the first heat transfer element 110 is attached to the radiation shield 40, the second heat transfer element 120 is attached to the superconducting coil 12, and the thermal switch 100 directly connects the superconducting coil 12 and the radiation shield 40. Alternatively, the first heat transfer element 110 may be attached to the first cooling stage 22a or the radiation shield 40 via a heat transfer member, and the second heat transfer element 120 may be attached to the second cooling stage 22b, the superconducting coil 12, or the heat transfer member 50 via a heat transfer member, thereby the thermal switch 100 may connect any part cooled to a first cooling temperature with any part cooled to a second cooling temperature.

[0026] The thermal switch 100 can thermally connect the high-temperature side and the low-temperature side by heat transfer between the heat transfer elements via the working gas in the gas gap when the temperatures of the first heat transfer element 110 and the second heat transfer element 120 are higher than the switching temperature. 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 sealed working gas. The gas gap is a very narrow gap for good heat transfer. The size of the gas gap (the shortest distance between the first heat transfer element 110 and the second heat transfer element 120) may be, for example, within 5 mm or within 2 mm.

[0027] On the other hand, the thermal switch 100 disconnects the thermal connection between the high-temperature and low-temperature sides when the temperature of at least one of the first heat transfer element 110 and the second heat transfer element 120 (usually the second heat transfer element 120) is lower than the switching temperature. This is because the working gas in the gas gap condenses on at least the surface of the second heat transfer element 120, the gas gap becomes a vacuum, and the first heat transfer element 110 and the second heat transfer element 120 are vacuum-insulated through the gas gap. This is the off state of the thermal switch 100.

[0028] Alternatively, as described later, when the temperatures of the first heat transfer element 110 and the second heat transfer element 120 are higher than the switching temperature of the thermal switch 100, the first heat transfer element 110 and the second heat transfer element 120 may come into contact due to thermal expansion, and the first heat transfer element 110 and the second heat transfer element 120 may be thermally connected to each other by heat conduction between these two heat transfer elements without a gas gap. In this way, the thermal switch 100 may be in the ON state.

[0029] On the other hand, when the thermal switch 100 is cooled, the thermal contraction of at least one of the first heat transfer element 110 and the second heat transfer element 120 may cause the heat transfer elements to separate, thereby forming a gas gap. In this case as well, when the temperature of at least one of the heat transfer elements is lower than the switching temperature, the thermal switch 100 releases the thermal connection between the high-temperature side and the low-temperature side through vacuum insulation via the gas gap. In this way, the thermal switch 100 may be in the off state.

[0030] The working gas sealed 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. 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 27.1K). Alternatively, the working gas may be hydrogen (approximately 20.4K) or helium (approximately 4.2K). Here, the boiling point of each gas at atmospheric pressure is indicated in parentheses after the gas type. For example, if neon is sealed in the thermal switch 100 as the working gas at atmospheric pressure, the switching temperature of the thermal switch 100 can be set to approximately 27.1K. The working gas may also 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 pressure of the operating gas.

[0031] 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 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 mixed gas.

[0032] The cryogenic apparatus 10 according to this embodiment operates as follows: When the cryogenic refrigerator 20 is started, the first cooling stage 22a of the cryogenic refrigerator 20 is cooled to a first cooling temperature, and the second cooling stage 22b is cooled to a second cooling temperature. The radiation shield 40 is cooled to a first cooling temperature by the first cooling stage 22a, and the superconducting coil 12 is cooled to a second cooling temperature by the second cooling stage 22b. 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 apparatus 10 can be operated.

[0033] 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 a thermal switch 100 is advantageous for initial cooling when the cryogenic apparatus 10 is started up. During initial cooling, the cryogenic refrigerator 20 is cooled from ambient temperature (e.g., room temperature) to the target cryogenic temperature. Therefore, at the beginning of initial cooling, the thermal switch 100 is turned on, and the radiation shield 40 and the superconducting coil 12 are thermally connected. Generally, the cooling capacity of the first cooling stage 22a of the cryogenic refrigerator 20 is greater than the cooling capacity of the second cooling stage 22b, so the cooling capacity of the first cooling stage 22a can be used to assist in the cooling of the superconducting coil 12 by the second cooling stage 22b. This can shorten the time required for initial cooling.

[0034] As cooling progresses, when the superconducting coil 12 cools to a temperature lower than the switching temperature of the thermal switch 100, the thermal switch 100 switches 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 22a, while the superconducting coil 12 is further cooled by the second cooling stage 22b, eventually cooling down to the second cooling temperature.

[0035] Figure 1(b) is a schematic diagram showing a cryogenic refrigerator 20 according to one embodiment. In Figure 1(a), the case in which the thermal switch 100 connects the radiation shield 40 and the superconducting coil 12 is explained as an example. Alternatively, or in conjunction with this, as shown in Figure 1(b), the thermal switch 100 may connect the first cooling stage 22a and the second cooling stage 22b of the cryogenic refrigerator 20.

[0036] Furthermore, while Figures 1(a) and 1(b) illustrate the case where a single thermal switch 100 is installed, the present invention is not limited to this. For example, the cryogenic apparatus 10 may be equipped with multiple thermal switches 100, and each of these thermal switches 100 may connect a part with a first cooling temperature, such as a radiation shield 40, to a part with a second cooling temperature, such as a superconducting coil 12. Also, the cryogenic refrigerator 20 may be equipped with multiple thermal switches 100, and each of these thermal switches 100 may connect a first cooling stage 22a and a second cooling stage 22b.

[0037] Figure 2 is a schematic cross-sectional view showing in more detail an exemplary configuration of the thermal switch 100 shown in Figures 1(a) and 1(b). Figure 2 shows a longitudinal section of the thermal switch 100 including the main shaft 102. The main shaft 102 may correspond to the central axis of the thermal switch 100. The thermal switch 100 may have a generally cylindrical shape extending along the main shaft 102.

[0038] The left side of Figure 2 shows the first state of the thermal switch 100, and the right side of Figure 2 shows the second state of the thermal switch 100. The thermal switch 100 takes the first state at a first temperature and takes the second state when it is cooled from the first temperature to a second temperature lower than the first temperature. The first temperature may be the ambient temperature (e.g., room temperature) and may be selected from a temperature range of, for example, 280K to 300K. The second temperature may be lower than the ambient temperature. The second temperature may be higher than the switching temperature of the thermal switch 100, and both the first and second states may be the ON state of the thermal switch 100. The second temperature may be selected from a temperature range of, for example, 50K to 250K.

[0039] As described above, the thermal switch 100 comprises a first heat transfer element 110 and a second heat transfer element 120. The first heat transfer element 110 has a first heat transfer surface 111, and the second heat transfer element 120 has a second heat transfer surface 121. The connecting container 130 extends along the main axis 102 so as to surround the first heat transfer element 110 and the second heat transfer element 120. The main axis 102 may correspond to the central axis of the connecting container 130.

[0040] The first heat transfer element 110 comprises a single projection 112 and a base 113. The projection 112 extends along the main shaft 102 within the connecting container 130. The projection 112 may have, for example, a cylindrical side surface centered on the main shaft 102. In this embodiment, the first heat transfer surface 111 is inclined with respect to the main shaft 102. The first heat transfer surface 111 is a single inclined surface formed on the projection 112 opposite the second heat transfer surface 121. The first heat transfer surface 111 is neither perpendicular nor parallel to the main shaft 102.

[0041] The projection 112 is thermally bonded to the first member 61 (for example, the radiation shield 40 or first cooling stage 22a shown in Figure 1(a)) which is cooled to a first cooling temperature, via the base 123. The base 113 may be, for example, a flange having a generally disc-like shape, and its circular end face may be in contact with the surface of the first member 61 and fixed to the first member 61. The projection 112 may be integrally formed with the base 113, or it may be prepared separately from the base 113 and joined to the base 113.

[0042] The second heat transfer element 120 comprises a single projection 122 and a base 123. The projection 122 extends along the main shaft 102 within the connecting container 130. The projection 122 may have, for example, a cylindrical side surface centered on the main shaft 102. In this embodiment, the second heat transfer surface 121 is inclined with respect to the main shaft 102. The second heat transfer surface 121 is a single inclined surface formed on the projection 122 opposite the first heat transfer surface 111. The second heat transfer surface 121 is neither perpendicular nor parallel to the main shaft 102.

[0043] The projection 122 is thermally coupled to the second member 62 (for example, the superconducting coil 12 or the second cooling stage 22b shown in Figure 1(a)) which is cooled to a second cooling temperature, via the base 123. The base 123 may be, for example, a flange having a generally disc-like shape, and its circular end face may be in contact with the surface of the second member 62 and fixed to the second member 62. The projection 122 may be integrally formed with the base 123, or it may be prepared separately from the base 123 and joined to the base 123.

[0044] The first heat transfer element 110 and the second heat transfer element 120 are formed from a metallic material such as copper or other material with high thermal conductivity, similar to the other heat transfer members in the cryogenic apparatus 10 described above. Although the first heat transfer element 110 and the second heat transfer element 120 are usually formed from the same material, they may be formed from different materials.

[0045] The connecting container 130 connects the first heat transfer element 110 and the second heat transfer element 120, and together with the first and second heat transfer elements 110 and 120 forms an airtight container for sealing the working gas of the thermal switch 100 inside. Thus, the internal volume of the connecting container 130 is isolated from the surrounding environment of the thermal switch 100 (for example, the vacuum region 32 shown in Figure 1(a)). The connecting container 130 may have, for example, a cylindrical shape extending along the main axis 102. The connecting container 130 may be connected at one end to the base 113 of the first heat transfer element 110 and at the other end to the base 123 of the second heat transfer element 120. The connecting container 130 may be joined to these heat transfer elements by, for example, brazing, bonding, or other appropriate joining methods.

[0046] The majority of the internal volume of the connecting container 130, for example, at least 80% or at least 90%, may be occupied by the first heat transfer element 110 and the second heat transfer element 120. Therefore, since the first heat transfer surface 111 is the surface of a single projection 112 of the first heat transfer element 110 as described above, it can be made relatively large within the connecting container 130. When considering the projected area when viewed along the main axis 102, the projected area of ​​the first heat transfer surface 111 may occupy the majority of the projected area of ​​the internal volume of the connecting container 130, for example, at least 80% or at least 90%. Similarly, the projected area of ​​the second heat transfer surface 121 may occupy the majority of the projected area of ​​the internal volume of the connecting container 130, for example, at least 80% or at least 90%.

[0047] The connecting container 130 is formed of a material with lower thermal conductivity than the first heat transfer element 110 and the second heat transfer element 120, such as an insulating material. Here, the 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 first heat transfer element 110 (or the second heat transfer element 120). The connecting container 130 may be formed of, for example, stainless steel, or glass fiber reinforced plastic (GFRP) or other plastic material. This prevents or minimizes heat intrusion from the first heat transfer element 110 to the second heat transfer element 120 through the connecting container 130 when the heat switch 100 is off.

[0048] In this embodiment, the connecting container 130 connects the first heat transfer element 110 and the second heat transfer element 120 such that the first heat transfer surface 111 and the second heat transfer surface 121 are in contact when the first heat transfer element 110 and the second heat transfer element 120 are at a first temperature. That is, when the thermal switch 100 is in the first state, the first heat transfer element 110 and the second heat transfer element 120 are arranged with their first heat transfer surface 111 and the second heat transfer surface 121 in contact with each other, as shown on the left side of Figure 2. The first heat transfer element 110 and the second heat transfer element 120 may form a single columnar body (e.g., a cylinder) extending along the main axis 102 when the first heat transfer surface 111 and the second heat transfer surface 121 are in contact.

[0049] Therefore, when the thermal switch 100 is in the first state, the first heat transfer element 110 and the second heat transfer element 120 thermally connect the high-temperature side first member 61 and the low-temperature side second member 62 through heat conduction between these two heat transfer elements, without the need for a gas gap. The mechanical contact between the two heat transfer elements increases the thermal conductance and thus the heat transfer efficiency of the thermal switch 100, thereby shortening the initial cooling time of the cryogenic device. Furthermore, the improvement in thermal conductance can help to miniaturize the thermal switch 100. In other words, it becomes possible to achieve a certain predetermined heat flow rate with a smaller thermal switch.

[0050] Furthermore, in this embodiment, the sum of the thermal contraction amounts along the main axis 102 of the first heat transfer element 110 and the second heat transfer element 120 due to cooling from the first temperature to the second temperature is greater than the thermal contraction amount along the main axis 102 of the connecting container 130 due to cooling from the first temperature to the second temperature. In other words, the first heat transfer element 110, the second heat transfer element 120, and the connecting container 130 are designed such that this magnitude relationship holds between the sum of the thermal contraction amounts of the first heat transfer element 110 and the second heat transfer element 120 and the thermal contraction amount of the connecting container 130.

[0051] For example, the materials for the first heat transfer element 110, the second heat transfer element 120, and the connecting container 130 may be selected to satisfy this magnitude relationship. Therefore, the amount of thermal shrinkage of the material forming the first heat transfer element 110 when cooled from a first temperature to a second temperature may be greater than the amount of thermal shrinkage of the material forming the connecting container 130 when cooled from a first temperature to a second temperature. Similarly, the amount of thermal shrinkage of the material forming the second heat transfer element 120 when cooled from a first temperature to a second temperature may be greater than the amount of thermal shrinkage of the material forming the connecting container 130 when cooled from a first temperature to a second temperature. For example, the amount of thermal shrinkage of copper when cooled from a first temperature (e.g., about 290K) to a second temperature (e.g., about 100K) is greater than the amount of thermal shrinkage of stainless steel when cooled from a first temperature to a second temperature. Therefore, the first heat transfer element 110 and the second heat transfer element 120 may be made of copper, and the connecting container 130 may be made of stainless steel.

[0052] Therefore, when the thermal switch 100 is in the second state, the first heat transfer surface 111 and the second heat transfer surface 121 are separated, as shown on the right side of Figure 2. As described above, in the first state the first heat transfer surface 111 and the second heat transfer surface 121 are in contact, whereas in the second state, due to cooling from the first temperature to the second temperature, the first heat transfer surface 111 and the second heat transfer surface 121 are separated by the gas gap 104 and are not in physical contact. If the second temperature is higher than the switching temperature of the thermal switch 100, the thermal switch 100 can maintain the ON state by thermally connecting the first member 61 on the high-temperature side and the second member 62 on the low-temperature side through heat transfer between the heat transfer elements via the working gas in the gas gap 104.

[0053] When the thermal switch 100 is cooled to a temperature lower than the switching temperature, the working gas in the connecting container 130 condenses on the surface of the heat transfer elements, and the gas gap 104 becomes a vacuum. The first heat transfer element 110 and the second heat transfer element 120 are vacuum-insulated through the gas gap 104, and the thermal connection between the high-temperature first member 61 and the low-temperature second member 62 is released. In this way, the thermal switch 100 switches to the off state. Because the thermal contraction of the first heat transfer element 110 and the second heat transfer element 120 due to cooling is greater than the thermal contraction of the connecting container 130, the gas gap 104 widens in the off state compared to the on state. This helps to reliably block heat transfer between the first heat transfer element 110 and the second heat transfer element 120.

[0054] As described above, the first heat transfer surface 111 and the second heat transfer surface 121 are inclined with respect to the main shaft 102. For example, the inclination angle of the first heat transfer surface 111 and the second heat transfer surface 121 with respect to the main shaft 102 may be in the range of 30 to 60 degrees.

[0055] In this way, the heat transfer area of ​​the thermal switch 100 can be increased compared to the case where the first heat transfer surface 111 and the second heat transfer surface 121 shown in Figure 6 are perpendicular to the main shaft 102. Therefore, the thermal conductance and thus the heat transfer efficiency of the thermal switch 100 can be increased, thereby shortening the initial cooling time of the cryogenic device 10.

[0056] Furthermore, according to this embodiment, the actual width of the gas gap 104 is narrower compared to the case shown in Figure 6. This also helps to improve the thermal conductance of the thermal switch 100. The actual width of the gas gap 104 corresponds to the size of the gas gap 104 in the direction normal to the first heat transfer surface 111 (and the second heat transfer surface 121). Because the two heat transfer surfaces are inclined with respect to the main axis 102, the actual width of the gas gap 104 is smaller than the sum of the thermal contraction amounts of the two heat transfer elements, i.e., the size of the gas gap 104 in the direction of the main axis 102. On the other hand, when the first heat transfer surface 111 and the second heat transfer surface 121 shown in Figure 6 are perpendicular to the main axis 102, the width of the gas gap 104 is relatively wide because it matches the sum of the thermal contraction amounts of the two heat transfer elements.

[0057] Figure 3 is a schematic diagram illustrating another example of the thermal switch 100 according to an embodiment. Similar to Figure 2, Figure 3 shows the first state of the thermal switch 100 on the left and the second state of the thermal switch 100 on the right. The thermal switch 100 takes the first state at a first temperature and takes the second state when it is cooled from the first temperature to a second temperature lower than the first temperature. The thermal switch 100 comprises a first heat transfer element 110, a second heat transfer element 120, and a connecting container 130. The first heat transfer surface 111 and the second heat transfer surface 121 are inclined with respect to the main axis 102.

[0058] In the example shown in Figure 3, the connecting container 130 connects the first heat transfer element 110 and the second heat transfer element 120 such that a first gas gap 104A is formed between the first heat transfer surface 111 and the second heat transfer surface 121 when the first heat transfer element 110 and the second heat transfer element 120 are at a first temperature. That is, when the thermal switch 100 is in the first state, the first heat transfer element 110 and the second heat transfer element 120 are arranged with their first heat transfer surface 111 and second heat transfer surface 121 spaced apart, as shown on the left side of Figure 3. Therefore, when the thermal switch 100 is in the first state, the first heat transfer element 110 and the second heat transfer element 120 can thermally connect the high-temperature side first member 61 and the low-temperature side second member 62 by heat transfer between the heat transfer elements via the working gas in the first gas gap 104A. Since the first heat transfer surface 111 and the second heat transfer surface 121 are inclined with respect to the main shaft 102, the heat transfer area can be increased, and the thermal conductance of the thermal switch 100 can be increased.

[0059] Furthermore, the sum of the thermal contraction amounts along the main axis 102 of the first heat transfer element 110 and the second heat transfer element 120 due to cooling from the first temperature to the second temperature is greater than the thermal contraction amount along the main axis 102 of the connecting container 130 due to cooling from the first temperature to the second temperature. Therefore, when the thermal switch 100 is in the second state, as shown on the right side of Figure 3, a second gas gap 104B wider than the first gas gap 104A is formed between the first heat transfer surface 111 and the second heat transfer surface 121 due to cooling. If the second temperature is higher than the switching temperature of the thermal switch 100, the thermal switch 100 can maintain the ON state by thermally connecting the high-temperature side first member 61 and the low-temperature side second member 62 through heat transfer between the heat transfer elements via the working gas in the second gas gap 104B. When the thermal switch 100 is cooled to a temperature lower than the switching temperature, the thermal switch 100 releases the thermal connection between the high-temperature first member 61 and the low-temperature second member 62 due to the vacuum insulation of the second gas gap 104B. In this way, the thermal switch 100 switches to the off state.

[0060] Figure 4 is a schematic diagram illustrating another example of the thermal switch 100 according to an embodiment. Similar to Figures 2 and 3, Figure 4 shows a longitudinal section of the thermal switch 100 including its main shaft 102. The thermal switch 100 comprises a first heat transfer element 110, a second heat transfer element 120, and a connecting container 130. The first heat transfer surface 111 and the second heat transfer surface 121 are inclined with respect to the main shaft 102.

[0061] In the embodiment shown in Figure 4, as in the embodiments shown in Figures 2 and 3, the connecting container 130 connects the first heat transfer element 110 and the second heat transfer element 120 such that when the first heat transfer surface 111 and the second heat transfer surface 121 are in contact or a first gas gap is formed between the first heat transfer surface 111 and the second heat transfer surface 121 when the first heat transfer element 110 and the second heat transfer element 120 are at the first temperature. At the same time, the total amount of thermal contraction along the main axis 102 of the first heat transfer element 110 and the second heat transfer element 120 due to cooling from the first temperature to the second temperature is greater than the amount of thermal contraction along the main axis 102 of the connecting container 130 due to cooling from the first temperature to the second temperature. As a result, cooling from the first temperature to the second temperature causes the first heat transfer surface 111 and the second heat transfer surface 121 to separate, or a second gas gap wider than the first gas gap is formed between the first heat transfer surface 111 and the second heat transfer surface 121.

[0062] However, in the thermal switch 100 shown in Figure 4, the configuration of the connecting container 130 differs from the examples in Figures 2 and 3. The connecting container 130 comprises an airtight partition 132 and a support 134.

[0063] The airtight partition 132 connects the first heat transfer element 110 and the second heat transfer element 120 so as to house the first heat transfer surface 111 and the second heat transfer surface 121 inside. The airtight partition 132, together with the first heat transfer element 110 and the second heat transfer element 120, forms an airtight container for sealing the working gas of the heat switch 100 inside. The airtight partition 132 is made of a material with lower thermal conductivity than the first heat transfer element 110 and the second heat transfer element 120, such as an insulating material. The airtight partition 132 is also flexible along the main axis 102. The airtight partition 132 may be a bellows that can expand and contract in the direction of the main axis 102. The airtight partition 132 may be connected at one end to the base 113 of the first heat transfer element 110 and at the other end to the base 123 of the second heat transfer element 120. The airtight partition wall 132 may be joined to these heat transfer elements by, for example, brazing, bonding, or other appropriate joining methods.

[0064] The support 134 connects the first heat transfer element 110 and the second heat transfer element 120 and has higher rigidity than the airtight partition wall 132 along the main axis 102. The support 134 is located outside the airtight partition wall 132. The support 134 is formed of a material with lower thermal conductivity than the first heat transfer element 110 and the second heat transfer element 120, such as an insulating material. The support 134 may be formed of, for example, stainless steel, or glass fiber reinforced plastic (GFRP) or other plastic material.

[0065] Unlike the connecting container 130 in the embodiments shown in Figures 2 and 3, the support 134 is not a cylindrical body surrounding the first heat transfer element 110 and the second heat transfer element 120. The support 134 may have multiple support columns, each connecting the first heat transfer element 110 and the second heat transfer element 120 in the direction of the main axis 102, and may have higher rigidity than the airtight partition wall 132 along the main axis 102. Each support column is fixed to the first heat transfer element 110 at one end and to the second heat transfer element 120 at the other end. As shown, each support column may be fixed to the first heat transfer element 110 and the second heat transfer element 120 by fastening members such as bolts. These support columns may be arranged around the airtight partition wall 132 at equal intervals in the circumferential direction around the main axis 102.

[0066] The connecting container 130 may also be equipped with spacers 136, such as shims. As shown in the figure, the spacers 136 may be placed between the support 134 and the first heat transfer element 110. Alternatively, or together with the support 134, the spacers 136 may be placed between the support 134 and the second heat transfer element 120. The distance between the first heat transfer element 110 and the second heat transfer element 120 can be determined by adjusting the thickness of the spacers 136 (e.g., the number of shims) in the direction of the main axis 102. For example, the first heat transfer surface 111 and the second heat transfer surface 121 can be brought into contact or separated. Alternatively, the size of the gas gap between the first heat transfer surface 111 and the second heat transfer surface 121 can be adjusted.

[0067] In a configuration where the first heat transfer surface 111 and the second heat transfer surface 121 are inclined with respect to the main shaft 102, the inclination angles of these heat transfer surfaces should ideally be exactly the same. However, in reality, the inclination angles of the two heat transfer surfaces may differ slightly due to various factors such as manufacturing tolerances. When the two heat transfer elements are connected by a rigid cylinder, as in the examples in Figures 2 and 3, the mismatch in the two inclination angles may make it difficult to bring the two heat transfer surfaces into full contact. As a result, there is a concern that the advantage of improved thermal conductance may not be fully realized.

[0068] In contrast, in the example shown in Figure 4, with the first heat transfer element 110 and the second heat transfer element 120 connected by an airtight partition 132, the airtight partition 132 is expandable and contractible, allowing the first heat transfer surface 111 and the second heat transfer surface 121 to come into full contact. Subsequently, while maintaining contact between the first heat transfer surface 111 and the second heat transfer surface 121, the first heat transfer element 110 and the second heat transfer element 120 can be connected by the support 134. Thus, the above-mentioned concerns are resolved. In this way, the connecting container 130 shown in Figure 4 is advantageous in the manufacture of the thermal switch 100.

[0069] Figure 5 is a schematic diagram illustrating another example of the thermal switch 100 according to an embodiment. In the example shown in Figure 5, as in the example in Figure 4, the thermal switch 100 comprises a first heat transfer element 110, a second heat transfer element 120, and a connecting container 130. The first heat transfer surface 111 and the second heat transfer surface 121 are inclined with respect to the main axis 102. The connecting container 130 comprises an airtight partition wall 132 and a support 134. The connecting container 130 may also include a spacer 136.

[0070] The support 134 may have a combination of materials with different amounts of thermal contraction due to cooling. For example, each support column constituting the support 134 may comprise a first portion 134a on the first heat transfer element 110 side and a second portion 134b on the second heat transfer element 120 side. The first portion 134a may be formed of a first material, and the second portion 134b may be formed of a second material that exhibits a different amount of thermal contraction due to cooling than the first material. For example, the first portion 134a may be formed of an insulating material such as stainless steel or glass fiber reinforced plastic (GFRP), and the second portion 134b may be formed of a metallic material such as copper.

[0071] In this way, the magnitude of thermal contraction of the support 134 due to cooling can be adjusted compared to the case where the support 134 is formed from a single material. This allows for adjustment of the gas gap between the first heat transfer surface 111 and the second heat transfer surface 121 (for example, gas gap 104, first gas gap 104A, and second gas gap 104B).

[0072] Figure 6 is a schematic diagram illustrating another example of the thermal switch 100 according to an embodiment. In the example shown in Figure 6, as in the example in Figure 4, the thermal switch 100 comprises a first heat transfer element 110, a second heat transfer element 120, and a connecting container 130. It is not essential that the first heat transfer surface 111 and the second heat transfer surface 121 are inclined with respect to the main axis 102; as shown in Figure 6, the first heat transfer surface 111 and the second heat transfer surface 121 may be perpendicular to the main axis 102. The connecting container 130 comprises an airtight partition wall 132 and a support 134. The connecting container 130 may also include a spacer 136.

[0073] Figure 7 is a schematic diagram illustrating another example of the thermal switch 100 according to an embodiment. The thermal switch 100 comprises a first heat transfer element 110, a second heat transfer element 120, and a connecting container 130. The first heat transfer surface 111 and the second heat transfer surface 121 are inclined with respect to the main axis 102.

[0074] As shown in Figure 7, the thermal switch 100 may include a getter material 150 that is thermally coupled to the second heat transfer element 120 and capable of adsorbing the working gas of the thermal switch 100. The getter material 150 may be, for example, activated carbon, or other porous material, or other adsorbent material, that has the ability to adsorb the working gas of the thermal switch 100 at cryogenic temperatures (i.e., temperatures below the switching temperature of the thermal switch 100, e.g., a second cooling temperature). The getter material 150 may be grounded in a getter chamber 152 formed within the second heat transfer element 120. Alternatively, the getter material 150 may be placed on the surface of the second heat transfer element 120 in an appropriate manner so that it can be cooled by the second heat transfer element 120.

[0075] Ideally, when the thermal switch 100 is cooled to a temperature below its switching temperature, the working gas condenses within the thermal switch 100 as described above, the gas gap becomes a vacuum, and the thermal switch 100 turns off. However, in reality, some working gas may remain in the gas gap. Such residual gas can cause heat transfer between the first heat transfer element 110 and the second heat transfer element 120. Undesirably, heat intrusion from the first heat transfer element 110 to the second heat transfer element 120 through the thermal switch 100, which should be off, may become significant.

[0076] In contrast, by providing a getter material 150 inside the thermal switch 100, residual gas can be adsorbed, and the vacuum level of the gas gap can be further increased. Therefore, the disconnection of the thermal connection when the thermal switch 100 is in the off state can be achieved more reliably.

[0077] The present invention has been described above based on examples. Those skilled in the art will understand that the present invention is not limited to the above embodiments, that various design changes are possible, and that various modifications are possible, and that such modifications also fall within the scope of the present invention. Various features described in relation to one embodiment are applicable to other embodiments. New embodiments resulting from combinations will possess the combined effects of each of the embodiments combined.

[0078] In the embodiments described above, the case in which the cryogenic refrigerator 20 is a multi-stage Gifford-McMahon refrigerator is 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 any other type of multi-stage cryogenic refrigerator. The thermal switch 100 according to the embodiments is applicable to various cryogenic refrigerators 20, or to cryogenic devices 10 equipped with cryogenic refrigerators 20.

[0079] In the above-described embodiment, the thermal switch 100 is applied to a conduction-cooled cryogenic apparatus 10 in which the object to be cooled is directly cooled by a cryogenic refrigerator 20. However, in one embodiment, the thermal switch 100 can also be applied to an immersion-cooled cryogenic apparatus in which the object to be cooled is cooled by immersing it in a cryogenic refrigerant such as liquid helium.

[0080] Although the present invention has been described using specific terms based on the embodiments, the embodiments only illustrate one aspect of the principle and application of the present invention, and many modifications and changes in arrangement are permitted in the embodiments, as long as they do not depart from the spirit of the present invention as defined in the claims. [Explanation of Symbols]

[0081] 10 Cryogenic device, 20 Cryogenic refrigerator, 22 Cooling stage, 22a First cooling stage, 22b Second cooling stage, 100 Thermal switch, 102 Main shaft, 104 Gas gap, 104A First gas gap, 104B Second gas gap, 110 First heat transfer element, 111 First heat transfer surface, 112 Protrusion, 120 Second heat transfer element, 121 Second heat transfer surface, 122 Protrusion, 130 Connecting container, 132 Airtight partition, 134 Support, 136 Spacer.

Claims

1. A first heat transfer element having a first heat transfer surface, A second heat transfer element having a second heat transfer surface, A connecting container extending along the main axis so as to surround the first heat transfer element and the second heat transfer element, the connecting container connecting the first heat transfer element and the second heat transfer element such that when the first heat transfer element and the second heat transfer element are at a first temperature, the first heat transfer surface and the second heat transfer surface are in contact or a first gas gap is formed between the first heat transfer surface and the second heat transfer surface, The sum of the thermal contraction amounts of the first and second heat transfer elements along their main axes due to cooling from the first temperature to a second temperature lower than the first temperature is greater than the thermal contraction amount of the connecting container along its main axis due to cooling, such that the first and second heat transfer surfaces are separated by the cooling or a second gas gap wider than the first gas gap is formed between the first and second heat transfer surfaces. A thermal switch characterized in that the first heat transfer surface and the second heat transfer surface are inclined with respect to the main shaft.

2. The thermal switch according to claim 1, characterized in that the inclination angles of the first heat transfer surface and the second heat transfer surface with respect to the main axis are in the range of 30 degrees to 60 degrees.

3. The first heat transfer element comprises a single projection extending along the main axis within the connecting container, and the first heat transfer surface is a single inclined surface formed on the single projection of the first heat transfer element opposite the second heat transfer surface. The thermal switch according to claim 1, wherein the second heat transfer element comprises a single projection extending along the main axis within the connecting container, and the second heat transfer surface is a single inclined surface formed on the single projection of the second heat transfer element opposite to the first heat transfer surface.

4. The aforementioned connecting container is The first heat transfer element and the second heat transfer element are connected so as to house the first heat transfer surface and the second heat transfer surface inside, and a flexible airtight partition is provided along the main axis, The thermal switch according to claim 1, further comprising a support that connects the first heat transfer element and the second heat transfer element and has higher rigidity than the airtight partition along the main axis.

5. The thermal switch according to claim 4, characterized in that the support is located outside the airtight partition.

6. The thermal switch according to claim 4, characterized in that the connecting container comprises a spacer disposed between the support and the first heat transfer element, or between the support and the second heat transfer element.

7. The connecting container connects the first heat transfer element and the second heat transfer element such that the first heat transfer surface and the second heat transfer surface are in contact when the first heat transfer element and the second heat transfer element are at the first temperature. The thermal switch according to claim 1, characterized in that the sum of the thermal contraction amounts of the first heat transfer element and the second heat transfer element along the main axis due to the cooling is greater than the thermal contraction amount of the connecting container along the main axis due to the cooling, such that the first heat transfer surface and the second heat transfer surface are separated by the cooling.

8. A first heat transfer element having a first heat transfer surface, A second heat transfer element having a second heat transfer surface, A connecting container extending along the main axis so as to surround the first heat transfer element and the second heat transfer element, the connecting container connecting the first heat transfer element and the second heat transfer element such that when the first heat transfer element and the second heat transfer element are at a first temperature, the first heat transfer surface and the second heat transfer surface are in contact or a first gas gap is formed between the first heat transfer surface and the second heat transfer surface, The sum of the thermal contraction amounts of the first and second heat transfer elements along their main axes due to cooling from the first temperature to a second temperature lower than the first temperature is greater than the thermal contraction amount of the connecting container along its main axis due to cooling, such that the first and second heat transfer surfaces are separated by the cooling or a second gas gap wider than the first gas gap is formed between the first and second heat transfer surfaces. The aforementioned connecting container is The first heat transfer element and the second heat transfer element are connected so as to house the first heat transfer surface and the second heat transfer surface inside, and a flexible airtight partition is provided along the main axis, A thermal switch comprising a support that connects the first heat transfer element and the second heat transfer element and has higher rigidity than the airtight partition along the main axis.

9. A cryogenic refrigerator comprising a first cooling stage that cools to a first cooling temperature and a second cooling stage that cools to a second cooling temperature lower than the first cooling temperature, A thermal switch according to any one of claims 1 to 8, comprising: A cryogenic apparatus characterized in that the first heat transfer element is thermally coupled to the first cooling stage, and the second heat transfer element is thermally coupled to the second cooling stage.

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