A heat treatment method for a Bi2212 high-temperature superconducting conductor with constant oxygen partial pressure

Abstract

This invention discloses a heat treatment method for a Bi2212 high-temperature superconducting conductor with constant oxygen partial pressure, comprising the following steps: 1. Opening a gas replacement hole in a silver tube; 2. Inserting a Bi2212 superconducting cable into the silver tube with the gas replacement hole to obtain a sub-conductor; 3. Closely arranging one empty silver tube and six sub-conductors and installing them into a heat-resistant and oxidation-resistant alloy tube; 4. Passing high-pressure gas through the Bi2212 high-temperature superconducting conductor and heating it to complete the heat treatment of the Bi2212 high-temperature superconducting conductor with constant oxygen partial pressure. This invention utilizes the low flow resistance characteristics of the central empty silver tube to eliminate long-distance pressure drop and achieves uniform oxygen supply through the gas replacement hole, ensuring the stability of the oxygen partial pressure and pressure inside the entire Bi2212 high-temperature superconducting conductor, thereby significantly improving the phase formation rate and current carrying capacity of the Bi2212 superconducting phase, and solving the problem of drastic gas pressure drop and oxygen partial pressure instability caused by the obstruction of the superconducting cable during long-distance heat treatment of existing armored conductors.

Description

Technical Field

[0001] This invention belongs to the field of heat treatment technology for Bi2212 high-temperature superconducting conductors, and specifically relates to a heat treatment method for Bi2212 high-temperature superconducting conductors with constant oxygen partial pressure. Background Technology

[0002] Heat treatment is essential in the fabrication of Bi-2212 high-temperature superconducting conductors. The core purpose is to transform the disordered powder after cold working into a superconducting phase with a high critical current density through partial melting and recrystallization, while also eliminating internal defects. Bi-2212 high-temperature superconducting conductors are highly sensitive to oxygen partial pressure and heat treatment pressure during heat treatment. Stable oxygen partial pressure ensures the stability of the superconducting phase in the Bi-2212 superconducting wire, while heat treatment at pressures exceeding 30 atm (typically 5 MPa) is required to ensure the absence of pores within the wire.

[0003] The fusion magnet in magnetic confinement fusion is made using armored Bi2212 high-temperature superconducting conductors. This involves stranding superconducting wires into superconducting cables, then inserting the superconducting cables into silver tubes to form sub-cables. Six sub-cables and one empty tube are then inserted into a high-temperature resistant oxide stainless steel tube (with the empty tube in the center) to prepare a 6+1 type Bi2212 high-temperature superconducting CICC (conduit cable conductor) initial conductor. When heat treatment is required, gas with the same pressure and oxygen partial pressure is introduced into the stainless steel tube, the six sub-cables, and the central empty tube. The purpose is to ensure stable oxygen partial pressure and pressure for heat treatment of the Bi2212 high-temperature superconducting conductor. However, a serious problem exists in existing technology: when an oxygen-argon mixture is passed through the sub-cable, a large flow rate is required to maintain a constant oxygen partial pressure. Due to the obstruction of the superconducting cable within the conductor, a rapid voltage drop occurs, reaching 5% to 10%. For a Bi2212 high-temperature superconducting conductor several hundred meters long, with an inlet pressure of 5 MPa, the outlet pressure will drop by at least one order of magnitude. This pressure drop will also cause the oxygen partial pressure to decrease by one order of magnitude, leading to a significant decrease in the stability and Bi2212 phase content of the Bi2212 high-temperature superconducting conductor. This significant decrease in the superconducting phase will result in a substantial reduction in the current-carrying capacity of the Bi2212 high-temperature superconducting conductor. Shortening the length of the Bi2212 high-temperature superconducting conductor inevitably increases the number of joints, thereby increasing cooling and manufacturing costs. Continuing to extend the conductor length exacerbates this problem, limiting the development of Bi2212 high-temperature superconducting conductors.

[0004] Therefore, a heat treatment method for Bi2212 high-temperature superconducting conductors with constant oxygen partial pressure is needed. Summary of the Invention

[0005] The technical problem this invention aims to solve is to address the shortcomings of existing technologies by providing a heat treatment method for Bi2212 high-temperature superconducting conductors with constant oxygen partial pressure. This method abandons the traditional approach of independent ventilation via sub-cables. Instead, it constructs a low-resistance main gas channel coupled with a symmetrically staggered array of gas replacement holes on the silver tube, creating a multi-field synergistic atmosphere control system. This is not simply a modification of the tube wall by opening holes, but rather a design that matches the entire set of topology and dimensional parameters through triple constraints of fluid transport, high-temperature oxygen diffusion, and structural mechanics. This provides a heat treatment scheme based on a special conductor structure, solving the problem of drastically increased gas pressure drop and unstable oxygen partial pressure caused by superconducting cables during long-distance heat treatment of existing Bi2212 high-temperature superconducting conductors.

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a heat treatment method for a Bi2212 high-temperature superconducting conductor with constant oxygen partial pressure, characterized in that the method includes the following steps: Step 1: Create a gas replacement hole in the silver tube to obtain a silver tube with a gas replacement hole; Step 2: Insert a Bi2212 superconducting cable into the silver tube with gas displacement holes obtained in Step 1 to obtain a sub-conductor; Step 3: Take a silver tube with gas replacement holes obtained in Step 1 as an empty silver tube, then arrange the empty silver tube and six sub-conductors obtained in Step 2 in close proximity, with the empty silver tube in the center, and then insert a heat-resistant and oxidation-resistant alloy tube to obtain a Bi2212 high-temperature superconducting conductor. Step 4: Place the Bi2212 high-temperature superconducting conductor obtained in Step 3 into a heat treatment furnace, then introduce high-pressure gas into the heat-resistant and oxidation-resistant alloy tube and heat it to complete the heat treatment of the Bi2212 high-temperature superconducting conductor with constant oxygen partial pressure.

[0007] This invention creates gas replacement holes in the silver tube, ensuring that both the sub-conductors and the empty silver tube in the subsequently prepared Bi2212 high-temperature superconducting conductor have these holes. This provides a rapid channel for the exchange of high-pressure gas between the sub-conductors and the empty silver tube. Furthermore, placing the empty silver tube at the very center facilitates uniform gas flow and the exchange of gas between the sub-conductors and the high-pressure gas in the empty silver tube. During subsequent heat treatment, high-pressure gas is introduced into the heat-resistant and oxidation-resistant alloy tube. This high-pressure gas primarily flows through the centrally located empty silver tube and exchanges gas with the interiors and gaps of each sub-conductor through the gas replacement holes. This maintains the oxygen partial pressure within the sub-conductors and their gaps, preventing pressure drop and thus achieving stability in the oxygen partial pressure and overall pressure within the entire Bi2212 high-temperature superconducting conductor. This completes the heat treatment of the Bi2212 high-temperature superconducting conductor with constant oxygen partial pressure.

[0008] The aforementioned heat treatment method for a Bi2212 high-temperature superconducting conductor with constant oxygen partial pressure is characterized in that the inner diameter of the silver tube in step one is not less than 10 mm. The core of this invention is a multi-field coupled synergistic atmosphere control architecture, not a simple improvement of the tube wall opening. Its working principle is as follows: The central empty silver tube acts as an oxygen supply station for stabilizing the oxygen partial pressure. When high-pressure gas is introduced into the heat-resistant and oxidation-resistant alloy tube, because the inner diameter of the central empty silver tube is much larger than the equivalent hydraulic diameter occupied by the Bi2212 superconducting cable inside the sub-conductor, the high-pressure gas will mainly flow rapidly along the central empty silver tube. Furthermore, because the inner diameter of the empty silver tube is not less than 10 mm, the high-pressure gas will not experience a pressure drop (for example, at a gas flow rate of 10 L / min, the pressure drop over a 1 km tube only decreases by 0). (1%, negligible) Even if the oxygen partial pressure decreases, it can be replaced by the newly introduced gas, thus ensuring the stability of the internal pressure and oxygen partial pressure of the empty silver tube; there are gas replacement holes on the sub-conductors and the empty silver tube. When the atmosphere inside the sub-conductors or the gap between the sub-conductors changes, it can quickly exchange with the gas in the empty silver tube. The central empty silver tube always maintains a high-pressure gas flow rate, and the changed atmosphere can be quickly flushed away by the new gas, thus ensuring the stability of the oxygen partial pressure in the central empty silver tube, and thus ensuring the stability of the oxygen partial pressure in the gap between the sub-conductors and inside the sub-conductors.

[0009] The above-mentioned heat treatment method for a Bi2212 high-temperature superconducting conductor with constant oxygen partial pressure is characterized in that the diameter of the gas replacement hole in step one is no greater than 0.5 mm. In this invention, considering the matching size of the gas replacement hole with the Bi2212 superconducting cable inside the sub-conductor, the diameter of the gas replacement hole needs to be smaller than the size of the Bi2212 superconducting cable. This avoids insufficient support for the Bi2212 superconducting cable near the hole under Lorentz force conditions, which could lead to performance degradation, or even the Bi2212 superconducting cable breaking due to leakage from the hole under Lorentz force. This ensures that the gas replacement hole of this size guarantees efficient gas replacement without significantly reducing the mechanical strength of the silver tube, and also prevents superconducting powder or debris from entering the pipe.

[0010] The above-mentioned heat treatment method for a Bi2212 high-temperature superconducting conductor with constant oxygen partial pressure is characterized in that, in step one, three rows of gas replacement holes are evenly arranged around the silver tube, and the spacing between two adjacent gas replacement holes in each row is 8cm to 12cm. In this invention, three rows of gas replacement holes are uniformly arranged around the circumference of the silver tube, one row every 120°, ensuring gas exchange channels exist in all 360° directions and avoiding dead zones in airflow. By controlling the hole spacing, a constant oxygen partial pressure is maintained with the fewest possible holes. Simulation calculations show that the concentration gradient between any two holes at this spacing is less than 0.05%, ensuring instantaneous equilibrium of local oxygen partial pressure and maintaining the mechanical properties of the Bi2212 high-temperature superconducting conductor. Furthermore, through the coordinated control of the three rows and hole spacing, the pressure difference between the inside and outside of the sub-conductor wall is extremely small, and gas exchange occurs through a mixture of diffusion and convection. Any drop in local oxygen partial pressure caused by oxygen absorption from the silver tube wall, oxygen absorption from the superconducting powder, or high-temperature oxidation reactions can be compensated by fresh gas from the central empty silver tube within seconds, thereby ensuring that the oxygen partial pressure at any location inside the entire Bi2212 high-temperature superconducting conductor remains stable at 1.8%~2.1%.

[0011] The above-mentioned heat treatment method for a Bi2212 high-temperature superconducting conductor with constant oxygen partial pressure is characterized in that adjacent rows of gas replacement holes are staggered by 2cm to 4cm along the axial direction of the silver tube. In this invention, by dislocating the three rows of gas replacement holes, dead zones in the gas flow are avoided, and the mechanical properties of the Bi2212 high-temperature superconducting conductor are guaranteed.

[0012] The above-mentioned heat treatment method for a Bi2212 high-temperature superconducting conductor with constant oxygen partial pressure is characterized in that the high-pressure gas in step four is an oxygen-argon mixture, wherein the oxygen partial pressure is 1.8%~2.1% and the pressure is above 5 MPa. This invention ensures the effectiveness of heat treatment by controlling the parameters of the high-pressure gas.

[0013] The above-described heat treatment method for a Bi2212 high-temperature superconducting conductor with constant oxygen partial pressure is characterized in that, during the introduction of high-pressure gas in step four, the gas flow rate inside the empty silver tube is maintained at 5 L / min to 10 L / min. This invention ensures stable gas exchange by controlling the gas flow rate.

[0014] Compared with the prior art, the present invention has the following advantages: 1. This invention provides a rapid channel for the exchange of high-pressure gas between the sub-conductor and the empty silver tube by opening gas replacement holes in the silver tube and adopting a strategy of unobstructed flow throughout the entire tube, central main flow, and side hole exchange. This facilitates the replacement of gas in the sub-conductor with high-pressure gas in the empty silver tube, ensuring the oxygen partial pressure inside the sub-conductor and between sub-conductors. This achieves the stability of the oxygen partial pressure and pressure inside the entire Bi2212 high-temperature superconducting conductor, and completes the heat treatment of Bi2212 high-temperature superconducting conductors with constant oxygen partial pressure. This solves the problem that only one of the oxygen content and pressure can be guaranteed in the existing technology, and is suitable for the heat treatment of long-scale Bi2212 superconducting coils such as large fusion magnets.

[0015] 2. Unlike existing Bi2212 high-temperature superconducting conductors where gas is introduced into each sub-conductor, this invention introduces gas into the entire Bi2212 high-temperature superconducting conductor. The gas flow mainly flows rapidly within the central hollow silver tube and replaces the sub-conductors with high-pressure gas through gas replacement holes. By controlling the inner diameter of the hollow silver tube, there is no pressure drop even at large flow rates, thus avoiding the pressure drop problem caused by directly introducing gas into the sub-conductors. Furthermore, the gas replacement holes enable the central hollow silver tube to act as an oxygen supply station, forming a rapid exchange channel between it and various oxygen-consuming areas, allowing for timely replenishment even if oxygen is consumed.

[0016] 3. This invention features three rows of gas replacement holes evenly arranged around the circumference of the silver tube. The multi-row design prevents one row of holes from being blocked by an adjacent silver tube. Based on the structure of the Bi2212 high-temperature superconducting conductor, the gas replacement holes are arranged at 120°, ensuring that at least two rows of holes are not blocked. In addition, it can reduce the mechanical problems caused by the pores, thereby improving mechanical performance while ensuring that there are gas exchange channels in all 360° directions, avoiding dead zones in airflow. Furthermore, by controlling the hole spacing and dislocation, the diffusion distance of gas in the conductor is further reduced, which is more conducive to gas exchange and does not affect the mechanical integrity of the silver tube and the heat-resistant and oxidation-resistant alloy tube, making it suitable for the engineering manufacturing of large magnets.

[0017] 4. This invention differs from conventional methods that merely address the symptoms of oxygen partial pressure attenuation by adjusting ventilation flow and shortening conductor length. It is not simply about opening gas replacement holes in the silver tube, but rather about coupling a large-diameter, low-resistance central air channel, a circumferentially symmetrical staggered hole array, and multi-dimensional matching parameters to form an integrated atmosphere homogenization system. None of these three elements can be omitted: an empty silver tube with a central hole alone cannot equalize the atmosphere of the sub-conductor core without a gas replacement hole; opening holes only in the tube wall lacks a central low-resistance main air channel, making it impossible to completely eliminate the problem of pressure drop attenuation over long distances; mismatches in hole arrangement, hole diameter, and axial misalignment dimensions can lead to problems such as dead airflow, extrusion and breakage of superconducting wires, and local oxygen partial pressure imbalance. Through the above improvements, this invention addresses the bottleneck of atmospheric instability in the heat treatment of kilometer-scale CICC conductors, a problem that has plagued the industry for over a decade. Through the synergistic design of triple constraints—fluid transport, high-temperature oxygen diffusion, and high-temperature mechanical load-bearing capacity of the tube—it achieves a long-scale, global oxygen partial pressure stabilization effect that is unpredictable by existing technologies.

[0018] 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

[0019] Figure 1 This is a schematic diagram of the cross-sectional structure of the Bi2212 high-temperature superconducting conductor in this invention.

[0020] Figure 2 This is a schematic diagram of the structure of the silver tube with gas displacement holes in this invention.

[0021] Figure 3 This is a schematic diagram of the unfolded structure of the silver tube with gas displacement holes in this invention.

[0022] Explanation of reference numerals in the attached figures: Detailed Implementation

[0023] Figure 1 This is a schematic diagram of the cross-sectional structure of the Bi2212 high-temperature superconducting conductor in this invention. Figure 1 As can be seen, a Bi2212 superconducting cable 3 is inserted into a silver tube 4 with a gas replacement hole to obtain a sub-conductor 2. A silver tube 4 with a gas replacement hole is used as an empty silver tube and arranged closely with six sub-conductors 2, with the empty silver tube located in the center. A heat-resistant and oxidation-resistant alloy tube 1 is then inserted to obtain a Bi2212 high-temperature superconducting conductor.

[0024] Figure 2 This is a schematic diagram of the structure of the silver tube with gas replacement holes in this invention. Figure 3 This is a schematic diagram of the unfolded structure of the silver tube with gas replacement holes in this invention. Figure 2 and Figure 3As can be seen, the silver tube 4 with gas replacement holes has gas replacement holes 5. The gas replacement holes 5 are evenly arranged in three rows around the silver tube 4 with gas replacement holes, and the gas replacement holes 5 in one row are offset from the gas replacement holes 5 in the next row along the axial direction of the silver tube 4 with gas replacement holes.

[0025] Example 1 This embodiment includes the following steps: Step 1: Gas replacement holes 5 are made in a 600m long silver tube to obtain a silver tube 4 with gas replacement holes; the inner diameter of the silver tube is 10mm; the diameter of the gas replacement holes 5 is 0.4mm; the gas replacement holes 5 are evenly arranged in three rows around the circumference of the silver tube, and the distance between two adjacent gas replacement holes 5 in each row is 10cm; the gas replacement holes 5 in one row are offset from the gas replacement holes 5 in the next row by 3.33cm along the axial direction of the silver tube. Step 2: Insert the Bi2212 superconducting cable 3 into the silver tube 4 with gas replacement holes obtained in Step 1 to obtain the sub-conductor 2; Step 3: Take a silver tube 4 with gas replacement holes obtained in Step 1 as an empty silver tube, and then arrange the empty silver tube and six sub-conductors 2 obtained in Step 2 in close proximity, with the empty silver tube in the center. Then insert the heat-resistant and oxidation-resistant alloy tube 1 to obtain the Bi2212 high-temperature superconducting conductor. The heat-resistant and oxidation-resistant alloy tube 1 is a 316L stainless steel tube with a wall thickness of 10mm. Step 4: Place the Bi2212 high-temperature superconducting conductor obtained in Step 3 into a heat treatment furnace, then introduce an oxygen-argon mixture with an oxygen partial pressure of 2% at a pressure of 5 MPa into the heat-resistant and oxidation-resistant alloy tube 1 and heat it. The gas flow rate in the empty silver tube is maintained at 8 L / min to complete the heat treatment of the Bi2212 high-temperature superconducting conductor with constant oxygen partial pressure.

[0026] Testing showed that, after high-pressure gas was introduced, the measured pressure drop along the 600m length of this embodiment was negligible, and the oxygen partial pressure decay did not exceed 0.05%, ensuring that the pressure along the entire length of the central empty silver tube was highly consistent with the oxygen partial pressure. This fundamentally solved the problem of sudden pressure drop at the outlet during long-distance gas transmission, and significantly improved the phase formation rate and current carrying capacity of the Bi2212 high-temperature superconducting conductor after heat treatment to achieve constant oxygen partial pressure.

[0027] Example 2 This embodiment includes the following steps: Step 1: Gas replacement holes 5 are made in a 500m long silver tube to obtain a silver tube 4 with gas replacement holes; the inner diameter of the silver tube is 11mm; the diameter of the gas replacement holes 5 is 0.5mm; the gas replacement holes 5 are evenly arranged in three rows around the circumference of the silver tube, and the distance between two adjacent gas replacement holes 5 in each row is 12cm; the gas replacement holes 5 in one row are offset by 4cm from the gas replacement holes 5 in the next row along the axial direction of the silver tube. Step 2: Insert the Bi2212 superconducting cable 3 into the silver tube 4 with gas replacement holes obtained in Step 1 to obtain the sub-conductor 2; Step 3: Take a silver tube 4 with gas replacement holes obtained in Step 1 as an empty silver tube, and then arrange the empty silver tube and six sub-conductors 2 obtained in Step 2 in close proximity, with the empty silver tube in the center. Then insert the heat-resistant and oxidation-resistant alloy tube 1 to obtain the Bi2212 high-temperature superconducting conductor. The heat-resistant and oxidation-resistant alloy tube 1 is a 316L stainless steel tube with a wall thickness of 10mm. Step 4: Place the Bi2212 high-temperature superconducting conductor obtained in Step 3 into a heat treatment furnace, and then introduce an oxygen-argon mixture with an oxygen partial pressure of 1.8% at a pressure of 5 MPa into the heat-resistant and oxidation-resistant alloy tube 1 and heat it. The gas flow rate in the empty silver tube is maintained at 5 L / min to complete the heat treatment of the Bi2212 high-temperature superconducting conductor with constant oxygen partial pressure.

[0028] Testing showed that, after high-pressure gas was introduced, the measured pressure drop along a 500m length was negligible, and the oxygen partial pressure decay did not exceed 0.05%, ensuring that the pressure along the entire length of the central empty silver tube was highly consistent with the oxygen partial pressure. This fundamentally solved the problem of a sudden drop in outlet pressure during long-distance gas transmission and significantly improved the phase formation rate and current carrying capacity of the Bi2212 high-temperature superconducting conductor after heat treatment to achieve constant oxygen partial pressure.

[0029] Example 3 This embodiment includes the following steps: Step 1: Gas replacement holes 5 are made in a 700m long silver tube to obtain a silver tube 4 with gas replacement holes; the inner diameter of the silver tube is 12mm; the diameter of the gas replacement holes 5 is 0.3mm; the gas replacement holes 5 are evenly arranged in three rows around the circumference of the silver tube, and the distance between two adjacent gas replacement holes 5 in each row is 8cm; the gas replacement holes 5 in one row are offset by 2cm from the gas replacement holes 5 in the next row along the axial direction of the silver tube; Step 2: Insert a Bi2212 superconducting cable into the silver tube with gas displacement holes obtained in Step 1 to obtain a sub-conductor; Step 3: Take a silver tube 4 with gas replacement holes obtained in Step 1 as an empty silver tube, and then arrange the empty silver tube and six sub-conductors 2 obtained in Step 2 in close proximity, with the empty silver tube in the center. Then insert the heat-resistant and oxidation-resistant alloy tube 1 to obtain the Bi2212 high-temperature superconducting conductor. The heat-resistant and oxidation-resistant alloy tube 1 is a 316L stainless steel tube with a wall thickness of 10mm. Step 4: Place the Bi2212 high-temperature superconducting conductor obtained in Step 3 into a heat treatment furnace, and then introduce an oxygen-argon mixture with an oxygen partial pressure of 2.1% at a pressure of 5 MPa into the heat-resistant and oxidation-resistant alloy tube 1 and heat it. The gas flow rate in the empty silver tube is maintained at 10 L / min to complete the heat treatment of the Bi2212 high-temperature superconducting conductor with constant oxygen partial pressure.

[0030] Testing revealed that, after the introduction of high-pressure gas, the measured pressure drop along the 700m length in this embodiment was negligible, and the oxygen partial pressure decay did not exceed 0.05%, ensuring that the pressure along the entire length of the central empty silver tube was highly consistent with the oxygen partial pressure. This fundamentally solved the problem of a sudden drop in outlet pressure during long-distance gas transmission, and significantly improved the phase formation rate and current-carrying capacity of the Bi2212 high-temperature superconducting conductor after heat treatment to achieve constant oxygen partial pressure.

[0031] 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 heat treatment method for a Bi₂₁₂ high-temperature superconducting conductor with constant oxygen partial pressure, characterized in that, The method includes the following steps: Step 1: Create a gas replacement hole in the silver tube to obtain a silver tube with a gas replacement hole; Step 2: Insert a Bi2212 superconducting cable into the silver tube with gas displacement holes obtained in Step 1 to obtain a sub-conductor; Step 3: Take a silver tube with gas replacement holes obtained in Step 1 as an empty silver tube, then arrange the empty silver tube and six sub-conductors obtained in Step 2 in close proximity, with the empty silver tube in the center, and then insert a heat-resistant and oxidation-resistant alloy tube to obtain a Bi2212 high-temperature superconducting conductor. Step 4: Place the Bi2212 high-temperature superconducting conductor obtained in Step 3 into a heat treatment furnace, then introduce high-pressure gas into the heat-resistant and oxidation-resistant alloy tube and heat it to complete the heat treatment of the Bi2212 high-temperature superconducting conductor with constant oxygen partial pressure.

2. The heat treatment method for a Bi₂₁₂ high-temperature superconducting conductor with constant oxygen partial pressure according to claim 1, characterized in that, The inner diameter of the silver tube mentioned in step one shall not be less than 10 mm.

3. The heat treatment method for a Bi₂₁₂ high-temperature superconducting conductor with constant oxygen partial pressure according to claim 1, characterized in that, The diameter of the gas replacement hole mentioned in step one is no greater than 0.5 mm.

4. The heat treatment method for a Bi₂₁₂ high-temperature superconducting conductor with constant oxygen partial pressure according to claim 1, characterized in that, In step one, the gas replacement holes are evenly arranged in three rows around the silver tube, and the distance between two adjacent gas replacement holes in each row is 8cm to 12cm.

5. The heat treatment method for a Bi₂₁₂ high-temperature superconducting conductor with constant oxygen partial pressure according to claim 4, characterized in that, The gas replacement holes in two adjacent rows are offset by 2cm to 4cm along the axial direction of the silver tube.

6. The heat treatment method for a Bi₂₁₂ high-temperature superconducting conductor with constant oxygen partial pressure according to claim 1, characterized in that, The high-pressure gas mentioned in step four is an oxygen-argon mixture, wherein the oxygen partial pressure is 1.8%~2.1% and the pressure is above 5MPa.

7. The heat treatment method for a Bi₂₁₂ high-temperature superconducting conductor with constant oxygen partial pressure according to claim 1, characterized in that, In step four, during the process of introducing high-pressure gas, the gas flow rate in the empty silver tube is maintained at 5L / min to 10L / min.

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