A three-stage GM refrigerator and a rapid cooling method thereof

Abstract

The present invention discloses a three-stage GM refrigerator and a rapid cooling method thereof. The three-stage GM refrigerator comprises a three-stage heat exchange cylinder container, a gas distribution component of two independent gas circuits, a two-stage refrigeration component, and a driving mechanism. The three-stage heat exchange cylinder container comprises a first heat exchanger, a second heat exchanger, a third heat exchanger, and a cylinder container. The two independent gas circuits are respectively located inside and outside the cylinder container, the first gas circuit realizes the expansion refrigeration of the gas, and the second gas circuit connects and fills each two heat exchangers with working gas (for example: helium, neon, hydrogen or a mixed gas) to form a three-stage cascade gas heat switch, which can greatly improve the cooling efficiency of the GM refrigerator when in use. At the same time, the three-stage heat exchange cylinder container and the shell of the low-temperature superconducting device are welded together to form a vacuum container. When the GM refrigerator needs to be replaced or repaired, the driving component and the two-stage refrigeration component of the refrigerator can be separately disassembled without destroying the vacuum condition.

Description

Technical Field

[0001] The invention relates to the field of low-temperature refrigerators, and in particular to a three-stage GM refrigerator and a method for rapidly cooling a low-temperature superconducting device thereof. Background Art

[0002] GM refrigerator (Gifford-McMahon refrigerator) is a high-efficiency refrigeration equipment widely used in the field of cryogenic technology. Its working principle is based on the adiabatic expansion and compression cycle of gas, and provides cooling capacity in different temperature zones through two cooling stages. GM refrigerators usually consist of two-stage cold heads: the operating temperature range of the first-stage cold head is 30K to 300K, and it can output tens to hundreds of watts of cooling power for medium-temperature cooling; the operating temperature of the second-stage cold head can be as low as 3K, but its cooling power is lower than that of the first-stage cold head, and it can only provide one to several watts of cooling capacity for deep cryogenic environments. With its compact structure, stable operation and no need for liquid helium consumption, GM refrigerators have been widely used in various cryogenic application scenarios.

[0003] In the field of low-temperature superconducting magnets, GM refrigerators play a key role. The traditional cooling method of superconducting magnets usually adopts liquid helium immersion cooling, placing the superconducting coil directly in liquid helium, quickly cooling it to the operating temperature (usually below 4K), and maintaining a stable superconducting state. However, this cooling method requires the consumption of a large amount of liquid helium, which is not only costly, but also increases the weight and complexity of the equipment. Once the magnet quenches, the huge heat generated in a short period of time will cause a large amount of liquid helium to volatilize, further exacerbating resource waste and cost burden. Generally, a refrigerator is installed in a low-temperature superconducting magnet to achieve zero volatilization of liquid helium.

[0004] In order to reduce the dependence on liquid helium, cooling technology with little or no liquid helium has gradually been developed. In this type of system, the GM refrigerator becomes the core refrigeration equipment. Its first-stage cold head is usually used for the cold screen (radiant heat screen) in the cooling system to reduce the environmental heat load; the second-stage cold head is directly or indirectly connected to the superconducting coil through a heat pipe to achieve deep cooling below 4K. This method can significantly reduce the use of liquid helium, reduce operating costs, and reduce the total weight of the equipment, improving the convenience of transportation and installation. However, due to the limited cooling power of the second-stage cold head of the GM refrigerator, it usually takes 20 to 30 days for the system to cool from ambient temperature to operating temperature (4K), and the cooling speed is slow, which brings considerable challenges to application scenarios that require frequent startup.

[0005] Therefore, how to further improve the efficiency of GM refrigerators in cooling superconducting magnets and shorten the cooling time has become the focus of current research on low-liquid helium and liquid-free helium technologies. Summary of the invention

[0006] Based on this, it is necessary to propose a three-stage GM refrigerator and a rapid cooling method thereof to address the problem of slow cooling rate of magnets with little or no liquid helium.

[0007] A three-stage GM refrigerator comprises:

[0008] The three-stage heat exchange cylinder container comprises a first heat exchanger, a second cooling stage, a second heat exchanger, a third heat exchanger, and a cylinder container. The first heat exchanger and the second heat exchanger are thermally connected to the cylinder container, and the third heat exchanger is thermally coupled to the first heat exchanger and the second heat exchanger through a gas path, and is not in direct contact with the cylinder container;

[0009] The driving mechanism, the crank connecting rod and the two-stage refrigeration assembly are arranged in the three-stage heat exchange cylinder container.

[0010] Two independent gas circuit gas distribution components include a first gas circuit and a second gas circuit. The first gas circuit is connected to the compressor, and the high-pressure gas enters the cylinder container from the compressor. After the gas expansion and refrigeration, the low-pressure gas flows into the compressor again. The second gas circuit is arranged outside the cylinder container, and the first heat exchanger, the second heat exchanger, and the third heat exchanger are connected in pairs to form a three-stage cascade thermal switch. The second gas circuit is connected to the high-pressure gas cylinder and is used to fill the gas ascending pipeline and the descending pipeline with working gas. The pipeline filling port passes through the mounting flange of the cylinder container, is located at room temperature, and is equipped with a safety valve, a pressure gauge, and a flow meter. The pressure of the working gas is adjustable. For different types of working gases, the operating pressure of the gas thermal switch circuit is different. For the same working gas, the flow state under different pressures is also different. The adjustable gas pressure is more suitable for adjusting according to different working conditions to obtain the best cooling effect.

[0011] In some embodiments, the drive mechanism of the cryogenic refrigerator may be electric or pneumatic.

[0012] In some embodiments, the working gas of the first gas loop and the second gas loop is helium, and the first stage temperature on the first heat exchanger is 35K~45K, the third stage temperature on the third heat exchanger is 25~35K, and the second stage temperature on the second heat exchanger is 3.5~4.5K.

[0013] In some embodiments, the low-temperature superconducting device cooled by the three-stage GM refrigerator can be a superconducting magnet. Another aspect of the present invention can provide a rapid cooling method for superconducting magnets. In particular, a superconducting magnet with little or no liquid helium. The cold screen cooling of the superconducting magnet is achieved by thermal connection with the first heat exchanger, and the connection method can be heat conduction of the cooling component, and the cooling component can be thermally coupled to the first heat exchanger; the material of the cooling component can be silver, high-purity copper or high-purity aluminum.

[0014] In some embodiments, the cooling of the cold shield in the superconducting magnet in the method is achieved by thermal connection with the first heat exchanger, and the connection method can be gas-liquid two-phase heat exchange in a heat pipe loop or single-phase gas or gas-liquid two-phase heat exchange in a thermal siphon pipeline.

[0015] In some embodiments, the cooling of the superconducting coil in the method is achieved by thermal connection with a second heat exchanger, and the connection method can be a cooling component, a gas-liquid two-phase heat exchange of a heat pipe loop, or a single-phase gas or gas-liquid two-phase heat exchange of a thermal siphon pipeline.

[0016] In some embodiments, other components in the superconducting magnet that need to be cooled have an operating temperature between the refrigeration limit temperatures of the first heat exchanger and the second heat exchanger. For example, some high-temperature superconducting materials such as YBCO, Bi2212, Bi2223, MgB2, etc. have an operating temperature above 25K. A third heat exchanger can be used to cool this part. The method can be thermal connection of the heat-conducting component or gas-liquid two-phase heat exchange of the heat pipe loop or single-phase gas or gas-liquid two-phase heat exchange of the thermal siphon pipeline. At this time, the heat exchanger can be adjusted accordingly to a structure that can have two gas paths for heat and mass exchange, such as a shell and tube heat exchanger, a sleeve heat exchanger, etc.

[0017] In some embodiments, the thermal connection between the heat exchangers is achieved through a gas circulation loop composed of a gas rising pipe and a gas descending pipe; the temperature gradient of the heat exchanger from bottom to top is used to form a natural siphon pipe, and the thermal switch is turned on. When the cooling continues until the temperature gradient is reversed, that is, the temperature of the heat exchanger at the lower end is lower than that of the heat exchanger at the upper end, the driving force required for natural siphoning disappears and the thermal switch is disconnected.

[0018] In some embodiments, the working gas in the second gas circuit may be one or a mixture of helium, hydrogen, nitrogen or neon.

[0019] In some embodiments, when the three-stage GM refrigerator is used in a strong magnetic field environment, a magnetic shielding assembly can be installed upwardly on the second heat exchanger, but not in contact with the third heat exchanger. The magnetic shielding assembly is made of high magnetic permeability materials, including but not limited to high-purity aluminum, silicon steel, low-carbon steel, etc.

[0020] In some embodiments, a heating device and a temperature control module are provided inside the cylinder container for accurately adjusting the temperature inside the cylinder during equipment maintenance. When it is necessary to disassemble or replace the refrigerator core, the temperature inside the cylinder container is first raised to a predetermined temperature range by a heating device. This process ensures that the cryogenic liquid working medium (such as liquid helium or liquid nitrogen) inside the container is completely gasified to avoid frost or ice crystal accumulation caused by residual liquid or condensation under low temperature conditions. The temperature control module monitors and adjusts the heating process in real time to ensure that the temperature is uniform and meets the operating requirements. The refrigerator core can only be safely disassembled or replaced after the environment inside the cylinder reaches the set temperature and stabilizes. It can effectively prevent the potential risks brought by low-temperature operation, improve the efficiency and safety of maintenance operations, and ensure the system reliability and stability of the working environment during the disassembly process. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The present invention will be more readily understood from the detailed description of exemplary embodiments set forth below considered in conjunction with the accompanying drawings, in which:

[0022] Figure 1 It is a schematic diagram of a three-stage GM refrigerator of the present invention;

[0023] Figure 2 A schematic diagram of the present invention being applied to a low-liquid-helium superconducting magnet;

[0024] Figure 3 The fin arrangement method of the heat exchanger in the present invention;

[0025] Figure 4 It is a schematic diagram of the application of the present invention in a conduction-cooled superconducting magnet.

[0026] In the figure: 111-first heat exchanger, 112-second heat exchanger, 113-second cooling stage, 114-third heat exchanger, 115-cylinder container, 116-temperature control device, 117-high-pressure gas cylinder, 118-flow meter, 119-safety valve, 120-driving mechanism, 121-crank connecting rod, 130-two-way independent gas circuit gas distribution assembly, 131-first gas circuit, 132-second gas circuit, 33a-gas rising pipeline, 33b-gas descending pipeline, 140-two-stage refrigeration assembly, 141-first regenerator, 142-first stage displacer, 143-second regenerator, 144-secondary displacer, 150-flange, 160-magnetic shielding assembly, 170-compressor, 171-low-pressure gas valve, 172-high-pressure gas valve, 210-40K cold shield, 220-low-temperature superconducting coil, 230-high-temperature superconducting coil, 240-300K shell, 211-cold shield gas circulation loop, 212-high-temperature superconducting coil gas circulation loop, 213-low-temperature superconducting coil gas circulation loop, 311-cold shield thermal conductive assembly, 312-high-temperature superconducting coil thermal conductive assembly, 313-low-temperature superconducting coil thermal conductive assembly. DETAILED DESCRIPTION

[0027] The present invention is further described below in conjunction with the accompanying drawings and specific embodiments.

[0028] See also Figure 1 An embodiment of the present invention provides a three-stage GM refrigerator, including a cylinder container 115, a first heat exchanger 111, a second heat exchanger 112, a third heat exchanger 114, a second cooling stage 113, a driving mechanism 120, a crank connecting rod 121, a primary displacer 142, a first regenerator 141, a secondary displacer 144 and a second regenerator 143. The primary displacer 142, the first regenerator 141, the secondary displacer 144 and the second regenerator 143 are all arranged inside the cylinder container 115.

[0029] The primary displacer 142 is connected to the driving mechanism 120 through the crank connecting rod 121, and the primary displacer 142 is connected to the secondary displacer 144 through the pin shaft and the pin seat. The driving mechanism 120 drives the primary displacer 142 and the secondary displacer 144 to reciprocate, thereby completing the core process of the refrigeration cycle and achieving efficient cooling in the system. In addition, the cylinder container 115 and the room temperature Dewar together form a vacuum container to provide a good thermal insulation environment, reduce the external heat input, and ensure the efficient operation of the low temperature cooling system.

[0030] The bottom position of the first heat exchanger 111 is close to the bottom dead center of the first displacer 142, the second heat exchanger 112 is close to the bottom dead center of the second displacer 144, and the third heat exchanger 114 is arranged between the first heat exchanger 111 and the second heat exchanger 112, close to the position of the first heat exchanger 111 at about one third to one half.

[0031] The first gas loop 131 is connected to the cylinder container 115, and provides a primary low-temperature environment for the system through circulating cooling. In this process, the gas first enters the first regenerator 141 and the first-stage displacer 142 to store and release heat, thereby initially reducing the gas temperature. Subsequently, the gas enters the second regenerator 143 and the second-stage displacer 144 to further reduce the temperature and transfer the cold to the subsequent cooling link, thereby achieving the required deep low-temperature refrigeration effect in the loop.

[0032] The second gas loop 132 is used for a three-stage cascade gas heat switch cycle. The loop drives the gas flow and controls the heat transfer through the temperature difference between the first heat exchanger 111 and the second heat exchanger 112. When the temperature difference is sufficient, the gas circulates in the loop to achieve effective heat exchange; when the temperature difference decreases, the gas flow in the loop stops, thereby cutting off the heat transfer. While meeting the heat management requirements of different temperature zones of the system, the refrigeration efficiency and operation stability are significantly improved. The second gas loop 132 includes a gas riser 33a and a gas descender 33b. The specific working process is as follows:

[0033] 1 When the temperature of the second heat exchanger 112 is higher than that of the first heat exchanger 111:

[0034] The gas flows upward from the gas riser 33a under the action of the thermal driving force;

[0035] After absorbing the heat in the second heat exchanger 112, the gas flows through the first heat exchanger 111, thereby realizing active heat transfer of the gas heat switch loop.

[0036] 2 When the temperature of the second heat exchanger 112 is lower than that of the first heat exchanger 111:

[0037] Heat transfer in the gas is inhibited and the flow of gas in the circuit stops;

[0038] Since the gas circulation stops, the thermal switch is in a closed state, which effectively blocks the heat transfer between the first heat exchanger 111 and the second heat exchanger 112, thereby ensuring the stability of the temperature gradient inside the system.

[0039] Figure 2The figure shows an exemplary device of a three-stage GM refrigerator that can be used in a low-liquid helium superconducting magnet. In this embodiment, the low-temperature superconducting device is a superconducting magnet, including a 300K shell 240, a 40K cold shield 210, and superconducting coils: including a low-temperature superconducting coil 220, a high-temperature superconducting coil 230, etc. The 40K cold shield 210 is arranged in the 300K shell 240 to isolate radiant heat, and the low-temperature superconducting coil 220 and the high-temperature superconducting coil 230 are arranged in the 40K cold shield 210.

[0040] In this embodiment, if Figure 2 As shown, during the cooling process of the superconducting magnet, the first heat exchanger 111 is thermally connected to the cold shield gas circulation loop 211 on the 40K cold shield 210 through the three-way interface reserved at the upper part of the gas rising pipeline 33a and the gas descending pipeline 33b. When the gas types are different or the working pressure difference is large, a heat exchanger can be added to make the gases of the two loops heat exchange in the heat exchanger to achieve heat exchange. The second heat exchanger 112 is thermally connected to the low-temperature superconducting coil gas circulation loop 213 of the low-temperature superconducting coil 220 through the three-way interface reserved at the lower part of the gas rising pipeline 33a and the gas descending pipeline 33b, and the third heat exchanger 114 is thermally connected to other components that need to be cooled (including but not limited to the high-temperature superconducting coil 230, other high-temperature superconducting materials that need to be cooled, etc.) through the high-temperature superconducting coil gas circulation loop 212 to achieve the cooling requirements of multiple components and multiple temperature zones. The first heat exchanger 111 and the second heat exchanger 112 are connected through the gas rising pipe 33a and the gas descending pipe 33b, wherein the gas descending pipe 33b flows through the third heat exchanger 114 as much as possible. For the convenience of structural installation, the third heat exchanger 114 adopts a semicircular structure, and the gas descending pipe 33b flows in parallel in the semicircular structure. In order to effectively protect the three-stage GM refrigerator and its internal components from the interference of the strong magnetic field of the superconducting magnet, a magnetic shielding assembly 160 is arranged above the second heat exchanger 112. The magnetic shielding assembly 160 can be fixed by welding or screw connection, and its material is high-purity aluminum. A certain gap is designed between the magnetic shielding assembly 160 and the cylinder container 115 to avoid direct contact and ensure the effectiveness of the magnetic shielding assembly 160.

[0041] At the beginning of cooling, the initial temperature of the superconducting magnet is room temperature 300K. At this time, the cooling power of the first heat exchanger 111 is higher than that of the second heat exchanger 112, forming the following temperature gradient: the temperature of the second heat exchanger 112> the temperature of the third heat exchanger 114> the temperature of the first heat exchanger 111. Since the temperature of the lower gas is high and the temperature of the upper gas is low, the gas has a density difference between the cold end and the hot end. When the density difference reaches a balance with the flow loss in the pipeline, the gas forms a self-driven cycle in the system, thereby transferring the cooling capacity of the upper heat exchanger to the lower heat exchanger, thereby increasing the cooling rate of the lower components.

[0042] As the temperature drops continuously, when the temperature of the second heat exchanger 112 drops to about 40K and is lower than that of the first heat exchanger 111, the density difference in the gas loop between the first heat exchanger 111 and the second heat exchanger 112 gradually disappears. At this time, the cold gas stops circulating upward at the bottom, and the gas thermal switch is disconnected, thereby cutting off the thermal connection between the first heat exchanger 111 and the second heat exchanger 112. Subsequently, the low-temperature superconducting coil 220 continues to be cooled by the second heat exchanger 112 until it reaches its operating temperature (e.g., 4K).

[0043] In this embodiment, in order to further improve the gas heat transfer efficiency of the first heat exchanger 111 and the second heat exchanger 112, vertically or parallel fins may be processed on the wall surface of the heat exchanger. Including but not limited to Figure 3 These fins disrupt the airflow and enhance the boundary layer heat transfer between the fluid and the solid wall, thereby significantly improving the heat exchange efficiency between the gas and the heat exchanger.

[0044] In addition, the cylinder container 115 in this embodiment is connected to the 300K shell 240 of the superconducting magnet by welding to form a vacuum container, providing an efficient heat-insulating environment for the system. When the three-stage GM refrigerator needs to be maintained or replaced, the drive mechanism 120, the two-stage refrigeration assembly 140 and other components of the three-stage GM refrigerator can be separately disassembled while maintaining the vacuum condition, thereby achieving fast and convenient maintenance operations.

[0045] In order to achieve efficient heat conduction, the second cold conduction stage 113 is connected to the cylinder container 115 by vacuum brazing to form a reliable heat conduction path. In addition, the second heat exchanger 112 is connected to the second cold conduction stage 113 by welding or riveting, thereby ensuring good thermal contact between the second heat exchanger 112 and the cylinder container 115. Through structural design, it can not only effectively shield the magnetic field and protect the key components of the three-stage GM refrigerator, but also ensure efficient thermal connection between the second heat exchanger 112 and the cylinder container 115. In this embodiment, the initial pressurization of the second gas circuit 132 is completed by an external high-pressure gas cylinder 117, and the specific filling gas and filling pressure are selected and adjusted according to the actual working temperature requirements. In order to monitor the gas flow in the second gas circuit 132, a flow meter 118 with a serial communication function is provided, which can realize real-time monitoring and data transmission of the gas flow, thereby ensuring accurate control of the system operation status. When the pressure in the second gas circuit 132 is lower than the design value due to operating loss or other reasons, the valve arranged on the filling pipeline can be opened to add an appropriate amount of gas to the system until the pressure returns to the set range, thereby ensuring that the system operates stably under the design pressure conditions. When the pressure in the second gas circuit 132 exceeds the upper limit of the pipeline design pressure, the safety valve 119 can release excess pressure to the outside to protect the internal structure from damage, ensuring the stability and reliability of the system operation, and providing accurate and efficient control means for pressure regulation and flow monitoring.

[0046] In one embodiment, if Figure 4 As shown, when the present invention is used in a conduction-cooled superconducting magnet, the first heat exchanger 111 is connected to the 40K cold shield 210 through the cold shield heat conductive component 311, the third heat exchanger 114 is connected to the high-temperature superconducting coil 230 through the high-temperature superconducting coil heat conductive component 312, the second heat exchanger 112 is connected to the low-temperature superconducting coil 220 through the low-temperature superconducting coil heat conductive component 313, and the first heat exchanger 111 and the second heat exchanger 112 are connected through a gas ascending pipeline 33a and a gas descending pipeline 33b.

[0047] The above is only a preferred embodiment of the present invention, and the protection scope of the present invention is not limited to the above embodiments. All technical solutions under the concept of the present invention belong to the protection scope of the present invention. It should be pointed out that for ordinary technicians in this technical field, some improvements and modifications without departing from the principle of the present invention should also be regarded as the protection scope of the present invention.

Claims

1. A three-stage GM refrigerator, characterized in that include: A three-stage heat exchange cylinder container, comprising a first heat exchanger, a second heat exchanger, a second cooling stage, a third heat exchanger and a cylinder container; A two-way independent gas circuit gas distribution assembly, comprising a first gas circuit and a second gas circuit; Driving mechanism, crank connecting rod; A two-stage refrigeration assembly, including a first regenerator, a first-stage displacer, a second regenerator, and a second-stage displacer, all of which are located in the three-stage heat exchange cylinder container; Compressor, high pressure gas valve, low pressure gas valve, high pressure gas cylinder; The first heat exchanger is thermally coupled to the outer wall of the cylinder container, close to the first-stage displacer; the first-stage displacer is connected to the driving mechanism through a crank connecting rod; the second cooling stage is arranged at the bottom of the cylinder container and welded to the outer wall of the cylinder container by vacuum brazing; the second heat exchanger is thermally coupled to the second cooling stage and fastened with screws; the third heat exchanger is thermally coupled to the middle of the first heat exchanger and the second heat exchanger through the gas path, and is close to one-third to one-half the height of the first heat exchanger; the two-way independent gas circuit gas distribution component, wherein the first gas circuit flows from the inside of the three-stage heat exchange cylinder container through the first regenerator and the first-stage displacer, realizes the first-stage gas expansion and refrigeration, and then flows through the second regenerator and the second-stage displacer, realizes the second-stage gas expansion and refrigeration, and then flows out of the three-stage heat exchange cylinder container to complete the refrigeration cycle; the second gas circuit is arranged outside the three-stage heat exchange cylinder container, and is connected to the first heat exchanger, the third heat exchanger, and the second heat exchanger in sequence; the second gas circuit is connected to the high-pressure gas cylinder and is closed after being filled with gas.

2. A three-stage GM refrigerator according to claim 1, characterized in that: The second gas circuit includes a gas rising pipeline and a gas descending pipeline. When the temperature of the second heat exchanger is higher, the gas flows from the gas rising pipeline from bottom to top, is cooled in the second heat exchanger, flows from the gas descending pipeline from top to bottom, and returns to the second heat exchanger. When the temperature of the second heat exchanger is lower than that of the first heat exchanger, the gas circulation stops and the thermal switch is disconnected.

3. A three-stage GM refrigerator according to claim 2, characterized in that: The working gas of the first gas circuit is helium, and the gas filled in the second gas circuit is any one of helium, hydrogen, nitrogen, and neon, or a mixed gas consisting of two of these gases.

4. A three-stage GM refrigerator according to claim 1, characterized in that: The temperature of the first heat exchanger is the first-stage temperature, the temperature of the second heat exchanger is the second-stage temperature, the temperature of the third heat exchanger is the third-stage temperature, and the first-stage temperature > the third-stage temperature > the second-stage temperature.

5. A three-stage GM refrigerator according to claim 3, characterized in that: The first gas circuit is connected to the compressor, and the circulation of the gas circuit inside the cylinder container is realized by periodically opening and closing the high-pressure gas valve and the low-pressure gas valve, thereby achieving a refrigeration effect.

6. A three-stage GM refrigerator according to claim 1, characterized in that: The three-stage heat exchange cylinder container can be installed on the shell of the low-temperature superconducting device through a flange plate. A temperature control device can be arranged inside the three-stage heat exchange cylinder container, including a heating resistor and a temperature monitoring module. When the refrigeration component needs to be removed or replaced, the heating component is started. When the temperature reaches a preset temperature, the connection between the three-stage heat exchange cylinder container and the shell of the low-temperature superconducting device can be opened.

7. A three-stage GM refrigerator according to claim 1, characterized in that: When used in a strong magnetic field environment, the magnetic shielding assembly can be optionally installed on the second heat exchanger, facing upwards and not in contact with the third heat exchanger.

8. A method for rapidly cooling a three-stage GM refrigerator as claimed in any one of claims 1 to 7, which can be used to cool a low-temperature superconducting device containing a high-temperature superconducting coil and a low-temperature superconducting coil, characterized in that: S1: The first heat exchanger initially cools the low-temperature superconducting device to a preset temperature T1 at the first stage temperature; S2: The third heat exchanger performs secondary cooling on the low-temperature superconducting device to a preset temperature T2 at a third stage temperature; S3: The second stage temperature of the second heat exchanger realizes ultimate cooling of the low-temperature superconducting device, cooling the low-temperature superconducting device from the preset temperature T2 to the operating temperature T3.

9. A rapid cooling method for a three-stage GM refrigerator according to claim 8, characterized in that: The material of the high-temperature superconducting coil is yttrium barium copper oxide (YBCO), or bismuth strontium calcium copper oxide (BSCCO), or magnesium diboride (MgB2); the material of the low-temperature superconducting coil is niobium titanium alloy (NbTi) or niobium tin (Nb3Sn), and the low-temperature superconducting device is a medical magnetic resonance imaging superconducting magnet, a magnetic pulling single crystal superconducting magnet, or a nuclear fusion superconducting magnet.

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