A pre-reacted and twisted bi2212 armored conductor and a method of manufacturing the same

Abstract

The application discloses a Bi2212 armored conductor prepared by pre-reaction and then stranding, which comprises a liquid helium channel, a superconducting wire layer, a fastening layer and an armor layer; the superconducting wire layer is prepared by layering and cross-stranding Bi2212 wires which have completed superconducting heat treatment along the outer wall of the liquid helium channel; in addition, the application also provides a preparation method of the armored conductor, wherein the Bi2212 wires which have completed superconducting heat treatment are layering and cross-stranded along the outer wall of the liquid helium channel, then wrapped with aluminum foil, finally threaded into the armor layer and processed by shrinkage. The application first proposes and realizes the Bi2212 armored conductor prepared by pre-reaction and then stranding, avoids the problems of temperature control, heat preservation time, oxygen partial pressure stable maintenance and high pressure equipment investment in the pre-stranding and then reaction route of the large magnet, effectively reduces the inductance and hysteresis loss through the cross-stranding structure, is suitable for preparing a high-performance large fusion magnet, and greatly reduces the preparation difficulty and risk of the large Bi2212 magnet.

Description

Technical Field

[0001] This invention belongs to the field of high-temperature superconducting materials technology, specifically relating to a Bi2212 armored conductor that is reacted and then stranded, and its preparation method. Background Technology

[0002] Currently, the conventional fabrication process for Bi2212 high-temperature superconducting magnets involves stranding followed by reaction. This means that Bi2212 wires, after plastic deformation, are first made into cables or conductors, then stranded into magnets, and finally, the magnets are subjected to high-pressure partial melting heat treatment to achieve superconductivity. This process is suitable for the fabrication of small magnets, but for large magnets used in fusion devices (with diameters and heights reaching several meters or even tens of meters, and thicknesses reaching several meters), the stranding-following-reaction route faces several insurmountable technical bottlenecks: Firstly, Bi2212 wire is extremely sensitive to heat treatment temperature, with an effective temperature window of only ±4℃. Achieving overall temperature uniformity control within ±4℃ on a spatial scale of several meters poses a significant challenge to existing large-scale high-pressure heat treatment furnaces. Secondly, Bi2212 wire is also sensitive to the melting and holding time, with the optimal holding time range being 15 minutes to 1.5 hours. For magnets with a thickness exceeding 1 meter, achieving uniform and thorough melting within such a short time is extremely difficult. Third, Bi2212 wire is highly sensitive to oxygen partial pressure. In large magnets, due to the excessive height and thickness, the diffusion rate of oxygen decreases significantly, making it difficult to maintain the balance between the oxygen partial pressure inside the wire and the oxygen partial pressure in the ambient atmosphere. Fourth, Bi2212 magnets are typically sintered in a high-pressure atmosphere with an oxygen partial pressure of 1 atm and a temperature of approximately 890°C. The outer armor material of the conductor (such as 316L stainless steel) also experiences a high-temperature and high-oxygen environment during sintering, making it prone to oxidation reactions and consuming large amounts of oxygen. This leads to a continuous decrease in the oxygen partial pressure inside the furnace, further exacerbating the instability of the oxygen partial pressure in the wire.

[0003] Furthermore, the manufacturing cost of a single large fusion magnet is as high as tens of millions to hundreds of millions of RMB, and failure in any of the aforementioned stages can lead to the failure of the entire magnet manufacturing process. The investment in high-pressure heat treatment furnaces required to meet the heat treatment requirements of large magnets is at least 100 million RMB. The high equipment investment combined with multiple technical risks greatly increases the difficulty of manufacturing large fusion Bi2212 magnets, resulting in very few research groups internationally conducting related research.

[0004] Therefore, to overcome the aforementioned bottlenecks, it is urgent to develop a reaction-before-stranding preparation route, that is, to first prepare a Bi2212 conductor with superconducting properties and then strand it into a magnet. The primary prerequisite for realizing this route is to obtain a Bi2212 armored conductor that is reacted before stranding. Summary of the Invention

[0005] The technical problem to be solved by this invention is to address the shortcomings of the prior art by providing a Bi2212 armored conductor that undergoes reaction followed by stranding. This reaction-following Bi2212 armored conductor can be directly used for stranding large fusion magnets, effectively avoiding the core challenges of temperature control, time, and oxygen partial pressure in the high-voltage heat treatment process of large magnets in traditional processes, as well as the excessive investment in high-voltage equipment. At the same time, the layered cross-stretching structure achieves inductance cancellation and hysteresis loss reduction while maximizing control of wire strain, providing a brand-new cable / conductor structure design solution for the Bi2212 conductor field.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a Bi2212 armored conductor that is reacted and then stranded, characterized in that the armored conductor includes a liquid helium channel, a superconducting wire layer is disposed outside the liquid helium channel, a fastening layer is tightly wrapped around the superconducting wire layer, and an armor layer is disposed outside the fastening layer by compression processing and covering the fastening layer; the superconducting wire layer is formed by multiple layers of Bi2212 wire that have undergone superconducting heat treatment and are cross-stretched along the outer wall of the liquid helium channel.

[0007] The above-mentioned Bi2212 armored conductor, which is reacted and then stranded, has a liquid helium channel made of stainless steel.

[0008] In the aforementioned Bi2212 armored conductor that is reacted and then stranded, each layer of Bi2212 wire that has undergone superconducting heat treatment in the superconducting wire layer is stranded in a spiral manner, and the spiral directions of adjacent layers of Bi2212 wire that have undergone superconducting heat treatment are opposite, forming a layered cross-contact structure.

[0009] In the aforementioned Bi2212 armored conductor that is reacted and then stranded, the stranding angle of each layer of Bi2212 wire that has undergone superconducting heat treatment in the superconducting wire layer is determined according to the equivalent support diameter of the location of that layer, so that the maximum bending strain of the Bi2212 wire that has undergone superconducting heat treatment in that layer does not exceed 0.5%.

[0010] The aforementioned Bi2212 armored conductor, which is reacted and then stranded, has a fastening layer formed by tension spiral winding of aluminum foil strip, and the thickness and winding density of the fastening layer are controlled by the amount of compression of the armor layer.

[0011] The aforementioned Bi2212 armored conductor, which is reacted and then stranded, has an armor layer made of stainless steel.

[0012] In addition, the present invention also provides a method for preparing a Bi2212 armored conductor by reacting first and then stranding, the method comprising the following steps: Step 1: Twist the Bi2212 wire that has undergone superconducting heat treatment onto the outer wall of the liquid helium channel in a predetermined spiral direction to form the first layer of wire; Step 2: Outside the first layer of wire formed in Step 1, the Bi2212 wire that has undergone superconducting heat treatment is further twisted in the opposite spiral direction to that in Step 1 to form a second layer of wire, and the second layer of wire is made to cross contact with the first layer of wire. Step 3: Repeat the process of Step 2, stranding the Bi2212 wire that has undergone superconducting heat treatment layer by layer until the designed number of superconducting wire layers is reached, and each layer of wire forms a cross contact structure with the adjacent layer to obtain a liquid helium channel with superconducting wire layers. Step 4: The liquid helium channel with a superconducting wire layer obtained in step 3 is externally wound with an aluminum foil strip in a tension spiral to obtain a liquid helium channel with a fastening layer and a superconducting wire layer. Step 5: Insert the liquid helium channel with the fastening layer and superconducting wire layer obtained in Step 4 into the armor layer to form the first layer of wire. Then, use multi-pass, small-deformation die rolling or drawing to perform compression processing to obtain the Bi2212 armored conductor that is reacted and then stranded.

[0013] This invention involves stranding Bi2212 wire, which has undergone superconducting heat treatment, onto the outer wall of an inner stainless steel tube, completing the first layer of stranding. The inner stainless steel tube and the first layer of wire together form a new cylindrical support. A second layer of stranding is then performed in the opposite spiral direction to the first layer. Since the first layer's deflection direction is clockwise, the second layer's deflection direction is counterclockwise, effectively creating a crossover that allows the two layers of wire to cross-contact, achieving a cable-like effect. The third layer of wire also crosses with the second layer, and subsequent layers follow the same pattern. This structure, while ensuring that the strain of each layer of wire meets requirements, maximizes the crossover angle between adjacent layers, ultimately creating a cable-like cross-arrangement effect. Through this design, the inductance generated by a single layer of wire is canceled out by the inductance of adjacent layers. Furthermore, because the stranding radius differs in each layer, the stranding angles of different layers vary, weakening the inductance perpendicular to the wire... The axial self-field component of the material significantly reduces hysteresis loss. After the multi-layer wire is stranded, aluminum foil is wound around its outer layer with a certain tension to form a soft fastening layer. The aluminum foil uniformly covers all the wires, which on the one hand firmly fixes the wires to the inner stainless steel tube, and on the other hand, utilizes the soft properties of aluminum foil to avoid hard contact damage between the outer stainless steel tube and the superconducting wires when they are subsequently tightened. After the aluminum foil is wound, it is inserted into the outer stainless steel tube. In order to reduce the gap between the component and the outer tube and prevent the superconducting cable from shifting during use, which may cause signal instability or wire damage, the outer stainless steel tube is subjected to multiple passes of small deformation tightening processing by die rolling or drawing. The upper limit of the tightening deformation is based on the fact that the current carrying capacity of the cable does not decrease. That is, when the current carrying capacity decreases due to further increase in deformation, it is considered to have reached the processing endpoint. The reaction and stranding process is completed to obtain the Bi2212 armored conductor, realizing the efficient and low-risk preparation of large fusion magnets.

[0014] In the above method, the twisting angles described in steps one and two both satisfy: ε = d / (2 R bend )≤0.5%, and R bend = R n sin 2 θ, where ε is the bending strain of the Bi2212 wire after superconducting heat treatment, and d is the diameter of the Bi2212 wire after superconducting heat treatment. R bend The equivalent bending radius of the Bi2212 wire that has undergone superconducting heat treatment. R nWhere θ is the equivalent cylinder radius, and θ is the stranding angle. In this invention, each layer of Bi2212 wire that has undergone superconducting heat treatment is stranded onto the outer wall of the inner stainless steel tube at a certain helical angle. The selection criteria for the stranding angle and wire diameter are: to ensure that the maximum bending strain of the wire during the stranding process does not exceed 0.5%, i.e., ε = d / (2 R bend )≤0.5%, and R bend = R n sin 2 After the first layer of stranding is completed, the inner stainless steel tube and the first layer of wire together form a new cylindrical support. When the second layer of wire is stranded, due to the increase in the diameter of the support, it is necessary to recalculate the angle between the wire and the axis of the inner stainless steel tube to ensure that the strain of the wire in this layer still meets the requirement of ≤0.5%. This process is repeated, and the stranding angle of each layer is appropriately increased with the number of layers to reduce conductor inductance and AC loss. By controlling the stranding angle, it is ensured that the wire in each layer has the best performance. The equivalent cylindrical radius is half of the equivalent support diameter at the location of that layer.

[0015] In the above method, the small deformation amount mentioned in step five is no more than 5%. The upper limit of the total deformation amount in the compression processing is determined by the criterion that the current-carrying capacity of the Bi2212 armored conductor begins to decrease. When further increasing the deformation amount leads to a decrease in current-carrying capacity, the compression processing is stopped. This invention, by using a small deformation amount in the processing, ensures the performance of the Bi2212 armored conductor and prevents excessive decrease in current-carrying capacity.

[0016] Compared with the prior art, the present invention has the following advantages: 1. This invention is the first to propose and realize the pre-reaction and post-stranding of Bi2212 armored conductors. The resulting Bi2212 armored conductors can be directly used for stranding large fusion magnets, effectively avoiding the core problems that must be overcome in the high-voltage heat treatment of large magnets in traditional processes, such as ±4℃ temperature control, 1.5h rapid burn-through, and stable maintenance of oxygen partial pressure, as well as the excessive investment in high-voltage equipment. At the same time, the layered cross-stranding structure achieves inductance cancellation and hysteresis loss reduction while maximizing the control of wire strain. This provides a brand-new cable / conductor structure design scheme for the field of Bi2212 conductors, significantly reducing the difficulty and risk of manufacturing large Bi2212 magnets.

[0017] 2. This invention utilizes a multi-layer cross-stranded wire structure to cancel out the inductance of each layer, effectively suppressing hysteresis loss and meeting the requirements for rapid magnetization and long-term stable operation. The use of interlayer contact cross-stranding instead of braiding ensures optimized electromagnetic performance and avoids the cracking of the Bi2212 ceramic core wire caused by excessive bending during the braiding process. 3. The present invention adopts a soft fastening layer design of aluminum foil, which ensures reliable wire fixation while avoiding hard contact between the wire and the outer stainless steel tube. During the tightening process, the external force is first applied to the aluminum foil, which is gradually compacted, and then the pressure is evenly transmitted to the wire layer. By controlling the amount of tightening, the density of the aluminum foil can be adjusted, thereby precisely controlling the pressure and fixation firmness of the wire, protecting the wire from damage and ensuring the overall structural stability.

[0018] 4. This invention uses Bi2212 wire that has undergone superconducting heat treatment to prepare the conductor, eliminating the need for subsequent high-temperature heat treatment. This avoids the metallurgical bonding between wires caused by long-term high-temperature diffusion at 800~890℃ / 50h in traditional processes, thereby reducing hysteresis loss. At the same time, there is no need to consider the problem of oxygen penetrating the silver layer during high-temperature treatment. A high-resistivity metal layer can be coated on the wire surface to further reduce hysteresis loss and obtain a high-temperature superconducting conductor with even lower loss.

[0019] 5. This invention is the first to propose and realize a method for preparing Bi2212 armored conductors by reacting first and then stranding. The conductors prepared can be directly used for stranding large fusion magnets, effectively avoiding the core problems of temperature control, time, and oxygen partial pressure in the high-voltage heat treatment process of large magnets in traditional processes, as well as the excessive investment in high-voltage equipment. At the same time, the layered cross-stretching structure achieves inductance cancellation and hysteresis loss reduction under the premise of maximizing control of wire strain, providing a brand-new cable / conductor structure design scheme for the field of Bi2212 conductors.

[0020] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the structure of the Bi2212 armored conductor that is reacted and then stranded according to the present invention.

[0022] Figure 2 A macroscopic view of the first layer of wire stranded in Embodiment 2 of the present invention.

[0023] Figure 3 A macroscopic view of the second layer of wire stranding process in Embodiment 2 of the present invention.

[0024] Figure 4 A macroscopic view of a cable made by directly twisting wires in the prior art.

[0025] Explanation of reference numerals in the attached figures: Detailed Implementation

[0026] The present invention provides a Bi2212 armored conductor that is reacted and then stranded in advance, as described in Example 1.

[0027] Example 1 like Figure 1 The diagram shows a Bi2212 armored conductor that is reacted and then stranded, comprising a liquid helium channel 1, a superconducting wire layer 2 disposed outside the liquid helium channel 1, a fastening layer 3 tightly wrapped around the superconducting wire layer 2, and an armor layer 4 disposed outside the fastening layer 3 by compression processing and covering the fastening layer 3; the superconducting wire layer 2 is formed by multiple layers of Bi2212 wires 5 that have undergone superconducting heat treatment and are cross-stretched along the outer wall of the liquid helium channel 1.

[0028] It should be noted that the internal liquid helium channel 1 is incorporated because the cooling medium for the magnets made from the Bi2212 armored conductor is liquid helium. To allow the liquid helium to quickly remove the heat generated within the magnet, a dedicated liquid helium channel is directly installed inside the conductor. The liquid helium flows rapidly along the conductor, thus quickly removing the heat from the magnet. Multiple layers of superconducting heat-treated Bi2212 wires 5 are interwoven on the outer wall of the liquid helium channel 1 as the current-carrying core. While ensuring that the strain of each layer meets the requirements, the intersecting angle between adjacent layers is maximized, ultimately creating a cross-arrangement effect similar to that of a cable. In this design, the inductance generated by a single layer of wire is canceled out by the inductance of adjacent layers. At the same time, the angle difference between different layers of wire weakens the self-field component perpendicular to the wire axis, thereby significantly reducing hysteresis loss. By tightly wrapping a fastening layer 3 around the superconducting wire layer 2, the superconducting heat-treated Bi2212 wire 5 is fixed and hard contact with the outer armor layer 4 is avoided, achieving uniform fixation and pressure buffering of the superconducting wire. To reduce the gap between the superconducting wire layer 2 and the outer tube and prevent displacement of the superconducting cable during use, which could lead to signal instability or wire damage, the armor layer 4, which is wrapped around the fastening layer 3, is compressed to form an integral armor structure.

[0029] In this embodiment, the liquid helium channel 1 is a stainless steel tube. By using a stainless steel tube with an internal cavity structure as a liquid helium flow channel, it has good low-temperature characteristics, excellent strength, and low cost.

[0030] In this embodiment, each layer of Bi2212 wire 5 that has undergone superconducting heat treatment in the superconducting wire layer 2 is helically stranded, and the helical directions of adjacent layers of Bi2212 wire 5 that have undergone superconducting heat treatment are opposite, forming a layered cross-contact structure. By designing this layered cross-contact structure, the inductance generated by the current from the symmetrically arranged wires in the cross structure can be canceled out, thereby reducing hysteresis loss. The first reason is that the superconducting core wire of the superconducting wire is a ceramic structure; directly stranding it like a steel wire rope often results in damage due to excessive bending strain. Therefore, the strain of this layered cross structure is completely controllable, thus significantly reducing wire damage. Another reason is that if it were directly stranded according to the structure of a steel wire rope, not only would the bending strain be difficult to strictly control, causing damage, but the cable pitch would also need to be very long, resulting in a less effective reduction in hysteresis loss compared to the layered cross structure of this invention.

[0031] In this embodiment, the stranding angle of each layer of Bi2212 wire 5 that has undergone superconducting heat treatment in the superconducting wire layer 2 is determined according to the equivalent support diameter at the location of that layer, so that the maximum bending strain of the Bi2212 wire 5 that has undergone superconducting heat treatment does not exceed 0.5%. In this invention, the stranding angle of each layer of wire is determined by the equivalent support diameter to ensure that the maximum bending strain of the wire does not exceed 0.5%, thus ensuring that the Bi2212 armored conductor has optimal performance.

[0032] It should be noted that the twisting angles all satisfy: ε=d / (2 R bend ≤0.5% and R bend = R n sin 2 θ, where ε is the bending strain of the Bi2212 wire after superconducting heat treatment, and d is the diameter of the Bi2212 wire after superconducting heat treatment. R bend The equivalent bending radius of the Bi2212 wire that has undergone superconducting heat treatment. R n The equivalent cylinder radius is given, and θ is the helical angle. Taking the outer diameter of liquid helium channel 1 as an example with diameters of 10 mm and 15 mm, the bending strain of Bi2212 wire 5 with different diameters after superconducting heat treatment is calculated at different helical angles. The parameters are preliminarily screened, and the results are shown in Tables 1 and 2. Table 1

[0033] Table 2

[0034] Based on the results in Tables 1 and 2, select appropriate wire diameter and helix angle, and make fine adjustments accordingly, while ensuring that the maximum bending strain does not exceed 0.5%.

[0035] In this embodiment, the fastening layer 3 is formed by spirally winding aluminum foil strip under tension. The thickness and winding density of the fastening layer 3 are controlled by the compression amount of the armor layer 4. In this invention, aluminum foil strip is spirally wound to the maximum tension it can withstand to obtain the fastening layer 3. If only aluminum foil is wound, the porosity of the superconducting wire is too high, which cannot meet the usage requirements. Therefore, the final porosity control requires the compression of the armor layer 4. The armor layer 4 is a metal tube, which, after compression, can better bind the aluminum foil and the superconducting wire. If aluminum foil is not used, the metal tube directly contacts the superconducting wire, and excessive binding force will cause deformation of the superconducting wire, resulting in damage. In fact, during the compression process of the armor layer 4, the aluminum foil is compressed. On the one hand, the gap between the aluminum foils decreases; on the other hand, the aluminum foil undergoes plastic deformation, transferring the binding force of the armor layer 4 to the superconducting wire, thereby reducing the gap between the superconducting wire layers 2. Therefore, the aluminum foil actually acts as a blanket, or a boxing glove, to prevent damage in certain areas. The aluminum foil tape achieves flexible contact with the superconducting wire. The aluminum foil's function is to adjust the force applied to the superconducting wire. The greater the outer armor compression, the thicker the aluminum foil tape needs to prevent excessive stress on the superconducting wire. Different cable thicknesses require different gaps. Generally, the more layers a superconducting wire has, the greater the force applied to the outermost layer needs to achieve the required porosity. A thicker aluminum foil layer allows for more even stress distribution on the outer layer, avoiding high stress concentration. Therefore, a thicker aluminum foil layer is essential for achieving lower porosity. Increasing the compression also requires a thicker aluminum foil. To ensure the final cable's internal porosity meets the standard, a larger compression is needed. If the aluminum foil is too thin, excessive compression may cause the superconducting wire to be subjected to excessive pressure and damaged.

[0036] In this embodiment, the armor layer 4 is made of stainless steel. Stainless steel, used in this invention, possesses good low-temperature properties, excellent strength, and low cost, making it suitable for subsequent compression processing.

[0037] The preparation method of Bi2212 armored conductor by reaction followed by stranding according to the present invention is described in detail through Examples 2 to 4.

[0038] Example 2 This embodiment includes the following steps: Step 1: Twist a 1mm diameter Bi2212 wire 5, which has undergone superconducting heat treatment, onto the outer wall of a 10mm diameter liquid helium channel 1 according to a preset helical direction and a helical angle of 8°, forming the first layer of wire 6. (See...) Figure 2,from Figure 2 It can be seen that the outer wall of the liquid helium channel 1 is spirally twisted with a first layer of wire 6; Step 2: Outside the first layer of wire 6 formed in Step 1, the Bi2212 wire 5, which has undergone superconducting heat treatment, is further stranded in the opposite spiral direction and at a spiral angle of 8.5° to that in Step 1. See... Figure 3 ,from Figure 3 As can be seen, the second layer of wire 7 is twisted in opposite spiral directions on the outside of the first layer of wire 6 to form the second layer of wire 7, and the second layer of wire 7 and the first layer of wire 6 are in cross contact to obtain a liquid helium channel with a superconducting wire layer. Step 3: Outside the liquid helium channel with superconducting wire layer obtained in Step 2, use an aluminum foil strip with a thickness of 0.02mm to spirally wind it at the maximum tension that the aluminum foil strip can withstand until the thickness reaches 0.5mm, thus obtaining a liquid helium channel with a fastening layer and a superconducting wire layer. Step 4: Insert the liquid helium channel with the fastening layer and superconducting wire layer obtained in Step 3 into the armor layer 4 with an inner diameter of 18 mm and a wall thickness of 3 mm. Then, perform compression processing by multi-pass die rolling with a single deformation amount of 1%. When the total deformation amount is 9%, the current carrying capacity begins to decrease, and the compression processing is stopped to obtain the Bi2212 armored conductor that is reacted and then stranded.

[0039] Testing revealed that the Bi2212 armored conductor prepared in this embodiment, with its layered structure, effectively avoids wire damage caused by bending strain in superconducting wires, achieving a significant improvement in cable current-carrying capacity. Compared with cables prepared by directly twisting fusion low-temperature superconducting wires, the current-carrying capacity of the wire is nearly doubled. Figure 4 This refers to cables made by directly twisting wires together in existing technologies, i.e., twisting wires directly to each other to form a cable. Figure 4 As can be seen, the wire exhibits irregular twisting and bulges in some areas, indicating damage to the wire. This means that directly twisting the wire to prepare the cable will damage the Bi2212 wire, resulting in a significant decrease in performance. Compared with conventional coaxial cables without cross-twisting, the Bi2212 armored conductor prepared in this embodiment effectively reduces inductance and lowers hysteresis loss by 47%. While coaxial cables without cross-twisting can avoid wire damage, the inductance formed by such cables cannot be offset, resulting in significant hysteresis loss. Therefore, this invention overcomes the shortcomings of existing self-twisted cables and coaxial cables, achieving the preparation of a high-performance conductor with both high current-carrying capacity and low hysteresis loss.

[0040] Example 3 This embodiment includes the following steps: Step 1: Twist a 0.75mm diameter Bi2212 wire that has undergone superconducting heat treatment onto the outer wall of a 10mm diameter liquid helium channel in a predetermined spiral direction and at a spiral angle of 11° to form the first layer of wire. Step 2: Outside the first layer of wire formed in Step 1, the Bi2212 wire that has undergone superconducting heat treatment is further twisted in the opposite spiral direction and at a spiral angle of 11.5° to form a second layer of wire, and the second layer of wire is made to cross contact with the first layer of wire. Step 3: Repeat the process of Step 2, stranding the Bi2212 wire that has undergone superconducting heat treatment layer by layer, with the helix angle of the third layer of wire being 11.8°, the helix angle of the fourth layer of wire being 12°, until the layered wire is formed, and each layer of wire forms a cross contact structure with the adjacent layer, to obtain a liquid helium channel with a superconducting wire layer. Step 4: Outside the liquid helium channel with superconducting wire layer obtained in step 3, use an aluminum foil strip with a thickness of 0.02 mm to spirally wind it at the maximum tension that the aluminum foil strip can withstand until the thickness reaches 0.8 mm, thus obtaining a liquid helium channel with a fastening layer and a superconducting wire layer. Step 5: Insert the liquid helium channel with the fastening layer and superconducting wire layer obtained in Step 4 into the armor layer with an inner diameter of 20 mm and a wall thickness of 3.5 mm. Then, perform two-pass drawing with a single deformation amount of 2%, followed by multiple-pass drawing with a single deformation amount of 1% for compression processing. When the total deformation amount reaches 10%, the current carrying capacity begins to decrease, and the compression processing is stopped to obtain the Bi2212 armored conductor that has been reacted and then stranded.

[0041] Testing revealed that the Bi2212 armored conductor prepared in this embodiment, with its layered structure, effectively avoids wire damage caused by bending strain in superconducting wires, achieving a significant improvement in cable current-carrying capacity. Compared with cables prepared by directly twisting fusion low-temperature superconducting wires, the current-carrying capacity of the wire is nearly doubled. Figure 4 This refers to cables made by directly twisting wires together in existing technologies, i.e., twisting wires directly to each other to form a cable. Figure 4 As can be seen, the wire exhibits irregular twisting and bulges in some areas, indicating damage to the wire. This means that directly twisting the wire to prepare the cable will damage the Bi2212 wire, resulting in a significant decrease in performance. Compared with conventional coaxial cables without cross-twisting, the Bi2212 armored conductor prepared in this embodiment effectively reduces inductance and lowers hysteresis loss by 68%. While coaxial cables without cross-twisting can avoid wire damage, the inductance formed by such cables cannot be offset, resulting in significant hysteresis loss. Therefore, this invention overcomes the shortcomings of existing self-twisted cables and coaxial cables, achieving the preparation of a high-performance conductor with both high current-carrying capacity and low hysteresis loss.

[0042] Example 4 This embodiment includes the following steps: Step 1: Twist a 0.82mm diameter Bi2212 wire that has undergone superconducting heat treatment onto the outer wall of a 15mm diameter liquid helium channel in a predetermined spiral direction and at a spiral angle of 17° to form the first layer of wire. Step 2: Outside the first layer of wire formed in Step 1, the Bi2212 wire that has undergone superconducting heat treatment is further twisted in the opposite spiral direction and at a spiral angle of 17.5° to form a second layer of wire, and the second layer of wire is made to cross contact with the first layer of wire. Step 3: Repeat the process of Step 2, stranding the Bi2212 wire that has undergone superconducting heat treatment layer by layer, with the helix angle of the third layer of wire being 17.8° and the helix angle of the fourth layer of wire being 18°, until 4 layers of wire are formed, and each layer of wire forms a cross contact structure with the adjacent layer, thus obtaining a liquid helium channel with superconducting wire layers. Step 4: Outside the liquid helium channel with superconducting wire layer obtained in step 3, use an aluminum foil strip with a thickness of 0.02 mm to spirally wind it at the maximum tension that the aluminum foil strip can withstand until the thickness reaches 0.8 mm, thus obtaining a liquid helium channel with a fastening layer and a superconducting wire layer. Step 5: Insert the liquid helium channel with the fastening layer and superconducting wire layer obtained in Step 4 into the armor layer with an inner diameter of 20 mm and a wall thickness of 3.5 mm. Then, perform two-pass drawing with a single deformation amount of 2%, followed by multiple-pass drawing with a single deformation amount of 1% for compression processing. When the total deformation amount reaches 10%, the current carrying capacity begins to decrease, and the compression processing is stopped to obtain the Bi2212 armored conductor that has been reacted and then stranded.

[0043] Testing revealed that the Bi2212 armored conductor prepared in this embodiment, with its layered structure, effectively avoids wire damage caused by bending strain in superconducting wires, achieving a significant improvement in cable current-carrying capacity. Compared with cables prepared by directly twisting fusion low-temperature superconducting wires, the current-carrying capacity of the wire is nearly doubled. Figure 4 This refers to cables made by directly twisting wires together in existing technologies, i.e., twisting wires directly to each other to form a cable. Figure 4As can be seen, the wire exhibits irregular twisting and bulges in some areas, indicating damage to the wire. This means that directly twisting the wire to prepare the cable will damage the Bi2212 wire, resulting in a significant decrease in performance. Compared with conventional coaxial cables without cross-twisting, the Bi2212 armored conductor prepared in this embodiment effectively reduces inductance and lowers hysteresis loss by 63%. While coaxial cables without cross-twisting can avoid wire damage, the inductance formed by such cables cannot be offset, resulting in significant hysteresis loss. Therefore, this invention overcomes the shortcomings of existing self-twisted cables and coaxial cables, achieving the preparation of a high-performance conductor with both high current-carrying capacity and low hysteresis loss.

[0044] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention in any way. Any simple modifications, alterations, and equivalent changes made to the above embodiments based on the inventive essence shall still fall within the protection scope of the present invention.

Claims

1. A Bi2212 armored conductor that is reacted before stranding, characterized in that, The armored conductor includes a liquid helium channel (1), a superconducting wire layer (2) is disposed outside the liquid helium channel (1), a fastening layer (3) is tightly wrapped around the superconducting wire layer (2), and an armor layer (4) is disposed outside the fastening layer (3) by compression processing and covered on the fastening layer (3); the superconducting wire layer (2) is formed by multiple layers of Bi2212 wire (5) that have undergone superconducting heat treatment and are cross-stretched along the outer wall of the liquid helium channel (1).

2. The Bi2212 armored conductor with pre-reaction and post-stretching as described in claim 1, characterized in that, The liquid helium channel (1) is a stainless steel tube.

3. The Bi2212 armored conductor with pre-reaction and post-stretching as described in claim 1, characterized in that, Each layer of Bi2212 wire (5) that has undergone superconducting heat treatment in the superconducting wire layer (2) is twisted in a spiral manner, and the spiral directions of the adjacent layers of Bi2212 wire (5) that have undergone superconducting heat treatment are opposite, forming a layered cross-contact structure.

4. The Bi2212 armored conductor with pre-reaction and post-stretching as described in claim 1, characterized in that, The stranding angle of each layer of Bi2212 wire (5) that has undergone superconducting heat treatment in the superconducting wire layer (2) is determined according to the equivalent support diameter of the location of the layer, so that the maximum bending strain of the Bi2212 wire (5) that has undergone superconducting heat treatment in the layer does not exceed 0.5%.

5. The Bi2212 armored conductor with pre-reaction and post-stretching as described in claim 1, characterized in that, The fastening layer (3) is formed by spirally winding aluminum foil strips under tension, and the thickness and winding density of the fastening layer (3) are controlled by the amount of compression of the armor layer (4).

6. The Bi2212 armored conductor with pre-reaction and post-stretching as described in claim 1, characterized in that, The armor layer (4) is made of stainless steel.

7. A method for preparing a Bi2212 armored conductor as described in any one of claims 1 to 6, characterized in that, The method includes the following steps: Step 1: Twist the Bi2212 wire (5) that has undergone superconducting heat treatment onto the outer wall of the liquid helium channel (1) in a preset spiral direction to form the first layer of wire (6). Step 2: Outside the first layer of wire (6) formed in Step 1, the Bi2212 wire (5) that has undergone superconducting heat treatment is further twisted in the opposite spiral direction to that in Step 1 to form the second layer of wire (7), and the second layer of wire (7) and the first layer of wire (6) are made to cross contact. Step 3: Repeat the process of step 2, stranding the Bi2212 wire (5) that has completed superconducting heat treatment layer by layer until the designed number of superconducting wire layers (2) is reached, and each layer of wire forms a cross contact structure with the adjacent layer to obtain a liquid helium channel with superconducting wire layers. Step 4: The liquid helium channel with a superconducting wire layer obtained in step 3 is externally wound with an aluminum foil strip in a tension spiral to obtain a liquid helium channel with a fastening layer and a superconducting wire layer. Step 5: Insert the liquid helium channel with the fastening layer and superconducting wire layer obtained in Step 4 into the armor layer (4), and then perform compression processing by multi-pass, small-deformation die rolling or drawing to obtain the Bi2212 armored conductor that is first reacted and then stranded.

8. The method according to claim 7, characterized in that, The twisting angles described in steps one and two both satisfy: ε = d / (2 R bend )≤0.5%, and R bend = R n sin 2 θ, where ε is the bending strain of the Bi2212 wire after superconducting heat treatment, and d is the diameter of the Bi2212 wire after superconducting heat treatment. R bend The equivalent bending radius of the Bi2212 wire that has undergone superconducting heat treatment. R n Let θ be the equivalent cylinder radius, and θ be the twisting angle.

9. The method according to claim 7, characterized in that, The small deformation amount mentioned in step five is no more than 5%. The upper limit of the total deformation amount of the compression process is determined by the criterion that the current carrying capacity of the Bi2212 armored conductor begins to decrease. When the deformation amount is further increased and the current carrying capacity decreases, the compression process is stopped.

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