Pre-cooling system for dilution refrigerator

Abstract

The invention provides a pre-cooling system for a dilution refrigerator, and relates to the technical field of mK-level dilution refrigeration, the pre-cooling system comprises a vacuum chamber comprising a normal temperature plate and multi-level cold plates, the multi-level cold plates comprise a first-level cold plate, a second-level cold plate and a third-level cold plate, and the vacuum chamber is internally provided with a pre-cooling unit arranged between the normal temperature plate and the second-level cold plate; the plurality of thermal switches are respectively arranged between two adjacent cold plates between the first-stage cold plate and the third-stage cold plate, and comprise a first-stage thermal switch and a plurality of second-stage thermal switches; the first-stage thermal switch and the plurality of second-stage thermal switches have conduction states in response to the fact that the temperature of the mixing chamber is higher than different target temperatures and disconnection states in response to the fact that the temperature of the mixing chamber is lower than different target temperatures; the dilution refrigeration unit comprises a mixing chamber arranged on a third-stage cold plate; the first-stage thermal switch and the multiple second-stage thermal switches work in the on state or the off state in response to the temperature change of the mixing chamber, so that the pre-cooling unit is adjusted between a first-stage pre-cooling mode and a second-stage pre-cooling mode.

Description

Technical Field

[0001] The present invention relates to the technical field of mK-level dilution refrigeration, and more specifically, to a pre-cooling system for a dilution refrigerator. Background Art

[0002] Dilution refrigerators are key equipment in the fields of quantum computing, condensed matter physics, and detectors. Especially in the field of quantum computing, the core computing element of quantum computing, the quantum computing chip, needs to work in an extremely low temperature environment as low as 10 mK to 100 mK to improve the quantum characteristics of superconducting qubits. Due to its characteristics of no electromagnetic interference and large cooling capacity, the dilution refrigerator is currently the general extremely low temperature technology that can meet the requirements of quantum computing.

[0003] A dilution refrigerator is a refrigeration device that utilizes the phase separation characteristics of a mixture of helium-3 ( 3 He) and helium-4 ( 4 He) to achieve extremely low temperatures. To maintain continuous refrigeration, the dilution refrigerator extracts the 3 He atoms in the dilution phase entering the mixing chamber through distillation and other methods, and recycles them back to the mixing chamber to form a continuous refrigeration cycle. By optimizing the design and operating conditions, the lowest temperature of the dilution refrigerator can reach the mK level.

[0004] With the rapid development of technologies such as quantum computing, high requirements are put forward for the cooling time of dilution refrigerators. The cooling time and rewarming time of dilution refrigeration directly determine the iteration speed of research such as quantum computing. Currently, when the dilution refrigerator is started, during the pre-cooling stage, in the process of cooling from room temperature to extremely low temperature, the pulse tube refrigerator at the top of the dilution refrigerator is responsible for pre-cooling. The pulse tube refrigerator includes a first-stage cold head and a second-stage cold head. The extremely low temperature region (mixing chamber) of the dilution refrigerator, i.e., the heat load, is connected to the second-stage cold head. However, the normal refrigeration power of the second-stage cold head is only about 1 to 2 watts, and the cooling rate is slow. The one-time cooling time of the dilution refrigerator can reach more than one week, seriously affecting the iteration speed of research such as quantum computing. Summary of the Invention

[0005] To solve at least one of the technical problems in the prior art, an embodiment of the present invention provides a pre-cooling system for a dilution refrigerator, which can improve the cooling rate of the dilution refrigeration unit.

[0006] The present invention provides a pre-cooling system for a dilution refrigerator, comprising: a vacuum chamber including a normal-temperature plate and a multi-stage cold plate, the multi-stage cold plate including a first-stage cold plate, a second-stage cold plate, and a third-stage cold plate that are sequentially and spaced apart in the vertical direction; a pre-cooling unit disposed between the normal-temperature plate and the second-stage cold plate in the vacuum chamber; a plurality of thermal switches respectively disposed between adjacent ones of the cold plates between the first-stage cold plate and the third-stage cold plate, the plurality of thermal switches including a first-stage thermal switch and a plurality of second-stage thermal switches, the first-stage thermal switch and the plurality of second-stage thermal switches respectively having a conducting state in response to the temperature of the mixing chamber being higher than different target temperatures and a non-conducting state in response to the temperature of the mixing chamber being lower than different target temperatures; a dilution refrigeration unit including the mixing chamber, the mixing chamber being disposed on the third-stage cold plate; wherein, the first-stage thermal switch and the plurality of second-stage thermal switches operate in the conducting state or the non-conducting state in response to the temperature change of the mixing chamber, so that the pre-cooling unit adjusts between a first-stage pre-cooling mode and a second-stage pre-cooling mode, and the refrigeration power in the first-stage pre-cooling mode is higher than that in the second-stage pre-cooling mode.

[0007] Optionally, the first-stage thermal switch is disposed between the first-stage cold plate and the second-stage cold plate, the first-stage thermal switch having a conducting state in response to the temperature of the mixing chamber being higher than a first target temperature and a non-conducting state in response to the temperature of the mixing chamber being lower than the first target temperature; a plurality of second-stage thermal switches respectively disposed between adjacent ones of the cold plates between the second-stage cold plate and the third-stage cold plate, each second-stage thermal switch having a conducting state in response to the temperature of the mixing chamber being higher than a second target temperature and a non-conducting state in response to the temperature of the mixing chamber being lower than the second target temperature, the first target temperature being higher than the second target temperature.

[0008] Optionally, in response to the temperature of the mixing chamber being higher than 50K and lower than a predetermined temperature, the first-stage thermal switch and the plurality of second-stage thermal switches are both in the conducting state, and the pre-cooling unit enters the first-stage pre-cooling mode.

[0009] Optionally, in response to the temperature of the mixing chamber being higher than 15K and lower than 50K, the first-stage thermal switch is in the non-conducting state, and the plurality of second-stage thermal switches are in the conducting state, and the pre-cooling unit enters the second-stage pre-cooling mode.

[0010] Optionally, in response to the temperature of the mixing chamber being lower than 15K, the first-stage thermal switch and the plurality of second-stage thermal switches are both in the non-conducting state, and the pre-cooling of the pre-cooling unit ends.

[0011] Optionally, the above-mentioned precooling unit includes: a hot end disposed on the above-mentioned normal-temperature plate; a first-stage cold head disposed between the above-mentioned normal-temperature plate and the above-mentioned first-stage cold plate; a second-stage cold head disposed between the above-mentioned first-stage cold plate and the above-mentioned second-stage cold plate, and the refrigeration power of the above-mentioned first-stage cold head is higher than that of the above-mentioned second-stage cold head; wherein, when the above-mentioned precooling unit enters the above-mentioned first-stage precooling mode, the above-mentioned precooling unit cools the above-mentioned mixing chamber through the above-mentioned first-stage cold head; when the above-mentioned precooling unit enters the above-mentioned second-stage precooling mode, the above-mentioned precooling unit cools the above-mentioned mixing chamber through the above-mentioned second-stage cold head.

[0012] Optionally, the above-mentioned first-stage thermal switch or each of the above-mentioned second-stage thermal switches includes: a housing configured as a tubular structure with openings at both ends; a first heat-conducting member contacting the cold plate with a higher temperature among two adjacent above-mentioned cold plates, and the first heat-conducting member includes: a first adjusting portion installed at the upper opening of the above-mentioned housing; a first elastic member located inside the above-mentioned housing and connected to the first adjusting portion; a first engaging portion connected to the first adjusting portion through the first elastic member; a second heat-conducting member installed at the lower opening of the above-mentioned housing and contacting the cold plate with a lower temperature among two adjacent above-mentioned cold plates, and the second heat-conducting member is configured to form a conduction state of heat conduction with the first heat-conducting member by pressing against the first engaging portion in response to the cold plate with a lower temperature being higher than the target temperature, and form a heat-insulated disconnection state from the first heat-conducting member by separating from the first engaging portion in response to the cold plate with a lower temperature being lower than the above-mentioned target temperature.

[0013] Optionally, a limiting boss is formed on the inner wall of the above-mentioned housing to prevent the first engaging portion from moving towards the second heat-conducting member under the drive of the first elastic member.

[0014] Optionally, the second heat-conducting member forms heat conduction with the first heat-conducting member at a first position, and the distance between the first position and the limiting boss is a preset distance. The second heat-conducting member is configured to reciprocate in the vertical direction to change the size of the preset distance, thereby adjusting the contact duration between the second heat-conducting member and the first engaging portion.

[0015] Optionally, the second heat-conducting member includes: a second engaging portion for pressing against or separating from the first engaging portion; a driving portion connected to one end of the second engaging portion and configured to expand or contract in response to the temperature change of the cold plate with a lower temperature to drive the second engaging portion to move in the vertical direction; a second adjusting portion rotatably installed on the above-mentioned housing and connected to the other end of the driving portion for adjusting the preset distance.

[0016] A pre-cooling system for a dilution refrigerator according to an embodiment of the present invention. The vacuum chamber includes a normal temperature plate and a multi-stage cold plate. The multi-stage cold plate includes a first-stage cold plate, a second-stage cold plate, and a third-stage cold plate that are sequentially arranged at intervals in the vertical direction. The pre-cooling unit is arranged between the normal temperature plate and the second-stage cold plate. A plurality of thermal switches are respectively arranged between adjacent two cold plates between the first-stage cold plate and the third-stage cold plate. The plurality of thermal switches include a first-stage thermal switch and a plurality of second-stage thermal switches. The first-stage thermal switch and the plurality of second-stage thermal switches respectively have a conducting state in response to the temperature of the mixing chamber being higher than different target temperatures and a disconnecting state in response to the temperature of the mixing chamber being lower than different target temperatures. The dilution refrigeration unit includes a mixing chamber, and the mixing chamber is arranged on the third-stage cold plate. The first-stage thermal switch and the plurality of second-stage thermal switches work in the conducting state or the disconnecting state in response to the temperature change of the mixing chamber, so that the pre-cooling unit adjusts between the first-stage pre-cooling mode and the second-stage pre-cooling mode. The refrigeration power in the first-stage pre-cooling mode is higher than that in the second-stage pre-cooling mode, which can improve the cooling speed of the dilution refrigeration unit. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 is a side view of a pre-cooling system for a dilution refrigerator according to an embodiment of the present invention;

[0018] Figure 2 is a perspective view of a thermal switch according to an embodiment of the present invention;

[0019] Figure 3 is a half-sectional view of a thermal switch according to an embodiment of the present invention, with the housing removed;

[0020] Figure 4 is a sectional view of a thermal switch according to an embodiment of the present invention;

[0021] Figure 5 is a sectional view of a thermal switch according to an embodiment of the present invention;

[0022] Figure 6 is Figure 5 a partial sectional view after removing the housing in the illustrated exemplary embodiment;

[0023] Figure 7 is a schematic diagram of the working process of a thermal switch according to an embodiment of the present invention.

[0024] In the said drawings, the meanings of the reference numerals are specifically as follows:

[0025] 1, First heat conducting member;

[0026] 11, First adjusting part;

[0027] 111, First end cap;

[0028] 112, First sleeve;

[0029] 12. First elastic member;

[0030] 13. First joint portion;

[0031] 14. Upper limit member;

[0032] 15. Lower limit member;

[0033] 151. Fastening bolt;

[0034] 152. Limit platform;

[0035] 153. Main body;

[0036] 16. Second elastic member

[0037] 2. Second heat conducting member;

[0038] 21. Second adjusting portion;

[0039] 211. Second end cap;

[0040] 212. Second sleeve;

[0041] 22. Driving portion;

[0042] 23. Second joint portion;

[0043] 3. Housing;

[0044] 31. Limit boss;

[0045] 4. Pre-cooling unit;

[0046] 41. Hot end;

[0047] 42. First-stage cold head;

[0048] 43. Second-stage cold head;

[0049] 5. Dilution refrigeration unit;

[0050] 51. Mixing chamber;

[0051] 6. Thermal switch;

[0052] 61. First-stage thermal switch;

[0053] 62. Second-stage thermal switch;

[0054] 7. Vacuum chamber;

[0055] 8. Normal temperature plate;

[0056] 9. First-stage cold plate;

[0057] 10. Second-stage cold plate;

[0058] 17. Three - stage cold plate. Detailed implementation manners

[0059] Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. However, it should be understood that these descriptions are merely exemplary and are not intended to limit the scope of the present invention. In the following detailed description, for the sake of explanation, many specific details are set forth in order to provide a comprehensive understanding of the embodiments of the present invention. However, obviously, one or more embodiments can also be implemented without these specific details. In addition, in the following description, descriptions of well - known structures and technologies are omitted to avoid unnecessarily obscuring the concepts of the present invention.

[0060] The terms used herein are merely for describing specific embodiments and are not intended to limit the present invention. The terms "including", "comprising", etc. as used herein indicate the presence of the described features, steps, operations, and / or components, but do not exclude the presence or addition of one or more other features, steps, operations, or components.

[0061] All terms used herein (including technical and scientific terms) have the meanings commonly understood by those skilled in the art, unless otherwise defined. It should be noted that the terms used herein should be interpreted as having a meaning consistent with the context of this specification and should not be interpreted in an idealized or overly rigid manner.

[0062] In cases where expressions such as "at least one of A, B, and C, etc." are used, generally, it should be interpreted according to the meaning commonly understood by those skilled in the art (for example, "a system having at least one of A, B, and C" should include, but is not limited to, a system having only A, only B, only C, having A and B, having A and C, having B and C, and / or having A, B, and C, etc.). In cases where expressions such as "at least one of A, B, or C, etc." are used, generally, it should be interpreted according to the meaning commonly understood by those skilled in the art (for example, "a system having at least one of A, B, or C" should include, but is not limited to, a system having only A, only B, only C, having A and B, having A and C, having B and C, and / or having A, B, and C, etc.).

[0063] To solve the problem that the cooling rate of the dilution refrigeration unit is relatively slow, according to the inventive concept of one aspect of the present invention, the vacuum chamber includes a normal temperature plate and a multi-stage cold plate. The multi-stage cold plate includes a first-stage cold plate, a second-stage cold plate, and a third-stage cold plate that are sequentially arranged at intervals in the vertical direction. The pre-cooling unit is arranged between the normal temperature plate and the second-stage cold plate. A plurality of thermal switches are respectively arranged between adjacent two cold plates between the first-stage cold plate and the third-stage cold plate. The plurality of thermal switches include a first-stage thermal switch and a plurality of second-stage thermal switches. The first-stage thermal switch and the plurality of second-stage thermal switches respectively have a conducting state in response to the temperature of the mixing chamber being higher than different target temperatures and a disconnected state in response to the temperature of the mixing chamber being lower than different target temperatures. The dilution refrigeration unit includes a mixing chamber, and the mixing chamber is arranged on the third-stage cold plate. The first-stage thermal switch and the plurality of second-stage thermal switches work in the conducting state or the disconnected state in response to the temperature change of the mixing chamber, so that the pre-cooling unit is adjusted between the first-stage pre-cooling mode and the second-stage pre-cooling mode. The refrigeration power of the first-stage pre-cooling mode is higher than that of the second-stage pre-cooling mode, and the cooling rate of the dilution refrigeration unit can be improved.

[0064] Figure 1 It is a side view of a pre-cooling system for a dilution refrigerator according to an embodiment of the present invention.

[0065] The pre-cooling system for a dilution refrigerator provided according to an embodiment of the present invention, as Figure 1 shown, includes a vacuum chamber 7. The vacuum chamber 7 includes a normal temperature plate 8 and a multi-stage cold plate. The multi-stage cold plate includes a first-stage cold plate 9, a second-stage cold plate 10, and a third-stage cold plate 17 that are sequentially arranged at intervals in the vertical direction. A pre-cooling unit 4, a plurality of thermal switches 6, and a dilution refrigeration unit 5 are arranged in the vacuum chamber 7. The pre-cooling unit 4 is arranged between the normal temperature plate 8 and the second-stage cold plate 10. The plurality of thermal switches 6 are respectively arranged between adjacent two cold plates between the first-stage cold plate 9 and the third-stage cold plate 17. The plurality of thermal switches 6 include a first-stage thermal switch 61 and a plurality of second-stage thermal switches 62. The first-stage thermal switch 61 and the plurality of second-stage thermal switches 62 respectively have a conducting state in response to the temperature of the mixing chamber 51 being higher than different target temperatures and a disconnected state in response to the temperature of the mixing chamber 51 being lower than different target temperatures. The dilution refrigeration unit 5 includes a mixing chamber 51, and the mixing chamber 51 is arranged on the third-stage cold plate 17. The first-stage thermal switch 61 and the plurality of second-stage thermal switches 62 work in the conducting state or the disconnected state in response to the temperature change of the mixing chamber 51, so that the pre-cooling unit 4 is adjusted between the first-stage pre-cooling mode and the second-stage pre-cooling mode. The refrigeration power of the first-stage pre-cooling mode is higher than that of the second-stage pre-cooling mode.

[0066] According to an embodiment of the present invention, the temperatures of the first-stage cold plate 9, the second-stage cold plate 10, and the third-stage cold plate 17 that are sequentially arranged at intervals in the vertical direction decrease gradually.

[0067] According to an embodiment of the present invention, the precooling unit 4 can be a pulse tube refrigerator, which is used to provide a low-temperature environment in the precooling stage, enabling the dilution refrigeration unit 5 to achieve a very low temperature (mK level) refrigeration effect. The precooling stage, as a pre-refrigeration stage of the dilution refrigeration unit 5, is used to cool the mixing chamber 51 of the dilution refrigeration unit 5 from room temperature (roughly 300K) to a low-temperature range of dozens of K (Kelvin) (roughly 20K to 50K), thereby creating suitable initial conditions for the subsequent dilution refrigeration stage. After the precooling stage ends, the temperature drops to a range where the dilution refrigeration unit 5 can work efficiently, reducing the heat load of the dilution refrigeration unit 5. The precooling effect of the pulse tube refrigerator reduces the amount of heat that the dilution refrigeration unit 5 needs to handle, enabling it to reach a very low temperature of mK level more efficiently. Moreover, the stable low-temperature environment provided by the pulse tube refrigerator can ensure that the dilution refrigeration unit 5 works under stable initial conditions. The design of the pulse tube refrigerator without moving parts gives it the advantages of high reliability and long life, reducing subsequent maintenance requirements.

[0068] According to an embodiment of the present invention, the vacuum chamber 7 includes a normal temperature plate 8 and a multi-stage cold plate. The multi-stage cold plate includes a first-stage cold plate 9, a second-stage cold plate 10, and a third-stage cold plate 17 that are sequentially spaced apart in the vertical direction. The precooling unit 4 is disposed between the normal temperature plate 8 and the second-stage cold plate 10. A plurality of thermal switches 6 are respectively disposed between adjacent two cold plates between the first-stage cold plate 9 and the third-stage cold plate 17. The plurality of thermal switches 6 include a first-stage thermal switch 61 and a plurality of second-stage thermal switches 62. The first-stage thermal switch 61 and the plurality of second-stage thermal switches 62 respectively have a conducting state in response to the temperature of the mixing chamber 51 being higher than different target temperatures and a non-conducting state in response to the temperature of the mixing chamber 51 being lower than different target temperatures. The dilution refrigeration unit 5 includes a mixing chamber 51, and the mixing chamber 51 is disposed on the third-stage cold plate 17 as a heat load. The first-stage thermal switch 61 and the plurality of second-stage thermal switches 62 work in the conducting state or the non-conducting state in response to the temperature change of the mixing chamber 51, enabling the precooling unit 4 to adjust between a first-stage precooling mode and a second-stage precooling mode. The refrigeration power of the first-stage precooling mode is higher than that of the second-stage precooling mode, which can improve the cooling rate of the dilution refrigeration unit 5.

[0069] According to an embodiment of the present invention, the first-stage thermal switch 61 is disposed between the first-stage cold plate 9 and the second-stage cold plate 10. The first-stage thermal switch 61 has a conducting state in response to the temperature of the mixing chamber 51 being higher than the first target temperature and a non-conducting state in response to the temperature of the mixing chamber 51 being lower than the first target temperature. The plurality of second-stage thermal switches 62 are respectively disposed between adjacent two cold plates between the second-stage cold plate 10 and the third-stage cold plate 17. Each second-stage thermal switch 62 has a conducting state in response to the temperature of the mixing chamber 51 being higher than the second target temperature and a non-conducting state in response to the temperature of the mixing chamber 51 being lower than the second target temperature, and the first target temperature is higher than the second target temperature.

[0070] According to an embodiment of the present invention, the number of the secondary thermal switches 62 can be 2, 3, etc. Taking 3 secondary thermal switches 62 as an example, as Figure 1 shown, the 3 secondary thermal switches 62 are respectively arranged between two adjacent cold plates between the secondary cold plate 10 and the tertiary cold plate 17 in a threaded connection manner.

[0071] According to an embodiment of the present invention, in response to the temperature of the mixing chamber 51 being higher than 50K and lower than a predetermined temperature, the primary thermal switch 61 and the multiple secondary thermal switches 62 are both in the conducting state, and the precooling unit 4 enters the primary precooling mode.

[0072] According to an embodiment of the present invention, the first target temperature of the primary thermal switch 61 is 50K.

[0073] According to an embodiment of the present invention, the predetermined temperature is room temperature, and the room temperature is approximately 25°C.

[0074] According to an embodiment of the present invention, in response to the temperature of the mixing chamber 51 being higher than 15K and lower than 50K, the primary thermal switch 61 is in the off state, and the multiple secondary thermal switches 62 are in the conducting state, and the precooling unit 4 enters the secondary precooling mode.

[0075] According to an embodiment of the present invention, the second target temperature of the secondary thermal switch 62 is 15K.

[0076] According to an embodiment of the present invention, in response to the temperature of the mixing chamber 51 being lower than 15K, the primary thermal switch 61 and the multiple secondary thermal switches 62 are both in the off state, and the precooling of the precooling unit 4 ends.

[0077] According to an embodiment of the present invention, the precooling unit 4 includes a hot end 41, a primary cold head 42, and a secondary cold head 43. The hot end 41 is arranged on the room temperature plate 8. The primary cold head 42 is arranged between the room temperature plate 8 and the primary cold plate 9. The secondary cold head 43 is arranged between the primary cold plate 9 and the secondary cold plate 10, and the refrigeration power of the primary cold head 42 is higher than that of the secondary cold head 43. When the precooling unit 4 enters the primary precooling mode, the precooling unit 4 cools the mixing chamber 51 through the primary cold head 42. When the precooling unit 4 enters the secondary precooling mode, the precooling unit 4 cools the mixing chamber 51 through the secondary cold head 43.

[0078] According to an embodiment of the present invention, the maximum refrigeration power of the primary cold head 42 can reach 10W, and the temperature range of the primary cold head 42 is approximately 40K - 45K. The refrigeration power of the secondary cold head 43 is approximately 1W - 2W, and the temperature range of the secondary cold head 43 is approximately 3K - 4K.

[0079] According to an embodiment of the present invention, in response to the temperature of the mixing chamber 51 being higher than 50K and lower than normal temperature, both the primary thermal switch 61 and the multiple secondary thermal switches 62 are in the conducting state, and the pre-cooling unit 4 enters the primary pre-cooling mode. The heat of the mixing chamber 51 is transferred to the primary cold plate 9, and then the heat of the mixing chamber 51 is taken away by the primary cold head 42. The primary cold head 42 with a relatively high power can rapidly cool down the mixing chamber 51. In response to the temperature of the mixing chamber 51 being higher than 15K and lower than 50K, the primary thermal switch 61 is in the off state, and the multiple secondary thermal switches 62 are in the conducting state. The pre-cooling unit 4 enters the secondary pre-cooling mode. The heat of the mixing chamber 51 is transferred to the secondary cold plate 10, and then the heat of the mixing chamber 51 is taken away by the secondary cold head 43. The secondary cold head 43 with a relatively low power can further lower the temperature of the mixing chamber 51. In response to the temperature of the mixing chamber 51 being lower than 15K, both the primary thermal switch 61 and the multiple secondary thermal switches 62 are in the off state, preventing the heat of the primary cold plate 9 and the secondary cold plate 10 from being transferred back to the mixing chamber 51, and the pre-cooling of the mixing chamber 51 by the pre-cooling unit 4 ends. After the pre-cooling of the mixing chamber 51 by the pre-cooling unit 4 ends, 3 He and 4 He mixed gas enters the vacuum chamber 7, and through the primary cold head 42 and the secondary cold head 43, 3 He and 4 He in the mixed gas 4 He can be liquefied ( 3 The boiling point of He is approximately 3.19K, 4 The boiling point of He is approximately 4.22K), and 4 He liquid is obtained. 4 He liquid is transferred to the mixing chamber 51 under the action of gravity. 3 He and 4 He in the mixed gas 3 He remains in a gaseous state. The gaseous 3 He undergoes throttling expansion. Due to the throttling refrigeration effect, the temperature of the throttled gaseous 3 He is further reduced. After condensation and liquefaction, 3 He liquid is obtained and transferred to the mixing chamber 51, causing the temperature of the mixing chamber 51 to decrease until it reaches approximately 0.87K. When the temperature of the mixing chamber 51 is approximately 0.87K, 3 He liquid and 4 He liquid undergo phase separation, obtaining a 3 He enriched phase (i.e., 3 He liquid) located in the upper layer and a 3 He dilute phase (i.e., 3 He and 4A mixture of He), at this time, the dilution refrigeration unit 5 can start the dilution refrigeration cycle. By using the first-stage cold head 42 to cool the mixing chamber 51 first and then switching to the second-stage cold head 43 to cool the mixing chamber 51, the cooling rate of the dilution refrigeration unit 5 can be increased and the time of the pre-cooling stage can be reduced.

[0080] According to an embodiment of the present invention, after the dilution refrigeration cycle ends, the mixing chamber 51 of the dilution refrigeration unit 5 gradually warms up to the room temperature environment. In response to the temperature of the mixing chamber 51 being higher than 15K and lower than 50K, the first-stage thermal switch 61 is in the off state and multiple second-stage thermal switches 62 are in the on state. The pre-cooling unit 4 warms up the mixing chamber 51 through the second-stage cold head 43. In response to the temperature of the mixing chamber 51 being higher than 50K and lower than the normal temperature, both the first-stage thermal switch 61 and multiple second-stage thermal switches 62 are in the on state. The pre-cooling unit 4 warms up the mixing chamber 51 through the first-stage cold head 42. By using the second-stage cold head 43 to warm up the mixing chamber 51 first and then switching to the first-stage cold head 42 to warm up the mixing chamber 51, the warming rate of the dilution refrigeration unit 5 can be increased and the time of the warming stage can be reduced.

[0081] Figure 2 is a perspective view of a thermal switch according to an embodiment of the present invention, Figure 3 is a half-sectional view of a thermal switch according to an embodiment of the present invention, with the housing removed, Figure 4 is a sectional view of a thermal switch according to an embodiment of the present invention, Figure 5 is a sectional view of a thermal switch according to an embodiment of the present invention, Figure 6 is Figure 5 a partial sectional view after removing the housing in the illustrated exemplary embodiment.

[0082] According to an embodiment of the present invention, multiple thermal switches 6 include a first-stage thermal switch 61 and multiple second-stage thermal switches 62. As Figures 2 to 6 shown, the first-stage thermal switch 61 or each second-stage thermal switch 62 includes a housing 3, a first heat conducting member 1, and a second heat conducting member 2. The housing 3 is configured as a tubular structure with openings at both ends. The first heat conducting member 1 contacts the cold plate with a higher temperature among two adjacent cold plates. The first heat conducting member 1 includes a first adjusting portion 11, a first elastic member 12, and a first engaging portion 13. The first adjusting portion 11 is installed at the upper opening of the housing 3. The first elastic member 12 is located inside the housing 3 and is connected to the first adjusting portion 11. The first engaging portion 13 is connected to the first adjusting portion 11 through the first elastic member 12. The second heat conducting member 2 is installed at the lower opening of the housing 3 and contacts the cold plate with a lower temperature among two adjacent cold plates. The second heat conducting member 2 has a conducting state in which it presses against the first engaging portion 13 in response to the cold plate with a lower temperature being higher than the target temperature and forms heat conduction with the first heat conducting member 1, and a disconnected state in which it disengages from the first engaging portion 13 in response to the cold plate with a lower temperature being lower than the target temperature and forms thermal isolation from the first heat conducting member 1.

[0083] According to an embodiment of the present invention, the first elastic member 12 is configured such that the deformation amount generated when the second heat conducting member 2 is in a conducting state can be adjusted by the first adjusting portion 11 to change the contact pressure between the second heat conducting member 2 and the first engaging portion 13.

[0084] In such an embodiment, the first heat conducting member 1 and the second heat conducting member 2 are respectively installed at the two open ends of the housing 3 to enclose the housing 3 to form a sealed cavity, and the sealed cavity is configured to be in a vacuum state. The first heat conducting member 1 contacts the cold plate with a higher temperature among the two adjacent cold plates, and the second heat conducting member 2 contacts the cold plate with a lower temperature among the two adjacent cold plates. When the temperature of the cold plate with a lower temperature is higher than the target temperature, the second heat conducting member 2 contacts the first heat conducting member 1 and presses against it with a certain pressure, so that the temperature of the cold plate with a lower temperature is transferred to the cold plate with a higher temperature through the second heat conducting member 2 and the first heat conducting member 1. When the temperature of the cold plate with a lower temperature drops below the target temperature, the second heat conducting member 2 disengages from the first heat conducting member 1. Since the sealed cavity is in a vacuum state, heat transfer no longer occurs between the cold plate with a higher temperature and the cold plate with a lower temperature.

[0085] Affected by different target temperatures, the contact pressure between the second heat conducting member 2 and the first heat conducting member 1 will change. Since the contact surfaces of the second heat conducting member 2 and the first heat conducting member 1 are not ideal smooth surfaces, the change in the contact pressure will affect the heat transfer efficiency. By adjusting the deformation amount of the first elastic member 12 through the first adjusting portion 11, the contact pressure between the second heat conducting member 2 and the first heat conducting member 1 can be adjusted according to different target temperatures (such as the first target temperature or the second target temperature), improving the heat transfer efficiency and reducing the time required for heat transfer.

[0086] According to an embodiment of the present invention, a limiting boss 31 is formed on the inner wall of the housing 3 to prevent the first engaging portion 13 from moving towards the second heat conducting member 2 under the drive of the first elastic member 12.

[0087] According to an embodiment of the present invention, when the second heat conducting member 2 is in a conducting state, the first elastic member 12 is compressed, and the second heat conducting member 2 resists the elastic force of the first elastic member 12. As the temperature of the cold plate with a lower temperature gradually decreases, the contact pressure between the second heat conducting member 2 and the first engaging portion 13 gradually decreases until it is the limiting boss 31 that resists the elastic force of the first elastic member 12. At this time, the second heat conducting member 2 and the first engaging portion 13 disengage, and the temperature of the cold plate with a lower temperature drops below the target temperature.

[0088] According to an embodiment of the present invention, the second heat conducting member 2 is further configured to reciprocate in the vertical direction so that the second heat conducting member 2 can switch between a conducting state and a disconnected state in response to different target temperatures.

[0089] In such an embodiment, when the cold plate with a high temperature and the cold plate with a low temperature change, or the target temperature changes, by adjusting the position of the second heat conducting member 2 in the vertical direction, the separation temperature of the thermal switch 6 is changed, the flexibility of use of the thermal switch 6 is improved, and the production and manufacturing costs are reduced.

[0090] Figure 7 It is a schematic diagram of the working process of a thermal switch according to an embodiment of the present invention.

[0091] According to an embodiment of the present invention, as Figure 7 shown, the second heat conducting member 2 forms heat conduction with the first heat conducting member 1 at the first position, the distance between the first position and the limiting boss 31 is a preset distance H, and the second heat conducting member 2 is configured to reciprocate in the vertical direction to change the size of the preset distance H, so as to adjust the contact duration between the second heat conducting member 2 and the first engaging portion 13.

[0092] In such an embodiment, the tubular housing 3 is arranged in the vertical direction, the first heat conducting member 1 and the second heat conducting member 2 are also arranged in sequence at both ends of the housing 3 in the vertical direction, and the first adjusting portion 11, the first elastic member 12 and the first engaging portion 13 of the first heat conducting member 1 are connected in sequence from top to bottom in the vertical direction. The second heat conducting member 2 presses against the first engaging portion 13 in response to the temperature of the cold plate with a low temperature being lower than the target temperature, and compresses the first elastic member 12. The pressing position, that is, the first position, is located above the limiting boss 31. As the temperature of the cold plate with a low temperature drops, the compression amount of the first elastic member 12 decreases, the contact pressure decreases, until the limiting boss 31 restricts the first engaging portion 13 from continuing to move, and then the second heat conducting member 2 disengages from the first engaging portion 13. After the temperature of the cold plate with a low temperature stabilizes, the upper surface of the second heat conducting member 2 (i.e., the contact surface with the first engaging portion 13) is located at the second position, and the second position is located below the limiting boss 31. The distance between the first position and the limiting boss 31 is the preset distance H. Exemplarily, when the second heat conducting member 2 moves upward, the preset distance H increases, and the time required for the second heat conducting member 2 and the first heat conducting member 1 to switch from heat conduction to heat isolation is longer. During this period, the heat transferred from the cold plate with a low temperature to the cold plate with a high temperature is more. When the second heat conducting member 2 and the first heat conducting member 1 form heat isolation, the temperature of the cold plate with a low temperature is lower, and at the same time the final isolation distance h is larger. In this way, the thermal switch 6 can be used in different target temperature usage scenarios, and the isolation temperature can be flexibly adjusted.

[0093] According to an embodiment of the present invention, the second heat conducting member 2 includes a second engaging portion 23, a driving portion 22, and a second adjusting portion 21. The second engaging portion 23 is used to press against or disengage from the first engaging portion 13. One end of the driving portion 22 is connected to the second engaging portion 23. The driving portion 22 is configured to expand or contract in response to a temperature change of the cold plate with a low temperature, so as to drive the second engaging portion 23 to move in the vertical direction. The second adjusting portion 21 is rotatably mounted on the housing 3 and is connected to the other end of the driving portion 22. The second adjusting portion 21 is used to adjust the preset distance H.

[0094] In such an embodiment, the second engaging portion 23, the driving portion 22, and the second adjusting portion 21 of the second heat conducting member 2 are sequentially connected from top to bottom in the vertical direction. The second engaging portion 23 has substantially the same shape as the first engaging portion 13, so as to have a larger contact area when pressing against, and improve the heat transfer efficiency. The driving portion 22 can expand as the temperature of the cold plate with a low temperature rises, and contract as the temperature of the cold plate with a low temperature drops. It should be noted that the coefficient of thermal expansion of the driving portion 22 is greater than that of the housing 3, so that when the temperature of the cold plate with a low temperature drops below the target temperature, the contraction amount of the driving portion 22 is greater than the contraction amount of the housing 3, thereby separating the second engaging portion 23 from the first engaging portion 13. The second adjusting portion 21 is rotatably mounted on the housing 3 and can generate a displacement in the vertical direction relative to the housing 3, so that the second heat conducting member 2 as a whole moves in the vertical direction, thereby adjusting the preset distance H.

[0095] Exemplarily, the driving portion 22 is preferably made of pure aluminum, and the housing 3 is preferably made of stainless steel. Stainless steel has higher low-temperature stability and is more reliable as the housing 3. At the same time, the expansion coefficients of stainless steel and pure aluminum are quite different in both the room temperature range and the extremely low temperature range, which is conducive to improving the response speed of the thermal switch 6.

[0096] According to an embodiment of the present invention, as Figure 6 shown, the second adjusting portion 21 includes a second end cap 211 and a second sleeve 212. The second end cap 211 is connected to the driving portion 22. The second sleeve 212 is sleeved outside the second end cap 211 and is threadedly connected to the housing 3, so as to drive the second end cap 211 to reciprocate in the vertical direction by rotation.

[0097] In such an embodiment, the second end cap 211 is used to connect the driving portion 22 and contact the cold plate with a low temperature. Therefore, it is installed on the housing 3 through the second sleeve 212 to avoid heat transfer along the housing 3 and affect the opening and closing of the thermal switch 6. The second sleeve 212 can be fixedly connected to the second end cap 211 by means of welding or interference fit, and then connected to the housing 3 through a simple and reliable threaded connection. By rotating the second end cap 211, the second heat conducting member 2 as a whole can be moved in the vertical direction.

[0098] Exemplarily, when the driving part 22 is made of pure aluminum, the second end cap 211 and the second joint part 23 are preferably made of oxygen-free copper, which can effectively improve the heat conductivity. The second sleeve 212 is preferably made of stainless steel. On the one hand, it can form a good fit with the housing 3 to reduce wear and has a long service life. On the other hand, it can prevent the heat of the second end cap 211 from leaking to the housing 3.

[0099] In some alternative embodiments, the second end cap 211 and the driving part 22 are connected by bolts, and the driving part 22 and the second joint part 23 are connected in a plug-in manner.

[0100] According to an embodiment of the present invention, as Figure 6 shown, the first adjusting part includes a first end cap and a first sleeve. The first end cap is connected to the first elastic member. The first sleeve is sleeved outside the first end cap and is threadedly connected to the housing to drive the first end cap to reciprocate in the vertical direction by rotation.

[0101] In such an embodiment, the first end cap 111 is used to connect the first elastic member 12 and contact the cold plate with high temperature. Therefore, it is installed on the housing 3 through the first sleeve 112 to prevent heat from being transferred along the housing 3 and affecting the opening and closing of the thermal switch 6. The first sleeve 112 can be fixedly connected to the first end cap 111 by welding or interference fit, etc., and then connected to the housing 3 through a simple and reliable threaded connection, so that when the first end cap 111 is rotated, the first end cap 111 can move in the vertical direction, and the deformation amount of the first elastic member 12 can be adjusted.

[0102] According to an embodiment of the present invention, the first end cap 111, the first elastic member 12 and the first joint part 13 are made of the same material, and the heat conductivity is greater than that of the housing 3.

[0103] In such an embodiment, after the heat of the cold plate with low temperature passes through the second heat conducting member 2, it needs to pass through the first end cap 111, the first elastic member 12 and the first joint part 13 in sequence to be transferred to the cold plate with high temperature. Therefore, materials with relatively high heat conductivity, especially greater than that of the housing 3, are required to achieve high-efficiency heat transfer. In addition, due to the special structure of the first elastic member 12, the three are made of the same material to reduce the connection difficulty.

[0104] Preferably, the first end cap 111, the first elastic member 12, and the first joint portion 13 are all made of oxygen-free copper. Since the first end cap 111 also needs to be equipped with a first sleeve 112 and threadedly connected to the housing 3, the diameter of the first end cap 111 is limited. Therefore, it is preferably that the first end cap 111 and the first elastic member 12 are integrally formed. The first elastic member 12 is a substantially S-shaped spring piece made of oxygen-free copper. The diameter of the first joint portion 13 is not limited. Therefore, the first joint portion 13 and the first elastic member 12 can be integrally formed, or can be connected by providing a connecting seat at the lower end of the first elastic member 12 to connect to the first joint portion 13, or without a connection relationship, so that the connecting seat presses against the first joint portion 13.

[0105] According to an embodiment of the present invention, the first end cap 111 is configured as a hollow cylindrical structure. The first heat conducting member 1 further includes an upper limiting member 14, a lower limiting member 15, and a second elastic member 16. The upper limiting member 14 covers the upper end of the first end cap 111. The lower limiting member 15 is disposed within the first end cap 111, passes out from the lower end of the first end cap 111, and presses against the first joint portion 13. The two ends of the second elastic member 16 respectively press against the upper limiting member 14 and the lower limiting member 15, and are configured in a compressed state to increase the contact pressure between the first joint portion 13 and the second heat conducting member 2.

[0106] In such an embodiment, the upper limiting member 14 is fixedly connected to the first end cap 111. A part of the lower limiting member 15 is located within the first end cap 111, and the other part passes through the lower end of the first end cap 111 and the central portion of the first elastic member 12 to press against the first joint portion 13. When the first end cap 111 adjusts the deformation amount of the first elastic member 12 by rotation, for example, when the first end cap 111 moves downward, the deformation amount of the first elastic member 12 increases, and the upper limiting member 14 moves downward accordingly. However, the lower limiting member 15 always presses against the first joint portion 13. Therefore, the deformation amount of the second elastic member 16 also becomes larger, and the pressure of the lower limiting member 15 on the first joint portion 13 increases.

[0107] In some alternative embodiments, as Figure 6 shown, the lower limiting member 15 includes a fastening bolt 151, a limiting platform 152, and a main body 153. The main body 153 passes out from the inside of the first end cap 111, passes through the first elastic member 12, and presses against the first joint portion 13. The limiting platform 152 is disposed on the main body 153 for limiting the second elastic member 16. The limiting platform 152 is configured as an annular disc. The fastening bolt 151 passes through the annular disc and is threadedly connected to the main body 153 to fix the limiting platform 152 to the main body 153.

[0108] In some other embodiments, a limiting protrusion is further provided at the lower end of the first end cap 111 for restricting the limiting platform 152 from coming out of the first end cap 111.

[0109] Those skilled in the art can understand that the features recited in the various embodiments and / or claims of the present invention can be combined or combined in various ways, even if such combinations or combinations are not explicitly recited in the present invention. In particular, without departing from the spirit and teachings of the present invention, the features recited in the various embodiments and / or claims of the present invention can be combined and / or combined in various ways. All such combinations and / or combinations fall within the scope of the present invention.

[0110] It should also be noted that the directional terms mentioned in the embodiments, such as "upper", "lower", "front", "rear", "left", "right", etc., are only references to the directions in the drawings and are not used to limit the protection scope of the present invention. Throughout the drawings, the same elements are denoted by the same or similar reference numerals. When it may cause confusion in the understanding of the present invention, the conventional structures or configurations will be omitted, and the shapes and sizes of the components in the drawings do not reflect the actual sizes and proportions, but only illustrate the content of the embodiments of the present invention.

[0111] Unless otherwise known to the contrary, the numerical parameters in this specification and the appended claims are approximate values and can be changed according to the required characteristics obtained through the content of the present invention. Specifically, all the numbers representing the contents of the components, reaction conditions, etc. used in the specification and the claims should be understood to be modified by the term "about" in all cases. Generally, the meaning expressed is that it includes a change of ±10% in some embodiments, a change of ±5% in some embodiments, a change of ±1% in some embodiments, and a change of ±0.5% in some embodiments for a specific quantity.

[0112] The ordinal numbers used in the specification and the claims, such as "first", "second", "third", etc., are used to modify the corresponding elements. They do not mean that the elements have any ordinal numbers in themselves, nor do they represent the order of one element and another element or the order in the manufacturing method. The use of these ordinal numbers is only to clearly distinguish an element with a certain name from another element with the same name.

[0113] In addition, unless specifically described or steps that must occur in sequence, the order of the above steps is not limited to the above list and can be changed or rearranged according to the required design. And the above embodiments can be used in combination with each other or combined with other embodiments based on considerations of design and reliability, that is, the technical features in different embodiments can be freely combined to form more embodiments.

[0114] The embodiments of the present invention have been described above. However, these embodiments are merely for illustrative purposes and not for limiting the scope of the present invention. Although the embodiments have been described separately above, this does not mean that the measures in each embodiment cannot be used advantageously in combination. The scope of the present invention is defined by the appended claims and their equivalents. Without departing from the scope of the present invention, those skilled in the art can make various substitutions and modifications, and all such substitutions and modifications should fall within the scope of the present invention.

Claims

1. A precooling system for a dilution refrigerator, characterized in that: include: A vacuum chamber comprises a normal temperature plate and a multi-stage cold plate, wherein the multi-stage cold plate comprises a primary cold plate, a secondary cold plate and a tertiary cold plate which are arranged in sequence in a vertical direction, and the vacuum chamber is provided with: A pre-cooling unit is arranged between the normal temperature plate and the secondary cold plate; A plurality of thermal switches are respectively arranged between two adjacent cold plates between the primary cold plate and the tertiary cold plate, the plurality of thermal switches comprising a primary thermal switch and a plurality of secondary thermal switches, the primary thermal switch and the plurality of secondary thermal switches respectively having an on state in response to the temperature of the mixing chamber being higher than different target temperatures and an off state in response to the temperature of the mixing chamber being lower than different target temperatures; A dilution refrigeration unit, comprising the mixing chamber, wherein the mixing chamber is arranged on the third-stage cold plate; Among them, the primary heat switch and the multiple secondary heat switches operate in the on state or the off state in response to the temperature change of the mixing chamber, so that the precooling unit is adjusted between the primary precooling mode and the secondary precooling mode, and the cooling power of the primary precooling mode is higher than the cooling power of the secondary precooling mode.

2. The precooling system for a dilution refrigerator according to claim 1, characterized in that: The primary thermal switch is disposed between the primary cold plate and the secondary cold plate, and the primary thermal switch has an on state in response to the temperature of the mixing chamber being higher than a first target temperature and an off state in response to the temperature of the mixing chamber being lower than the first target temperature; A plurality of secondary thermal switches are respectively arranged between two adjacent cold plates between the secondary cold plate and the tertiary cold plate, each of the secondary thermal switches having an on state in response to the temperature of the mixing chamber being higher than a second target temperature and an off state in response to the temperature of the mixing chamber being lower than the second target temperature, the first target temperature being higher than the second target temperature.

3. The precooling system for a dilution refrigerator according to claim 2, characterized in that: In response to the temperature of the mixing chamber being higher than 50K and lower than a predetermined temperature, the primary thermal switch and the plurality of secondary thermal switches are all in the on state, and the precooling unit enters the primary precooling mode.

4. The precooling system for a dilution refrigerator according to claim 2, characterized in that: In response to the temperature of the mixing chamber being higher than 15K and lower than 50K, the primary thermal switch is in the disconnected state, the plurality of secondary thermal switches are in the on state, and the precooling unit enters the secondary precooling mode.

5. The precooling system for a dilution refrigerator according to claim 2, characterized in that: In response to the temperature of the mixing chamber being lower than 15K, the primary thermal switch and the plurality of secondary thermal switches are all in the disconnected state, and the precooling of the precooling unit ends.

6. The precooling system for a dilution refrigerator according to claim 1, characterized in that: The precooling unit comprises: A hot end, arranged on the constant temperature plate; A primary cold head, arranged between the normal temperature plate and the primary cold plate; A secondary cold head is arranged between the primary cold plate and the secondary cold plate, and the cooling power of the primary cold head is higher than the cooling power of the secondary cold head; Wherein, when the precooling unit enters the primary precooling mode, the precooling unit cools the mixing chamber through the primary cold head; When the precooling unit enters the secondary precooling mode, the precooling unit cools the mixing chamber through the secondary cold head.

7. The precooling system for a dilution refrigerator according to claim 1, characterized in that: The primary thermal switch or each of the secondary thermal switches comprises: The shell is constructed as a tubular structure with two ends open; A first heat conducting member is in contact with a cold plate with a higher temperature among the two adjacent cold plates, and the first heat conducting member comprises: A first adjusting portion is installed at the upper opening of the shell; A first elastic member, located in the housing and connected to the first adjusting portion; a first joint portion, connected to the first adjusting portion through the first elastic member; The second heat conductive member is installed at the lower end opening of the shell and contacts the cold plate with the lower temperature among the two adjacent cold plates. The second heat conductive member has a conductive state in which the second heat conductive member presses against the first joint portion in response to the cold plate with the lower temperature being higher than the target temperature, thereby forming a heat conduction state with the first heat conductive member, and a disconnected state in which the second heat conductive member is thermally isolated in response to the cold plate with the lower temperature being lower than the target temperature and thereby being detached from the first joint portion.

8. The precooling system for a dilution refrigerator according to claim 7, characterized in that: A limiting boss is formed on the inner wall of the shell, which is used to prevent the first engaging portion from moving toward the second heat conducting member under the drive of the first elastic member.

9. The precooling system for a dilution refrigerator according to claim 8, characterized in that: The second heat-conducting member forms heat conduction with the first heat-conducting member at a first position, the distance between the first position and the limiting boss is a preset spacing, and the second heat-conducting member is configured to move back and forth in a vertical direction to change the size of the preset spacing, thereby adjusting the contact time between the second heat-conducting member and the first joint portion.

10. The precooling system for a dilution refrigerator according to claim 9, characterized in that: The second heat conducting member comprises: A second engaging portion, used for pressing against or disengaging from the first engaging portion; a driving portion, one end of which is connected to the second joint portion and configured to expand or contract in response to a temperature change of the cold plate with a low temperature, so as to drive the second joint portion to move in a vertical direction; The second adjusting part is rotatably mounted on the shell and connected to the other end of the driving part, and is used for adjusting the preset distance.

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