Compound superconducting precursor wire, compound superconducting precursor stranded wire, and compound superconducting stranded wire

Abstract

To provide a compound superconducting precursor wire, a compound superconducting precursor stranded wire, and a compound superconducting stranded wire which are more excellent in stranded wire fabrication properties and superconducting characteristics as compared with a conventional type.SOLUTION: A compound superconducting precursor wire 1 has: a compound superconducting precursor part 10 composed of a plurality of compound superconducting precursor filaments 11 and a first matrix precursor 12 in which the plurality of compound superconducting precursor filaments is embedded and which includes a first stabilizing material; a reinforcing material part 30 disposed on the outer peripheral side of the compound superconducting precursor part; and a stabilizing material part 40 which is disposed on at least one of the inner peripheral side and the outer peripheral side of the reinforcing material part and is formed from a second stabilizing material. The Vickers hardness (HV) of the stabilizing material part is 90 or less, and the 0.2% tensile proof stress of the compound superconducting precursor wire is 200 MPa or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to a compound superconducting precursor wire, a compound superconducting precursor stranded wire, and a compound superconducting stranded wire. [Background technology]

[0002] In compound superconducting stranded wires, which are used in large superconducting magnets for generating strong magnetic fields and are made by twisting together multiple compound superconducting wires such as Nb3Sn to increase the current density of the conductor, the twist pitch may be shortened and the void ratio (the proportion of voids in the stranded wire) of the stranded wire may be reduced in order to suppress performance degradation caused by the movement of the wires due to the electromagnetic stress applied when the magnet is in operation and to increase the conductor current density.

[0003] However, in the process of twisting strands (twisting process) of strands before the compound superconductivity-generating heat treatment (hereinafter also referred to as compound superconducting precursor strands), if the twist pitch is shortened and the void fraction of the twisted strands is reduced in the subsequent compression process, large localized processing stresses are applied to the compound superconducting precursor strands more frequently, causing abnormal deformation and breakage of the compound superconducting precursor strands, resulting in a significant decrease in manufacturing yield. Furthermore, in an Nb3Sn superconducting magnet obtained by twisting together strands of Nb3Sn precursor strands in this abnormal state and then subjecting them to the superconductivity-generating heat treatment, electromagnetic stresses generated during magnetization apply large strains to the Nb3Sn filaments in the Nb3Sn strands, resulting in not only a decrease in superconducting properties but also, in extreme cases, cracks in the Nb3Sn filaments, making it impossible to maintain a superconducting state.

[0004] On the other hand, Nb3Sn superconducting magnets obtained by superconductivity generation heat treatment using high-strength Nb3Sn precursor wires, which are composites of high-strength materials inside Nb3Sn precursor wires, and stranded wires made by twisting multiple strands, exhibit excellent superconducting properties even under the large electromagnetic stresses that occur during magnetization. However, Nb3Sn precursor wires composited with high-strength materials exhibit large springback of the wires themselves, depending on their configuration. This makes it difficult to control the dimensions required for a given stranded wire structure when shortening the twist pitch or reducing the void fraction of the stranded wire, posing problems in the manufacturability of the stranded wire. To date, many technological developments have been carried out to address these issues.

[0005] For example, Patent Document 1 describes an Nb3Sn superconducting wire composited with a CuNb reinforcement material in which many Nb filaments are embedded in a Cu base material. Patent Document 2 also describes a CuNb-reinforced compound superconducting stranded wire in which the cross-sectional structure of the compound superconducting element wire is specified and high strength is prioritized. However, Patent Documents 1 and 2 focus on improving superconducting performance under stress and do not consider improving stranding processability, so they cannot be directly applied to the manufacture of large-capacity conductors.

[0006] Furthermore, Patent Document 3 discloses a technology for stranding Nb3Sn superconducting precursor wires produced by the PIT method with a specific Sn diffusion barrier structure, thereby ensuring stabilization by Cu with high conductivity and obtaining particularly good current stability. However, Patent Document 3 does not intend to improve the manufacturability of the stranded wire or strengthen the stranded wire itself, and therefore cannot be applied to compound superconducting stranded wire conductors to which large electromagnetic stresses are applied during operation.

[0007] Furthermore, Patent Document 4 discloses a method of improving the workability of a stranded wire by annealing alloy wires. Furthermore, Patent Document 5 discloses a method of improving the shape by annealing a stranded wire of specified dimensions and then forming it. Furthermore, Patent Document 6 discloses a method of improving the shape of a stranded wire by forming annealed wires or primary strands and then re-annealing them. However, although Patent Documents 4 to 6 all aim to improve the workability of stranded wires, they cannot be applied directly to compound superconducting stranded wire conductors, which are subjected to large electromagnetic stresses during operation.

[0008] Furthermore, Non-Patent Documents 1 and 2 show the performance of Cu-Nb reinforced Nb3Sn wires produced by the Nb rod method, but do not show technology for improving the manufacturability of compound superconducting precursor stranded wires used in large-capacity conductors.

[0009] Furthermore, Non-Patent Documents 3 and 4 introduce a technology for suppressing performance degradation due to strong electromagnetic stress during operation by shortening the twist pitch and reducing the void fraction of the twisted wire in order to improve the electrical conductivity of the conductor for ITER-CS (conductor for the center solenoid of the International Fusion Experimental Reactor), but they do not show a technology for improving the manufacturability of the twisted wire.

[0010] Furthermore, Non-Patent Document 5 reports on the development results of a multi-stranded wire in which many copper wires are twisted together, the twist pitch is increased, the void ratio of the twisted wire is reduced, and the wire is made rectangular, but does not disclose a technology for improving the manufacturability of the twisted wire.

[0011] Patent Documents 1 to 6 and Non-Patent Documents 1 to 5 describe the results of academic research aimed at optimizing the design of compound superconducting wires and stranded conductors. In order to rationally design and manufacture stranded conductors for actual coils, it is necessary to solve two problems: improving the superconducting properties under electromagnetic stress during operation and improving the manufacturability of the stranded wire. [Prior art documents] [Patent documents]

[0012] [License 1] Patent No. 6155253 [License 2] International Publication No. 2020 / 066908 [License 3] Patent No. 6425673 [License 4] Patent No. 6201815 [Patent Document 5] Patent No. 3148212 [License 6] Patent No. 2930994 [Non-licensed literature]

[0013] [Non-licensed Document 1] M. Sugimoto, et al., "Development of Nb-rod-method Cu-Nb rein-forced Nb3Sn Rutherford cables for react-and-wind processed wide-bore high magnetic field coils", IEEE Trans. Appl. Supercond., Vol.25 No.3(2015)6000605 [Non-licensed Document 2] M. Sugimoto, et al., "Evaluation of Various Nb-Rod-Method Cu-Nb / Nb3Sn Wires designed for Practical React-and-Wind Coils", IEEE Trans. Appl. Supercond., Vol.30 No.4 (2020)6000905 [Non-licensed Document 3] IEEE Trans. on Appl. Super., 24 3(2014)4802404, Y.Takahashi [Non-licensed Document 4] IEEE Trans. on Appl. Super., 24 3(2014)4200705, Y.Nabara [Non-Patent Document 5] IEEE Trans. on Appl. Super., 27 4(2017)4800206, L.Muzzi Summary of the Invention [Problem to be solved by the invention]

[0014] Large superconducting conductors used in the manufacture of large superconducting magnets using compound superconducting wires such as Nb3Sn have a twisted wire structure. These twisted wire structures can be round or rectangular, but they are subjected to molding (compression) processing to improve the current density per cross section of the twisted wire and prevent the twist from breaking down. In such twisted wire structures, the twisted wire is not produced as a single twist (a twisted wire in which the wires are twisted together only once), but may be produced as a multi-twisted structure (high-order twisted structure) in which the wires are twisted together multiple times.

[0015] As described above, in the prior art, in Nb3Sn superconducting stranded wires used in large superconducting magnets, a configuration is adopted in which the twist pitch is shortened or the void fraction of the stranded wire is reduced in order to suppress movement of the superconducting strands due to increased current density and electromagnetic stress during current flow. As a result, in the stranded wire manufacturing process using strands before the Nb3Sn-producing heat treatment (Nb3Sn precursor strands), the strands can break during the stranding process to shorten the twist pitch, or abnormal deformation of the structural materials inside the strands can occur during the compression process to reduce the void fraction of the stranded wire, leading to wire breakage in extreme cases. In both Nb3Sn superconducting magnets in which a defective Nb3Sn precursor stranded conductor is used to wind a coil and then undergo Nb3Sn formation heat treatment (using the wind-and-react method), and in Nb3Sn superconducting magnets in which Nb3Sn formation heat treatment is performed and then coil winding is performed (using the react-and-wind method), the electromagnetic stress generated during magnet operation applies large strain to the Nb3Sn filaments in the wires that make up the Nb3Sn superconducting stranded wire, degrading the superconducting properties, and in extreme cases causing cracks to form in the Nb3Sn filaments, making it impossible to maintain a superconducting state.

[0016] An object of the present disclosure is to provide a compound superconducting precursor wire, a compound superconducting precursor stranded wire, and a compound superconducting stranded wire that are superior to conventional wires in terms of strand manufacturability and superconducting properties. [Means for solving the problem]

[0017] [1] A compound superconducting precursor strand having a compound superconducting precursor section comprising a plurality of compound superconducting precursor filaments, a first matrix precursor in which the plurality of compound superconducting precursor filaments are embedded and which contains a first stabilizing material, a reinforcing material section disposed on the outer periphery of the compound superconducting precursor section, and a stabilizing material section disposed on at least one of the inner and outer periphery sides of the reinforcing material section and made of a second stabilizing material, wherein the Vickers hardness (HV) of the stabilizing material section is 90 or less, and the 0.2% tensile yield strength of the compound superconducting precursor strand is 200 MPa or more. [2] The compound superconducting precursor wire according to [1] above, wherein the reinforcing material portion is made of one metal selected from the group consisting of Nb, Ta, V, W, Mo, Fe, Ti, and Hf, or an alloy or composite made of two or more metals. [3] The compound superconducting precursor wire according to [1] above, wherein the reinforcement portion is composed of a plurality of reinforcement filaments and a third matrix in which the plurality of reinforcement filaments are embedded and which contains a third stabilizing material. [4] The compound superconducting precursor wire according to [3] above, wherein the reinforcing filament is made of one metal or an alloy of two or more metals selected from the group consisting of Nb, Ta, V, W, Mo, Fe, Ti, and Hf, and the third stabilizing material is copper or a copper alloy. [5] A compound superconducting precursor wire according to any one of [1] to [4] above, wherein the compound superconducting precursor filament is a NbSn precursor, and further comprises a Sn diffusion prevention part made of Nb or Ta or an alloy or composite thereof between the compound superconducting precursor part and the reinforcing material part. [6] The compound superconducting precursor wire according to any one of the above [1] to [5], wherein the first stabilizing material is copper or a copper alloy. [7] The compound superconducting precursor wire according to any one of the above [1] to [6], wherein the second stabilizing material is copper or a copper alloy. [8] A compound superconducting precursor wire according to any one of [1] to [7] above, wherein the space factor of the reinforcement material portion is 5.0% or more and 40.0% or less, and is smaller than the space factor of the compound superconducting precursor portion, and the space factor of the stabilization material portion arranged on the outer periphery of the reinforcement material portion is 15.0% or more. [9] A compound superconducting precursor stranded wire having, as a constituent element, a second stranded wire formed by stranding together a plurality of first stranded wires each formed by stranding together a plurality of compound superconducting precursor wires according to any one of [1] to [8] above.

[10] A compound superconducting precursor stranded wire having, as a constituent element, a secondary stranded wire formed by stranding together a plurality of primary stranded wires each formed by stranding together one or more compound superconducting precursor wires according to any one of [1] to [8] above and one or more copper wires or copper alloy wires.

[11] The compound superconducting stranded precursor wire according to the above

[10] , wherein the copper wires or copper alloy wires have a Vickers hardness (HV) of 90 or less.

[12] The compound superconducting precursor stranded wire according to any one of [9] to

[11] above, wherein, in a cross section of one or more of the compound superconducting precursor strands constituting the compound superconducting precursor stranded wire, the maximum flattening ratio of the compound superconducting precursor portion is greater than 0 and not greater than 0.2.

[13] A compound superconducting stranded wire obtained by heating the compound superconducting precursor stranded wire according to any one of the above [9] to

[12] . [Effects of the Invention]

[0018] According to the present disclosure, it is possible to provide a compound superconducting precursor wire, a compound superconducting precursor stranded wire, and a compound superconducting stranded wire that are superior to conventional wires in terms of stranded wire manufacturability and superconducting properties. [Brief explanation of the drawings]

[0019] [Figure 1] FIG. 1 is a cross-sectional view showing an example of a compound superconductor precursor wire according to an embodiment. [Figure 2] FIG. 2 is a cross-sectional view showing another example of a compound superconductor precursor wire according to an embodiment. [Figure 3] FIG. 3 is a cross-sectional view showing an example of a compound superconducting stranded precursor wire according to an embodiment. [Figure 4] FIG. 4 is a cross-sectional view showing an example of a compound superconducting precursor strand constituting a compound superconducting precursor stranded wire of an embodiment. [Figure 5] FIG. 5 is a cross-sectional view showing an example of a compound superconducting element wire constituting a compound superconducting stranded wire of an embodiment. [Figure 6] FIG. 6 is a cross-sectional view showing another example of a compound superconducting element wire constituting a compound superconducting stranded wire according to an embodiment. [Figure 7] FIG. 7 is a cross-sectional view showing another example of a compound superconducting element wire constituting a compound superconducting stranded wire according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0020] Hereinafter, a detailed description will be given based on an embodiment.

[0021] The present inventors have conducted extensive research into compound superconducting precursor stranded wires, such as NbSn precursor stranded wires, which are obtained by stranding a plurality of compound superconducting wires together, in order to ensure that the wires are easy to manufacture and that they have excellent superconducting properties when incorporated into a superconducting magnet as a compound superconducting stranded wire. As a result, they have invented a compound superconducting precursor wire that solves the problems of the prior art by ensuring that the properties of the stabilizing material that constitutes the compound superconducting wire and the properties of the compound superconducting precursor wire satisfy predetermined relationships, a compound superconducting precursor stranded wire using the same, and a compound superconducting stranded wire obtained by performing a compound superconductivity generation heat treatment to generate a compound superconducting phase after stranding.

[0022] First, a compound superconducting precursor wire according to an embodiment will be described.

[0023] A compound superconductor precursor wire according to an embodiment includes a compound superconductor precursor portion including a plurality of compound superconductor precursor filaments and a first matrix precursor having the plurality of compound superconductor precursor filaments embedded therein and containing a first stabilizing material; a reinforcing material portion disposed on the outer periphery of the compound superconductor precursor portion; and a stabilizing material portion disposed on at least one of the inner and outer periphery sides of the reinforcing material portion and made of a second stabilizing material, wherein the Vickers hardness (HV) of the stabilizing material portion is 90 or less, and the 0.2% tensile yield strength of the compound superconductor precursor wire is 200 MPa or more.

[0024] 1 is a cross-sectional view showing an example of a compound superconductor precursor wire according to an embodiment. As shown in FIG. 1, the compound superconductor precursor wire 1 has a compound superconductor precursor portion 10, a reinforcing material portion 30, and a stabilizing material portion 40.

[0025] The compound superconductor precursor section 10 constituting the compound superconductor precursor wire 1 is composed of a plurality of compound superconductor precursor filaments 11 and a first matrix precursor 12. The compound superconductor precursor section 10 is linear and extends along the axial direction (wire axial direction) of the compound superconductor precursor wire 1. The first matrix precursor 12 has the plurality of compound superconductor precursor filaments 11 embedded therein and includes a first stabilizing material.

[0026] The compound superconducting precursor filament 11 becomes a compound superconducting filament 21 containing a compound superconducting phase as shown in Figs. 5 to 7, which will be described later, by subjecting it to a compound superconducting generation heat treatment for generating a compound superconducting phase, which will be described later. Since the compound superconducting phase constituting the compound superconducting element wire 3, which will be described later, is preferably a metal compound superconducting phase formed of Nb3Sn, the compound superconducting precursor filament 11 is preferably an Nb3Sn precursor, and more preferably Nb. The material constituting the compound superconducting precursor filament 11 is appropriately selected depending on the type of compound superconducting phase.

[0027] The first matrix precursor 12 containing the first stabilizing material is subjected to a compound superconductivity-generating heat treatment to become a first matrix 22 containing the first stabilizing material shown in Figures 5 to 7. The first matrix 22 can have the effects of suppressing damage to the compound superconducting filaments 21 in the compound superconducting element wire 3, and of magnetic stabilization and thermal stabilization. If the first stabilizing material constituting the first matrix precursor 12 is copper or a copper alloy, these effects are further improved.

[0028] Furthermore, since the compound superconducting phase is preferably a metallic compound superconducting phase formed of Nb3Sn, the first stabilizing material is preferably formed of a Cu-Sn alloy. The material for forming the first stabilizing material is appropriately selected depending on the type of compound superconducting phase that forms the compound superconducting element wire 3.

[0029] When the first stabilizing material of the first matrix precursor 12 is a Cu-Sn alloy, the first stabilizing material may contain up to 15.8 mass % Sn (solid solubility limit). In addition, the first stabilizing material of the first matrix precursor 12 may contain small amounts of elements other than Cu and Sn, and preferably contains, for example, Ti in the range of 0.20 mass % to 0.35 mass %.

[0030] 1 and Figures 2, 5 and 6 described later show an example in which the Nb3Sn compound superconducting phase is produced by the bronze process, but other methods such as the internal tin process may be used to produce the Nb3Sn compound superconducting phase. Also, although an example in which the compound superconducting phase is Nb3Sn is shown here, the compound superconducting phase may be a compound superconductor having superconducting properties with greater strain sensitivity than alloy-based superconductors such as NbTi.

[0031] The reinforcement material portion 30 constituting the compound superconductor precursor wire 1 is cylindrical and disposed on the outer periphery of the compound superconductor precursor portion 10. The reinforcement material portion 30 is preferably made of one metal selected from the group consisting of Nb, Ta, V, W, Mo, Fe, Ti, and Hf, or an alloy or composite made of two or more metals. The reinforcement material portion 30 may contain inevitable impurities. The reinforcement material portion 30 can exhibit the effect of providing high strength that is resistant to tensile strain and bending strain.

[0032] 2, the reinforcement material section 30a may be composed of a plurality of reinforcing filaments 31 and a third matrix 32. The third matrix 32 has the plurality of reinforcing filaments 31 embedded therein and contains a third stabilizing material. Compared to the reinforcement material section 30, the reinforcement material section 30a including the plurality of reinforcing filaments 31 and the third matrix 32 can exhibit the effect of appropriately providing not only high strength but also stabilization function.

[0033] The reinforcing filaments 31 constituting the reinforcing material portion 30a are preferably made of one metal selected from the group consisting of Nb, Ta, V, W, Mo, Fe, Ti, and Hf, or an alloy made of two or more metals. Note that the reinforcing filaments 31 may contain inevitable impurities.

[0034] For example, when the reinforcing filament 31 mainly contains Nb, the inevitable impurities may include, for example, 150 ppm or less of O, 15 ppm or less of H, 100 ppm or less of C, 100 ppm or less of N, 50 ppm or less of Fe, 50 ppm or less of Ni, 20 ppm or less of Ti, 50 ppm or less of Si, 300 ppm or less of W, and 1000 ppm or less of Ta. Also, when the reinforcing filament 31 mainly contains Ta, the inevitable impurities may include O, H, C, N, Fe, Ni, Ti, Si, W, Nb, and Mo.

[0035] These metals or alloys constituting the reinforcing filament 31 are unlikely to dissolve in Cu during the heat treatment for producing the compound superconductivity, and therefore are unlikely to form compounds with Cu, which effectively contributes to improving the bending distortion characteristics. Among these, in consideration of the effect on the compound superconducting element wire 3, the reinforcing filament 31 is preferably made of one metal or an alloy composed of two or more metals selected from the group consisting of Nb, Ta, V, W, Mo, and Hf, which do not exhibit ferromagnetism, and furthermore, from the viewpoint of workability, it is more preferable that the reinforcing filament 31 be made of one metal or an alloy composed of two or more metals selected from the group consisting of Nb, Ta, and V.

[0036] Furthermore, the alloy composed of two or more metals selected from the above element group constituting the reinforcing filament 31 is preferably a Nb-Ta alloy, which is excellent in composite processability with copper or a copper alloy. Furthermore, the alloy composed of copper and a metal selected from the above element group is preferably a Cu-Nb alloy or a Cu-V alloy, which is excellent in composite processability with copper or a copper alloy.

[0037] The above-mentioned "hardly dissolve in Cu" means that the proportion of the metal or alloy constituting the reinforcing filament 31 that dissolves in Cu is less than 1 at % during the compound superconducting heat treatment (for example, 600°C to 750°C).

[0038] As described above, in the reinforcement material portion 30a, a plurality of reinforcing filaments 31 made of a metal material that is not easily dissolved in Cu are embedded in the third matrix 32. This makes it possible to suppress the generation of intermetallic compounds in the reinforcing filaments 31 in the reinforcement material portion 30a, and the reinforcement material portion 30a can function as a high-strength component that is resistant to tensile strain and bending strain compared to the reinforcement material portion 30.

[0039] The third stabilizing material constituting the third matrix 32 of the reinforcement material portion 30a is preferably copper or a copper alloy. The third stabilizing material may contain inevitable impurities. Examples of inevitable impurities in the third stabilizing material include O, Fe, S, and Bi. The third matrix 32 containing the third stabilizing material can provide the reinforcement material portion 30 with a stabilizing function in addition to a reinforcing function.

[0040] The stabilizer portion 40 constituting the compound superconducting precursor strand 1 is cylindrical and is disposed on at least one of the inner and outer circumferential sides of the reinforcement portion 30. The stabilizer portion 40 is made of a second stabilizer. FIGS. 1 and 2 show an example in which the stabilizer portion 40 is disposed on both the inner and outer circumferential sides of the reinforcement portion 30. The stabilizer portion 40 can suppress abnormal deformation of the reinforcement portion 30 during processing, and has the effect of providing a stabilizing function.

[0041] The second stabilizing material constituting the stabilizer portion 40 is preferably copper or a copper alloy, and more preferably oxygen-free copper. The second stabilizing material may contain inevitable impurities. Examples of the inevitable impurities in the second stabilizing material include O, Fe, S, and Bi.

[0042] As described above, the compound superconductor precursor wire 1 includes a first stabilizer constituting the compound superconductor precursor portion 10, a second stabilizer constituting the stabilizer portion 40, and a third stabilizer constituting the reinforcement portion 30a. The stabilizers referred to here are, as defined in JIS H 7005:2005, materials, typically metals, that are in electrical and / or thermal contact with the superconductor to ensure thermal contact with the refrigerant and / or function as an electrical shunt circuit. These stabilizers refer to normal-conducting metal materials that are incorporated into the superconductor to increase its stability. Specifically, normal-conducting metals such as copper and aluminum have low resistivity and good thermal conductivity at cryogenic temperatures. Therefore, when used as the matrix for a superconducting wire, even if a transition from the superconducting state to the normal-conducting state occurs, current bypasses these normal-conducting metals. This suppresses heat generation in the compound superconducting wire 3 (described later), and the generated heat is quickly propagated, diffused, and cooled. Furthermore, normal conducting metals such as copper and aluminum, which damp external magnetic flux fluctuations and do not transmit the magnetic flux fluctuations directly to the superconductor, are widely used as stabilizing materials for superconducting wires.

[0043] The stabilizer portion 40 has a Vickers hardness (HV) of 90 or less, and the compound superconducting precursor wire 1 has a 0.2% tensile yield strength of 200 MPa or more. The Vickers hardness of the stabilizer portion 40 is the Vickers hardness of the stabilizer portion 40 in a cross section perpendicular to the axial direction of the compound superconducting precursor wire 1. The 0.2% tensile yield strength of the compound superconducting precursor wire 1 is the 0.2% tensile yield strength in the axial direction of the compound superconducting precursor wire 1.

[0044] When the Vickers hardness (HV) of the stabilizer portion 40 is 90 or less and the 0.2% tensile strength of the entire compound superconducting precursor strand 1 is 200 MPa or more, conventional breakage of the compound superconducting precursor strand 1 and abnormal deformation of the compound superconducting precursor portion 10 inside the compound superconducting precursor strand 1 can be suppressed, improving the manufacturability of the stranded wire. Furthermore, a compound superconducting magnet manufactured using a compound superconducting precursor stranded wire formed by stranding a plurality of compound superconducting precursor strands 1 is robust even under the strong electromagnetic stress generated when magnetized and can maintain excellent superconducting properties. Thus, the compound superconducting precursor strand 1 and the compound superconducting precursor stranded wire 2 are easy to manufacture, and the compound superconducting stranded wire is robust and has excellent superconducting properties, so it can be used for rationally designed compound superconducting magnets.

[0045] For the above reasons, the Vickers hardness of the stabilizer portion 40 is 90 or less, preferably 80 or less, and more preferably 70 or less. For the same reasons, the 0.2% tensile proof stress of the compound superconducting precursor strand 1 is 200 MPa or more, preferably 230 MPa or more, and more preferably 250 MPa or more. The Vickers hardness of the stabilizer portion 40 is desirably 50 or more to prevent unacceptable abnormal deformation and harmful external damage during the stranding and compression processes. The 0.2% tensile proof stress of the compound superconducting precursor strand 1 is desirably 400 MPa or less to maintain good stranding processability.

[0046] Furthermore, when the compound superconducting precursor filament 11 of the compound superconducting precursor portion 10 is a NbSn precursor, the compound superconducting precursor wire 1 preferably further has an Sn diffusion prevention portion 50 made of Nb or Ta, or an alloy or composite thereof, between the compound superconducting precursor portion 10 and the reinforcement portion 30.

[0047] The Sn diffusion prevention section 50 prevents Sn in the Cu-Sn alloy that constitutes the first matrix precursor 12 for forming Nb3Sn filaments into the compound superconductor section 20 from diffusing into the reinforcement section 30 and the stabilizer section 40 during the compound superconductivity generation heat treatment, thereby suppressing a decrease in the residual resistance ratio of the second stabilizer that constitutes the stabilizer section 40 and the third stabilizer that constitutes the reinforcement section 30, and has the function of retaining the amount of Sn in the Cu-Sn alloy that is necessary to react with the Nb filaments of the compound superconductivity precursor filaments 11 to generate Nb3Sn.

[0048] In the compound superconducting precursor wire 1, it is preferable that the space factor of the reinforcement material section 30 is 5.0% or more and 40.0% or less, and is smaller than the space factor of the compound superconducting precursor section 10, and that the space factor of the stabilizer section 40 arranged on the outer periphery of the reinforcement material section 30 is 15.0% or more. When the space factor of the reinforcement material section 30 and the space factor of the stabilizer section 40 are each within the above ranges, the critical current of the compound superconducting precursor wire 1 can be further improved.

[0049] The space factor of each component is the proportion of the area of ​​each component to the cross-sectional area perpendicular to the axial direction of the compound superconductor precursor wire 1. Specifically, the space factor of the reinforcement material section 30 is the proportion of the area of ​​the reinforcement material section 30 to the cross-sectional area of ​​the compound superconductor precursor wire 1. The space factor of the compound superconductor precursor section 10 is the proportion of the area of ​​the compound superconductor precursor section 10 to the cross-sectional area of ​​the compound superconductor precursor wire 1. The space factor of the stabilizer material section 40 is the proportion of the area of ​​the stabilizer material section 40 to the cross-sectional area of ​​the compound superconductor precursor wire 1.

[0050] Next, the compound superconducting stranded precursor wire of the embodiment will be described.

[0051] A compound superconducting precursor stranded wire of an embodiment has as its constituent element a secondary strand formed by stranding together a plurality of primary strands, each of which is formed by stranding together a plurality of compound superconducting precursor strands of the above embodiment. Furthermore, a compound superconducting precursor stranded wire of another embodiment has as its constituent element a secondary strand formed by stranding together a plurality of primary strands, each of which is formed by stranding together one or more compound superconducting precursor strands of the above embodiment with one or more copper wires or copper alloy wires. While the compound superconducting precursor stranded wire of the above embodiment has as its constituent element a secondary strand formed solely of compound superconducting precursor strands, in the compound superconducting precursor stranded wires of other embodiments, each primary strand contains one or more copper wires or copper alloy wires.

[0052] 3 is a cross-sectional view showing an example of a compound superconducting precursor stranded wire according to another embodiment. The compound superconducting precursor stranded wire 2 shown here is made up of a secondary stranded wire 2b, which is made up of three primary stranded wires 2a each formed by co-twisting two compound superconducting precursor strands 1 and one copper wire 60, and a tertiary stranded wire 2c, which is made up of four secondary stranded wires 2b twisted together, and which is then formed into a rectangular shape.

[0053] During the manufacture of the compound superconducting precursor stranded wire 2, the compound superconducting precursor strand 1 is tempered by heat treatment at 200°C to 500°C for several seconds to several hours before being subjected to shaping. This tempering may be performed on the compound superconducting precursor strand 1 before being twisted, the first twisted wire 2a, the second twisted wire 2b, or the third twisted wire 2c, as long as it is in a state before being twisted. This tempering controls the Vickers hardness of the stabilizer portion 40 and the 0.2% tensile yield strength of the compound superconducting precursor strand. When tempering a twisted wire such as the first twisted wire, it is preferable to perform tempering to control the strength of the copper or copper alloy strands twisted into the compound superconducting precursor strand.

[0054] In the compound superconducting precursor stranded wire 2, the copper wires or copper alloy wires preferably have a Vickers hardness (HV) of 90 or less, more preferably 80 or less, and even more preferably 70 or less. The Vickers hardness of the copper wires or copper alloy wires is the Vickers hardness of the copper wires or copper alloy wires in a cross section perpendicular to the axial direction of the copper wires or copper alloy wires. The compound superconducting precursor stranded wire 2 having copper wires or copper alloy wires with a Vickers hardness (HV) within the above range is suitable for use in large superconducting magnets for generating strong magnetic fields to be installed in nuclear fusion reactors and the like.

[0055] FIG. 4 is a cross-sectional view showing an example of a compound superconductor precursor wire constituting a compound superconductor stranded wire of an embodiment. Among the cross sections of one or more compound superconductor precursor wires 1 constituting the compound superconductor stranded wire, the maximum flattening ratio of the compound superconductor precursor portion 10 is preferably greater than 0 and not greater than 0.2. In other words, among the cross sections of one or more compound superconductor precursor wires 1 constituting the compound superconductor stranded wire, the most deformed compound superconductor precursor portion 10 is preferably greater than 0 and not greater than 0.2. When the compound superconductor stranded wire contains only one compound superconductor precursor wire 1, the compound superconductor precursor portion 10 constituting that single compound superconductor precursor wire 1 is preferably greater than 0 and not greater than 0.2. When the compound superconductor precursor portion 10 has an flattening ratio of 0, the cross-sectional shape of the compound superconductor precursor portion 10 is a perfect circle.

[0056] The flattening ratio of the compound superconductor precursor portion 10 is defined as (1-(b / a)). a is the long axis length of the compound superconductor precursor portion 10 in the cross section (cross section perpendicular to the wire axis direction) of the compound superconductor precursor strand 1. b is the short axis length of the compound superconductor precursor portion 10 in the cross section of the compound superconductor precursor strand 1. The long axis length of the compound superconductor precursor portion 10 corresponds to the maximum outer dimension of the compound superconductor precursor portion 10, and the short axis length of the compound superconductor precursor portion 10 corresponds to the minimum outer dimension of the compound superconductor precursor portion 10.

[0057] When the flattening ratio of the compound superconductor precursor section 10 is within the above range, the compound superconducting stranded wire obtained by subjecting the compound superconducting precursor stranded wire to a compound superconductivity-generating heat treatment can maintain a high critical current. For these reasons, the smaller the flattening ratio of the compound superconductor precursor section 10, the better the superconducting properties of the compound superconducting stranded wire.

[0058] Next, a compound superconducting stranded wire of an embodiment will be described. The compound superconducting stranded wire of the embodiment is obtained by heating the compound superconducting precursor stranded wire of the embodiment described above. This heat treatment is a compound superconducting generation heat treatment for generating a compound superconducting phase.

[0059] Fig. 5 is a cross-sectional view showing an example of a compound superconducting strand constituting a compound superconducting wire of an embodiment, and is a cross-sectional view of a compound superconducting strand formed by heating a compound superconducting precursor strand having the configuration of Fig. 1. Fig. 6 is a cross-sectional view of a compound superconducting strand formed by heating a compound superconducting precursor strand having the configuration of Fig. 2. Fig. 7 is a cross-sectional view of a compound superconducting strand formed by heating a compound superconducting precursor strand in the state of Fig. 4.

[0060] 5 to 7, the compound superconducting wire 3 has a compound superconductor portion 20, reinforcing material portions 30, 30a, and a stabilizing material portion 40. The compound superconducting wire 3 can be obtained by subjecting a compound superconducting precursor stranded wire 2 including a plurality of compound superconducting precursor strands 1 to a compound superconducting heat treatment for generating compound superconductivity. The compound superconducting heat treatment may be performed on the compound superconducting precursor stranded wire 2 before coil winding, or on the compound superconducting precursor stranded wire 2 after coil winding.

[0061] The compound superconductor portion 20 constituting the compound superconducting element wire 3 is composed of a plurality of compound superconducting filaments 21 containing a compound superconducting phase and a first matrix 22. The compound superconductor portion 20 is linear and extends along the axial direction of the compound superconducting element wire 3. The first matrix 22 embeds the plurality of compound superconducting filaments 21 and includes a first stabilizing material.

[0062] The compound superconducting phase is preferably a metal compound superconducting phase formed of Nb3Sn, but is not limited to Nb3Sn and may be formed of, for example, Nb3Al or other metal compound superconducting phases having superconducting properties.

[0063] The first matrix 22 containing the first stabilizing material can exert the effects of suppressing damage to the compound superconducting filaments 21, and of magnetic stabilizing and thermal stabilizing the compound superconducting wire 3. If the first stabilizing material constituting the first matrix 22 is copper or a copper alloy, these effects are further improved.

[0064] Since the compound superconducting phase is preferably a metallic compound superconducting phase formed of Nb3Sn, in the case of a bronze process Nb3Sn precursor wire, the first stabilizer is preferably formed of a Cu-Sn alloy. Furthermore, the material constituting the first stabilizer is appropriately selected depending on the type of compound superconducting phase.

[0065] When the first stabilizer of the first matrix 22 is a Cu—Sn alloy, the Sn content in the first matrix 22 is smaller than the Sn content in the first matrix precursor 12 constituting the compound superconducting precursor strand 1. As a result of the Sn in the Cu—Sn alloy being used to produce Nb3Sn filaments as the compound superconducting filaments 21, even if the Sn content in the first matrix 22 is reduced to about 0.1 mass % or more and 2.0 mass %, the first matrix 22 does not function as a stabilizer equivalent to Cu.

[0066] 5 and 6 show compound superconductor portion 20 manufactured by the bronze process. In the bronze process, when compound superconductor precursor wire 1, in which a plurality of Nb filaments serving as compound superconductor precursor filaments 11 are embedded in first matrix precursor 12 of a Cu-Sn alloy serving as a first stabilizing material, is subjected to a compound superconductivity-generating heat treatment for generating a compound superconducting phase, Sn in first matrix precursor 12 diffuses and reacts with the surface of the Nb filaments, thereby generating Nb3Sn filaments serving as compound superconducting filaments 21 from the Nb filaments.

[0067] 5 and 6 show an example in which there is a core portion 23 of unreacted Nb that remains without reacting with Sn. However, depending on the amount of Sn contained in the first matrix precursor 12 of the compound superconducting precursor strand 1 and the diameter size of the compound superconducting precursor filament 11 of the compound superconducting precursor strand 1, the unreacted core portion 23 may not be present in the compound superconducting filament 21 of the compound superconductor portion 20, and the compound superconducting filament 21 may consist of Nb3Sn.

[0068] The reinforcement material portions 30 are arranged cylindrically or concentrically distributed in the circumferential direction, and are arranged on the outer periphery of the compound superconductor portion 20. The reinforcement material portions 30 constituting the compound superconducting element wire 3 basically have the same configuration and function as the reinforcement material portions 30 constituting the compound superconducting precursor element wire 1.

[0069] The stabilizer portion 40 is cylindrical and is disposed on at least one of the inner and outer peripheral sides of the reinforcing material portion 30. Figures 5 to 7 show an example in which the stabilizer portion 40 is disposed on both the inner and outer peripheral sides of the reinforcing material portion 30. The stabilizer portion 40 constituting the compound superconducting element wire 3 has basically the same configuration and function as the stabilizer portion 40 constituting the compound superconducting precursor element wire 1.

[0070] As described above, the 0.2% tensile yield strength of the compound superconductor precursor strand 1 is within a predetermined range, and the reinforcement portions 30, 30a in the compound superconductor precursor strand 1 can maintain an appropriate tensile yield strength. This prevents breakage of the compound superconductor precursor strand, which previously occurred during the twisting process to shorten the twist pitch or during molding (compression) to reduce the void fraction of the twisted wire. Furthermore, the Vickers hardness of the stabilizer portion 40 is within a predetermined range, and the reinforcement portions 30, 30a protect the compound superconductor precursor portion 10. Therefore, during molding to reduce the void fraction of the twisted wire, the stabilizer portion 40 is selectively deformed, thereby preventing abnormal deformation of the compound superconductor precursor portion 10. As a result, twisted wire manufacturability is improved, and a compound superconductor precursor stranded wire 2 can be obtained with minimal deformation of the compound superconductor precursor portion 10.

[0071] Furthermore, in both cases of a compound superconducting magnet manufactured by a method of winding a compound superconducting precursor stranded wire 2 into a coil and then performing a compound superconductivity generation heat treatment (wind and react method), and a compound superconducting magnet manufactured by a method of winding a compound superconducting precursor stranded wire 2 into a coil after performing a compound superconductivity generation heat treatment (react and wind method), the strain applied to the compound superconducting filaments 21 of the compound superconducting element wire 3 due to the electromagnetic force applied to the compound superconducting element wire 3 in the twisted wire when the magnet is excited is not only reduced by the combination of reinforcing material sections 30, 30a, but also the deformation of the compound superconductor section 20 is reduced, resulting in improved superconducting properties.

[0072] These improvements improve both the manufacturability of stranded wire and its superconducting properties, ultimately enabling rational magnet design. Specifically, in compound superconducting magnets manufactured using the wind-and-react method, when the electromagnetic stress generated during excitation is repeatedly applied to the compound superconducting stranded wire, processing strain is applied to the reinforcement material, increasing its strength, and the residual strain in the compound superconducting filaments is alleviated, improving the superconducting properties. Furthermore, in compound superconducting magnets manufactured using the react-and-wind method, excellent superconducting properties can be obtained by applying an appropriate pre-bending strain to the compound superconducting stranded wire at room temperature. As a result, rational compound superconducting magnet design is possible regardless of the manufacturing method.

[0073] According to the embodiment described above, the characteristics of the stabilizing material portion constituting the compound superconducting wire and the characteristics of the compound superconducting precursor wire satisfy predetermined relationships, thereby enabling more efficient twisting manufacturability and superconducting characteristics than ever before, and enabling rational magnet design.

[0074] Although the embodiments have been described above, the present invention is not limited to the above embodiments, but includes all aspects encompassed by the concept and scope of the claims of the present disclosure, and can be modified in various ways within the scope of the present disclosure. [Example]

[0075] Next, examples and comparative examples will be described, but the present disclosure is not limited to these examples.

[0076] Example 1 A compound superconducting stranded wire was manufactured, which includes a plurality of compound superconducting strands, each of which has a compound superconductor portion made of Nb3Sn formed by the bronze process, a Sn diffusion prevention portion made of Ta, a reinforcement portion made of a Cu-Nb composite material in which Nb filaments are embedded in an oxygen-free copper matrix, and an oxygen-free copper stabilizer portion on the outer periphery of the reinforcement portion. This will be explained in detail below.

[0077] A billet containing multiple Nb rods embedded in a Ti-added CuSn alloy was extruded and drawn to obtain a composite wire of Nb rods and a CuSn alloy. Subsequently, multiple composite wires were arranged in the center of an oxygen-free copper tube to form an assembly. A tubular Ta was placed around the assembly as a Sn diffusion barrier. An oxygen-free copper tube was placed around the tubular Ta. A billet containing multiple Nb rods embedded in oxygen-free copper was extruded and drawn to obtain a Cu-Nb reinforcement wire around the oxygen-free copper tube, thereby obtaining a billet for a compound superconducting precursor wire. Subsequently, the billet for the compound superconducting precursor wire was extruded and drawn to obtain a wire. The wire was then tempered by heat treatment at 200°C to 500°C for several seconds to several hours to obtain a compound superconducting precursor wire.

[0078] Next, as shown in Figure 3, two compound superconducting precursor wires with a diameter of 0.83 mm were twisted together with one copper wire with a diameter of 0.83 mm to form a first twist, three first twisted wires were twisted together to form a second twist, and four second twisted wires were twisted together to form a third twist. The third twisted wire was then formed into a rectangular shape to obtain a compound superconducting precursor stranded wire. The twist pitches of the first twist, second twist, and third twist were 25 mm, 48 mm, and 90 mm, respectively. The rectangular shape of the third twisted wire resulted in a void fraction of 30%. Here, the void fraction of the stranded wire is the percentage of the area within the rectangular dotted line in Figure 3 excluding the total area of ​​all compound superconducting precursor wires and all copper wires.

[0079] Subsequently, the compound superconducting stranded precursor wire was subjected to a compound superconducting heat treatment at 570° C. to 670° C. for several hundred hours to produce the compound superconducting stranded wires shown in Table 1.

[0080] Example 2 A compound superconducting stranded wire was manufactured in the same manner as in Example 1, except that the reinforcing material portion was changed to Ta, stabilizing material portions were provided on the inner and outer sides of the reinforcing material portion, and the space factor of the reinforcing material portion and stabilizing material portion and the 0.2% tensile yield strength of the compound superconducting precursor strand were changed to the values ​​in Table 1.

[0081] (Comparative Example 1) A compound superconducting stranded wire was produced in the same manner as in Example 1, except that no tempering was carried out.

[0082] (Comparative Example 2) A compound superconducting stranded wire was produced in the same manner as in Example 2, except that no tempering was carried out.

[0083] (Comparative Example 3) A compound superconducting stranded wire was produced in the same manner as in Example 1, except that no reinforcing material portion was provided and the space factor of the stabilizing material portion was changed to the value in Table 1.

[0084] Comparative Example 4 A compound superconducting stranded wire was produced in the same manner as in Comparative Example 3, except that no tempering was carried out.

[0085] The following properties were investigated for the compound superconducting precursor strands taken out from the compound superconducting precursor stranded wires produced in the above Examples and Comparative Examples, and for the compound superconducting stranded wires taken out from the compound superconducting stranded wires. The results are shown in Table 1.

[0086] The Vickers hardness of the stabilizer portion was measured as follows. First, a sample in which a compound superconducting precursor wire was embedded in an epoxy resin was cut perpendicular to the axial direction of the compound superconducting precursor wire, and the cut surface was polished. Next, the Vickers hardness of the stabilizer portion was measured using a micro-Vickers hardness test in accordance with JIS Z 2244, in which a pyramidal diamond indenter was pressed against the cross section of the compound superconducting precursor wire with a load of 10 g for 15 seconds, and the resulting indentation was measured.

[0087] The 0.2% tensile yield strength of the compound superconducting precursor wire was determined by a method conforming to Section 5 (Tension) of JIS C 3002. Specifically, both ends of a 180 mm long compound superconducting precursor wire were chucked at 40 mm, and a tensile strain of 0.2% to 0.5% was applied in the axial direction and then unloaded. The straight line equivalent to the Young's modulus obtained when this was applied was offset to a strain of 0.2%, and the intersection (stress level) of this line with the stress-strain curve was taken as the 0.2% tensile yield strength.

[0088] The critical current of the compound superconducting wire was measured as follows: A 5 cm long compound superconducting wire was placed in liquid helium (4.2 K) and an external magnetic field of 14.5 T was applied perpendicular to the axial direction of the wire. A current was passed through the compound superconducting wire, and the critical current was the current value when an electric field of 0.1 μV / cm was generated in the compound superconducting wire using the four-terminal method (voltage tap distance 1 cm).

[0089] [Table 1]

[0090] As shown in Table 1, when a compound superconducting precursor wire having a stabilizer portion with a Vickers hardness of 90 or less and a 0.2% tensile strength of 200 MPa or more was used, the manufacturability of the stranded wire and the superconducting properties were excellent.

[0091] Furthermore, when Example 1 is compared with Comparative Example 1, and Example 2 is compared with Comparative Example 2, it is found that by performing tempering to control the Vickers hardness of the stabilizing material portion and the 0.2% tensile yield strength of the compound superconducting precursor strand, the flattening ratio of the compound superconducting precursor portion of the compound superconducting precursor strand, which has the greatest deformation in the cross section of the compound superconducting precursor strand, becomes 0.2 or less, and as a result, the critical current of the untwisted compound superconducting strand is maintained at a relatively high value.

[0092] Furthermore, in Examples 1 and 2, the frequency of abnormal deformation of the compound superconductor precursor portion was lower than in Comparative Examples 3 and 4, and the flattening ratio of the most deformed compound superconductor precursor portion was smaller, so that the effect of the present disclosure improved the productivity of stranded wires. Furthermore, due to the effect of combining with the reinforcing material portion, the critical current (4.2 K, 14.5 T) when a tensile stress of 200 MPa was applied was nearly 30% higher than when no reinforcing material portion was used.

[0093] While it is effective to disperse Nb in the Cu-Nb composite in the form of filaments in a Cu matrix, as in the above examples, a similar effect can be obtained by laminating Cu and Nb in the form of sheets. Furthermore, in the above examples, the compound superconducting precursor strands and copper strands were not surface-treated, but if the strand surfaces are treated with Cr plating or the like, the oxygen-free copper portions on the strand surfaces that come into contact in the strand will not fuse together during the heat treatment for generating compound superconductivity in the compound superconducting precursor stranded wire, which improves the flexibility of the compound superconducting stranded wire itself and suppresses the generation of additional AC losses due to coupling currents that flow between the strands when a fluctuating magnetic field is applied during superconducting magnet operation. Furthermore, in the above examples, the effects were confirmed for specific values ​​that make it difficult to manufacture stranded wires, such as the wire diameter, the number of twists in each order, the twist pitch, the twist order (the number of times twisted multiple times), and the void ratio after molding. However, the effects of the present invention are not limited to these values, and are effective for any wire diameter, number of twists in each order of stranded wire, twist pitch, twist order, and void ratio that are arbitrarily designed to satisfy the required characteristics, such as the current-carrying capacity, of the compound superconducting stranded wire.

[0094] 1 Compound superconducting precursor wire 2. Compound superconducting precursor strand 2a primary stranded wire 2b secondary stranded wire 2c tertiary stranded wire 3 Compound superconducting wire 10 Compound superconducting precursor section 11 Compound superconducting precursor filament 12. First matrix precursor 20 Compound superconductor section 21 Compound superconducting filament 22 First Matrix 23 Core part 30, 30a Reinforcement part 31 Reinforced Filament 32 The Third Matrix 40 Stabilizing material section 50 Sn diffusion prevention part 60 Copper wire

Claims

1. a compound superconductor precursor portion including a plurality of compound superconductor precursor filaments and a first matrix precursor in which the plurality of compound superconductor precursor filaments are embedded and which includes a first stabilizing material; a reinforcing material portion disposed on the outer periphery of the compound superconductor precursor portion; a stabilizing material portion made of a second stabilizing material, the stabilizing material portion being disposed on at least one of the inner peripheral side and the outer peripheral side of the reinforcing material portion; A compound superconducting precursor wire having the following structure: A compound superconductor precursor strand, wherein the stabilizer portion has a Vickers hardness (HV) of 90 or less, and the compound superconductor precursor strand has a 0.2% tensile yield strength of 200 MPa or more.

2. 2. The compound superconducting precursor wire according to claim 1, wherein the reinforcing material portion is made of one metal selected from the group consisting of Nb, Ta, V, W, Mo, Fe, Ti, and Hf, or an alloy or composite material composed of two or more metals selected from the group consisting of Nb, Ta, V, W, Mo, Fe, Ti, and Hf.

3. 2. The compound superconductor precursor strand according to claim 1, wherein the reinforcement portion is composed of a plurality of reinforcement filaments and a third matrix in which the plurality of reinforcement filaments are embedded and which contains a third stabilizing material.

4. 4. The compound superconductor precursor wire according to claim 3, wherein the reinforcing filament is made of one metal or an alloy composed of two or more metals selected from the group consisting of Nb, Ta, V, W, Mo, Fe, Ti, and Hf, and the third stabilizing material is copper or a copper alloy.

5. The compound superconducting precursor filament is Nb ３ The compound superconducting precursor wire according to any one of claims 1 to 4, which is an Sn precursor and further has an Sn diffusion prevention part made of Nb, Ta, or an alloy or composite thereof between the compound superconducting precursor part and the reinforcement part.

6. 6. The compound superconductor precursor wire according to claim 1, wherein the first stabilizing material is copper or a copper alloy.

7. 7. The compound superconductor precursor wire according to claim 1, wherein the second stabilizing material is copper or a copper alloy.

8. In the compound superconducting precursor wire, a space factor of the reinforcement portion is 5.0% or more and 40.0% or less, and is smaller than a space factor of the compound superconductor precursor portion; 8. The compound superconductor precursor wire according to claim 1, wherein the stabilizing material portion arranged on the outer periphery of the reinforcing material portion has a space factor of 15.0% or more.

9. 9. A compound superconducting precursor stranded wire having as a constituent element a secondary stranded wire formed by stranding together a plurality of primary stranded wires each formed by stranding together a plurality of compound superconducting precursor wires according to any one of claims 1 to 8.

10. 9. A compound superconducting precursor stranded wire having as a constituent element a secondary stranded wire formed by stranding together a plurality of primary strands each formed by stranding together one or more of the compound superconducting precursor strands according to any one of claims 1 to 8 and one or more copper wires or copper alloy wires.

11. 11. The compound superconducting stranded precursor wire according to claim 10, wherein the copper wires or the copper alloy wires have a Vickers hardness (HV) of 90 or less.

12. 12. The compound superconducting precursor stranded wire according to claim 9, wherein, in a cross section of one or more of the compound superconducting precursor strands constituting the compound superconducting precursor stranded wire, the maximum flattening ratio of the compound superconducting precursor portion is greater than 0 and not greater than 0.

2.

13. A compound superconducting stranded wire which is a heating product of the compound superconducting precursor stranded wire according to any one of claims 9 to 12.

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