Cryogenic refrigeration machine and cold head mounting structure

Abstract

To suppress tilting of a cold head with respect to a cold head mounting structure.SOLUTION: A cryogenic refrigeration machine 20 includes: a cold head 22 that can be inserted in a sleeve 50, and includes a first cooling stage 30, a second cooling stage 34 cooled at a temperature lower than the first cooling stage 30 and a second cylinder 32 for connecting the first cooling stage 30 and the second cooling stage 34; and a slide guide 62 that is provided at the second cylinder 32 or at the second cooling stage 34 so as to slide with the sleeve 50 when the cold head 22 is inserted into the sleeve 50.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a cryogenic refrigerator and a cold head mounting structure. [Background technology]

[0002] Cryogenic refrigerators are used to cool equipment that operates at extremely low temperatures, such as superconducting devices. The cryogenic refrigerator is installed in a vacuum vessel that contains the object to be cooled (e.g., a superconducting coil). During the long-term operation of such cryogenic equipment, maintenance such as inspection, repair, and replacement of the cryogenic refrigerator may be required.

[0003] It is known to mount the cold head of a cryogenic refrigerator on a vacuum vessel via a so-called maintenance sleeve. The maintenance sleeve is configured to keep the vacuum vessel airtight and extends from the wall of the vacuum vessel to the inside, and the cold head is removably mounted inside the sleeve. An operator can perform maintenance on the cold head by lifting the cold head somewhat out of the maintenance sleeve and releasing the thermal contact between the cold head and the maintenance sleeve. The cold head is heated to a temperature suitable for the maintenance work, for example room temperature, and is recooled after the work is completed. Meanwhile, the object to be cooled can be kept at a low temperature by releasing the contact of the cold head. Therefore, this maintenance method can shorten the time required for recooling the object to be cooled, and can shorten the time required for maintenance, compared to the case where the object to be cooled is heated to room temperature together with the cold head and then maintenance is performed on the cold head. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2018-84347 A Summary of the Invention [Problem to be solved by the invention]

[0005] The present inventors have studied the above-mentioned sleeve-type cold head mounting structure and independently recognized the following problem. When an operator mounts a cold head, the worker pays close attention to ensure that the cold head is in the correct position (e.g., that the central axis of the cold head is aligned vertically). However, it has been found that in some cases, the cold head is mounted on the cold head mounting structure with a slight inclination from the correct position. The mounted cold head is pressed against the mounting structure with a strong force to achieve good thermal contact. Therefore, the inclination of the cold head makes the stress distribution acting on the cold head non-uniform, leading to distortion of the cold head, which may undesirably adversely affect the refrigeration capacity of the cryogenic refrigerator. In addition, the inclination of the cold head may affect the contact state between the cold head and the mounting structure, leading to an increase in the contact thermal resistance between the two.

[0006] It is an exemplary object of an embodiment of the present invention to provide a technique for suppressing tilt of a cold head relative to a cold head mounting structure. [Means for solving the problem]

[0007] According to one embodiment of the present invention, a cryogenic refrigerator includes a cold head insertable into a cold head accommodating sleeve, the cold head including a first cooling stage, a second cooling stage cooled to a lower temperature than the first cooling stage, and a cylinder connecting the first cooling stage and the second cooling stage, and a sliding guide provided on the cylinder or the second cooling stage so as to slide against the cold head accommodating sleeve when the cold head is inserted into the cold head accommodating sleeve.

[0008] According to one embodiment of the present invention, a cryogenic refrigerator includes a first cooling stage, a second cooling stage that is cooled to a lower temperature than the first cooling stage, a cylinder that connects the first cooling stage and the second cooling stage, and a sliding guide attached to the cylinder.

[0009] According to one embodiment of the present invention, a cold head mounting structure includes a cold head accommodating sleeve capable of receiving a cold head of a cryogenic refrigerator, the cold head accommodating sleeve having a first heat transfer stage, a second heat transfer stage cooled to a lower temperature than the first heat transfer stage, and a sleeve member connecting the first heat transfer stage and the second heat transfer stage, and a sliding support provided on the first heat transfer stage, the sleeve member or the second heat transfer stage so as to slide against the cold head when the cold head is inserted into the cold head accommodating sleeve. Effect of the Invention

[0010] According to the present invention, it is possible to suppress inclination of the cold head with respect to the cold head mounting structure. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 is a schematic diagram of a cryogenic apparatus and a cold head mounting structure according to an embodiment. [Diagram 2] FIG. 1 is a schematic diagram of a cryogenic apparatus and a cold head mounting structure according to an embodiment. [Diagram 3] 3(a), 3(b), and 3(c) are diagrams illustrating schematic configurations of the sliding guide and the sliding support according to the embodiment. [Figure 4] 4(a) and 4(b) are perspective views illustrating schematic views of other examples of the sliding guide according to the embodiment. [Diagram 5] 5(a) and 5(b) are diagrams illustrating schematic diagrams of another example of the sliding guide according to the embodiment. [Figure 6] 11A and 11B are diagrams illustrating another example of the sliding guide in the embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, the embodiments for carrying out the present invention will be described in detail with reference to the drawings. In the description and drawings, the same or equivalent components, members, and processes are given the same reference numerals, and duplicated descriptions are omitted as appropriate. The scale and shape of each part shown in the drawings are set for convenience in order to facilitate the description, and are not to be interpreted as being limiting unless otherwise specified. The embodiments are merely examples, and do not limit the scope of the present invention in any way. All features and combinations thereof described in the embodiments are not necessarily essential to the invention.

[0013] Figures 1 and 2 are schematic diagrams showing a cryogenic device and a cold head mounting structure according to an embodiment. Figure 1 shows a state in which an object to be cooled in the cryogenic device is thermally coupled to a cold head of a cryogenic refrigerator provided in the cryogenic device, and Figure 2 shows a state in which the cold head and the object to be cooled are thermally released due to the movement of the cold head.

[0014] The cryogenic device 10 is installed in a vacuum vessel 12, also called a cryostat, and is used as a cooling source that provides a cryogenic environment within the vacuum vessel 12. A cooled object 14 that is cooled by the cryogenic device 10 is placed within the vacuum vessel 12. The cryogenic device 10, together with the vacuum vessel 12 and the cooled object 14, may constitute a part of cryogenic application equipment. The cryogenic application equipment may be, for example, a single crystal pulling device, an NMR system, an MRI system, an accelerator such as a cyclotron, a high-energy physics system such as a nuclear fusion system, or other high magnetic field application equipment, in which case the cooled object 14 may be a superconducting coil.

[0015] The cryogenic device 10 includes a cryogenic refrigerator 20 having a cold head 22 and a compressor 24, and a cold head receiving sleeve (hereinafter also simply referred to as a sleeve) 50 as a cold head mounting structure. The sleeve 50 is installed in the vacuum vessel 12 so as to be combined with the vacuum vessel 12 to define a vacuum region 13 within the vacuum vessel 12. The cold head 22 is mounted on the sleeve 50 while being inserted into the sleeve 50. An airtight region 18 isolated from an ambient environment 16 is formed between the cold head 22 and the sleeve 50. The ambient environment 16 is, for example, an atmospheric pressure environment at room temperature. The airtight region 18 may be evacuated to a vacuum.

[0016] The compressor 24 of the cryogenic refrigerator 20 is provided to circulate a working gas (e.g., helium gas) through the cryogenic refrigerator 20. The compressor 24 is disposed in the ambient environment 16. The compressor 24 is configured to supply a high-pressure working gas to the cold head 22, and to recover from the cold head 22 the low-pressure working gas that has been decompressed by adiabatic expansion in an expansion space within the cold head 22, and to re-pressurize the working gas.

[0017] The cryogenic refrigerator 20 is illustratively a two-stage Gifford-McMahon (GM) refrigerator. Thus, the cold head 22 includes a mounting flange 26, a first cylinder 28, a first cooling stage 30, a second cylinder 32, and a second cooling stage 34. These components of the cold head 22 are arranged in this order along a central axis C of the cold head 22. The mounting flange 26 is disposed in the ambient environment 16, and the first cylinder 28, the first cooling stage 30, the second cylinder 32, and the second cooling stage 34 are disposed in the hermetic region 18.

[0018] The first cylinder 28 connects the mounting flange 26 to the first cooling stage 30, and the second cylinder 32 connects the first cooling stage 30 to the second cooling stage 34. Typically, the first cylinder 28 and the second cylinder 32 are hollow cylindrical members extending coaxially with the central axis C of the cold head 22, and the first cylinder 28 has a larger diameter than the second cylinder 32. The mounting flange 26, the first cylinder 28, and the second cylinder 32 are formed of a metal such as stainless steel.

[0019] The first cooling stage 30 is fixed to an end of the first cylinder 28 on the axially opposite side to the mounting flange 26, and its axial length is shorter than that of the first cylinder 28. The second cooling stage 34 is fixed to an end of the second cylinder 32 on the axially opposite side to the first cooling stage 30, and its axial length is shorter than that of the second cylinder 32. The first cooling stage 30 and the second cooling stage 34 typically have a cylindrical outer shape coaxial with the central axis C of the cold head 22, and the first cooling stage 30 has a larger diameter than the second cooling stage 34. The first cooling stage 30 and the second cooling stage 34 are formed of a highly thermally conductive metal such as copper (e.g., pure copper) or other thermally conductive material. The thermal conductivity of the thermally conductive material forming the cooling stage is higher than that of the material forming the cylinder.

[0020] Furthermore, the cold head 22 includes a first displacer 36 and a second displacer 38 connected to each other at their ends, and a drive unit 40 that drives these displacers in the axial direction.

[0021] The first displacer 36 and the second displacer 38 extend coaxially with the central axis C of the cold head 22, and are arranged axially movably in the first cylinder 28 and the second cylinder 32, respectively. A regenerator material is built in the first displacer 36 and the second displacer 38. A first expansion space for the working gas is formed between the first displacer 36 and the first cooling stage 30 in the first cylinder 28, and a second expansion space for the working gas is formed between the second displacer 38 and the second cooling stage 34 in the second cylinder 32.

[0022] The drive unit 40 includes a drive motor 40a that drives the cold head 22, and a drive unit housing 40b to which the drive motor 40a is attached. The drive motor 40a is, for example, an electric motor that outputs rotation. As shown in the figure, the drive motor 40a is attached to the drive unit housing 40b on one side with respect to the central axis C of the cold head 22 (and the sleeve 50). The drive unit housing 40b is provided on the mounting flange 26. The drive unit housing 40b is fixed to the mounting flange 26 (main flange 42 described later) so as to maintain airtightness inside the cold head 22. The drive unit housing 40b accommodates a motion conversion mechanism such as a Scotch yoke mechanism that converts the rotation of the drive motor 40a into linear reciprocating motion. This motion conversion mechanism is connected to the first displacer 36 on the axially opposite side to the second displacer 38. Therefore, the first displacer 36 and the second displacer 38 can be reciprocated in the axial direction via the motion conversion mechanism by driving the electric motor.

[0023] The drive unit 40 also includes a built-in valve for controlling the pressure of the expansion space. The pressure control valve is configured to alternately switch between supplying high-pressure working gas from the compressor 24 to the expansion space via the regenerator material and recovering low-pressure working gas from the expansion space to the compressor 24 via the regenerator material. The drive unit 40 is configured to appropriately synchronize the volume change of the expansion space caused by the axial reciprocating motion of the first displacer 36 and the second displacer 38 with the pressure change of the expansion space caused by the pressure control valve. By such an operation of the cryogenic refrigerator 20, the first cooling stage 30 is cooled to a first cooling temperature, for example, 30K to 80K, and the second cooling stage 34 is cooled to a second cooling temperature, for example, 3K to 20K, which is lower than the first cooling temperature.

[0024] The drive unit 40 is disposed in the ambient environment 16 together with the mounting flange 26, and is fixed to the mounting flange 26 on the side opposite the first cylinder 28 by fastening members (not shown), such as bolts. When performing maintenance on the cryogenic refrigerator 20, the drive unit 40 can be released from the mounting flange 26. This allows the first displacer 36 and the second displacer 38 to be pulled out of the first cylinder 28 and the second cylinder 32, respectively, and the drive unit 40 can be removed from the cold head 22 together with the first displacer 36 and the second displacer 38.

[0025] When the cryogenic refrigerator 20 is of a two-stage type, the sleeve 50 is also configured of a two-stage type correspondingly. Thus, the sleeve 50 includes a sleeve-side flange 52, a first sleeve member 54, a first heat transfer stage 56, a second sleeve member 58, and a second heat transfer stage 60. These components of the sleeve 50 are arranged along the central axis C of the cold head 22 in the order described above.

[0026] The first sleeve member 54 connects the sleeve side flange 52 to the first heat transfer stage 56, and the second sleeve member 58 connects the first heat transfer stage 56 to the second heat transfer stage 60. The first sleeve member 54 and the second sleeve member 58 are hollow cylindrical members extending coaxially with the central axis C of the cold head 22, and the first sleeve member 54 has a larger diameter than the second sleeve member 58. Thus, the central axis C of the sleeve 50 coincides with the central axis C of the cold head 22. The sleeve side flange 52, the first sleeve member 54 and the second sleeve member 58 are formed of a metal such as stainless steel.

[0027] The first sleeve member 54 and the second sleeve member 58 are disposed so as to surround the first cylinder 28 and the second cylinder 32, respectively. The diameter of the first sleeve member 54 is somewhat larger than the diameter of the first cylinder 28, and there is a gap between the first sleeve member 54 and the first cylinder 28, so they do not come into contact with each other. Similarly, the diameter of the second sleeve member 58 is somewhat larger than the diameter of the second cylinder 32, and there is a gap between the second sleeve member 58 and the second cylinder 32, so they do not come into contact with each other.

[0028] The first heat transfer stage 56 is fixed to an end of the first sleeve member 54 on the axially opposite side to the sleeve-side flange 52, and the second heat transfer stage 60 is fixed to an end of the second sleeve member 58 on the axially opposite side to the first heat transfer stage 56. An opening 56a is formed in the center of the first heat transfer stage 56, penetrating the first heat transfer stage 56 so as to connect the internal space of the first sleeve member 54 to the internal space of the second sleeve member 58. The second cylinder 32 and the second cooling stage 34 of the cold head 22 are inserted into the internal space of the second sleeve member 58 from this opening 56a. The first heat transfer stage 56 and the second heat transfer stage 60 are formed of a highly heat-conductive metal such as copper (e.g., pure copper) or other heat-conductive material. The thermal conductivity of the heat-conductive material forming the heat transfer stage is higher than that of the material forming the sleeve member.

[0029] The first heat transfer stage 56 is thermally coupled to the first cooling stage 30 through physical contact therewith. The second heat transfer stage 60 is thermally coupled to the second cooling stage 34 through physical contact therewith. In this embodiment, the contact surface between the heat transfer stage and the cooling stage is a flat surface. However, the cooling stage may have a non-flat surface such as a tapered surface, an inclined surface, or an uneven surface, and the heat transfer stage may have a non-flat surface corresponding to the non-flat surface. The heat transfer stage and the cooling stage may be in direct contact with each other, or may be in thermal contact with each other through a soft intervening layer, such as an indium sheet, that contributes to good heat transfer.

[0030] An object to be cooled other than the object to be cooled 14 (for example, a heat shield surrounding the object to be cooled 14) is attached to the outer surface of the first heat transfer stage 56 exposed to the vacuum region 13, or is thermally coupled to the object to be cooled via an appropriate heat transfer member. Thus, when the first cooling stage 30 is in contact with the first heat transfer stage 56, the first object to be cooled can be cooled to a first cooling temperature by the first cooling stage 30 via the first heat transfer stage 56. Also, the object to be cooled 14 is attached to the outer surface of the second heat transfer stage 60 exposed to the vacuum region 13, or is thermally coupled to the object to be cooled via an appropriate heat transfer member. Thus, when the second cooling stage 34 is in contact with the second heat transfer stage 60, the object to be cooled 14 can be cooled to a second cooling temperature by the second cooling stage 34 via the second heat transfer stage 60.

[0031] The sleeve side flange 52 is disposed in the surrounding environment 16 and is coupled to the mounting flange 26. As an example, the sleeve side flange 52 is fixed to an opening formed in the top plate of the vacuum vessel 12, and the first sleeve member 54 and the second sleeve member 58 extend from this opening into the vacuum vessel 12. Thus, the cold head 22 is installed in the vacuum vessel 12 with its central axis C parallel to the vertical direction, the drive unit 40 facing upward, and the cooling stage facing downward. However, the installation orientation of the cold head 22 is not limited to this vertical orientation, and it may be installed in other orientations such as horizontal or oblique. The sleeve 50 may be formed on any surface of the vacuum vessel 12, such as the side or bottom surface.

[0032] As an exemplary configuration, the sleeve-side flange 52 includes an annular first flange 52a to which the mounting flange 26 is attached, an annular second flange 52b fixed to the vacuum vessel 12, and a cylindrical outer tubular portion 52c connecting the first flange 52a and the second flange 52b. The first flange 52a, the second flange 52b, and the outer tubular portion 52c are arranged coaxially with the central axis C of the cold head 22. The second flange 52b extends radially outward from an end of the first sleeve member 54, the outer tubular portion 52c extends from the second flange 52b in the axially opposite direction to the first sleeve member 54, and the first flange 52a extends radially outward from an end of the outer tubular portion 52c in the axially opposite direction to the second flange 52b.

[0033] The mounting flange 26 is a combination of two flanges, a main flange 42 and a transition flange 44. The main flange 42 extends radially outward from an end of the first cylinder 28 axially opposite the first cooling stage 30. The main flange 42 may be formed integrally with the first cylinder 28.

[0034] The transition flange 44 is fixed to the main flange 42 and combined with the sleeve-side flange 52 to form an airtight region 18 between the sleeve 50 and the cold head 22. The transition flange 44 has an annular flange portion 44a and a cylindrical inner tube portion 44b. The flange portion 44a is fixed to the lower surface of the main flange 42 (the surface axially opposite to the drive portion 40) by a fastening member (not shown) such as a bolt, and faces the first flange 52a of the sleeve-side flange 52 with a gap in the axial direction. The inner tube portion 44b extends from the inner periphery of the flange portion 44a to the axially opposite side to the main flange 42, and is inserted into the outer tube portion 52c of the sleeve-side flange 52. The inner tube portion 44b surrounds the upper end portion of the first cylinder 28.

[0035] Between the cold head 22 and the sleeve 50, a seal member 46 is provided to seal the airtight region 18 from the ambient environment 16 of the vacuum vessel 12. The outer cylinder portion 52c of the sleeve side flange 52 is disposed adjacent to the outer side of the inner cylinder portion 44b of the transition flange 44. The diameter of the outer cylinder portion 52c is, for example, several mm larger than the diameter of the inner cylinder portion 44b, and there is a gap between the inner peripheral surface of the outer cylinder portion 52c and the outer peripheral surface of the inner cylinder portion 44b, so that they do not contact each other. A seal member 46 for maintaining the airtightness of the airtight region 18 is disposed between the outer cylinder portion 52c and the inner cylinder portion 44b. The seal member 46 is, for example, a seal member such as an O-ring disposed in a circumferential groove formed in the inner cylinder portion 44b. In the illustrated example, the seal member 46 is attached to the inner cylinder portion 44b, but may be attached to the outer cylinder portion 52c.

[0036] Flange fastening members 48, such as bolts, are provided at multiple locations on the mounting flange 26 so as to surround the drive unit 40 of the cold head 22. The flange fastening members 48 are threadedly engaged with bolt holes in the sleeve-side flange 52 through insertion holes or cutouts formed in the mounting flange 26, thereby fastening the mounting flange 26 to the sleeve-side flange 52. When the flange fastening members 48 are released from the fastening, the mounting flange 26 becomes movable in the axial direction along the main guide 70 relative to the sleeve-side flange 52.

[0037] In this embodiment, the cold head 22 includes a sliding guide 62. The sliding guide 62 is provided on the second cylinder 32 so as to slide with the sleeve 50 when the cold head 22 is inserted into the sleeve 50. The sliding guide 62 extends in the direction of the central axis C of the cold head 22 over at least a part of the entire axial length of the second cylinder 32 between the first cooling stage 30 and the second cooling stage 34. The sliding guide 62 has a cylindrical or annular shape and is arranged coaxially with the second cylinder 32. The sliding guide 62 is arranged radially outside the second cylinder 32 so as to surround the second cylinder 32. The outer diameter of the sliding guide 62 is larger than the outer diameter of the second cylinder 32. At least a part of the inner circumferential surface of the sliding guide 62 contacts the outer circumferential surface of the second cylinder 32.

[0038] The sliding guide 62 is attached to the second cylinder 32 by other appropriate fixing methods, such as adhesive bonding or welding. Alternatively, the sliding guide 62 may be fixed at one end to the first cooling stage 30 or the second cooling stage 34. For example, an outer flange provided at an end of the sliding guide 62 may be fixed to the first cooling stage 30 (or the second cylinder 32) by a fastening member such as a bolt.

[0039] The sleeve 50 may also include a sliding support 64. The sliding support 64 is provided on the second sleeve member 58 so as to slide with the sliding guide 62 of the cold head 22 when the cold head 22 is inserted into the sleeve 50. The sliding support 64 extends in the direction of the central axis C of the cold head 22 between the first heat transfer stage 56 and the second sleeve member 58, over at least a part of the entire axial length of the second sleeve member 58. The sliding support 64 has a cylindrical or annular shape, and is arranged coaxially with the second sleeve member 58. The sliding support 64 is arranged radially inside the second sleeve member 58 so as to be surrounded by the second sleeve member 58. The inner diameter of the sliding support 64 is smaller than the inner diameter of the second sleeve member 58. At least a part of the outer circumferential surface of the sliding support 64 contacts the inner circumferential surface of the second sleeve member 58.

[0040] The sliding support 64 is attached to the second sleeve member 58 by any other suitable fastening method, such as gluing, welding, or the like. Alternatively, the sliding support 64 may be fixed at one end to the first heat transfer stage 56 or to the second heat transfer stage 60.

[0041] The position and length of the sliding guide 62 in the direction of the central axis C are determined so that the outer circumferential surface of the sliding guide 62 contacts the inner circumferential surface of the sliding support 64 when the cold head 22 is attached to the sleeve 50. The outer diameter of the sliding guide 62 is equal to the inner diameter of the sliding support 64. The sliding guide 62 contacts the sliding support 64 in any of a first state in which the cold head 22 and the sleeve 50 are in thermal contact as shown in FIG. 1, a second state in which the cold head 22 and the sleeve 50 are released from thermal contact as shown in FIG. 2, and a third state between these two states. Thus, the sliding guide 62 can slide with the sliding support 64 when the cold head 22 moves axially relative to the sleeve 50.

[0042] In the illustrated example, the sliding guide 62 is provided over at least a portion of the axial middle portion of the second cylinder 32 (for example, in a range of ¼ to ¾ of the total axial length of the second cylinder 32). The sliding support 64 is provided over at least a portion of the upper portion of the second sleeve member 58 (a portion of the second sleeve member 58 closer to the first heat transfer stage 56 than the middle portion). The axial length of the sliding guide 62 is longer than the axial length of the sliding support 64. However, such axial positions and lengths of the sliding guide 62 and the sliding support 64 are merely examples and are not limited to these.

[0043] The material forming the sliding guide 62 and the sliding support 64 may be, for example, a synthetic resin material having good sliding properties, such as a fluororesin material such as polytetrafluoroethylene, engineering plastic, or other appropriate material. In order to reduce heat inflow to the cold head 22 through the sliding guide 62 and the sliding support 64 during operation of the cryogenic refrigerator 20, the material forming the sliding guide 62 and the sliding support 64 may be a heat insulating material or a material with low thermal conductivity (for example, a material with lower thermal conductivity than the material forming the second cylinder 32 or the second sleeve member 58). At least one of the sliding guide 62 and the sliding support 64 may be formed of such a material with high sliding properties and / or low thermal conductivity.

[0044] The outer diameter D2 (see FIG. 2) of the sliding guide 62 is smaller than or equal to the inner diameter D1 of the opening 56a of the first heat transfer stage 56 so that the sliding guide 62 can axially pass through the opening 56a of the first heat transfer stage 56 when the cold head 22 is inserted into the sleeve 50. In order for the sliding guide 62 to easily pass through the opening 56a, it is preferable that the outer diameter D2 of the sliding guide 62 is smaller than the inner diameter D1 of the opening 56a of the first heat transfer stage 56. Since the outer diameter D2 of the sliding guide 62 and the inner diameter of the sliding support 64 are equal, the inner diameter of the sliding support 64 is also smaller than the inner diameter D1 of the opening 56a of the first heat transfer stage 56.

[0045] Also, the inner diameter of the sliding support 64 is larger than or equal to the outer diameter D3 of the second cooling stage 34 so that the second cooling stage 34 can pass through the sliding support 64 in the axial direction when the cold head 22 is inserted into the sleeve 50. In order for the second cooling stage 34 to easily pass through the sliding support 64, it is preferable that the inner diameter of the sliding support 64 is larger than the outer diameter D3 of the second cooling stage 34. Since the outer diameter D2 of the sliding guide 62 and the inner diameter of the sliding support 64 are equal, the outer diameter D2 of the sliding guide 62 is also larger than the outer diameter D3 of the second cooling stage 34.

[0046] The sliding guide 62 may be a single cylindrical member. Alternatively, the sliding guide 62 may have a divided structure. For example, the sliding guide 62 may be formed into a cylindrical shape by combining a plurality of arc-shaped parts divided in the circumferential direction. For example, the sliding guide 62 may be configured to form one cylinder by combining two semi-cylindrical parts of the same diameter. In this case, each of the parts is attached to the second cylinder 32. Like the sliding guide 62, the sliding support 64 may also be a single member or have a divided structure. As described later, the sliding guide 62 and / or the sliding support 64 may be divided in the axial direction.

[0047] In the cryogenic device 10 according to the embodiment, as described below, the first cooling stage 30 and the second cooling stage 34 come into contact with or are separated from the first heat transfer stage 56 and the second heat transfer stage 60, respectively, by movement of the mounting flange 26 relative to the sleeve side flange 52.

[0048] When the time arrives when maintenance of the cryogenic refrigerator 20 is permitted, the cooling operation of the cryogenic refrigerator 20 is stopped. At this time, as shown in FIG. 1, the first cooling stage 30 is in physical and thermal contact with the first heat transfer stage 56, and the second cooling stage 34 is in physical and thermal contact with the second heat transfer stage 60.

[0049] First, the flange fastening member 48 is removed by an operator, and the fastening between the mounting flange 26 and the sleeve side flange 52 is released. The mounting flange 26 is lifted from the sleeve side flange 52, and the cold head 22 is raised from the sleeve 50. This lifting height L C is about several mm, for example, about 2 to 3 mm. As shown in Fig. 2, the first cooling stage 30 and the second cooling stage 34 are separated from the first heat transfer stage 56 and the second heat transfer stage 60, respectively, and thermal contact is released. A seal member 46 is provided between the mounting flange 26 and the sleeve-side flange 52, so that the isolation of the airtight region 18 from the surrounding environment 16 is maintained. The temperature of the cold head 22 can be raised while the object to be cooled 14 is maintained at a low temperature.

[0050] Maintenance of the cryogenic refrigerator 20 is performed. The drive unit 40 of the cold head 22 may be removed from the cold head 22 together with the first displacer 36 and the second displacer 38. In this case, the first cylinder 28, the first cooling stage 30, the second cylinder 32, and the second cooling stage 34 are still installed in the sleeve 50. Then, the drive unit and displacer that have been maintained (or are new) are attached to the cold head 22. Then, the cooling operation of the cryogenic refrigerator 20 is resumed.

[0051] Thereafter, the mounting flange 26 is pressed into the sleeve-side flange 52, and the first cooling stage 30 and the second cooling stage 34 are again in contact with the first heat transfer stage 56 and the second heat transfer stage 60, respectively. The mounting flange 26 and the sleeve-side flange 52 are again fastened by the flange fasteners 48, the cold head 22 is fixed to the sleeve 50, and the first cooling stage 30 and the second cooling stage 34 are pressed against the first heat transfer stage 56 and the second heat transfer stage 60, respectively, and are again in thermal contact with each other, as shown in FIG.

[0052] Such cold head mounting work at the site where the cryogenic refrigerator is used is performed with the utmost care so that the cold head 22 is in the correct position (for example, so that the central axis C of the cold head 22 is aligned vertically). However, according to the study by the present inventors, it has been found that in some cases, the cold head 22 is mounted on the sleeve 50 at a slight angle from the correct position.

[0053] The first and second cooling stages 30 and 34 of the mounted cold head 22 are pressed against the first and second heat transfer stages 56 and 60 of the sleeve 50 with a strong force to ensure good thermal contact. Therefore, even a slight tilt of the cold head 22 may cause uneven distribution of stress on the cold head 22, resulting in distortion of the cold head 22. As a result, the refrigeration capacity may be adversely affected, which is undesirable. For example, the gap between the second cylinder 32 and the second displacer 38 may be locally enlarged. In this case, the working gas flow in the second cylinder 32, which should pass through the regenerator material in the second displacer 38, may bypass the regenerator material and pass through this gap, which may reduce the refrigeration capacity of the second cooling stage 34 of the cold head 22. If the reduction in refrigeration capacity is large, there is a concern that the cooling of the object to be cooled 14 may be adversely affected.

[0054] Also, the inclination of the cold head 22 may affect the contact state between the cooling stage of the cold head 22 and the heat transfer stage of the sleeve 50, resulting in an increase in the contact thermal resistance between them, which may also affect the cooling of the object 14 to be cooled.

[0055] According to the embodiment, when the cold head 22 is inserted into the sleeve 50 (e.g., when the cold head 22 is moved axially relative to the sleeve 50 to switch the thermal contact state), the sliding guide 62 of the cold head 22 slides against the sliding support 64 of the sleeve 50, thereby maintaining the cold head 22 in a normal position. This makes it possible to suppress tilting of the cold head 22 that may occur during the cold head mounting operation. This also helps to improve the thermal contact between the cooling stage of the cold head 22 and the heat transfer stage of the sleeve 50.

[0056] In addition, since the sliding guide 62 is provided on the second cylinder 32, it is possible to suppress deformation of the second cylinder 32, that is, fluctuations in the gap between the second cylinder 32 and the second displacer 38. This makes it possible to suppress a decrease in the refrigeration capacity of the cold head 22.

[0057] 3(a), 3(b), and 3(c) are diagrams illustrating another example of the configuration of the sliding guide 62 and the sliding support 64 according to the embodiment. As shown in FIG. 3(a), the sliding guide 62 may be provided in the second cylinder 32 of the cold head 22 so as to be slidable with the first heat transfer stage 56 of the sleeve 50. In this case, the outer diameter of the sliding guide 62 is equal to the inner diameter of the opening 56a of the first heat transfer stage 56. The inner peripheral surface of the first heat transfer stage 56 corresponds to the sliding support 64.

[0058] Similarly, the sliding guide 62 may be provided in the second cylinder 32 of the cold head 22 so as to be slidable with a portion of the sleeve 50 (e.g., the second sleeve member 58). In this case, the portion of the sleeve 50 (e.g., the inner circumferential surface of the second sleeve member 58) corresponds to the sliding support 64.

[0059] 3(b), the sliding support 64 may be provided on the second heat transfer stage 60 of the sleeve 50. The sliding support 64 may be a cylindrical member extending from the second heat transfer stage 60, and the sliding support 64 may slide on the sliding guide 62 of the cold head 22 on its inner circumferential surface.

[0060] 3(c), the sliding guide 62 may be provided on the second cooling stage 34 of the cold head 22. The sliding guide 62 may be provided on a side surface (i.e., an outer peripheral surface) of the second cooling stage 34 so as to be slidable with a sliding support 64 of the sleeve 50. The sliding support 64 may be provided on the second sleeve member 58 or on the second heat transfer stage 60.

[0061] 4(a) and 4(b) are perspective views showing another example of the sliding guide 62 according to the embodiment. As shown in FIG. 4(a), the sliding guide 62 may be configured by combining two semi-cylindrical parts 62a having the same diameter to form one cylinder. The sliding guide 62 may extend over the entire axial length of the second cylinder 32 from the first cooling stage 30 to the second cooling stage 34.

[0062] As shown in Fig. 4(b), the sliding guide 62 may be provided partially in the circumferential direction. The sliding guide 62 may include a plurality of bars 62b arranged in the circumferential direction of the second cylinder 32. Each bar 62b may extend over the entire axial length of the second cylinder 32 from the first cooling stage 30 to the second cooling stage 34. These bars 62b may be arranged at equal angular intervals in the circumferential direction of the second cylinder 32. In the illustrated example, four bars 62b are arranged at 90 degree intervals.

[0063] 5(a) and 5(b) are diagrams showing another example of the sliding guide 62 according to the embodiment. In general, the cooling capacity of the first stage of the cryogenic refrigerator 20 is considerably higher than that of the second stage. Therefore, during re-cooling after the cold head 22 is attached to the sleeve 50 or after maintenance of the cold head 22, the first cooling stage 30 may be cooled faster than the second cooling stage 34, which may cause a temperature distribution in the axial direction of the second cylinder 32. In an extreme case, when the first cooling stage 30 is cooled to 40K, the second cooling stage 34 may still be at room temperature (e.g., 300K), and a significant temperature distribution of 40K at the upper end and 300K at the lower end may occur in the second cylinder 32. Due to such a temperature distribution, a conical thermal deformation occurs in the second cylinder 32, in which the upper end shrinks more than the lower end, and bending thermal stress may be induced in the sliding guide 62 attached to the second cylinder 32.

[0064] To address this, as shown in FIG. 5(a), the sliding guide 62 (e.g., multiple bars 62b) may be divided in the axial direction. The sliding guide 62 may include multiple guide pieces 62b1-62b4 divided in the axial direction of the cold head 22, and each guide piece 62b1-62b4 may be attached to the second cylinder 32. In this way, the axial length of each guide piece is shortened, the temperature difference between both ends of the guide piece is reduced, and the thermal stress acting on the guide piece may also be reduced. Such axial division for dealing with thermal stress may be similarly applied to the cylindrical sliding guide 62 shown in FIG. 4(a).

[0065] 5(b), the sliding guide 62 may be attached to the second cylinder 32 at a portion of the entire length of the sliding guide 62 in the axial direction of the cold head 22. By attaching the sliding guide 62 to a local portion of the second cylinder 32 in this manner, the temperature difference and therefore the thermal stress acting on the sliding guide 62 can be reduced.

[0066] Similarly to the sliding guide 62, the sliding support 64 may be divided in the axial direction to deal with thermal stress.

[0067] 6 is a diagram showing another example of the sliding guide 62 according to the embodiment. The sliding guide 62 may have a wiring passage 66 such as a slit. In the example shown in the figure, the wiring passage 66 is formed between the sliding guide 62 and the second cylinder 32. When a component requiring wiring, such as a temperature sensor, is installed on the second cooling stage 34, the wiring can be conveniently arranged to pass through the wiring passage 66. The wiring passage 66 may be similarly applied to the cylindrical sliding guide 62 shown in FIG. 4(a).

[0068] The present invention has been described above based on examples. It will be understood by those skilled in the art that the present invention is not limited to the above-described embodiments, that various design changes are possible, that various modifications are possible, and that such modifications are also within the scope of the present invention. Various features described in relation to one embodiment can also be applied to other embodiments. A new embodiment resulting from a combination has the combined effects of each of the combined embodiments.

[0069] In the above embodiment, an example has been described in which the sliding guide 62 is provided in the second stage of the cold head 22 and the sliding support 64 is provided in the second stage of the sleeve 50. However, in addition to or instead of this, the sliding guide 62 may be provided in the first stage of the cold head 22 and the sliding support 64 may be provided in the first stage of the sleeve 50. For example, the sliding guide 62 may be provided in the first cylinder 28 of the cold head 22 and the sliding support 64 may be provided in the first sleeve member 54 of the sleeve 50.

[0070] In the above embodiment, the cryocooler 20 is a two-stage GM refrigerator, but the cryocooler 20 may be a single-stage GM refrigerator. In this case, the cold head mounting structure has one heat transfer stage corresponding to the cold head 22 having one cooling stage. The cryocooler 20 may also be a pulse tube refrigerator, a Stirling refrigerator, or other types of cryocooler.

[0071] The present invention has been described using specific terms based on the embodiments, but the embodiments merely show one aspect of the principles and applications of the present invention, and many modifications and changes in arrangement are permitted to the embodiments without departing from the spirit of the present invention as defined in the claims. [Explanation of symbols]

[0072] 10 cryogenic device, 20 cryogenic refrigerator, 22 cold head, 28 first cylinder, 30 first cooling stage, 32 second cylinder, 34 second cooling stage, 50 sleeve, 54 first sleeve member, 56 first heat transfer stage, 56a opening, 58 second sleeve member, 60 second heat transfer stage, 62 sliding guide, 64 sliding support.

Claims

1. a cold head insertable into a cold head receiving sleeve, the cold head including a first cooling stage, a second cooling stage cooled to a lower temperature than the first cooling stage, and a cylinder connecting the first cooling stage and the second cooling stage; a sliding guide provided on the cylinder or the second cooling stage so as to slide against the cold head accommodating sleeve when the cold head is inserted into the cold head accommodating sleeve.

2. 2. The cryogenic refrigerator according to claim 1, wherein the sliding guide is provided on the cylinder.

3. 3. The cryogenic refrigerator according to claim 2, wherein the sliding guide comprises a plurality of guide pieces divided in an axial direction of the cold head, each guide piece being attached to the cylinder.

4. 3. The cryogenic refrigerator according to claim 2, wherein the sliding guide is attached to the cylinder at a portion of the entire length of the sliding guide in the axial direction of the cold head.

5. 5. The cryogenic refrigerator according to claim 2, wherein an outer diameter of the sliding guide is larger than an outer diameter of the second cooling stage.

6. the cold head receiving sleeve has an opening and includes a first heat transfer stage thermally coupled to the first cooling stage; 2. The cryogenic refrigerator according to claim 1, wherein an outer diameter of the sliding guide is smaller than an inner diameter of the opening of the first heat transfer stage.

7. A first cooling stage; a second cooling stage that is cooled to a temperature lower than that of the first cooling stage; a cylinder connecting the first cooling stage and the second cooling stage; a sliding guide attached to the cylinder.

8. a cold head accommodating sleeve capable of receiving a cold head of a cryogenic refrigerator, the cold head accommodating sleeve including a first heat transfer stage, a second heat transfer stage cooled to a lower temperature than the first heat transfer stage, and a sleeve member connecting the first heat transfer stage and the second heat transfer stage; a sliding support provided on the first heat transfer stage, the sleeve member or the second heat transfer stage so as to slide with the cold head when the cold head is inserted into the cold head receiving sleeve.

9. 9. The cold head mounting structure according to claim 8, wherein the sliding support is provided on the sleeve member.

10. the cold head includes a first cooling stage and a second cooling stage that is cooled to a lower temperature than the first cooling stage; 10. The cold head mounting structure of claim 9, wherein the inner diameter of the sliding support is larger than the outer diameter of the second cooling stage.

11. 11. The cold head mounting structure according to claim 8, wherein an inner diameter of the sliding support is smaller than an inner diameter of the opening of the first heat transfer stage.

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