Cryogenic freezer and cryogenic device

Abstract

To reduce measurement error of a temperature sensor used together with a cryogenic freezer.SOLUTION: A cryogenic freezer comprises: a cooling stage, such as a second cooling stage 24; and a temperature sensor 44 mounted to the cooling stage, the temperature sensor 44 including a plurality of resistance temperature detectors 50 connected to generate a combined resistance, and a common lead-out wiring 45 connected to the plurality of resistance temperature detectors 50 to enable measurement of the combined resistance. The plurality of resistance temperature detectors 50 may include at least three resistance temperature detectors.SELECTED DRAWING: Figure 5

Description

Technical Field

[0001] The present invention relates to cryogenic refrigerators and cryogenic devices.

Background Art

[0002] Conventionally, it is known to attach the cold head of a cryogenic refrigerator to a vacuum vessel via a so-called maintenance sleeve. In the vacuum vessel, a cooled object such as a superconducting coil is accommodated, and this cooled 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 cooled object via the maintenance sleeve.

[0003] During long-term operation of a cryogenic refrigerator, maintenance of the cryogenic refrigerator may be required periodically. An operator can lift the cold head slightly from the maintenance sleeve, release the thermal contact between the cold head and the maintenance sleeve, and perform maintenance on the cold head. The cold head is heated to a temperature convenient for maintenance work, such as room temperature, and then re-cooled after the work is completed. On the other hand, by releasing the contact of the cold head, the cooled object can be kept at a low temperature. Therefore, this maintenance method can shorten the re-cooling time of the cooled object compared to the case where the cooled object is heated to room temperature together with the cold head and then maintenance is performed on the cold head, and can shorten the required time for maintenance.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] As one of the steps in the above maintenance, the cold head may be disassembled. The disassembly work may include a step of removing the internal components of the cold head from the cold head cylinder while leaving the cold head cylinder in the maintenance sleeve. At this time, the inner surface of the cold head cylinder is exposed to the air flowing in from the surrounding environment. When the cylinder is at a lower temperature than the ambient temperature, moisture in the air may condense on the surface of this cylinder and frost or ice may adhere. Before reassembling the cold head, the cold head cylinder is heated to the ambient temperature or a somewhat higher temperature (for example, about 20 to 40 °C) in order to remove such frost. Temperature control in the heating operation is usually performed using a temperature sensor provided in the cold head cylinder.

[0006] Although the cold head employs a temperature sensor suitable for extremely low temperature measurement, such a temperature sensor for extremely low temperatures is not necessarily guaranteed to have sufficient accuracy for temperature measurement at room temperature levels in the above heating operation. In that case, there is a risk of overheating of the cold head cylinder during heating. That is, it is conceivable that an undesirable situation may occur in which, although the cold head cylinder is actually heated to a temperature excessively higher than the desired temperature, this cannot be detected due to a temperature measurement error.

[0007] One of the exemplary purposes of an aspect of the present invention is to reduce the measurement error of a temperature sensor used with an extremely low temperature refrigerator.

Means for Solving the Problem

[0008] According to an aspect of the present invention, an extremely low temperature refrigerator includes a cooling stage, and a temperature sensor attached to the cooling stage, the temperature sensor including a plurality of temperature measuring resistors connected so as to generate a combined resistance, and a common lead wire connected to the plurality of temperature measuring resistors so as to enable measurement of the combined resistance.

[0009] According to an aspect of the present invention, a cryogenic apparatus includes a vacuum vessel that houses an object to be cooled, a cryogenic refrigerator that is installed in the vacuum vessel and cools the object to be cooled, and a temperature sensor that measures the temperature of the object to be cooled. The temperature sensor includes a plurality of resistance temperature detectors connected so as to generate a combined resistance, and a common lead wire connected to the plurality of resistance temperature detectors so as to enable measurement of the combined resistance.

Advantages of the Invention

[0010] According to the present invention, it is possible to reduce the measurement error of the temperature sensor used together with the cryogenic refrigerator.

Brief Description of the Drawings

[0011]

Figure 1

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Figure 10

Best Mode for Carrying Out the Invention

[0012] Hereinafter, with reference to the drawings, embodiments for carrying out the present invention will be described in detail. In the description and the drawings, the same or equivalent components, members, and processes are denoted by the same reference numerals, and redundant descriptions are omitted as appropriate. The scales and shapes of the respective parts shown are set for convenience in order to facilitate the explanation, and are not to be construed in a limited sense unless otherwise specified. The embodiments are illustrative 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] FIGS. 1 and 2 are diagrams schematically showing a cryogenic apparatus 100 according to an embodiment. FIG. 1 shows a state in which the thermal coupling between the cryogenic refrigerator 10 and a cooled object 90 such as a superconducting coil is released, and FIG. 2 shows a state in which the two are thermally coupled.

[0014] The cryogenic refrigerator 10 is a two-stage Gifford-McMahon (GM) refrigerator in this embodiment. 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, boost the recovered refrigerant gas, and supply the refrigerant gas to the cold head 14 again. The cold head 14, also referred to as an expander, can generate cold by adiabatically expanding 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 an appropriate combination of pressure fluctuation and volume fluctuation of the refrigerant gas in the cold head 14, thereby constituting a refrigeration cycle (for example, 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, also referred to as a working gas, 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 cylinder 18, a first cooling stage 20, a second cylinder 22, and a second cooling stage 24, which are coaxially arranged along the central axis of the cold head 14.

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

[0018] The cold head drive unit 16 is attached to the cold head flange 17. The cold head drive unit 16 includes a motor that reciprocates a first displacer and a second displacer housed in the first cylinder 18 and the second cylinder 22, respectively, in the axial direction. The cold head drive unit 16 also houses a pressure switching valve that is driven in synchronization with the displacer by this motor. The pressure switching valve is configured to periodically switch between receiving high-pressure refrigerant gas into the cold head 14 and sending out low-pressure refrigerant gas. The compressor 12, the cold head drive unit 16, and the cold head flange 17 are arranged in the ambient environment 27.

[0019] By operating the cryogenic refrigerator 10, the first cooling stage 20 is cooled to the first cooling temperature, and the second cooling stage 24 is cooled to the second cooling temperature lower than the first cooling temperature. The first cooling temperature may be selected from a temperature range of, for example, 30 K or more and 80 K or less (usually 30 K or more and 50 K or less), and may be, for example, about 40 K. The second cooling temperature may be selected from a temperature range of, for example, 3 K or more and 20 K or less (usually 3 K or more and 4.2 K or less), and may be, for example, about 4 K.

[0020] The mounting structure 30 of the cryogenic refrigerator 10 is a device for mounting the cold head 14 on a vacuum vessel 26 (for example, a cryogenic vacuum vessel such as a cryostat). The mounting structure 30 may be referred to as a cold head housing sleeve or simply a sleeve. The mounting structure 30 is installed in the vacuum vessel 26 so as to form an airtight region 28 isolated from the surrounding environment 27 between the cold head 14 and the mounting structure 30. The surrounding 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. Further, the mounting structure 30 is installed in the vacuum vessel 26 so as to partition a vacuum region 29 in the vacuum vessel 26 in combination with the vacuum vessel 26.

[0021] The mounting structure 30 may be provided to the customer by the manufacturer of the cryogenic refrigerator 10 together with the cryogenic refrigerator 10. It can also be said that a cooling device for cooling the object to be cooled 90 is composed of the cryogenic refrigerator 10 and the mounting structure 30.

[0022] The mounting structure 30 is also configured in a two-stage manner corresponding to the cold head 14. The mounting structure 30 includes a sleeve flange 32, a first sleeve body 34, a first heat transfer stage 36, a second sleeve body 38, and a second heat transfer stage 40, which are coaxially arranged along the central axis of the cold head 14.

[0023] The sleeve flange 32 is fixed, for example, to an opening formed in the top plate of the vacuum vessel 26, and the mounting structure 30 extends into the vacuum vessel 26 from this opening. Further, a cold head flange 17 is attached to the sleeve flange 32 by a fastening member 33 such as a bolt. When the cold head flange 17 and the sleeve flange 32 are fastened, the first cooling stage 20 and the second cooling stage 24 are pressed against the first heat transfer stage 36 and the second heat transfer stage 40, respectively. The sleeve flange 32 has an opening for receiving the cold head 14 radially inward of the fastening member 33, and the cold head flange 17 is in contact with the inner peripheral surface of this opening.

[0024] When the fastening between the cold head flange 17 and the sleeve flange 32 by the fastening member 33 is released, the cold head flange 17 is axially slidable relative to the sleeve flange 32, whereby the cold head 14 is axially (the vertical direction in FIGS. 1 and 2) movable relative to the mounting structure 30. The movable range is, for example, within several millimeters, for example, about 2 to 3 mm. The operator can manually, or by using an auxiliary tool such as a hydraulic jack, or if a lifting device having a power source is connected to the cold head 14, by operating this, raise and lower the cold head 14 axially within this movable range.

[0025] 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 in the inner peripheral surface of the opening of the sleeve flange 32. Since the seal member 42 is provided, the hermetic region 28 is isolated from the ambient environment 27 even when the cold head 14 is axially moved relative to the mounting structure 30 within the above-described movable range.

[0026] The first sleeve body 34 connects the sleeve flange 32 to the first heat transfer stage 36, and the second sleeve body 38 connects the first heat transfer stage 36 to the second heat transfer stage 40. The first sleeve body 34 and the second sleeve body 38 are respectively arranged to surround the first cylinder 18 and the second cylinder 22. An opening is provided at the center of the first heat transfer stage 36 to connect the internal space of the first sleeve body 34 to the internal space of the second sleeve body 38. The second cylinder 22 and the second cooling stage 24 of the cold head 14 are inserted into the internal space of the second sleeve body 38 from this opening. The first heat transfer stage 36 and the second heat transfer stage 40 are formed of a high thermal conductivity metal such as copper (e.g., pure copper), or other heat conductive materials. The first sleeve body 34 and the second 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 that of the material forming the sleeve body.

[0027] Therefore, the first heat transfer stage 36 of the mounting structure 30 comes into contact with or is disengaged from the first cooling stage 20 of the cold head 14 due to the movement of the cold head 14 of the cryogenic refrigerator 10. Similarly, the second heat transfer stage 40 of the mounting structure 30 comes into contact with or is disengaged from the second cooling stage 24 due to the movement of the cold head 14.

[0028] A temperature sensor 44 may be provided on the cold head cylinder 15. The temperature sensor 44 may be provided at the bottom of the second cooling stage 24 to measure the temperature of the second cooling stage 24. The temperature sensor 44 is a cryogenic temperature sensor suitable for measuring the cryogenic temperature achieved at the second cooling stage 24. The temperature sensor 44 may be a thermometer of the type having a resistance temperature detector, and the resistance temperature detector may be, for example, a platinum resistance thermometer, a platinum cobalt resistance thermometer, or a ruthenium oxide (RuO2) resistance temperature detector.

[0029] The temperature sensor 44 may be connected to the temperature indicator 46 by the lead wire 45. The lead wire 45 may be spirally wound around the cold head cylinder 15 in the hermetic region 28 and drawn out to the ambient environment 27 through the feed-through 47 of the cold head flange 17. The temperature indicator 46 may be connected to the temperature indicator 46 arranged in the ambient environment 27. The temperature indicator 46 can obtain the output of the temperature sensor 44 through the lead wire 45 and display the measured temperature or output it to other devices. The temperature indicator 46 may form part of a controller that controls the cryogenic refrigerator 10.

[0030] Also, 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 to be cooled 90 in order to thermally protect the object to be cooled 90. Only a part of the radiation shield 92 is shown in FIGS. 1 and 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. Also, the 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.

[0031] As shown in FIG. 1, when the thermal contact between the cold head 14 and the mounting structure 30 is released, the cold head 14 is located, for example, at the upper end of the movable range. At this time, the first cooling stage 20 is physically separated from the first heat transfer stage 36, and the second cooling stage 24 is physically separated from the second heat transfer stage 40. Therefore, the cryogenic refrigerator 10 does not cool the object to be cooled 90 and the radiation shield 92. Even if the cold head 14 is heated to a temperature higher than that of the object to be cooled 90 and the radiation shield 92, for example, room temperature, the thermal influence from the cold head 14 to the object to be cooled 90 and the radiation shield 92 is limited or negligible. The object to be cooled 90 and the radiation shield 92 are maintained at extremely low temperatures.

[0032] As shown in FIG. 2, when the cold head 14 and the mounting structure 30 are in thermal contact, the cold head 14 is located at the lower end of the movable range. At this time, the first cooling stage 20 is physically in contact with the first heat transfer stage 36, whereby the first cooling stage 20 is in thermal contact with the radiation shield 92 via the first heat transfer stage 36. At the same time, the second cooling stage 24 is physically in contact with the second heat transfer stage 40, whereby the second cooling stage 24 is in thermal contact with the object to be cooled 90 via the second heat transfer stage 40. Thus, the cryogenic refrigerator 10 can cool the object to be cooled 90 and the radiation shield 92. The radiation shield 92 is cooled to the first cooling temperature, and the object to be cooled 90 is cooled to the second cooling temperature.

[0033] An example of the operation of the cryogenic apparatus 100 having the above configuration will be described. When the timing at which maintenance of the cryogenic refrigerator 10 is allowed arrives, the cooling operation of the cryogenic refrigerator 10 is stopped. At this time, as shown in FIG. 2, the first cooling stage 20 is physically and thermally in contact with the first heat transfer stage 36, and the second cooling stage 24 is physically and thermally in contact with the second heat transfer stage 40.

[0034] When the operator operates the fastening member 33, the fastening between the cold head flange 17 and the sleeve flange 32 is released. Then, the cold head 14 is slightly lifted from the mounting structure 30. Since the seal member 42 is provided between the cold head flange 17 and the sleeve flange 32, the isolation of the hermetic region 28 from the surrounding environment 27 is maintained.

[0035] In this way, as shown in FIG. 1, the first cooling stage 20 becomes physically separated from the first heat transfer stage 36 and thermally non-contact, and the second cooling stage 24 becomes physically separated from the second heat transfer stage 40 and thermally non-contact. Therefore, the cold head 14 can be heated while keeping the object to be cooled 90 and the radiation shield 92 at a low temperature.

[0036] Maintenance of the cryogenic refrigerator 10 is performed. FIGS. 3 and 4 are diagrams schematically showing the cold head 14 of the cryogenic refrigerator 10 during maintenance according to the embodiment. As shown in FIG. 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 displacer 19 and the second displacer 23 are respectively pulled out from the first cylinder 18 and the second cylinder 22. The cold head cylinder 15 (that is, the cold head flange 17, the first cylinder 18, the first cooling stage 20, the second cylinder 22, and the second cooling stage 24) remains mounted on the mounting structure 30 as it is. The removed cold head drive unit 16, the first displacer 19, and the second displacer 23 are subjected to maintenance such as replacement of consumable parts, cleaning, and repair, or are replaced with a new cold head drive unit or displacer.

[0037] By removing the internal structure of the cold head 14 from the cold head cylinder 15 in this way, the internal surface of the cold head cylinder 15 is exposed to the ambient environment 27. During the cooling operation of the cryogenic refrigerator 10, the members cooled to cryogenic temperatures, such as the first cooling stage 20, the second cylinder 22, and the second cooling stage 24, may still be at low temperatures, and frost may adhere to the surfaces of these members from the ambient environment 27.

[0038] Therefore, before reassembling the cold head 14, the cold head cylinder 15 may be heated to remove the frost adhering inside the cold head cylinder 15. For this heating, as shown in FIG. 4, a warm air generator 48 such as a heat gun or a dryer may be used. The cold head cylinder 15 may be heated by supplying warm air 49 from the warm air generator 48 into the cold head cylinder 15.

[0039] Subsequently, the cryogenic refrigerator 10 is reassembled again. The maintained (or new) cold head drive unit 16, the first displacer 19, and the second displacer 23 are inserted into the cold head cylinder 15, and the cold head drive unit 16 is reinstalled on the cold head flange 17. It returns to the state shown in FIG. 1. Then, the cooling operation of the cryogenic refrigerator 10 is resumed.

[0040] The cold head 14 is moved relative to the mounting structure 30 so that the first cooling stage 20 and the second cooling stage 24 are respectively brought into contact with the first heat transfer stage 36 and the second heat transfer stage 40. The cold head 14 is pushed back into the mounting structure 30.

[0041] By the movement of the cold head 14, 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 by the fastening member 33. Thus, it returns to the state shown in FIG. 2.

[0042] Therefore, according to the cryogenic apparatus 100 according to the embodiment, the thermal contact with the mounting structure 30 is released by the movement of the cold head 14, and the cold head 14 can be heated up for maintenance while keeping the object to be cooled 90 and the radiation shield 92 at a low temperature. Compared with the case where the object to be cooled 90 and the radiation shield 92 are heated up to room temperature together with the cold head 14 for maintenance of the cryogenic refrigerator 10, the recooling time of the object to be cooled 90 and the radiation shield 92 can be shortened, and the required time for maintenance can be shortened.

[0043] The temperature control of the cold head cylinder 15 in the heating process is performed using the temperature sensor 44 provided in the cold head 14. As described above, a temperature sensor suitable for measuring cryogenic temperatures is used as the temperature sensor 44. However, depending on its specifications, such a cryogenic temperature sensor does not guarantee sufficient accuracy for measuring a temperature range of about room temperature that should be measured in the heating process of the cold head cylinder 15.

[0044] A temperature sensor having a resistance temperature detector, such as the temperature sensor 44, measures the temperature by utilizing the fact that the electrical resistance of the resistance temperature detector changes depending on the temperature. That is, the resistance value of the resistance temperature detector is measured, and the measured resistance value is converted into a temperature, whereby the measured temperature is obtained. For example, the above-described temperature indicator 46 is configured to perform such conversion. In order to convert the resistance value into a temperature value, a table showing the relationship between the resistance value and the temperature value in the resistance temperature detector is prepared in advance and used. Although there may be variations due to individual differences for each individual resistance temperature detector in this conversion table, it is not always practical as an industrial product to prepare the conversion table individually, and therefore, a standard conversion table, also called a standard curve, is used.

[0045] Therefore, for a certain resistance temperature detector, if the actual relationship between the resistance of the resistance temperature detector and the temperature deviates from the standard conversion table due to individual differences, an error will occur in the measured temperature. Through independent research, the inventor of the present invention has recognized that the standard curve, which is optimally adjusted for ultra-low temperature measurement, tends to deviate from the actual relationship between the resistance and temperature of the resistance temperature detector at temperatures near room temperature where the temperature difference from such ultra-low temperatures is large, leading to temperature measurement errors near room temperature.

[0046] In such a case, there is a risk that the second cooling stage 24 of the cold head cylinder 15 may be overheated during the heating process. That is, a situation may occur where, although the second cooling stage 24 is actually heated to a temperature excessively higher than the desired temperature around room temperature, this cannot be detected due to temperature measurement errors, which is an undesirable situation.

[0047] The overheating of the second cooling stage 24 may, in some cases, adversely affect the operation of the ultra-low temperature freezer 10 after reassembly. For example, grease or adhesive may be used between the temperature sensor 44 and the second cooling stage 24 to improve heat conduction between them, but such intervening substances often have low heat resistance. If the intervening substance is damaged due to overheating, a decrease in the accuracy of subsequent temperature measurement by the temperature sensor 44 is a concern. In the worst case, additional maintenance work that is not originally required, such as removing the cold head cylinder 15 from the mounting structure 30 and then repairing or replacing the temperature sensor 44 and the second cooling stage 24, may occur.

[0048] FIG. 5 is a diagram schematically showing an example of the temperature sensor 44 that can be mounted on the cryogenic refrigerator 10 according to the embodiment. As described above, the temperature sensor 44 is attached to the second cooling stage 24 of the cryogenic refrigerator 10. In this embodiment, the temperature sensor 44 includes a plurality of resistance temperature detectors 50. The temperature sensor 44 may include at least three resistance temperature detectors 50, and in the illustrated example, includes four resistance temperature detectors 50. The temperature sensor 44 may include at most 10 or at most 8 resistance temperature detectors 50. The resistance temperature detector 50 may be, for example, a chip resistor. The plurality of resistance temperature detectors 50 may be evenly arranged on the second cooling stage 24, for example, may be arranged at equal intervals in the circumferential direction of the second cooling stage 24.

[0049] The plurality of resistance temperature detectors 50 are connected so as to generate a combined resistance R0. In the example of FIG. 5, the plurality of resistance temperature detectors 50, specifically four resistance temperature detectors 50, are connected in series. Therefore, when the resistances of these resistance temperature detectors 50 are R1, R2, R3, and R4, the combined resistance R0 is the sum of the resistances as is known, so R0 = R1 + R2 + R3 + R4.

[0050] The lead wiring 45 is connected to the plurality of resistance temperature detectors 50 so as to enable measurement of the combined resistance R0 of the plurality of resistance temperature detectors 50. The lead wiring 45 connects the terminals 52 at both ends of the plurality of resistance temperature detectors 50, that is, both ends of the combined resistance R0, to the temperature indicator 46. As an example, the connection method of the lead wiring 45 may be a two-wire type as shown in the figure. Alternatively, the lead wiring 45 may be other connection methods such as a three-wire type or a four-wire type.

[0051] The temperature indicator 46 is configured to measure the combined resistance R0 from the voltage between both ends of the combined resistance R0 and the current flowing through the lead wiring 45, and output the measured temperature of the second cooling stage 24 based on the measured combined resistance R0. The temperature indicator 46 may include a conversion table 54 showing the relationship between resistance and temperature, and obtain the measured temperature of the second cooling stage 24 from the measured combined resistance R0 and the conversion table 54. The conversion table 54 may be a standard curve.

[0052] Since existing temperature sensors have only one resistance temperature detector, problems with measurement errors due to individual differences in resistance temperature detectors as described above can occur. In contrast, according to the embodiment, since the combined resistance R0 is the sum of the resistances of a plurality of resistance temperature detectors 50, due to the averaging effect, the relationship between the combined resistance R0 and the temperature of the second cooling stage 24 is expected to deviate less from the standard curve than the relationship between the resistance and temperature for each individual resistance temperature detector 50.

[0053] Therefore, the temperature sensor 44 can reduce temperature measurement errors. It is possible to prevent overheating or reduce the risk thereof during the heating process of the cold head cylinder 15 during maintenance of the cryogenic refrigerator 10. Adverse effects on the temperature sensor 44 of the cold head 14 that may be caused by overheating can also be avoided.

[0054] The lead wiring 45 is a current path between the temperature indicator 46 and the plurality of resistance temperature detectors 50, and can also be a heat transfer path from the ambient environment 27 to the second cooling stage 24. If wiring were connected individually for each resistance temperature detector 50, since each wiring would become a heat transfer path, there is concern that the heat input to the second cooling stage 24 would increase. In contrast, according to the embodiment, the plurality of resistance temperature detectors 50 are collectively connected to a common lead wiring 45. Thus, an increase in the heat input that is a concern can be avoided. Also, an increase in cost due to an increase in wiring can be avoided.

[0055] FIG. 6 is a diagram schematically showing another example of a temperature sensor 44 that can be mounted on the cryogenic refrigerator 10 according to the embodiment. The plurality of resistance temperature detectors 50 may be connected in parallel. In this case, as is known, the combined resistance R0 is obtained from 1 / R0 = 1 / R1 + 1 / R2 + 1 / R3 + 1 / R4. The lead wiring 45 connects the terminals 52 at both ends of the plurality of resistance temperature detectors 50, that is, both ends of the combined resistance R0, to the temperature indicator 46. Even in this case, similar to the example shown in FIG. 5, the temperature sensor 44 can reduce temperature measurement errors due to the averaging effect.

[0056] FIG. 7 is a diagram schematically showing an exemplary configuration of the packaging of the temperature sensor 44 according to the embodiment. In addition to the plurality of resistance temperature detectors 50 and the common lead-out wiring 45 connected thereto, the temperature sensor 44 includes a support 56 on which the plurality of resistance temperature detectors 50 are mounted and which is attached to the second cooling stage 24. The plurality of resistance temperature detectors 50 are connected in series or in parallel as described above to generate a combined resistance. The resistance temperature detector 50 may be disposed on the contact surface of the support 56 with the second cooling stage 24, or may be embedded in the support 56. The support 56 is attached to the surface of the second cooling stage 24, for example, the side surface. The planar shape of the support 56 may be any shape such as a rectangle or a circle. The support 56 may be attached to the second cooling stage 24 by a fastening member such as a bolt, or by any other appropriate fixing method such as adhesion or welding. The support 56 is formed of, for example, a metal material such as copper or stainless steel, or may be formed of any other appropriate material.

[0057] FIG. 8 is a perspective view schematically showing an exemplary configuration of the packaging of the temperature sensor 44 according to the embodiment. The temperature sensor 44 includes a plurality of resistance temperature detectors 50 and a common lead-out wiring 45 connected thereto. The temperature sensor 44 may include a plurality of stacked chip resistors as the plurality of resistance temperature detectors 50. These chip resistors are connected in series or in parallel as described above to generate a combined resistance. The stacking of the chip resistors enables miniaturization of the temperature sensor 44. As a countermeasure against electromagnetic noise, the plurality of chip resistors may be arranged on the support 56 without gaps between them.

[0058] FIG. 9 is a diagram schematically showing an exemplary arrangement of the temperature sensor 44 according to the embodiment. The temperature sensor 44 includes a plurality of resistance temperature detectors 50 and a common lead-out wiring 45 connected thereto. As shown, each of the plurality of resistance temperature detectors 50 may be attached to the second cooling stage 24. For example, the plurality of resistance temperature detectors 50 may be arranged side by side in a vertical groove 58 formed, for example, on the side surface of the second cooling stage 24 and accommodated in this vertical groove. The vertical groove may be covered with a cover. Alternatively, the vertical groove may be filled with a resin molding material.

[0059] FIG. 10 is a diagram schematically showing an exemplary arrangement of the temperature sensor 44 according to the embodiment. In the above-described embodiment, the temperature sensor 44 is provided on the second cooling stage 24 of the cryogenic refrigerator 10. Instead of or in addition to that, as shown in FIG. 10, the temperature sensor 44 according to the embodiment may be attached to the heat transfer stage of the mounting structure 30, for example, the second heat transfer stage 40. Alternatively, the temperature sensor 44 may be attached to any part of the cryogenic apparatus 100.

[0060] As described above, the present invention has been described based on the examples. It is understood by those skilled in the art that the present invention is not limited to the above-described embodiments, various design changes are possible, various modifications are possible, and such modifications are also within the scope of the present invention. The various features described in connection with one embodiment are also applicable to other embodiments. The new embodiments resulting from the combination have the effects of the respective embodiments combined.

[0061] In the above-described embodiment, the temperature sensor 44 is provided at a site of the second cooling temperature, such as the second cooling stage 24 of the cryogenic refrigerator 10 or the second heat transfer stage 40 of the mounting structure 30. Instead of or in addition to that, the temperature sensor 44 may be provided at a site of the first cooling temperature, such as the first cooling stage 20 of the cryogenic refrigerator 10 or the first heat transfer stage 36 of the mounting structure 30.

[0062] In the above-described embodiment, the case where the cryogenic refrigerator 10 is a two-stage GM refrigerator has been described as an example. However, the cryogenic refrigerator 10 may be a single-stage or multi-stage GM refrigerator such as a three-stage GM refrigerator. Further, the cryogenic refrigerator 10 is not limited to a GM refrigerator. The cryogenic refrigerator 10 may be a pulse tube refrigerator, a Stirling refrigerator, or other types of cryogenic refrigerators.

[0063] Based on the embodiment, the present invention has been described using specific terms. However, the embodiment merely shows one aspect of the principle and application of the present invention. In the embodiment, many modifications and arrangement changes are recognized without departing from the idea of the present invention defined in the claims.

Description of Reference Numerals

[0064] 10 Cryogenic refrigerator, 20 First cooling stage, 24 Second cooling stage, 26 Vacuum vessel, 44 Temperature sensor, 45 Lead wiring, 50 Resistance temperature detector, 56 Support, 90 Object to be cooled, 100 Cryogenic device.

Claims

1. A cooling stage, A temperature sensor mounted on the cooling stage, the temperature sensor comprising a plurality of resistance temperature detectors connected so as to generate a combined resistance, and a common lead wire connected to the plurality of resistance temperature detectors so as to enable measurement of the combined resistance. A cryogenic refrigerator characterized by comprising:

2. The cryogenic refrigerator according to claim 1, wherein the plurality of resistance temperature detectors include at least three resistance temperature detectors.

3. The cryogenic refrigerator according to claim 1, wherein the temperature sensor includes a support mounted with the plurality of resistance temperature detectors and attached to the cooling stage.

4. The cryogenic refrigerator according to claim 1, wherein each of the plurality of resistance temperature detectors is attached to the cooling stage.

5. The cryogenic refrigerator according to claim 1, wherein the plurality of resistance temperature detectors include a plurality of stacked chip resistors.

6. The cryogenic refrigerator includes a first cooling stage and a second cooling stage cooled to a temperature lower than that of the first cooling stage, The cryogenic refrigerator according to claim 1, wherein the cooling stage on which the temperature sensor is mounted is the second cooling stage.

7. A vacuum vessel for accommodating an object to be cooled, A cryogenic refrigerator installed in the vacuum vessel for cooling the object to be cooled, A temperature sensor for measuring the temperature of the object to be cooled, the temperature sensor comprising a plurality of resistance temperature detectors connected so as to generate a combined resistance, and a common lead wire connected to the plurality of resistance temperature detectors so as to enable measurement of the combined resistance. A cryogenic apparatus characterized by comprising:

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