Method and system for reducing resistance of high temperature superconducting tape joints

Abstract

The application provides a method and system for reducing joint resistance of high-temperature superconducting tape, a protective layer is plated on the whole superconducting long tape, and superconducting annealing treatment is completed; then the joint resistance of the superconducting tape is measured, for the superconducting tape with substandard joint resistance, the protective layer of the joint area of the superconducting tape is removed, and then a dense protective layer is plated on the joint area of the superconducting tape; finally, annealing treatment is performed again, so that the superconducting layer inside and outside reaches the best conduction state. The application establishes a perfect long tape recycling mechanism with high joint resistance, which can be repeatedly operated and is helpful to improve the yield of the superconducting tape; and belongs to an optimized material resistivity process, in combination with the existing tape winding and bonding technology, the application can further reduce the joint resistance and make it approach the theoretical limit.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of superconducting tape post-processing process, in particular, to a method and system for reducing the joint resistance of high-temperature superconducting tape. BACKGROUND

[0002] Since the first discovery of superconductivity in 1911, superconducting materials have been regarded as the seed of the next industrial revolution due to their enormous economic value without energy consumption, attracting countless scientists to invest blood and tears. In the past decade, the first generation of high-temperature superconducting wires made by the powder-in-tube method and the second generation of high-temperature superconducting tapes made by the base tape coating method have matured, making it possible for people to use superconducting materials on a large scale.

[0003] The first generation is represented by BSCCO materials coated with silver, and the second generation is represented by superconducting materials ReBCO (ReBa2Cu3O 7-δ , Re is a rare earth element such as Y, Eu). The first generation of high-temperature superconducting wires has an advantage, but the second generation of superconducting tapes has stronger current-carrying capacity, better magnetic field performance and lower material cost, so it has a broader development prospect in many fields such as large scientific research devices, medical treatment, energy and the like.

[0004] The second generation of superconducting tapes, also known as coated conductors. Because the coherence length of the superconducting material ReBCO is too small, it is easy to lose superconductivity due to weak connection of the grain boundary, so in order to make a long-distance current transmission wire, a superconducting film with copper-oxygen surface collimation needs to be grown on a base tape coated with a stable biaxial textured buffer film layer as a superconducting current-carrying core, and then a protective layer shell is plated on the upper and lower surfaces to protect the superconducting film layer. The superconducting tape plated with the protective layer on the surface needs to go through an annealing process to induce the internal superconducting layer ReBCO to convert into a stable superconducting phase so as to have superconducting electrical properties, and finally the outermost layer is plated with a corresponding cladding layer for encapsulation to become a finished product for use.

[0005] Superconducting tapes have many evaluation indicators, such as critical current, single-strand length, critical magnetic field, joint resistance, and tensile strength. Different customers have different application needs, and therefore different requirements for these indicators. However, specifically in the post-processing stage of superconducting film deposition, each customer hopes that various post-processing steps will not damage the superconducting film itself, ensuring the entire tape is free of defects (which would lead to low critical current points), and maintaining its existing properties such as high critical current, high critical magnetic field, and high critical current uniformity. Although defects can be removed through post-processing such as cutting, this results in a shorter tape length, which may not meet application requirements. Currently, the latest technology in the superconducting field can produce single tapes nearly a kilometer long without low critical current points, and possessing high critical current and high critical magnetic field, meeting most needs. However, for large scientific devices such as tokamak magnetic confinement fusion, a length of nearly a kilometer is still insufficient. Several superconducting tapes must be joined together to form ultra-long current transport conductor coils for use. For these requirements, in addition to single-strand length, another indicator—joint resistance—must also be strictly controlled.

[0006] Joint resistance is essentially energy dissipation, occurring at the contact and overlap of two superconducting tapes, i.e., the joint region. Since the superconducting layers are not in direct contact, current must pass through a protective layer-cladding layer-cladding layer-protective layer to reach the other superconducting layer. This process leads to energy dissipation, macroscopically manifested as joint resistance. The existence of joint resistance limits the lossless current transmission of superconducting materials, causing additional energy loss. In high-field magnet applications, even a slight loss and heat generation can be exponentially amplified under the strong magnetic field environment and the enormous energy input of the device itself, ultimately leading to circuit breakage and detachment. For the past half-century, researchers have been continuously exploring methods to reduce joint resistance, but most research has focused on the macroscopic realm, namely optimizing the tape winding method and tightness of the fit at the joint. The latest technology has enabled practical direct contact welding between protective layers of long strips (patent CN107393652A), meaning that the current only needs to pass through the protective layer to reach another superconducting layer, greatly saving intermediate energy consumption. It can be said that the strip winding and bonding method has been optimized to the extreme. However, when the research reached this point, the resistivity of the protective layer material itself became the biggest constraint.

[0007] Currently, the production of nearly 1,000-meter-long high-temperature superconducting tapes utilizes a protective layer coating in a high-vacuum, inert gas environment. This conventional coating technology ensures that almost all long tapes are free of critical current low points. However, due to process fluctuations, it is impossible to guarantee that individual tapes are free of defects while minimizing the resistivity of the protective layer. Therefore, the general approach is mass production, inspection and classification, and different order supply models. This involves large-scale production, followed by joint resistance testing of finished products. Long tapes with high joint resistance are supplied to orders such as cables that do not require splicing multiple tapes, while long tapes with low joint resistance are supplied to contracts for high-field magnets and other products with stringent joint resistance requirements.

[0008] But with the demand for low joint resistance long tape more and more, low joint resistance long tape inventory is seriously insufficient, but the high joint resistance long tape is seriously overstocked, facing the risk of scrap, such operation mode is more and more difficult to continue. There is room for improvement. SUMMARY

[0009] In view of the defects in the prior art, the purpose of the present application is to provide a method and system for reducing the joint resistance of high-temperature superconducting tape.

[0010] According to the method for reducing the joint resistance of high-temperature superconducting tape provided by the present application, the following steps are included:

[0011] Step S1, a protective layer is plated on the whole superconducting long tape, and a conventional superconducting annealing process is completed;

[0012] Step S2, the joint resistance of the superconducting tape in step S1 is measured, and is divided into two categories: joint resistance up to standard and joint resistance not up to standard;

[0013] Step S3, for the superconducting tape with joint resistance not up to standard, the protective layer of the joint area of the superconducting tape is removed;

[0014] Step S4, for the superconducting tape with the protective layer of the joint area removed in step S3, a dense protective layer is plated on the joint area of the superconducting tape again;

[0015] Step S5, the superconducting tape with the dense protective layer plated again in step S4 is subjected to an unconventional superconducting annealing process;

[0016] Step S6, the joint resistance of the superconducting tape in step S5 is measured, and is divided into two categories: joint resistance up to standard and joint resistance not up to standard;

[0017] If the joint resistance of the superconducting tape in step S6 is joint resistance up to standard, the process is ended;

[0018] If the joint resistance of the superconducting tape in step S6 is joint resistance not up to standard, steps S3, S4, S5 and S6 are repeated in order.

[0019] Preferably, in step S1, the material of the protective layer includes any one of platinum, silver and gold;

[0020] In step S4, the material of the dense protective layer includes any one of platinum, silver and gold.

[0021] Preferably, for the protective layer in step S1 and the dense protective layer in step S4, the joint resistance of the dense protective layer is smaller than that of the protective layer, and the joint resistance of the dense protective layer is smaller than or equal to the joint resistance of the delivery standard.

[0022] Preferably, for the conventional superconducting annealing process in step S1, a method for inducing the superconducting material in the just-formed superconducting layer to transform into a superconducting phase; the parameters are an annealing temperature of 400 to 600°C, a time of 1.5 to 4 hours, and the tape disc is placed;

[0023] For the unconventional superconducting annealing process in step S5, a method for inducing the superconducting material in the superconducting layer at the junction between the dense coating and the conventional coating to transform into a superconducting phase; the parameters are an annealing temperature of 400 to 800°C, a time of 3 to 8 hours, and the tape joint area needs to be placed in an open space.

[0024] Preferably, for removing the protective layer of the superconducting tape joint area in step S3, a chemical etching method is used.

[0025] According to the system for reducing the joint resistance of high-temperature superconducting tapes provided by the application, the system comprises:

[0026] Module M1 is used for coating a protective layer on the whole superconducting long tape and completing superconducting annealing.

[0027] Module M2 is used for measuring the joint resistance of the superconducting tapes in module M1 and classifying them into two categories: joint resistance up to standard and joint resistance not up to standard.

[0028] Module M3 is used for removing the protective layer of the superconducting tape joint area for the superconducting tapes with joint resistance not up to standard.

[0029] Module M4 is used for coating a dense protective layer on the joint area of the superconducting tapes for the superconducting tapes with the protective layer of the joint area removed in module M3.

[0030] Module M5 is used for performing unconventional annealing processing on the superconducting tapes with the dense protective layer coated in module M4.

[0031] Module M6 is used for measuring the joint resistance of the superconducting tapes in module M5 and classifying them into two categories: joint resistance up to standard and joint resistance not up to standard.

[0032] Module M7 is used for ending the process if the joint resistance of the superconducting tapes in module M6 is joint resistance up to standard, and repeating module M3, module M4, module M5 and module M6 in sequence if the joint resistance of the superconducting tapes in module M6 is joint resistance not up to standard.

[0033] Preferably, in module M1, the material of the protective layer comprises any one of platinum, silver and gold.

[0034] In module M4, the material of the dense protective layer comprises any one of platinum, silver and gold.

[0035] Preferably, for the protective layer in module M1 and the dense protective layer in module M4, the joint resistance of the dense protective layer is less than the joint resistance of the protective layer, and the joint resistance of the dense protective layer is less than or equal to the joint resistance of the delivery standard.

[0036] Preferably, for the conventional superconducting annealing process in module M1, a method for inducing the superconducting material in the as-deposited superconducting layer to become a superconducting phase; the parameters are an annealing temperature of 400 to 600 DEG C, a time of 1.5 to 4 hours, and a tape disc belt placement;

[0037] For the unconventional superconducting annealing process in module M5, a method for inducing the superconducting material in the superconducting layer at the junction between the dense plated film and the conventional plated film to become a superconducting phase again; the parameters are an annealing temperature of 400 to 800 DEG C, a time of 3 to 8 hours, and a tape joint area that needs to be placed in an open space.

[0038] Preferably, for the removal of the protective layer of the superconducting tape joint area in module M3, a chemical etching method is used for removal.

[0039] Compared with the prior art, the present application has the following beneficial effects:

[0040] 1、 The present application first adopts a conventional method to plate a protective layer on the entire superconducting long tape, which has less critical current low point situation, can ensure the effective length of a single superconducting tape, and then removes the protective layer of the superconducting tape joint area and re-plates a dense protective layer by using a dense plating process to obtain lower joint resistance performance; the dense plating process has additional stress extrusion, and if the plating length is short, such as the superconducting tape joint area, the stress can provide additional binding force to make it densify as a whole; however, for a long tape of hundreds of meters, the internal stress accumulates too much, which easily leads to the fracture of the superconducting layer and affects the superconducting performance; the technical scheme of the present application combines the two plating methods together, and simultaneously obtains the advantages of long effective length of the superconducting tape by the conventional plating method and low joint resistance by the dense plating method, and improves the overall competitiveness of the product.

[0041] 2、 The present application establishes a perfect long tape recycling mechanism with high joint resistance, which can be repeatedly operated and can realize an extremely high yield; and belongs to an optimized material resistivity process, in combination with the existing tape winding and bonding technology, the technical scheme of the present application can further reduce the joint resistance to approach the theoretical limit.

[0042] 3、The technical scheme of the present application provides a set of reusable circulation process for high-temperature superconducting long strips with large joint resistance caused by other process fluctuations, solves the problem of increased joint resistance caused by direct bonding and welding by re-plating the joint area protective layer, restores the performance decline of the superconducting layer at the different process film plating boundaries caused by re-plating by extending the annealing time and increasing the temperature, and finally makes the superconducting layer inside and outside reach the best current-carrying state. Accordingly, a perfect recycling mechanism is established, so that such problem strips do not have to face the risk of scrapping directly, and huge economic losses are recovered. BRIEF DESCRIPTION OF DRAWINGS

[0043] Other features, objects and advantages of the present application will become more apparent from the following detailed description of non-limiting embodiments with reference to the attached drawings:

[0044] Figure 1 The present application mainly embodies the overall process flowchart;

[0045] Figure 2 The present application mainly embodies the recycling mechanism schematic diagram;

[0046] Figure 3 The present application mainly embodies the scanning electron micrograph of the silver layer of the long strip with high joint resistance under the conventional film plating process;

[0047] Figure 4 The present application mainly embodies the schematic diagram of the microcosmic change of the joint resistance in the implementation process;

[0048] Figure 5 The present application mainly embodies the boundary diagram of the un-etched area and the etched area after chemical corrosion;

[0049] Figure 6 The present application mainly embodies the boundary diagram of the un-etched area and the etched area after physical vapor deposition;

[0050] Figure 7 The present application mainly embodies the microcosmic state comparison diagram of the conventional film plating process and the improved dense film plating process;

[0051] Figure 8 The present application mainly embodies the critical current diagram of the typical problem long strip after the dense film plating process;

[0052] Figure 9 The present application mainly embodies the high-resolution transmission electron micrograph of the low point area of the critical current of the typical problem long strip;

[0053] Figure 10 The present application mainly embodies the phase change schematic diagram of the superconducting material in the implementation process;

[0054] Figure 11The application mainly embodies the superconducting layer phase transition schematic diagram at the boundary between the conventional coating and the dense coating;

[0055] Figure 12 The application mainly embodies the superconducting performance change comparison chart of the strip before and after the unconventional superconducting annealing;

[0056] Figure 13 The application mainly embodies the joint resistance change comparison chart of the substandard strip before and after the treatment by the application;

[0057] Figure 14 The application mainly embodies the joint resistance distribution chart of the dense coating process;

[0058] Figure 15 The application mainly embodies the joint resistance distribution chart of the conventional coating process. DETAILED DESCRIPTION

[0059] The application will be described in detail below with specific embodiments. The following embodiments will help those skilled in the art to further understand the application, but do not limit the application in any form. It should be pointed out that those skilled in the art can make some changes and improvements without departing from the concept of the application. These all belong to the protection scope of the application.

[0060] Example One

[0061] As shown in Figure 1 and Figure 2 , a method for reducing the joint resistance of high-temperature superconducting strip provided by the application includes the following steps:

[0062] Step S1, coating a protective layer on the whole superconducting long strip and completing the conventional superconducting annealing treatment.

[0063] Step S2, measuring the joint resistance of the superconducting strip in step S1, and dividing it into two categories: joint resistance up to standard and joint resistance not up to standard.

[0064] Step S3, for the superconducting strip with joint resistance not up to standard, removing the protective layer in the joint area of the superconducting strip.

[0065] Step S4, for the superconducting strip with the joint area protective layer removed in step S3, re-coating a dense protective layer on the joint area of the superconducting strip.

[0066] Step S5, for the superconducting strip with the dense protective layer re-coated in step S4, performing unconventional superconducting annealing treatment.

[0067] Step S6, measuring the joint resistance of the superconducting strip in step S5, and dividing it into two categories: joint resistance up to standard and joint resistance not up to standard.

[0068] If the joint resistance of the superconducting tape in step S6 is a joint resistance that meets the standard, the process ends.

[0069] If the joint resistance of the superconducting tape in step S6 is a joint resistance that does not meet the standard, steps S3, S4, S5 and S6 are repeated in order.

[0070] Specifically, in step S1, the material of the protective layer includes any one of platinum, silver and gold. In step S4, the material of the dense protective layer includes any one of platinum, silver and gold. The superconducting tape is a second-generation high-temperature superconducting tape with a length of more than 100 meters. The joint region is the end region of the superconducting tape, with a length of less than 10 centimeters.

[0071] Further specifically, the joint resistance that meets the standard and the joint resistance that does not meet the standard are divided according to the size of the joint resistance, and the size of the joint resistance can be determined according to the delivery standard of the actual order. If the detected joint resistance is greater than the resistance of the delivery standard of the actual order, the joint resistance does not meet the standard; if the detected joint resistance is less than or equal to the resistance of the delivery standard of the actual order, the joint resistance meets the standard. The resistance of the delivery standard can be determined by a person skilled in the art according to the actual situation.

[0072] Further, for the protective layer in step S1 and the dense protective layer in step S4, the joint resistance of the dense protective layer is less than the joint resistance of the protective layer, and the joint resistance of the dense protective layer is less than or equal to the joint resistance of the delivery standard. The specific operation is: for step S1, the whole superconducting long tape is plated with a protective layer, which is a physical vapor deposition technology in a low-pressure inert gas environment; the parameters are pressure 5-10 mTorr, the inert gas filled is argon, and the flow rate is 50-100 sccm. For step S4, the joint region of the superconducting tape is re-plated with a dense protective layer, which is a physical vapor deposition technology in a lower-pressure inert gas environment; the parameters are pressure 15-25 mTorr, the inert gas filled is argon, and the flow rate is 50-100 sccm.

[0073] Further, for the conventional superconducting annealing process in step S1, it is a method for inducing the superconducting material in the just-formed superconducting layer to become a superconducting phase; the parameters are annealing temperature 400-600℃, time 1.5-4 hours, and tape disc placement. For the unconventional superconducting annealing process in step S5, it is a method for inducing the superconducting material in the superconducting layer at the junction between the dense plated film and the conventional plated film to become a superconducting phase; the parameters are annealing temperature 400-800℃, time 3-8 hours, and the joint region of the tape needs to be placed in an open space.

[0074] For removing the protective layer of the joint region of the superconducting tape in step S3, chemical etching is used.

[0075] Example Two

[0076] Based on embodiment one, a system for reducing the joint resistance of high-temperature superconducting tapes is provided according to the present application, the system comprising:

[0077] Module M1, for plating a protective layer on the whole superconducting long tape and completing a conventional superconducting annealing process;

[0078] Module M2, for measuring the joint resistance of the superconducting tape in module M1, and dividing into two categories of joint resistance meeting the standard and joint resistance not meeting the standard;

[0079] Module M3, for removing the protective layer of the joint area of the superconducting tape whose joint resistance does not meet the standard;

[0080] Module M4, for re-plating a dense protective layer on the joint area of the superconducting tape whose joint area protective layer is removed in module M3;

[0081] Module M5, for performing an unconventional annealing process on the superconducting tape whose joint area is re-plated with a dense protective layer in module M4;

[0082] Module M6, for measuring the joint resistance of the superconducting tape in module M5, and dividing into two categories of joint resistance meeting the standard and joint resistance not meeting the standard;

[0083] Module M7, if the joint resistance of the superconducting tape in module M6 meets the standard, the process ends; if the joint resistance of the superconducting tape in module M6 does not meet the standard, repeating modules M3, M4, M5 and M6 in order.

[0084] Preferably, in module M1, the material of the protective layer includes any one of platinum, silver and gold. In module M4, the material of the dense protective layer includes any one of platinum, silver and gold.

[0085] Preferably, for the protective layer in module M1 and the dense protective layer in module M4, the joint resistance of the dense protective layer is less than that of the protective layer, and the joint resistance of the dense protective layer is less than or equal to the joint resistance of the delivery standard.

[0086] Preferably, for the conventional superconducting annealing process in module M1, it is a method for inducing the superconducting material in the just-formed superconducting layer to become a superconducting phase; the parameters are an annealing temperature of 400 to 600℃, a time of 1.5 to 4 hours, and the tape is placed in a reel;

[0087] For the unconventional superconducting annealing process in module M5, it is a method for inducing the superconducting material in the dense plated film and the conventional plated film to become a superconducting phase again; the parameters are an annealing temperature of 400 to 800℃, a time of 3 to 8 hours, and the joint area of the tape needs to be placed in an open space.

[0088] Preferably, the protective layer in the module M3 is removed by chemical etching.

[0089] Example Three

[0090] Based on the first embodiment, according to the method for reducing the joint resistance of high-temperature superconducting tapes provided by the present application, the second embodiment is to the same batch of conventional film-coated high-temperature superconducting EuBa2Cu3O 7-δ Long tapes, two typical samples with greatly different finished joint resistances are subjected to the same remedial treatment (sample 1 is a comparative sample; sample 2 is an experimental sample, and the micro-scan of the silver layer of the experimental sample is shown in Figure 3 ), and the micro changes in the process are shown in Figure 4 , including the following steps:

[0091] An etching solution is prepared by mixing ammonia and hydrogen peroxide at a ratio of 1:1, and the tape joint area is soaked for 7 cm. After sufficient reaction, the tape is taken out, and the residual solution is washed with alcohol, as shown in Figure 5 ;

[0092] A dense silver layer is plated on the etched area by a physical vapor deposition method of direct current magnetron sputtering with a pressure of 20 mTorr, an inert gas of argon, and a flow rate of 70 sccm, as shown in Figure 6 ;

[0093] The re-plated silver tape is subjected to high-temperature annealing in oxygen at a temperature of 500℃ for 4 hours.

[0094] After annealing, the joint resistance is measured by directly contacting the silver layer-silver layer.

[0095] In this embodiment, a dense film coating process is used, which increases the pressure parameter (i.e., reduces the environmental vacuum degree) compared to the traditional conventional film coating process. According to relevant literature, maintaining a certain inert gas in the pseudo-vacuum environment is beneficial to reduce the overall sputtering effect of the thin film (Journal of Applied Surface Science, 2007, 254, 760-764), which is extended to the field of film coating process of superconducting tape protective layer, and a dense protective layer coating with greatly reduced defects is successfully achieved. The microscopic explanation is shown in Figure 7 , and the appropriate concentration of inert gas will exert a certain binding force on the protective layer around it, making it denser as a whole.

[0096] The applicant needs to emphasize that the compact plating process in the technical solution of the application can only act on the short sample, i.e., the joint area, and cannot replace the conventional plating process to plate a protective layer on the whole long tape. Otherwise, the long tape is prone to have a critical current low point, as shown in Figure 8 . This is a secondary effect of the compact plating process, i.e., the residual stress of the protective layer causes the protective layer to have additional stress extrusion under the action of the inert gas restraint force. When the short tape is used, the stress accumulation is insufficient, so no special attention is needed. However, for a long tape of hundreds of meters, the internal stress is too large, and if the lower superconducting layer is unfortunately broken, the superconducting performance of this area will be affected, and the macroscopic performance is that a critical current low point appears at this position, and the microscopic scanning at the low point is as shown in Figure 9 .

[0097] In the embodiment, the magnetron sputtering used causes the superconducting layer to be oxygen-deficient, resulting in the degeneration of the superconducting layer into a non-superconducting tetragonal phase, so that annealing treatment needs to be performed again. The phase transition principle is as shown in Figure 10 . In particular, at the corrosion and non-corrosion boundary, the protective layer covering this area is twice as thick as the initial annealing (see Figure 11 ), and oxygen needs to diffuse a longer distance to reach the superconducting layer. Therefore, a non-conventional annealing method needs to be used, i.e., the high-temperature annealing in oxygen needs to be longer than the conventional annealing, so as to complete the oxygen supplement. In addition, the long tape needs to be spread out to ensure sufficient contact with oxygen. The effect after the non-conventional annealing is as shown in Figure 12 .

[0098] It needs to be emphasized that the application first eliminates the defects in the silver layer deep in the joint area of the substandard product by combining chemical corrosion with magnetron sputtering, and then solves the oxygen deficiency problem of the superconducting layer at the boundary caused by the above operation by changing the annealing process, successfully converting the substandard product into a good product, and the result is as shown in Figure 13 , which avoids significant economic losses (for example, the European Center for Nuclear Research CERN requires that the joint resistance be less than 50 nΩ, and after remediation, the sample 2 is reduced from 157 nΩ to 43 nΩ, which meets the delivery standard of the European Center for Nuclear Research).

[0099] Example Four

[0100] Based on Embodiment Three, a method for reducing the joint resistance of a high-temperature superconducting tape is provided according to the application. According to the method for reducing the joint resistance of a high-temperature superconducting tape described in Embodiment Three, the compact plating process is continuously performed on the joint area of the end of the high-temperature superconducting EuBa2Cu3O 7-δ long tape for several batches within 112 days, and the joint resistance data distribution measured in the first cycle is as shown in Figure 14 .

[0101] The corrosion solution is prepared by mixing ammonia and hydrogen peroxide in a ratio of 1:1, and the strip joint area is soaked in the solution. The joint length is 7 cm. After sufficient reaction, the strip is taken out and rinsed with alcohol to remove the residual solution.

[0102] A dense silver layer is plated on the corrosion area by physical vapor deposition method of direct current magnetron sputtering, with a pressure of 20 mTorr, an inert gas of argon, and a flow rate of 70 sccm.

[0103] The silver-plated strip is annealed in oxygen at a temperature of 500°C for 4 hours.

[0104] After annealing, the joint area is welded by direct contact of the silver layer-silver layer, and the joint resistance is measured to determine whether it meets the order delivery standard.

[0105] If not, the joint area of the end joint is cut off, and the remaining part of the long strip is again subjected to step S1 until the end joint resistance is reduced to meet the standard.

[0106] The joint resistance of the process in this application is currently lower than 40 nΩ (336 nΩ•cm 2 ). It should be emphasized that this standard can be adjusted flexibly according to recent order requirements.

[0107] This embodiment ensures the overall density of the silver layer by increasing the plating pressure, and there are almost no defects. Large-scale testing for more than 100 days proves that before using this scheme ( Figure 15 ) the proportion of joint resistance lower than 40 nΩ (336 nΩ•cm 2 ) is 30.3%, and the proportion lower than 25 nΩ (210 nΩ•cm 2 ) is only 15.3%; but after using this scheme ( Figure 13 ) the proportion of joint resistance lower than 40 nΩ (336 nΩ•cm 2 ) is as high as 98.4% for the first time, and the proportion lower than 25 nΩ (210 nΩ•cm 2 ) can also reach 81.4%, which fully proves the effectiveness and repeatability of this method.

[0108] In the description of the present application, it should be understood that the terms "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and do not indicate or imply that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation on the present application.

[0109] The specific embodiments of the present application are described above. It needs to be understood that the present application is not limited to the specific embodiments described above, and various changes or modifications can be made by those skilled in the art within the scope of the claims, which does not affect the essential content of the present application. The embodiments of the present application and the features in the embodiments can be combined with each other at will without conflict.

Claims

1. A method for reducing the resistance of high-temperature superconducting tape joints, characterized in that, Includes the following steps: Step S1: Apply a protective layer to the entire superconducting strip and complete the conventional superconducting annealing process; Step S2: Measure the joint resistance of the superconducting tape in step S1 and classify it into two categories: joint resistance meets the standard and joint resistance does not meet the standard. Step S3: For superconducting tapes with substandard joint resistance, remove the protective layer in the joint area of ​​the superconducting tape. Step S4: For the superconducting tape whose joint area protective layer was removed in step S3, a dense protective layer is re-plated on the joint area of ​​the superconducting tape. The joint resistance of the dense protective layer is less than the joint resistance of the protective layer, and the joint resistance of the dense protective layer is less than or equal to the joint resistance of the delivery standard. Step S5: Perform unconventional superconducting annealing on the superconducting tape with the re-deposited dense protective layer in step S4. Step S6: Measure the joint resistance of the superconducting tape in step S5 and classify it into two categories: joint resistance meets the standard and joint resistance does not meet the standard. If the joint resistance of the superconducting tape in step S6 meets the standard, the process ends. If the joint resistance of the superconducting tape in step S6 is not up to standard, then repeat steps S3, S4, S5 and S6 in sequence.

2. The method for reducing the joint resistance of high-temperature superconducting tapes as described in claim 1, characterized in that, In step S1, the material of the protective layer includes any one of platinum, silver, and gold; In step S4, the material of the dense protective layer includes any one of platinum, silver, and gold.

3. The method for reducing the joint resistance of high-temperature superconducting tapes as described in claim 1, characterized in that, For the conventional superconducting annealing treatment in step S1, it is a method to induce the superconducting material in the newly formed superconducting layer to transform into a superconducting phase; the parameters are annealing temperature of 400 to 600°C, time of 1.5 to 4 hours, and strip placement on a coil; For the unconventional superconducting annealing treatment in step S5, a method is used to induce the superconducting material in the superconducting layer at the boundary between dense coating and conventional coating to revert to the superconducting phase; the parameters are an annealing temperature of 400 to 800°C, a time of 3 to 8 hours, and the strip joint area needs to be unfolded and placed.

4. The method for reducing the joint resistance of high-temperature superconducting tapes as described in claim 1, characterized in that, For the protective layer in the superconducting tape joint area to be removed in step S3, chemical etching is used to remove it.

5. A system for reducing the resistance of high-temperature superconducting tape joints, characterized in that, The system for implementing the method for reducing the resistance of high-temperature superconducting tape joints according to any one of claims 1-4 comprises: Module M1 is used to coat the entire superconducting strip with a protective layer and complete the conventional superconducting annealing process; Module M2 is used to measure the joint resistance of the superconducting tape in module M1, and classifies it into two categories: joint resistance meets the standard and joint resistance does not meet the standard. Module M3 is used to remove the protective layer in the joint area of ​​superconducting tapes with substandard joint resistance. Module M4 is used to re-plat a dense protective layer on the joint area of ​​the superconducting tape for which the protective layer in the joint area has been removed in Module M3. The joint resistance of the dense protective layer is less than the joint resistance of the protective layer, and the joint resistance of the dense protective layer is less than or equal to the joint resistance of the delivery standard. Module M5 is used for unconventional annealing of the superconducting tape in Module M4, which has been re-plated with a dense protective layer. Module M6 is used to measure the joint resistance of the superconducting tape in module M5, and classifies it into two categories: joint resistance meets the standard and joint resistance does not meet the standard. If the joint resistance of the superconducting tape in module M7 meets the standard, the process ends; if the joint resistance of the superconducting tape in module M6 does not meet the standard, then repeat modules M3, M4, M5 and M6 in sequence.

6. The system for reducing the resistance of high-temperature superconducting tape joints as described in claim 5, characterized in that, In module M1, the protective layer can be made of any one of platinum, silver, or gold. In module M4, the dense protective layer can be made of any one of platinum, silver, or gold.

7. The system for reducing the resistance of high-temperature superconducting tape joints as described in claim 5, characterized in that, For the conventional superconducting annealing treatment in module M1, the method is to induce the superconducting material in the newly formed superconducting layer to transform into the superconducting phase; the parameters are annealing temperature of 400 to 600℃, time of 1.5 to 4 hours, and strip placement on a coil; For the unconventional superconducting annealing treatment in module M5, a method is used to induce the superconducting material in the superconducting layer at the boundary between dense coating and conventional coating to revert to the superconducting phase; the parameters are an annealing temperature of 400 to 800°C and a time of 3 to 8 hours, and the strip joint area needs to be unfolded and placed.

8. The system for reducing the resistance of high-temperature superconducting tape joints as described in claim 5, characterized in that, For the protective layer in the superconducting tape joint area of ​​module M3, chemical etching is used to remove it.

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