Superconducting stabilizer, superconducting wire, and superconducting coil

Abstract

To provide a superconducting stabilizer capable of achieving a sufficiently high residual resistivity ratio (RRR) even after heat treatment at low temperature following processing, a superconducting wire having the superconducting stabilizer, and a superconducting coil formed of the superconducting wire.SOLUTION: A superconducting stabilizer used for a superconducting wire comprises a copper material, wherein the copper material contains Mg together with one or two or more additive elements selected from Ca and rare earth elements (excluding Y), the total content of the one or two or more additive elements selected from Ca and rare earth elements (excluding Y) and Mg is in a range of 3 mass ppm to 100 mass ppm, and the remainder consists of Cu and unavoidable impurities. The superconducting stabilizer has a GAM value of 1.0 or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a superconducting stabilizer used in a superconducting wire, a superconducting wire provided with this superconducting stabilizer, and a superconducting coil provided with this superconducting wire. [Background technology]

[0002] The above-mentioned superconducting wires are used in fields such as MRI, NMR, particle accelerators, linear motor cars, and also in energy storage devices. This superconducting wire has a multi-core structure in which multiple strands made of superconductors such as Nb-Ti alloys and Nb3Sn are bundled together with a superconducting stabilizer in between. Tape-shaped superconducting wires made by laminating superconductors and superconducting stabilizers are also available. To further enhance stability and safety, superconducting wires equipped with a channel member made of pure copper are also available.

[0003] In the above-mentioned superconducting wire, if the superconducting state is broken in part of the superconductor, the resistance will increase significantly in that part, causing the temperature of the superconductor to rise, and the entire superconductor may rise above its critical temperature and transition to a normal conducting state. Therefore, in the superconducting wire, a superconducting stabilizer with relatively low resistance, such as copper, is arranged in contact with the superconductor, so that if the superconducting state is broken partially, the current flowing through the superconductor is temporarily diverted to the superconducting stabilizer, during which time the superconductor is cooled and restored to a superconducting state.

[0004] The above-mentioned superconducting stabilizer is required to have a sufficiently low resistance at cryogenic temperatures in order to efficiently divert the current. The residual resistance ratio (RRR) is widely used as an index of electrical resistance at cryogenic temperatures. This residual resistance ratio (RRR) is calculated by dividing the resistance ρ at room temperature (293K) by the 293K and resistivity ρ at liquid helium temperature (4.2K) 4.2K Ratio ρ 293K / ρ 4.2KThe higher this residual resistivity ratio (RRR), the better the performance of the material as a superconducting stabilizer.

[0005] Here, examples of copper materials with a high residual resistance ratio (RRR) include ultra-high purity copper (6NCu) with a purity of 99.9999 mass% or more, in which impurity elements have been reduced to the utmost limit. However, with ultra-high purity copper, in which impurity elements have been reduced to the utmost limit, the manufacturing process to highly purify the copper is extremely complicated, which has the problem of significantly increasing manufacturing costs.

[0006] Therefore, Patent Documents 1 to 3 provide a technique for obtaining a copper material with a sufficiently high residual resistivity ratio (RRR) without increasing the purity more than necessary by adding one or more additive elements selected from Ca, Sr, Ba, and rare earth elements, or one or more additive elements selected from Mg, Mn, Ti, Y, and Zr, fixing S, Se, and Te as compounds, and suppressing the solid solution of S, Se, and Te in the copper matrix. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Publication No. 2017-186622 [Patent Document 2] Japanese Patent Application Publication No. 2017-186623 [Patent Document 3] Japanese Patent Application Laid-Open No. 2017-188339 Summary of the Invention [Problem to be solved by the invention]

[0008] However, in the above-mentioned superconducting stabilizer, when the superconducting wire is significantly deformed by wire drawing, it becomes a substantial processed structure, and the number of lattice defects such as dislocations increases significantly, which results in an increase in resistance and a decrease in the residual resistivity ratio (RRR). For this reason, it is necessary to recover the residual resistivity ratio (RRR) by performing heat treatment after processing to form a recrystallized structure and sufficiently reduce the lattice defects in the parent phase.

[0009] Here, the superconducting stabilizers described in Patent Documents 1 to 3 do not assume that the superconducting wire will be subjected to a thermomechanical treatment in an air atmosphere after it is formed. Since elements such as Ca, Sr, Ba, rare earth elements, or Mg, Mn, Ti, Y, and Zr are easily oxidized, when they are subjected to thermomechanical processing in the atmosphere, oxygen diffuses into the superconducting stabilizer, oxidizing the elements such as Ca, Sr, Ba, rare earth elements, or Mg, Mn, Ti, Y, and Zr. As a result, S, Se, and Te cannot be sufficiently fixed, and there is a risk that the residual resistivity ratio (RRR) cannot be sufficiently improved.

[0010] Furthermore, if the heat treatment temperature is sufficiently high, for example, 800°C or higher, the residual resistivity ratio (RRR) can be recovered by sufficiently reducing lattice defects in the parent phase as a recrystallized structure. On the other hand, in the manufacturing process of Nb3Sn-based superconducting wires, for example, low-temperature conditions of 600°C to 700°C are used to improve the superconducting properties, so the residual resistivity ratio (RRR) does not always increase stably.

[0011] The present invention has been made in consideration of the above-mentioned circumstances, and aims to provide a superconducting stabilizer that can maintain a sufficiently high residual resistance ratio (RRR) even when heat-treated at a low temperature condition, for example, at 600°C or higher and 700°C or lower after processing, a superconducting wire including this superconducting stabilizer, and a superconducting coil made of this superconducting wire. [Means for solving the problem]

[0012] In order to solve the above problems, a superconducting stabilizer according to a first aspect of the present invention is a superconducting stabilizer used for a superconducting wire, which comprises one or more additive elements selected from Ca and rare earth elements (excluding Y) together with Mg, wherein the total content of the one or more additive elements selected from Ca and rare earth elements (excluding Y) and Mg is in the range of 3 ppm by mass to 100 ppm by mass, with the balance being Cu and unavoidable impurities, and is characterized in that the superconducting stabilizer has a GAM value of 1.0 or less. In the present invention, the rare earth elements (excluding Y) are La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, and Sc.

[0013] According to the superconducting stabilizer of aspect 1 of the present invention, one or more additive elements selected from Ca and rare earth elements (excluding Y) are added together with Mg, so that S, Se, and Te can be fixed as compounds by the one or more additive elements selected from Ca and rare earth elements (excluding Y), and it is possible to prevent S, Se, and Te from dissolving in the copper matrix. Furthermore, since Mg is added, oxygen that diffuses into the superconducting stabilizer when heat-treated in the air atmosphere can be trapped by Mg, and one or more added elements selected from Ca and rare earth elements (excluding Y) can be prevented from being converted into oxides and consumed, resulting in a high residual resistance ratio (RRR). Furthermore, since the GAM value is 1.0 or less, the amount of strain is small, and it is possible to increase the residual resistance ratio (RRR).

[0014] The superconducting stabilizer of aspect 2 of the present invention is characterized in that, in the superconducting stabilizer of aspect 1 of the present invention, the mass ratio [Mg] / [Ca, RE] of the content of Mg [Mg] to the content of one or more additive elements selected from Ca and rare earth elements (excluding Y) [Ca, RE] is within the range of 0.2 or more and 10 or less. According to the superconducting stabilizer of the second aspect of the present invention, one or more additive elements selected from Ca and rare earth elements (excluding Y) and Mg are contained in a well-balanced manner, and it is possible to reliably increase the residual resistance ratio (RRR).

[0015] A superconducting stabilizer according to a third aspect of the present invention is characterized in that, in the superconducting stabilizer according to the first or second aspect of the present invention, the mass ratio [Mg, Ca, RE] / [S, Se, Te] of the total content [Mg, Ca, RE] of one or more additive elements selected from Ca and rare earth elements (excluding Y) and Mg to the total content [S, Se, Te] of S, Se, Te is in the range of 0.5 or more and 20 or less. According to the superconducting stabilizer of the third aspect of the present invention, the ratio of the total content of one or more additive elements selected from Ca and rare earth elements (excluding Y) and Mg to the total content of S, Se, and Te is specified as described above, so that S, Se, and Te can be sufficiently fixed, and the presence of excess additive elements and Mg can be suppressed, thereby making it possible to reliably increase the residual resistivity ratio (RRR).

[0016] A superconducting stabilizer according to a fourth aspect of the present invention is characterized in that, in the superconducting stabilizer according to any one of the first to third aspects of the present invention, the Mg content is in the range of 1 mass ppm or more and 50 mass ppm or less. According to the superconducting stabilizer of the fourth aspect of the present invention, the content of Mg is specified within the above range, so that it is possible to reliably increase the residual resistivity ratio (RRR).

[0017] A superconducting stabilizer of aspect 5 of the present invention is characterized in that, in the superconducting stabilizer of any one of aspects 1 to 4 of the present invention, the total content of Fe, Ni, As, Ag, Sn, Sb, Pb, Bi, and P is 60 mass ppm or less. According to the superconducting stabilizer of aspect 5 of the present invention, the total content of Fe, Ni, As, Ag, Sn, Sb, Pb, Bi, and P is 60 mass ppm or less, so that the decrease in the residual resistance ratio (RRR) due to these elements can be suppressed and further the residual resistance ratio (RRR) can be improved.

[0018] A superconducting stabilizer according to a sixth aspect of the present invention is characterized in that, in the superconducting stabilizer according to any one of the first to fifth aspects of the present invention, the residual resistivity ratio (RRR) is 500 or more. According to the superconducting stabilizer of the sixth aspect of the present invention, the residual resistance ratio (RRR) is set to 500 or more, so that the resistance value is low at cryogenic temperatures, and it becomes possible to divert the current well.

[0019] A superconducting wire according to a seventh aspect of the present invention is characterized by comprising a wire containing a superconductor and the superconducting stabilizer according to any one of the first to sixth aspects of the present invention. According to the superconducting wire of the seventh aspect of the present invention, as described above, the wire is provided with a superconducting stabilizer having a high residual resistance ratio (RRR). Therefore, even if the superconducting state of the superconductor is broken, the current flowing through the superconductor can be reliably diverted to the superconducting stabilizer, and the propagation of the normal conducting state throughout the superconductor can be suppressed.

[0020] A superconducting coil according to an eighth aspect of the present invention is characterized by having a structure including a winding portion in which the superconducting wire according to the seventh aspect of the present invention is wound around the circumferential surface of a bobbin. According to the superconducting coil of the eighth aspect of the present invention, as described above, a superconducting wire having a high residual resistance ratio (RRR) is used, and therefore, stable use is possible. [Effects of the Invention]

[0021] According to the present invention, it is possible to provide a superconducting stabilizer that can sufficiently increase the residual resistance ratio (RRR) even when heat-treated at a low temperature condition, for example, at 600°C or higher and 700°C or lower after processing, a superconducting wire including this superconducting stabilizer, and a superconducting coil made of this superconducting wire. [Brief explanation of the drawings]

[0022] [Figure 1] 1 is a schematic cross-sectional view of a superconducting wire provided with a superconducting stabilizer according to one embodiment of the present invention. [Figure 2]FIG. 2 is a schematic vertical cross-sectional view of a filament used in the superconducting wire shown in FIG. [Figure 3] 1 is a flow chart showing an example of a method for producing a superconducting stabilizer according to an embodiment of the present invention. [Figure 4] FIG. 10 is a schematic diagram of a superconducting wire provided with a superconducting stabilizer according to another embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0023] A superconducting stabilizer 20 and a superconducting wire 10 according to one embodiment of the present invention will be described below with reference to the accompanying drawings.

[0024] The superconducting wire 10 of this embodiment is wound around the circumferential surface of a bobbin to form the winding portion of a superconducting coil. As shown in Figure 1, the superconducting wire 10 in this embodiment comprises a core portion 11, a plurality of filaments 12 arranged on the outer periphery of this core portion 11, and an outer shell portion 13 arranged on the outer periphery of these filaments 12.

[0025] In this embodiment, the filament 12 has a structure in which a wire 15 made of a superconductor is covered with a superconducting stabilizer 20, as shown in FIGS. Here, as shown in Fig. 2, the superconducting stabilizer 20 temporarily diverts the current I flowing through the superconducting wire 15 when the superconducting state is broken in a part of the superconducting wire 15 and a normal conducting region A occurs. The core 11 and the outer shell 13 may also have the above-mentioned role as a superconducting stabilizer. In this case, it is preferable to use the superconducting stabilizer of the present invention for the core 11 and the outer shell 13 as well.

[0026] The superconducting stabilizer 20 of this embodiment is characterized by containing one or more additive elements selected from Ca and rare earth elements (excluding Y) and Mg in a total range of 2 mass ppm to 100 mass ppm, with the remainder being copper material containing Cu and unavoidable impurities, and having a GAM value of 1.0 or less.

[0027] Here, in the superconducting stabilizer 20 of this embodiment, it is preferable that the mass ratio [Mg] / [Ca,RE] of the content of Mg [Mg] to the content of one or more additive elements selected from Ca and rare earth elements (excluding Y) [Ca,RE] is in the range of 0.2 or more and 10 or less.

[0028] In the superconducting stabilizer 20 of this embodiment, it is preferable that the mass ratio [Mg,Ca,RE] / [S,Se,Te] of the total content [Mg,Ca,RE] of one or more additive elements selected from Ca and rare earth elements (excluding Y) and Mg to the total content [S,Se,Te] of S, Se, and Te is in the range of 0.5 or more and 20 or less. In the superconducting stabilizer 20 of this embodiment, the Mg content is preferably within the range of 1 mass ppm to 50 mass ppm.

[0029] In the superconducting stabilizer 20 of this embodiment, the total content of Fe, Ni, As, Ag, Sn, Sb, Pb, Bi, and P is preferably 60 mass ppm or less. In the superconducting stabilizer 20 of this embodiment, the residual resistivity ratio (RRR) is preferably 500 or more.

[0030] Here, the reasons for specifying the component composition, GAM value, and residual resistance ratio (RRR) as described above in the superconducting stabilizer 20 of this embodiment will be explained below.

[0031] (Total content of one or more additive elements selected from Ca and rare earth elements (excluding Y) and Mg: 3 mass ppm or more and 100 mass ppm or less) Among the unavoidable impurities contained in copper, S, Se, and Te are elements that significantly reduce the residual resistance ratio (RRR) when they dissolve in copper. Therefore, in order to improve the residual resistance ratio (RRR), it is necessary to eliminate the effects of S, Se, and Te. Here, one or more additive elements selected from Ca and rare earth elements (excluding Y), and Mg are elements that are highly reactive with S, Se, and Te, and therefore, by forming compounds with S, Se, and Te, it is possible to suppress the solid solution of S, Se, and Te in copper, thereby making it possible to sufficiently improve the residual resistance ratio (RRR) of the superconducting stabilizer 20.

[0032] Note that one or more additive elements selected from Ca and rare earth elements (excluding Y) are elements that are difficult to dissolve in copper, but they may form intermetallic compounds with Cu, and the grain boundary pinning effect of these intermetallic compounds may inhibit crystal growth. On the other hand, Mg may dissolve in copper and increase the resistance value. For this reason, in this embodiment, by adding both the above-mentioned additive elements and Mg, excessive addition of the additive elements and Mg is suppressed.

[0033] Here, if the total content of one or more additive elements selected from Ca and rare earth elements (excluding Y) and Mg is less than 2 ppm by mass, the effect of fixing S, Se, and Te may not be fully achieved. On the other hand, if the total content of one or more additive elements selected from Ca and rare earth elements (excluding Y) and Mg exceeds 100 ppm by mass, the residual resistance ratio (RRR) may decrease due to the formation of intermetallic compounds and an increase in resistance due to Mg. For the above reasons, in this embodiment, the total content of one or more additive elements selected from Ca and rare earth elements (excluding Y) and Mg is specified to be within the range of 3 mass ppm or more and 100 mass ppm or less.

[0034] In order to reliably fix S, Se, and Te, the lower limit of the total content of one or more additive elements selected from Ca and rare earth elements (excluding Y) and Mg is preferably 4 ppm by mass or more, and more preferably 5 ppm by mass or more. On the other hand, in order to reliably suppress a decrease in the residual resistance ratio (RRR), the upper limit of the total content of one or more additive elements selected from Ca and rare earth elements (excluding Y) and Mg is preferably 80 ppm by mass or less, and more preferably 70 ppm by mass or less.

[0035] (GAM value is 1.0 or less) The GAM (Grain Average Misorientation) value measured by EBSD is calculated by averaging the misorientation between a crystal grain and its neighboring crystal grains. Using this GAM value, it is possible to visualize the local misorientation, i.e., the distribution of strain. Here, by setting the GAM value to 1.0 or less, there is not much strain and the residual resistance ratio (RRR) can be improved. The GAM value is preferably 0.9 or less, and more preferably 0.85 or less.

[0036] (Mass ratio [Mg] / [Ca,RE]: 0.2 or more and 10 or less) In this embodiment, when the mass ratio [Mg] / [Ca,RE] of the content of Mg [Mg] to the content of one or more additive elements selected from Ca and rare earth elements (excluding Y) [Ca,RE] is 0.2 or more, the content of Mg is ensured and the content of one or more additive elements selected from Ca and rare earth elements (excluding Y) is kept low, thereby suppressing the formation of intermetallic compounds. On the other hand, when the mass ratio [Mg] / [Ca,RE] is 10 or less, the content of one or more additive elements selected from Ca and rare earth elements (excluding Y) is ensured and the content of Mg is kept low, thereby suppressing an increase in resistance value due to the solid solution of Mg. The lower limit of the mass ratio [Mg] / [Ca,RE] is preferably 0.3 or more, and more preferably 0.5 or more, and the upper limit of the mass ratio [Mg] / [Ca,RE] is preferably 8 or less, and more preferably 6 or less.

[0037] (Mass ratio [Mg,Ca,RE] / [S,Se,Te]: 0.5 or more and 20 or less) In this embodiment, when the mass ratio [Mg,Ca,RE] / [S,Se,Te] of the total content [Mg,Ca,RE] of one or more additive elements selected from Ca and rare earth elements (excluding Y) and Mg to the total content [S,Se,Te] of S, Se, and Te is 0.5 or more, S, Se, and Te can be sufficiently fixed by the one or more additive elements selected from Ca and rare earth elements (excluding Y) and Mg, and the residual resistance ratio (RRR) can be reliably increased. On the other hand, when the mass ratio [Mg,Ca,RE] / [S,Se,Te] is 20 or less, there is little excess Mg and additive elements that do not react with S, Se, and Te, which can suppress the generation of intermetallic compounds containing the additive elements and suppress an increase in resistance due to the solid solution of Mg. The lower limit of the mass ratio [Mg, Ca, RE] / [S, Se, Te] is preferably 0.7 or more, and more preferably 1.0 or more, and the upper limit of the mass ratio [Mg, Ca, RE] / [S, Se, Te] is preferably 15 or less, and more preferably 10 or less.

[0038] (Mg content: 1 mass ppm or more and 50 mass ppm or less) In this embodiment, when the Mg content is 1 ppm by mass or more, the content of one or more additive elements selected from Ca and rare earth elements (excluding Y) can be reduced, and the generation of intermetallic compounds containing the additive elements can be suppressed. On the other hand, when the Mg content is 50 ppm by mass or less, an increase in resistance due to the solid solution of excess Mg can be suppressed. The lower limit of the Mg content is more preferably 2 ppm by mass or more, and even more preferably 3 ppm by mass or more, while the upper limit of the Mg content is more preferably 30 ppm by mass or less, and even more preferably 20 ppm by mass or less.

[0039] (Total content of Fe, Ni, As, Ag, Sn, Sb, Pb, Bi, and P: 60 ppm by mass or less) Since specific impurity elements such as Fe, Ni, As, Ag, Sn, Sb, Pb, Bi, and P have the effect of lowering the residual resistance ratio (RRR), it is possible to reliably suppress the decrease in the residual resistance ratio (RRR) by specifying the total content of these elements. Therefore, in this embodiment, by limiting the total content of Fe, Ni, As, Ag, Sn, Sb, Pb, Bi, and P to 60 ppm by mass or less, it is possible to reliably increase the residual resistance ratio (RRR). The upper limit of the total content of Fe, Ni, As, Ag, Sn, Sb, Pb, Bi, and P is more preferably 50 ppm by mass or less, and even more preferably 40 ppm by mass or less.

[0040] (Residual resistance ratio (RRR): 500 or more) In this embodiment, when the residual resistance ratio (RRR) is 500 or more, the resistance value is low at extremely low temperatures, and it is possible to effectively divert the current. The residual resistance ratio (RRR) is more preferably 700 or more, even more preferably 300 or more, and even more preferably 850 or more.

[0041] Next, an example of a method for manufacturing the superconducting stabilizer 20 according to this embodiment will be described.

[0042] (Melting and casting process S01) The above-mentioned elements are added to the molten copper obtained by melting the copper raw material to adjust the composition, thereby producing a molten copper alloy. The various elements can be added in the form of simple elements or master alloys. Raw materials containing the above-mentioned elements may also be melted together with the copper raw material. The molten copper is preferably pure copper with a purity of 99.99% by mass or more, or 99.999% by mass or more. The molten copper alloy with the adjusted composition is then poured into a mold to produce an ingot. When mass production is taken into consideration, it is preferable to use a continuous casting method or a semi-continuous casting method.

[0043] Alternatively, a copper wire having the composition shown in this embodiment may be produced by a continuous casting and rolling method such as the SCR method, and the superconducting stabilizer of this embodiment may be produced using this as a raw material. In this case, production efficiency is improved and manufacturing costs can be significantly reduced. The continuous casting and rolling method referred to here refers to a process in which a copper wire rod is manufactured using a continuous casting and rolling facility equipped with, for example, a belt-wheel type continuous casting machine and a continuous rolling device, and this copper wire rod is used as a raw material to manufacture a drawn copper wire (copper wire rod).

[0044] (Assembly process S02) Next, the superconducting stabilizer and Nb3Sn superconductor prepared as described above are assembled so as to have an arrangement as shown in the cross-sectional view of FIG.

[0045] (Hot extrusion process S03) Next, the assembled body is subjected to hot extrusion, which is carried out by holding the body in an air atmosphere at 500°C to 1000°C for at least one hour, and then hot extrusion at 500°C to 1000°C.

[0046] (Wire drawing process S04) After the hot extrusion step S03, wire drawing is performed. There is no particular limitation on the processing rate (area reduction rate) at this time, but the total processing rate (total area reduction rate) of the wire drawing is preferably 10% or more. There is also no particular limitation on the temperature conditions in the wire drawing step S04, but it is preferably within the range of -50°C to 150°C, which corresponds to cold or warm drawing.

[0047] (Heat treatment process S05) After the wire drawing process S05, a heat treatment is performed to improve the superconducting properties of the Nb3Sn superconductor. In order to improve the superconducting properties and sufficiently reduce the GAM value, the heat treatment is performed by holding the Nb3Sn superconductor at a temperature of 600°C to 700°C for at least one hour.

[0048] Through the steps described above, the superconducting stabilizer 20 of this embodiment is manufactured.

[0049] According to the superconducting stabilizer 20 of this embodiment configured as described above, one or more additive elements selected from Ca and rare earth elements (excluding Y) are added together with Mg, so that by reducing the amount of one or more additive elements selected from Ca and rare earth elements (excluding Y), oxygen that diffuses inward during heat treatment in an air atmosphere can be trapped by Mg, thereby suppressing oxygen diffusion. This makes it possible to suppress the one or more additive elements selected from Ca and rare earth elements (excluding Y) from becoming oxides and being consumed, and elements such as S, Se, and Te can be reliably fixed, thereby obtaining a high residual resistivity ratio (RRR).

[0050] Furthermore, since the GAM value is set to 1.0 or less, the amount of distortion is small, and it is possible to increase the residual resistance ratio (RRR).

[0051] In the superconducting stabilizer 20 of this embodiment, when the mass ratio [Mg] / [Ca, RE] of the content of Mg [Mg] to the content of one or more additive elements selected from Ca and rare earth elements (excluding Y) [Ca, RE] is within the range of 0.2 to 10, the one or more additive elements selected from Ca and rare earth elements (excluding Y) and Mg are contained in a balanced manner, and it is possible to reliably increase the residual resistance ratio (RRR).

[0052] In the superconducting stabilizer 20 of this embodiment, when the mass ratio [Mg,Ca,RE] / [S,Se,Te] of the total content [Mg,Ca,RE] of one or more additive elements selected from Ca and rare earth elements (excluding Y) and Mg to the total content [S,Se,Te] of S, Se, and Te is within the range of 0.5 to 20, S, Se, and Te can be sufficiently fixed, and the presence of excess additive elements and Mg can be suppressed, making it possible to reliably increase the residual resistivity ratio (RRR).

[0053] In the superconducting stabilizer 20 of this embodiment, when the content of Mg is within the range of 1 mass ppm or more and 50 mass ppm or less, the excessive addition of one or more additive elements selected from Ca and rare earth elements (excluding Y) and Mg can be suppressed, and the residual resistivity ratio (RRR) can be reliably increased.

[0054] In the superconducting stabilizer 20 of this embodiment, when the total content of Fe, Ni, As, Ag, Sn, Sb, Pb, Bi, and P is 60 mass ppm or less, the decrease in the residual resistance ratio (RRR) due to these elements can be suppressed, and the residual resistance ratio (RRR) can be further improved.

[0055] In the superconducting stabilizer 20 of this embodiment, when the residual resistance ratio (RRR) is 500 or more, the resistance value is low at cryogenic temperatures, and it becomes possible to divert the current well.

[0056] The superconducting wire 10 of this embodiment comprises a core portion 11, a plurality of filaments 12 arranged on the outer periphery of this core portion 11, and an outer shell portion 13 arranged on the outer periphery of these plurality of filaments 12. The filaments 12 have a structure in which a wire 15 made of a superconductor is covered with a superconducting stabilizer 20. Therefore, even if the superconducting state of the superconductor is broken, the current flowing through the wire 15 can be reliably diverted to the superconducting stabilizer 20, and the propagation of the normal conducting state throughout the superconductor can be prevented.

[0057] The above describes the superconducting stabilizer and superconducting wire according to the embodiment of the present invention, but the present invention is not limited to this and can be modified as appropriate within the scope of the technical concept of the invention. For example, the core portion 11 and the outer shell portion 13 constituting the superconducting wire 10 may also be made of a copper material having the same composition as the superconducting stabilizer 20 of this embodiment.

[0058] The above describes the superconducting wire and superconducting coil as embodiments of the present invention, but the present invention is not limited to this and can be modified as appropriate within the scope of the technical concept of the invention. In the above embodiment, the superconducting wire 10 has been described as having a structure in which a plurality of filaments 12 are bundled together as shown in Fig. 1, but the present invention is not limited to this. For example, as shown in Fig. 4, the superconducting wire 110 may have a structure in which a superconductor 115 and a superconducting stabilizer 120 are stacked on a tape-shaped substrate 113. [Example]

[0059] The results of confirmation experiments conducted to confirm the effects of the present invention will be described below.

[0060] Using various master alloys made from copper raw materials with a Cu purity of 99.99 mass% or higher, pure metal with a purity of 2N (99 mass%) or higher, and copper raw materials with a Cu purity of 99.99 mass% or higher, billets (80 mm in diameter, 280 mm in length) with the compositions listed in Tables 1 to 3 were prepared. They were heated at 880°C for 1 hour and then hot extruded at 880°C to produce rods (32 mm in diameter, 1200 mm in length). Next, wire drawing was performed, followed by heat treatment for 1 hour under the conditions listed in Tables 4 and 5, to obtain superconducting stabilizers with a diameter of 0.8 mm.

[0061] The compositions, GAM values, and residual resistance ratios (RRR) of the obtained superconducting stabilizers of the invention examples and comparative examples were measured as follows. The measurement results are shown in Tables 4 and 5. The composition and GAM value were measured at the target locations on a cross section of the superconducting stabilizer with a diameter of 0.8 mm.The residual resistance ratio (RRR) was measured using the superconducting stabilizer.

[0062] (composition) Ca, one or more added elements selected from rare earth elements (excluding Y), and Mg were measured by inductively coupled plasma optical emission spectrometry, while other elements were measured using a glow discharge mass spectrometer (GD-MS).

[0063] (GAM value) The average GAM value was calculated using an EBSD measurement device and OIM analysis software as follows: After mechanical polishing using waterproof polishing paper and diamond abrasive grains, the specimen was polished using colloidal silica solution. EBSD measurement equipment (FEI Quanta FEG 450, EDAX / TSL (now AMETEK) OIM Data Collection) and analysis software (EDAX / TSL (now AMETEK) OIM Data Analysis ver.7.3.1) was used to measure the electron beam acceleration voltage of 15 kV and 10,000 μm 2 The above measurement area was analyzed for the misorientation of each crystal grain, excluding measurement points where the CI value was 0.1 or less at measurement intervals of 0.25 μm. Measurement points where the misorientation between adjacent measurement points was 15° or more were considered to be grain boundaries, and the average grain size A was calculated using the area fraction analysis software OIM. After that, measurements were made at measurement intervals of 1 / 10 or less of the average grain size A, and a 10,000 μm field was used in multiple fields of view to include a total of 1,000 or more crystal grains. 2 In the measurement area above this, measurement points where the CI value analyzed by the data analysis software OIM was 0.1 or less were excluded from the analysis, and the boundary where the orientation difference between adjacent pixels was 5° or more was considered to be a grain boundary, and the GAM values of all analyzed pixels were calculated, and the average value was calculated.

[0064] [Table 1]

[0065] [Table 2]

[0066] [Table 3]

[0067] [Table 4]

[0068] (Residual resistance ratio (RRR)) Electrical resistivity (ρ 293K ) and electrical resistivity (ρ 4.2K ) and RRR = ρ 293K / ρ 4.2K was calculated.

[0069] In Comparative Example 1, Mg was not contained, and the residual resistance ratio (RRR) was as low as 330. In Comparative Example 2, one or more additive elements selected from Ca and rare earth elements (excluding Y) were not contained, and the residual resistance ratio (RRR) was as low as 315. In Comparative Example 3, the total content of one or more additive elements selected from Ca, rare earth elements (excluding Y), and Mg was not sufficient, and the residual resistance ratio (RRR) was low at 289. This is presumably because Ca reacted with oxygen. In Comparative Example 4, the total content of one or more additive elements selected from Ca and rare earth elements (excluding Y) and Mg was excessive, so the residual resistance ratio (RRR) was low at 321. This is presumably because the excess Mg was dissolved in solid solution. In Comparative Example 5, the GAM value was high and the residual resistance ratio (RRR) was low at 435.

[0070] In contrast, in the present invention, the residual resistance ratio (RRR) is 502 or more, and it is possible to provide a superconducting wire that can realize a high residual resistance ratio (RRR). [Explanation of symbols]

[0071] 10 Superconducting wire 11 Core 12 filaments 13 Outer shell 15 wire 20 Superconducting stabilizer

Claims

1. A superconducting stabilizer used in a superconducting wire, A copper material containing one or more additive elements selected from Ca and rare earth elements (excluding Y) and Mg, wherein the total content of the one or more additive elements selected from Ca and rare earth elements (excluding Y) and Mg is in the range of 3 ppm by mass or more and 100 ppm by mass or less, with the balance being Cu and inevitable impurities; A superconducting stabilizer characterized in that the GAM value is 1.0 or less.

2. 2. The superconducting stabilizer according to claim 1, wherein the mass ratio [Mg] / [Ca, RE] of the content of Mg [Mg] to the content of one or more additive elements selected from Ca and rare earth elements (excluding Y) [Ca, RE] is within the range of 0.2 or more and 10 or less.

3. 2. The superconducting stabilizer according to claim 1, wherein the mass ratio [Mg, Ca, RE] / [S, Se, Te] of the total content of one or more additive elements selected from Ca and rare earth elements (excluding Y) and Mg [Mg, Ca, RE] to the total content of S, Se, Te [S, Se, Te] is within the range of 0.5 or more and 20 or less.

4. 2. The superconducting stabilizer according to claim 1, wherein the Mg content is in the range of 1 mass ppm to 50 mass ppm.

5. 2. The superconducting stabilizer according to claim 1, wherein the total content of Fe, Ni, As, Ag, Sn, Sb, Pb, Bi, and P is 60 mass ppm or less.

6. 2. The superconducting stabilizer according to claim 1, wherein the residual resistivity ratio (RRR) is 500 or more.

7. A superconducting wire comprising: a wire containing a superconductor; and the superconducting stabilizer according to any one of claims 1 to 6.

8. A superconducting coil having a structure in which the superconducting wire according to claim 7 is wound.

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