Compact air-cooled binary current lead for cryostat and manufacturing method

Abstract

The invention relates to the technical field of superconducting magnet current leads, and particularly provides a compact air-cooled binary current lead for a cryostat and a manufacturing method. The lead comprises a high-temperature superconducting section and a normal-temperature section, wherein the high-temperature superconducting section is used for transmitting current to the superconducting magnet without resistance in a low-temperature environment; one end of the normal-temperature section is connected with the high-temperature superconducting section, a cooling structure is arranged in the normal-temperature section, and high-pressure helium is introduced for cooling. By optimizing the cooling structure, the radial size of the lead is remarkably reduced, the sealing performance is improved, the heat exchange efficiency of the normal temperature section is effectively improved, the high-temperature superconducting section is ensured to work under the safety margin, and the structure has the advantages that the Passon discharge phenomenon caused by high voltage generated after the superconducting magnet is quenched in the helium environment is prevented; therefore, the binary current lead meets the requirements of compact size, high air tightness and breakdown prevention, integrated installation of multiple groups of current leads in a single thermostat can be realized, and stable operation of a superconducting magnet system is guaranteed.

Description

Technical Field

[0001] The invention relates to the technical field of superconducting magnet current leads, and in particular to a compact air-cooled binary current lead for a cryostat and a manufacturing method thereof. Background Art

[0002] In the accelerator, quadrupole magnets focus or defocus the beam. They usually exist in a combination of three, that is, three quadrupole magnets form a group. Opposite currents are loaded between each two adjacent magnets to form opposite magnetic fields, integrating the beam in a focusing-defocusing-focusing or defocusing-focusing-defocusing manner.

[0003] For three-combination magnets, if a superconducting magnet is used, it needs to be placed in a cryostat to work properly. If three cryostat are set for three superconducting magnets, that is, each superconducting magnet uses a separate cryostat, the manufacturing price is high, and each cryostat needs to be equipped with a corresponding cryovalve box, the overall heat leakage is large, and the heat load of the cryogenic system is increased. For this reason, consider using one cryostat for three superconducting magnets. This solution only requires one cryovalve box, and the heat load of the thermostat is lower than the total heat leakage of three separate cryostat, which can greatly reduce the overall heat load of the cryogenic system and reduce construction costs.

[0004] CCT / DCT (Canted Cosine Theta, Canted Solenoid, Discrete CosineTheta) superconducting magnets are used in the thermostat. This type of superconducting magnet has the advantages of high field quality, low current operation, and light weight. Each superconducting magnet is cylindrical and nested. In addition to the main coil being a quadrupole coil, it may also be nested with a hexapolar coil, an octapole coil, a bidirectional correction coil, etc., that is, a superconducting magnet contains multiple coils and can operate simultaneously. Three superconducting magnets are placed in a cryostat, that is, each cryostat has multiple coils. According to physical requirements, three groups of superconducting magnets are equipped with a maximum of 10 coils, and each coil is independently powered, that is, the thermostat needs to be equipped with a maximum of 20 current leads.

[0005] The thermostat has many current leads, and the operating current of each current lead is about 500A. If the current lead uses the traditional binary (HTS+copper lead) conduction cooling method, the conduction cooling efficiency is low and the heat load is too large, which increases the burden on the cryogenic station and even burns the current lead. If the number of leads in the thermostat is small, the current lead can be cooled by evaporating gas with an absolute temperature of 4K. However, for the above-mentioned multi-current lead form, the cooling method is generally cooling by cooling gas. At the same time, in order to reduce the heat leakage value of the current lead at an absolute temperature of 4.2K, a binary lead structure of HTS+normal temperature copper lead is used. The gas source is high-pressure helium with an absolute temperature of 50K, and the maximum pressure of high-pressure helium can reach 17.5bara. Higher pressure can increase the heat exchange efficiency of the normal temperature copper lead and make the current lead work at a safe temperature, but higher pressure will increase the risk of leakage of the seal. At the same time, due to the large number of leads, the current lead must be compact in structure when designed and does not interfere with other parts of the thermostat. Since the cooling medium is helium, the high voltage generated after the superconducting magnet quenches may cause Parsons discharge, breakdown of the current lead, and cause irreversible consequences. Summary of the invention

[0006] The present invention aims to solve at least one of the technical problems existing in the related art. To this end, the present invention proposes a compact air-cooled binary current lead for a cryostat and a manufacturing method thereof, so as to solve the problems that the existing binary current lead occupies a large space, has low sealing performance and is prone to discharge.

[0007] In a first aspect, the present invention provides a compact air-cooled binary current lead for a cryostat, the binary current lead comprising: High-temperature superconducting section, used to transmit electric current to superconducting magnet without resistance in low-temperature environment; A normal temperature section, one end of which is connected to the high temperature superconducting section and is used to transmit current from a normal temperature environment to the high temperature superconducting section; The normal temperature section is also provided with a cooling structure for introducing high-pressure helium to cool the normal temperature section.

[0008] According to a compact air-cooled binary current lead for a cryostat provided by the present invention, the cooling structure comprises a copper tube, a large stainless steel tube, a small stainless steel tube, an air inlet tube, an air outlet tube and a ceramic insulating member; The large stainless steel tube and the small stainless steel tube are sleeved on the outside of the copper tube, an annular cavity is formed between the inner wall of the large stainless steel tube, the inner wall of the small stainless steel tube and the outer wall of the copper tube, the ceramic insulating member is arranged at the end of the annular cavity, and the air inlet pipe and the air outlet pipe are respectively arranged at the small stainless steel tube and connected to the annular cavity; A through hole is provided on the side wall of the copper tube, so that the pipeline inside the copper tube is connected with the annular cavity.

[0009] According to a compact air-cooled binary current lead for a low-temperature thermostat provided by the present invention, a position on the outer circumference of the copper tube avoiding the through hole is coated with polyimide tape in a semi-overlapping manner to avoid Parson's discharge in a helium atmosphere.

[0010] According to a compact air-cooled binary current lead for a cryostat provided by the present invention, the cooling structure further comprises a ceramic shunt sleeved on the wall of the copper tube, and a gap is provided between the outer peripheral surface of the ceramic shunt and the side wall of the large stainless steel tube; The ceramic insulating member, the through hole and the ceramic diverter are sequentially arranged from both ends of the normal temperature section to the middle of the normal temperature section, so that after the high-pressure helium enters the annular cavity, a larger portion of the high-pressure helium enters the pipeline inside the copper tube through the through hole, and a smaller portion of the high-pressure helium passes through the gap between the outer peripheral surface of the ceramic diverter and the side wall of the large stainless steel tube.

[0011] According to the present invention, a compact air-cooled binary current lead for a low-temperature thermostat also includes a Kovar alloy for sealed connection, one end of the ceramic insulating part is vacuum brazed with the copper tube through the Kovar alloy, and the other end of the ceramic insulating part is vacuum brazed with the small stainless steel tube through the Kovar alloy.

[0012] In a second aspect, the present invention provides a method for manufacturing a compact air-cooled binary current lead, which is applied to any of the above compact air-cooled binary current leads for cryostat, wherein the cooling structure comprises a copper tube, a through hole, a large stainless steel tube, a small stainless steel tube, an air inlet pipe, an air outlet pipe, a ceramic insulator, a kovar alloy, a ceramic shunt and a polyimide tape; The manufacturing method comprises: S1, sealing and welding the ceramic insulating member with the small stainless steel tube and the copper tube by vacuum brazing through the Kovar alloy; S2. Wrap the polyimide tape on the outside of the copper tube using a half-overlapping method, and note that the through hole must not be wrapped; S3, bonding the ceramic shunt and the copper tube using low-temperature glue; S4, sleeve the large stainless steel tube onto the outside of the copper tube, and seal-weld the large stainless steel tube and the small stainless steel tube using argon arc welding; S5. After welding is completed, the cooling structure is immersed in liquid nitrogen to reduce its overall temperature to K, and then taken out of the liquid nitrogen and leak tested using a helium negative pressure method; S6. After the leak detection is qualified using the helium negative pressure method, the cooling structure is immersed in liquid nitrogen again to reduce its overall temperature to 77K, and then taken out of the liquid nitrogen, the air inlet pipe or the air outlet pipe is sealed, and then helium is introduced into the cooling structure through the unsealed air outlet pipe or the air inlet pipe, and a leak detection is performed using the helium absorption method.

[0013] According to a method for manufacturing a compact air-cooled binary current lead provided by the present invention, in step S5: leak detection is performed using a helium negative pressure method, and the leak detection result must be better than 5e-9Pa·m³ / s.

[0014] According to a method for manufacturing a compact air-cooled binary current lead provided by the present invention, helium is introduced into the cooling structure and a helium absorption method is used to perform leak detection, which specifically includes: Helium is introduced into the cooling structure through the air inlet pipe or the air outlet pipe, and the pressure is gradually loaded to 2MPa with a pressure value between 0.3MPa and 0.5MPa as a step. After each step is loaded to a stable pressure, a helium absorption method is used for leak detection, and the leak detection results are better than 5e-7Pa·m³ / s. After the pressure is loaded to 2MPa and the helium absorption method leak detection is qualified, the pressure is maintained for 2h without dropping.

[0015] According to a method for manufacturing a compact air-cooled binary current lead provided by the present invention, after the sealing test of the cooling structure is completed, the electrical insulation performance test is then performed.

[0016] According to a method for manufacturing a compact air-cooled binary current lead provided by the present invention, the electrical insulation performance test specifically includes: Keeping the helium environment in the normal temperature section unchanged, use an insulation tester to test the compact air-cooled binary current lead, starting from 100V, and perform step-by-step testing every 200~300V, with a testing time of not less than 30s until the voltage is pressed to 1500V, to detect whether the resistance of the normal temperature section is better than 10^9 ohm level.

[0017] The above one or more technical solutions in the present invention have at least one of the following technical effects: the cooling structure greatly reduces the radial size of the current lead, improves the sealing performance of the current lead to high-pressure helium in a low-temperature environment, can use high-pressure helium for cooling, and improves the heat exchange efficiency in the normal temperature section. At the same time, the cooling structure can also avoid the discharge phenomenon caused by high voltage, so that the binary current lead meets the requirements of the low-temperature thermostat for compact size, high airtightness and anti-breakdown, so that a sufficient number of current leads that meet the operation requirements of the superconducting magnet can be installed in a low-temperature thermostat.

[0018] In addition to the technical problems solved by the present invention, the technical features of the technical solutions constituted, and the advantages brought about by the technical features of these technical solutions described above, other technical features of the present invention and the advantages brought about by these technical features will be further explained in conjunction with the accompanying drawings or will be understood through the practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or related technologies, the drawings required for use in the embodiments or related technical descriptions are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0020] Figure 1 A schematic diagram of the structure of a compact air-cooled binary current lead for a cryostat provided in an embodiment of the present invention.

[0021] Figure 2 for Figure 1 A magnified schematic diagram of the partial image in center A.

[0022] Figure 3 for Figure 1 A magnified schematic diagram of the partial image in middle B.

[0023] Reference numerals: 1. High-temperature superconducting section; 2. Normal temperature section; 3. Inlet pipe; 4. Outlet pipe; 5. Copper tube; 6. Ceramic insulation; 7. Kovar alloy; 8. Through hole; 9. Polyimide tape; 10. Ceramic shunt; 11. Large stainless steel tube; 12. Small stainless steel tube. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical solution and advantages of the present invention clearer, the technical solution of the present invention will be clearly described below in conjunction with the drawings of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0025] In the description of the embodiments of the present invention, it should be noted that the terms "center", "longitudinal", "lateral", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside" and the like indicate positions or positional relationships based on the positions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the embodiments of the present invention and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a specific orientation, be constructed and operate in a specific orientation, and therefore cannot be understood as limitations on the embodiments of the present invention. In addition, the terms "first", "second", and "third" are used for descriptive purposes only and cannot be understood as indicating or implying relative importance.

[0026] In the description of the embodiments of the present invention, it should be noted that, unless otherwise clearly specified and limited, the terms "connected" and "connection" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium. For ordinary technicians in this field, the specific meanings of the above terms in the embodiments of the present invention can be understood according to specific circumstances.

[0027] In the embodiments of the present invention, unless otherwise clearly specified and limited, a first feature being "above" or "below" a second feature may mean that the first and second features are in direct contact, or the first and second features are in indirect contact through an intermediate medium. Moreover, a first feature being "above", "above" or "above" a second feature may mean that the first feature is directly above or obliquely above the second feature, or simply means that the first feature is higher in level than the second feature. A first feature being "below", "below" or "below" a second feature may mean that the first feature is directly below or obliquely below the second feature, or simply means that the first feature is lower in level than the second feature.

[0028] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the embodiment of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0029] In the present invention, high pressure helium refers to helium at an absolute temperature of 50K and a pressure of 17.5 bara.

[0030] Low temperature refers to a temperature not higher than the liquefaction point of nitrogen, that is, not higher than the absolute temperature 77K.

[0031] High-temperature superconductors (HTS) refer to materials that can exhibit superconductivity at higher temperatures (generally liquid nitrogen temperature, i.e., absolute temperature 77K) than the temperature of liquid helium (4.2K).

[0032] Kovar, also known as iron-nickel-cobalt alloy, acts as a transition layer between ceramic parts and metal parts during vacuum brazing, which can significantly reduce the temperature stress caused by the different expansion coefficients of different materials, reduce the risk of leakage after welding, and greatly improve the reliability of the weld.

[0033] like Figures 1 to 3 As shown, in an embodiment of the present invention, a compact air-cooled binary current lead for a cryostat is introduced.

[0034] The compact air-cooled binary current lead includes a high-temperature superconducting section 1 and a normal temperature section 2.

[0035] The high temperature superconducting section 1 is used to transmit current to the superconducting magnet without resistance in a low temperature environment (not higher than the absolute temperature 77K). One end of the normal temperature section 2 is connected to the high temperature superconducting section 1 and is used to transmit current from the normal temperature environment to the high temperature superconducting section 1.

[0036] In particular, the normal temperature section 2 is also provided with a cooling structure for introducing high-pressure helium to cool the normal temperature section 2 .

[0037] Furthermore, the cooling structure includes a copper tube 5 , a large stainless steel tube 11 , a small stainless steel tube 12 , an air inlet pipe 3 , an air outlet pipe 4 and a ceramic insulating member 6 .

[0038] The large stainless steel tube 11 and the small stainless steel tube 12 are sleeved on the outside of the copper tube 5. An annular cavity is formed between the inner wall of the large stainless steel tube 11 and the inner wall of the small stainless steel tube 12 and the outer wall of the copper tube 5. The ceramic insulator 6 is arranged at the end of the annular cavity.

[0039] The air inlet pipe 3 and the air outlet pipe 4 are respectively arranged at the small stainless steel pipe 12 and communicate with the annular cavity.

[0040] A through hole 8 is provided on the side wall of the copper tube 5 to connect the pipeline inside the copper tube 5 with the annular cavity. For example, at an absolute temperature of 50K, helium with a pressure of 17.5 bara enters from the inlet pipe 3, exchanges heat with the copper tube 5 in the cavity, and is discharged from the outlet pipe 4.

[0041] In this embodiment, the cooling structure greatly reduces the radial size of the current lead, improves the sealing performance of the current lead to high-pressure helium in a low-temperature environment (not higher than absolute temperature 77K), can use high-pressure helium to cool down, and improves the heat exchange efficiency in the normal temperature section. At the same time, the cooling structure can also avoid the discharge phenomenon caused by high voltage, so that the binary current lead meets the requirements of the low-temperature thermostat for low heat load, high airtightness and anti-breakdown.

[0042] Based on the above embodiments, another embodiment of the present invention introduces a compact air-cooled binary current lead for a cryostat.

[0043] The outer circumference of the copper tube 5 is covered with a polyimide tape 9 in a semi-overlapping manner at a position avoiding the through hole 8, so as to avoid Parson discharge in a helium atmosphere. Furthermore, the cooling structure also includes a ceramic shunt 10 sleeved on the wall of the copper tube 5. There is a gap between the outer circumference of the ceramic shunt 10 and the side wall of the large stainless steel tube 11.

[0044] The ceramic insulating part 6, the through hole 8 and the ceramic diverter 10 are arranged in sequence from both ends of the normal temperature section 2 to the middle of the normal temperature section 2, so that after the high-pressure helium enters the annular cavity, a larger part of the high-pressure helium enters the pipeline inside the copper tube 5 through the through hole 8, and a smaller part of the high-pressure helium passes through the gap between the outer peripheral surface of the ceramic diverter 10 and the side wall of the large stainless steel tube 11.

[0045] In this embodiment, the outside of the copper tube 5 is wrapped with a polyimide tape 9 to avoid discharge. Since the polyimide tape 9 has poor thermal conductivity, it is wrapped around the outside of the copper tube 5, resulting in poor convection heat transfer on the outside. However, since the ceramic shunt 10 and the through hole 8 guide a large amount of gas to the inside of the copper tube 5, it can better contact with the side wall of the copper tube 5 for heat exchange, and then take away the Joule heat generated in the normal operation of the current lead, thereby avoiding discharge and better improving the heat exchange effect of the normal temperature section 2 of the current lead.

[0046] Based on the above embodiments, another embodiment of the present invention introduces a compact air-cooled binary current lead for a cryostat.

[0047] The high temperature superconducting section 1 is configured as a thin-walled stainless steel tube with grooves on the surface, wherein soldered high temperature superconductor (HTS) strips are embedded in the grooves.

[0048] Specifically, the high temperature superconducting section 1 and the normal temperature section 2 are connected by soldering and bolts. The normal temperature section 2 uses a copper tube 5. The high temperature superconducting section 1 is set as a thin-walled stainless steel tube. A groove is opened on its surface. A soldered high temperature superconductor (HTS) strip is embedded in the groove.

[0049] In addition, the number of strips of the high-temperature superconducting section 1 can be selected according to the current carrying capacity. The high-temperature superconductor (HTS) strip uses 4mm strips from Sumitomo Heavy Industries of Japan. Each strip has a current carrying capacity of 180A at an absolute temperature of 77K.

[0050] Furthermore, the cooling structure also includes Kovar alloy 7 for sealing connection.

[0051] One end of the ceramic insulator 6 is vacuum brazed with the copper tube 5 through the Kovar alloy 7. The other end of the ceramic insulator 6 is vacuum brazed with the small stainless steel tube 12 through the Kovar alloy 7.

[0052] The vacuum brazing seam formed by the ceramic insulating member 6 through the Kovar alloy 7 can effectively resist high-pressure helium at a temperature range of 300K-50K and a pressure of 17.5 bara.

[0053] Since the binary current lead has a compact structure and is small in radial direction, although the expansion coefficients of ceramics, copper and stainless steel are different, the stress between the connecting surfaces of different materials caused by low temperature (not higher than absolute temperature 77K) is relatively small, and the weld can still meet the low temperature (not higher than absolute temperature 77K) and pressure requirements.

[0054] On the other hand, in an embodiment of the present invention, a method for manufacturing a compact air-cooled binary current lead is introduced, which is used to manufacture the compact air-cooled binary current lead described in any of the above embodiments. The cooling structure includes a copper tube 5, a through hole 8, a large stainless steel tube 11, a small stainless steel tube 12, an air inlet pipe 3, an air outlet pipe 4, a ceramic insulator 6, a kovar alloy 7, a ceramic shunt 10 and a polyimide tape 9; The manufacturing method comprises: S1, passing the ceramic insulating part 6 through the Kovar alloy 7, and using a vacuum brazing method to perform sealing welding with the small stainless steel tube 12 and the copper tube 5.

[0055] S2. Wrap the polyimide tape 9 on the outside of the copper tube 5 using a half-wrapping method, and note that the through hole 8 must not be wrapped.

[0056] S3. Use low-temperature glue to bond the ceramic shunt 10 and the copper tube 5.

[0057] S4, sleeve the large stainless steel tube 11 onto the outside of the copper tube 5, and seal-weld the large stainless steel tube 11 and the small stainless steel tube 12 using argon arc welding.

[0058] S5. After welding is completed, the cooling structure is immersed in liquid nitrogen to reduce its overall temperature to 77K, and then taken out of the liquid nitrogen and leak tested using a helium negative pressure method.

[0059] S6. After the leak detection is qualified using the helium negative pressure method, the cooling structure is immersed in liquid nitrogen again to reduce its overall temperature to 77K, and then taken out of the liquid nitrogen, the air inlet pipe 3 or the air outlet pipe 4 is sealed, and then helium is introduced into the cooling structure through the unsealed air outlet pipe 4 or the air inlet pipe 3, and a leak detection is performed using the helium absorption method.

[0060] Specifically, the ceramic insulating member 6 is connected to the copper tubes 5 and the small stainless steel tube 12 on both sides by vacuum brazing through the Kovar alloy 7. The outer side of the copper tube 5 is half-wrapped with a polyimide tape 9, and the polyimide tape 9 is kept away from the through hole 8. The ceramic shunt 10 is bonded to the copper tube 5 using a low-temperature glue. Then the large stainless steel tube 11 is sleeved onto the outer side of the copper tube 5, and the various parts of the cooling structure are sealed and welded using argon arc welding.

[0061] The high temperature superconducting section 1 is connected to the bottom of the normal temperature section 2 by soldering and bolts. After welding, the cooling structure is immersed in liquid nitrogen to reduce its overall temperature to 77K, and then taken out of the liquid nitrogen and leaked by using the helium negative pressure method, and the leak rate is controlled to be better than 5e-9Pa·m³ / s.

[0062] The high-temperature superconducting section 1 is connected to the normal-temperature section 2 by soldering and bolts, and then the cooling structure is tested for sealing: the compact air-cooled binary current lead is immersed in liquid nitrogen as a whole to reduce its temperature to 77K, and then taken out of the liquid nitrogen, and the inlet pipe 3 or the outlet pipe 4 is sealed, and then helium is introduced into the cooling structure from the outlet pipe 4 or the inlet pipe 3 that is not sealed, and the pressure value between 0.3MPa and 0.5MPa is used as a step, and is gradually loaded to 2MPa. After each step is loaded to a stable pressure, a helium absorption method is used for leak detection, and the leak detection result is better than 5e-7Pa·m³ / s. After the pressure is loaded to 2MPa and the helium absorption method leak detection is qualified, the pressure is maintained for 2h without a drop.

[0063] Furthermore, a platinum resistance thermometer is set between the high-temperature superconducting section 1 and the room-temperature section 2. After the compact air-cooled binary current lead is energized to the design current of 500A, its temperature is lower than the critical temperature of the high-temperature superconducting current lead. Voltage monitoring points are set on both sides of the high-temperature superconducting section 1 to ensure that when the current lead works normally, the voltage drop of the high-temperature superconducting section 1 is better than 1μV / cm.

[0064] When the compact air-cooled binary current lead is operating normally, the low-temperature superconducting wire on the lower side of the high-temperature superconducting section 1 is immersed in liquid helium, and the entire compact air-cooled binary current lead is located in the helium space above the liquid helium, which can ensure that the temperature of the high-temperature superconducting section 1 is lower than the critical temperature of the high-temperature superconducting tape, ensuring its normal operation. When the low-temperature high-pressure helium with a temperature of 50K and a pressure of 17.5 bara enters the normal temperature section 2 through the inlet pipe 3, the presence of the ceramic shunt 10 allows a large amount of helium to enter the pipeline inside the copper tube 5 through the through hole 8, and a small amount of helium passes through the gap between the large stainless steel tube 11 and the ceramic shunt 10.

[0065] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A compact air-cooled binary current lead for a cryostat, characterized in that include: A high temperature superconducting section (1) for transmitting electric current to a superconducting magnet without resistance in a low temperature environment; A normal temperature section (2), one end of the normal temperature section (2) being connected to the high temperature superconducting section (1) and used for transmitting electric current from a normal temperature environment to the high temperature superconducting section (1); The normal temperature section (2) is also provided with a cooling structure for introducing high-pressure helium to cool the normal temperature section (2).

2. The compact air-cooled binary current lead for a cryostat according to claim 1, characterized in that The cooling structure comprises a copper tube (5), a large stainless steel tube (11), a small stainless steel tube (12), an air inlet pipe (3), an air outlet pipe (4) and a ceramic insulating member (6); The large stainless steel tube (11) and the small stainless steel tube (12) are sleeved on the outside of the copper tube (5); an annular cavity is formed between the inner wall of the large stainless steel tube (11), the inner wall of the small stainless steel tube (12) and the outer wall of the copper tube (5); the ceramic insulating member (6) is arranged at the end of the annular cavity; the air inlet pipe (3) and the air outlet pipe (4) are respectively arranged at the small stainless steel tube (12) and are connected to the annular cavity; A through hole (8) is provided on the side wall of the copper tube (5) to connect the pipeline inside the copper tube (5) with the annular cavity.

3. The compact air-cooled binary current lead for a cryostat according to claim 2, characterized in that The position of the outer peripheral surface of the copper tube (5) avoiding the through hole (8) is coated with a polyimide tape (9) in a semi-overlapping manner to avoid the Parson's discharge phenomenon in a helium atmosphere.

4. A compact air-cooled binary current lead for a cryostat according to claim 2 or 3, characterized in that The cooling structure further comprises a ceramic shunt (10) sleeved on the wall of the copper tube (5), wherein a gap is provided between the outer peripheral surface of the ceramic shunt (10) and the side wall of the large stainless steel tube (11); The ceramic insulating member (6), the through hole (8) and the ceramic diverter (10) are arranged in sequence from both ends of the normal temperature section (2) to the middle of the normal temperature section (2), so that after the high-pressure helium enters the annular cavity, a larger portion of the high-pressure helium enters the pipeline inside the copper tube (5) through the through hole (8), and a smaller portion of the high-pressure helium passes through the gap between the outer peripheral surface of the ceramic diverter (10) and the side wall of the large stainless steel tube (11).

5. The compact air-cooled binary current lead for a cryostat according to claim 4, characterized in that It also includes a Kovar alloy (7) for sealing connection, one end of the ceramic insulating part (6) is vacuum brazed with the copper tube (5) through the Kovar alloy (7), and the other end of the ceramic insulating part (6) is vacuum brazed with the small stainless steel tube (12) through the Kovar alloy (7).

6. A method for manufacturing a compact air-cooled binary current lead, characterized in that: A compact air-cooled binary current lead for a cryostat as claimed in any one of claims 1 to 5, wherein the cooling structure comprises a copper tube (5), a through hole (8), a large stainless steel tube (11), a small stainless steel tube (12), an air inlet tube (3), an air outlet tube (4), a ceramic insulator (6), a Kovar alloy (7), a ceramic shunt (10) and a polyimide tape (9); The manufacturing method comprises: S1, sealing and welding the ceramic insulating member (6) with the small stainless steel tube (12) and the copper tube (5) through the Kovar alloy (7) using a vacuum brazing method; S2. Wrap the polyimide tape (9) on the outside of the copper tube (5) using a half-wrapping method, and note that the through hole (8) must not be wrapped; S3, using low-temperature glue to bond the ceramic shunt (10) and the copper tube (5); S4, sleeve the large stainless steel tube (11) onto the outside of the copper tube (5), and seal-weld the large stainless steel tube (11) and the small stainless steel tube (12) using argon arc welding; S5. After welding is completed, the cooling structure is immersed in liquid nitrogen to reduce its overall temperature to 77K, and then taken out of the liquid nitrogen and leak tested using a helium negative pressure method; S6. After the leak detection is qualified using the helium negative pressure method, the cooling structure is immersed in liquid nitrogen again to reduce its overall temperature to 77K, and then taken out of the liquid nitrogen, the air inlet pipe (3) or the air outlet pipe (4) is sealed, and then helium is introduced into the cooling structure through the unsealed air outlet pipe (4) or the air inlet pipe (3) and a leak detection is performed using the helium absorption method.

7. The method for manufacturing a compact air-cooled binary current lead according to claim 6, characterized in that: In step S5: a helium negative pressure method is used for leak detection, and the leak detection result must be better than 5e-9Pa·m³ / s.

8. The method for manufacturing a compact air-cooled binary current lead according to claim 7, characterized in that: Introducing helium into the cooling structure and using the helium absorption method to perform leak detection specifically includes: Helium is introduced into the cooling structure through the air inlet pipe (3) or the air outlet pipe (4), and the pressure is gradually loaded to 2MPa with a pressure value between 0.3MPa and 0.5MPa as a step. After each step is loaded until the pressure is stable, a helium absorption method is used for leak detection, and the leak detection results are better than 5e-7Pa·m³ / s. After the pressure is loaded to 2MPa and the helium absorption method leak detection is qualified, the pressure is maintained for 2 hours without any drop.

9. The method for manufacturing a compact air-cooled binary current lead according to claim 6, characterized in that: After the sealing test of the cooling structure is completed, the electrical insulation performance test is then performed.

10. The method for manufacturing a compact air-cooled binary current lead according to claim 9, characterized in that: The electrical insulation performance test specifically includes: The helium environment in the normal temperature section (2) is maintained unchanged, and the compact air-cooled binary current lead is tested using an insulation tester, starting from 100 V and stepwisely tested every 200 to 300 V, with the testing time being not less than 30 seconds, until the voltage reaches 1500 V, to detect whether the resistance of the normal temperature section (2) is better than 10^9 ohm level.

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