Heat transfer member connection structure for cryogenic device and cryogenic device

Abstract

To make it possible to reduce the contact thermal resistance of a connection part of a heat transfer member.SOLUTION: In a heat transfer member connection structure of a cryogenic device, a superconducting coil 11 is conduction-cooled to a cryogenic temperature via a second heat transfer member 16 by a cryogenic refrigerator 12. The second heat transfer member 16 comprises a low-temperature side heat transfer member 17 connected to the cryogenic refrigerator, and a high-temperature side heat transfer member 18 connected to the superconducting coil. A convex part 23 is formed in one of the high-temperature side heat transfer member and the low-temperature side heat transfer member, and a hole 24 having a shape following the shape of the convex part is formed in an end part 27 of the other. Under the same temperature condition of the high-temperature side heat transfer member 18 and the low-temperature side heat transfer member 17 at the time of manufacturing, the internal diameter of the hole 24 is set equal to or smaller than the external diameter of the convex part 23. The convex part is fitted into the hole by heating or cooling, and thereby the high-temperature side heat transfer member 18 and the low-temperature side heat transfer member 17 are connected.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] An embodiment of the present invention relates to a heat transfer member connection structure of a cryogenic device that conducts and cools objects to be cooled, such as superconducting coils, to cryogenic temperatures via a heat transfer member using a cryogenic refrigerator, and to a cryogenic device having a heat transfer member to which the connection structure is applied. [Background technology]

[0002] Conventionally, conduction cooling cryogenic devices have been developed that utilize cryogenic refrigerators capable of cooling to extremely low temperatures of 77K or below, and conduction cool objects such as superconducting coils by solid thermal conduction through heat transfer components made of good thermal conductors.

[0003] In this cooling method, flexible heat transfer materials are used in part to alleviate thermal stress caused by differences in thermal contraction between the cylinder of the cryogenic refrigerator and the structural materials. Multiple heat transfer materials are connected by bolting or welding, etc., to form a heat path from the object to be cooled to the cooling stage of the cryogenic refrigerator.

[0004] 6, at the connection points between the heat transfer members, the surface of the heat transfer member 100 at the connection portion between the low-temperature side heat transfer member 101 and the high-temperature side heat transfer member 102 has minute irregularities, which creates minute voids 103 at the contact surfaces between the low-temperature side heat transfer member 101 and the high-temperature side heat transfer member 102, and these voids 103 hinder heat conduction. For this reason, the connection portions of the heat transfer members 100 may have a contact thermal resistance that is greater than the thermal resistance of the heat transfer members 100 themselves.

[0005] Generally, thermal contact resistance tends to decrease in inverse proportion to the actual contact area or pressing pressure. Therefore, an effective method for reducing thermal contact resistance is to reduce the gap 103 and increase the actual contact area. To achieve this, a method is used in which a surface pressure sufficient to plastically deform the minute irregularities on the surface is applied, or, as shown in Figure 7, a contact heat transfer medium 104, such as thermally conductive grease or a soft metal sheet to promote heat transfer, is placed on the contact surface to fill the gap 103 and increase the actual contact area. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-192253 [Patent Document 2] Patent No. 5520740 Summary of the Invention [Problem to be solved by the invention]

[0007] Bolt fastening is a commonly used method for connecting heat transfer members. In addition, Patent Document 1 discloses a structure in which two members with different thermal shrinkage rates are connected by a fitting structure, and Patent Document 2 discloses a structure in which a heat shrink ring with a large thermal shrinkage rate is arranged on the outer side of the fitting structure for connection.

[0008] As described above, in the heat conduction at the connection between the low-temperature-side heat transfer member 101 and the high-temperature-side heat transfer member 102 in the heat transfer member 100, the heat flow is restricted by the gaps 103 formed by the minute irregularities on the contact surface, resulting in contact thermal resistance. In order to reduce this contact thermal resistance, a contact heat transfer medium 104 such as thermally conductive grease or a soft metal sheet can be placed on the contact surface to fill the gaps 103. However, in the cryogenic temperature range, the thermal conductivity of the contact heat transfer medium 104 is extremely low compared to the heat transfer member 100 made of high-purity aluminum or copper, and therefore the contact heat transfer medium 104 cannot fully exert its effect as the contact heat transfer medium 104.

[0009] Another method for reducing thermal contact resistance is to apply strong surface pressure to reduce the gap 103 by promoting deformation of the minute irregularities on the contact surface. However, when applying pressure by tightening bolts, which is typically done, pressure is applied only to the area around the bolt hole, known as the Letschel cone of influence. As a result, as shown in Figure 8, undulations occur in the low-temperature side heat transfer member 101 and the high-temperature side heat transfer member 102, which are made of aluminum or copper, resulting in contact only around the bolt 105, which creates a problem of inability to reduce thermal contact resistance.

[0010] Furthermore, in the fitting structure of Patent Document 1, no surface pressure is applied to the joint at room temperature, which increases thermal resistance and may lead to the risk of separation in some cases. In the fitting structure of Patent Document 2, a heat shrink ring is used for fastening, but similarly, clearance occurs at room temperature, which increases contact thermal resistance.

[0011] The embodiments of the present invention have been made in consideration of the above circumstances, and aim to provide a heat transfer member connection structure for a cryogenic device and a cryogenic device that can reduce the contact thermal resistance of the connection portion of the heat transfer member. [Means for solving the problem]

[0012] In an embodiment of the present invention, a heat transfer member connection structure for a cryogenic device is a heat transfer member connection structure for a cryogenic device in which an object to be cooled is conductively cooled to a cryogenic temperature via a heat transfer member by a cryogenic refrigerator, the heat transfer member comprising a low-temperature side heat transfer member connected to the cryogenic refrigerator and a high-temperature side heat transfer member connected to the object to be cooled, a convex portion is formed on one end of the high-temperature side heat transfer member and a concave portion of a shape that conforms to the shape of the convex portion is formed on the other end of the high-temperature side heat transfer member and the low-temperature side heat transfer member, and the high-temperature side heat transfer member and the low-temperature side heat transfer member are configured such that, under the same temperature conditions of the high-temperature side heat transfer member and the low-temperature side heat transfer member during manufacture, the inner diameter of the concave portion is set to be equal to or smaller than the outer diameter of the convex portion, and the convex portion is fitted into the concave portion by heating or cooling, thereby connecting the high-temperature side heat transfer member and the low-temperature side heat transfer member.

[0013] The cryogenic device in an embodiment of the present invention is characterized by comprising a cryogenic refrigerator, a heat transfer member configured by applying the heat transfer member connection structure of the cryogenic device described in the embodiment and thermally connecting the cryogenic refrigerator and the object to be cooled, and a vacuum container that stores the cryogenic refrigerator, the object to be cooled, and the heat transfer member. [Effects of the Invention]

[0014] According to the embodiment of the present invention, the contact thermal resistance of the connection portion of the heat transfer member can be reduced. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a schematic cross-sectional view showing the overall configuration of a cryogenic device having a heat transfer member to which a heat transfer material connection structure for a cryogenic device according to a first embodiment is applied. [Figure 2] FIG. 2 is a cross-sectional view showing the heat transfer member of FIG. [Figure 3] 3 is a cross-sectional view showing a modified example of the heat transfer member of FIG. 2. [Figure 4] FIG. 10 is a cross-sectional view showing a heat transfer member to which the heat transfer member connection structure of the cryogenic device according to the second embodiment is applied. [Figure 5] 10 is a graph showing the thermal expansion coefficient of materials including a base material constituting a heat transfer member to which the heat transfer member connection structure of the cryogenic device according to the third embodiment is applied. [Figure 6] FIG. 4 is a conceptual diagram illustrating minute gaps on the contact surface of the heat transfer member. [Figure 7] FIG. 10 is a conceptual diagram showing a state in which a contact heat transfer medium is interposed between the contact surfaces of the heat transfer members. [Figure 8] 10A and 10B are conceptual diagrams illustrating undulations that occur when heat transfer members are joined by bolt fastening. DETAILED DESCRIPTION OF THE INVENTION

[0016] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. [A] First embodiment (Figs. 1 to 3) Fig. 1 is a schematic cross-sectional view showing the overall configuration of a cryogenic device having a heat transfer member to which the heat transfer material connection structure for a cryogenic device according to the first embodiment is applied. The cryogenic device 10 shown in Fig. 1 conduction-cools a superconducting coil 11 and a heat shield 14, which are objects to be cooled, to a cryogenic temperature of 77 K or less by a cryogenic refrigerator 12, and is configured with a vacuum vessel 13, the cryogenic refrigerator 12, the heat shield 14, a first heat transfer member 15, and a second heat transfer member 16.

[0017] The vacuum vessel 13 supports the cryocooler 12 and houses a heat shield 14, which houses the superconducting coil 11. The cryocooler 12 is a Gifford-McMahon (GM) refrigerator or a pulse tube refrigerator, and has a first cooling stage 21 that generates cold at about 20 K to 50 K, and a second cooling stage 22 that generates cold at about 3 K to 30 K. The first cooling stage 21 is disposed within the vacuum vessel 13, and the second cooling stage 22 is disposed within the heat shield 14.

[0018] First heat transfer member 15 thermally connects first cooling stage 21 of cryocooler 12 to heat shield 14 as the object to be cooled, and heat shield 14 is conduction-cooled to a cryogenic temperature (approximately 20 K to 50 K) by first cooling stage 21 via first heat transfer member 15. Second heat transfer member 16 thermally connects second cooling stage 22 of cryocooler 12 to superconducting coil 11 as the object to be cooled, and superconducting coil 11 is conduction-cooled to a cryogenic temperature (approximately 3 K to 30 K) by second cooling stage 22 via second heat transfer member 16.

[0019] In the following, in the first to third embodiments, the configuration and effects of the second heat transfer member 16 will be described, but the first heat transfer member 15 may also have a configuration similar to that of the second heat transfer member 16, in which case the first heat transfer member 15 will also have the same effects as the second heat transfer member 16.

[0020] The second heat transfer member 16 is configured to include a low-temperature-side heat transfer member 17 thermally connected to the second cooling stage 22 of the cryocooler 12, and a high-temperature-side heat transfer member 18 thermally connected to the superconducting coil 11. As shown in FIG. 2, a convex portion 23 is formed on one of the low-temperature-side heat transfer member 17 and the high-temperature-side heat transfer member 18, for example, on the high-temperature-side heat transfer member 18, and a hole 24 is formed as a concave portion on the other of the low-temperature-side heat transfer member 17 and the high-temperature-side heat transfer member 18, for example, on an end portion 27 (described later) having rigidity of the low-temperature-side heat transfer member 17. The concave portion is not limited to a hole penetrating the end portion 27 as shown in FIG. 2, but may also be a hole 25 bored out of, for example, the bottom portion of the end portion 27 as shown in FIG. 3. The hole 24 and the hole 25 are formed in a shape that follows the shape of the convex portion 23 of the high-temperature-side heat transfer member 18, for example, a shape that fits the convex portion 23.

[0021] The protrusions 23 of the high-temperature-side heat transfer member 18 are preferably formed by machining the base material of the high-temperature-side heat transfer member 18, but the protrusions 23 may also be manufactured as separate members from the main body of the high-temperature-side heat transfer member 18 and then joined to the main body of the high-temperature-side heat transfer member 18 by welding or fastened with bolts or the like. The base material constituting the high-temperature-side heat transfer member 18 including the protrusions 23 is desirably a material with high thermal conductivity, particularly at cryogenic temperatures, such as pure aluminum (purity of 99.5% or more) containing high-purity aluminum (purity of 99.99% or more), or pure copper (purity of 99.9% or more) containing high-purity copper (purity of 99.96% or more).

[0022] Low-temperature-side heat transfer member 17 is constructed by joining, for example, rigid end portion 27 to one end of flexible member 26 and end portion 28 to the other end. Flexible member 26 is provided to relieve thermal stress caused by the difference in thermal contraction between cryogenic refrigerator 12 and superconducting coil 11, which is the object to be cooled, and is constructed from a plurality of foils or thin wires. End portion 28 of low-temperature-side heat transfer member 17 is attached to second cooling stage 22 of cryogenic refrigerator 12.

[0023] The base material constituting the flexible member 26 is preferably a material with high thermal conductivity at cryogenic temperatures, such as a foil or thin wire of pure aluminum (purity 99.5% or higher) containing high-purity aluminum (purity 99.99% or higher), a foil or thin wire of pure copper (purity 99.9% or higher) containing high-purity copper (purity 99.96% or higher), or a foil or thin wire made of carbon fiber. The flexible member 26 may also be formed by using foils or thin wires of the above-mentioned aluminum, copper, and carbon fiber in parallel.

[0024] The base material constituting the ends 27 and 28 of the low-temperature side heat transfer member 17 is also preferably a material with high thermal conductivity at cryogenic temperatures, such as pure aluminum (purity of 99.5% or more) containing high-purity aluminum (purity of 99.99% or more), or pure copper (purity of 99.9% or more) containing high-purity copper (purity of 99.96% or more).

[0025] Incidentally, under the same temperature conditions for the high-temperature side heat transfer member 18 and the low-temperature side heat transfer member 17 during manufacturing of the second heat transfer member 16 at room temperature, the inner diameter of the holes 24 or holes 25 in the low-temperature side heat transfer member 17 is set to a dimension equal to or smaller than the outer diameter of the protrusions 23 of the high-temperature side heat transfer member 18. Then, by fitting the protrusions 23 into the holes 24 or holes 25 by heating or cooling, the low-temperature side heat transfer member 17 and the high-temperature side heat transfer member 18 are connected to manufacture the second heat transfer member 16. In other words, the protrusions 23 of the high-temperature side heat transfer member 18 are cooled to a low temperature, and the outer diameter of the protrusions 23 is reduced by thermal contraction, and then the protrusions 23 are fitted into the holes 24 or holes 25 of the low-temperature side heat transfer member 17. Alternatively, the end 27 of the low-temperature side heat transfer member 17 is heated, and the inner diameter of the hole 24 or hole 25 is enlarged by thermal expansion, and the protrusion 23 of the high-temperature side heat transfer member 18 is fitted into this hole 24 or hole 25.

[0026] Therefore, the holes 24 or holes 25 of the low-temperature side heat transfer member 17, which serve as the connecting portions of the second heat transfer member 16, and the protrusions 23 of the high-temperature side heat transfer member 18 are in a state where uniform pressure acts on the side surfaces (outer peripheral surfaces) of the protrusions 23 due to thermal stress of the end portions 27 of the low-temperature side heat transfer member 17. As a result, the end portions 27 of the low-temperature side heat transfer member 17 and the protrusions 23 of the high-temperature side heat transfer member 18 are connected without using bolts, welding, soldering, or the like.

[0027] As configured as above, the first embodiment provides the following effects (1) and (2). (1) The high-temperature-side heat transfer member 18 and the low-temperature-side heat transfer member 17 constituting the second heat transfer member 16 have a protrusion 23 formed on one side (for example, the high-temperature-side heat transfer member 18) and a hole 24 or a hole 25 formed in an end 27 of the other side (for example, the low-temperature-side heat transfer member 17) that conforms to the shape of the protrusion 23. Under the same temperature conditions as when the second heat transfer member 16 is manufactured, the inner diameter of the hole 24 or the hole 25 is set to be equal to or smaller than the outer diameter of the protrusion 23. Then, the high-temperature-side heat transfer member 18 and the low-temperature-side heat transfer member 17 are connected by fitting the protrusion 23 into the hole 24 or the hole 25 by heating or cooling, thereby manufacturing the second heat transfer member 16.

[0028] Therefore, in the connected state of high-temperature-side heat transfer member 18 and low-temperature-side heat transfer member 17, even before cooling by cryogenic refrigerator 12, uniform pressure due to thermal stress acts on the contact surface between protrusion 23, which is the connecting portion, and hole 24 or hole 25, so that a sufficient contact area can be secured at the contact surface, thereby reducing contact thermal resistance. As a result, the temperature difference between cryogenic refrigerator 12 and superconducting coil 11 can be maintained low.

[0029] (2) The second heat transfer member 16 is manufactured by fitting the protrusions 23 of the high-temperature side heat transfer member 18 into the holes 24 or holes 25 of the low-temperature side heat transfer member 17 by heating or cooling to connect the low-temperature side heat transfer member 17 and the high-temperature side heat transfer member 18. Therefore, in the second heat transfer member 16, uniform pressure due to thermal stress acts on the contact surface between the protrusions 23 and the holes 24 or holes 25, which are the connection parts, across the entire temperature range in operation of the cryogenic refrigerator 12. As a result, the second heat transfer member 16 can reduce the contact thermal resistance of the contact surface at the connection part across the entire temperature range in operation of the cryogenic refrigerator 12, without causing the low-temperature side heat transfer member 17 and the high-temperature side heat transfer member 18 to fall off.

[0030] [B] Second embodiment (Fig. 4) 4 is a cross-sectional view showing a heat transfer member to which the heat transfer member connection structure for a cryogenic device according to the second embodiment is applied. In the second embodiment, the same parts as those in the first embodiment are denoted by the same reference numerals as those in the first embodiment, and the description thereof will be simplified or omitted.

[0031] The second heat transfer member 32 (FIG. 4) of the cryogenic device 30 (FIG. 1) of the second embodiment differs from that of the first embodiment in that a flexible metal plating layer (metal plating layer 33) having a Mohs hardness of less than 2.9 is provided on at least a part of the outer peripheral surface of the protrusion 23 of the high-temperature-side heat transfer member 18 and the inner peripheral surface of the hole 24 or hole 25 (e.g., hole 24) of the low-temperature-side heat transfer member 17.

[0032] The softer the base material, the greater the microscopic contact area and the lower the contact thermal resistance. When the high-temperature-side heat transfer member 18 and the low-temperature-side heat transfer member 17 of the second heat transfer member 32 are made of aluminum, for example, their Vickers hardness is approximately 200 to 300 MPa, and their Mohs hardness, which is a measure of surface hardness, is 2.9. The metal plating layer 33 is preferably made of a material that is at least softer than aluminum, such as gold, silver, tin, or indium. In the second embodiment, the metal plating layer 33 is formed of indium, which has a Vickers hardness of approximately 9 MPa and a Mohs hardness of 1.2, making it the softest material. However, other materials such as gold, silver, and tin may also be used. Furthermore, electrolytic plating is preferred as a method for forming the metal plating layer 33, but ultrasonic soldering or cold spray welding may also be used.

[0033] As configured as above, the second embodiment also achieves the same effects as the effects (1) and (2) of the first embodiment, and also achieves the following effect (3).

[0034] (3) In the second heat transfer member 32, the inner diameter of the holes 24 or holes 25 of the low-temperature side heat transfer member 17 is set to be equal to or smaller than the outer diameter of the protrusions 23 of the high-temperature side heat transfer member 18 under the same temperature conditions at room temperature during manufacture, and the protrusions 23 are fitted into the holes 24 or holes 25 by heating or cooling, thereby connecting the low-temperature side heat transfer member 17 and the high-temperature side heat transfer member 18 to manufacture the second heat transfer member 32. For this reason, pressure due to thermal stress is generated on the inner circumferential surface of the holes 24 or holes 25 of the low-temperature side heat transfer member 17 and the outer circumferential surface of the protrusions 23 of the high-temperature side heat transfer member 18, which are in contact with each other.

[0035] Therefore, the metal plating layer 33 provided on these contact surfaces is deformed more than the low-temperature side heat transfer member 17 and the high-temperature side heat transfer member 18 due to the pressure caused by the thermal stress before cooling by the cryogenic refrigerator 12 begins, and is able to fill minute gaps on the contact surfaces. As a result, the contact thermal resistance of the contact surface between the low-temperature side heat transfer member 17 and the high-temperature side heat transfer member 18 in the second heat transfer member 32 (the contact surface between the holes 24 or holes 25 and the protrusions 23) can be further reduced.

[0036] [C] Third embodiment (Fig. 5) 5 is a graph showing the thermal expansion coefficients of materials including the base material constituting the heat transfer member to which the heat transfer member connection structure for a cryogenic device according to the third embodiment is applied. In this third embodiment, parts similar to those in the first embodiment are assigned the same reference numerals as in the first embodiment, and the description thereof will be simplified or omitted.

[0037] The second heat transfer member 42 (FIGS. 2 and 3) of the cryogenic device 40 (FIG. 1) of the third embodiment differs from that of the first embodiment in that the convex portion 43 of the high-temperature side heat transfer member 18 is made of pure copper (purity of 99.9% or more), and the rigid end portion 47 of the low-temperature side heat transfer member 17, where the hole 24 or the hole 25 is formed, is made of pure aluminum (purity of 99.5% or more).

[0038] As shown in Figure 5, it is known that the coefficient of thermal expansion (coefficient of thermal contraction) of aluminum is greater than that of copper. By forming the rigid end 47 of the low-temperature-side heat transfer member 17 from aluminum, which has a large coefficient of thermal expansion, this end 47 tends to thermally contract by approximately 0.1% (1‰) more than the convex portion 43 of the high-temperature-side heat transfer member 18 when the second heat transfer member 42 is cooled by operation of the cryogenic refrigerator 12. For this reason, when the second heat transfer member 42 is cooled by operation of the cryogenic refrigerator 12, thermal stress greater than that at room temperature is generated at each contact surface between the hole 24 or hole 25 of the end 47 of the low-temperature-side heat transfer member 17 and the convex portion 43 of the high-temperature-side heat transfer member 18.

[0039] As configured as above, the third embodiment provides the following effect (4) in addition to the effects (1) and (2) of the first embodiment.

[0040] (4) The convex portion 43 of the high-temperature-side heat transfer member 18 of the second heat transfer member 42 is made of pure copper, and the end portion 47 of the low-temperature-side heat transfer member 17 is made of pure aluminum, which has a higher thermal expansion coefficient (thermal contraction coefficient) than pure copper. Therefore, when the convex portion 43 is fitted into the hole 24 or hole 25 of the end portion 47, the pressure due to thermal stress at the contact surface between the hole 24 or hole 25 and the convex portion 43 is larger due to thermal contraction of the pure aluminum end portion 47 during cooling of the second heat transfer member 42 by operation of the cryogenic refrigerator 12 than during manufacturing at room temperature, in which the low-temperature-side heat transfer member 17 and the high-temperature-side heat transfer member 18 are connected to manufacture the second heat transfer member 42. As a result, during operation of the cryogenic refrigerator 12, the contact thermal resistance of the contact surface between the low-temperature-side heat transfer member 17 and the high-temperature-side heat transfer member 18 in the second heat transfer member 42 (the convex portion 43 and the hole 24 or hole 25 of the end portion 47) can be further reduced.

[0041] Although several embodiments of the present invention have been described above, these embodiments are presented as examples and are not intended to limit the scope of the invention. These embodiments can be implemented in various other forms, and various omissions, substitutions, changes, and combinations can be made without departing from the spirit of the invention. Furthermore, such substitutions, changes, and combinations are included in the scope and spirit of the invention, and are also included in the inventions and their equivalents as set forth in the claims. [Explanation of symbols]

[0042] 10... cryogenic device, 11... superconducting coil (object to be cooled), 12... cryogenic refrigerator, 13... vacuum vessel, 14... heat shield (object to be cooled), 15... first heat transfer member, 16... second heat transfer member, 17... low-temperature side heat transfer member, 18... high-temperature side heat transfer member, 23... convex portion, 24... hole (recess), 25... hole (recess), 27... end, 30... cryogenic device, 32... second heat transfer member, 33... metal plating layer, 40... cryogenic device, 42... second heat transfer member, 43... convex portion, 47... end

Claims

1. A heat transfer member connection structure for a cryogenic device that conducts and cools an object to cryogenic temperatures using a cryogenic refrigerator via a heat transfer member, the heat transfer member comprises a low-temperature side heat transfer member connected to the cryogenic refrigerator and a high-temperature side heat transfer member connected to the object to be cooled, a convex portion is formed on one end of the high-temperature side heat transfer member and the low-temperature side heat transfer member, and a concave portion having a shape that conforms to the shape of the convex portion is formed on an end of the other end of the high-temperature side heat transfer member and the low-temperature side heat transfer member, an inner diameter of the recessed portion is set to be equal to or smaller than an outer diameter of the protruding portion under the same temperature conditions of the high-temperature side heat transfer member and the low-temperature side heat transfer member during manufacturing; A heat transfer member connection structure for a cryogenic device, characterized in that the high-temperature side heat transfer member and the low-temperature side heat transfer member are connected by fitting the convex portion into the concave portion by heating or cooling.

2. 2. The heat transfer member connection structure for a cryogenic device according to claim 1, wherein at least one of the protrusion and the end portion where the recess is formed is made of pure aluminum or pure copper.

3. 3. The heat transfer member connection structure for a cryogenic device according to claim 1, wherein at least a portion of the outer circumferential surface of the protrusion and the inner circumferential surface of the recess are plated with a metal having a Mohs hardness of less than 2.

9.

4. 2. The heat transfer member connection structure for a cryogenic device according to claim 1, wherein the protrusion is made of pure copper, and the end portion where the recess is formed is made of pure aluminum.

5. A cryogenic refrigerator, a heat transfer member that is configured by applying the heat transfer member connection structure of claim 1 or 4 to thermally connect the cryogenic refrigerator and an object to be cooled; a vacuum vessel for storing the cryogenic refrigerator, the object to be cooled, and the heat transfer member;

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