Temperature increase auxiliary tool and temperature increase method of cold head cylinder

Abstract

To provide a temperature increase auxiliary tool and a temperature increase method of a cold head cylinder that are useful for appropriate temperature increases of the cold head cylinder.SOLUTION: A temperature increase auxiliary tool 60 of a cold head cylinder is provided. The temperature increase auxiliary tool 60 comprises a body 62 comprising a heater 61 and insertable into the cold head cylinder, and a temperature sensor 63 attached to the body 62 closer to the tip side than the heater 61. The temperature sensor 63 may be attached to the body 62 so as to be closer to a bottom surface of the cold head cylinder than the heater 61, when the body 62 is inserted into the cold head cylinder.SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] The present invention relates to a heating aid and a heating method for a cold head cylinder. [Background technology]

[0002] It is known that the cold head of a cryogenic refrigerator is attached to a vacuum vessel via a so-called maintenance sleeve. An object to be cooled, such as a superconducting coil, is accommodated in the vacuum vessel, and the object is thermally coupled to the maintenance sleeve. By bringing the cold head into contact with the maintenance sleeve, the cryogenic refrigerator can cool the object via the maintenance sleeve.

[0003] During long-term operation of the cryogenic refrigerator, periodic maintenance of the cryogenic refrigerator may be required. 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, such as 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 to recool the object to be cooled, and 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 2004-53068 A Summary of the Invention [Problem to be solved by the invention]

[0005] One step in the above-mentioned maintenance is disassembly of the coldhead. Disassembly may include removing the internal components of the coldhead from the coldhead cylinder while leaving the coldhead cylinder in the maintenance sleeve. In this case, the internal surfaces of the coldhead cylinder are exposed to air flowing in from the surrounding environment. If the cylinder is colder than the ambient temperature, moisture in the air may condense on the cylinder surfaces, causing frost or ice to form. Before reassembling the coldhead, the coldhead cylinder is heated to ambient temperature or a slightly higher temperature (e.g., about 20 to 40° C.) to remove such frost. Temperature control during the heating operation is typically performed using a temperature sensor provided on the coldhead cylinder.

[0006] The cold head employs a temperature sensor suitable for measuring extremely low temperatures, but such a temperature sensor for extremely low temperatures is not necessarily guaranteed to be accurate enough to measure temperatures at room temperature during the heating process described above. In such cases, there is a risk that the cold head cylinder may overheat during heating. In other words, an undesirable situation may occur in which the cold head cylinder is actually heated to a temperature that is excessively higher than the desired temperature, but this cannot be detected due to temperature measurement errors. Overheating, especially at the bottom of the cold head cylinder, may adversely affect the operation of the cryogenic refrigerator after reassembly.

[0007] An exemplary object of an embodiment of the present invention is to provide a heating aid and a heating method for a cold head cylinder that are useful for properly heating the cold head cylinder. [Means for solving the problem]

[0008] According to one aspect of the present invention, there is provided a heating assist device for a cold head cylinder. The heating assist device includes a main body including a heater and capable of being inserted into the cold head cylinder, and a temperature sensor attached to the main body closer to the tip end than the heater.

[0009] According to one aspect of the invention, a method for heating a coldhead cylinder is provided, the method comprising: disposing a heater and a temperature sensor in the coldhead cylinder with the temperature sensor closer to a bottom surface of the coldhead cylinder than the heater; and heating the coldhead cylinder with the heater while measuring the temperature of the coldhead cylinder using the temperature sensor. Effect of the Invention

[0010] According to the present invention, it is possible to provide a heating aid and a heating method for a cold head cylinder that are useful for appropriately heating the cold head cylinder. [Brief description of the drawings]

[0011] [Figure 1] 1 is a diagram illustrating a schematic diagram of a cryogenic device according to an embodiment; [Diagram 2] 1 is a diagram illustrating a schematic diagram of a cryogenic device according to an embodiment; [Diagram 3] FIG. 2 is a diagram illustrating a schematic diagram of a cold head of a cryogenic refrigerator undergoing maintenance in an embodiment. [Figure 4] FIG. 2 is a diagram illustrating a schematic diagram of a cold head of a cryogenic refrigerator undergoing maintenance in an embodiment. [Diagram 5] FIG. 1 is a diagram illustrating a conventional heating assist device. [Figure 6] FIG. 1 is a diagram illustrating a temperature rise auxiliary device according to an embodiment of the present invention. [Figure 7] 1 is a schematic diagram showing a method for increasing the temperature of a cold head cylinder according to an embodiment of the present invention; [Figure 8] FIG. 13 is a diagram illustrating a modified example of the temperature rise auxiliary device according to 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] 1 and 2 are schematic diagrams showing a cryogenic device 100 according to an embodiment. Fig. 1 shows a state in which the cryogenic refrigerator 10 and an object to be cooled 90, such as a superconducting coil, are thermally decoupled, and Fig. 2 shows a state in which the two are thermally coupled.

[0014] In this embodiment, the cryogenic refrigerator 10 is a two-stage Gifford-McMahon (GM) refrigerator. The cryogenic refrigerator 10 includes a compressor 12 and a two-stage cold head 14.

[0015] The compressor 12 is configured to recover the refrigerant gas of the cryogenic refrigerator 10 from the cold head 14, increase the pressure of the recovered refrigerant gas, and supply the refrigerant gas to the cold head 14 again. The cold head 14 is also called an expander, and can generate cold by adiabatic expansion of the supplied refrigerant gas in an internal expansion chamber. The circulation of the refrigerant gas between the compressor 12 and the cold head 14 is performed with a combination of appropriate pressure fluctuation and volume fluctuation of the refrigerant gas in the cold head 14, thereby forming a refrigeration cycle (e.g., a GM cycle) of the cryogenic refrigerator 10, whereby each cooling stage of the cold head 14 is cooled to a desired cryogenic temperature. The refrigerant gas is also called a working gas, and is usually helium gas, but other appropriate gases may be used.

[0016] The cold head 14 includes a cold head cylinder 15 and a cold head drive unit 16. The cold head cylinder 15 includes a cold head flange 17, a first-stage cylinder 18, a first-stage cooling stage 20, a second-stage cylinder 22, and a second-stage cooling stage 24, which are coaxially arranged along the central axis of the cold head 14.

[0017] The first-stage cylinder 18 connects the cold head flange 17 to the first-stage cooling stage 20, and the second-stage cylinder 22 connects the first-stage cooling stage 20 to the second-stage cooling stage 24. The first-stage cooling stage 20 and the second-stage cooling stage 24 are formed of a highly heat-conductive metal such as copper (e.g., pure copper) or other heat-conductive material. The first-stage cylinder 18 and the second-stage cylinder 22 are formed of a metal such as stainless steel. In general, the thermal conductivity of the heat-conductive material forming the cooling stage is higher than that of the material forming the cylinder.

[0018] The cold head drive 16 is attached to the cold head flange 17. The cold head drive 16 includes a motor for axially reciprocating a first-stage displacer and a second-stage displacer housed in a first-stage cylinder 18 and a second-stage cylinder 22, respectively. The cold head drive 16 also includes a pressure switching valve that is driven by the motor in synchronization with the displacers. The pressure switching valve is configured to periodically switch between receiving high-pressure refrigerant gas and sending low-pressure refrigerant gas to the cold head 14. The compressor 12, the cold head drive 16, and the cold head flange 17 are disposed in an ambient environment 27.

[0019] The mounting structure 30 of the cryogenic refrigerator 10 is a device for mounting the cold head 14 to a vacuum vessel 26 (e.g., a cryogenic vacuum vessel such as a cryostat). The mounting structure 30 may also be referred to as a cold head receiving sleeve, or simply as a sleeve. The mounting structure 30 is installed in the vacuum vessel 26 so as to form an airtight region 28 isolated from an ambient environment 27 between the cold head 14 and the mounting structure 30. The ambient environment 27 is, for example, an atmospheric pressure environment at room temperature. The airtight region 28 may be evacuated to a vacuum or may be filled with an inert gas that does not liquefy at cryogenic temperatures, such as helium gas. The mounting structure 30 is installed in the vacuum vessel 26 so as to define a vacuum region 29 within the vacuum vessel 26 in combination with the vacuum vessel 26.

[0020] The mounting structure 30 may be provided to a customer by a manufacturer of the cryogenic refrigerator 10 together with the cryogenic refrigerator 10. It can also be said that a cooling device for cooling an object 90 to be cooled is composed of the cryogenic refrigerator 10 and the mounting structure 30.

[0021] The mounting structure 30 is also configured in two stages corresponding to the cold head 14. The mounting structure 30 includes a sleeve flange 32, a first-stage sleeve body 34, a first-stage heat transfer stage 36, a second-stage sleeve body 38, and a second-stage heat transfer stage 40, which are coaxially arranged along the central axis of the cold head 14.

[0022] For example, the sleeve flange 32 is fixed to an opening formed in the top plate of the vacuum vessel 26, and the mounting structure 30 extends from this opening into the vacuum vessel 26. The cold head flange 17 is attached to the sleeve flange 32 with fastening members 33 such as bolts. When the cold head flange 17 and the sleeve flange 32 are fastened, the first-stage cooling stage 20 and the second-stage cooling stage 24 are pressed against the first-stage heat transfer stage 36 and the second-stage heat transfer stage 40, respectively. The sleeve flange 32 has an opening for receiving the cold head 14 radially inward from the fastening members 33, and the cold head flange 17 is in contact with the inner peripheral surface of this opening.

[0023] When the fastening of the cold head flange 17 and the sleeve flange 32 by the fastening members 33 is released, the cold head flange 17 is axially slidable relative to the sleeve flange 32, and the cold head 14 is thereby movable axially (up and down in Figs. 1 and 2) relative to the mounting structure 30. The movable range is, for example, within a few mm, for example, about 2 to 3 mm. An operator can raise and lower the cold head 14 in the axial direction within this movable range manually, by using an auxiliary tool such as a hydraulic jack, or by operating a lifting device having a power source if one is connected to the cold head 14.

[0024] A seal member 42, such as an O-ring, is sandwiched between the cold head flange 17 and the sleeve flange 32. The seal member 42 is disposed in a circumferential groove formed on the inner circumferential surface of the opening of the sleeve flange 32. Because the seal member 42 is provided, the airtight region 28 is isolated from the surrounding environment 27 even if the cold head 14 is moved axially relative to the mounting structure 30 within the above-mentioned movable range.

[0025] The first-stage sleeve body 34 connects the sleeve flange 32 to the first-stage heat transfer stage 36, and the second-stage sleeve body 38 connects the first-stage heat transfer stage 36 to the second-stage heat transfer stage 40. The first-stage sleeve body 34 and the second-stage sleeve body 38 are arranged to surround the first-stage cylinder 18 and the second-stage cylinder 22, respectively. An opening is provided in the center of the first-stage heat transfer stage 36 to connect the internal space of the first-stage sleeve body 34 to the internal space of the second-stage sleeve body 38. The second-stage cylinder 22 and the second-stage cooling stage 24 of the cold head 14 are inserted into the internal space of the second-stage sleeve body 38 through this opening. The first-stage heat transfer stage 36 and the second-stage heat transfer stage 40 are formed of a highly heat-conductive metal such as copper (e.g., pure copper) or other heat-conductive material. The first-stage sleeve body 34 and the second-stage sleeve body 38 are formed of a metal such as stainless steel. The thermal conductivity of the heat-conductive material forming the heat transfer stage is higher than the thermal conductivity of the material forming the sleeve body.

[0026] Therefore, the first-stage heat transfer stage 36 of the mounting structure 30 is brought into contact with or released from the first-stage cooling stage 20 of the cold head 14 as the cold head 14 of the cryogenic refrigerator 10 moves. Similarly, the second-stage heat transfer stage 40 of the mounting structure 30 is brought into contact with or released from the second-stage cooling stage 24 as the cold head 14 moves.

[0027] The cold head cylinder 15 may be provided with a temperature sensor 44. The temperature sensor 44 may be provided at the bottom of the two-stage cooling stage 24 to measure the temperature of the two-stage cooling stage 24. The temperature sensor 44 is a temperature sensor for cryogenic temperatures suitable for measuring the cryogenic temperatures realized in the two-stage cooling stage 24, and may be, for example, a ruthenium oxide thermometer. The temperature sensor 44 may be connected to a temperature indicator 46 by a wire 45. The wire 45 may be spirally wound around the cold head cylinder 15 in the airtight region 28 and led out to the ambient environment 27 through a feedthrough 47 of the cold head flange 17. The temperature indicator 46 may be connected to a temperature indicator 46 arranged in the ambient environment 27. The temperature indicator 46 may obtain the output of the temperature sensor 44 through the wire 45 and display the measured temperature or output it to another device. The temperature indicator 46 may form a part of a controller that controls the cryogenic refrigerator 10.

[0028] A radiation shield 92 is thermally coupled to the outer surface of the first heat transfer stage 36 exposed to the vacuum region 29. The radiation shield 92 is arranged to surround the object 90 to be cooled in order to thermally protect the object 90. Only a part of the radiation shield 92 is shown in FIG. 1 and FIG. 2. The radiation shield 92 may be directly attached to the first heat transfer stage 36, or may be connected via a rigid or flexible heat transfer member. Another object to be cooled may be thermally coupled to the first heat transfer stage 36 together with or instead of the radiation shield 92. A object to be cooled 90 is thermally coupled to the outer surface of the second heat transfer stage 40 exposed to the vacuum region 29. The object to be cooled 90 may be directly attached to the second heat transfer stage 40, or may be connected via a rigid or flexible heat transfer member.

[0029] 1, when the cold head 14 is released from thermal contact with the mounting structure 30, the cold head 14 is located, for example, at the upper end of the movable range. At this time, the first-stage cooling stage 20 is physically separated from the first-stage heat transfer stage 36, and the second-stage cooling stage 24 is physically separated from the second-stage heat transfer stage 40, so that the cryogenic refrigerator 10 does not cool the object 90 and the radiation shield 92. Even if the cold head 14 is heated to a temperature higher than the object 90 and the radiation shield 92, for example, to room temperature, the thermal influence from the cold head 14 to the object 90 and the radiation shield 92 is limited or negligible. The object 90 and the radiation shield 92 are maintained at a cryogenic temperature.

[0030] As shown in FIG. 2, when the cold head 14 and the mounting structure 30 are in thermal contact with each other, the cold head 14 is located at the lower end of the movable range. At this time, the first-stage cooling stage 20 is in physical contact with the first-stage heat transfer stage 36, so that the first-stage cooling stage 20 is in thermal contact with the radiation shield 92 via the first-stage heat transfer stage 36. At the same time, the second-stage cooling stage 24 is in physical contact with the second-stage heat transfer stage 40, so that the second-stage cooling stage 24 is in thermal contact with the object 90 to be cooled via the second-stage heat transfer stage 40. In this way, the cryogenic refrigerator 10 can cool the object 90 to be cooled and the radiation shield 92. The radiation shield 92 can be cooled to, for example, 30K to 80K (usually 30K to 50K, for example 40K), and the object 90 to be cooled can be cooled to, for example, 3K to 20K (usually 3K to 4K).

[0031] An example of the operation of the cryogenic device 100 having the above configuration will be described. When the time arrives when maintenance of the cryogenic refrigerator 10 is permitted, the cooling operation of the cryogenic refrigerator 10 is stopped. At this time, as shown in Fig. 2, the first cooling stage 20 is in physical and thermal contact with the first heat transfer stage 36, and the second cooling stage 24 is in physical and thermal contact with the second heat transfer stage 40.

[0032] An operator operates the fastening member 33 to release the cold head flange 17 from the sleeve flange 32. Then, the cold head 14 is lifted somewhat from the mounting structure 30. Since a seal member 42 is provided between the cold head flange 17 and the sleeve flange 32, the isolation of the airtight region 28 from the surrounding environment 27 is maintained.

[0033] 1, the first-stage cooling stage 20 is physically separated from the first-stage heat transfer stage 36 and is not in thermal contact with them, and the second-stage cooling stage 24 is physically separated from the second-stage heat transfer stage 40 and is not in thermal contact with them. Therefore, the object to be cooled 90 and the radiation shield 92 can be kept at low temperatures while the cold head 14 is heated.

[0034] Maintenance of the cryogenic refrigerator 10 is performed. Figures 3 and 4 are diagrams illustrating the cold head 14 of the cryogenic refrigerator 10 undergoing maintenance according to an embodiment. As shown in Figure 3, the cold head drive unit 16 of the cold head 14 is removed from the cold head flange 17. Together with the cold head drive unit 16, the first-stage displacer 19 and the second-stage displacer 23 are pulled out from the first-stage cylinder 18 and the second-stage cylinder 22, respectively. The cold head cylinder 15 (i.e., the cold head flange 17, the first-stage cylinder 18, the first-stage cooling stage 20, the second-stage cylinder 22, and the second-stage cooling stage 24) are mounted as they are on the mounting structure 30. The removed cold head drive unit 16, the first-stage displacer 19, and the second-stage displacer 23 are subjected to maintenance such as replacement of consumable parts, cleaning, and repair, or are replaced with new cold head drive units or displacers.

[0035] By removing the internal structure of the coldhead 14 from the coldhead cylinder 15 in this manner, the internal surfaces of the coldhead cylinder 15 are exposed to the ambient environment 27. The components that are cooled to a cryogenic temperature during the cooling operation of the cryogenic refrigerator 10, such as the first cooling stage 20, the second cylinder 22, and the second cooling stage 24, may still be at a low temperature, and frost may form on the surfaces of these components from the ambient environment 27.

[0036] Therefore, before reassembling the cold head 14, the cold head cylinder 15 may be heated to remove frost adhering to the inside of the cold head cylinder 15. For this heating, a hot air generator 48 such as a heat gun or a hair dryer may be used as shown in Fig. 4. The cold head cylinder 15 may be heated by supplying hot air 49 from the hot air generator 48 into the cold head cylinder 15.

[0037] Next, the cryogenic refrigerator 10 is reassembled. The maintained (or new) cold head drive 16, the first stage displacer 19, and the second stage displacer 23 are inserted into the cold head cylinder 15, and the cold head drive 16 is reattached to the cold head flange 17, returning to the state shown in FIG. 1. Then, the cooling operation of the cryogenic refrigerator 10 is resumed.

[0038] The cold head 14 is moved relative to the mounting structure 30 so that the first and second cooling stages 20, 24 contact the first and second heat transfer stages 36, 40, respectively. The cold head 14 is pressed back into the mounting structure 30.

[0039] As the cold head 14 moves, the first cooling stage 20 comes into physical and thermal contact with the first heat transfer stage 36, and the second cooling stage 24 comes into physical and thermal contact with the second heat transfer stage 40. Then, the cold head flange 17 and the sleeve flange 32 are fastened together by the fastening member 33. This returns the state shown in FIG.

[0040] Therefore, according to the cryogenic device 100 of the embodiment, the movement of the cold head 14 releases thermal contact with the mounting structure 30, and the temperature of the object to be cooled 90 and the radiation shield 92 can be kept low while the temperature of the object to be cooled 90 and the radiation shield 92 is raised and maintenance can be performed. Compared to the case where the object to be cooled 90 and the radiation shield 92 are raised to room temperature together with the cold head 14 to perform maintenance on the cryogenic refrigerator 10, the time required to re-cool the object to be cooled 90 and the radiation shield 92 can be shortened, and the time required for maintenance can be shortened.

[0041] FIG. 5 is a schematic diagram of a conventional heating aid 50. In the above-mentioned heating process for the cold head cylinder 15, the heating aid 50 may be used to promote heating and defrosting. The heating aid 50 has a hollow cylindrical shape with both ends open, and has an outer diameter somewhat smaller than the inner diameters of the two-stage cylinder 22 and the two-stage cooling stage 24 so that one end of the heating aid 50 can be inserted into the cold head cylinder 15 and brought into close proximity to the two-stage cooling stage 24. The heating aid 50 also has an axial length somewhat longer than the axial depth of the cold head cylinder 15 (i.e., the axial distance from the cold head flange 17 to the bottom 24a of the two-stage cooling stage 24) so ​​that the other end of the heating aid 50 is positioned outside the cold head cylinder 15 when inserted into the cold head cylinder 15.

[0042] When the temperature-raising auxiliary tool 50 is inserted into the cold head cylinder 15, one open end of the temperature-raising auxiliary tool 50 located outside the cold head cylinder 15 is used as a hot air inlet 51. A hot air outlet of the hot air generator 48 is connected to the hot air inlet 51. Hot air 49 from the hot air generator 48 is introduced into the temperature-raising auxiliary tool 50 from the hot air inlet 51. The other open end of the temperature-raising auxiliary tool 50 arranged adjacent to the two-stage cooling stage 24 inside the cold head cylinder 15 is used as a hot air outlet 52. The hot air 49 introduced into the temperature-raising auxiliary tool 50 from the hot air inlet 51 is blown out from the hot air outlet 52 toward the bottom 24a of the two-stage cooling stage 24. The hot air 49 first heats the bottom 24a of the two-stage cooling stage 24, and through thermal conduction from the bottom 24a, it can heat the side 24b of the two-stage cooling stage 24 and other parts of the cold head cylinder 15, such as the two-stage cylinder 22.

[0043] Since the temperature rise assistant 50 is not provided with a temperature sensor, the temperature of the cold head cylinder 15 in the heating process is managed using the temperature sensor 44 provided in the cold head 14. As described above, a temperature sensor suitable for measuring extremely low temperatures is used as the temperature sensor 44. However, depending on the specifications, such a temperature sensor for extremely low temperatures is not guaranteed to have sufficient accuracy for measuring temperatures in the room temperature range that should be measured in the heating process of the cold head cylinder 15.

[0044] The inventors have recognized that in such a case, there is a risk that the temperature of the two-stage cooling stage 24 of the cold head cylinder 15 will be excessively increased during the heating process. In other words, it is possible that an undesirable situation may occur in which, even though the two-stage cooling stage 24 is actually heated to a temperature excessively higher than the desired temperature, which is approximately room temperature, this cannot be detected due to a temperature measurement error.

[0045] In some cases, the overheating of the second-stage cooling stage 24 may adversely affect the operation of the cryogenic refrigerator 10 after reassembly. For example, grease or adhesive may be used between the bottom of the second-stage cooling stage 24 to which the temperature sensor 44 is attached and the temperature sensor 44 to improve thermal conduction, but such an intervening material often has low heat resistance. If the intervening material is damaged by the overheating, there is a concern that the accuracy of subsequent temperature measurements by the temperature sensor 44 may decrease. In the worst case, unnecessary additional maintenance work may be required, such as removing the cold head cylinder 15 from the mounting structure 30 and repairing or replacing the temperature sensor 44 and the second-stage cooling stage 24.

[0046] 6 is a diagram showing a schematic diagram of a temperature rise auxiliary tool 60 according to an embodiment. Like the above-mentioned temperature rise auxiliary tool 50, the temperature rise auxiliary tool 60 is used to efficiently heat the cold head cylinder 15. The temperature rise auxiliary tool 60 includes a main body 62 including a heater 61, and a temperature sensor 63 provided in the main body 62.

[0047] The body 62 of the temperature rise assistant 60 has a shape that allows it to be inserted into the cold head cylinder 15. As an example, as shown in Fig. 7, the body 62 has a hollow cylindrical shape with an outer diameter somewhat smaller than the inner diameters of the two-stage cylinder 22 and the two-stage cooling stage 24 so that its tip can be inserted into the cold head cylinder 15 and brought into close proximity to the two-stage cooling stage 24. In addition, the body 62 has an axial length somewhat longer than the axial depth of the cold head cylinder 15 so that the other end is located outside the cold head cylinder 15 when inserted into the cold head cylinder 15.

[0048] One open end of the temperature-raising assist tool 60 located outside the cold head cylinder 15 when the temperature-raising assist tool 60 is inserted into the cold head cylinder 15 is used as a hot air inlet 64, as shown in Fig. 6. A hot air outlet of the hot air generator 48 is removably connected to the hot air inlet 64. Hot air 49 from the hot air generator 48 is introduced into the temperature-raising assist tool 60 from the hot air inlet 64.

[0049] The heater 61 is provided at the tip of the main body 62. The heater 61 includes a hot air outlet 65 configured to blow out the hot air 49 from the hot air generator 48. The hot air outlet 65 is configured to direct the hot air 49 so as to deviate from the temperature sensor 63. Specifically, for example, the hot air outlet 65 may be a plurality of holes formed in the heater 61 such that the hot air 49 is discharged radially outward from the heater 61. The plurality of holes may be aligned in the circumferential direction so that the hot air 49 can be discharged over the entire circumference of the heater 61.

[0050] 7, the hot air outlet 65 is configured to direct the hot air 49 toward a side surface of the cold head cylinder 15 (for example, the side portion 24b of the two-stage cooling stage 24) when the main body 62 is inserted into the cold head cylinder 15. In other words, the hot air outlet 65 is configured so that the hot air 49 is not blown directly toward the bottom portion 24a of the two-stage cooling stage 24.

[0051] The temperature sensor 63 is attached closer to the tip of the main body 62 than the heater 61. Therefore, when the main body 62 is inserted into the cold head cylinder 15, the temperature sensor 63 is closer to the bottom surface of the cold head cylinder 15 (i.e., the bottom 24a of the two-stage cooling stage 24) than the heater 61.

[0052] A contact-type thermometer may be used as the temperature sensor 63. When the main body 62 is inserted into the cold head cylinder 15, the temperature sensor 63 or a portion to which the temperature sensor 63 is attached (for example, a temperature measuring unit 66b described later) comes into contact with the bottom 24a of the two-stage cooling stage 24, and the temperature of the bottom 24a can be measured. The temperature sensor 63 may be capable of measuring temperature with better accuracy than the temperature sensor 44 of the cold head 14 in a temperature range of about room temperature (for example, a temperature range of about 0 to 50°C), and may be, for example, an inexpensive general-purpose temperature sensor such as a thermocouple or a platinum temperature sensor.

[0053] In this embodiment, the temperature sensor 63 is attached to the main body 62 via a shock absorbing material 66. In this example, as shown in FIG. 6, the shock absorbing material 66 is a flexible connecting member, and includes a base 66a attached to the bottom surface of the main body 62, a temperature measuring part 66b to which the temperature sensor 63 is attached, and a flexible part 66c connecting the base 66a and the temperature measuring part 66b. When the main body 62 is inserted into the cold head cylinder 15 and the temperature sensor 63 or the temperature measuring part 66b contacts the bottom part 24a of the two-stage cooling stage 24, the flexible part 66c of the shock absorbing material 66 can absorb or mitigate the impact of the temperature rise assistance tool 60 hitting the two-stage cooling stage 24. Instead of the flexible part 66c, or together with the flexible part 66c, the shock absorbing material 66 may include a spring material connecting the base 66a and the temperature measuring part 66b.

[0054] It should be noted that the shock absorbing material 66 is not required. In one embodiment, the temperature sensor 63 may be directly attached to the bottom of the body 62.

[0055] A temperature indicator 70 may be provided attached to the temperature rise assisting tool 60. The temperature sensor 63 may be connected to the temperature indicator 70 by a wire 67. The wire 67 may extend from the temperature sensor 63, be spirally wound around the main body 62, and be drawn out to the outside of the cold head cylinder 15. The temperature indicator 70 can obtain the output of the temperature sensor 63 through the wire 67 and display the measured temperature or output it to another device. The temperature indicator 70 may be the same as the above-mentioned temperature indicator 46 for displaying the measured temperature of the temperature sensor 44 of the cold head 14, or may be provided separately from the temperature indicator 46. The temperature indicator 70 may be, for example, a commercially available temperature tester.

[0056] FIG. 7 is a schematic diagram showing a method for increasing the temperature of the cold head cylinder 15 according to an embodiment. First, as a first step of the method, as shown on the left side of FIG. 7, a heater 61 and a temperature sensor 63 are arranged in the cold head cylinder 15 such that the temperature sensor 63 is closer to the bottom surface of the cold head cylinder 15 than the heater 61. This arrangement step can be performed by inserting the main body 62 of the temperature increase assistance tool 60 into the cold head cylinder 15. The main body 62 is inserted into the cold head cylinder 15, the hot air outlet 65 of the heater 61 is arranged to face the side part 24b of the two-stage cooling stage 24, and the temperature sensor 63 (or temperature measuring part 66b) is arranged in contact with the bottom part 24a of the two-stage cooling stage 24.

[0057] Before the first step, the cold head cylinder 15 may be naturally heated by heat inflow from the surrounding environment. For example, when the operation of the cryogenic refrigerator 10 is terminated, the two-stage cooling stage 24 is at an extremely low temperature, for example, about 4K. The cold head cylinder 15 (i.e., the two-stage cooling stage 24) may be naturally heated from this operation termination temperature to a predetermined heating start temperature (for example, liquid nitrogen temperature). The temperature of the two-stage cooling stage 24 during the natural heating can be known from the temperature measured by the temperature sensor 44. The operator may continue or end the natural heating based on the temperature measured by the temperature sensor 44. The following second step may be performed after the natural heating is completed.

[0058] Next, as a second step, as shown on the right side of FIG. 7, the cold head cylinder 15 is heated using a heating assistance tool 60. In this embodiment, the cold head cylinder 15 is heated using hot air 49 from a hot air generator 48. The hot air 49 introduced into the body 62 of the heating assistance tool 60 from a hot air inlet 64 (see FIG. 6) is blown out toward the side portion 24b of the two-stage cooling stage 24 through a hot air outlet 65 of a heater 61. Therefore, the hot air 49 first heats the side portion 24b of the two-stage cooling stage 24 with priority. Then, the side portion 24b of the two-stage cooling stage 24 and other parts of the cold head cylinder 15, such as the two-stage cylinder 22, are heated mainly by heat conduction from the side portion 24b.

[0059] Simultaneously with the heating of the cold head cylinder 15, the temperature of the cold head cylinder 15 is measured using a temperature sensor 63. The temperature of the bottom 24a of the two-stage cooling stage 24 is measured by the temperature sensor 63, and information indicating the measured temperature is transmitted from the temperature sensor 63 to a temperature display 70 (see FIG. 6). The measured temperature is displayed by or output from the temperature display 70. Using the temperature display 70, an operator can grasp the temperature of the cold head cylinder 15, specifically, the temperature of the bottom 24a of the two-stage cooling stage 24. The operator may end this heating method when the measured temperature reaches a heating end temperature (e.g., about 20 to 40° C.).

[0060] According to the embodiment, as described above, the temperature sensor 63 is arranged to measure the temperature of the bottom 24a of the two-stage cooling stage 24. Therefore, the heating temperature can be accurately measured by the temperature sensor 44 of the cold head 14 provided at the bottom 24a of the two-stage cooling stage 24. Therefore, it is possible to prevent or reduce the risk of excessive heating of the cold head cylinder 15 caused by temperature measurement errors of the temperature sensor 44 when the conventional heating assistant 50 is used. It is also possible to avoid adverse effects on the temperature sensor 44 of the cold head 14 that may be caused by excessive heating.

[0061] According to the embodiment, by heating the cold head cylinder 15 using the heating assistance tool 60, the side portion 24b of the two-stage cooling stage 24 is heated before the bottom portion 24a. Therefore, even if an overheat occurs, it will first occur at the side portion 24b of the two-stage cooling stage 24. This also helps to reduce the risk of an overheat at the bottom portion 24a of the two-stage cooling stage 24.

[0062] In addition, the fact that the hot air 49 does not directly hit the temperature sensor 63 and that a temperature sensor with good measurement accuracy near room temperature can be used as the temperature sensor 63 also helps to accurately know the heating temperature at the temperature sensor 44 of the cold head 14.

[0063] Since the side surface of the cold head cylinder 15 (for example, the inner peripheral surface of the two-stage cylinder 22) becomes a sliding surface with the two-stage displacer 23 during operation of the cryogenic refrigerator 10, high dimensional accuracy is required for the radial clearance between the cold head cylinder 15 and the two-stage displacer 23. If the side surface of the cold head cylinder 15 is damaged for some reason and this radial clearance changes, this may have a significant effect on the cryogenic refrigerator 10, such as a decrease in the refrigeration performance of the cryogenic refrigerator 10.

[0064] According to the embodiment, since the temperature sensor 63 is in contact with the bottom 24a of the two-stage cooling stage 24, the heating assistant 60 does not need to contact the side surface of the cold head cylinder 15 (for example, the inner peripheral surface of the two-stage cylinder 22). This makes it possible to avoid damage that may occur if the heating assistant 60 comes into contact with the side surface of the cold head cylinder 15, and also to avoid the above-mentioned problems.

[0065] In the above embodiment, the temperature rise assisting device 60 is configured to heat the cold head cylinder 15 with hot air 49, but the temperature rise assisting device 60 may also use other heating methods.

[0066] FIG. 8 is a diagram showing a schematic diagram of a modified example of the temperature rise assisting tool 60 according to the embodiment. The temperature rise assisting tool 60 includes a main body 62 including a heater 61, and a temperature sensor 63 provided on the main body 62. The heater 61 may be an appropriate heater, such as an electric heater. The heater 61 may be provided on the tip of the main body 62 so as to face the side portion 24b of the two-stage cooling stage 24 when the main body 62 is inserted into the cold head cylinder 15 in order to efficiently heat the side portion 24b. The temperature sensor 63 is attached to the tip side of the main body 62 rather than the heater 61. When the main body 62 is inserted into the cold head cylinder 15, the temperature sensor 63 can contact the bottom surface of the cold head cylinder 15 (i.e., the bottom portion 24a of the two-stage cooling stage 24) rather than the heater 61. As shown in the figure, the temperature sensor 63 may be directly attached to the bottom of the main body 62.

[0067] 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.

[0068] In the above embodiment, the case where the temperature-raising auxiliary tool 60 heats the two-stage cooling stage 24 of the cold head 14 has been described as an example, but the temperature-raising auxiliary tool 60 can also be used to heat the first-stage cooling stage 20 of the cold head 14. In that case, the temperature-raising auxiliary tool 60 is inserted into the cold head cylinder 15, the hot air outlet 65 of the heater 61 is disposed facing the side of the first-stage cooling stage 20, and the temperature sensor 63 (or the temperature measuring part 66b) may be disposed in contact with the bottom of the first-stage cooling stage 20. Then, the cold head cylinder 15 may be heated using the heater 61. The hot air 49 may be blown toward the side of the first-stage cooling stage 20 through the hot air outlet 65 of the heater 61. At the same time as the cold head cylinder 15 is heated, the temperature sensor 63 may be used to measure the temperature of the cold head cylinder 15 (for example, the temperature of the bottom of the first-stage cooling stage 20).

[0069] In the above embodiment, the cryocooler 10 is a two-stage GM refrigerator, but the cryocooler 10 may be a single-stage GM refrigerator or another multi-stage GM refrigerator such as a three-stage GM refrigerator. Also, the cryocooler 10 is not limited to a GM refrigerator. The cryocooler 10 may be a pulse tube refrigerator, a Stirling refrigerator, or another type of cryocooler.

[0070] 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]

[0071] 14 cold head, 15 cold head cylinder, 44 temperature sensor, 48 hot air generator, 49 hot air, 60 heating assistance device, 61 heater, 62 main body, 63 temperature sensor, 65 hot air outlet, 66 shock absorbing material.

Claims

1. A heating aid for a cold head cylinder, comprising: a body including a heater and insertable into a cold head cylinder; A temperature sensor attached to the tip side of the main body relative to the heater.

2. The heating aid according to claim 1, characterized in that the temperature sensor is attached to the main body so that when the main body is inserted into the cold head cylinder, the temperature sensor is closer to the bottom surface of the cold head cylinder than the heater.

3. The heater includes a hot air outlet configured to blow out hot air from a hot air generator, 3. The heating assistance device according to claim 1, wherein the hot air outlet is configured to direct the hot air so as to deviate from the temperature sensor.

4. The heating aid according to claim 3, characterized in that the hot air outlet is configured to direct the hot air toward a side surface of the cold head cylinder when the main body is inserted into the cold head cylinder.

5. 3. The heating assistance device according to claim 1, wherein the temperature sensor is attached to the main body via a shock absorbing material.

6. A method for increasing the temperature of a cold head cylinder, comprising the steps of: disposing a heater and a temperature sensor within the cold head cylinder such that the temperature sensor is closer to a bottom surface of the cold head cylinder than the heater; heating the cold head cylinder with the heater while measuring a temperature of the cold head cylinder with the temperature sensor.

Images