A superconducting magnet conduction-cooled cryogenic device

Abstract

The present invention relates to the technical field of superconducting magnet cooling, and discloses a conduction-cooled cryogenic device for a superconducting magnet, comprising: a vacuum chamber, on which a refrigerator assembly is installed, a liquid helium tank is installed at the refrigerating end of the refrigerator assembly, a superconducting magnet is installed in the vacuum chamber, the superconducting magnet is annular, and a heat conducting plate is installed between the superconducting magnet and the refrigerating end of the refrigerator assembly; a sample chamber, which 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 of the sample rod assembly extending into the sample chamber is adapted to install a sample body; a helium buffer tank, 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 the sample body is soaked with liquid helium, so that the sample body always works in a low-temperature environment, and a stable low-temperature environment is maintained for the sample body for a long time.

Description

Technical Field

[0001] The present invention relates to the technical field of superconducting magnet cooling, and particularly relates to a conduction-cooled cryogenic device for superconducting magnets. Background Art

[0002] Superconducting magnets are widely used in biomedical, scientific research instruments and other fields because they can generate strong magnetic fields. Due to the properties of superconductivity, the magnet must operate at liquid helium temperature. The traditional method of cooling superconducting magnets is to immerse the superconducting magnet in liquid helium. However, helium resources in China are scarce, helium gas has long relied on imports and is expensive, and the site using liquid helium requires professional maintenance and regular replenishment of liquid helium, making the liquid helium immersion superconducting magnet system complex and costly. Compared with the liquid helium immersion superconducting magnet, using a cryogenic refrigerator to cool the superconducting magnet has a lower cost, a simpler system structure and a shorter maintenance time. Using a helium-free high-field and high-uniformity superconducting magnet is the current trend in the research and use of magnets.

[0003] In the prior art, the method of conducting heat to cool the magnet is to use a heat conduction device such as copper braid at the second-stage cold head of the refrigerator, directly connect it to the superconducting magnet, 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 second-stage cold head to provide a vacuum environment for the space where the superconducting magnet and the sample are located. For a cryogenic refrigerator, the cooling capacity of the second-stage cold head is extremely precious, and its heat load includes magnet AC loss, thermal radiation, heat conduction, etc. However, existing cryogenic refrigerators for superconducting magnets usually connect the second-stage cold head to the superconducting magnet through heat conduction components such as copper, and then provide a low-temperature environment for the sample through heat conduction. However, the setting of the heat conduction components will inevitably cause loss of cooling capacity during the conduction process, resulting in unstable temperature of the low-temperature environment in the magnet area and affecting the working performance of the sample. Summary of the Invention

[0004] In view of this, the present invention provides a conduction-cooled cryogenic device for superconducting magnets to solve the problem of unstable low-temperature environment generated in the superconducting magnet area of the conduction-cooled superconducting magnet cryogenic system.

[0005] To solve the above technical problems, the present invention provides a conduction-cooled cryogenic device for superconducting magnets, including:

[0006] A vacuum cavity, on which a refrigerator assembly is installed, a liquid helium tank is installed at the refrigeration end of the refrigerator assembly, a superconducting magnet is installed in the vacuum cavity, the superconducting magnet is annular, and a heat conduction plate is installed between the superconducting magnet and the refrigeration end of the refrigerator assembly;

[0007] A sample chamber is disposed inside a vacuum chamber. The sample chamber extends to the annular center of a superconducting magnet. A refrigerant pipe is connected between a liquid helium tank and the sample chamber. A sample rod assembly is installed inside the sample chamber. One end of the sample rod assembly extending into the sample chamber is adapted to install a sample body.

[0008] A helium buffer tank is connected to the liquid helium tank by a helium discharge pipe. The sample chamber is connected to the helium discharge pipe by a discharge pipe.

[0009] Before the superconducting magnet conduction-cooled cryogenic device is used, the entire sample chamber is evacuated. The pre-stored high-purity helium gas is stored in the helium buffer tank. When the sample needs to work in a low-temperature environment, the helium gas is output from the helium buffer tank through the helium discharge pipe and enters the refrigeration end of the refrigeration machine assembly, where it is cooled by the refrigeration machine and becomes liquid helium. The temperature drops below 4.2K, and the liquid helium is finally stored inside the liquid helium tank. The cold of the liquid helium cools the superconducting magnet below the superconducting critical temperature through a heat conduction plate. The superconducting magnet enters the superconducting state, can be energized and excited to generate a strong magnetic field in the center. The sample rod assembly carrying the sample body is inserted into the sample chamber at the annular center of the superconducting magnet, so that the liquid helium inside the liquid helium tank is output from the refrigerant pipe and enters the sample chamber, and the sample body is immersed in the 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 can maintain a stable low-temperature environment for the sample body for a long time. The helium gas vaporized during the operation of the sample body can return to the helium discharge pipe from the discharge pipe and is cooled by the refrigeration machine assembly again to become liquid helium and enter the liquid helium tank. This enables the cryogenic device to operate without replenishing liquid helium and without replacing the liquid helium tank or the refrigeration machine assembly, 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 refrigeration machine assembly includes a cryogenic refrigerator and a refrigerator cold head. A helium liquefaction heat exchanger is installed 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 as a split type, the cold generated on the refrigerator cold head during the operation of the cryogenic refrigerator is transferred to the helium gas by the helium liquefaction heat exchanger, causing the helium gas to liquefy inside the liquid helium tank. When replacing the cryogenic refrigerator, the cryogenic refrigerator can be directly removed from the cryogenic cavity, and the newly replaced cryogenic refrigerator can be directly inserted without opening the entire cryogenic device, greatly reducing the complexity of replacing the cryogenic refrigerator and shortening the replacement time.

[0012] In an alternative embodiment, the cold head of the refrigerator includes a primary cold head and a secondary cold head. The helium release pipe is connected to the primary cold head through a heat exchanger, and the helium release pipe is connected to the secondary cold head through a spiral pipe. A radiation shield is further provided in the vacuum chamber. The radiation shield encloses to form a closed space. The primary cold head is in contact connection with the radiation shield, and the sample chamber extends into the closed space. The heat conducting plate is in contact connection with the secondary cold head.

[0013] By providing the radiation shield, the sample body or the superconducting magnet and the sample body are wrapped inside the radiation shield by using the closed space formed by the radiation shield, and the cooling is performed by using the cold quantity on the primary cold head of the cryogenic refrigerator, which can greatly reduce the thermal load of the thermal radiation at room temperature on the superconducting magnet or the sample body.

[0014] In an alternative embodiment, an upper bellows is installed between the inner side wall of the vacuum chamber and the primary cold head, and a lower bellows is installed between the radiation shield and the secondary cold head.

[0015] Both the upper bellows and the lower bellows are made of metallic pipes with elastic functions. By using the cooperation of the upper bellows and the lower bellows, the primary cold head, the radiation shield and the secondary cold head are installed between the liquid helium tank and the vacuum chamber by extrusion. After the cryogenic refrigerator is installed, the vacuum chamber is evacuated first and then the cryogenic refrigerator can be started. By using the cooperation of the upper bellows and the lower bellows to extrude and install other components except the cryogenic refrigerator in the refrigerator assembly, the cryogenic refrigerator is a separate component separated from the primary cold head and the secondary cold head. When the cryogenic refrigerator is installed, it is possible to cool the object to be cooled without using screws or other parts inside, and the cryogenic refrigerator can be installed in a separate direct plug-and-play manner, which is convenient for replacement.

[0016] In an alternative embodiment, the cryogenic refrigerator is fixed to the vacuum chamber through a connecting flange, and a shock pad is installed between the cryogenic refrigerator and the connecting flange;

[0017] And / or, the primary cold head and the radiation shield are fixed through a first welded flange;

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

[0019] In an alternative embodiment, an upper head is installed at the opening end of the liquid helium tank, the 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 in heat conduction connection with the helium liquefaction heat exchanger through the upper head.

[0020] In an alternative embodiment, the helium liquefaction heat exchanger is a fin heat exchanger, and the helium liquefaction heat exchanger is arranged perpendicular to the upper head.

[0021] In an alternative embodiment, a bend is provided in the refrigerant pipe in the area close to the liquid helium tank, and the maximum height position of the bend is not lower than the upper top surface of the liquid helium tank body. By providing a bend in the refrigerant pipe, the liquid level inside the refrigerant pipe is higher than that of the liquid helium tank. When the sample body does not need to be cooled, the liquid helium is stored in the liquid helium tank. Since the position of the bend is higher than that of the liquid helium tank, the liquid helium cannot flow out through the refrigerant pipe under its own gravity. When the sample body needs to be cooled, a pressure difference needs to be provided for the liquid helium under an external force, and the liquid helium can flow out of the refrigerant pipe, cross the bend, and enter the cooling chamber at the bottom of the sample chamber for containing the sample body to cool the sample body.

[0022] In an alternative embodiment, a cryogenic throttle valve is installed on the refrigerant pipe.

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

[0024] In an alternative embodiment, a heating element is also 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] After the sample body finishes working, the heating element works, causing all the liquid helium in the sample chamber to vaporize. The vaporized helium gas enters the helium discharge pipe through the discharge pipe and returns to the helium buffer tank for storage.

[0026] In an alternative embodiment, a dry vacuum pump is installed on the discharge pipe, and 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 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 embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for use in the description of the specific embodiments or the prior art. Obviously, the following drawings are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0028] Figure 1 It is a schematic structural diagram of a superconducting magnet conduction-cooled cryogenic device provided by an embodiment of the present invention.

[0029] Figure 2 It is a schematic structural diagram of a refrigerator assembly provided by an embodiment of the present invention.

[0030] Figure 3Schematic diagram of the cooperative connection structure of the upper corrugated pipe and the lower corrugated pipe provided by the embodiment of the present invention.

[0031] Figure 4 Schematic diagram of the structure of the liquid helium tank provided by the embodiment of the present invention.

[0032] Figure 5 Schematic diagram of the structure of the sample rod assembly provided by the 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; 302, vacuum pumping port; 303, mounting flange; 304, helium filling port; 305, internal gas passage port; 306, measurement lead; 307, sample base; 4, sample chamber; 5, vacuum chamber; 6, radiation shield; 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, cryogenic refrigerator; 1402, shock pad; 1403, upper corrugated pipe; 1404, first cold head; 1405, first welding flange; 1406, lower corrugated pipe; 1407, second welding flange; 1408, connection flange; 1409, connection block; 1410, second cold head; 1411, upper head; 1412, helium liquefaction heat exchanger; 1413, liquid helium tank; 1414, lower head; 15, heat exchanger; 16, spiral tube; 17, helium release pipe; 18, helium buffer tank; 19, magnet heat conducting plate; 20, refrigerant pipe; 21, heating wire; 22, cryogenic throttle valve. Detailed implementation manners

[0034] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts shall fall within the protection scope of the present invention.

[0035] The following combines Figures 1 to 5 , to describe the embodiments of the present invention.

[0036] According to an embodiment of the present invention, a conduction-cooled cryogenic device for a superconducting magnet 10 is provided, which includes a vacuum chamber 5, a sample chamber 4, and a helium buffer tank 18. A refrigerator assembly 14 is installed on the vacuum chamber 5, a liquid helium tank 1413 is installed at the refrigerating end of the refrigerator assembly 14, a superconducting magnet 10 is installed in the vacuum chamber 5, the superconducting magnet 10 is annular, and a heat conducting plate is installed between the superconducting magnet 10 and the refrigerating end of the refrigerator assembly 14. The 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 adapted to install 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.

[0037] Before the conduction-cooled cryogenic device for the superconducting magnet 10 is used, the whole sample chamber 4 is evacuated, and the pre-stored high-purity helium gas is stored in the helium buffer tank 18. When the sample needs to work in a low-temperature environment, the helium gas is output from the helium buffer tank 18 through the helium discharge pipe 17 and enters the refrigerating end of the refrigerator assembly 14, and then is cooled by the refrigerator to become liquid helium, and the temperature drops below 4.2 K. Finally, the liquid helium is stored inside the liquid helium tank 1413. The cold of the liquid helium cools the superconducting magnet 10 below the superconducting critical temperature through the heat conducting plate, and the superconducting magnet 10 enters the superconducting state, and can be energized to 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 pipe 20 and enters the sample chamber 4, and the sample body 7 is immersed with the liquid helium, and the sample body 7 can always be in the liquid helium environment, so that the sample body 7 always works in a temperature environment below 4.2 K, and a stable low-temperature environment can be maintained for the sample body 7 for a long time. The helium gas vaporized during the operation of the sample body 7 can return to the helium discharge pipe 17 from the discharge pipe, and is cooled by the refrigerator assembly 14 again to become liquid helium and enter the liquid helium tank 1413. This enables the cryogenic device to operate without replenishing the liquid helium and without replacing the liquid helium tank 1413 or the refrigerator assembly 14, thus 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 cryocooler assembly 14 includes a cryocooler 1401 and a cryocooler cold head. A helium liquefaction heat exchanger 1412 is installed on the cryocooler cold head, and the helium liquefaction heat exchanger 1412 extends into the liquid helium tank 1413. The cryocooler 1401 is used to generate cooling capacity, and the cryocooler cold head is used to output the cooling capacity generated by the cryocooler 1401 to the outside. The helium liquefaction heat exchanger 1412 transfers the cooling capacity output by the cryocooler 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 cryocooler 1401 as a split type, the helium liquefaction heat exchanger 1412 is used to transfer the cooling capacity generated on the cryocooler cold head during the operation of the cryocooler 1401 to the helium gas, so that the helium gas is liquefied in the liquid helium tank 1413. When replacing the cryocooler 1401, the cryocooler 1401 can be directly removed from the cryogenic cavity, and the newly replaced cryocooler 1401 can be directly inserted without opening the entire cryogenic device, which greatly reduces the complexity of replacing the cryocooler 1401 and shortens the replacement time.

[0040] In one embodiment, the cryocooler cold head includes a first-stage cold head 1404 and a second-stage cold head 1410. The helium discharge pipe 17 is communicated with the first-stage cold head 1404 through a heat exchanger 15, and the helium discharge pipe 17 is communicated with the second-stage cold head 1410 through a spiral pipe 16. A radiation shield 6 is further provided in the vacuum cavity 5. The radiation shield 6 encloses a closed space. The first-stage cold head 1404 is in contact connection with the radiation shield 6, and the sample chamber 4 extends into the closed space; the heat conducting plate is in contact connection with the second-stage cold head 1410.

[0041] Part of the helium gas in the helium discharge pipe 17 enters the first-stage cold head 1404 through the heat exchanger 15 for heat exchange and cooling, and the remaining helium gas enters the second-stage cold head 1410 through the spiral pipe 16 for heat exchange and liquefaction. By setting the radiation shield 6, the sample body 7 or the superconducting magnet 10 and the sample body 7 are wrapped inside the radiation shield 6 by using the closed space formed by the radiation shield 6. The cold capacity on the first-stage cold head 1404 of the cryocooler 1401 is used to cool the radiation shield 6, so that a lower temperature level can be maintained in the closed space formed by the radiation shield 6, avoiding the influence of the heat generated by the operation of the devices in the device and the ambient temperature on the temperature of the sample body 7, and greatly reducing the heat load of the room-temperature thermal radiation on the superconducting magnet 10 or the sample body 7.

[0042] In one embodiment, an upper bellows 1403 is installed between the inner sidewall of the vacuum chamber 5 and the first-stage cold head 1404, and a lower bellows 1406 is installed between the radiation shield 6 and the second-stage cold head 1410. When the temperature of the first-stage cold head 1404 and the second-stage cold head 1410 changes, due to thermal expansion and contraction, the distance between the first-stage cold head 1404 and the second-stage cold head 1410 will deform. Since the coefficients of thermal expansion and contraction of each part in the device are different, the amount of deformation during deformation is different. Both the upper bellows 1403 and the lower bellows 1406 are made of metal pipes with elastic functions, thereby eliminating the influence of the deformation of the first-stage cold head 1404 and the second-stage cold head 1410 on the device during temperature changes. At the same time, by using the cooperation of the upper bellows 1403 and the lower bellows 1406, the first-stage cold head 1404, the radiation shield 6, and the second-stage cold head 1410 are installed between the liquid helium tank 1413 and the vacuum chamber 5 by extrusion. After the cryogenic refrigerator 1401 is installed, the vacuum chamber 5 is evacuated first and then the cryogenic refrigerator 1401 can be started. By using the cooperation of the upper bellows 1403 and the lower bellows 1406 to extrude and install other components in the cryogenic refrigerator assembly 14 except the cryogenic refrigerator 1401, the cryogenic refrigerator 1401 is a separate component separated from the first-stage cold head 1404 and the second-stage cold head 1410. When the cryogenic refrigerator 1401 is installed, it is not necessary to use screws and other parts to connect inside, and the object to be cooled can be cooled. Moreover, the cryogenic refrigerator 1401 can be installed in a separate direct plug-and-play manner, which is convenient for replacement.

[0043] In one embodiment, the cryogenic refrigerator 1401 is hermetically fixed to the vacuum chamber 5 through a connecting flange 1408 to facilitate the installation and disassembly 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 displacement between the cryogenic refrigerator 1401 and the connecting flange 1408 caused by thermal vibration during the temperature change process, and to ensure 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 through a first welded flange 1405. The second-stage cold head 1410 is fixed to the liquid helium tank 1413 through a second welded flange 1407.

[0044] Further, an upper head 1411 is installed at the open end of the liquid helium tank 1413, and the helium liquefaction heat exchanger 1412 is installed on the side of the upper head 1411 facing the inner cavity of the liquid helium tank 1413. The cold head of the refrigerator is thermally connected to the helium liquefaction heat exchanger 1412 through the upper head 1411. A lower head 1414 is installed on the lower side of the liquid helium tank 1413. The upper head 1411 transfers the cold from the second-stage cold head 1410, causing the helium gas to liquefy in the liquid helium tank 1413 to form liquid helium. The lower head 1414 transfers the cold in the liquid helium to the magnet heat conducting plate 19, and then cools the superconducting magnet 10.

[0045] In this embodiment, the helium liquefaction heat exchanger 1412 is a finned heat exchanger or a copper foam heat exchanger, which increases the contact area of helium gas to improve the heat exchange efficiency, thereby reducing the time for helium liquefaction. The helium liquefaction heat exchanger 1412 is vertically arranged with respect to the upper head 1411.

[0046] In one embodiment, a detour section is provided in the area where the refrigerant pipe 20 is close to the liquid helium tank 1413, and the maximum height position of the detour section is not lower than the upper top surface of the liquid helium tank 1413 body. By providing the detour section on the refrigerant pipe 20, the liquid level inside the refrigerant pipe 20 is higher than that of 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. Since the position of the detour section is higher than that of the liquid helium tank 1413, the liquid helium cannot flow out through the refrigerant pipe 20 under its own gravity. When the sample body 7 needs to be cooled, an external force is required to provide a pressure difference for the liquid helium, and the liquid helium can flow out from the refrigerant pipe 20, cross the detour section, and enter the cooling chamber at the bottom of the sample chamber 4 for containing 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, 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 operation of the sample body 7 is completed, the heating element operates, causing all the liquid helium in the sample chamber 4 to vaporize. The vaporized helium gas enters the helium discharge pipe through the discharge 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, which is used to drive the liquid helium or helium gas or a mixed fluid of both in the discharge pipe to return to the helium relief pipe 17 or the helium gas 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 relief pipe 17. The connection between the discharge pipe and the helium relief pipe 17 is located upstream of the third control valve 13. The third control valve 13 is used to control whether the helium gas buffer tank 18 is connected to the liquid helium tank 1413. When the third control valve 13 is opened, the helium gas buffer tank 18 is connected to the liquid helium tank 1413, and the helium gas in the helium gas buffer tank 18 flows to the liquid helium tank 1413 through the helium relief pipe 17; when the third control valve 13 is closed, the helium gas buffer tank 18 is not connected to the liquid helium tank 1413, and the helium gas sent back to the helium relief pipe 17 from the discharge pipe flows back to the helium gas buffer tank 18 through the helium relief pipe 17 for storage again.

[0050] Before the conduction-cooled cryogenic device of the superconducting magnet 10 is used, the whole is evacuated. High-purity helium gas is stored in the helium gas buffer tank 18 and enters the internal pipeline of the system through the helium relief pipe 17 and the third control valve 13. The helium gas inside the pipeline is pre-cooled to about 50K by the heat exchanger 15 and then enters the first-stage cold head 1404. Subsequently, part of the helium gas enters the liquid helium tank 1413 through the spiral pipe 16. The helium gas is liquefied into liquid helium inside the liquid helium tank 1413 assembly, and the temperature drops below 4.2K. The cold of the liquid helium cools the superconducting magnet 10 below the superconducting critical temperature through the magnet heat conduction plate 19, and the superconducting magnet 10 enters the superconducting state, and can be energized to 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. Driven by the pressure difference, the liquid helium enters the cryogenic 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 forms helium gas, and then reaches the external first control valve 2 through the discharge 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 inside the sample rod assembly 3 will also be cooled. When it is not necessary 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 vaporized and discharged.

[0052] The function of the radiation shield 6 is to reduce the thermal load on the superconducting magnet 10 caused by radiation at room temperature. The radiation shield 6 is cooled by the cooling capacity transferred by the first-stage 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 thermal load on the superconducting magnet 10 due to heat conduction, and enable the magnet to withstand the impact force during transportation.

[0053] In the refrigerator assembly 14, the cryogenic refrigerator 1401 is selected as a Gifford-McMahon cycle refrigerator; a GM-type refrigerator, or a pulse tube refrigerator. It can generate a refrigerating capacity below 4.2K at the second-stage cold head 1410 and can generate a refrigerating capacity in the temperature range of 40K to 50K at the first-stage cold head 1404. An indium sheet is padded on the surface of the second-stage cold head 1410, and the indium sheet is press-fitted onto the second welding flange 1407. The cooling capacity below 4.2K is transferred from the second-stage cold head 1410 to the second welding flange 1407, and then transferred to the inside of the liquid helium tank 1413, thereby liquefying the helium gas. An indium sheet is padded on the surface of the first-stage cold head 1404, and the cooling capacity of the first-stage cold head 1404 is transferred to the first welding flange 1405 through extrusion. The radiation shield 6 and the connecting block 1409 for connecting the heat exchanger 15 installed on it are cooled to below 50K.

[0054] In the refrigeration machine installation assembly, the cryogenic refrigeration machine 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 functions. After the cryogenic refrigeration machine 1401 is installed, the first stage cold head 1404 and the second stage cold head 1410 can be in thermal contact with the first welding flange 1405 and the second welding flange 1407 respectively, and at the same time have the advantage of low heat leakage. The first welding flange 1405 and the second welding flange 1407 play the role of transferring the cooling capacity of the first stage cold head 1404 and the second stage cold head 1410 to the object to be cooled. After the cryogenic refrigeration machine 1401 is installed, the inside of the vacuum chamber 5 needs to be evacuated as a whole before the cryogenic refrigeration machine 1401 can be started. The refrigeration machine assembly 14 enables the cryogenic refrigeration machine 1401 to be installed without using parts such as screws inside, and can realize cooling the object to be cooled. The cryogenic refrigeration machine 1401 can be installed and used in a direct plug-and-play manner. In the prior art GM refrigeration machine, there are holes in the first stage cold head 1404 and the second stage cold head 1410. In order to ensure the tight connection between the object to be cooled and the cold head, bolts are generally used to lock the cold head and the object to be cooled. However, there will be a problem that it is difficult to remove. Because the working environment of the refrigeration machine and the object to be cooled is vacuum and low temperature, if the refrigeration machine needs to be replaced, the bolts of the object to be cooled and the cold head need to be removed, which will surely damage the vacuum and low temperature environment of the object to be cooled, and the removal will become very difficult. In the refrigeration machine assembly 14 provided in this embodiment, the connection of the cryogenic refrigeration machine 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 pipe with a telescopic structure, when the cryogenic refrigeration machine 1401 is installed, a force will be applied to the upper bellows 1403 and the lower bellows 1406. The upper bellows 1403 and the lower bellows 1406 react with a pressure to the cryogenic refrigeration machine 1401. This pressure will make the first stage cold head 1404 of the cryogenic refrigeration machine 1401 tightly connected to the first welding flange 1405, and the second stage cold head 1410 and the second welding flange 1407 tightly connected. 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 refrigeration machine 1401 is mechanically isolated without affecting heat transfer. When replacing the cryogenic refrigeration machine 1401, there is no need to damage the environment of the object to be cooled, and the cryogenic refrigeration machine 1401 can be taken out separately. Because the cold heads of the refrigeration machine assembly 14 except the motor are in a slender shape, the installation and removal are similar to plugging and unplugging a data cable, so it is called a plug-and-play structure.

[0055] In the liquid helium tank 1413, the upper head 1411 transfers the cooling capacity from the second-stage cold head 1410, and the lower head 1414 transfers the cooling capacity to the magnet heat conducting plate 19 and then cools the superconducting magnet 10. The helium liquefaction heat exchanger 1412 is a finned heat exchanger or a copper foam heat exchanger, which increases the contact area of helium gas and improves the heat exchange efficiency, thereby reducing the time for helium liquefaction. The conduction-cooled cryogenic device with superconducting magnet 10 provided in this embodiment uses the dual-target cooling of the superconducting magnet 10 and the sample body 7, including a refrigerator assembly 14 for liquefying helium gas, and then cooling the superconducting magnet 10 through conduction; the liquid helium flow rate is adjusted by a throttle valve and a dry vacuum pump 1 to cool the sample stage 8 and the sample body 7 at the first stage. The cryogenic device not only cools the sample body 7 but also cools the superconducting magnet 10 because the superconducting magnet 10 must reach the superconducting state and work normally at low temperature, while sample cooling is the 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, and the cooling requirements for different sample bodies 7 are different. For the cooling of the superconducting magnet 10, a magnet heat conducting plate 19 is installed at the bottom of the liquid helium tank 1413, and the magnet is cooled down by the method of conduction cooling because the temperature of the liquid helium in the liquid helium tank 1413 remains at 4.2K, which can meet the cooling requirements for maintaining the superconducting magnet at a stable low temperature. For the cooling and temperature control of the sample, the method of liquid helium circulation cooling combined with heating by the heating wire 21 is adopted. A refrigerant pipe 20 is led out from the liquid helium tank 1413. After throttling by the cryogenic throttle valve 22, the temperature of the liquid helium can be reduced to below 2K, and the sample chamber 4 at the bottom of the sample rod assembly 3 is cooled. The sample stage 8 is arranged inside the sample chamber 4. The sample stage 8 is made of copper and has good heat conduction performance. The sample stage 8 is also in contact with the sample body 7 at the bottom of the sample rod body. Therefore, after the liquid helium cools the sample stage 8 in the sample chamber 4, the sample body 7 can be further cooled to a low temperature. A bypass section is provided after the refrigerant pipe 20 is led out from the liquid helium tank 1413, so that the highest liquid level in the bypass section 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 bypass section is higher than the liquid helium tank 1413, and the liquid helium cannot flow out of the bypass section. When the sample needs to be cooled, the dry vacuum pump 1 operates to provide a pressure difference, and the liquid helium can flow out from the refrigerant pipe 20, cross the bypass section, and enter the sample chamber 4 through the cryogenic throttle valve 22.

[0056] In the sample rod assembly 3, the sample rod body is mounted on the sample chamber 4 through the mounting flange 303, forming a sealed cavity with the sample chamber 4. An air extraction channel is provided inside the sample rod body, and an air extraction port 302 is provided above the sample rod body and communicated with the air extraction channel, so that the gas inside the sample chamber 4 can be pumped to 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 inside the sample chamber 4. After vacuum pumping, high-purity helium is filled into the sample chamber 4 through the helium filling port 304, and then vacuum pumping is carried out again. This process is repeated three times and finally pumped to vacuum to ensure that the gas component remaining in the sample chamber 4 is helium, so that the sample will not frost and damage the sample body 7 after cooling. The sample body 7 is mounted on the sample stage 8. The sample stage 8 is made of copper and is equipped with a thermometer. It is in thermal contact with the heat exchange base to cool the sample body 7. At the same time, a circuit is connected inside the sample base 307. The measurement 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, so as to lead out 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 sample measurement, and other components of the system provide low temperature and magnetic field for the sample. After welding four leads to the sample body 7, it is adhered to the sample base 307 at the bottom of the sample rod body using low-temperature varnish or low-temperature thermal grease to fix the sample body 7 and enhance heat transfer. The four leads are then connected to the measurement lead 306 and connected to an ammeter-voltmeter and a computer acquisition system through the external lead 301. After the sample rod assembly 3 is inserted into the sample chamber 4, a closed environment is formed inside the sample chamber 4. In order to reduce heat leakage, it is necessary to evacuate the sample chamber 4. The inside of the sample rod body has a hollow structure. The air extraction port 302 is connected to a vacuum pump. The gas inside the sample chamber 4 enters the inside of the sample rod body through the internal gas channel port 305 and is finally pumped out from the air extraction port 302. When measuring is completed and the next sample is replaced, it is necessary to protect the gas environment inside the sample chamber 4. Because the wall surface of the sample chamber 4 that has just been measured is still at a relatively low temperature, if air is introduced, the water vapor in the air may condense and accumulate inside the sample chamber 4, causing damage. Therefore, helium needs to be filled to protect the environment inside the sample chamber 4 before changing the sample. Helium is filled through the helium filling port 304. After the sample chamber 4 is filled with helium at one atmosphere and the temperature rises to room temperature, the sample rod assembly 3 can be taken out to replace the next sample to be measured.

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

Claims

1. A superconducting magnet conduction-cooled cryogenic device, characterized in that, Comprising: A vacuum chamber (5) on which a refrigerator assembly (14) is mounted. A liquid helium tank (1413) is mounted at the refrigerating end of the refrigerator assembly (14). A superconducting magnet (10) is mounted in the vacuum chamber (5). The superconducting magnet (10) is annular. A heat conducting plate is mounted between the superconducting magnet (10) and the refrigerating 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) so that the liquid helium inside the liquid helium tank (1413) is output from the refrigerant pipe (20) and enters the sample chamber (4). A sample rod assembly (3) is mounted in the sample chamber (4). One end of the sample rod assembly (3) extending into the sample chamber (4) is adapted to mount a sample body (7). The sample body (7) is soaked with liquid helium, and the sample body (7) can always be in a liquid helium environment; A helium buffer tank (18) is connected to the liquid helium tank (1413) through a helium discharge pipe (17). A discharge pipe (9) is connected between the sample chamber (4) and the helium discharge pipe (17).

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

3. The superconducting magnet conduction-cooled cryogenic device according to claim 2, characterized in that, 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). The helium discharge pipe (17) is connected to the secondary cold head (1410) through a spiral pipe (16); A radiation shield (6) is further arranged in the vacuum chamber (5). The radiation shield (6) encloses a closed space. The primary cold head (1404) is in contact connection with the radiation shield (6). The sample chamber (4) extends into the closed space; The heat conducting plate is in contact connection with the secondary cold head (1410).

4. The superconducting magnet conduction-cooled cryogenic device according to claim 3, wherein, An upper bellows (1403) is mounted between the inner side wall of the vacuum chamber (5) and the primary cold head (1404), and / or a lower bellows (1406) is mounted between the radiation shield (6) and the secondary cold head (1410).

5. The superconducting magnet conduction-cooled cryogenic device according to claim 3 or 4, characterized in that, The cryogenic refrigerator (1401) is fixed to the vacuum chamber (5) through a connecting flange (1408). A shock absorber pad (1402) is mounted between the cryogenic refrigerator (1401) and the connecting flange (1408); and / or, the primary cold head (1404) is fixed to the radiation shield (6) through a first welding flange (1405); and / or, the secondary cold head (1410) is fixed to the liquid helium tank (1413) through a second welding flange (1407).

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

7. The superconducting magnet conduction-cooled cryogenic device according to any one of claims 1 to 4, characterized in that, In the area where the refrigerant pipe (20) is close to the liquid helium tank (1413), a bypass section is provided, and the maximum height position of the bypass section is not lower than the upper top surface of the liquid helium tank (1413).

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

9. The superconducting magnet conduction-cooled 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 the sample body (7).

10. The superconducting magnet conduction-cooled 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 the connection between the discharge pipe (9) and the helium discharge pipe (17) is located upstream of the third control valve (13).

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