An ultra-low temperature refrigeration system and a refrigeration method thereof

Abstract

The application relates to an ultra-low-temperature refrigeration system and a refrigeration method thereof, which comprises a Stirling refrigeration unit and an adiabatic demagnetization refrigeration unit coupled with the Stirling refrigeration unit; the Stirling refrigeration unit comprises a pulse tube cold finger unit connected with the adiabatic demagnetization refrigeration unit and a pulse tube compressor unit connected with the pulse tube cold finger unit, wherein the pulse tube compressor unit is used for driving the pulse tube cold finger unit to refrigerate, the pulse tube cold finger unit is used for refrigerating to provide pre-cooling refrigeration capacity for the adiabatic demagnetization refrigeration unit, and the adiabatic demagnetization refrigeration unit is used for realizing refrigeration based on a magnetocaloric effect; the ultra-low-temperature refrigeration system directly combines a long-life Stirling type architecture with the adiabatic demagnetization refrigeration, fully utilizes the advantages of the Stirling type refrigeration machine and the adiabatic demagnetization refrigeration system, can greatly reduce the complexity of space ultra-low-temperature technology, and further improves the efficiency of the whole system.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of extremely low temperature refrigeration, in particular to an extremely low temperature refrigeration system and a refrigeration method thereof. BACKGROUND

[0002] Deep space exploration expands human understanding of the earth, the solar system and the universe, promotes the development and utilization of space resources and the innovation of space science and technology, and is an important field of competition among big countries. Deep space exploration has become one of the most active frontiers of science and technology in the world, which needs support of a series of key scientific and technological fields, including extremely low temperature refrigeration technology. Extremely low temperature refrigeration technology generally refers to refrigeration technology for obtaining a temperature below 1K and providing a certain amount of cold. In addition to the field of space exploration, it also plays an important role in basic and cutting-edge scientific research fields such as condensed matter physics and quantum technology. An extremely low temperature refrigeration technology system usually includes a pre-cooling refrigeration system and an extremely low temperature refrigeration subsystem.

[0003] The main functions of extremely low temperature are: 1) to provide an extreme physical environment for studying special physical effects (such as helium-3 superfluid transition and quantum anomalous Hall effect, etc.); 2) to improve the range and resolution of instruments, for example, instruments for observing X-ray to far-infrared waveband in space exploration need to work below 1K, and the lower the temperature, the higher the resolution; 3) to reduce the thermal noise level and improve the signal-to-noise ratio. In commonly used extremely low temperature refrigeration technology, the adiabatic demagnetization refrigerator (ADR) has the outstanding advantages of wide temperature coverage, high intrinsic efficiency, and independence from gravity or scarce working medium, and has become the mainstream technology route in space applications. At the same time, ADR has a broad application prospect in ground laboratories due to its wide range of working medium, compact structure and relatively low cost. The typical single-stage ADR thermodynamic cycle includes four processes of isothermal magnetization, adiabatic demagnetization, isothermal demagnetization and adiabatic magnetization.

[0004] Current space-used extremely low temperature refrigerators all need pre-cooling in the 4K temperature range, and the implementation is basically a combination of multi-stage Stirling and J-T throttling technology. The system is extremely complex, and the latter has particularly high requirements for the cleanliness of the working medium; the mainstream 4K temperature range refrigerator for ground use adopts G-M type pulse tube refrigeration technology, which is low in efficiency and large in size, uses an oil-lubricated compressor, and needs regular maintenance. Moreover, the 4K temperature range is low in efficiency, resulting in low system efficiency. In view of the current situation, it is of great significance to develop compact and efficient extremely low temperature systems suitable for space applications and ground scientific research. SUMMARY

[0005] The application aims to provide an ultra-low temperature refrigeration system and a refrigeration method thereof, which directly combines a long-life Stirling type architecture with an adiabatic demagnetization refrigeration, fully utilizes the advantages of the Stirling type refrigeration machine and the adiabatic demagnetization refrigeration system, greatly reduces the complexity of the space ultra-low temperature technology, and further improves the efficiency of the whole system.

[0006] In one aspect, the application provides an ultra-low temperature refrigeration system, comprising a Stirling refrigeration unit and an adiabatic demagnetization refrigeration unit coupled to the Stirling refrigeration unit; the Stirling refrigeration unit comprises a pulse tube cold finger unit connected to the adiabatic demagnetization refrigeration unit and a pulse tube compressor unit connected to the pulse tube cold finger unit, wherein the pulse tube compressor unit is used to drive the pulse tube cold finger unit to refrigerate, the pulse tube cold finger unit is used to refrigerate to provide pre-cooling capacity for the adiabatic demagnetization refrigeration unit, and the adiabatic demagnetization refrigeration unit is used to realize refrigeration based on the magnetocaloric effect.

[0007] In one embodiment of the application, the ultra-low temperature refrigeration system further comprises a vacuum cover, and the pulse tube cold finger unit and the adiabatic demagnetization refrigeration unit are both arranged in the vacuum cover.

[0008] In one embodiment of the application, the pulse tube cold finger unit is a two-stage pulse cold finger unit, and the two-stage pulse cold finger unit comprises a first-stage pulse tube adopting a coaxial structure and a second-stage pulse tube adopting a U-shaped structure.

[0009] The first-stage pulse tube comprises a first-stage phase adjuster, a first-stage hot end heat exchanger connected to the first-stage phase adjuster, a first-stage regenerator connected to the first-stage hot end heat exchanger, a first-stage cold head connected to the first-stage regenerator, and a first-stage pulse tube connected to the first-stage cold head.

[0010] The second-stage pulse tube comprises a second-stage intermediate heat exchanger connected to the first-stage cold head through a thermal bridge, a second-stage high-temperature section regenerator and a second-stage low-temperature section regenerator connected to upper and lower sides of the second-stage intermediate heat exchanger respectively, a second-stage hot end heat exchanger connected to the second-stage high-temperature section regenerator, a second-stage cold head connected to the second-stage low-temperature section regenerator, a second-stage pulse tube cold end heat exchanger connected to the second-stage cold head through a U-shaped connecting pipe, and a second-stage pulse tube connected to the second-stage pulse tube cold end heat exchanger.

[0011] In one embodiment of the application, the first-stage pulse tube further comprises a first-stage cold screen arranged in the vacuum cover, the first-stage cold head, the thermal bridge, and the intermediate low-temperature section regenerator are arranged outside the first-stage cold screen, and part of the structure of the second-stage pulse tube cold end heat exchanger, the U-shaped connecting pipe, and the second-stage low-temperature section regenerator are arranged in the first-stage cold screen.

[0012] The second-stage pulse tube also includes a second-stage cold plate connected to the first-stage cold head and in contact with the second-stage cold head, a second-stage cold screen connected to the second-stage cold plate, and a first thermal switch disposed between the first-stage cold head and the second-stage cold plate;

[0013] The heat insulation and demagnetization refrigeration unit is located inside the secondary cold shield.

[0014] In one embodiment of the present invention, the thermal insulation and demagnetization unit includes a superconducting magnet disposed within the secondary cold screen, a magnetothermal module suspended between the superconducting magnets, a second thermal switch disposed between the secondary cold plate and the magnetothermal module, and a cold end connected to the magnetothermal module.

[0015] In one embodiment of the present invention, the magnetocaloric module is any one of gadolinium gallium garnet, lithium gadolinium fluoride, iron ammonium alum, and chromium potassium alum; and / or, the first thermal switch is a convection thermal switch; and / or, the second thermal switch is an active air gap thermal switch, which achieves the switching of on / off states by heating or cooling the adsorption bed to desorb or adsorb the gas.

[0016] In one embodiment of the present invention, the pulse tube compressor unit includes a pulse tube driven compressor connected to a primary hot-end heat exchanger and a secondary hot-end heat exchanger of the pulse tube cold finger unit via gas pipelines, and a phase-adjusting compressor connected to the hot end of the secondary pulse tube.

[0017] In one embodiment of the present invention, the Stirling refrigeration unit provides a pre-cooling temperature of 2 to 20 K for the adiabatic demagnetizing refrigeration unit.

[0018] In another aspect, the present invention provides a refrigeration method for an ultra-low temperature refrigeration system, comprising the steps of:

[0019] Start the pulse compressor unit;

[0020] The pulse tube compressor unit drives the pulse tube cold finger unit for refrigeration, providing pre-cooling capacity for the adiabatic demagnetizing refrigeration unit.

[0021] When the adiabatic demagnetizing refrigeration unit is precooled to the target precooling temperature, an electric current is applied to the adiabatic demagnetizing refrigeration unit, and the adiabatic demagnetizing refrigeration unit achieves refrigeration based on the magnetocaloric effect.

[0022] In one embodiment of the present invention, the refrigeration method of the cryogenic refrigeration system specifically includes the following steps:

[0023] Start the pulse-driven compressor of the pulse compressor unit;

[0024] The pulse tube cold finger unit is driven by the pulse tube driven compressor, thereby cooling the first-stage cold head of the pulse tube cold finger unit.

[0025] Because of the temperature difference between the two ends of the first thermal switch, the internal airflow begins to convect and exchange heat, thus causing the first thermal switch to open automatically.

[0026] When the temperature of the adiabatic demagnetizing refrigeration unit is the same as the temperature of the first-stage cold head, the first thermal switch is turned off.

[0027] When the temperature of the secondary cold head of the pulse tube cold finger unit reaches the target pre-cooling temperature, the second thermal switch of the pulse tube cold finger unit is turned on to cool the superconducting magnet and magnetothermal module of the adiabatic demagnetizing refrigeration unit to the target pre-cooling temperature.

[0028] An electric current is applied to the superconducting magnet, thereby applying a magnetic field to the magnetocaloric module. The magnetocaloric module generates magnetization heat, which is then conducted to the secondary cold head via a second thermal switch.

[0029] When the temperature of the magnetic heating module reaches near the temperature of the secondary cold head, the second thermal switch is turned off to demagnetize the magnetic heating module, and the temperature of the magnetic heating module decreases, thus achieving cooling.

[0030] The target precooling temperature is 2–20 K.

[0031] This invention utilizes a highly efficient Stirling refrigerator coupled with an adiabatic demagnetizing refrigeration system to obtain extremely low temperature refrigeration. Compared with the traditional ultra-low temperature ADR system architecture, the ultra-low temperature refrigeration system of this invention makes full use of the advantages of the Stirling refrigerator and the ADR subsystem, and has the advantages of simple system structure, high efficiency and high operability.

[0032] The further objects and advantages of the invention will become fully apparent from the following description and accompanying drawings. Attached Figure Description

[0033] Figure 1 This is a schematic diagram of the structure of the cryogenic refrigeration system according to a preferred embodiment of the present invention.

[0034] Explanation of reference numerals: 100 for cryogenic refrigeration system;

[0035] Stirling refrigeration unit 1; pulse tube cold finger unit 10; first-stage pulse tube 11; first-stage phase adjuster 111; first-stage hot-end heat exchanger 112; first-stage regenerator 113; first-stage cold head 114; first-stage cold shield 115; first-stage pulse tube 116; second-stage pulse tube 12; second-stage intermediate heat exchanger 121; second-stage high-temperature section regenerator 122; second-stage low-temperature section regenerator 123; second-stage hot-end heat exchanger 124; second-stage cold head 125; second-stage pulse tube cold-end heat exchanger 126; second-stage cold plate 127; second-stage cold shield 128; first thermal switch 129; second-stage pulse tube 130; thermal bridge 13; U-shaped connecting pipe 14; pulse tube compressor unit 20; pulse tube driven compressor 21; phase-adjusting compressor 22; adiabatic demagnetizing refrigeration unit 30; superconducting magnet 31; magnetothermal module 32; second thermal switch 33; cold end 34; vacuum chamber 2. Detailed Implementation

[0036] The following description is intended to disclose the present invention and enable those skilled in the art to implement it. The preferred embodiments described below are merely examples, and other obvious variations will occur to those skilled in the art. The basic principles of the invention defined in the following description can be applied to other embodiments, modifications, improvements, equivalents, and other technical solutions that do not depart from the spirit and scope of the invention.

[0037] Those skilled in the art should understand that, in the disclosure of this invention, the terms "vertical," "horizontal," "up," "down," "front," "back," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, the above terms should not be construed as limiting this invention.

[0038] It is understood that the term "a" should be understood as "at least one" or "one or more", that is, in one embodiment, the number of an element can be one, while in another embodiment, the number of the element can be multiple, and the term "a" should not be understood as a limitation on the number.

[0039] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection, an electrical connection, or a connection that allows for communication; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0040] This invention designs a Stirling-cooled coupled adiabatic demagnetizing (ADR) cryogenic refrigeration system, which directly combines a long-life Stirling architecture with adiabatic demagnetizing (ADR) refrigeration. It also allows for the selection of increasing the pre-cooling temperature of the cryogenic system, making full use of the advantages of the Stirling refrigerator and the ADR subsystem. This is expected to significantly reduce the complexity of space cryogenic technology and further improve the efficiency of the entire system.

[0041] like Figure 1 As shown, the specific structure of the cryogenic refrigeration system 100 according to a preferred embodiment of the present invention is illustrated. The cryogenic refrigeration system 100 includes a Stirling refrigeration unit 1 and an adiabatic demagnetizing refrigeration unit 30 coupled to the Stirling refrigeration unit 1; the Stirling refrigeration unit 1 includes a pulse tube cold finger unit 10 connected to the adiabatic demagnetizing refrigeration unit 30 and a pulse tube compressor unit 20 connected to the pulse tube cold finger unit 10, wherein the pulse tube compressor unit 20 is used to drive the pulse tube cold finger unit 10 to refrigerate, the pulse tube cold finger unit 10 is used to refrigerate to provide pre-cooling capacity to the adiabatic demagnetizing refrigeration unit 30, and the adiabatic demagnetizing refrigeration unit 30 is used to achieve refrigeration based on the magnetocaloric effect.

[0042] In other words, the cryogenic refrigeration system 100 of the present invention mainly consists of the pulse tube compressor unit 20, the pulse tube cold finger unit 10, and the adiabatic demagnetizing refrigeration unit 30. The pulse tube cold finger unit 10 can be a multi-stage pulse tube cold finger unit 10, and the adiabatic demagnetizing refrigeration unit 30 can be a single-stage, multi-stage, or isothermal stage structure; the present invention does not impose any limitations on these aspects.

[0043] It is worth mentioning that the pulse tube compressor unit 20 and the pulse tube cooling finger unit 10 are connected by a gas pipeline; the pulse tube cooling finger unit 10 and the adiabatic demagnetizing refrigeration unit 30 are connected by a solid thermal connection.

[0044] Furthermore, the cryogenic refrigeration system 100 also includes a vacuum chamber 2, and the pulse tube cooling finger unit 10 and the adiabatic demagnetizing refrigeration unit 30 are both disposed inside the vacuum chamber 2.

[0045] In this specific embodiment of the present invention, the vascular cold finger unit 10 is a two-stage pulse cold finger unit, which includes a first-stage vascular 11 with a coaxial structure and a second-stage vascular 12 with a U-shaped structure.

[0046] The first-stage pulse tube 11 includes a first-stage phase modulator 111, a first-stage hot-end heat exchanger 112 connected to the first-stage phase modulator 111, a first-stage regenerator 113 connected to the first-stage hot-end heat exchanger 112, a first-stage cold head 114 connected to the first-stage regenerator 113, and a first-stage pulse tube 116 connected to the first-stage cold head 114.

[0047] The second-stage pulse tube 12 includes a secondary intermediate heat exchanger 121 connected to the primary cold head 114 via a thermal bridge 13, a secondary high-temperature section regenerator 122 and a secondary low-temperature section regenerator 123 respectively connected to the upper and lower sides of the secondary intermediate heat exchanger 121, a secondary hot-end heat exchanger 124 connected to the secondary high-temperature section regenerator 122, a secondary cold head 125 connected to the secondary low-temperature section regenerator 123, a secondary pulse tube cold-end heat exchanger 126 connected to the secondary cold head 125 via a U-shaped connecting pipe 14, and a secondary pulse tube 130 connected to the secondary pulse tube cold-end heat exchanger 126.

[0048] In this specific embodiment of the present invention, the first-stage pulse tube 11 further includes a first-stage cold screen 115 disposed within the vacuum shroud 2. The first-stage cold head 114, the thermal bridge 13, and the intermediate low-temperature section regenerator are disposed outside the first-stage cold screen 115. Part of the structure of the second-stage pulse tube cold end heat exchanger 126, the U-shaped connecting pipe 14, and the second-stage low-temperature section regenerator 123 are all disposed within the first-stage cold screen 115.

[0049] The second-stage pulse tube 12 also includes a secondary cooling plate 127 connected to the primary cooling head 114 and in contact with the secondary cooling head 125, a secondary cooling screen 128 connected to the secondary cooling plate 127, and a first thermal switch 129 disposed between the primary cooling head 114 and the secondary cooling plate 127.

[0050] It is worth mentioning that, in this specific embodiment of the present invention, the first thermal switch 129 is a convection thermal switch, connected between the first-stage cold head 114 and the second-stage cold plate 127, for accelerating the cooling rate of the adiabatic demagnetizing refrigeration unit 30 in the initial stage of cooling of the ultra-low temperature refrigeration system 100.

[0051] Specifically, the adiabatic demagnetizing refrigeration unit 30 is disposed within the secondary cold shield 128, meaning that the adiabatic demagnetizing refrigeration unit 30 is enclosed by the secondary cold plate 127. The adiabatic demagnetizing unit specifically includes a superconducting magnet 31 disposed within the secondary cold shield 128, a magnetocaloric module 32 suspended between the superconducting magnets 31, a second thermal switch 33 disposed between the secondary cold plate 127 and the magnetocaloric module 32, and a cold end 34 connected to the magnetocaloric module 32.

[0052] The cooling principle of the adiabatic demagnetizing refrigeration unit 30 based on the magnetocaloric effect is as follows: When the temperature of the secondary cold head 125 reaches near the target pre-cooling temperature, the second thermal switch 33 is turned on to cool the superconducting magnet 31 and the magnetocaloric module 32 to near the target pre-cooling temperature. At this time, an electric current is applied to the superconducting magnet 31, thereby applying a magnetic field to the magnetocaloric module 32. The magnetocaloric module 32 generates magnetization heat, which is conducted to the secondary cold head 125 through the second thermal switch 33. When the temperature of the magnetocaloric module 32 reaches near the temperature of the secondary cold head 125, the second thermal switch 33 is turned off to demagnetize the magnetocaloric module 32, and the temperature of the magnetocaloric module 32 decreases, thus achieving cooling.

[0053] It is worth mentioning that the secondary cold head 125 of the secondary pulse tube cooling finger unit 10 provides the required pre-cooling amount for the adiabatic demagnetizing refrigeration unit 30. Specifically, the pre-cooling temperature provided by the secondary pulse tube cooling finger unit 10 for the adiabatic demagnetizing refrigeration unit 30 is 2 to 20 K, that is, the target pre-cooling temperature range of the adiabatic demagnetizing refrigeration unit 30 is 2 to 20 K.

[0054] It is also worth mentioning that the second thermal switch 33 is an active air gap thermal switch, which heats or cools the adsorption bed to desorb or adsorb the gas, thereby achieving the switching of the on and off states.

[0055] Furthermore, the pulse tube compressor unit 20 includes a pulse tube driven compressor 21 connected to the primary hot-end heat exchanger 112 and the secondary hot-end heat exchanger 124 of the pulse tube cold finger unit 10 via gas pipelines, and a phase-adjusting compressor 22 connected to the hot end of the secondary pulse tube 130.

[0056] Specifically, the pulse tube driven compressor 21 is used to drive the secondary pulse tube cooling unit 10 to cool, thereby providing the required pre-cooling capacity for the adiabatic demagnetizing refrigeration unit 30.

[0057] It should be understood that the specific structure of the cryogenic refrigeration system 100 of the present invention is not necessarily limited to the current description. Different cycles can be achieved by changing the number of stages, architecture, and quantity of the Stirling refrigeration unit 1 and the number of stages (single stage, multi-stage, isothermal stage) of the adiabatic demagnetizing refrigeration unit 30. Various minimum refrigeration temperatures and various thermal switching forms are applicable to the structure described in the present invention, and the present invention does not limit them.

[0058] It is worth mentioning that if the adiabatic demagnetizing refrigeration unit 30 adopts a single-stage structure, the magnetothermal material of the magnetothermal module 32 can be gadolinium gallium garnet or gadolinium lithium fluoride. If the adiabatic demagnetizing refrigeration unit 30 adopts a multi-stage structure, the magnetothermal material of the magnetothermal module 32 can be ferric ammonium alum or chromium potassium alum. The present invention does not impose any restrictions on this.

[0059] It is understood that, in another aspect, the present invention also provides a cooling method for the cryogenic refrigeration system 100, comprising the steps of:

[0060] Start the pulse compressor unit 20;

[0061] The pulse tube compressor unit 20 drives the pulse tube cooling finger unit 10 to provide pre-cooling capacity for the adiabatic demagnetizing refrigeration unit 30.

[0062] When the adiabatic demagnetizing refrigeration unit 30 is precooled to the target precooling temperature, an electric current is applied to the adiabatic demagnetizing refrigeration unit 30, and the adiabatic demagnetizing refrigeration unit 30 achieves refrigeration based on the magnetocaloric effect.

[0063] Specifically, taking a pre-cooling temperature of 10K and the adiabatic demagnetizing refrigeration unit 30 as a single-stage structure as an example, the refrigeration method of the ultra-low temperature refrigeration system 100 specifically includes the following steps:

[0064] During the cooling process, the pulse drive compressor 21 of the pulse compressor unit 20 is started first;

[0065] The pulse tube cold finger unit 10 is driven by the pulse tube driven compressor 21, so that the first-stage cold head 114 of the pulse tube cold finger unit 10 is cooled down.

[0066] Because of the temperature difference between the two ends of the first thermal switch 129, the internal airflow begins to convect and exchange heat, thereby causing the first thermal switch 129 to turn on automatically and accelerate the cooling rate of the adiabatic demagnetizing refrigeration unit 30.

[0067] When the temperature of the adiabatic demagnetizing refrigeration unit 30 is the same as the temperature of the first-stage cold head 114, the first thermal switch 129 is disconnected.

[0068] When the temperature of the secondary cold head 125 of the pulse tube cold finger unit 10 reaches around 10K, the second thermal switch 33 of the pulse tube cold finger unit 10 is turned on to cool the superconducting magnet 31 and the magnetocaloric module 32 of the adiabatic demagnetizing refrigeration unit 30 to around 10K.

[0069] An electric current is applied to the superconducting magnet 31, thereby applying a magnetic field to the magnetocaloric module 32. The magnetocaloric module 32 generates magnetization heat, which is then conducted to the secondary cold head 125 via the second thermal switch 33.

[0070] When the temperature of the magnetic heating module 32 reaches near the temperature of the secondary cold head 125, the second thermal switch 33 is disconnected to demagnetize the magnetic heating module 32, and the temperature of the magnetic heating module 32 decreases, thus achieving cooling.

[0071] This invention utilizes a highly efficient Stirling refrigerator coupled with an adiabatic demagnetizing refrigeration system to obtain extremely low temperatures. Compared with the traditional ultra-low temperature ADR system architecture, the ultra-low temperature refrigeration system 100 of this invention fully utilizes the advantages of the Stirling refrigerator and the ADR subsystem, and has the advantages of simple system structure, high efficiency, and high operability, making it suitable for space applications and ground scientific research.

[0072] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0073] The above embodiments merely illustrate preferred implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the protection scope of the present invention. Therefore, the protection scope of this invention should be determined by the appended claims.

Claims

1. A cryogenic refrigeration system, characterized in that, The system includes a Stirling refrigeration unit and an adiabatic demagnetizing refrigeration unit coupled to the Stirling refrigeration unit. The Stirling refrigeration unit includes a pulse tube cold finger unit connected to the adiabatic demagnetizing refrigeration unit and a pulse tube compressor unit connected to the pulse tube cold finger unit. The pulse tube compressor unit is used to drive the pulse tube cold finger unit to refrigerate, the pulse tube cold finger unit is used to provide pre-cooling capacity to the adiabatic demagnetizing refrigeration unit, and the adiabatic demagnetizing refrigeration unit is used to achieve refrigeration based on the magnetocaloric effect. It also includes a vacuum chamber, and the pulse tube cooling finger unit and the thermal insulation and demagnetizing refrigeration unit are both disposed inside the vacuum chamber; The vascular cold finger unit is a two-stage pulse cold finger unit, which includes a first-stage vascular unit with a coaxial structure and a second-stage vascular unit with a U-shaped structure. The first-stage pulse tube includes a first-stage phase modulator, a first-stage hot-end heat exchanger connected to the first-stage phase modulator, a first-stage regenerator connected to the first-stage hot-end heat exchanger, a first-stage cold head connected to the first-stage regenerator, and a first-stage pulse tube connected to the first-stage cold head. The second-stage pulse tube includes a secondary intermediate heat exchanger connected to the primary cold head via a thermal bridge, a secondary high-temperature section regenerator and a secondary low-temperature section regenerator respectively connected to the upper and lower sides of the secondary intermediate heat exchanger, a secondary hot-end heat exchanger connected to the secondary high-temperature section regenerator, a secondary cold head connected to the secondary low-temperature section regenerator, a secondary pulse tube cold-end heat exchanger connected to the secondary cold head via a U-shaped connecting pipe, and a secondary pulse tube connected to the secondary pulse tube cold-end heat exchanger.

2. The cryogenic refrigeration system according to claim 1, characterized in that, The first-stage pulse tube also includes a first-stage cold screen disposed inside the vacuum chamber. The first-stage cold head, the thermal bridge, and the first-stage regenerator are disposed outside the first-stage cold screen. Part of the structure of the second-stage pulse tube cold end heat exchanger, the U-shaped connecting pipe, and the second-stage low-temperature section regenerator are all disposed inside the first-stage cold screen. The second-stage pulse tube also includes a second-stage cold plate connected to the first-stage cold head and in contact with the second-stage cold head, a second-stage cold screen connected to the second-stage cold plate, and a first thermal switch disposed between the first-stage cold head and the second-stage cold plate; The heat insulation and demagnetization refrigeration unit is located inside the secondary cold shield.

3. The cryogenic refrigeration system according to claim 2, characterized in that, The adiabatic demagnetizing refrigeration unit includes a superconducting magnet disposed within the secondary cold screen, a magnetocaloric module suspended between the superconducting magnets, a second thermal switch disposed between the secondary cold plate and the magnetocaloric module, and a cold end connected to the magnetocaloric module.

4. The cryogenic refrigeration system according to claim 3, characterized in that, The magnetocaloric module is any one of gadolinium gallium garnet, lithium gadolinium fluoride, iron ammonium alum, and chromium potassium alum; and / or, the first thermal switch is a convection thermal switch; and / or, the second thermal switch is an active air gap thermal switch, which achieves the switching of on and off states by heating or cooling the adsorption bed to desorb or adsorb the gas.

5. The cryogenic refrigeration system according to claim 3, characterized in that, The pulse tube compressor unit includes a pulse tube driven compressor connected to a primary hot-end heat exchanger and a secondary hot-end heat exchanger of the pulse tube cold finger unit via gas pipelines, and a phase-adjusting compressor connected to the hot end of the secondary pulse tube.

6. The cryogenic refrigeration system according to any one of claims 1 to 5, characterized in that, The Stirling refrigeration unit provides a pre-cooling temperature of 2–20 K for the adiabatic demagnetizing refrigeration unit.

7. A refrigeration method for an ultra-low temperature refrigeration system according to any one of claims 1 to 5, characterized in that, Including the following steps: Start the pulse compressor unit; The pulse tube compressor unit drives the pulse tube cold finger unit for refrigeration, providing pre-cooling capacity for the adiabatic demagnetizing refrigeration unit. When the adiabatic demagnetizing refrigeration unit is precooled to the target precooling temperature, an electric current is applied to the adiabatic demagnetizing refrigeration unit, and the adiabatic demagnetizing refrigeration unit achieves refrigeration based on the magnetocaloric effect.

8. The refrigeration method of the cryogenic refrigeration system according to claim 7, characterized in that, The specific steps include: Start the pulse-driven compressor of the pulse compressor unit; The pulse tube cold finger unit is driven by the pulse tube driven compressor, thereby cooling the first-stage cold head of the pulse tube cold finger unit. Because of the temperature difference between the two ends of the first thermal switch, the internal airflow begins to convect and exchange heat, thus causing the first thermal switch to open automatically. When the temperature of the adiabatic demagnetizing refrigeration unit is the same as the temperature of the first-stage cold head, the first thermal switch is turned off. When the temperature of the secondary cold head of the pulse tube cold finger unit reaches the target pre-cooling temperature, the second thermal switch of the pulse tube cold finger unit is turned on to cool the superconducting magnet and magnetothermal module of the adiabatic demagnetizing refrigeration unit to the target pre-cooling temperature. An electric current is applied to the superconducting magnet, thereby applying a magnetic field to the magnetocaloric module. The magnetocaloric module generates magnetization heat, which is then conducted to the secondary cold head via a second thermal switch. When the temperature of the magnetic heating module reaches near the temperature of the secondary cold head, the second thermal switch is turned off to demagnetize the magnetic heating module, and the temperature of the magnetic heating module decreases, thus achieving cooling. The target precooling temperature is 2–20 K.

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