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

Abstract

The present invention relates to the technical field of superconducting magnet current leads, and specifically provides a compact gas-cooled binary current lead for a cryostat and a manufacturing method thereof. The lead includes a high-temperature superconducting section and a normal-temperature section: the high-temperature superconducting section is used to transmit current to the superconducting magnet without resistance in a low-temperature environment; one end of the normal-temperature section is connected to the high-temperature superconducting section, and a cooling structure is provided inside and high-pressure helium gas is introduced for cooling. By optimizing the cooling structure, the radial size of the lead is significantly reduced and the sealing performance is improved, the heat exchange efficiency of the normal-temperature section is effectively increased, and it is ensured that the high-temperature superconducting section operates below the safety margin. This structure also has the function of preventing the Paschen discharge phenomenon caused by the high voltage generated after the superconducting magnet quenches in a helium gas environment, enabling the binary current lead to meet the requirements of being compact in size, having high airtightness and anti-breakdown, and realizing the integrated installation of multiple groups of current leads in a single cryostat, thus ensuring the stable operation of the superconducting magnet system.

Description

Technical Field

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

[0002] In an accelerator, quadrupole magnets focus or defocus the beam, and generally exist in a triple combination form, that is, three quadrupole magnets form a group. Opposite currents are applied between every two adjacent magnets to form opposite magnetic fields, so as to integrate the beam bunch in a focusing-defocusing-focusing or defocusing-focusing-defocusing manner.

[0003] For a triple-combination magnet, if a superconducting magnet is used, it needs to be placed in a cryostat to work properly. If three cryostats are set for three superconducting magnets, that is, each superconducting magnet uses a separate cryostat, the manufacturing cost is relatively high, and each cryostat needs to be equipped with a corresponding cryogenic valve box, resulting in a large overall heat leakage and increasing the heat load of the cryogenic system. Therefore, it is considered to use one cryostat for three superconducting magnets. This scheme only needs to be equipped with one cryogenic valve box, and the heat load of this cryostat is lower than the total heat leakage of three separate cryostats, which can greatly reduce the overall heat load of the cryogenic system and reduce the construction cost.

[0004] CCT / DCT (Canted Cosine Theta, skew solenoid type, Discrete Cosine Theta, discrete type cosine) superconducting magnets are used inside the cryostat. This type of superconducting magnet has the advantages of high field quality, low-current operation, and light weight. Each superconducting magnet is in a cylindrical shape and is formed by nesting. In addition to the main coil being a quadrupole coil, it may also be nested with sextupole coils, octupole coils, two-way correction coils, etc. That is, one superconducting magnet contains multiple coils and can operate simultaneously. After three superconducting magnets are placed in one cryostat, each cryostat has multiple coils. According to physical requirements, there are at most 10 coils for the three groups of superconducting magnets, and each coil is independently powered, that is, at most 20 current leads need to be set for this cryostat.

[0005] The thermostat has many current leads, and the operating current of each current lead is approximately 500 A. If the traditional binary (HTS + copper lead) conduction cooling method is used for the current leads, due to the low conduction cooling efficiency and excessive heat load, the burden on the cryogenic station will increase, and in severe cases, the current leads may be burned out. If the number of leads inside the thermostat is small, the current leads can be cooled by the evaporated gas at an absolute temperature of 4 K. However, for the above-mentioned multi-current lead form, the cooling method is generally gas cooling with cooling gas. At the same time, to reduce the heat leakage value of the current leads at an absolute temperature of 4.2 K, a binary lead structure of HTS + normal temperature copper lead is used. The gas source is high-pressure helium gas at an absolute temperature of 50 K, and the maximum pressure of the high-pressure helium gas can reach 17.5 bara. The higher pressure can increase the heat transfer efficiency of the normal temperature copper lead and keep the current leads operating at a safe temperature, but the higher pressure will increase the leakage risk of the seals. At the same time, the large number of leads requires the structure of the current leads to be compact during design to avoid interference with other components of the thermostat. Since the cooling medium is helium gas, the high voltage generated after the superconducting magnet quenches may cause the occurrence of Paschen discharge, breaking down the current leads and causing 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. For this purpose, the present invention provides a compact gas-cooled binary current lead for a cryogenic thermostat and a manufacturing method thereof to solve the problems of large space occupation, low sealing performance, and easy occurrence of discharge phenomena of the existing binary current leads.

[0007] In a first aspect, the present invention provides a compact gas-cooled binary current lead for a cryogenic thermostat, and the binary current lead includes:

[0008] A high-temperature superconducting section for transmitting current to the superconducting magnet without resistance in a low-temperature environment;

[0009] A normal-temperature section, one end of the normal-temperature section is connected to the high-temperature superconducting section, and is used for transmitting current from the normal-temperature environment to the high-temperature superconducting section;

[0010] Wherein, the normal-temperature section is further provided with a cooling structure for introducing high-pressure helium gas to cool the normal-temperature section.

[0011] According to a compact gas-cooled binary current lead for a cryogenic thermostat provided by the present invention, the cooling structure includes a copper tube, a large stainless-steel tube, a small stainless-steel tube, an inlet pipe, an outlet pipe, and a ceramic insulating part;

[0012] The large stainless-steel tube and the small stainless-steel tube are sleeved outside the copper tube. An annular cavity is formed between the inner side walls of the large stainless-steel tube and the small stainless-steel tube and the outer side wall of the copper tube. The ceramic insulating member is arranged at the end of the annular cavity. The inlet pipe and the outlet pipe are respectively arranged at the small stainless-steel tube and communicate with the annular cavity;

[0013] A through hole is formed in the side wall of the copper tube to communicate the pipeline inside the copper tube with the annular cavity.

[0014] According to a compact air-cooled binary current lead for a cryostat provided by the present invention, the position on the outer peripheral surface of the copper tube that avoids the through hole is coated with a polyimide tape in a semi-overlapping wrapping manner to avoid the Paschen discharge phenomenon in a helium atmosphere.

[0015] According to a compact air-cooled binary current lead for a cryostat provided by the present invention, the cooling structure further includes a ceramic shunt arranged sleeved on the tube wall of the copper tube. There is a gap between the outer peripheral surface of the ceramic shunt and the side wall of the large stainless-steel tube;

[0016] From both ends of the normal temperature section to the middle of the normal temperature section, the ceramic insulating member, the through hole and the ceramic shunt are arranged in sequence. After the high-pressure helium enters the annular cavity, a larger part of the high-pressure helium enters the pipeline inside the copper tube through the through hole, and a smaller part of the high-pressure helium passes through the gap between the outer peripheral surface of the ceramic shunt and the side wall of the large stainless-steel tube.

[0017] According to a compact air-cooled binary current lead for a cryostat provided by the present invention, it further includes a kovar alloy for sealed connection. One end of the ceramic insulating member is vacuum brazed with the copper tube through the kovar alloy, and the other end of the ceramic insulating member is vacuum brazed with the small stainless-steel tube through the kovar alloy.

[0018] In a second aspect, the present invention provides a manufacturing method of a compact air-cooled binary current lead, which is applied to the compact air-cooled binary current lead for a cryostat described in any one of the above. The cooling structure includes a copper tube, a through hole, a large stainless-steel tube, a small stainless-steel tube, an inlet pipe, an outlet pipe, a ceramic insulating member, a kovar alloy, a ceramic shunt and a polyimide tape;

[0019] The manufacturing method includes: S1. Vacuum brazing the ceramic insulating member with the small stainless-steel tube and the copper tube through the kovar alloy by using a vacuum brazing method for sealed welding;

[0020] S2. Coating the polyimide tape on the outside of the copper tube in a semi-overlapping wrapping method, and note that the through hole should not be wrapped;

[0021] S3. Bond the ceramic shunt and the copper pipe using a low-temperature adhesive;

[0022] S4. Sleeve the large stainless-steel pipe outside the copper pipe and seal-weld the large stainless-steel pipe and the small stainless-steel pipe using argon arc welding;

[0023] S5. After welding, immerse the cooling structure in liquid nitrogen to reduce its overall temperature to K, then take it out from the liquid nitrogen and use the helium negative pressure method to detect leaks;

[0024] S6. After passing the leak detection using the helium negative pressure method, immerse the cooling structure in liquid nitrogen again to reduce its overall temperature to 77K, then take it out from the liquid nitrogen, seal the inlet pipe or the outlet pipe, and then introduce helium into the cooling structure through the non-sealed outlet pipe or inlet pipe and use the helium absorption method to detect leaks.

[0025] According to the manufacturing method of a compact air-cooled binary current lead provided by the present invention, in step S5: when using the helium negative pressure method to detect leaks, the leak detection result should be better than 5e-9 Pa·m³ / s.

[0026] According to the manufacturing method of a compact air-cooled binary current lead provided by the present invention, introducing helium into the cooling structure and using the helium absorption method to detect leaks specifically includes:

[0027] Introduce helium into the cooling structure through the inlet pipe or the outlet pipe, and use a pressure value between 0.3 MPa and 0.5 MPa as a step, gradually load up to 2 MPa. After each step is loaded to a stable pressure, use the helium absorption method to detect leaks, and the leak detection results are all better than 5e-7 Pa·m³ / s. After the pressure is loaded to 2 MPa and the leak detection using the helium absorption method is qualified, maintain the pressure for 2 h without a decrease.

[0028] According to the manufacturing method of a compact air-cooled binary current lead provided by the present invention, after the sealing performance of the cooling structure is detected, the electrical insulation performance is detected.

[0029] According to the manufacturing method of a compact air-cooled binary current lead provided by the present invention, the electrical insulation performance detection specifically includes:

[0030] Keep the helium environment in the normal temperature section unchanged, use an insulation tester to apply voltage to the compact air-cooled binary current lead, starting from 100 V, and perform stepwise voltage application every 200 - 300 V for no less than 30 s until the voltage is applied to 1500 V, and detect whether the resistance in the normal temperature section is better than the 10^9 ohm level.

[0031] One or more of the above 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 gas in a low-temperature environment, can use high-pressure helium gas for cooling, improves the heat exchange efficiency in the normal temperature section, and at the same time the cooling structure can also avoid the discharge phenomenon caused by high voltage, enabling the binary current lead to meet the requirements of the cryostat for compact size, high airtightness and anti-breakdown, so that a sufficient number of current leads meeting the operation requirements of the superconducting magnet can be installed in a cryostat.

[0032] In addition to the technical problems solved by the present invention, the technical features of the technical solutions constituted, and the advantages brought by these technical features described above, other technical features of the present invention and the advantages brought by these technical features will be further described in conjunction with the accompanying drawings or understood through the practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or in the related technologies, the following will briefly introduce the drawings required for use in the description of the embodiments or the related technologies. Obviously, the drawings in the following description are only 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.

[0034] Figure 1 It is a schematic structural diagram of a compact air-cooled binary current lead for a cryostat provided by an embodiment of the present invention.

[0035] Figure 2 is Figure 1 an enlarged schematic view of a partial view A in

[0036] Figure 3 is Figure 1 an enlarged schematic view of a partial view B in

[0037] REFERENCE SIGNS:

[0038] 1, high-temperature superconducting section; 2, normal temperature section; 3, inlet pipe; 4, outlet pipe; 5, copper pipe; 6, ceramic insulating part; 7, kovar alloy; 8, through hole; 9, polyimide tape; 10, ceramic shunt; 11, large stainless steel pipe; 12, small stainless steel pipe. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0039] To make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions in the present invention will be clearly described below with reference to the accompanying drawings in the present invention. Apparently, the described embodiments are some but not all of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present invention without creative efforts shall fall within the protection scope of the present invention.

[0040] In the description of the embodiments of the present invention, it should be noted that the orientation or positional relationship indicated by the terms "center", "longitudinal", "transverse", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the embodiments of the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to the embodiments of the present invention. In addition, the terms "first", "second", and "third" are only used for descriptive purposes and should not be construed as indicating or implying relative importance.

[0041] 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 "coupled" should be understood in a broad sense. For example, it may be a fixed connection, a detachable connection, or an integral connection; it may be a mechanical connection or an electrical connection; it may be directly connected or indirectly connected through an intermediate medium. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of the present invention can be understood according to specific circumstances.

[0042] In the embodiments of the present invention, unless otherwise clearly specified and limited, the first feature being "on" or "under" the second feature may be that the first and second features are in direct contact, or the first and second features are indirectly in contact through an intermediate medium. Moreover, the first feature being "above", "over" and "on top of" the second feature may be that the first feature is directly above or obliquely above the second feature, or merely indicates that the first feature has a higher horizontal height than the second feature. The first feature being "under", "beneath" and "underneath" the second feature may be that the first feature is directly below or obliquely below the second feature, or merely indicates that the first feature has a lower horizontal height than the second feature.

[0043] In the description of this specification, the descriptions referring to terms such as "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. mean that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the embodiments of the present invention. In this specification, the schematic expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0044] In the present invention, high-pressure helium gas refers to helium gas at an absolute temperature of 50K and a pressure of 17.5 bara.

[0045] Low temperature refers to a temperature not higher than the liquefaction point of nitrogen, that is, not higher than an absolute temperature of 77K.

[0046] High-temperature superconductor (HTS) refers to a material that can exhibit superconductivity at a relatively high temperature (generally referring to the temperature of liquid nitrogen, that is, an absolute temperature of 77K) compared to the temperature of liquid helium (absolute temperature of 4.2K).

[0047] Kovar alloy, also known as iron-nickel-cobalt alloy. When vacuum brazing, Kovar alloy is used as a transition layer between ceramic parts and metal parts, which can significantly reduce the temperature stress generated due to different expansion coefficients of different materials, reduce the leakage risk after welding, and greatly improve the reliability of the weld.

[0048] As Figures 1 to 3 shown, in the embodiment of the present invention, a compact air-cooled binary current lead for a cryostat is introduced.

[0049] Among them, the compact air-cooled binary current lead includes a high-temperature superconducting section 1 and a normal-temperature section 2.

[0050] 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 an absolute temperature of 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.

[0051] In particular, the normal-temperature section 2 is also provided with a cooling structure for introducing high-pressure helium gas to cool the normal-temperature section 2.

[0052] Furthermore, the cooling structure includes a copper tube 5, a large stainless-steel tube 11, a small stainless-steel tube 12, an inlet pipe 3, an outlet pipe 4 and a ceramic insulating member 6.

[0053] The large stainless steel tube 11 and the small stainless steel tube 12 are sleeved outside the copper tube 5. An annular cavity is formed between the inner side walls of the large stainless steel tube 11 and the small stainless steel tube 12 and the outer side wall of the copper tube 5. The ceramic insulator 6 is arranged at the end of the annular cavity.

[0054] The intake pipe 3 and the exhaust pipe 4 are respectively arranged at the small stainless steel tube 12 and communicate with the annular cavity.

[0055] A through hole 8 is formed in the side wall of the copper tube 5 to communicate the pipeline inside the copper tube 5 with the annular cavity. For example, helium gas with a pressure of 17.5 bara enters from the intake pipe 3 at an absolute temperature of 50K, exchanges heat with the copper tube 5 in the cavity, and then discharges from the exhaust pipe 4.

[0056] In this embodiment, the cooling structure greatly reduces the radial dimension of the current lead, improves the sealing performance of the current lead to high-pressure helium gas in a low-temperature environment (not higher than an absolute temperature of 77K), can use high-pressure helium gas for cooling, improves the heat exchange efficiency in the normal temperature section, and 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 cryostat for low heat load, high airtightness and anti-breakdown.

[0057] On the basis of the above embodiment, in another embodiment of the present invention, a compact air-cooled binary current lead for a cryostat is introduced.

[0058] The outer peripheral surface of the copper tube 5 at a position avoiding the through hole 8 is coated with a polyimide tape 9 in a semi-overlapping manner to avoid the Paschen discharge phenomenon in a helium atmosphere. Further, the cooling structure further includes a ceramic shunt 10 sleeved on the pipe wall of the copper tube 5. There is a gap between the outer peripheral surface of the ceramic shunt 10 and the side wall of the large stainless steel tube 11.

[0059] From both ends of the normal temperature section 2 to the middle of the normal temperature section 2, the ceramic insulator 6, the through hole 8 and the ceramic shunt 10 are sequentially arranged. After the high-pressure helium gas enters the annular cavity, a larger part of the high-pressure helium gas enters the pipeline inside the copper tube 5 through the through hole 8, and a smaller part of the high-pressure helium gas passes through the gap between the outer peripheral surface of the ceramic shunt 10 and the side wall of the large stainless steel tube 11.

[0060] In this embodiment, a polyimide tape 9 is wound around the outer side of the copper tube 5, which can avoid the discharge phenomenon. Since the polyimide tape 9 has poor thermal conductivity itself, after being wound around the outer side of the copper tube 5, the convective heat transfer effect on its outer surface is relatively poor. However, since the ceramic current divider 10 and the through hole 8 guide a large amount of gas to the inner side of the copper tube 5, it can better contact the side wall of the copper tube 5 for heat transfer, and then take away the Joule heat generated during the normal operation of the current lead, thereby not only avoiding the discharge phenomenon, but also better improving the heat transfer effect of the normal temperature section 2 of the current lead.

[0061] On the basis of the above embodiment, in another embodiment of the present invention, a compact air-cooled binary current lead for a cryostat is introduced.

[0062] The high-temperature superconducting section 1 is set as a thin-walled stainless steel tube with grooves on its surface. The grooves are embedded with soldered high-temperature superconductor (HTS) tapes.

[0063] 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. Grooves are provided on its surface. The grooves are embedded with soldered high-temperature superconductor (HTS) tapes.

[0064] Moreover, the number of tapes can be selected according to the magnitude of the current carried in the high-temperature superconducting section 1. The high-temperature superconductor (HTS) tapes use 4mm tapes from Sumitomo Heavy Industries, Japan. The current-carrying capacity of each tape is 180A at an absolute temperature of 77K.

[0065] Furthermore, the cooling structure further includes a kovar alloy 7 for sealed connection.

[0066] One end of the ceramic insulator 6 is vacuum brazed to the copper tube 5 through the kovar alloy 7. The other end of the ceramic insulator 6 is vacuum brazed to the small stainless steel tube 12 through the kovar alloy 7.

[0067] The vacuum brazing weld formed by the ceramic insulator 6 through the kovar alloy 7 can effectively resist high-pressure helium gas in the temperature range of 300K - 50K and a pressure of 17.5bara.

[0068] Since the binary current lead has a compact structure and a small radial dimension, although the expansion coefficients of ceramics, copper, and stainless steel are different, the stress between the joints of different materials caused by low temperature (not higher than an absolute temperature of 77K) is relatively small, and this weld can still meet the requirements of low temperature (not higher than an absolute temperature of 77K) and pressure resistance.

[0069] On the other hand, in an embodiment of the present invention, a method for fabricating a compact gas-cooled binary current lead is introduced, which is used to fabricate the compact gas-cooled binary current lead described in any of the above embodiments. Among them, 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 inlet pipe 3, an outlet pipe 4, a ceramic insulator 6, a kovar alloy 7, a ceramic shunt 10, and a polyimide tape 9;

[0070] The fabrication method includes: S1. Sealing and welding the ceramic insulator 6 to the small stainless steel tube 12 and the copper tube 5 through the kovar alloy 7 using vacuum brazing.

[0071] S2. Coating the polyimide tape 9 on the outer side of the copper tube 5 using a semi-overlapping wrapping method, noting that the through hole 8 should not be wrapped.

[0072] S3. Bonding the ceramic shunt 10 and the copper tube 5 using a low-temperature adhesive.

[0073] S4. Sleeving the large stainless steel tube 11 outside the copper tube 5 and sealing and welding the large stainless steel tube 11 to the small stainless steel tube 12 using argon arc welding.

[0074] S5. After welding, soaking the cooling structure in liquid nitrogen to reduce its overall temperature to 77K, then taking it out of the liquid nitrogen and using the helium negative pressure method for leak detection.

[0075] S6. After passing the leak detection using the helium negative pressure method, soaking the cooling structure in liquid nitrogen again to reduce its overall temperature to 77K, then taking it out of the liquid nitrogen, sealing the inlet pipe 3 or the outlet pipe 4, and then introducing helium into the cooling structure through the non-sealed outlet pipe 4 or inlet pipe 3 and using the helium absorption method for leak detection.

[0076] Specifically, the ceramic insulator 6 is vacuum brazed to the copper tubes 5 and the small stainless steel tube 12 on both sides through the kovar alloy 7 for connection. The polyimide tape 9 is semi-overlapped and wrapped on the outer side of the copper tube 5, and the polyimide tape 9 is made to avoid the through hole 8. The ceramic shunt 10 is bonded to the copper tube 5 using a low-temperature adhesive. Then, the large stainless steel tube 11 is sleeved outside the copper tube 5, and argon arc welding is used to seal and weld each part of the cooling structure.

[0077] The high-temperature superconducting section 1 is connected to the bottom of the normal-temperature section 2 by soldering and bolts. After welding, soaking the cooling structure in liquid nitrogen to reduce its overall temperature to 77K, then taking it out of the liquid nitrogen and using the helium negative pressure method for leak detection, controlling the leak rate to be better than 5e-9 Pa·m³ / s.

[0078] Connect the high-temperature superconducting section 1 to the normal-temperature section 2 by soldering with tin and bolts, and then conduct a leak tightness test on the cooling structure: Immerse the compact air-cooled binary current lead as a whole into liquid nitrogen to cool its temperature to 77K, then take it out of the liquid nitrogen, seal the air inlet pipe 3 or the air outlet pipe 4, and then introduce helium gas into the cooling structure from the unsealed air outlet pipe 4 or air inlet pipe 3. Take the pressure value between 0.3MPa and 0.5MPa as a step, and gradually load it to 2MPa. After each step is loaded to a stable pressure, use the helium suction method for leak detection. The leak detection result is better than 5e-7Pa·m³ / s. After the pressure is loaded to 2MPa and the leak detection by the helium suction method is qualified, maintain the pressure for 2h without any decrease.

[0079] Further, a platinum resistance thermometer is arranged between the high-temperature superconducting section 1 and the normal-temperature section 2. After the compact air-cooled binary current lead is energized to the designed current of 500A, its temperature is lower than the critical temperature of the high-temperature superconducting current lead. Voltage monitoring points are arranged 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.

[0080] When the compact air-cooled binary current lead operates normally, the low-temperature superconducting wire at the lower side of the high-temperature superconducting section 1 is immersed in liquid helium, and the whole 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, thus ensuring its normal operation. When the low-temperature and high-pressure helium gas at a temperature of 50K and a pressure of 17.5bara enters the normal-temperature section 2 from the air inlet pipe 3, the presence of the ceramic shunt 10 enables a large amount of helium gas to enter the pipeline inside the copper pipe 5 through the through hole 8, and a small amount of helium gas passes through the gap between the large stainless steel pipe 11 and the ceramic shunt 10.

[0081] 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 foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate 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, Comprising: A high-temperature superconducting section (1) for transmitting 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) is connected to the high-temperature superconducting section (1) for transmitting current from a normal-temperature environment to the high-temperature superconducting section (1); Wherein, the normal-temperature section (2) is further provided with a cooling structure for introducing high-pressure helium gas to cool the normal-temperature section (2); The cooling structure includes a copper pipe (5), a large stainless-steel pipe (11), a small stainless-steel pipe (12), an inlet pipe (3), an outlet pipe (4), and a ceramic insulator (6); The large stainless-steel pipe (11) and the small stainless-steel pipe (12) are sleeved outside the copper pipe (5), an annular cavity is formed between the inner side walls of the large stainless-steel pipe (11) and the small stainless-steel pipe (12) and the outer side wall of the copper pipe (5), the ceramic insulator (6) is arranged at the end of the annular cavity, and the inlet pipe (3) and the outlet pipe (4) are respectively arranged at the small stainless-steel pipe (12) and communicate with the annular cavity; A through hole (8) is opened on the side wall of the copper pipe (5) to communicate the pipeline inside the copper pipe (5) with the annular cavity.

2. The compact air-cooled binary current lead for a cryostat according to claim 1, wherein The outer peripheral surface of the copper pipe (5) at a position avoiding the through hole (8) is coated with a polyimide tape (9) in a semi-overlapping wrapping manner to avoid the Paschen discharge phenomenon in a helium atmosphere.

3. The compact air-cooled binary current lead for a cryostat according to claim 2, characterized in that, The cooling structure further includes a ceramic diverter (10) sleeved on the pipe wall of the copper pipe (5), and there is a gap between the outer peripheral surface of the ceramic diverter (10) and the side wall of the large stainless-steel pipe (11); From both ends of the normal-temperature section (2) to the middle of the normal-temperature section (2), the ceramic insulator (6), the through hole (8), and the ceramic diverter (10) are sequentially arranged. After the high-pressure helium gas enters the annular cavity, a relatively large part of the high-pressure helium gas enters the pipeline inside the copper pipe (5) through the through hole (8), and a relatively small part of the high-pressure helium gas passes through the gap between the outer peripheral surface of the ceramic diverter (10) and the side wall of the large stainless-steel pipe (11).

4. The compact air-cooled binary current lead for a cryostat according to claim 3, characterized in that Also included is a kovar alloy (7) for sealed connection. One end of the ceramic insulator (6) is vacuum brazed to the copper pipe (5) through the kovar alloy (7), and the other end of the ceramic insulator (6) is vacuum brazed to the small stainless-steel pipe (12) through the kovar alloy (7).

5. A manufacturing method of a compact air-cooled binary current lead, characterized in that, Applied to the compact air-cooled binary current lead for a cryostat as described in any one of claims 1 to 4, the cooling structure includes a copper pipe (5), a through hole (8), a large stainless-steel pipe (11), a small stainless-steel pipe (12), an inlet pipe (3), an outlet pipe (4), a ceramic insulator (6), a kovar alloy (7), a ceramic diverter (10), and a polyimide tape (9); The manufacturing method includes: S1. The ceramic insulator (6) is hermetically welded to the small stainless-steel pipe (12) and the copper pipe (5) by using a vacuum brazing method through the kovar alloy (7); S2. Wrap the polyimide tape (9) around the outside of the copper tube (5) using the half-overlap method, taking care not to wrap the through-hole (8). S3. Bond the ceramic shunt (10) and the copper tube (5) using a low-temperature adhesive. S4. Slip the large stainless steel tube (11) over the outside of the copper tube (5), and use argon arc welding to seal-weld the large stainless steel tube (11) to the small stainless steel tube (12). S5. After welding, immerse the cooling structure in liquid nitrogen to reduce its overall temperature to 77K, then remove it from the liquid nitrogen and use the helium negative pressure method to detect leaks. S6. After passing the leak detection using the helium negative pressure method, immerse the cooling structure in liquid nitrogen again to reduce its overall temperature to 77K, then remove it from the liquid nitrogen, seal the inlet pipe (3) or the outlet pipe (4), and then introduce helium into the cooling structure through the non-sealed outlet pipe (4) or inlet pipe (3) and use the helium absorption method to detect leaks.

6. The manufacturing method of the compact air-cooled binary current lead according to claim 5, wherein, In step S5: Use the helium negative pressure method to detect leaks, and the leak detection result should be better than 5e-9 Pa·m³ / s.

7. The manufacturing method of the compact air-cooled binary current lead according to claim 6, characterized in that, Introducing helium into the cooling structure and using the helium absorption method to detect leaks specifically includes: Introduce helium into the cooling structure through the inlet pipe (3) or the outlet pipe (4), and use a pressure value between 0.3 MPa and 0.5 MPa as a step, gradually load up to 2 MPa. After each step is loaded to a stable pressure, use the helium absorption method to detect leaks, and the leak detection results are all better than 5e-7 Pa·m³ / s. After the pressure is loaded to 2 MPa and the leak detection using the helium absorption method is qualified, maintain the pressure for 2 h without any decrease.

8. The manufacturing method of the compact air-cooled binary current lead according to claim 5, characterized in that, After the leak tightness test of the cooling structure is completed, conduct the electrical insulation performance test.

9. The manufacturing method of the compact air-cooled binary current lead according to claim 8, characterized in that, The electrical insulation performance test specifically includes: Keep the helium environment in the normal temperature section (2) unchanged, use an insulation tester to apply voltage to the compact air-cooled binary current lead, starting from 100V, stepwise increase the voltage by 200 - 300V each time, with the voltage application time not less than 30s until the voltage reaches 1500V, and detect whether the resistance of the normal temperature section (2) is better than the 10^9 ohm level.

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