Dry-type closed-cycle low-temperature system adaptive to pulse paramagnetic resonance spectrometer

Abstract

The utility model discloses a dry-type closed-cycle cryogenic system adaptive to a pulse paramagnetic resonance spectrometer. The dry-type closed-cycle cryogenic system comprises a liquefier assembly, a low-loss infusion tube assembly, a cryostat module assembly, a pulse probe and a circulating gas circuit assembly. According to the dry-type closed-cycle low-temperature system adaptive to the pulse paramagnetic resonance spectrometer, liquid helium used for reducing ultralow temperature and ultralow vibration is provided, the temperature of a low-temperature experiment environment is as low as 2.5 k, the vibration is smaller than 20 nm, a special structure that a GM refrigerating machine is externally arranged and helium circulation is utilized is adopted, the experiment conditions of ultralow temperature and ultralow vibration are achieved, and the experiment efficiency is improved. The low-temperature thermostat is connected through the low-loss infusion tube, the low-loss infusion tube is fixed through the fixing frame, at the moment, vibration transmitted by the liquefier part is filtered, and therefore the effect of ultralow vibration is achieved.

Description

Technical Field

[0001] This application relates to the field of cryogenic experimental apparatus, and in particular to a dry closed-loop cryogenic system adapted to a pulsed paramagnetic resonance spectrometer. Background Technology

[0002] With the advancement of science and technology, low temperature, paramagnetic resonance, and low vibration have become indispensable auxiliary technologies for scientific experiments in physics, chemistry, materials, biology, and other fields. Low temperature cooling devices are mainly divided into two types: the first type uses refrigerant cooling, which involves storing liquid helium in a container or continuously transporting liquid helium to the part that needs to be cooled through pipelines; the second type uses closed-loop refrigeration, and the refrigeration machines mainly include GM refrigeration machines and pulse tube refrigeration machines.

[0003] However, due to the non-renewable nature, high price, and reliance on imports of liquid helium, the cost of using liquid helium transport for cooling is too high, making long-term experimental testing impossible. Directly cooling magnets and samples using GM / pulse tube refrigerators results in excessive vibration, unsuitable for researchers' needs. Throttling expansion technology, also known as Joule-Thomson expansion, involves a fluid at higher pressure undergoing adiabatic expansion towards lower pressure through a throttling valve. According to thermodynamic principles, pressure causes temperature changes, known as the JT effect. Helium exhibits a positive JT effect when the ambient temperature is above the Joule-Thomson transition temperature, meaning the gas temperature increases as pressure decreases; conversely, it exhibits a negative JT effect when the ambient temperature is below the Joule-Thomson transition temperature, meaning the gas temperature decreases as pressure decreases. Throttling expansion technology could achieve ultra-low temperatures of around 2K using existing 4K refrigerators without consuming large amounts of liquid helium. However, current technologies lack methods and devices for achieving ultra-low temperatures using throttling expansion technology. Utility Model Content

[0004] The existing cryogenic testing equipment has always used liquid helium transfer for cooling, which is costly and cannot be used for long-term experimental testing. The use of GM refrigerators / pulse tube refrigerators to directly cool magnets and samples results in too much vibration, which cannot meet the technical requirements of scientific researchers. Therefore, this utility model proposes a dry closed-loop cryogenic system adapted to pulse paramagnetic resonance spectrometer.

[0005] This application provides a dry closed-loop cryogenic system adapted for pulsed paramagnetic resonance spectrometers, employing the following technical solution:

[0006] A dry closed-loop cryogenic system adapted to a pulsed paramagnetic resonance spectrometer includes a liquefier assembly, a low-loss infusion tubing assembly, a cryostat module assembly, a pulse probe, and a circulating gas path assembly.

[0007] The low-loss infusion tubing assembly is fixedly installed on the outer surface of the liquefier assembly, the outer surface of the cryogenic thermostat module assembly is fixedly installed on the outer surface of the liquefier assembly, the outer surface of the pulse probe is fixedly installed on the outer surface of the low-loss infusion tubing assembly, and the circulating gas path assembly is disposed inside the cryogenic thermostat module assembly.

[0008] Optionally, the liquefier assembly includes a vacuum port, a GM refrigerator, a vacuum explosion-proof valve, a needle valve handle, a shock-absorbing bellows, a vacuum chamber, a primary cold head, a cold shield, a secondary cold head, a secondary cold plate, a cryogenic needle valve, a primary cold head heat exchanger, and a secondary cold head heat exchanger.

[0009] Optionally, one end of the vacuum extraction port is fixedly installed on the outer surface of the vacuum chamber using a KF25 standard clamp. A shock-absorbing bellows is fixedly installed on the outer surface of the GM refrigerator. The shock-absorbing bellows is fixedly installed on the outer surface of the vacuum chamber. The vacuum explosion-proof valve is fixedly bonded to the outer surface of the vacuum chamber using epoxy resin adhesive. The needle valve handle is fixedly installed on the outer surface of the cryogenic needle valve. The primary cold head and the secondary cold head are respectively fixedly installed on the outer surface of the GM refrigerator. The cold shield is fixedly installed on the outer surface of the primary cold head using hexagonal screws. The secondary cold plate is fixed on the outer surface of the secondary cold head using hexagonal screws. The cryogenic needle valve is fixedly welded to the outer surface of the vacuum chamber using argon arc welding. The primary cold head heat exchanger is fixedly installed on the outer surface of the cold shield using hexagonal screws. The secondary cold head heat exchanger is fixedly installed on the outer surface of the secondary cold plate using hexagonal screws. One end of the primary cold head heat exchanger and one end of the secondary cold head heat exchanger are fixedly installed by brazing with a 3.2mm stainless steel capillary tube.

[0010] Optionally, the low-loss infusion tubing assembly includes a low-loss infusion tubing, a mounting bracket, a cryogenic thermostat, a KF25 corrugated metal tube, a circulation pump, a first KF16 corrugated metal tube, a second KF16 corrugated metal tube, an isolation valve, a third KF16 corrugated metal tube, a helium tank, a 1 / 4-inch stainless steel pipe, positive and negative pressure gauges, and an air inlet.

[0011] Optionally, after the fixing bracket is fixedly installed on the ground, it clamps the low-loss infusion tube between the vacuum chamber and the cryogenic thermostat. One end of the low-loss infusion tube is fixedly installed on the outer surface of the vacuum chamber using a KF50 standard clamp. Both ends of the KF25 corrugated metal pipe are fixedly installed on the outer surface of the cryogenic thermostat and one end of the air inlet of the circulating pump, respectively, using KF25 clamps. Both ends of the first KF16 corrugated metal pipe are fixedly installed on one end of the air outlet and one end of the air inlet of the circulating pump, respectively, using KF16 standard clamps. The isolation valve... One end of the first KF16 metal bellows is fixedly installed at one end of the second KF16 metal bellows and the third KF16 metal bellows by KF16 standard clamps. One end of the second KF16 metal bellows is connected to one end of the first KF16 metal bellows by argon arc welding. The third KF16 metal bellows is connected to the outlet end of the helium tank by argon arc welding. The positive and negative pressure gauges are fixedly bonded to one end of the 1 / 4 joint stainless steel pipe 24 by epoxy resin glue. The 1 / 4 joint stainless steel pipe is connected to the outer surface of the helium tank by argon arc welding.

[0012] Optionally, the cryogenic thermostat module assembly includes a dry closed-loop refrigeration module socket, a circulating helium return port, a communication line, a thermostat vacuum Dewar, a thermostat vacuum Dewar vacuum extraction port, a fixing nut, a sample tube, a sample insertion / removal valve, and a sample area thermometer. The circulating gas path assembly includes a helium inlet capillary tube, a cold finger heat exchanger, a cold finger thermometer, a cold finger heater, and a helium return stainless steel pipe.

[0013] Optionally, the dry closed-loop refrigeration module socket is fixedly installed on the outer surface of the GM refrigerator, the circulating helium return port is fixedly installed on the outer surface of the GM refrigerator, the communication line is electrically connected to the sample area thermometer, the cold finger thermometer, and the cold finger heater, the vacuum dewar of the thermostat evacuates the air inside the vacuum dewar, the two ends of the fixing nut are fixedly installed on the outer surface of the low-temperature thermostat of the pulse paramagnetic resonance spectrometer and one end of the pulse probe, respectively, one end of the sample tube is movably inserted into the inside of the pulse probe, the sample insertion / removal valve is set on the outer surface of the sample tube to control the insertion / removal of the sample tube, the cold finger heat exchanger is fixedly installed inside the vacuum dewar of the thermostat, one end of the helium inlet capillary is fixedly installed at the inlet end of the cold finger heat exchanger, one end of the helium return stainless steel pipe is fixedly installed at the outlet end of the cold finger heat exchanger, the cold finger thermometer is fixedly installed inside the cold finger heat exchanger, and the cold finger heater is fixedly installed inside the cold finger heat exchanger.

[0014] In summary, this application includes at least one of the following beneficial technical effects:

[0015] By setting up a dry closed-loop cryogenic system with a pulsed paramagnetic resonance spectrometer, the use of liquid helium for ultra-low temperature and ultra-low vibration is reduced. The temperature of the cryogenic experimental environment is as low as 2.5K, and the vibration is less than 20nm. An external GM refrigerator is used, and the special structure of the helium circulation achieves ultra-low temperature and ultra-low vibration experimental conditions. The cryogenic thermostat is connected through a low-loss liquid infusion tube, which is fixed by a bracket. At this time, the vibration transmitted from the liquefaction unit is filtered out, thus achieving ultra-low vibration. This solves the technical problems of existing cryogenic experimental devices that use liquid helium transfer for cooling, which is costly and cannot be used for long-term experimental testing. The GM refrigerator / pulse tube refrigerator directly cools the magnet and sample, resulting in too much vibration, which cannot meet the requirements of scientific researchers. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of a dry closed-loop cryogenic system adapted to a pulsed paramagnetic resonance spectrometer proposed in this utility model.

[0017] Figure 2 A perspective view of a vacuum explosion-proof valve structure adapted to a dry closed-loop cryogenic system of a pulse paramagnetic resonance spectrometer, as proposed in this utility model.

[0018] Figure 3 A three-dimensional view of the vacuum cavity structure of a dry closed-loop cryogenic system adapted to a pulsed paramagnetic resonance spectrometer proposed in this utility model.

[0019] Figure 4 A three-dimensional view of a vacuum Dewar structure for a thermostat adapted to a dry closed-loop cryogenic system of a pulsed paramagnetic resonance spectrometer, as proposed in this utility model.

[0020] Figure 5 This is a perspective view of a cold finger heat exchanger structure adapted to a dry closed-loop cryogenic system for a pulsed paramagnetic resonance spectrometer, as proposed in this utility model.

[0021] In the diagram: 1. Vacuum extraction port; 2. GM refrigerator; 3. Vacuum explosion-proof valve; 4. Needle valve handle; 5. Vibration-damping bellows; 6. Vacuum chamber; 7. First-stage cold head; 8. Cold shield; 9. Second-stage cold head; 10. Second-stage cold plate; 11. Low-temperature needle valve; 12. First-stage cold head heat exchanger; 13. Second-stage cold head heat exchanger; 14. Low-loss infusion tubing; 15. Mounting bracket; 16. Low-temperature thermostat; 17. KF25 metal bellows; 18. Circulation pump; 19. First KF16 metal bellows; 20. Second KF16 metal bellows; 21. Isolation valve; 22. Third KF1 6. Metal bellows; 23. Helium cylinder; 24. 1 / 4 joint stainless steel pipe; 25. Positive and negative pressure gauges; 26. Gas inlet; 30. Dry closed-loop refrigeration module socket; 31. Circulating helium return port; 32. Communication line; 33. Thermostat vacuum Dewar; 34. Thermostat vacuum Dewar vacuum extraction port; 35. Fixing nut; 36. Pulse probe; 37. Sample tube; 38. Sample valve; 39. Sample area thermometer; 40. Helium inlet capillary tube; 41. Cold finger heat exchanger; 42. Cold finger thermometer; 43. Cold finger heater; 44. Helium return stainless steel pipe. Detailed Implementation

[0022] The following is in conjunction with the appendix Figures 1-4 This application will be described in further detail.

[0023] Reference Figures 1-4 A dry closed-loop cryogenic system adapted to a pulsed paramagnetic resonance spectrometer includes a liquefier assembly, a low-loss infusion tubing assembly, a cryostat module assembly, a pulse probe 36, and a circulating gas path assembly.

[0024] The low-loss infusion tubing assembly is fixedly installed on the outer surface of the liquefier assembly, the outer surface of the low-temperature thermostat module assembly is fixedly installed on the outer surface of the liquefier assembly, the outer surface of the pulse probe 36 is fixedly installed on the outer surface of the low-loss infusion tubing assembly, and the circulating gas circuit assembly is located inside the low-temperature thermostat module assembly.

[0025] Specifically, the liquefier assembly includes a vacuum port 1, a GM chiller 2, a vacuum explosion-proof valve 3, a needle valve handle 4, a shock-absorbing bellows 5, a vacuum chamber 6, a primary cold head 7, a cold shield 8, a secondary cold head 9, a secondary cold plate 10, a low-temperature needle valve 11, a primary cold head heat exchanger 12, and a secondary cold head heat exchanger 13.

[0026] Specifically, vacuum port 1 is fixed to the outer surface of vacuum chamber 6 using KF25 standard clamps to evacuate the inner vacuum of vacuum chamber 6. GM refrigerator 2 is fixed to the outer surface of vacuum chamber 6 using shock-absorbing bellows 5 to provide a low-temperature environment. Vacuum explosion-proof valve 3 is fixed to the outer surface of vacuum chamber 6 with epoxy resin adhesive to prevent helium leakage and potential safety accidents. Needle valve handle 4 is used to achieve adiabatic expansion, ensuring that the temperature of the liquefied helium reaches below 2K. Cold shield 8 is fixed to the primary cold head 7 using hexagonal screws. The secondary cold plate 10 is fixed to the secondary cold head 9 with hex screws. The low-temperature needle valve 11 is fixed to the vacuum chamber 6 by argon arc welding and is regulated by the needle valve handle 4. The primary cold head heat exchanger 12 is fixed to the cold screen 8 with hex screws. The secondary cold head heat exchanger 13 is fixed to the secondary cold plate 10 with hex screws. The primary cold head heat exchanger 12 and the secondary cold head heat exchanger 13 are brazed together by a 3.2mm stainless steel capillary tube. The low-loss infusion tube 14 is fixed to the vacuum chamber 6 with a KF50 standard clamp.

[0027] Specifically, the low-loss infusion tubing 14 assembly includes a low-loss infusion tubing 14, a mounting bracket 15, a cryogenic thermostat 16, a KF25 metal bellows 17, a circulation pump 18, a first KF16 metal bellows 19, a second KF16 metal bellows 20, an isolation valve 21, a third KF16 metal bellows 22, a helium tank 23, a 1 / 4 joint stainless steel pipe 24, positive and negative pressure gauges 25, and an air inlet.

[0028] Specifically, after the fixing bracket 15 is fixedly installed on the ground, it clamps the low-loss infusion tube 14 between the vacuum chamber 6 and the cryogenic thermostat 16. One end of the low-loss infusion tube 14 is fixedly installed on the outer surface of the vacuum chamber 6 using a KF50 standard clamp. Both ends of the KF25 metal bellows 17 are fixedly installed on the outer surface of the cryogenic thermostat 16 and one end of the air inlet of the circulation pump 18, respectively, using KF25 clamps. Both ends of the first KF16 metal bellows 19 are fixedly installed on one end of the air outlet and one end of the air inlet 26 of the circulation pump 18, respectively, using KF16 standard clamps. Isolation valve 2 One end of the tube 1 is fixedly installed at one end of the second KF16 metal bellows 20 and the third KF16 metal bellows 22 by a KF16 standard clamp. One end of the second KF16 metal bellows 20 is connected to one end of the first KF16 metal bellows 19 by argon arc welding. The third KF16 metal bellows 22 is connected to the outlet end of the helium tank 23 by argon arc welding. The positive and negative pressure gauges 25 are fixedly bonded to one end of the 1 / 4 joint stainless steel pipe 24 by epoxy resin glue. The 1 / 4 joint stainless steel pipe 24 is connected to the outer surface of the helium tank 23 by argon arc welding.

[0029] Specifically, the low-temperature thermostat 16 module assembly includes a dry closed-loop refrigeration module socket 30, a circulating helium return port 31, a communication line 32, a thermostat vacuum Dewar 33, a thermostat vacuum Dewar vacuum extraction port 34, a fixing nut 35, a sample tube 37, a sample insertion / removal valve 38, and a sample area thermometer 39. The circulating gas path assembly includes a helium inlet capillary tube 40, a cold finger heat exchanger 41, a cold finger thermometer 42, a cold finger heater 43, and a helium return stainless steel pipe 44.

[0030] Specifically, the dry closed-loop refrigeration module connector 30 is used to connect to the GM refrigerator 2, the circulating helium return port 31 is used to connect to the GM refrigerator 2, the communication line 32 communicates with the sample area thermometer 39, the cold finger thermometer 42 and the cold finger heater 43 to realize temperature reading and temperature control, the thermostat vacuum Dewar vacuum extraction port 34 is used to extract the air in the thermostat vacuum Dewar 33, the fixing nut 35 is used to connect the pulse paramagnetic resonance spectrometer low temperature thermostat 16 and the pulse probe 36, the sample tube 37 is inserted into the inside of the pulse probe 36, and the sample insertion / removal valve 38 is used to control the insertion / removal of the sample tube 37.

[0031] The cold finger heat exchanger 41 is fixedly installed inside the thermostat vacuum Dewar 33. One end of the helium inlet capillary tube 40 is fixedly installed to the inlet end of the cold finger heat exchanger 41. Helium enters the system through the helium inlet capillary tube 40 at a controlled flow rate. The small inner diameter of the capillary tube ensures flow regulation. It is then directly connected to the inlet end of the cold finger heat exchanger 41 to provide a gas source for heat exchange. One end of the helium return stainless steel pipe 44 is fixedly installed to the outlet end of the cold finger heat exchanger 41. Helium that has undergone heat exchange treatment exits from the cold finger heat exchanger 41. The gas flows out through the outlet and returns to the system or an external collection device via a pressure-resistant and corrosion-resistant helium return stainless steel pipe 44, completing the circulation path. The cold finger thermometer 42 is fixedly installed on the outer surface of the cold finger heat exchanger 41, and the cold finger heater 43 is fixedly installed on the outer surface of the cold finger heat exchanger 41. The cold finger thermometer 42 is installed inside the heat exchanger to monitor temperature data in real time and ensure accurate control. The cold finger heater 43 is arranged close to the thermometer and dynamically adjusts the heating power based on the feedback temperature signal to prevent overcooling or maintain a constant temperature.

[0032] By setting up a dry closed-loop cryogenic system with a pulsed paramagnetic resonance spectrometer, the use of liquid helium for ultra-low temperature and ultra-low vibration is reduced. The temperature of the cryogenic experimental environment is as low as 2.5K, and the vibration is less than 20nm. An external GM refrigerator is used, and the special structure of the helium circulation is used to achieve ultra-low temperature and ultra-low vibration experimental conditions. The cryogenic thermostat 16 is connected through a low-loss liquid infusion tube 14, and the low-loss liquid infusion tube 14 is fixed by a bracket 15. At this time, the vibration transmitted from the liquefaction unit is filtered out, thus achieving ultra-low vibration. This solves the technical problems of existing cryogenic experimental devices that use liquid helium transfer for cooling, which is costly and cannot be used for long-term experimental testing. The GM refrigerator / pulse tube refrigerator directly cools the magnet and sample, resulting in too much vibration, which cannot meet the technical conditions of scientific researchers.

[0033] Working principle: First, turn on the GM refrigerator 2. When the first-stage cold head 7 and the second-stage cold head 9 reach 40K and 4K respectively, then open the isolation valve 21, the cryogenic needle valve 11, and the circulation pump 18. After opening the circulation pump 18, due to the pressure difference, the high-purity helium in the helium tank 23 enters the first-stage cold head heat exchanger 12 through the inlet 26. The high-purity helium entering the first-stage cold head heat exchanger 12 will undergo heat exchange to reach 40K, and then the 40K high-purity helium enters the second-stage cold head heat exchanger 13. The high-purity helium entering the second-stage cold head heat exchanger 13 will undergo heat exchange to reach 3K. At this time, the 3K cryogenic helium passes through the cryogenic needle valve 11. Due to the throttling expansion technology, also known as Joule-Thomson expansion, the 3K cryogenic helium passing through the cryogenic needle valve 11 will be cooled to 2K. The 2K cryogenic helium reaches the cryogenic thermostat 16 through the low-loss infusion pipe 14 and exchanges heat with the cold finger heat exchanger 41. The 2K cryogenic helium then passes through the sample area helium inlet... Helium gas enters the sample area through capillary tube 40, enabling the sample area to be cooled from 2K to 300K. After the low-temperature helium in the sample area has exchanged heat, it enters the circulating helium return port 31 from stainless steel tube 44. This allows the temperature of the cryostat 16 to gradually decrease until it reaches the experimental temperature of 2.5K-300K. The helium that has undergone heat exchange is drawn away by circulating pump 18 and then enters the first KF16 metal bellows 19 from the outlet of circulating pump 18. It then enters the first-stage cold head heat exchanger 12 and the second-stage cold head heat exchanger 13 through inlet 26. This completes a closed-loop cooling system. Since the cryostat 16 is connected through low-loss infusion tube 14 and the low-loss infusion tube 14 is fixed by the low-loss infusion tube 14 fixing bracket 15, the vibration transmitted from the liquefaction unit is filtered out, thus achieving ultra-low vibration.

[0034] The above are all preferred embodiments of this application, and are not intended to limit the scope of protection of this application. Therefore, all equivalent changes made in accordance with the structure, shape and principle of this application should be covered within the scope of protection of this application.

Claims

1. A dry closed-loop cryogenic system adapted for pulsed paramagnetic resonance spectrometers, characterized in that: This includes a liquefier assembly, a low-loss infusion tubing assembly, a cryostat module assembly, a pulse probe 36, and a recirculating gas circuit assembly. The low-loss infusion tubing assembly is fixedly installed on the outer surface of the liquefier assembly, the outer surface of the cryogenic thermostat module assembly is fixedly installed on the outer surface of the liquefier assembly, the outer surface of the pulse probe 36 is fixedly installed on the outer surface of the low-loss infusion tubing assembly, and the circulating gas path assembly is disposed inside the cryogenic thermostat module assembly.

2. The dry closed-loop cryogenic system adapted for pulsed paramagnetic resonance spectrometers according to claim 1, characterized in that: The liquefier assembly includes a vacuum port (1), a GM refrigerator (2), a vacuum explosion-proof valve (3), a needle valve handle (4), a shock-absorbing bellows (5), a vacuum chamber (6), a primary cold head (7), a cold shield (8), a secondary cold head (9), a secondary cold plate (10), a low-temperature needle valve (11), a primary cold head heat exchanger (12), and a secondary cold head heat exchanger (13).

3. The dry closed-loop cryogenic system adapted for pulsed paramagnetic resonance spectrometers according to claim 2, characterized in that: The vacuum port (1) is fixedly installed on the outer surface of the vacuum chamber (6) by KF25 standard clamps. A shock-absorbing bellows (5) is fixedly installed on the outer surface of the GM refrigerator (2). The shock-absorbing bellows (5) is fixedly installed on the outer surface of the vacuum chamber (6). The vacuum explosion-proof valve (3) is fixedly bonded to the outer surface of the vacuum chamber (6) by epoxy resin adhesive. The needle valve handle (4) is fixedly installed on the outer surface of the low-temperature needle valve (11). The first-stage cold head (7) and the second-stage cold head (9) are respectively fixedly installed on the outer surface of the GM refrigerator (2). The cold shield (8) is fixed by hexagonal screws. The first-stage cold head (7) is installed on the outer surface of the second-stage cold head (9). The second-stage cold plate (10) is fixed to the outer surface of the second-stage cold head (9) by hexagon screws. The low-temperature needle valve (11) is fixedly welded to the outer surface of the vacuum chamber (6) by argon arc welding. The first-stage cold head heat exchanger (12) is fixedly installed on the outer surface of the cold screen (8) by hexagon screws. The second-stage cold head heat exchanger (13) is fixedly installed on the outer surface of the second-stage cold plate (10) by hexagon screws. One end of the first-stage cold head heat exchanger (12) and one end of the second-stage cold head heat exchanger (13) are fixedly installed by brazing with a 3.2mm stainless steel capillary tube.

4. The dry closed-loop cryogenic system adapted for pulsed paramagnetic resonance spectrometers according to claim 3, characterized in that: The low-loss infusion tubing (14) assembly includes a low-loss infusion tubing (14), a mounting bracket (15), a cryogenic thermostat (16), a KF25 metal bellows (17), a circulation pump (18), a first KF16 metal bellows (19), a second KF16 metal bellows (20), an isolation valve (21), a third KF16 metal bellows (22), a helium tank (23), a 1 / 4 joint stainless steel pipe, positive and negative pressure gauges (25), and an air inlet (26).

5. The dry closed-loop cryogenic system adapted for pulsed paramagnetic resonance spectrometers according to claim 4, characterized in that: After the fixing bracket (15) is fixedly installed on the ground, it clamps the low-loss infusion tube (14) between the vacuum chamber (6) and the cryogenic thermostat (16). One end of the low-loss infusion tube (14) is fixedly installed on the outer surface of the vacuum chamber (6) by a KF50 standard clamp. The two ends of the KF25 metal bellows (17) are fixedly installed on the outer surface of the cryogenic thermostat (16) and the air inlet of the circulation pump (18) by KF25 clamps, respectively. The two ends of the first KF16 metal bellows (19) are fixedly installed on the air outlet of the circulation pump (18) and the air inlet (26) by KF16 standard clamps, respectively. The isolation valve One end of (21) is fixedly installed on one end of the second KF16 metal bellows (20) and the third KF16 metal bellows (22) by KF16 standard clamp. One end of the second KF16 metal bellows (20) is connected to one end of the first KF16 metal bellows (19) by argon arc welding. The third KF16 metal bellows (22) is connected to the outlet end of the helium tank (23) by argon arc welding. The positive and negative pressure gauges (25) are fixedly bonded to one end of the 1 / 4 joint stainless steel pipe (24) by epoxy resin glue. The 1 / 4 joint stainless steel pipe (24) is connected to the outer surface of the helium tank (23) by argon arc welding.

6. The dry closed-loop cryogenic system adapted for pulsed paramagnetic resonance spectrometers according to claim 5, characterized in that: The cryogenic thermostat module assembly includes a dry closed-loop refrigeration module socket (30), a circulating helium return port (31), a communication line (32), a thermostat vacuum dewar (33), a thermostat vacuum dewar vacuum extraction port (34), a fixing nut (35), a sample tube (37), a sample insertion / removal valve (38), and a sample area thermometer (39). The circulating gas path assembly includes a helium inlet capillary tube (40), a cold finger heat exchanger (41), a cold finger thermometer (42), a cold finger heater (43), and a helium return stainless steel pipe (44).

7. A dry closed-loop cryogenic system adapted for pulsed paramagnetic resonance spectrometers according to claim 6, characterized in that: The dry closed-loop refrigeration module socket (30) is fixedly installed on the outer surface of the GM refrigerator (2). The circulating helium return port (31) is fixedly installed on the outer surface of the GM refrigerator (2). The communication line (32) is electrically connected to the sample area thermometer (39), the cold finger thermometer (42), and the cold finger heater (43), respectively. The vacuum evacuation port (34) of the thermostat vacuum Dewar evacuates the air inside the thermostat vacuum Dewar (33). The two ends of the fixing nut (35) are fixedly installed on the outer surface of the low-temperature thermostat (16) of the pulse paramagnetic resonance spectrometer and one end of the pulse probe (36), respectively. One end of the sample tube (37) The sample tube (37) is connected to the pulse probe (36) and the sample insertion / removal valve (38) is located on the outer surface of the sample tube (37) to control the insertion / removal of the sample tube (37). The cold finger heat exchanger (41) is fixedly installed inside the thermostat vacuum dewar (33). One end of the helium inlet capillary tube (40) is fixedly installed at the inlet end of the cold finger heat exchanger (41). One end of the helium return stainless steel tube (44) is fixedly installed at the outlet end of the cold finger heat exchanger (41). The cold finger thermometer (42) is fixedly installed inside the cold finger heat exchanger (41). The cold finger heater (43) is fixedly installed inside the cold finger heat exchanger (41).

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