Conduction cooling type low-temperature device for superconducting magnet

Abstract

The invention relates to the technical field of superconducting magnet cooling, and discloses a superconducting magnet conduction cooling type low-temperature device which comprises a vacuum cavity, a refrigerating machine assembly is installed on the vacuum cavity, a liquid helium tank is installed at the refrigerating end of the refrigerating machine assembly, and an annular superconducting magnet is installed in the vacuum cavity. A heat conducting plate is mounted between the superconducting magnet and the refrigerating end of the refrigerating machine assembly; the sample chamber is arranged in the vacuum chamber, the sample chamber extends to the annular center of the superconducting magnet, a refrigerant pipe is communicated between the liquid helium tank and the sample chamber, a sample rod assembly is installed in the sample chamber, and one end, extending into the sample chamber, of the sample rod assembly is suitable for installing a sample body; a helium discharge pipe is communicated between the helium buffer tank and the liquid helium tank, and a discharge pipe is communicated between the sample chamber and the helium discharge pipe. The sample body works in the sample chamber and is soaked by liquid helium, so that the sample body works in a low-temperature environment all the time, and the stable low-temperature environment is maintained for the sample body for a long time.

Description

Technical Field

[0001] The invention relates to the technical field of superconducting magnet cooling, and in particular to a superconducting magnet conduction cooling type cryogenic device. Background Art

[0002] Superconducting magnets are widely used in biomedicine, scientific research instruments and other fields because they can generate strong magnetic fields. Due to the nature of superconductivity, magnets must work at liquid helium temperature. The traditional method of cooling superconducting magnets is to immerse the superconducting magnets in liquid helium. However, my country's helium resources are scarce, and helium has long been dependent on imports and is expensive. In addition, the sites using liquid helium require professional maintenance and regular replenishment of liquid helium, making the liquid helium-immersed superconducting magnet system complex and costly. Compared with liquid helium-immersed superconducting magnets, the cost of using a cryogenic refrigerator to cool a superconducting magnet is lower, the system structure is simpler and the maintenance time is shorter. The use of high-field, high-uniformity superconducting magnets without liquid helium is the current trend in the research and development and use of magnets.

[0003] In the prior art, the method of cooling the magnet by conduction is to connect the secondary cold head of the refrigerator directly to the superconducting magnet using a heat-conducting device such as copper braiding, and then place the sample at the center of the superconducting magnet, use the superconducting magnet to provide a magnetic field for the sample, and use the secondary cold head to provide a vacuum environment for the superconducting magnet and the space where the sample is located. For a low-temperature refrigerator, the cooling capacity of the secondary cold head is extremely precious, and its heat load includes magnet AC loss, thermal radiation, thermal conduction, etc. However, existing low-temperature refrigerators for superconducting magnets usually connect the secondary cold head to the superconducting magnet through heat-conducting parts such as copper, and then provide a low-temperature environment for the sample by heat conduction. However, the setting of the heat-conducting parts will inevitably lead to the loss of cooling capacity during the conduction process, causing the low-temperature environment temperature in the magnet area to be unstable, affecting the working performance of the sample. Summary of the invention

[0004] In view of this, the present invention provides a superconducting magnet conduction cooling type cryogenic device to solve the problem of unstable low temperature environment generated by the conduction cooling superconducting magnet cryogenic system in the superconducting magnet region.

[0005] In order to solve the above technical problems, the present invention provides a superconducting magnet conduction cooling type cryogenic device, comprising:

[0006] A vacuum cavity is provided with a refrigerator assembly, a liquid helium tank is provided at the refrigeration end of the refrigerator assembly, a superconducting magnet is provided in the vacuum cavity, the superconducting magnet is in a ring shape, and a heat conducting plate is provided between the superconducting magnet and the refrigeration end of the refrigerator assembly;

[0007] The sample chamber is arranged in the vacuum chamber, the sample chamber extends to the annular center of the superconducting magnet, a refrigerant pipe is connected between the liquid helium tank and the sample chamber, a sample rod assembly is installed in the sample chamber, and one end of the sample rod assembly extending into the sample chamber is suitable for installing the sample body;

[0008] A helium discharge pipe is connected between the helium buffer tank and the liquid helium tank, and a discharge pipe is connected between the sample chamber and the helium discharge pipe.

[0009] Before using the superconducting magnet conduction cooling cryogenic device, the sample chamber is evacuated as a whole, and the pre-stored high-purity helium is stored in the helium buffer tank. When the sample needs to work in a low-temperature environment, the helium is output from the helium buffer tank through the helium discharge pipe and enters the refrigeration end of the refrigerator assembly, and is cooled by the refrigerator to become liquid helium. The temperature drops below 4.2K, and the liquid helium is finally stored in the liquid helium tank. The coldness of the liquid helium cools the superconducting magnet to below the superconducting critical temperature through the heat conduction plate. The superconducting magnet enters the superconducting state, can be powered on and excited, and a strong magnetic field is generated in the center. The sample rod assembly carrying the sample body is inserted into the sample chamber in the ring center of the superconducting magnet, so that the liquid helium inside the liquid helium tank is output from the refrigerant pipe into the sample chamber, and the sample body is soaked in liquid helium. The sample body can always be in a liquid helium environment, so that the sample body always works in a temperature environment of 2K, and a stable low-temperature environment can be maintained for a long time for the sample body. During the operation of the sample body, the gasified helium can return from the discharge pipe to the helium discharge pipe, and then be cooled by the refrigerator component again to become liquid helium and enter the liquid helium tank. This makes it unnecessary to replenish the liquid helium during the operation of the cryogenic device, and it is unnecessary to replace the liquid helium tank or refrigerator component, thus ensuring that the sample body can work continuously and stably in a low-temperature environment for a long time.

[0010] In an optional embodiment, the refrigerator assembly includes a cryogenic refrigerator and a refrigerator cold head, a helium liquefaction heat exchanger is mounted on the refrigerator cold head, and the helium liquefaction heat exchanger extends into the liquid helium tank.

[0011] By setting the liquid helium tank and the cryogenic refrigerator to be separate, the cold energy generated on the cold head of the cryogenic refrigerator during operation is transferred to the helium by using the helium liquefaction heat exchanger, so that the helium is liquefied in the liquid helium tank. When replacing the cryogenic refrigerator, the cryogenic refrigerator can be directly removed from the cryogenic cavity, and the replaced cryogenic refrigerator can be directly inserted without opening the entire cryogenic device, which greatly reduces the complexity of replacing the cryogenic refrigerator and shortens the replacement time.

[0012] In an optional embodiment, the refrigerator cold head includes a primary cold head and a secondary cold head, the helium discharge pipe is connected to the primary cold head through a heat exchanger, and the helium discharge pipe is connected to the secondary cold head through a spiral tube; a radiation screen is also provided in the vacuum chamber, the radiation screen is surrounded to form a closed space, the primary cold head is in contact with the radiation screen, and the sample chamber extends into the closed space; the heat conduction plate is in contact with the secondary cold head.

[0013] By setting up a radiation screen, utilizing the closed space formed by the radiation screen to wrap the sample body or the superconducting magnet and the sample body inside the radiation screen, and utilizing the cold energy on the first-stage cold head on the low-temperature refrigerator for cooling, the heat load on the superconducting magnet or the sample body caused by thermal radiation at room temperature can be greatly reduced.

[0014] In an optional implementation, an upper bellows is installed between the inner wall of the vacuum chamber and the first-stage cold head, and a lower bellows is installed between the radiation shield and the second-stage cold head.

[0015] The upper bellows and the lower bellows are both made of metal pipes with elastic functions. The upper bellows and the lower bellows are used to cooperate with each other to install the first-stage cold head, the radiation screen and the second-stage cold head between the liquid helium tank and the vacuum chamber by extrusion. After the cryogenic refrigerator is installed, the vacuum chamber is evacuated before the cryogenic refrigerator can be turned on. By using the upper bellows and the lower bellows to cooperate with each other to extrude and install other components other than the cryogenic refrigerator in the refrigerator assembly, the cryogenic refrigerator is a separate component separated from the first-stage cold head and the second-stage cold head. When the cryogenic refrigerator is installed, there is no need to use screws and other parts to connect them internally, so that the object to be cooled can be cooled, and the cryogenic refrigerator can be installed and used separately by direct plug-in, which is easy to replace.

[0016] In an optional embodiment, the cryogenic refrigerator and the vacuum chamber are fixed via a connecting flange, and a shock-absorbing pad is installed between the cryogenic refrigerator and the connecting flange;

[0017] And / or, the first-stage cold head and the radiation screen are fixed via a first welding flange;

[0018] And / or, the secondary cold head and the liquid helium tank are fixed via a second welding flange.

[0019] In an optional embodiment, an upper head is installed at the open end of the liquid helium tank, a helium liquefaction heat exchanger is installed on the side of the upper head facing the inner cavity of the liquid helium tank, and the cold head of the refrigerator is thermally connected to the helium liquefaction heat exchanger through the upper head.

[0020] In an optional embodiment, the helium liquefaction heat exchanger is a finned heat exchanger, and the helium liquefaction heat exchanger is arranged vertically to the upper head.

[0021] In an optional embodiment, a detour is provided in the area of ​​the refrigerant tube close to the liquid helium tank, and the maximum height position of the detour is not lower than the upper top surface of the liquid helium tank body. By providing a detour on the refrigerant tube, the liquid level inside the refrigerant tube is higher than the liquid helium tank. When the sample body does not need to be cooled, the liquid helium is stored in the liquid helium tank. Because the position of the detour is higher than the liquid helium tank, the liquid helium cannot flow out through the refrigerant tube under its own gravity. When the sample body needs to be cooled, it is necessary to provide a pressure difference for the liquid helium under the action of an external force, and the liquid helium can flow out of the refrigerant tube and pass over the detour into the cooling cavity at the bottom of the sample chamber for holding the sample body to cool the sample body.

[0022] In an optional implementation, a low-temperature throttle valve is installed on the refrigerant pipe.

[0023] By setting a low-temperature throttle valve, the liquid helium output from the liquid helium tank and entering the refrigerant pipe is throttled and cooled by the low-temperature throttle valve before entering the sample chamber, thereby reducing the temperature and liquefaction degree of the liquid helium entering the sample chamber.

[0024] In an optional embodiment, a heating element is further installed in the sample chamber, and the heating element extends to one end of the sample rod assembly suitable for installing the sample body.

[0025] When the sample body is finished working, the heating element works to vaporize the liquid helium in the sample chamber. The vaporized helium enters the helium discharge pipe through the discharge pipe and returns to the helium buffer tank for storage.

[0026] In an optional embodiment, a dry vacuum pump is installed on the discharge pipe, a first control valve is installed upstream of the dry vacuum pump and / or a second control valve is installed downstream of the dry vacuum pump; and / or a third control valve is installed on the helium discharge pipe, and the connection point between the discharge pipe and the helium discharge pipe is located upstream of the third control valve. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0028] Figure 1 A schematic diagram of the structure of a superconducting magnet conduction cooling type cryogenic device provided in an embodiment of the present invention.

[0029] Figure 2 A schematic structural diagram of a refrigerator assembly provided in an embodiment of the present invention.

[0030] Figure 3A schematic diagram of the structure of the upper bellows and the lower bellows provided in an embodiment of the present invention in cooperation with each other.

[0031] Figure 4 A schematic structural diagram of a liquid helium tank provided in an embodiment of the present invention.

[0032] Figure 5 A schematic structural diagram of a sample rod assembly provided in an embodiment of the present invention.

[0033] Description of reference numerals: 1. dry vacuum pump; 2. first control valve; 3. sample rod assembly; 301. external lead wire; 302. vacuum port; 303. mounting flange; 304. helium filling port; 305. internal gas channel port; 306. measuring lead wire; 307. sample base; 4. sample chamber; 5. vacuum chamber; 6. radiation screen; 7. sample body; 8. sample stage; 9. discharge pipe; 10. superconducting magnet; 11. support frame; 12. second control valve; 13. third control valve; 14. refrigerator assembly; 1401. low temperature refrigerator; 14 02. Shock-absorbing pad; 1403. Upper bellows; 1404. Primary cold head; 1405. First welding flange; 1406. Lower bellows; 1407. Second welding flange; 1408. Connecting flange; 1409. Connecting block; 1410. Secondary cold head; 1411. Upper head; 1412. Helium liquefaction heat exchanger; 1413. Liquid helium tank; 1414. Lower head; 15. Heat transfer device; 16. Spiral tube; 17. Helium discharge pipe; 18. Helium buffer tank; 19. Magnetic heat conduction plate; 20. Refrigerant pipe; 21. Heating wire; 22. Low-temperature throttle valve. DETAILED DESCRIPTION

[0034] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0035] Combine the following Figures 1 to 5 , describing an embodiment of the present invention.

[0036] According to an embodiment of the present invention, a superconducting magnet 10 conduction cooling type cryogenic device is provided, comprising a vacuum cavity 5, a sample chamber 4 and a helium buffer tank 18. A refrigerator assembly 14 is installed on the vacuum cavity 5, a liquid helium tank 1413 is installed at the cooling end of the refrigerator assembly 14, a superconducting magnet 10 is installed in the vacuum cavity 5, the superconducting magnet 10 is annular, and a heat conduction plate is installed between the superconducting magnet 10 and the cooling end of the refrigerator assembly 14. The sample chamber 4 is arranged in the vacuum cavity 5, the sample chamber 4 extends to the center of the annular shape of the superconducting magnet 10, a refrigerant pipe 20 is connected between the liquid helium tank 1413 and the sample chamber 4, a sample rod assembly 3 is installed in the sample chamber 4, and one end of the sample rod assembly 3 extending into the sample chamber 4 is suitable for installing a sample body 7. A helium discharge pipe 17 is connected between the helium buffer tank 18 and the liquid helium tank 1413, and an exhaust pipe 9 is connected between the sample chamber 4 and the helium discharge pipe 17.

[0037] Before the superconducting magnet 10 conduction cooling type cryogenic device is used, the sample chamber 4 is evacuated as a whole, and the pre-stored high-purity helium is stored in the helium buffer tank 18. When the sample needs to work in a low-temperature environment, the helium is output from the helium buffer tank 18 through the helium discharge pipe 17 and enters the refrigeration end of the refrigerator assembly 14, and is cooled by the refrigerator to become liquid helium, and the temperature drops below 4.2.K. The liquid helium is finally stored in the liquid helium tank 1413. The coldness of the liquid helium cools the superconducting magnet 10 to below the superconducting critical temperature through the heat conduction plate, and the superconducting magnet 10 enters the superconducting state, and can be electrically excited and generate a strong magnetic field at the center. The sample rod assembly 3 carrying the sample body 7 is inserted into the sample chamber 4 at the annular center of the superconducting magnet 10, so that the liquid helium inside the liquid helium tank 1413 is output from the refrigerant tube 20 into the sample chamber 4, and the sample body 7 is soaked in liquid helium, so that the sample body 7 can always be in a liquid helium environment, so that the sample body 7 always works in a temperature environment below 4.2K, and a stable low-temperature environment can be maintained for a long time for the sample body 7. During the operation of the sample body 7, the gasified helium can return from the discharge pipe to the helium discharge pipe 17, and is cooled again by the refrigerator assembly 14 to become liquid helium and enter the liquid helium tank 1413. It is unnecessary to replenish the liquid helium during the operation of the cryogenic device, and it is unnecessary to replace the liquid helium tank 1413 or the refrigerator assembly 14, thereby ensuring that the sample body 7 can work continuously and stably in a low-temperature environment for a long time.

[0038] In one embodiment, the refrigerator assembly 14 includes a cryogenic refrigerator 1401 and a refrigerator cold head, on which a helium liquefaction heat exchanger 1412 is mounted, and the helium liquefaction heat exchanger 1412 extends into a liquid helium tank 1413. The cryogenic refrigerator 1401 is used to generate cold energy, and the refrigerator cold head is used to output the cold energy generated by the cryogenic refrigerator 1401 to the outside. The helium liquefaction heat exchanger 1412 transfers the cold energy output by the refrigerator cold head to the helium gas entering the liquid helium tank 1413 from the helium discharge pipe 17, so that the helium gas is cooled and liquefied into liquid helium and temporarily stored in the liquid helium tank 1413.

[0039] By setting the liquid helium tank 1413 and the cryogenic refrigerator 1401 as a split type, the cold energy generated on the cold head of the cryogenic refrigerator 1401 during operation is transferred to the helium by the helium liquefaction heat exchanger 1412, so that the helium is liquefied in the liquid helium tank 1413. When replacing the cryogenic refrigerator 1401, the cryogenic refrigerator 1401 can be directly removed from the cryogenic cavity, and the replaced cryogenic refrigerator 1401 can be directly inserted without opening the entire cryogenic device, which greatly reduces the complexity of replacing the cryogenic refrigerator 1401 and shortens the replacement time.

[0040] In one embodiment, the refrigerator cold head includes a primary cold head 1404 and a secondary cold head 1410, the helium discharge pipe 17 is connected to the primary cold head 1404 through a heat transfer device 15, and the helium discharge pipe 17 is connected to the secondary cold head 1410 through a spiral tube 16. A radiation screen 6 is also provided in the vacuum chamber 5, and the radiation screen 6 is surrounded to form a closed space, the primary cold head 1404 is in contact with the radiation screen 6, and the sample chamber 4 extends into the closed space; the heat conducting plate is in contact with the secondary cold head 1410.

[0041] Part of the helium in the helium discharge pipe 17 enters the primary cold head 1404 through the heat transfer device 15 for heat exchange and cooling, and the remaining part of the helium enters the secondary cold head 1410 through the spiral tube 16 for heat exchange and cooling and liquefaction. By setting the radiation screen 6, the sample body 7 or the superconducting magnet 10 and the sample body 7 are wrapped inside the radiation screen 6 by using the closed space formed by the radiation screen 6, and the radiation screen 6 is cooled by using the cold energy on the primary cold head 1404 on the low-temperature refrigerator 1401, so that the closed space formed by the radiation screen 6 can maintain a low temperature level, avoiding the heat generated by the working of the components in the device and the ambient temperature from affecting the temperature of the sample body 7, and can greatly reduce the heat load of the superconducting magnet 10 or the sample body 7 caused by thermal radiation at room temperature.

[0042] In one embodiment, an upper bellows 1403 is installed between the inner wall of the vacuum chamber 5 and the primary cold head 1404, and a lower bellows 1406 is installed between the radiation shield 6 and the secondary cold head 1410. When the temperature of the primary cold head 1404 and the secondary cold head 1410 changes, due to thermal expansion and contraction, the distance between the primary cold head 1404 and the secondary cold head 1410 will be deformed. Since the thermal expansion and contraction coefficients of various parts in the device are different, the deformation amounts when deformation occurs are different. The upper bellows 1403 and the lower bellows 1406 are both made of metal pipes with elastic functions, thereby eliminating the influence of the deformation of the primary cold head 1404 and the secondary cold head 1410 on the device during the temperature change process. At the same time, the upper bellows 1403 and the lower bellows 1406 are used to cooperate with each other, and the primary cold head 1404, the radiation shield 6 and the secondary cold head 1410 are installed between the liquid helium tank 1413 and the vacuum chamber 5 by extrusion. After the low temperature refrigerator 1401 is installed, the vacuum chamber 5 is evacuated before the low temperature refrigerator 1401 can be turned on. By using the upper bellows 1403 and the lower bellows 1406 to cooperate with each other to squeeze and install the other components other than the low temperature refrigerator 1401 in the refrigerator assembly 14, the low temperature refrigerator 1401 is a separate component separated from the primary cold head 1404 and the secondary cold head 1410. When the low temperature refrigerator 1401 is installed, it is not necessary to use screws and other parts to connect them internally, so that the object to be cooled can be cooled, and the low temperature refrigerator 1401 can be installed and used in a separate direct plug-in manner, which is easy to replace.

[0043] In one embodiment, the cryogenic refrigerator 1401 is sealed and fixed to the vacuum chamber 5 by a connecting flange 1408, so as to facilitate the installation and removal of the cryogenic refrigerator 1401 on the vacuum chamber 5. A shock-absorbing pad 1402 is installed between the cryogenic refrigerator 1401 and the connecting flange 1408 to prevent the displacement between the cryogenic refrigerator 1401 and the connecting flange 1408 caused by thermal vibration during the temperature change process, thereby ensuring the stability of the connection between the cryogenic refrigerator 1401 and the vacuum chamber 5. The first-stage cold head 1404 is fixed to the radiation shield 6 by a first welding flange 1405. The second-stage cold head 1410 is fixed to the liquid helium tank 1413 by a second welding flange 1407.

[0044] Furthermore, an upper end cap 1411 is installed at the open end of the liquid helium tank 1413, and a helium liquefaction heat exchanger 1412 is installed on the side of the upper end cap 1411 facing the inner cavity of the liquid helium tank 1413, and the refrigerator cold head is thermally connected to the helium liquefaction heat exchanger 1412 through the upper end cap 1411. A lower end cap 1414 is installed on the lower side of the liquid helium tank 1413, and the upper end cap 1411 transfers the cold energy from the secondary cold head 1410, so that the helium gas is liquefied in the liquid helium tank 1413 to form liquid helium. The lower end cap 1414 transfers the cold energy in the liquid helium to the magnet heat conduction plate 19, thereby cooling the superconducting magnet 10.

[0045] In this embodiment, the helium liquefaction heat exchanger 1412 is a fin heat exchanger or a foam copper heat exchanger, which increases the helium contact area and improves the heat exchange efficiency, thereby reducing the helium liquefaction time. The helium liquefaction heat exchanger 1412 is arranged vertically with the upper head 1411.

[0046] In one embodiment, a detour is provided in the area of ​​the refrigerant tube 20 near the liquid helium tank 1413, and the maximum height position of the detour is not lower than the upper top surface of the liquid helium tank 1413. By providing a detour on the refrigerant tube 20, the liquid level inside the refrigerant tube 20 is higher than the liquid helium tank 1413. When the sample body 7 does not need to be cooled, the liquid helium is stored in the liquid helium tank 1413. Because the position of the detour is higher than the liquid helium tank 1413, the liquid helium cannot flow out through the refrigerant tube 20 under its own gravity. When the sample body 7 needs to be cooled, it is necessary to provide a pressure difference for the liquid helium under the action of an external force, and the liquid helium can flow out of the refrigerant tube 20 and pass over the detour into the cooling cavity at the bottom of the sample chamber 4 for holding the sample body 7 to cool the sample body 7.

[0047] In one embodiment, a cryogenic throttle valve 22 is installed on the refrigerant pipe 20. By providing the cryogenic throttle valve 22, the liquid helium output from the liquid helium tank 1413 and entering the refrigerant pipe 20 is throttled and cooled by the cryogenic throttle valve 22 before entering the sample chamber 4, thereby reducing the temperature and liquefaction degree of the liquid helium entering the sample chamber 4.

[0048] In one embodiment, a heating element is further installed in the sample chamber 4, and the heating element extends to one end of the sample rod assembly 3 suitable for installing the sample body 7. When the sample body 7 is finished working, the heating element works to make the liquid helium in the sample chamber 4 completely gasified, and the gasified helium enters the helium discharge pipe 17 through the exhaust pipe and returns to the helium buffer tank 18 for storage.

[0049] In one embodiment, a dry vacuum pump 1 is installed on the discharge pipe to drive the liquid helium or helium or a mixed fluid of the two in the discharge pipe to return from the discharge pipe to the helium discharge pipe 17 or the helium buffer tank 18 for reuse. A first control valve 2 is installed upstream of the dry vacuum pump 1, and a second control valve 12 is installed downstream of the dry vacuum pump 1. The first control valve 2 and the second control valve 12 are respectively used to control the flow rate of the fluid upstream and downstream of the dry vacuum pump 1 and the on-off of the discharge pipe. A third control valve 13 is installed on the helium discharge pipe 17. The connection point between the discharge pipe and the helium discharge pipe 17 is located upstream of the third control valve 13. The third control valve 13 is used to control whether the helium buffer tank 18 is connected to the liquid helium tank 1413. When the third control valve 13 is opened, the helium buffer tank 18 is connected to the liquid helium tank 1413, and the helium in the helium buffer tank 18 flows to the liquid helium tank 1413 through the helium discharge pipe 17; when the third control valve 13 is closed, the helium buffer tank 18 is not connected to the liquid helium tank 1413, and the helium sent back to the helium discharge pipe 17 from the discharge pipe flows back to the helium buffer tank 18 through the helium discharge pipe 17 and is stored again.

[0050] The conduction cooling cryogenic device of the superconducting magnet 10 is evacuated as a whole before use. High-purity helium is stored in the helium buffer tank 18, and enters the pipeline inside the system after passing through the helium discharge pipe 17 and the third control valve 13. The helium inside the pipeline enters the first-stage cold head 1404 through the heat transfer device 15 to be cooled to about 50K, and the subsequent part of the helium enters the liquid helium tank 1413 through the spiral tube 16. The helium is liquefied into liquid helium in the liquid helium tank 1413 component, and the temperature drops below 4.2K. The coldness of the liquid helium cools the superconducting magnet 10 to below the superconducting critical temperature through the magnet heat conduction plate 19, and the superconducting magnet 10 enters the superconducting state, which can be excited by electricity and generate a strong magnetic field at the center.

[0051] The sample rod assembly 3 is inserted into the sample chamber 4 at the center of the superconducting magnet 10. The bottom of the sample chamber 4 is the sample stage 8, and the sample stage 8 is in contact with the bottom of the sample rod. The second function of the liquid helium in the liquid helium tank 1413 is to cool the sample. The cooling method is to open the first control valve 2, the second control valve 12 and the third control valve 13, start the dry vacuum pump 1, and start the liquid helium circulation. The dry vacuum pump 1 generates a pressure difference when it works. Driven by the pressure difference, the liquid helium enters the low-temperature throttle valve 22 through the liquid helium pipe, and the temperature of the liquid helium is further reduced to below 2K. The liquid helium reaches the bottom of the sample chamber 4 to cool the sample stage 8 and then cool the sample body 7. The liquid helium after releasing the cold energy is vaporized to form helium, and then reaches the external first control valve 2 from the exhaust pipe 9 to complete the cycle. The sample stage 8 is in thermal contact with the bottom of the sample rod assembly 3. When the sample stage 8 is cooled by the liquid helium, the sample body 7 in the sample rod assembly 3 will also be cooled. When there is no need to cool the sample body 7 , the heating wire 21 as a heating element is started to heat the sample stage 8 so that the liquid helium in the sample chamber 4 is completely gasified and discharged.

[0052] The function of the radiation shield 6 is to reduce the heat load of the radiation at room temperature on the superconducting magnet 10. The radiation shield 6 cools the cold transferred by the primary cold head 1404 and the first welding flange 1405 in the refrigerator assembly 14. A support frame 11 is installed at the bottom of the superconducting magnet 10 to support and fix the superconducting magnet 10 inside the vacuum chamber 5, reduce the heat load of the superconducting magnet 10 caused by heat conduction, and enable the magnet to withstand the impact force during transportation.

[0053] In the refrigerator assembly 14, the low-temperature refrigerator 1401 uses a Gifford-McMahon cycle refrigerator; a GM refrigerator, or a pulse tube refrigerator. It can generate a cooling capacity below 4.2K at the secondary cold head 1410 and a cooling capacity in the temperature range of 40K to 50K at the primary cold head 1404. The surface of the secondary cold head 1410 is padded with an indium sheet, which is extruded and installed on the second welding flange 1407. The cooling capacity below the temperature range of 4.2K is transferred from the secondary cold head 1410 to the second welding flange 1407, and then to the inside of the liquid helium tank 1413, thereby liquefying the helium. The surface of the primary cold head 1404 is padded with an indium sheet, and the cooling capacity of the primary cold head 1404 is transferred to the first welding flange 1405 by extrusion. The radiation screen 6 installed thereon and the connecting block 1409 for connecting the heat transferr 15 are cooled to below 50K.

[0054] In the refrigerator installation assembly, the low-temperature refrigerator 1401 is installed at the corresponding installation position on the vacuum chamber 5 through the connecting flange 1408. The upper bellows 1403 and the lower bellows 1406 are metal pipes with elastic function. After the low-temperature refrigerator 1401 is installed, the first-level cold head 1404 and the second-level cold head 1410 can be thermally contacted with the first welding flange 1405 and the second welding flange 1407 respectively, and have the advantage of low heat leakage. The first welding flange 1405 and the second welding flange 1407 play the role of transferring the coldness of the first-level cold head 1404 and the second-level cold head 1410 to the object to be cooled. After the low-temperature refrigerator 1401 is installed, the low-temperature refrigerator 1401 can be turned on only after the vacuum chamber 5 is evacuated as a whole. The refrigerator assembly 14 can enable the low-temperature refrigerator 1401 to be installed without using parts such as screws inside, and the object to be cooled can be cooled. The low-temperature refrigerator 1401 can be installed and used in a direct plug-in manner. The GM refrigerator in the prior art has holes on its first-stage cold head 1404 and second-stage cold head 1410. In order to ensure that the object to be cooled is tightly connected to the cold head, bolts are generally used to lock the cold head and the object to be cooled. However, this will cause the problem of difficulty in removal, because the working environment of the refrigerator and the object to be cooled is vacuum and low temperature. If the refrigerator is to be replaced, the bolts between the object to be cooled and the cold head must be removed, which will definitely destroy the vacuum and low temperature environment of the object to be cooled, and removal will become very difficult. In the refrigerator assembly 14 provided in this embodiment, the connection between the low-temperature refrigerator 1401, the first-stage cold head 1404, and the second-stage cold head 1410 does not require the use of bolts. Because the bellows is a stainless steel tube with a telescopic structure, when the cryogenic refrigerator 1401 is installed, a force will be applied to the upper bellows 1403 and the lower bellows 1406, and the upper bellows 1403 and the lower bellows 1406 will react to give pressure to the cryogenic refrigerator 1401. This pressure will cause the first-level cold head 1404 of the cryogenic refrigerator 1401 to be tightly connected to the first welding flange 1405, and the second-level cold head 1410 to be tightly connected to the second welding flange 1407. The object to be cooled only needs to be connected to the first welding flange 1405 or the second welding flange 1407 to ensure heat transfer, and the cryogenic refrigerator 1401 is mechanically isolated without affecting heat transfer. When replacing the cryogenic refrigerator 1401, there is no need to destroy the environment of the object to be cooled, and the cryogenic refrigerator 1401 can be taken out separately. Because the cold head of the refrigerator assembly 14 except the motor is slender, installation and removal are similar to plugging and unplugging data cables, so it is called a plug-in structure.

[0055] In the liquid helium tank 1413, the upper head 1411 transfers the cold from the secondary cold head 1410, and the lower head 1414 transfers the cold to the magnet heat conduction plate 19 to cool the superconducting magnet 10. The helium liquefaction heat exchanger 1412 is a finned heat exchanger or a foam copper heat exchanger, which increases the helium contact area and improves the heat exchange efficiency, thereby reducing the time for helium liquefaction. The conduction cooling type cryogenic device for the superconducting magnet 10 provided in this embodiment adopts dual-target cooling of the superconducting magnet 10 and the sample body 7, including a refrigerator assembly 14 to liquefy helium, and then cools the superconducting magnet 10 by conduction; the first stage adjusts the liquid helium flow rate through a throttle valve and a dry vacuum pump 1 to cool the sample stage 8 and the sample body 7. The cryogenic device not only cools the sample body 7 but also cools the superconducting magnet 10, because the superconducting magnet 10 must be at a low temperature to reach the superconducting state and work normally, and sample cooling is a requirement for sample testing. The superconducting magnet 10 is cooled to 4.2K and remains constant, while the operating temperature range of the sample body 7 is between 2K and 300K. Different sample bodies 7 have different cooling requirements. For the cooling of the superconducting magnet 10, a magnet heat conduction plate 19 is installed at the bottom of the liquid helium tank 1413, and the magnet is cooled by conduction cooling. Because the temperature of the liquid helium in the liquid helium tank 1413 is maintained at 4.2K, this can meet the cooling requirements of the conductive magnet to maintain a stable low temperature. For the cooling and temperature control of the sample, a method of liquid helium circulation cooling combined with heating by a heating wire 21 is used. A refrigerant pipe 20 is led out of the liquid helium tank 1413. After throttling by a low-temperature throttle valve 22, the temperature of the liquid helium can be reduced to below 2K, cooling the sample chamber 4 at the bottom of the sample rod assembly 3. The sample stage 8 is arranged inside the sample chamber 4. The sample stage 8 is made of copper and has good thermal conductivity. The sample stage 8 is in contact with the sample body 7 at the bottom of the sample rod body, so the liquid helium can further cool the sample body 7 to a low temperature after cooling the sample stage 8 in the sample chamber 4. A detour is set after the refrigerant pipe 20 is led out from the liquid helium tank 1413, so that the highest liquid level in the detour is higher than the top of the liquid helium tank 1413. When the sample does not need to be cooled, the liquid helium is stored in the liquid helium tank 1413. Because the highest position of the detour is higher than the liquid helium tank 1413, the liquid helium cannot flow out of the detour. When the sample needs to be cooled, the dry vacuum pump 1 runs to provide a pressure difference, and the liquid helium can flow out of the refrigerant pipe 20 and pass through the detour through the low-temperature throttle valve 22 into the sample chamber 4.

[0056] In the sample rod assembly 3, the sample rod body is mounted on the sample chamber 4 through the mounting flange 303, and forms a closed cavity with the sample chamber 4. An exhaust channel is provided inside the sample rod body, and a vacuum port 302 is provided above the sample rod body to communicate with the exhaust channel, so that the gas inside the sample chamber 4 can be evacuated to a vacuum through the internal gas channel port 305 on the side wall of the sample rod body. The helium filling port 304 is used to flush the residual gas in the sample chamber 4. After the vacuum is exhausted, high-purity helium is filled into the sample chamber 4 through the helium filling port 304, and then the vacuum is exhausted again. The flushing is repeated three times and finally evacuated to a vacuum, ensuring that the gas component remaining in the sample chamber 4 is helium, and the sample will not frost and damage the sample body 7 after the sample is cooled down. The sample body 7 is installed on the sample stage 8. The sample stage 8 is made of copper and is equipped with a thermometer. The thermal contact with the heat exchange base can cool the sample body 7. At the same time, the circuit is connected inside the sample base 307. The measuring lead 306 is connected to the sample base 307 and extends from the top of the sample rod body to the outside of the sample rod body, thereby leading the electrical signal to the external lead 301 to convert the electrical signal into a temperature signal and collect it.

[0057] The sample rod assembly 3 is a subsystem for measuring the sample, and the other components of the system provide low temperature and magnetic field to the sample. After welding the four leads to the sample body 7, use low-temperature varnish or low-temperature thermal grease to stick it to the sample base 307 at the bottom of the sample rod body to fix the sample body 7 and enhance heat transfer. The four leads are connected to the measurement leads 306, and are connected to the current and voltage meter and the computer acquisition system through the external leads 301. After the sample rod assembly 3 is inserted into the sample chamber 4, a closed environment is formed in the sample chamber 4. In order to reduce heat leakage, the sample chamber 4 needs to be evacuated. The interior of the sample rod body is a hollow structure, and the vacuum port 302 is connected to the vacuum pump. The gas in the sample chamber 4 enters the interior of the sample rod body from the internal gas channel port 305, and is finally extracted from the vacuum port 302. When the measurement is completed and the next sample is replaced, the gas environment in the sample chamber 4 must be protected, because the wall temperature of the sample chamber 4 that has just been measured is still relatively low. If air is allowed to enter, water vapor in the air may condense and accumulate in the sample chamber 4, causing damage. Therefore, helium must be filled in before changing the sample to protect the environment in the sample chamber 4. Helium is filled in through the helium filling port 304. After the sample chamber 4 is filled with helium at one atmospheric pressure and the temperature rises to room temperature, the sample rod assembly 3 can be taken out and replaced with the next measurement sample.

[0058] Although the embodiments of the present invention have been described in conjunction with the accompanying drawings, those skilled in the art may make various modifications and variations without departing from the spirit and scope of the present invention, and such modifications and variations are all within the scope defined by the appended claims.

Claims

1. A superconducting magnet conduction cooling type cryogenic device, characterized in that: include: A vacuum chamber (5) is provided with a refrigerator assembly (14), a liquid helium tank (1413) is provided at a cooling end of the refrigerator assembly (14), a superconducting magnet (10) is provided in the vacuum chamber (5), the superconducting magnet (10) is annular, and a heat conduction plate is provided between the superconducting magnet (10) and the cooling end of the refrigerator assembly (14); A sample chamber (4) is arranged in the vacuum chamber (5), the sample chamber (4) extends to the annular center of the superconducting magnet (10), a refrigerant pipe (20) is connected between the liquid helium tank (1413) and the sample chamber (4), a sample rod assembly (3) is installed in the sample chamber (4), and one end of the sample rod assembly (3) extending into the sample chamber (4) is suitable for installing a sample body (7); A helium discharge pipe (17) is connected between the helium buffer tank (18) and the liquid helium tank (1413), and a discharge pipe (9) is connected between the sample chamber (4) and the helium discharge pipe (17).

2. The superconducting magnet conduction cooling type cryogenic device according to claim 1, characterized in that: The refrigerator assembly (14) comprises a low-temperature refrigerator (1401) and a refrigerator cold head, a helium liquefaction heat exchanger (1412) is mounted on the refrigerator cold head, and the helium liquefaction heat exchanger (1412) extends into the liquid helium tank (1413).

3. The superconducting magnet conduction cooling type cryogenic device according to claim 2, characterized in that: The refrigerator cold head comprises a primary cold head (1404) and a secondary cold head (1410); the helium discharge pipe (17) is connected to the primary cold head (1404) via a heat transfer device (15); and the helium discharge pipe (17) is connected to the secondary cold head (1410) via a spiral pipe (16); A radiation screen (6) is also provided in the vacuum cavity (5), the radiation screen (6) is arranged to form a closed space, the first-level cold head (1404) is in contact with and connected to the radiation screen (6), and the sample chamber (4) extends into the closed space; The heat conducting plate is in contact with and connected to the secondary cold head (1410).

4. The superconducting magnet conduction cooling type cryogenic device according to claim 3, characterized in that: An upper bellows (1403) is installed between the inner wall of the vacuum chamber (5) and the first-stage cold head (1404), and / or a lower bellows (1406) is installed between the radiation screen (6) and the second-stage cold head (1410).

5. The superconducting magnet conduction cooling type cryogenic device according to claim 3 or 4, characterized in that: The low-temperature refrigerator (1401) and the vacuum chamber (5) are fixed via a connecting flange (1408), and a shock-absorbing pad (1402) is installed between the low-temperature refrigerator (1401) and the connecting flange (1408); And / or, the first-stage cold head (1404) and the radiation screen (6) are fixed via a first welding flange (1405); And / or, the secondary cold head (1410) and the liquid helium tank (1413) are fixed via a second welding flange (1407).

6. The superconducting magnet conduction cooling type cryogenic device according to any one of claims 2 to 4, characterized in that: An upper sealing head (1411) is installed at the open end of the liquid helium tank (1413), the helium liquefaction heat exchanger (1412) is installed on a side of the upper sealing head (1411) facing the inner cavity of the liquid helium tank (1413), and the cold head of the refrigerator is heat-conductingly connected to the helium liquefaction heat exchanger (1412) through the upper sealing head (1411).

7. The superconducting magnet conduction cooling type cryogenic device according to any one of claims 1 to 4, characterized in that: A detour is provided in the area of ​​the refrigerant pipe (20) close to the liquid helium tank (1413), and the maximum height of the detour is not lower than the upper top surface of the liquid helium tank (1413).

8. The superconducting magnet conduction cooling type cryogenic device according to any one of claims 1 to 4, characterized in that: A low-temperature throttle valve (22) is installed on the refrigerant pipe (20).

9. The superconducting magnet conduction cooling type cryogenic device according to any one of claims 1 to 4, characterized in that: A heating element is also installed in the sample chamber (4), and the heating element extends to one end of the sample rod assembly (3) suitable for installing a sample body (7).

10. The superconducting magnet conduction cooling type cryogenic device according to any one of claims 1 to 4, characterized in that: A dry vacuum pump (1) is installed on the discharge pipe (9), a first control valve (2) is installed upstream of the dry vacuum pump (1) and / or a second control valve (12) is installed downstream of the dry vacuum pump (1); and / or a third control valve (13) is installed on the helium discharge pipe (17), and a connection point between the discharge pipe (9) and the helium discharge pipe (17) is located upstream of the third control valve (13).

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