Refrigeration unit and superconducting magnet device

Abstract

To enable the reduction of temperature difference between a second cooling unit of a cryogenic refrigerator and a sleeve provided in a vacuum container and coming in thermal contact with an object to be cooled, and further to enable the improvement of detachability between the second cooling unit and the sleeve.SOLUTION: A refrigeration unit includes: a vacuum container storing a superconducting coil and a radiation shield; and a cryogenic refrigerator 13 attached to the vacuum container, the vacuum container comprises a sleeve 14 storing the cryogenic refrigerator, the cryogenic refrigerator comprises a second cooling stage 16 cooling the superconducting coil, a coating layer 26 made of soft metal having good thermal conductivity is formed on a contact surface 28 in the second cooling stage by work including plating, cold spray or deposition, a separation type release layer 27 for releasing the coating layer is formed on a second sleeve 22 of the sleeve 14 at a position facing the coating layer by coating execution, and the second cooling stage 16 and the second sleeve 22 are thermally and detachably joined through the coating layer and the separation type release layer.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] An embodiment of the present invention relates to a refrigeration unit and a superconducting magnet device to which the refrigeration unit is applied for cooling a superconducting coil. [Background technology]

[0002] In a conduction-cooling type superconducting magnet device, a structure is known in which a sleeve is provided in a vacuum vessel and a cryogenic refrigerator is attached, as in a cryostat. In other words, a superconducting coil is housed inside the vacuum vessel. This superconducting coil is placed in the vacuum vessel and vacuum-insulated to prevent heat from entering. In addition, the amount of heat entering the superconducting coil is further reduced by placing a radiation shield between the superconducting coil and the vacuum vessel.

[0003] Here, the radiation shield is in thermal contact with a first cooling stage of the cryogenic refrigerator via a first sleeve, and the superconducting coil is in thermal contact with a second cooling stage of the cryogenic refrigerator via a second sleeve, so that the cryogenic refrigerator cools the radiation shield via the first sleeve and the superconducting coil via the second sleeve. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6509473 [Patent Document 2] JP 2017-183526 A Summary of the Invention [Problem to be solved by the invention]

[0005] In general, when a cryogenic refrigerator is operated for a long period of time, periodic maintenance is required. In this case, Patent Document 1 describes a mounting structure that allows the cryogenic refrigerator to be replaced without breaking the vacuum in the vacuum container by attaching and detaching the cryogenic refrigerator in the sleeve. When replacing the cryogenic refrigerator, the thermal contact between the cooling stage and the sleeve is released. If the mounting structure of Patent Document 1 is applied to the attachment and detachment structure between the second cooling stage and the second sleeve, it is expected that a temperature difference of several K will occur between the second cooling stage and the second sleeve, while the temperature of the second cooling stage is 4 K during normal operation. In this case, the superconducting coil will not be able to operate because its operating limit temperature is in the 5 K range.

[0006] This temperature difference occurs because oxygen-free copper and other materials that are typically used in the thermal contact parts of the second cooling stage and second sleeve of a cryogenic refrigerator have minute irregularities, which create gaps in the thermal contact parts, making the effective area for heat conduction extremely small.If the gap in the thermal contact part is a vacuum, heat transfer in the thermal contact part will be limited to thermal conduction and radiation, resulting in an even larger temperature difference between the second cooling stage and the second sleeve of the cryogenic refrigerator.

[0007] In Patent Document 2, a heat-conducting sheet is inserted between the first cooling stage and the flange of the first sleeve to improve thermal contact. However, since the indium in this heat-conducting sheet is prone to migrate to the flange side and cannot be used repeatedly, a heat-conducting peeling layer is disposed on the flange side.

[0008] However, in Patent Document 2, as shown in FIG. 5, even if a heat conductive sheet (indium sheet) 103 is interposed in the thermal contact portion between the first cooling stage 101 and the flange 102 of the first sleeve, a gap 104 still exists between the first cooling stage 101 and the flange 102 of the first sleeve. As a result, a large temperature difference of about several K occurs between the first cooling stage 101 and the first sleeve during normal operation. In particular, when the gap 104 occurring in the thermal contact portion is a vacuum, the heat transfer from the first cooling stage 101 to the flange 102 of the first sleeve is only the thermal conduction and radiation of the thermal contact portion, so there is a problem that an even larger temperature difference occurs between the first cooling stage 101 and the flange 102 of the first sleeve.

[0009] The embodiments of the present invention have been made in consideration of the above-mentioned circumstances, and aim to provide a refrigeration unit and a superconducting magnet device that can reduce the temperature difference between the second cooling section of a cryogenic refrigerator and a sleeve that is provided in a vacuum vessel and in thermal contact with an object to be cooled, and further, can improve the ease of attachment and detachment of the second cooling section and the sleeve. [Means for solving the problem]

[0010] A refrigeration unit according to an embodiment of the present invention includes a radiation shield that houses an object to be cooled, a vacuum vessel that houses the object to be cooled and the radiation shield, and a cryogenic refrigerator attached to the vacuum vessel, the vacuum vessel includes a sleeve that houses the cryogenic refrigerator, the cryogenic refrigerator includes a first cooling section that cools the radiation shield and a second cooling section that cools the object to be cooled, and a coating layer made of a soft metal with good thermal conductivity that can fill a gap between the outer surface and the sleeve is formed on at least a part of an outer surface of the second cooling section by application including plating, cold spraying, or welding, and the sleeve includes The second cooling section A release layer is formed on the contact surface at a position facing the coating layer by coating, and the release layer enables the coating layer to be peeled off when the coating layer is attached to or detached from the contact surface. Release layeris formed with a film thickness that can ensure thermal conductivity between the sleeve and the second cooling portion when it comes into contact with the coating layer, and the second cooling portion and the sleeve are thermally and detachably joined via the coating layer and the release layer.

[0011] A superconducting magnet device in an embodiment of the present invention is characterized in that an object to be cooled by the second cooling section of the cryogenic refrigerator in the refrigeration unit according to the embodiment is a superconducting coil. Effect of the Invention

[0012] According to an embodiment of the present invention, the temperature difference between the second cooling section of the cryogenic refrigerator and the sleeve provided in the vacuum container and in thermal contact with the object to be cooled can be reduced, and further, the ease of attachment and detachment of the second cooling section and the sleeve can be improved. [Brief description of the drawings]

[0013] [Figure 1] 1 is a schematic diagram showing a superconducting magnet device to which a refrigeration unit according to a first embodiment is applied. [Diagram 2] 2A and 2B are cross-sectional views of the essential parts showing the thermal contact portion between the second cooling stage and the second sleeve in FIG. 1, in which (A) shows the case where the second cooling stage and the second sleeve are not in contact, and (B) shows the case where the second cooling stage and the second sleeve are in contact. [Diagram 3] FIG. 3 is an enlarged cross-sectional view showing part A in FIG. 2(B). [Figure 4] 13A and 13B are cross-sectional views showing the thermal contact portion between the second cooling stage and the second sleeve of a superconducting magnet device to which a refrigeration unit according to a second embodiment is applied, in which (A) shows the case where the second cooling stage and the second sleeve are not in contact, and (B) shows the case where the second cooling stage and the second sleeve are in contact. [Diagram 5] 13 is an enlarged cross-sectional view showing a conventional thermal contact portion between a first cooling stage and a flange of a first sleeve. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] 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 diagram showing a superconducting magnet device to which a refrigeration unit according to the first embodiment is applied. A superconducting magnet device 10 as a refrigeration unit shown in Fig. 1 cools a superconducting coil 1 as an object to be cooled to a cryogenic temperature by a conduction cooling method using a cryogenic refrigerator 13, and is configured with a vacuum vessel 11, a radiation shield 12, the cryogenic refrigerator 13, and a sleeve 14.

[0015] Vacuum vessel 11 accommodates superconducting coil 1 and radiation shield 12 therein, and supports cryogenic refrigerator 13. Superconducting coil 1 is further accommodated within radiation shield 12 within vacuum vessel 11. By disposing superconducting coil 1 within vacuum vessel 11, penetration of heat is suppressed by vacuum insulation. Furthermore, by disposing superconducting coil 1 within radiation shield 12, the amount of heat penetration is further reduced.

[0016] Cryogenic refrigerator 13, which is supported and attached to vacuum vessel 11, is configured to have a first cooling stage 15 as a first cooling section that cools radiation shield 12, and a second cooling stage 16 as a second cooling section that cools superconducting coil 1. Here, first cooling stage 11 is coupled to a first-stage cold head 17 of cryogenic refrigerator 13, and second cooling stage 16 is coupled to a second-stage cold head 18 of cryogenic refrigerator 13, for example, by screws.

[0017] The sleeve 14 is provided in the vacuum vessel 11 to house the cryogenic refrigerator 13, and includes a first sleeve 21 and a second sleeve 22. The first sleeve 21 is supported by the vacuum vessel 11. As shown in FIG. 2, the second sleeve 22 is supported by the radiation shield 12 using a stud bolt 23, a nut 24, and a disc spring 25. As shown in FIG. 1 and FIG. 2, the first sleeve 21 houses the first cooling stage 15 and the first stage cold head 17 of the cryogenic refrigerator 13, and the second sleeve 22 houses the second cooling stage 16 and the second stage cold head 18 of the cryogenic refrigerator 13. The second sleeve 22 is pressed against the second cooling stage 16 by the elastic force of the disc spring 25 to come into contact with the second cooling stage 16 as shown in FIG. 2(B).

[0018] 1, the first cooling stage 15 of the cryogenic refrigerator 13 is in thermal contact with the radiation shield 12 via the first sleeve 21, and cools the radiation shield 12. Also, as shown in Figs. 1 and 2, the second cooling stage 16 of the cryogenic refrigerator 13 is in thermal contact with the superconducting coil 1 via the second sleeve 22 in contact therewith, and cools the superconducting coil 1.

[0019] In the first embodiment, as shown in FIG. 2, the second cooling stage 16 of the cryogenic refrigerator 13 and the second sleeve 22 are thermally and detachably joined via a coating layer 26 and a release layer 27.

[0020] That is, the coating layer 26 is formed on at least a part of the outer surface of the second cooling stage 16, for example, on the contact surface 28 with the second sleeve 22. This coating layer 26 is made of a metal with good thermal conductivity that is soft enough to fill gaps 29 with the contact surface 28 formed by minute irregularities on the contact surface 28 (FIG. 3) of the second cooling stage 16. Specifically, this metal is copper, nickel, rhodium, ruthenium, etc., but when copper (Mohs hardness 3) is used as the material for the second cooling stage 16, the metal is selected from at least one of indium, aluminum (e.g. high purity aluminum), gold, silver, tin, and zinc, which are metals softer than copper and have a Mohs hardness of 3 or less.

[0021] When the second cooling stage 16 and the second sleeve 22 are each made of, for example, oxygen-free copper, a gap 29 is generated at the contact portion between the second cooling stage 16 and the second sleeve 22 due to minute irregularities on the respective contact surfaces, and the effective area of ​​thermal contact becomes extremely small, resulting in a large temperature difference between the second cooling stage 16 and the second sleeve 22. In contrast, as in the first embodiment, the coating layer 26 made of the above-mentioned soft metal with good thermal conductivity is formed on the contact surface 28 of the second cooling stage 16, so that the coating layer 26 can fill the gap 29. This makes it possible to improve the contact heat transfer characteristics between the second cooling stage 16 and the second sleeve 22.

[0022] Furthermore, the coating layer 26 is formed on the contact surface 28 of the second cooling stage 16 by a process including plating, cold spraying, or welding of the above-mentioned soft metal with good thermal conductivity. The coating layer 26 is formed by these processes, and thus the adhesion of the coating layer 26 is increased. The thickness of the coating layer 26 is set to 10 μm to 500 μm in consideration of the crushing allowance. The contact surface 28 of the second cooling stage 16 on which the coating layer 26 is formed and the contact surface 30 formed on the second sleeve 22 opposite to the contact surface 28 and in contact with the contact surface 28 are not limited to being flat, but may be curved or uneven.

[0023] The release peeling layer 27 is formed by coating at a position on the second sleeve 22 facing the coating layer 26, for example, on the contact surface 30. If the release peeling layer 27 did not exist, there was a risk that the coating layer 26 formed on the second cooling stage 16 would migrate to the second sleeve 22 side when the second cooling stage 16 and the second sleeve 22 were attached or detached from each other. However, by forming the release peeling layer 27 on the contact surface 30 of the second sleeve 22, migration of the coating layer 26 to the second sleeve 22 can be prevented, and the coating layer 26 becomes easier to peel off from the second sleeve 22.

[0024] The release layer 27 is formed by a first coating process in which a coating agent made of an alkylsilane coupling agent and a fluorine-based resin is applied and coated, or by a second coating process in which a fluorine-based organic material or a silicone-based organic material is applied and coated after the second copper sleeve 22 is irradiated with plasma.

[0025] The release layer 27 is made of a nonmetallic material and has low thermal conductivity as described above, and therefore the thickness thereof is set thin. That is, the release layer 27 is set to a thickness of about 10 μm when formed by the first coating application, and is set to a thickness of about several nm to 1 μm when formed by the second coating application.

[0026] As configured as above, the first embodiment provides the following advantages (1) and (2). (1) The second cooling stage 16 of the cryogenic refrigerator 13 and the second sleeve 22 that houses the second cooling stage 16 and is in thermal contact with the superconducting coil 1 are thermally and detachably joined via the coating layer 26 and the release layer 27. The coating layer 26 is made of a metal with good thermal conductivity that is soft enough to fill the gap 29 with the contact surface 28 of the second cooling stage 42. Furthermore, the coating layer 26 is formed on the contact surface 28 of the second sleeve 22 by application including plating, cold spraying, or welding, so that it has high adhesion. For these reasons, the coating layer 26 can improve the contact heat transfer characteristics between the second cooling stage 16 of the cryogenic refrigerator 13 and the second sleeve 22. As a result, the temperature difference between the second cooling stage 16 and the second sleeve 22 is reduced, and the superconducting coil 1 can be well cooled by the second cooling stage 16 via the second sleeve 22.

[0027] (2) The release layer 27 is for peeling off the coating layer 26, and is formed with a thin film thickness by coating on the contact surface 30 of the second sleeve 22 that faces the coating layer 26. This improves the ease of attachment and detachment between the second cooling stage 16 and the second sleeve 22 of the cryogenic refrigerator 13, and also ensures thermal conductivity between the second cooling stage 16 and the second sleeve 22, thereby suppressing an increase in the temperature difference between the two (the second cooling stage 16 and the second sleeve 22).

[0028] [B] Second embodiment (Fig. 4) 4 is a cross-sectional view showing a thermal contact portion between the second cooling stage and the second sleeve of a superconducting magnet device to which a refrigeration unit according to the second embodiment is applied, in which (A) shows a case where the second cooling stage and the second sleeve are not in contact with each other, and (B) shows a case where the second cooling stage and the second sleeve are in contact with each other. In this second embodiment, the same parts as those in the first embodiment are given the same reference numerals as those in the first embodiment, and the description thereof will be simplified or omitted.

[0029] The difference between the superconducting magnet device 40 as a refrigeration unit of the second embodiment and the first embodiment is the contact structure between the second cooling stage 42 of the cryogenic refrigerator 13 and the second sleeve 44 that houses this second cooling stage 42 and is in thermal contact with the superconducting coil 1.

[0030] That is, a contact surface 45 where the second cooling stage 42 contacts the second sleeve 44 and a contact surface 46 where the second sleeve 44 contacts the second cooling stage 42 are both formed in a tapered shape with the same inclination angle. Then, a coating layer 26 is formed on the contact surface 45 of the second cooling stage 42 in the same manner as in the first embodiment. Also, a release layer 27 is formed on the contact surface 46 of the second sleeve 44 in the same manner as in the first embodiment.

[0031] Therefore, according to the second embodiment, in addition to the effects (1) and (2) of the first embodiment, the following effect (3) is achieved.

[0032] (3) The contact surface 45 of the second cooling stage 42 on which the coating layer 26 is formed and the contact surface 46 of the second sleeve 44 on which the release layer 27 is formed are tapered, so that the contact area between the second cooling stage 42 and the second sleeve 44 can be enlarged compared to the case of a flat shape. This makes it possible to improve the contact heat transfer characteristics between the second cooling stage 42 and the second sleeve 44 via the coating layer 26 and the release layer 27 compared to the first embodiment. As a result, the temperature difference between the second cooling stage 42 and the second sleeve 44 can be reduced compared to the first embodiment, and the superconducting coil 1 can be cooled more suitably.

[0033] 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, and modifications can be made without departing from the spirit of the invention, and these substitutions and modifications are included in the scope and spirit of the invention, as well as in the scope of the invention and its equivalents described in the claims.

[0034] For example, in the cryogenic refrigerator 13, the second cooling stage 16 may be omitted, and the second stage cold head 18 may be configured to contact the second sleeve 22 of the sleeve 14, with a coating layer 26 formed on the contact surface of the second stage cold head 18 as the second cooling part that comes into contact in this manner, and a release layer 27 formed on the contact surface of the second cooling stage 42.

[0035] In addition, in the first and second embodiments, the superconducting magnet devices 10, 40 are described in which the object to be cooled is a superconducting coil 1, but the object to be cooled by the refrigeration unit may be a sample collected from underground or the seabed, or a biological specimen, etc. [Explanation of symbols]

[0036] Reference Signs List 1...superconducting coil (object to be cooled), 10...superconducting magnet device (refrigeration unit), 11...vacuum vessel, 12...radiation shield, 13...ultra-low temperature refrigerator, 14...sleeve, 15...first cooling stage, 16...second cooling stage, 42...second sleeve, 26...coating layer, 27...release layer, 28...contact surface, 29...gap, 30...contact surface, 40...superconducting magnet device (refrigeration unit), 42...second cooling stage, 44...second sleeve, 45, 46...contact surface

Claims

1. The cooling system includes a radiation shield that houses an object to be cooled, a vacuum vessel that houses the object to be cooled and the radiation shield, and a cryogenic refrigerator that is attached to the vacuum vessel; the vacuum vessel includes a sleeve that houses the cryogenic refrigerator; the cryogenic refrigerator includes a first cooling unit that cools the radiation shield and a second cooling unit that cools the object to be cooled, A coating layer made of a soft metal having good thermal conductivity capable of filling a gap between the outer surface and the sleeve is formed on at least a part of an outer surface of the second cooling portion by application including plating, cold spraying, or welding; a release layer is formed by coating on a contact surface of the sleeve with the second cooling part at a position facing the coating layer, the release layer being formed to a thickness that allows the coating layer to be peeled off when the coating layer is attached to or detached from the sleeve, and that ensures thermal conductivity between the sleeve and the second cooling part when the release layer comes into contact with the coating layer; A refrigeration unit, characterized in that the second cooling section and the sleeve are thermally and detachably joined via the coating layer and the release layer.

2. 2. The refrigeration unit according to claim 1, wherein the coating layer is made of a metal having a Mohs hardness of 3 or less.

3. 3. The refrigeration unit according to claim 1 or 2, wherein the coating layer is made of at least one selected from the group consisting of indium, aluminum, gold, silver, tin, and zinc.

4. 4. The refrigeration unit according to claim 1, wherein the release layer is formed by coating a fluorine-based or silicone-based organic material.

5. 5. The refrigeration unit according to claim 1, wherein a contact surface between the second cooling section of the cryogenic refrigerator and the sleeve of the vacuum vessel is formed in a tapered shape.

6. 6. A superconducting magnet device, wherein an object cooled by the second cooling section of the cryogenic refrigerator in the refrigeration unit according to claim 1 is a superconducting coil.

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