A cryogenic apparatus for obtaining the nitrogen fixation required by superconducting magnets

Abstract

The utility model discloses a kind of for obtaining the low-temperature equipment required for nitrogen fixation of superconducting magnet, it is related to low-temperature refrigeration and superconducting magnet cooling field, obtain the low-temperature equipment required for nitrogen fixation of superconducting magnet includes cold helium circulation unit and magnet dewar mechanism, this equipment uses helium as circulating cooling medium, cold quantity delivery path is long, flexibility is big, for compact space requirement, cooling unit can be separated from the cooling equipment arrangement, both avoid the sealing and maintenance risk caused by pluggable cold head, cold helium circulation unit can be made into independent module, the size of magnet dewar is effectively reduced, for the case of large space restriction such as vehicle-mounted;In addition, vehicle-mounted superconducting magnet vibrates violently, and vibration is extremely likely to cause superconducting magnet to shake out of superconducting state, traditional pull rod cannot comprehensively fasten magnet, and replace nitrogen fixation, which can wrap magnet in all directions, difficult to move, greatly reduce the risk of out of superconducting state.

Description

Technical Field

[0001] This utility model relates to the field of cryogenic refrigeration and superconducting magnet cooling technology, specifically to a cryogenic device for obtaining nitrogen fixation required for superconducting magnets. Background Technology

[0002] Superconducting magnets require extremely low temperatures during operation, typically achieved through nitrogen fixation to maintain thermal stability and superconductivity. Liquid nitrogen undergoes a liquid-solid phase transition at around 63 K, and further cooling solidifies it, resulting in fixed nitrogen. Fixed nitrogen is easy to prepare, lightweight, has a high heat capacity, and good electrical insulation, making it an inexpensive refrigerant for cooling superconducting magnets at extremely low temperatures. A solid-solid phase transition occurs at around 35.6 K, causing a sharp increase in the heat capacity of fixed nitrogen, allowing it to absorb a significant amount of heat. Therefore, when fixed nitrogen is used to cool superconducting magnets, its unique phase transition characteristics allow it to absorb more heat and suppress temperature rise in magnets operating below 35.6 K, thus resulting in better thermal stability.

[0003] Currently, a feasible solution for obtaining nitrogen fixation in superconducting magnets is to use an integrated cryostat with a pluggable cold head. This solution inserts the cryostat cold head into the magnet's Dewar via a detachable sealed interface, allowing the cold head to mechanically contact the heat conductor inside the Dewar. Liquid nitrogen within the chamber is cooled via solid-state conduction to form solid nitrogen. However, for size-constrained environments such as vehicle-mounted superconducting magnetic levitation systems, using a cryostat for nitrogen fixation still exceeds size requirements. Making the cold head pluggable reduces some of the conductive cooling performance and introduces operational risks. Utility Model Content

[0004] In order to overcome the above-mentioned technical problems, the purpose of this utility model is to provide a cryogenic device for obtaining nitrogen fixation required for superconducting magnets.

[0005] The objective of this utility model can be achieved through the following technical solution: a cryogenic device for obtaining nitrogen fixation required for superconducting magnets, comprising a cold helium gas circulation unit and a magnet Dewar mechanism; The magnet Dewar mechanism includes a magnet Dewar and a nitrogen fixation acquisition component disposed within the magnet Dewar; The cold helium circulation unit is used to generate and circulate cryogenic helium. It is connected to the nitrogen fixation assembly through a pipeline. The cryogenic helium is introduced into the nitrogen fixation assembly to cool and solidify the liquid nitrogen inside the magnet dewar to encapsulate the superconducting magnet.

[0006] As a further embodiment of this utility model: the cold helium circulation unit includes a high-pressure helium pump, a pressure buffer tank, a filter, a flow controller, a waste heat recovery heat exchanger, and a cold head coil heat exchanger connected sequentially through pipelines along the helium flow direction; The cold head coil heat exchanger is thermally connected to a refrigeration unit cold head.

[0007] As a further embodiment of this utility model: the cold head coil heat exchanger is a coil brazed on the cold head of the refrigerator, used to cool helium to a low temperature of 20K@1MPa.

[0008] As a further embodiment of this utility model: the cold flow channel outlet of the waste heat recovery heat exchanger is connected to the inlet of the cold head coil heat exchanger, the outlet of the cold head coil heat exchanger is connected to the air inlet pipe of the magnet Dewar, and the hot flow channel inlet of the waste heat recovery heat exchanger is connected to the return gas pipe from the magnet Dewar.

[0009] As a further embodiment of this invention: the magnet dewar is provided with a nitrogen-fixing cavity, which is used to contain the superconducting magnet and liquid nitrogen. The nitrogen-fixing acquisition component includes a cold helium coil disposed in the nitrogen-fixing cavity. The inlet of the cold helium coil is connected to the outlet of the cold head coil heat exchanger through a pipeline, and the outlet of the cold helium coil is connected to the hot flow channel inlet of the waste heat recovery heat exchanger through a pipeline, forming a closed loop.

[0010] As a further embodiment of this utility model: the magnet Dewar mechanism also includes a liquid nitrogen Dewar with built-in liquid nitrogen, the liquid nitrogen Dewar being connected to the liquid inlet on the magnet Dewar via a heat-insulating hose, and the liquid nitrogen being pressed into the nitrogen-fixing chamber by the liquid nitrogen Dewar through the heat-insulating hose; The insulated hose is equipped with an inlet valve.

[0011] As a further embodiment of this invention: a U-shaped groove is provided on the wall of the nitrogen-fixing chamber, and the cold helium coil is embedded in the U-shaped groove.

[0012] As a further embodiment of this invention: the total depth of the U-shaped groove is less than the outer diameter of the cold helium coil, and the cold helium coil is deformed by a rolling process and thus fitted into the U-shaped groove.

[0013] As a further embodiment of this invention: the cold helium coil and the U-shaped groove are fixed by vacuum brazing with silver solder.

[0014] As a further aspect of this invention: the nitrogen-fixing chamber is connected to a cold nitrogen vent via an exhaust valve.

[0015] The beneficial effects of this invention are as follows: When the device is working, the cold helium circulation unit continuously outputs low-temperature helium gas, which enters the nitrogen-fixing component along the vacuum insulated pipeline. The liquid nitrogen inside the magnet Dewar is cooled down and solidified, causing the liquid nitrogen temperature to drop below the freezing point, thus solidifying and encapsulating the superconducting magnet. The temperature of the helium gas rises after absorbing heat and returns to the cold helium circulation unit through the return pipeline. It is then cooled again and output again, thereby forming a closed continuous cycle that continuously provides a stable nitrogen-fixing environment for the superconducting magnet.

[0016] This device utilizes a closed-loop helium gas circulation unit to transfer cooling energy from the cold helium gas circulation unit to the nitrogen fixation assembly, causing the liquid nitrogen to continuously release heat and undergo a liquid-solid phase transition, thereby forming a nitrogen fixation layer around the superconducting magnet. Helium is used as the circulating cooling medium, resulting in a long and flexible cooling energy delivery path. For space-constrained applications, the cooling unit can be separated from the cooled equipment, avoiding the sealing and maintenance risks associated with pluggable cold heads. Furthermore, the cold helium gas circulation unit can be made into an independent module, effectively reducing the size of the magnet Dewar, making it suitable for applications with significant space constraints, such as vehicle-mounted applications. In addition, vehicle-mounted superconducting magnets experience severe vibrations, which can potentially cause them to wobble and lose quench. Traditional tie rods cannot fully secure the magnet, but nitrogen fixation can completely encapsulate it, making it difficult to move and greatly reducing the risk of quench loss. Attached Figure Description

[0017] The present invention will be further described below with reference to the accompanying drawings.

[0018] Figure 1 This is a schematic diagram of the overall structure of an embodiment of the present utility model; Figure 2 This is a schematic diagram of the cold helium gas circulation unit according to an embodiment of the present invention; Figure 3 This is a schematic diagram of the magnet Dewar and nitrogen fixation acquisition component according to an embodiment of the present invention; Figure 4 This is a partial structural schematic diagram of the magnet Dewar and nitrogen fixation acquisition component according to an embodiment of the present invention.

[0019] Explanation of reference numerals in the attached diagram: 1. Cold helium circulation unit; 2. Magnet Dewar mechanism; 21. Magnet Dewar; 22. Nitrogen fixation acquisition component; 11. High-pressure helium pump; 12. Pressure buffer tank; 13. Filter; 14. Flow controller; 15. Waste heat recovery heat exchanger; 16. Cold head coil heat exchanger; 17. Refrigeration unit cold head; 23. Liquid nitrogen Dewar; 231. Insulated hose; 232. Liquid inlet valve; 221. Nitrogen fixation chamber; 222. Cold helium coil; 223. U-shaped groove; 224. Exhaust valve; 225. Cold nitrogen vent; 226. Nitrogen fixation chamber safety release device; 18. Cold helium safety release device. Detailed Implementation

[0020] The technical solutions of the present utility model will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some embodiments of the present utility model, and not all embodiments. Based on the embodiments of the present utility model, all other embodiments obtained by those skilled in the art without creative effort are within the protection scope of the present utility model.

[0021] See Figure 1 This invention discloses a cryogenic device for obtaining nitrogen fixation required for superconducting magnets, comprising a cold helium circulation unit 1 and a magnet Dewar mechanism 2. The magnet Dewar mechanism 2 includes a magnet Dewar 21 and a nitrogen fixation acquisition component 22 disposed within the magnet Dewar 21. The cold helium circulation unit 1 generates and circulates cryogenic helium, and is connected to the nitrogen fixation acquisition component 22 via a pipeline. The cryogenic helium is introduced into the nitrogen fixation acquisition component 22 to cool and solidify the liquid nitrogen within the magnet Dewar 21 to encapsulate the superconducting magnet. It should be noted that "Dewar" is short for "Dewar container," which is often directly written as "Dewar" in Chinese technical literature. It refers to a double-walled, high-vacuum insulated container used to store cryogenic liquids such as liquid nitrogen, liquid oxygen, and liquid helium, or to maintain a cryogenic environment.

[0022] Specifically, during operation, the cold helium circulation unit 1 continuously outputs low-temperature helium gas, which enters the nitrogen-fixing assembly 22 through a vacuum-insulated pipeline. The liquid nitrogen inside the magnet Dewar 21 is cooled and solidified by absorbing heat, causing the liquid nitrogen temperature to drop below the freezing point, thus solidifying and encapsulating the superconducting magnet. The temperature of the helium gas rises after absorbing heat and returns to the cold helium circulation unit 1 through the return pipeline. It is then cooled again and output again, thus forming a closed-loop continuous cycle that continuously provides a stable nitrogen-fixing environment for the superconducting magnet.

[0023] Furthermore, closed-loop helium is used to transport the cooling capacity from the cold helium circulation unit 1 to the nitrogen fixation assembly 22, causing the liquid nitrogen to continuously release heat and undergo a liquid-solid phase change, thereby forming a nitrogen fixation layer around the superconducting magnet. This device uses helium as the circulating cooling medium, with a long and flexible cooling capacity delivery path. For compact space requirements, the cooling unit can be separated from the cooled equipment, avoiding the sealing and maintenance risks associated with pluggable cold heads. The cold helium circulation unit 1 can also be made into an independent module, effectively reducing the size of the magnet Dewar 21, making it suitable for applications with large space constraints, such as vehicle-mounted applications. In addition, vehicle-mounted superconducting magnets vibrate violently, which could potentially cause the superconducting magnet to wobble and lose quench. Traditional tie rods cannot fully secure the magnet, but nitrogen fixation can completely encapsulate the magnet, making it difficult to move and greatly reducing the risk of losing quench.

[0024] See Figures 1-2Optionally, the cold helium circulation unit 1 includes a high-pressure helium pump 11, a pressure buffer tank 12, a filter 13, a flow controller 14, a waste heat recovery heat exchanger 15, and a cold head coil heat exchanger 16, which are connected sequentially through pipelines along the helium flow direction. A refrigerator cold head 17 is thermally connected to the cold head coil heat exchanger 16, and a cold helium safety relief device is connected to the pressure buffer tank 12. The cold helium safety relief device immediately releases helium when the buffer tank is overpressurized, limiting the pressure inside the tank to below a set value, preventing high-pressure helium from impacting downstream components and ensuring system safety.

[0025] In this embodiment, the ambient temperature helium in the cold helium circulation unit 1 is supplied with high pressure and driving power by the high-pressure helium pump 11, then the pressure value is stabilized by the pressure buffer tank 12, then passes through the filter 13, and then the flow rate is controlled by the flow controller 14. After pre-cooling by the waste heat recovery heat exchanger 15, it enters the cold head coil heat exchanger 16 on the single unit cold head to reach a low temperature of 20K@1MPa, and is delivered to the magnet Dewar 21 to cool the magnet. After the temperature rises, it returns to the waste heat recovery heat exchanger 15 in the cold helium circulation unit 1 to be heated by ambient temperature helium. The pressure buffer tank 12 and the filter 13 can ensure the stable and clean flow in the cold helium circulation unit 1, and the waste heat recovery can improve the energy utilization rate of the cold helium circulation unit 1.

[0026] See Figures 1-2 Optionally, the cold head coil heat exchanger 16 is a coil brazed onto the cold head 17 of the refrigerator, used to cool helium to a cryogenic state of 20K@1MPa.

[0027] In this embodiment, the coil is directly brazed to the metal wall of the cold head, resulting in a large contact area and low thermal resistance. High-pressure helium gas flows through the coil at high speed and can be cooled to the target temperature in a short time.

[0028] See Figures 1-2 Optionally, the cold runner outlet of the waste heat recovery heat exchanger 15 is connected to the inlet of the cold head coil heat exchanger 16, the outlet of the cold head coil heat exchanger 16 is connected to the inlet pipe of the magnet Dewar 21, and the hot runner inlet of the waste heat recovery heat exchanger 15 is connected to the return pipe from the magnet Dewar 21.

[0029] In this embodiment, the cold flow channel outlet of the waste heat recovery heat exchanger 15 is first connected to the inlet of the cold head coil heat exchanger 16, allowing the recirculated low-temperature return gas to reserve the remaining cold energy for the newly entering helium, which can reduce the load on the cold head. The heated helium then returns to the high-pressure helium pump 11 through the pipeline, while the pre-cooled new helium is further cooled by the cold head coil heat exchanger 16 and then enters the magnetic Dewar 21 through the pipeline. This allows the cold head and the magnetic Dewar 21 to be modularly separated, and the cold helium circulation unit 1 and the magnetic Dewar mechanism 2 to be modularly separated. This can avoid the sealing and maintenance risks caused by the cold head being directly inserted into the Dewar, and can also improve the energy utilization rate through the recovery of the waste heat system, making the system more energy-efficient and reliable.

[0030] See Figures 1-4 Optionally, the magnet Dewar 21 is provided with a nitrogen fixation chamber 221, which is used to contain the superconducting magnet and liquid nitrogen. The nitrogen fixation acquisition component 22 includes a cold helium coil 222 disposed in the nitrogen fixation chamber 221. The inlet of the cold helium coil 222 is connected to the outlet of the cold head coil heat exchanger 16 through a pipeline, and the outlet of the cold helium coil 222 is connected to the hot flow channel inlet of the waste heat recovery heat exchanger 15 through a pipeline, forming a closed loop.

[0031] In this embodiment, cryogenic helium gas flows from the outlet of the cold head coil heat exchanger 16 into the cold helium coil 222 inside the nitrogen fixation chamber 221. The cold helium coil 222 then exchanges heat with the liquid nitrogen in the nitrogen fixation chamber 221. After the helium gas in the cold helium coil 222 heats up, it flows out from the outlet of the cold helium coil 222, and then enters the hot runner of the waste cold recovery heat exchanger 15 through the return gas pipeline, and then returns to the high-pressure helium pump 11, forming a closed loop. Furthermore, the cold helium gas flows inside the cold helium coil 222, and conducts heat exchange with the liquid nitrogen through the tube wall. The liquid nitrogen solidifies by thermal conduction and natural convection.

[0032] See Figures 1-3 Optionally, the magnet Dewar mechanism 2 also includes a liquid nitrogen Dewar 23 with built-in liquid nitrogen. The liquid nitrogen Dewar 23 is connected to the liquid inlet on the magnet Dewar 21 through a heat-insulating hose 231. Liquid nitrogen is pressed into the nitrogen solidification chamber 221 by the liquid nitrogen Dewar 23 through the heat-insulating hose 231. A liquid inlet valve 232 is installed near the heat-insulating hose 231.

[0033] In this embodiment, the liquid nitrogen dewar 23 has a built-in low pressure, so after the inlet is opened, the liquid nitrogen dewar 23 can press liquid nitrogen into the nitrogen solidification chamber 221 through the heat-insulating hose 231.

[0034] See Figures 3-4 Optionally, a U-shaped groove 223 is provided on the wall of the nitrogen fixation chamber 221, and a cold helium coil 222 is embedded in the U-shaped groove 223. The cold helium coil 222 can be made of TU0 copper tubing.

[0035] In this embodiment, the U-shaped groove 223 can not only provide positioning for the cold helium coil 222, but also expand the contact area between the cold helium coil 222 and the nitrogen fixation chamber 221, thereby significantly improving the thermal conductivity of the cold helium coil 222.

[0036] See Figures 3-4 Optionally, the total depth of the U-shaped groove 223 is less than the outer diameter of the cold helium coil 222, and the cold helium coil 222 is deformed by the rolling process and locked into the U-shaped groove 223.

[0037] In this embodiment, a rolling process is used to locally plastically deform the coil, and the cold helium coil 222 is directly engaged in the U-shaped groove 223 with a depth slightly smaller than the diameter of the tube. The assembly of the fast cold helium coil 222 and the nitrogen-fixing chamber 221 can be completed at room temperature, eliminating the need for cumbersome tooling positioning before welding.

[0038] See Figures 3-4 Optionally, the cold helium coil 222 and the U-shaped groove 223 are fixed by vacuum brazing with silver solder.

[0039] In this embodiment, the silver brazing filler metal is wetted and spread in a vacuum environment to metallurgically seal the micro-gap between the cold helium coil 222 and the U-shaped groove 223, eliminating contact thermal resistance and forming a continuous solid heat conduction chain, which significantly improves heat exchange efficiency.

[0040] See Figures 1-3 Optionally, the nitrogen-fixing chamber 221 is connected to a cold nitrogen vent 225 via a pipeline and an exhaust valve 224, and the nitrogen-fixing chamber 221 is connected to a nitrogen-fixing chamber safety relief device 226 via a pipeline to prevent the nitrogen-fixing chamber 221 from deforming or bursting due to a sudden increase in pressure.

[0041] In this embodiment, by opening the exhaust valve 224, the nitrogen gas released during the curing process can be released immediately through the cold nitrogen vent 225, thus avoiding pressure buildup that could lead to cavity deformation or sealing failure.

[0042] It should be noted that when the cold helium circulation unit 1 lowers the temperature of the nitrogen-fixing chamber 221 to approximately 77K, the liquid nitrogen Dewar 23 is connected to the liquid inlet on the magnetic Dewar 21 via the insulated hose 231. The liquid inlet valve 232 is opened, and the exhaust valve 224 near the cold nitrogen vent 226 is also opened simultaneously, allowing liquid nitrogen to accumulate in the nitrogen-fixing chamber 221 of the magnetic Dewar 21. Once the liquid nitrogen level meets the requirements, the liquid inlet valve 232 and the exhaust valve 224 are closed. The nitrogen-fixing chamber 221 then begins to gradually cool the input liquid nitrogen, achieving nitrogen fixation at approximately 63K. The cooling process continues until the nitrogen-fixing chamber 221 reaches the target temperature (approximately 20K).

[0043] In the description of this utility model, it should be understood that the terms "upper," "lower," "left," and "right," etc., indicating orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, are only for the convenience of describing this utility model and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or a specific orientational structure and operation. Therefore, they should not be construed as limitations on this utility model. Furthermore, "first" and "second" are only for descriptive purposes and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this utility model, unless otherwise stated, "multiple" means two or more.

[0044] In the description of this utility model, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," "joining," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this utility model based on the specific circumstances.

[0045] The above description provides a detailed account of one embodiment of the present invention. However, this description is merely a preferred embodiment and should not be construed as limiting the scope of the present invention. All equivalent variations and improvements made within the scope of the claims of the present invention should still fall within the patent coverage of the present invention.

Claims

1. A cryogenic device for obtaining nitrogen fixation required for superconducting magnets, characterized in that, It includes a cold helium gas circulation unit (1) and a magnet Dewar mechanism (2). The magnet Dewar mechanism (2) includes a magnet Dewar (21) and a nitrogen fixation acquisition component (22) disposed within the magnet Dewar (21). The cold helium circulation unit (1) is used to generate and circulate cryogenic helium. It is connected to the nitrogen fixation assembly (22) through a pipeline. The cryogenic helium is introduced into the nitrogen fixation assembly (22) to cool and solidify the liquid nitrogen in the magnet Dewar (21) to encapsulate the superconducting magnet.

2. The cryogenic apparatus for obtaining nitrogen fixation required for superconducting magnets according to claim 1, characterized in that, The cold helium circulation unit (1) includes a high-pressure helium pump (11), a pressure buffer tank (12), a filter (13), a flow controller (14), a waste heat recovery heat exchanger (15), and a cold head coil heat exchanger (16) connected sequentially through pipelines along the helium flow direction. The refrigeration unit cold head (17) is thermally connected to the cold head coil heat exchanger (16).

3. The cryogenic apparatus for obtaining nitrogen fixation required for superconducting magnets according to claim 2, characterized in that, The cold head coil heat exchanger (16) is a coil brazed onto the cold head (17) of the refrigerator, used to cool helium to a low temperature of 20K@1MPa.

4. The cryogenic apparatus for obtaining nitrogen fixation required for superconducting magnets according to claim 3, characterized in that, The cold flow outlet of the waste heat recovery heat exchanger (15) is connected to the inlet of the cold head coil heat exchanger (16), the outlet of the cold head coil heat exchanger (16) is connected to the inlet pipe of the magnet Dewar (21), and the hot flow inlet of the waste heat recovery heat exchanger (15) is connected to the return pipe from the magnet Dewar (21).

5. The cryogenic apparatus for obtaining nitrogen fixation required for superconducting magnets according to claim 4, characterized in that, The magnet Dewar (21) is provided with a nitrogen-fixing chamber (221), which is used to contain the superconducting magnet and liquid nitrogen. The nitrogen-fixing acquisition component (22) includes a cold helium coil (222) disposed in the nitrogen-fixing chamber (221). The inlet of the cold helium coil (222) is connected to the outlet of the cold head coil heat exchanger (16) through a pipeline. The outlet of the cold helium coil (222) is connected to the hot flow inlet of the waste heat recovery heat exchanger (15) through a pipeline, forming a closed loop.

6. The cryogenic apparatus for obtaining nitrogen fixation required for superconducting magnets according to claim 5, characterized in that, The magnet Dewar mechanism (2) also includes a liquid nitrogen Dewar (23) with built-in liquid nitrogen. The liquid nitrogen Dewar (23) is connected to the liquid inlet on the magnet Dewar (21) through a heat-insulating hose (231). Liquid nitrogen is pressed into the nitrogen-fixing chamber (221) by the liquid nitrogen Dewar (23) through the heat-insulating hose (231). The insulated hose (231) is equipped with an inlet valve (232).

7. The cryogenic apparatus for obtaining nitrogen fixation required for superconducting magnets according to claim 6, characterized in that, A U-shaped groove (223) is provided on the wall of the nitrogen fixation chamber (221), and the cold helium coil (222) is embedded in the U-shaped groove (223).

8. The cryogenic apparatus for obtaining nitrogen fixation required for superconducting magnets according to claim 7, characterized in that, The total depth of the U-shaped groove (223) is less than the outer diameter of the cold helium coil (222), and the cold helium coil (222) is deformed by the rolling process and locked into the U-shaped groove (223).

9. The cryogenic apparatus for obtaining nitrogen fixation required for superconducting magnets according to claim 8, characterized in that, The cold helium coil (222) and the U-shaped groove (223) are fixed together by vacuum brazing with silver solder.

10. The cryogenic apparatus for obtaining nitrogen fixation required for superconducting magnets according to claim 6 or 9, characterized in that, The nitrogen-fixing chamber (221) is connected to a cold nitrogen vent (225) via an exhaust valve (224).

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