Refrigeration System of a Magneto-Optical Measurement Device and Its Control Method

Abstract

The present invention provides a refrigeration system for a magneto-optical measurement device and its control method. The GM refrigerator is externally placed and a helium gas circulation throttling expansion structure is adopted to obtain ultra-low temperature liquid helium at 2K and below using the GM refrigerator without consuming a large amount of liquid helium. Moreover, a low-loss liquid delivery pipe is used to connect the GM refrigerator and the optical high magnetic field thermostat, and a fixing bracket is used to fix the low-loss liquid delivery pipe, thereby filtering out the vibration transmitted from the GM refrigerator part, achieving experimental conditions of ultra-low temperature, high magnetic field, and ultra-low vibration. At the same time, after the cooled liquid helium enters the optical high magnetic field thermostat, it is divided into two parts without mutual influence and is respectively used to cool the sample area and the magnet cold shield, thereby improving the cooling efficiency and reducing the consumption of liquid helium.

Description

Technical Field

[0001] The present invention relates to the technical field of cryogenic refrigeration, more specifically to a magneto-optical measurement device applying cryogenic refrigeration technology, and still further to a refrigeration system of a magneto-optical measurement device and its control method. Background Art

[0002] With the continuous progress and development of science and technology, cryogenic technology, optical technology, and strong magnetic field and low vibration technology have become indispensable auxiliary technical means in many scientific experimental fields such as physics, chemistry, materials science, quantum physics, and superconducting technology. In these experiments, it is necessary to construct a magneto-optical measurement device. The magneto-optical measurement device is a highly sensitive tool for studying the magnetic and optical properties of materials using the magneto-optical effect, and is widely used in fields such as materials science, biomedicine, and information technology. The magneto-optical measurement device usually consists of a light source, a magnetic field generator, a detector, and a data acquisition and analysis system.

[0003] The cryogenic refrigeration system plays a crucial role in the magneto-optical measurement device. The cryogenic refrigeration system mainly provides the following supports for the magneto-optical measurement device: (1) Cooling the sample to a low temperature (such as liquid helium or liquid nitrogen temperature) to study the magnetic and optical properties of the material at low temperature. (2) Providing a stable low-temperature environment, reducing the interference of thermal noise on the measurement, ensuring that the experimental conditions are precisely controllable, and obtaining high-precision magneto-optical and optical data at low temperature. (3) Supporting the study of the phase transition behavior of materials at low temperature, such as superconductivity or magnetic phase transition, expanding the research scope of the magneto-optical measurement device, and enabling it to explore more low-temperature physical phenomena.

[0004] The refrigeration methods of the magneto-optical measurement device can be mainly divided into two categories: The first category is the device that uses a refrigerant for refrigeration. This type of device usually stores liquid helium in a special container or continuously transports liquid helium to the experimental parts that need to be cooled through a pipeline system; the second category is the device that uses a closed-cycle refrigerator for refrigeration. The refrigerators in this type of device mainly include GM refrigerators and pulse tube refrigerators. For the first type of refrigeration method using liquid helium as a refrigerant, since liquid helium is a non-renewable resource, its price is expensive and it mainly relies on imports. Therefore, the long-term use of liquid helium for refrigeration will lead to a significant increase in experimental costs, which is undoubtedly a huge economic burden for scientific research work that requires long-term experimental testing. For the second type of refrigeration method using a closed-cycle refrigerator for refrigeration, although it can directly cool the magnet and the sample, the vibration generated by it is often too large, which usually makes it difficult to meet the strict requirements of stability and precision in the experiment for scientific researchers. Summary of the Invention

[0005] The object of the present invention is to solve the technical problems discussed above, and thus provides a refrigeration system for a magneto-optical measurement device and its control method. A closed-cycle GM refrigerator is used for refrigeration, and the throttling expansion technology and low-loss liquid infusion pipes are combined to connect the GM refrigerator and the magneto-optical measurement device, thereby achieving low-vibration cooling and stable operation under dry conditions. The refrigeration system for the magneto-optical measurement device and its control method of the present invention are specifically as follows:

[0006] A refrigeration system for a magneto-optical measurement device, wherein the magneto-optical measurement module in the magneto-optical measurement device is in cyclic communication with the dry closed-cycle refrigeration module through a helium circulation pipeline section. The magneto-optical measurement module specifically includes an optical strong magnetic thermostat, which includes a magneto-optical module vacuum chamber, a magnet cold shield arranged inside the magneto-optical module vacuum chamber, and a superconducting magnet arranged inside the magnet cold shield. The superconducting magnet is fixed on the magnet cold shield by a magnet fixing block, and the magnet cold shield is directly fixed on the magneto-optical module vacuum chamber; one side of the superconducting magnet is in close contact connection with a helium magnet heat-conducting copper block, and the other side of the magnet heat-conducting copper block is in contact connection with a cold finger heat exchanger; the helium circulation pipeline section includes a low-loss liquid infusion pipe, one end of which is communicated with the cold finger heat exchanger through the liquid helium inlet of the optical strong magnetic thermostat, and the other end is communicated with the liquid helium outlet of the dry closed-cycle refrigeration module to send the liquid helium from the dry closed-cycle refrigeration module into the optical strong magnetic thermostat to cool the cold finger heat exchanger.

[0007] Furthermore, the helium circulation pipeline section further includes a circulation pump, a first metal bellows, a second metal bellows, and a third metal bellows. The first metal bellows and the second metal bellows are arranged between the outlet of the magneto-optical measurement module and the inlet of the circulation pump, and the third metal bellows is arranged between the outlet of the circulation pump and the inlet of the dry closed-cycle refrigeration module; a low-loss liquid infusion pipe fixing bracket is fixedly arranged on the ground to clamp the part of the low-loss liquid infusion pipe between the liquid helium outlet of the dry closed-cycle refrigeration module and the liquid helium inlet of the magneto-optical measurement module.

[0008] Furthermore, the dry closed-cycle refrigeration module includes a GM refrigerator, a vibration damping bellows, a refrigerator vacuum chamber, a cold shield, a secondary cold plate, a cryogenic needle valve, a primary cold head heat exchanger, and a secondary cold head heat exchanger. The GM refrigerator is fixed on the refrigerator vacuum chamber through the vibration damping bellows and includes a primary cold head and a secondary cold head located inside the refrigerator vacuum chamber. The cold shield is arranged in the refrigerator vacuum chamber and fixed on the primary cold head, and the secondary cold plate is fixed on the secondary cold head; the primary cold head heat exchanger is fixed on the cold shield, and the secondary cold head heat exchanger is fixed on the secondary cold plate; the primary cold head heat exchanger and the secondary cold head heat exchanger are brazed together through a stainless steel capillary tube. The primary cold head heat exchanger is communicated with the air inlet of the dry closed-cycle refrigeration module, and the cryogenic needle valve is connected and fixed inside the refrigerator vacuum chamber and communicated with the secondary cold head heat exchanger, so that helium gas passes through the primary cold head heat exchanger, the secondary cold head heat exchanger, and the cryogenic needle valve in sequence from the air inlet; the outlet of the cryogenic needle valve is communicated with a low-loss liquid delivery pipe to convey the throttled and expanded liquid helium to it.

[0009] Furthermore, the cryogenic needle valve is regulated through a needle valve handle arranged outside the refrigerator vacuum chamber to realize the adiabatic expansion process of liquid helium, so that the temperature of the liquefied liquid helium reaches 2K or below.

[0010] Furthermore, the helium circulation pipeline part also includes a helium gas tank, which is communicated with the pipeline between the outlet of the circulation pump and the air inlet of the dry closed-cycle refrigeration module through a fourth metal bellows and a fifth metal bellows, and a cut-off valve is arranged between the fourth metal bellows and the fifth metal bellows.

[0011] Furthermore, a sample area is formed inside the superconducting magnet. A sample to be measured is placed in the sample area. A sample area heat exchange space is formed around the sample area, and the liquid helium from the low-loss liquid delivery pipe is respectively communicated with the magnet area helium capillary and the sample area helium capillary after heat exchange with the cold finger heat exchanger; the liquid helium passing through the sample area helium capillary enters the sample area heat exchange space to cool the sample area; the low-temperature helium passing through the magnet area helium capillary enters the cold shield heat exchange module, exchanges heat with the cold shield heat exchange module and cools it, and the cold shield heat exchange module contacts and exchanges heat with the magnet cold shield, thereby cooling the magnet cold shield.

[0012] Furthermore, a liquid helium inlet is arranged at the right end of the optical high magnetic field thermostat, which is connected to the helium liquefier to input liquid helium from the helium liquefier into the optical high magnetic field thermostat and reach the cold finger heat exchanger to continuously cool it.

[0013] Furthermore, the helium gas generated after the liquid helium entering the sample area heat exchange space exchanges heat enters the sample area helium gas outlet pipe and enters the circulation pump through the sample area helium gas return port and the first metal bellows; the helium gas generated after the liquid helium entering the cold shield heat exchange module exchanges heat enters the magnet area helium gas return port and enters the circulation pump through the second metal bellows.

[0014] Furthermore, one end of the cold shield heat exchange module includes an end heat exchange block. Liquid helium from the helium capillary in the magnet region exchanges heat with this end heat exchange block. A plurality of slits evenly distributed in the circumferential direction are provided on the end heat exchange block, so that the helium gas generated after heat exchange passes through it and enters the helium gas return port in the magnet region.

[0015] The present invention further provides a control method for a refrigeration system of the magneto-optical measurement device as described above, including the following steps:

[0016] S1: After the system starts, first turn on the GM refrigerator. When the temperatures of the first-stage cold head and the second-stage cold head reach 40K and 4K respectively, control to open the isolation valve, the cryogenic needle valve, and the circulation pump;

[0017] S2: After the circulation pump is turned on, due to the pressure difference, the high-purity helium gas in the helium gas cylinder enters the first-stage cold head heat exchanger through the air inlet. The high-purity helium gas entering the first-stage cold head heat exchanger is cooled to 40K through heat exchange, and then the 40K high-purity helium gas enters the second-stage cold head heat exchanger;

[0018] S3: The high-purity helium gas entering the second-stage cold head heat exchanger is cooled to 4K through heat exchange. At this time, the liquid helium at a temperature of 4K passes through the cryogenic needle valve. Due to the throttling expansion effect, the liquid helium passing through the cryogenic needle valve will be cooled to a temperature of 2K and below;

[0019] S4: The liquid helium at a temperature of 2K and below reaches the optical high-field cryostat through the low-loss liquid delivery pipe and exchanges heat with the cold finger heat exchanger;

[0020] S5: A part of the liquid helium after heat exchange enters the sample area through the sample area helium capillary, cools the sample area in the heat exchange space in the sample area, and realizes temperature regulation in the temperature range of 2K - 300K in the sample area. This part of the liquid helium becomes helium gas after heat exchange, leaves the heat exchange space in the sample area, and enters the sample area helium gas return port of the optical high-field cryostat;

[0021] S6: Another part of the low-temperature helium after heat exchange in the cold finger heat exchanger enters the cold shield heat exchange module through the magnet region helium capillary, exchanges heat with the end heat exchange block at one end of the cold shield heat exchange module, and cools it. This part of the liquid helium becomes helium gas after heat exchange and enters the magnet region helium gas return port of the optical high-field cryostat;

[0022] S7: The helium gas flowing out from the sample area helium gas return port and the magnet region helium gas return port of the optical high-field cryostat enters the first metal bellows and the second metal bellows respectively, and then is pumped away by the circulation pump;

[0023] S8: Helium enters the third metal bellows from the outlet of the circulation pump, and then enters the primary cold head heat exchanger and the secondary cold head heat exchanger of the GM refrigerator through the air inlet again for cooling, thus realizing a complete closed-cycle temperature reduction.

[0024] For the refrigeration system of the magneto-optical measurement device of the present application, the GM refrigerator is placed outside, and a helium gas circulation throttling expansion structure is adopted. Without consuming a large amount of liquid helium, a cryogenic condition of 2K and below can be obtained by using a commonly used 4K refrigerator in the prior art. Moreover, a low-loss liquid delivery pipe is used to connect the GM refrigerator and the optical high magnetic field thermostat, and a fixing bracket is used to fix the low-loss liquid delivery pipe, so that the vibration transmitted from the liquefier part is filtered out, realizing experimental conditions of ultra-low temperature, high magnetic field and ultra-low vibration. At the same time, after the cooled cryogenic liquid helium enters the optical high magnetic field thermostat, it is divided into two parts without affecting each other, and is respectively used to cool the sample area and the magnet cold shield, thereby improving the cooling efficiency and reducing the consumption of liquid helium. Brief Description of the Drawings

[0025] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required to be used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained based on these drawings.

[0026] Figure 1 : Schematic diagram of the overall composition structure of the magneto-optical measurement device of the present application;

[0027] Figure 2 : Schematic diagram of the circulation process of the refrigeration system of the magneto-optical measurement device of the present application;

[0028] Figure 3 : Top view of the external structure of the optical high magnetic field thermostat of the present application;

[0029] Figure 4 : Figure 3 Vertical sectional view of the optical high magnetic field thermostat shown along the A-A direction;

[0030] Figure 5 : Figure 3 Horizontal sectional view of the optical high magnetic field thermostat shown;

[0031] Figure 6 : Partial enlarged view of one end of the cold shield heat exchange module of the present application.

[0032] Reference Signs:

[0033] 1: Magneto-optical measurement module; 2: Dry closed-cycle refrigeration module; 3: Helium circulation pipeline section; 4: GM refrigerator; 5: Vibration damping bellows; 6: Refrigerator vacuum chamber; 7: First-stage cold head; 8: Cold screen; 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 tube; 15: Low-loss infusion tube fixing bracket; 16: Optical strong magnetic thermostat; 17-1: First metal bellows; 17-2: Second metal bellows; 18: Circulation pump; 19: Third metal bellows; 20: Fourth metal bellows; 21: Isolation valve; 22: Fifth metal bellows; 23: Helium gas cylinder; 24: 1 / 4 joint stainless steel pipe; 25: Positive and negative pressure gauges; 26: Air inlet; 27: Vacuum pumping port of optical strong magnetic thermostat; 28: Low-temperature superconducting magnet current source joint; 29: Helium gas return port in magnet area; 30: Liquid helium inlet; 31: Communication signal interface; 32: Helium gas return port in sample area; 33: Magnet cold screen; 34: Magneto-optical module vacuum chamber; 35: Magnet fixing block; 36: Vacuum view window; 37: Magnet heat-conducting copper block; 38: Cold finger heat exchanger; 39: Helium capillary in magnet area; 40: Cold screen heat exchange module; 41: Superconducting magnet; 42: Helium capillary in sample area; 43: Sample area; 44: Helium gas outlet pipe in sample area. Detailed implementation manners

[0034] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0035] As Figure 1 shown, the refrigeration system of a magneto-optical measurement device of the present invention, wherein the magneto-optical measurement module 1 of the magneto-optical measurement device is circularly communicated with the dry closed-cycle refrigeration module 2 through the helium circulation pipeline section 3. The magneto-optical measurement module 1 specifically includes an optical strong magnetic thermostat 16. Specifically, as Figure 2 shown, the dry closed-cycle refrigeration module 2 mainly includes a GM refrigerator 4. The GM refrigerator 4 is fixed on the refrigerator vacuum chamber 6 through a vibration damping bellows 5 to provide a low-temperature environment. A vacuum pumping port (not shown) is fixed on the refrigerator vacuum chamber 6 through a KF25 standard clamp to evacuate the inside of the refrigerator vacuum chamber 6. A vacuum explosion-proof valve (not shown) is adhered to the refrigerator vacuum chamber 6 with epoxy resin glue to prevent helium gas leakage and thus avoid safety accidents. A cold screen 8 is arranged inside the refrigerator vacuum chamber 6, which is fixed on the first-stage cold head 7 of the GM refrigerator 4 through an internal hexagonal screw, and the second-stage cold plate 10 is fixed on the second-stage cold head 9 of the GM refrigerator 4 through an internal hexagonal screw.

[0036] The cryogenic needle valve 11 is fixed on the vacuum chamber 6 of the refrigerator by argon arc welding and is adjusted by a needle valve handle (not shown) provided outside the vacuum chamber 6 of the refrigerator to achieve the adiabatic expansion process of liquid helium, so that the temperature of liquid helium reaches 2K or below. The cryogenic needle valve 11 uses the throttling expansion technology (also known as the Joule-Thomson (J-T) expansion), that is, the process of adiabatic expansion of a fluid at a higher pressure through a throttle valve to a lower pressure direction. According to the thermodynamic principle, pressure can cause temperature changes, which is also known as the J-T effect. When the ambient temperature of helium is higher than the Joule-Thomson inversion temperature, it exhibits a positive J-T effect, that is, the gas temperature rises as the pressure drops; when the ambient temperature of helium is lower than the Joule-Thomson inversion temperature, it exhibits a negative J-T effect, that is, the gas temperature drops as the pressure drops. Using the throttling expansion technology can obtain ultra-low temperature liquid helium of 2K or below by using a 4K refrigerator commonly used in the prior art without consuming a large amount of liquid helium.

[0037] The primary cold head heat exchanger 12 is fixed on the cold shield 8 by an Allen screw, and the secondary cold head heat exchanger 13 is fixed on the secondary cold plate 10 by an Allen screw. The primary cold head heat exchanger 12 and the secondary cold head heat exchanger 13 are brazed together by a 3.2 mm stainless steel capillary tube. The helium circulation pipeline part 3 includes a low-loss infusion tube 14 connected between the magneto-optical measurement module 1 and the dry closed-cycle refrigeration module 2 and a low-loss infusion tube fixing bracket 15. The magneto-optical measurement module 1 has an optical high magnetic field thermostat 16. The low-loss infusion tube 14 is fixed on the vacuum chamber 6 of the refrigerator by a KF50 standard clamp, and the low-loss infusion tube fixing bracket 15 is fixed on the ground to clamp the part of the low-loss infusion tube 14 between the vacuum chamber 6 of the refrigerator and the optical high magnetic field thermostat 16.

[0038] The first metal bellows 17-1 and the second metal bellows 17-2 are respectively fixed on the optical high magnetic field thermostat 16 and the intake port of the circulation pump 18 through KF25 clamps. The third metal bellows 19 is fixed between the outlet port and the intake port 26 of the circulation pump 18 through a KF16 standard clamp. The circulation gas pump 18 functions to return the helium gas flowing out of the optical high magnetic field thermostat 16 to the GM refrigerator 4, thereby realizing the circulating flow of helium gas. The isolation valve 21 is fixed between the fourth metal bellows 20 and the fifth metal bellows 22 through a KF16 standard clamp. The fourth metal bellows 20 is connected to the third metal bellows 19 by argon arc welding, and the fifth metal bellows 22 is connected to the helium gas tank 23 by argon arc welding. The helium gas tank 23 functions to store helium gas, and controls the on-off of the helium gas tank 23 and the helium gas circulation system through the isolation valve 21 to supplement or recover helium gas to the helium gas circulation system. The helium circulation pipeline section 3 is the helium circulation pipeline formed between the magneto-optical measurement module 1 and the dry closed-cycle refrigeration module 2, wherein the liquid helium flowing from the GM refrigerator 4 to the optical high magnetic field thermostat 16 of the magneto-optical measurement module 1, and the helium gas flowing out of the optical high magnetic field thermostat 16 and returning to the GM refrigerator 4. The positive and negative pressure gauges 25 function to monitor the pressure of the helium gas in the helium gas tank 23, and are fixed on the 1 / 4 joint stainless steel pipe 24 through epoxy resin glue. The 1 / 4 joint stainless steel pipe 24 is connected to the helium gas tank 23 by argon arc welding.

[0039] The magneto-optical measurement module 1 mainly includes an optical high magnetic field thermostat 16, specifically as Figure 3 shown in the top view of the external structure. An optical high magnetic field thermostat vacuum pumping port 27 is fixed on the optical high magnetic field thermostat 16 through a KF16 clamp, and is connected to an external vacuum pumping device (not shown) to evacuate the inside of the optical high magnetic field thermostat 16. The low-temperature superconducting magnet current source connector 28 is fixed on the optical high magnetic field thermostat 16 through an Allen screw and is connected to an external power supply for power supply. The helium gas return port 29 in the magnet area is welded to the optical high magnetic field thermostat 16 by argon arc welding to return the helium gas to the second metal bellows 17-2. A liquid helium inlet 30 is provided at the right end of the optical high magnetic field thermostat 16, which is connected to a helium liquefier (not shown) to input liquid helium from the helium liquefier into the optical high magnetic field thermostat 16 and reach the cold finger heat exchanger 38 and continuously cool it. A communication signal interface 31 is also provided on the optical high magnetic field thermostat 16 to access the communication signal line. Similar to the helium gas return port 29 in the magnet area, a helium gas return port 32 in the sample area is also provided on the optical high magnetic field thermostat 16, which is communicated with the first metal bellows 17-1 to return the helium gas returned from the sample area 43 to the first metal bellows 17-1, and then enter the circulation pump 18.

[0040] Figure 4 For Figure 3 the vertical sectional view along the A-A direction, Figure 5 ForFigure 3 Horizontal cross-sectional view, specifically showing the internal structure of the optical high magnetic field thermostat 16. Refer to Figure 4 and 5 As shown, the optical high magnetic field thermostat 16 includes a magneto-optical module vacuum chamber 34, a magnet cold shield 33 disposed inside the magneto-optical module vacuum chamber 34, and a superconducting magnet 41 disposed inside the magnet cold shield 33. The superconducting magnet 41 is fixed to the magnet cold shield 33 by a magnet fixing block 35, and the magnet cold shield 33 is directly fixed to the magneto-optical module vacuum chamber 34 by titanium alloy screws. A sample area 43 is formed inside the superconducting magnet 41, and a sample to be measured is placed in the sample area 43. A high-strength magnetic field is formed in the sample area 43 by the superconducting magnet 41. The periphery of the sample area 43 includes a sample area heat exchange space 45. A magnet heat conducting copper block 37 is in close contact connection with the superconducting magnet 41. One side of the magnet heat conducting copper block 37 is also in contact connection with a cold finger heat exchanger 38. As described above, the cold finger heat exchanger 38 exchanges heat with the liquid helium introduced from the helium liquefier through the liquid helium inlet 30 and is cooled. The cold finger heat exchanger 38 further cools the magnet heat conducting copper block 37, and the magnet heat conducting copper block 37 transfers the cold quantity to the superconducting magnet 41 to lower its temperature to the liquid helium temperature range.

[0041] The cold finger heat exchanger 38 is also connected to the low-loss infusion pipe 14, and as Figure 4 shown, the space where the cold finger heat exchanger 38 is located is respectively connected to the magnet area helium capillary 39 and the sample area helium capillary 42. The liquid helium after throttling expansion by the low-temperature needle valve 11 enters the optical high magnetic field thermostat 16 and exchanges heat with the cold finger heat exchanger 38. A part of the liquid helium after heat exchange enters the sample area heat exchange space 45 of the sample area through the sample area helium capillary 42, realizing the variable temperature regulation of the sample area in the range of 2K - 300K. The helium gas generated by this part of the liquid helium after heat exchange enters the sample area helium gas outlet pipe 44, and the sample area helium gas outlet pipe 44 is further connected to the sample area helium gas return port 32. The sample area helium gas return port 32 is connected to the first metal bellows 17-1. Thus, the helium gas generated by the liquid helium after heat exchange in the sample area heat exchange space 45 enters the sample area helium gas outlet pipe 44 and then enters the first metal bellows 17-1 through the sample area helium gas return port 32, and then enters the circulation pump 18.

[0042] Another part of the liquid helium after heat exchange with the cold finger heat exchanger 38 enters the cold shield heat exchange module 40 through the magnet area helium capillary 39 to cool it, and as Figure 5As shown, the cold screen heat exchange module 40 is in contact with the magnet cold screen 33, thereby achieving the cooling of the magnet cold screen 33. The helium gas generated after the heat exchange of this part of the liquid helium is communicated with the helium gas return port 29 in the magnet area. An annular interlayer space is formed between the pipeline where the liquid helium inlet 30 is located and the cold screen heat exchange module 40. The magnet area helium capillary 39 is actually communicated with this annular interlayer space, and this interlayer space extends to be communicated with the helium gas return port 29 in the magnet area, thereby sending the helium gas return in the magnet area into the second bellows 17-2 and then entering the circulation pump 18.

[0043] Figure 6 Figure 4 is a partial enlarged view of one end of the cold screen heat exchange module 40. It can be seen from Figure 6 that at one end thereof, there is an end heat exchange block. The liquid helium from the magnet area helium capillary 39 actually exchanges heat with this end heat exchange block and transfers the cold quantity to the magnet cold screen 33. In addition, in order to allow the helium gas generated after the heat exchange of the liquid helium from the magnet area helium capillary 39 to pass through, a plurality of circumferentially uniformly distributed slits (not shown) are provided on this end heat exchange block, and the left and right annular interlayer spaces are communicated through the slits.

[0044] The control method and the corresponding process of the refrigeration system of the magneto-optical measurement device of the present invention are specifically as follows:

[0045] After the work starts, first turn on the GM refrigerator 4. Wait until the temperatures of the first-stage cold head 7 and the second-stage cold head 9 reach 40K and 4K respectively, and then turn on the isolation valve 21, the cryogenic needle valve 11, and the circulation pump 18. After turning on the circulation pump 18, due to the pressure difference, the high-purity helium gas in the helium gas cylinder 23 enters the first-stage cold head heat exchanger 12 through the air inlet 26. The high-purity helium gas entering the first-stage cold head heat exchanger 12 will be heat-exchanged to 40K, and then the 40K high-purity helium gas enters the second-stage cold head heat exchanger 13. The high-purity helium gas entering the second-stage cold head heat exchanger 13 is cooled to 4K to become liquid helium through heat exchange. At this time, the liquid helium at 4K temperature passes through the cryogenic needle valve 11. Due to the throttling expansion effect, the liquid helium passing through the cryogenic needle valve 11 will be cooled to 2K and below. The cryogenic liquid helium at 2K and below reaches the optical high magnetic field thermostat 16 through the low-loss liquid delivery pipe 14 and exchanges heat with the cold finger heat exchanger 38. Part of the liquid helium after heat exchange enters the sample area helium capillary 42 and then enters the sample area heat exchange space 45, where it cools the sample area 43, realizing the temperature regulation of the sample area 43 in the temperature range of 2K - 300K. The helium gas generated after heat exchange of this part of the liquid helium entering the sample area 43 enters the first metal bellows 17-1 from the sample area helium gas outlet pipe 44 through the sample area helium gas return port 32. Another part of the liquid helium after heat exchange in the cold finger heat exchanger 38 enters the cold shield heat exchange module 40 through the magnet area helium capillary 39, exchanges heat with the heat exchange block at one end of the cold shield heat exchange module 40 and cools it. The helium gas generated after heat exchange is connected to the magnet area helium gas return port 29, and thus the magnet area helium gas return is sent into the second bellows 17-2 and then enters the circulation pump 18. The cold shield heat exchange module 40 is then in close contact with the magnet cold shield 33, and the magnet cold shield 33 is cooled to 55K through the remaining cold. Through heat exchange with the cryogenic liquid helium at 2K and below from the low-loss liquid delivery pipe 14, the temperature of the cold finger heat exchanger 38 is reduced to 2 - 3K. It is connected to the superconducting magnet 41 through the magnet thermal conduction copper block 37 in close contact with it, and thus the superconducting magnet 41 can be cooled to 3 - 4K. Through the above process, the temperature of the optical high magnetic field thermostat 16 slowly drops until it reaches the experimental temperature.

[0046] The helium gas flowing out from the helium return port 29 in the magnet area and the helium return port 32 in the sample area of the optical strong magnetic thermostat 16 respectively enters the second metal bellows 17-2 and the first metal bellows 17-1, and then is pumped away by the circulation pump 18. Then, it enters the third metal bellows 19 from the outlet of the circulation pump 18, and then enters the primary cold head heat exchanger 12 and the secondary cold head heat exchanger 13 of the GM refrigerator 4 again through the air inlet 26 for cooling. Thus, a complete closed-loop cooling system is realized. Since the optical strong magnetic thermostat 16 is connected by the low-loss infusion tube 14, and the low-loss infusion tube 14 is fixed by the low-loss infusion tube fixing bracket 15, the vibration transmitted from the liquefier part will be filtered, so that ultra-low vibration is achieved.

[0047] Advantages of the present invention:

[0048] For the refrigeration system of the magneto-optical measurement device of the present application, the GM refrigerator is externally placed, and the helium gas circulation throttling expansion structure is used to obtain ultra-low temperature liquid helium at 2K and below by using a commonly used 4K refrigerator in the prior art without consuming a large amount of liquid helium. And the GM refrigerator and the optical strong magnetic thermostat are connected by a low-loss infusion tube, and the low-loss infusion tube is fixed by a fixing bracket, so that the vibration transmitted from the liquefier part is filtered out, realizing the experimental conditions of ultra-low temperature, strong magnetic field and ultra-low vibration; at the same time, after the cooled ultra-low temperature liquid helium enters the optical strong magnetic thermostat, it is divided into two parts without affecting each other, and is respectively used to cool the sample area and the magnet cold shield, thereby improving the cooling efficiency and reducing the consumption of liquid helium.

[0049] The above has introduced in detail a magneto-optical measurement device and its control method provided by the present invention. Specific examples are used in this article to elaborate on the principle and implementation manner of the present invention. The description of the above embodiments is only used to help understand the method and its core idea of the present invention. For those of ordinary skill in the art, the technical solution of the present invention is not limited to the solution defined by the specific implementation manner. The technical solutions formed by other obvious changes that can be achieved according to the common general knowledge in the art are all within the protection scope of the present invention.

Claims

1. A refrigeration system for a magneto-optical measurement device, wherein the magneto-optical measurement module (1) in the magneto-optical measurement device is in cyclic communication with the dry closed-cycle refrigeration module (2) through the helium circulation pipeline section (3). The magneto-optical measurement module (1) specifically includes an optical high-magnetic thermostat (16), which has a magneto-optical module vacuum chamber (34), a magnet cold shield (33) arranged inside the magneto-optical module vacuum chamber (34), and a superconducting magnet (41) arranged inside the magnet cold shield (33). The superconducting magnet (41) is fixed on the magnet cold shield (33) by a magnet fixing block (35), and the magnet cold shield (33) is directly fixed on the magneto-optical module vacuum chamber (34). It is characterized in that: The superconducting magnet (41) is in close contact connection with one side of a magnet heat-conducting copper block (37), and a cold finger heat exchanger (38) is in contact connection with the other side of the magnet heat-conducting copper block (37); the helium circulation pipeline section (3) includes a low-loss infusion pipe (14), one end of which is communicated with the cold finger heat exchanger (38) through the liquid helium inlet of the optical high-magnetic thermostat (16), and the other end is communicated with the liquid helium outlet of the dry closed-cycle refrigeration module (2) to send the liquid helium from the dry closed-cycle refrigeration module (2) into the optical high-magnetic thermostat (16) to cool the cold finger heat exchanger (38). A sample area (43) is formed inside the superconducting magnet (41), and a sample to be measured is placed in the sample area (43). A sample area heat exchange space (45) is formed around the sample area (43); and, the liquid helium from the low-loss infusion pipe (14) is respectively communicated with a magnet area helium capillary (39) and a sample area helium capillary (42) after exchanging heat with the cold finger heat exchanger (38). The liquid helium passing through the sample area helium capillary (42) enters the sample area heat exchange space (45) to cool the sample area (43); the liquid helium passing through the magnet area helium capillary (39) enters the cold shield heat exchange module (40), exchanges heat with the cold shield heat exchange module (40) and cools it, and the cold shield heat exchange module (40) exchanges heat with the magnet cold shield (33), thereby cooling the magnet cold shield (33).

2. The refrigeration system of the magneto-optical measurement device according to claim 1, wherein: The helium circulation pipeline section (3) further further includes a circulation pump (18), a first metal bellows (17-1), a second metal bellows (17-2) and a third metal bellows (19). The first metal bellows (17-1) and the second metal bellows (17-2) are arranged between the outlet of the magneto-optical measurement module (1) and the inlet of the circulation pump (18), and the third metal bellows (19) is arranged between the outlet of the circulation pump (18) and the air inlet (26) of the dry closed-cycle refrigeration module (2); a low-loss infusion pipe fixing bracket (15) is fixedly arranged on the ground to clamp the part of the low-loss infusion pipe (14) between the liquid helium outlet of the dry closed-cycle refrigeration module (2) and the liquid helium inlet of the magneto-optical measurement module (1).

3. The refrigeration system of the magneto-optical measurement device according to claim 2, wherein: The dry closed-cycle refrigeration module (2) includes a GM refrigerator (4), a vibration damping bellows (5), a refrigerator vacuum chamber (6), a cold shield (8), a secondary cold plate (10), a cryogenic needle valve (11), a primary cold head heat exchanger (12) and a secondary cold head heat exchanger (13). The GM refrigerator (4) is fixed on the refrigerator vacuum chamber (6) through the vibration damping bellows (5) and includes a primary cold head (7) and a secondary cold head (9) located inside the refrigerator vacuum chamber (6). The cold shield (8) is arranged inside the refrigerator vacuum chamber (6) and fixed on the primary cold head (7). The secondary cold plate (10) is fixed on the secondary cold head (9). The primary cold head heat exchanger (12) is fixed on the cold shield (8), and the secondary cold head heat exchanger (13) is fixed on the secondary cold plate (10). The primary cold head heat exchanger (12) and the secondary cold head heat exchanger (13) are brazed together through a stainless steel capillary tube. The primary cold head heat exchanger (12) is communicated with the air inlet (26) of the dry closed-cycle refrigeration module (2). The cryogenic needle valve (11) is connected and fixed inside the refrigerator vacuum chamber (6) and communicated with the secondary cold head heat exchanger (13), so that helium gas passes through the primary cold head heat exchanger (12), the secondary cold head heat exchanger (13) and the cryogenic needle valve (11) in sequence from the air inlet (26). The outlet of the cryogenic needle valve (11) is communicated with a low-loss liquid delivery pipe (14) to convey the throttled and expanded liquid helium to it.

4. The refrigeration system of the magneto-optical measurement device according to claim 3, wherein: The cryogenic needle valve (11) is regulated through a needle valve handle arranged outside the refrigerator vacuum chamber (6) to realize the adiabatic expansion of liquid helium, so that the temperature of the expanded liquid helium reaches 2K or below.

5. The refrigeration system of the magneto-optical measurement device according to claim 2, wherein: The helium circulation pipeline part (3) further includes a helium gas tank (23), which is communicated with the pipeline between the outlet of the circulation pump (18) and the air inlet (26) of the dry closed-cycle refrigeration module (2) through a fourth metal bellows (20) and a fifth metal bellows (22), and a cut-off valve (21) is arranged between the fourth metal bellows (20) and the fifth metal bellows (22).

6. The refrigeration system of the magneto-optical measurement device according to any one of claims 1-5, wherein: The optical high magnetic field thermostat (16) is further provided with a liquid helium inlet (30), which is kept connected with a helium liquefier to input liquid helium from the helium liquefier into the optical high magnetic field thermostat (16) and reach the cold finger heat exchanger (38) to continuously cool it.

7. The refrigeration system of the magneto-optical measurement device according to claim 6, wherein: The helium gas generated after the liquid helium entering the heat exchange space (45) of the sample area exchanges heat enters the helium gas outlet pipe (44) of the sample area and enters the circulation pump (18) through the helium gas return port (32) of the sample area and the first metal bellows (17-1); the helium gas generated after the liquid helium entering the cold shield heat exchange module (40) exchanges heat enters the helium gas return port (29) of the magnet area and enters the circulation pump (18) through the second metal bellows (17-2).

8. The refrigeration system of the magneto-optical measurement device according to claim 6 or 7, wherein: One end part of the cold shield heat exchange module (40) includes an end heat exchange block. The liquid helium from the helium capillary tube (39) of the magnet area exchanges heat with the end heat exchange block. A plurality of slits evenly distributed in the circumferential direction are arranged on the end heat exchange block, so that the helium gas generated after the liquid helium from the helium capillary tube (39) of the magnet area exchanges heat passes through it and enters the helium gas return port (29) of the magnet area.

9. A control method for a refrigeration system of a magneto-optical measurement device as described in claim 8, comprising the following steps: S1: After the system starts, first turn on the GM refrigerator (4). When the temperatures of the first-stage cold head (7) and the second-stage cold head (9) reach 40K and 4K respectively, control to open the isolation valve (21), the cryogenic needle valve (11), and the circulation pump (18); S2: After the circulation pump (18) is turned on, due to the pressure difference, the high-purity helium gas in the helium gas cylinder (23) enters the first-stage cold head heat exchanger (12) through the air inlet (26). The high-purity helium gas entering the first-stage cold head heat exchanger (12) is cooled to 40K through heat exchange, and then the 40K high-purity helium gas enters the second-stage cold head heat exchanger (13); S3: The high-purity helium gas entering the second-stage cold head heat exchanger (13) is cooled to 4K to become liquid helium through heat exchange. At this time, the liquid helium at 4K temperature passes through the cryogenic needle valve (11). Due to the throttling expansion effect, the liquid helium passing through the cryogenic needle valve (11) will be cooled to 2K and below; S4: The liquid helium at 2K and below reaches the optical high-field cryostat (16) through the low-loss liquid delivery pipe (14) and exchanges heat with the cold finger heat exchanger (38); S5: A part of the liquid helium after heat exchange enters the sample area heat exchange space (45) through the sample area helium capillary (42), and cools the sample area (43) in the sample area heat exchange space (45), realizing temperature regulation in the temperature range of 2K - 300K in the sample area. The helium gas generated after heat exchange of this part of the liquid helium leaves the sample area heat exchange space (45) and enters the sample area helium gas return port (32) of the optical high-field cryostat (16); S6: Another part of the liquid helium after heat exchange in the cold finger heat exchanger (38) enters the cold shield heat exchange module (40) through the magnet area helium capillary (39), exchanges heat with the end heat exchange block at one end of the cold shield heat exchange module (40) and cools it. The helium gas generated after heat exchange of this part of the liquid helium enters the magnet area helium gas return port (29) of the optical high-field cryostat (16); S7: The helium gas flowing out from the sample area helium gas return port (32) and the magnet area helium gas return port (29) of the optical high-field cryostat (16) enters the first metal bellows (17-1) and the second metal bellows (17-2) respectively, and then is pumped away by the circulation pump (18); S8: The helium gas enters the third metal bellows (19) from the outlet of the circulation pump (18), and then enters the first-stage cold head heat exchanger (12) and the second-stage cold head heat exchanger (13) of the GM refrigerator (4) again through the air inlet (26) for cooling, thus realizing a complete closed-cycle cooling.

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