Liquid helium dewar with micro-perturbation zero-evaporation cooling system

Abstract

This invention pertains to superconducting cryogenic technology and relates to a liquid helium Dewar micro-perturbation zero-evaporation cooling system. Liquid helium is selected as the cooling medium, and utilizing the siphon principle, a closed-loop circulation system is formed by the main installation chamber for the cryogenic instruments, the secondary installation chamber for the refrigerator, the liquid helium connecting pipe, and the evaporated helium recovery pipe. This system is used to cool the coil of the superconducting cryogenic current comparator and the superconducting quantum interference device (QFID). The circulation system is placed within an outer cylinder. The main installation chamber contains an equipment passage, and a well-like structure is located on the western side of the equipment passage. The superconducting cryogenic current comparator coil and the superconducting QFID are installed in a shielded box and embedded in the well-like structure. The top of the well-like structure has a through-hole connecting the liquid phase space and the gas phase space of the equipment passage. The lower surface of the refrigerator's cold head is located above the liquid helium surface, and the vertical distance between it and the upper surface of the well-like structure is at least 100 mm. This invention features low cost and high liquid helium utilization.

Description

Technical Field

[0001] This invention belongs to the field of superconducting cryogenic technology, specifically, it relates to a liquid helium Dewar micro-disturbance zero-evaporation cooling system. Background Technology

[0002] Superconducting cryogenic current comparators (CCCs) are essential precision instruments in cutting-edge research fields such as quantum resistance measurement, quantum current measurement, and weak current measurement in high-voltage ionization chambers. They must operate within a liquid helium cryogenic Dewar. However, without effective insulation and cooling measures, CCCs are prone to liquid helium surface oscillations and evaporation during operation, severely interfering with CCC stability. Currently, a key challenge for liquid helium Dewars is achieving gas-liquid circulation of helium resources within the Dewar, maintaining a constant total amount of liquid helium, improving utilization, and ensuring operational stability. Researchers have already begun investigating this issue.

[0003] Chinese patent CN 103985499 B discloses a zero-evaporation cooling system for liquid helium in high-temperature superconducting magnets. It uses liquid nitrogen as the cooling medium and employs the thermosiphon principle to cool the superconducting magnet in a closed-loop system consisting of a refrigerator with a Dewar radiator, a magnet cooling Dewar radiator, a liquid nitrogen connecting pipe, and an evaporating nitrogen connecting pipe. This patent uses two cavities and two connecting pipes to form a closed-loop system, achieving lossless circulation of helium gas and liquid within the system, while protecting the refrigerator from damage in the event of coil quench failure. However, the system has insufficient thermal insulation design, resulting in severe external heat radiation; the overall diameter of the cavities is too large, leading to low liquid helium utilization; it cannot accurately acquire real-time information from inside the Dewar radiator; and the system has poor anti-interference capabilities.

[0004] Chinese patent application CN 115711359 A discloses a zero-evaporation liquid nitrogen storage tank suitable for high-purity germanium detection, including a refrigerator, a liquid nitrogen Dewar, a storage tank, and an inlet cap assembly. The storage tank contains a vacuum chamber, and the liquid nitrogen Dewar is suspended within the vacuum chamber with a gap between its bottom and the inner wall of the tank bottom. The inlet cap assembly is connected to the liquid nitrogen Dewar via a corrugated main neck tube passing through the top of the tank. The refrigerator is located at the top of the tank. This patent application uses a heat-insulated vacuum chamber and a refrigerator with shock-absorbing components to achieve lossless gas-liquid circulation of helium and reduce lateral vibration of the refrigerator. However, liquid helium dripping during recondensation disturbs the liquid surface, preventing the liquid helium from circulating properly, resulting in low utilization and potential damage to the refrigerator in the event of a cryogenic coil quench. Summary of the Invention

[0005] To address the aforementioned problems in the prior art, this invention provides a liquid helium Dewar micro-disturbance zero-evaporation cooling system. On the one hand, it enables zero-loss recycling of liquid helium, reducing liquid helium storage space and lowering costs; on the other hand, it enables liquid helium flow heat exchange, increasing liquid helium utilization.

[0006] This invention provides a liquid helium Dewar micro-disturbance zero-evaporation cooling system, comprising:

[0007] The outer cylinder has a vacuum port on its wall.

[0008] The main cavity is installed and fixed inside the outer cylinder;

[0009] The auxiliary cavity is installed and fixed inside the outer cylinder, and together with the main cavity, they form the Dewar inner cylinder. A space is provided between the Dewar inner cylinder and the outer cylinder to connect to the vacuum port.

[0010] The equipment passage is located inside the main installation cavity, and the top of the equipment passage is mounted on the outer cylinder; the equipment passage is provided with a well-type structure, which is located at the lower part of the equipment passage, and the top of the well-type structure is provided with a through hole connecting the liquid phase space and the gas phase space of the equipment passage;

[0011] A liquid helium connecting pipe connects the device passage to the liquid phase space of the mounting sub-cavity;

[0012] An evaporating helium gas connecting pipe connects the equipment passage to the gas phase space of the mounting sub-cavity;

[0013] A refrigeration unit is installed on the top of the outer cylinder. The cold head of the refrigeration unit is located in the mounting sub-cavity. The lower surface of the cold head is above the liquid helium surface and the vertical distance between it and the upper surface of the well structure is at least 100mm.

[0014] The sample rod has a top wiring storage box fixed to the top of the equipment passage, and a bottom shielding box extending into the equipment passage and buried in the well-type structure.

[0015] The superconducting cryogenic current comparator coil is installed inside the shielding box;

[0016] The superconducting quantum interference device is installed inside the shielding box.

[0017] In some embodiments, a control device is further included, the control device including a controller and a control component, the controller being connected to the refrigerator and the control component respectively; the control component includes a liquid level sensor, a first temperature sensor, a second temperature sensor, a heating element and a pressure sensor, the liquid level sensor, the first temperature sensor and the heating element being disposed at the well structure, the second temperature sensor being disposed at the cold head of the refrigerator, and the pressure sensor being fixed in the detection channel led out from the device passage.

[0018] In some embodiments, the controller is configured to: control the refrigerator to operate when the liquid level sensor detects that the liquid helium level in the device passage is lower than a preset lower limit; control the refrigerator to stop operating when the liquid level sensor detects that the liquid helium level in the device passage rises to the preset lower limit; control the heating element to operate when the liquid level sensor detects that the liquid helium level in the device passage exceeds the preset upper limit; and control the heating element to stop operating when the liquid level sensor detects that the liquid helium level in the device passage drops to the preset upper limit.

[0019] In some embodiments, a safety component located at the top of the device passage is also included. The safety component includes a pressure gauge, a safety valve, a solenoid vent valve, and a manual vent valve. The solenoid vent valve is electrically connected to the controller. When the pressure sensor detects that the helium pressure in the device passage exceeds a preset pressure threshold, the controller controls the solenoid vent valve to open. When the pressure sensor detects that the helium pressure in the device passage drops to the preset pressure threshold, the controller controls the solenoid vent valve to close.

[0020] In some embodiments, the top of the device pathway is further provided with a wiring pathway for integrating outgoing device wiring.

[0021] In some embodiments, the cold head includes a primary cold head and a secondary cold head connected below the primary cold head. The lower surface of the secondary cold head is located above the liquid helium surface and is at least 100 mm away from the upper surface of the well structure.

[0022] In some embodiments, the centerline of the evaporating helium gas connecting pipe is located in the middle section of the primary cold head.

[0023] In some embodiments, a damping component is further included, the damping component comprising:

[0024] The first shock absorber is disposed between the refrigeration unit and the outer cylinder;

[0025] An elastic buffer, one end of which is connected to the primary cold head, and the other end of which is connected to the inner wall platform of the mounting sub-cavity;

[0026] The second shock absorber is disposed between the elastic buffer and the first-stage cold head;

[0027] The third shock absorber is disposed between the elastic buffer and the inner wall platform;

[0028] An insulating support is used to fix the second and third shock absorbers.

[0029] In some embodiments, the main mounting cavity and the secondary mounting cavity are fixed above the bottom of the outer cylinder by a mounting base located at the bottom of the outer cylinder.

[0030] In some embodiments, the space between the mounting cavity and the device passage is filled with thermal insulation material.

[0031] Compared with the prior art, the advantages and positive effects of the present invention are as follows:

[0032] (1) The liquid helium Dewar micro-perturbation zero-evaporation cooling system of the present invention selects liquid helium as the cooling medium and uses the siphon principle to form a closed system consisting of a secondary installation cavity with a refrigerator, a main installation cavity with cryogenic instruments (i.e., a superconducting cryogenic current comparator coil and a superconducting quantum interference device), a liquid helium connecting pipe, and an evaporated helium recovery pipe. This system is used to cool the shielding box with the superconducting cryogenic current comparator coil and the superconducting quantum interference device installed. Specifically, before the superconducting cryogenic current comparator and the superconducting quantum interference device start working, the heat load of the system itself will cause the liquid helium to evaporate into helium gas. This helium gas will be condensed back into liquid helium after the refrigerator is turned on. After the system starts working, the working heat of the cryogenic instruments (i.e., the superconducting cryogenic current comparator coil and the superconducting quantum interference device) in the main installation cavity will cause the liquid helium to evaporate. The evaporated helium gas reaches the secondary installation cavity through the evaporated helium recovery pipe, is cooled and condensed by the refrigerator, and the cooling liquid helium in the secondary installation cavity exchanges heat with the liquid helium in the main installation cavity through the liquid helium connecting pipe to cool the shielding box. During system operation, there is no loss of liquid helium, requiring no replenishment. The siphon effect in the closed-loop system eliminates the need for a cryogenic liquid helium pump, reducing system assembly and operating costs. The cryogenic instruments (i.e., the superconducting cryogenic current comparator coil and the superconducting quantum interference device) and the cryostat are installed in the main installation chamber and the secondary installation chamber, respectively, to avoid liquid surface disturbance caused by recondensed liquid helium dripping and to prevent damage to the cryostat from coil timeout.

[0033] (2) The liquid helium Dewar micro-disturbance zero-evaporation cooling system of the present invention uses ultra-low temperature resistant flexible material for connecting the liquid helium connecting pipe and the evaporating helium connecting pipe of the main and auxiliary cavities, which reduces the vibration transmission during the operation of the refrigerator and maintains the stability of the main cavity.

[0034] (3) The liquid helium Dewar micro-disturbance zero-evaporation cooling system of the present invention adopts an outer cylinder containing an inner cylinder. The inner cylinder is fixed to the bottom of the outer cylinder by a mounting base, and the cavity between the outer cylinder and the inner cylinder is evacuated to a vacuum through a vacuum port. On the one hand, it avoids direct heat exchange between the inner cylinder and the outside world, reduces the system's cooling loss, and protects the internal structure from the influence of the external environment; on the other hand, it integrates the system into a whole, making it convenient for transportation and movement.

[0035] (4) The liquid helium Dewar micro-disturbance zero-evaporation cooling system of the present invention uses vibration damping components to fix the refrigerator. On the one hand, it reduces the impact of refrigerator vibration on the overall system and increases system stability; on the other hand, it reduces heat leakage at the refrigerator cold head and improves cooling efficiency.

[0036] (5) The liquid helium Dewar micro-disturbance zero-evaporation cooling system of the present invention has an equipment passage set in the main cavity. The equipment passage has a well structure. The shielding box containing the superconducting cryogenic current comparator coil and the superconducting quantum interference device is buried in the well structure. The well structure is the only liquid helium flow route in the main cavity, ensuring that the cryogenic liquid helium flows around the shielding box and increasing the utilization rate of liquid helium. The upper surface of the well structure is reserved with through holes for the flow of evaporated helium gas, ensuring that the evaporated helium gas around the well structure can be smoothly circulated.

[0037] (6) The liquid helium Dewar micro-disturbance zero-evaporation cooling system of the present invention uses control components including a liquid level sensor, a temperature sensor, a pressure sensor, and a heating element to detect the liquid level, temperature, and helium pressure inside the inner cylinder of the Dewar. Based on the detected liquid level and pressure, the controller controls the operation of the refrigerator and the heating element to maintain the stability of the liquid helium level and helium pressure. Based on the detected temperature, the controller controls the working environment temperature so that the liquid helium level fluctuation range inside the inner cylinder of the Dewar is ±0.3%, the pressure fluctuation range is ±100Pa, and the temperature fluctuation range is ±10mK.

[0038] (7) The liquid helium Dewar micro-disturbance zero-evaporation cooling system of the present invention integrates the power supply leads of the control components, superconducting cryogenic current comparator and superconducting quantum interference device into the circuit path of the top cover of the equipment, which can be put in and taken out together, making it convenient for equipment replacement and maintenance. Attached Figure Description

[0039] Figure 1 This is an assembly diagram of the liquid helium Dewar micro-disturbance zero-evaporation cooling system according to an embodiment of the present invention;

[0040] Figure 2 for Figure 1 A partial enlarged view of the installation location of the refrigeration unit;

[0041] Figure 3 for Figure 1 A magnified view of a portion of the well-type structure of the equipment access passageway;

[0042] Figure 4 for Figure 1 A close-up view of the safety component of the outer cylinder top cover;

[0043] Figure 5 This is a perspective view of the liquid helium Dewar micro-disturbance zero-evaporation cooling system described in an embodiment of the present invention;

[0044] Figure 6This is a control principle diagram of the liquid helium Dewar micro-disturbance zero-evaporation cooling system described in an embodiment of the present invention.

[0045] In the diagram, 1. Outer cylinder; 101. Vacuum port; 2. Main installation chamber; 3. Secondary installation chamber; 301. Inner wall platform; 4. Cavity; 5. Equipment passageway; 6. Well-type structure; 601. Through hole; 7. Liquid helium connecting pipe; 8. Evaporated helium connecting pipe; 9. Refrigeration unit; 901. First-stage cold head; 902. Second-stage cold head; 10. Sample rod; 11. Circuit storage box; 12. Shielding box; 13. Controller; 14. Liquid level sensor; 15. ... 16. Temperature sensor, 17. Second temperature sensor, 18. Heating element, 19. Pressure sensor, 20. Pressure gauge, 21. Safety valve, 22. Electromagnetic vent valve, 23. Manual vent valve, 24. Circuit path, 25. Liquid helium level, 26. First shock absorber, 27. Elastic buffer, 28. Second shock absorber, 29. Third shock absorber, 30. Insulating support, 31. Mounting base, 32. Thermal insulation material, 33. Liquid helium injection pipeline. Detailed Implementation

[0046] The present invention will now be described in detail through exemplary embodiments. However, it should be understood that, without further description, elements, structures, and features in one embodiment may be advantageously incorporated into other embodiments.

[0047] In the description of this invention, it should be understood that the terms "center", "lateral", "longitudinal", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0048] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0049] See Figures 1 to 5 This paper provides an illustrative embodiment of the liquid helium Dewar micro-disturbance zero-evaporation cooling system described in this invention. The liquid helium Dewar micro-disturbance zero-evaporation cooling system includes:

[0050] The outer cylinder 1 has a vacuum port 101 on its cylinder wall;

[0051] Install the main cavity 2 and fix it inside the outer cylinder 1;

[0052] The auxiliary cavity 3 is fixed inside the outer cylinder 1 and together with the main cavity 2, forms the Dewar inner cylinder. A cavity 4 is provided between the Dewar inner cylinder and the outer cylinder 1 to communicate with the vacuum port 101.

[0053] The equipment passage 5 is located inside the main installation cavity 2, and the top of the equipment passage 5 is mounted on the outer cylinder 1; the equipment passage 5 is provided with a well structure 6, which is located at the lower part of the equipment passage 5, and the top of the well structure 5 is provided with a through hole 601 connecting the liquid phase space and the gas phase space of the equipment passage.

[0054] Liquid helium connecting pipe 7 connects the equipment passage to the liquid phase space of the mounting sub-cavity;

[0055] Evaporated helium connecting pipe 8 connects the equipment passage to the gas phase space of the installation sub-cavity;

[0056] A refrigeration unit 9 is installed on the top of the outer cylinder 1. The cold head of the refrigeration unit 9 is located in the mounting sub-cavity 3. The lower surface of the cold head is above the liquid helium surface and the vertical distance between it and the upper surface of the well structure 6 is at least 100mm.

[0057] The sample rod 10 has a top wiring storage box 11 fixed to the top of the equipment passage 5, and a bottom shielding box 12 extending into the equipment passage and buried in the well structure 6.

[0058] The superconducting cryogenic current comparator coil (not shown in the figure) is installed inside the shielding box 12;

[0059] A superconducting quantum interference device (not shown in the figure) is installed inside the shielding box 12.

[0060] In some embodiments, see Figure 6The aforementioned liquid helium Dewar micro-disturbance zero-evaporation cooling system also includes a control device. This control device comprises a controller 13 and a control component. The controller 13 is connected to the refrigerator 9 and the control component, respectively. The control component includes a liquid level sensor 14, a first temperature sensor 15, a second temperature sensor 16, a heating element 17, and a pressure sensor 18. The liquid level sensor 14, the first temperature sensor 15, and the heating element 16 are located at the well-type structure 6. The second temperature sensor is located at the cold head of the refrigerator 9. The pressure sensor 18 is fixed in the detection channel leading out from the equipment passage 5. The liquid helium level in the equipment passage is detected by the liquid level sensor. The controller controls the operation of the refrigerator and the heating element based on the liquid helium level detected by the liquid level sensor, ensuring that the liquid helium level in the equipment passage fluctuates within ±0.3%. The liquid helium temperature near the well-type structure is detected by the first temperature sensor to ensure the operating environment temperature of the equipment inside the shielded box. The cold head temperature of the refrigerator is detected by the second temperature sensor to ensure helium recondensation efficiency. The pressure sensor detects the helium pressure at the top of the equipment passage so that pressure relief can be carried out if the helium pressure is too high.

[0061] In some embodiments, the controller is configured to: control the refrigerator to operate when the liquid level sensor detects that the liquid helium level in the device passage is lower than a preset lower limit; control the refrigerator to stop operating when the liquid level sensor detects that the liquid helium level in the device passage rises to a preset upper limit; control the heating element to operate when the liquid level sensor detects that the liquid helium level in the device passage exceeds the preset upper limit; and control the heating element to stop operating when the liquid level sensor detects that the liquid helium level in the device passage drops to the preset upper limit. Specifically, the heating element is a heating wire.

[0062] In some embodiments, the above-described liquid helium Dewar micro-disturbance zero-evaporation cooling system further includes a safety component located at the top of the equipment passage. This safety component includes a pressure gauge 19, a safety valve 20, an electromagnetic vent valve 21, and a manual vent valve 22. The electromagnetic vent valve 21 is electrically connected to the controller 13. When the pressure sensor 18 detects that the helium pressure in the equipment passage 5 exceeds a preset pressure threshold, the controller 13 controls the electromagnetic vent valve 21 to open. When the pressure sensor 18 detects that the helium pressure in the equipment passage 5 decreases to the preset pressure threshold, the controller 13 controls the electromagnetic vent valve 21 to close. The pressure gauge is used to detect the helium pressure in the equipment passage, allowing operators to directly read the helium pressure. When the helium pressure in the equipment passage exceeds a preset voltage threshold, the manual vent valve is opened for pressure relief. When the coil of the superconducting cryogenic current comparator fails to quench and a large amount of evaporated helium is generated, the pressure of the evaporated helium will open the safety valve, allowing the evaporated helium to be discharged in time to prevent the system from being in danger due to excessive pressure; after the helium pressure drops, the external atmospheric pressure will close the safety valve.

[0063] In some embodiments, see continue to see Figure 4 , Figure 5 The top of the device passage 5 is also provided with a wiring passage 23 for integrating and leading out device wiring, facilitating device replacement and maintenance. Specifically, the device includes control components, a superconducting cryogenic current comparator, and a superconducting quantum interference device, etc.

[0064] In some embodiments, see continue to see Figure 1 , Figure 2 The cold head includes a primary cold head 901 and a secondary cold head 902 connected below the primary cold head 901. The lower surface of the secondary cold head 902 is located above the liquid helium surface 24, and the vertical distance between it and the upper surface of the well structure 6 is at least 100mm. It should be noted that this vertical distance can be set according to actual needs, but it cannot be less than 100mm.

[0065] In some embodiments, see continue to see Figure 1 , Figure 2 The centerline of the evaporating helium gas connecting pipe 8 is located in the middle section of the first-stage cold head 901. This facilitates the condensation of the evaporating helium gas by the refrigerator and improves condensation efficiency.

[0066] In some embodiments, see continue to see Figure 4 The aforementioned liquid helium Dewar micro-disturbance zero-evaporation cooling system also includes a vibration damping component, which comprises:

[0067] The first shock absorber 25 is disposed between the refrigeration unit 9 and the outer cylinder 1;

[0068] Elastic buffer 26, one end of which is connected to the first-stage cold head 901, and the other end of which is connected to the inner wall platform 301 of the mounting sub-cavity 3;

[0069] The second shock absorber 27 is disposed between the elastic buffer 26 and the first-stage cold head 901;

[0070] The third shock absorber 28 is disposed between the elastic buffer 26 and the inner wall platform 301;

[0071] Insulating support member 29 fixes the second shock absorber 27 and the third shock absorber 28.

[0072] Using vibration damping components to secure the refrigeration unit reduces the impact of refrigeration unit vibration on the overall system, increasing system stability. It also reduces heat leakage at the refrigeration unit's cold head, improving cooling efficiency.

[0073] Specifically, in some embodiments, the first, second, and third damping components are, but are not limited to, damping pads, and the elastic buffer is, but is not limited to, a bellows.

[0074] In some embodiments, see continue to see Figure 1 The main mounting cavity 2 and the secondary mounting cavity 3 are fixed above the bottom of the outer cylinder 1 by a mounting base 30 located at the bottom of the outer cylinder 1. The mounting base creates space between the bottom of the main mounting cavity and the secondary mounting cavity and the outer cylinder, preventing direct heat exchange between the Dewar inner cylinder and the outside environment after vacuuming, reducing heat loss, and protecting the internal structure from the influence of the external environment.

[0075] In some embodiments, see continue to see Figure 1 The space between the main installation cavity 2 and the equipment passage 5 is filled with thermal insulation material 31. This reduces excess liquid helium storage space and increases liquid helium utilization. It also reduces the system's exposure to external heat radiation and minimizes system cooling loss.

[0076] Specifically, in some embodiments, the liquid helium connecting pipe and the evaporated helium connecting pipe are made of a cryogenically resistant flexible material. This can further reduce the impact of refrigerator vibration on the Dewar inner cylinder, avoid the liquid surface fluctuations caused by the recondensation of liquid helium during refrigerator operation affecting the stability of the operating environment of cryogenic instruments (i.e., the superconducting cryogenic current comparator coil and the superconducting quantum interference device), and at the same time avoid damage to the refrigerator caused by the superconducting cryogenic current comparator coil failing to quench.

[0077] In use, the inner Dewar cylinder is installed inside the outer cylinder. Before liquid helium filling, the cavity between the inner and outer cylinders is evacuated through a vacuum port. The equipment passage is installed in the main installation cavity, with insulation material filling the space between them. The refrigerator is installed in the secondary installation cavity and mounted on the top cover of the outer cylinder via a first shock absorber. The cold head of the refrigerator is connected to the inner wall of the secondary installation cavity via an elastic buffer. Liquid helium is added to the equipment passage and the secondary installation cavity to a preset value through a liquid helium injection pipe located on the main installation cavity and connected to the equipment passage. At this time, the amount of liquid helium evaporation caused by the system's own heat load is small, and the evaporated helium is subsequently condensed by the refrigerator, so the total amount of helium in the system will not decrease. The sample rod is inserted into the main installation cavity through the equipment passage. The wiring storage box at the top of the sample rod is fixed to the top cover of the equipment passage via an external flange interface, and the shielding box at the bottom of the sample rod is inserted into the well structure of the equipment passage.

[0078] After the system starts operating, the heat generated by devices such as the superconducting cryogenic current comparator and the superconducting quantum interference device increases the evaporation of liquid helium. The evaporated helium then travels through the helium recovery pipe to the secondary installation chamber, where it is re-condensed by the refrigerator. When the liquid level detected by the level sensor is below the preset lower limit, the controller activates the refrigerator. When the liquid level sensor detects that the liquid helium level in the equipment passage has risen to the preset upper limit, the controller stops the refrigerator. When the liquid level sensor detects that the liquid helium level in the equipment passage exceeds the preset upper limit, the controller activates the heating element to accelerate liquid helium evaporation. When the liquid level sensor detects that the liquid helium level in the equipment passage has dropped to the preset upper limit, the controller stops the heating element, maintaining the liquid helium level within the preset range. The re-condensed cryogenic liquid helium convects with the liquid helium in the equipment passage. The well-like structure in the equipment passage is the only liquid helium flow path inside the main installation chamber, ensuring that the cryogenic liquid helium can pass through the shielding box for sufficient cooling. The controller detects the helium pressure at the top of the equipment passage using a pressure sensor, and controls the opening and closing of the electromagnetic vent valve based on the detected helium pressure. A first temperature sensor monitors the liquid helium temperature near the well structure to ensure a stable operating environment for the superconducting cryogenic current comparator and the superconducting quantum interference device. Simultaneously, a second temperature sensor monitors the cold head temperature of the cryostat to ensure efficient helium recondensation.

[0079] During the operation of the above system, there is no loss of liquid helium and no need for subsequent replenishment. Cryogenic liquid helium convection can be achieved without equipment such as cryogenic liquid helium pumps, saving operating costs. During the liquid helium circulation process, the utilization rate is higher when passing near the shielding box. Disturbances in the secondary installation cavity have minimal impact on the main installation cavity; liquid level, pressure, and other indicators are controllable; and the operating environment of the cryogenic instruments (i.e., the superconducting cryogenic current comparator coil and the superconducting quantum interference device) is highly stable.

[0080] The above embodiments are used to explain the present invention, but not to limit the present invention. Any modifications and changes made to the present invention within the spirit and scope of the claims shall fall within the protection scope of the present invention.

Claims

1. A liquid helium dewar micro-perturbation zero boil-off cooling system, characterized in that, include: The outer cylinder has a vacuum port on its wall. The main cavity is installed and fixed inside the outer cylinder; The auxiliary cavity is installed and fixed inside the outer cylinder, and together with the main cavity, they form the Dewar inner cylinder. A cavity is provided between the Dewar inner cylinder and the outer cylinder to communicate with the vacuum port. The equipment passage is located inside the main installation cavity, and the top of the equipment passage is mounted on the outer cylinder; the equipment passage is provided with a well-type structure, which is located at the lower part of the equipment passage, and the top of the well-type structure is provided with a through hole connecting the liquid phase space and the gas phase space of the equipment passage; A liquid helium connecting pipe connects the device passage to the liquid phase space of the mounting sub-cavity; An evaporating helium gas connecting pipe connects the equipment passage to the gas phase space of the mounting sub-cavity; A refrigeration unit is installed on the top of the outer cylinder. The cold head of the refrigeration unit is located in the mounting sub-cavity. The lower surface of the cold head is above the liquid helium surface and the vertical distance between it and the upper surface of the well structure is at least 100mm. The sample rod has a top wiring storage box fixed to the top of the equipment passage, and a bottom shielding box extending into the equipment passage and buried in the well-type structure. The superconducting cryogenic current comparator coil is installed inside the shielding box; A superconducting quantum interference device is installed inside the shielding box; The system also includes a control device comprising a controller and a control component. The controller is connected to the refrigerator and the control component, respectively. The control component includes a liquid level sensor, a first temperature sensor, a second temperature sensor, a heating element, and a pressure sensor. The liquid level sensor, the first temperature sensor, and the heating element are located at the well-type structure. The second temperature sensor is located at the cold head of the refrigerator. The pressure sensor is fixed in the detection channel leading out from the equipment passage. The controller is configured to: control the refrigerator to operate when the liquid level sensor detects that the liquid helium level in the equipment passage is lower than a preset lower limit; control the refrigerator to stop operating when the liquid level sensor detects that the liquid helium level in the equipment passage rises to a preset upper limit; control the heating element to operate when the liquid level sensor detects that the liquid helium level in the equipment passage exceeds the preset upper limit; and control the heating element to stop operating when the liquid level sensor detects that the liquid helium level in the equipment passage drops to the preset upper limit.

2. The liquid helium dewar micro-perturbation zero boil-off cooling system of claim 1, wherein, It also includes a safety component located at the top of the equipment passage, the safety component including a pressure gauge, a safety valve, a solenoid vent valve, and a manual vent valve; the solenoid vent valve is electrically connected to the controller, when the pressure sensor detects that the helium pressure in the equipment passage exceeds a preset pressure threshold, the controller controls the solenoid vent valve to open, and when the pressure sensor detects that the helium pressure in the equipment passage drops to the preset pressure threshold, the controller controls the solenoid vent valve to close.

3. The liquid helium dewar micro-perturbation zero boil-off cooling system of claim 1, wherein, The top of the equipment passage is also provided with a wiring passage for integrating and leading out equipment wiring.

4. The liquid helium dewar micro-perturbation zero boil-off cooling system of claim 1, wherein, The cold head includes a primary cold head and a secondary cold head connected below the primary cold head. The lower surface of the secondary cold head is located above the liquid helium surface and the vertical distance between it and the upper surface of the well structure is at least 100 mm.

5. The liquid helium dewar micro-perturbation zero boil-off cooling system of claim 4, wherein, The centerline of the helium evaporation connecting pipe is located in the middle section of the first-stage cold head.

6. The liquid helium dewar micro-perturbation zero boil-off cooling system of claim 4, wherein, It also includes a shock-absorbing component, which includes: The first shock absorber is disposed between the refrigeration unit and the outer cylinder; An elastic buffer, one end of which is connected to the primary cold head, and the other end of which is connected to the inner wall platform of the mounting sub-cavity; The second shock absorber is disposed between the elastic buffer and the first-stage cold head; The third shock absorber is disposed between the elastic buffer and the inner wall platform; An insulating support is used to fix the second and third shock absorbers.

7. The liquid helium dewar micro-perturbation zero boil-off cooling system of any one of claims 1 to 6, wherein, The main mounting cavity and the secondary mounting cavity are fixed above the bottom of the outer cylinder by a mounting base located at the bottom of the outer cylinder.

8. The liquid helium dewar micro-perturbation zero boil-off cooling system of any one of claims 1 to 6, wherein, The space between the main installation cavity and the equipment passage is filled with heat insulation material.

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