Mgb2 superconducting wire, method for manufacturing mgb2 superconducting wire, superconducting coil, and magnetic generator

Abstract

The present invention provides: a MgB2 superconducting wire that has a barrier layer of highly uniform thickness covering a MgB2 core and that reduces MgB2 filament defects and is suitable for thinning and lengthening; a MgB2 superconducting wire manufacturing method for manufacturing the same; a superconducting coil using the same; and a magnetic generator including the superconducting coil. A MgB2 superconducting wire (200) comprises: a core material (210); a MgB2 filament (220) in which a MgB2 core (221) is covered with a barrier layer (222); and a metal sheath (230). The MgB2 filament (220) has a barrier layer (222) thickness on the outer peripheral side of the wire not more than three times the barrier layer (222) thickness on the core side of the wire. The method for manufacturing the MgB2 superconducting wire includes a step for forming a single core wire, a step for forming an embedded material, a surface reduction processing step, and a heat treatment step. The embedded material is formed by arranging the single core wire in a recess formed in the outer surface of the core material or by incorporating a spacer in a gap.

Description

MgB2 superconducting wire, manufacturing method for MgB2 superconducting wire, superconducting coil and magnetic field generating device

[0001] The present invention relates to magnesium diboride (MgB ２ ) using MgB ２ Superconducting wire, MgB ２ The present invention relates to a method for manufacturing a superconducting wire, a superconducting coil, and a magnetic field generating device.

[0002] The advantage of superconducting wire is that it allows current to flow with zero resistance. Traditionally, niobium titanium (NbTi) wire has been widely used for superconducting coils. Superconducting coils using NbTi wire have a low operating temperature of approximately 4 K, so they are cooled with liquid helium. However, in recent years, there have been concerns about a tight supply and demand of helium. Therefore, efforts are being made to develop and produce wires of superconductors with high critical temperatures that do not require liquid helium.

[0003] Niobium tin (Nb ３ Sn), yttrium (Y)-based oxides, bismuth (Bi)-based oxides, magnesium diboride (MgB ２ ) are known. ２ MgB has the highest critical temperature of about 39K among metallic superconductors. In addition, the raw materials are relatively easy to obtain, and it has light weight and excellent mechanical properties. ２ MgB ２ Superconducting wires are expected to be used in a variety of applications.

[0004] MgB ２ The Powder In Tube (PIT) method is a common method for manufacturing superconducting wire. In the PIT method, raw material powder is filled into a metal tube, and the metal tube is then drawn. There are two types of PIT methods: ex situ and in situ. In the ex situ method, pre-synthesized MgB ２ The in situ method is a method in which magnesium powder and boron powder are filled into a metal tube and then heat treated to produce MgB ２ This is a method for generating

[0005] Most of the superconducting wires that have been put to practical use so far have a multi-core structure with many superconducting filaments in order to stabilize the magnetic flux. ２ For superconducting wires, multi-filamentary wires are considered important due to magnetic and metallurgical factors. ２ When manufacturing superconducting wire, MgB is placed in a metal tube that does not react with the raw material. ２ Then, a plurality of embedded single-core wires are embedded in a metal sheath tube that forms a metal sheath to produce an embedded material with a multi-core structure. The embedded material is subjected to area reduction processing and heat treatment to form a multi-core structure. ２ A superconducting wire is produced.

[0006] Patent Document 1 discloses that there is a problem in that breakage occurs inside the multi-filament superconducting wire when the multi-filament superconducting wire is lengthened. Furthermore, a technology for providing a multi-filament superconducting wire that does not break, in response to this problem, is disclosed. In Patent Document 1, a hard metal portion is provided between adjacent single-filament superconducting wires. The hard metal portion is made of a metal that is harder than the metal that constitutes the stabilizing phase. By providing the hard metal portion, plastic deformation of the stabilizing phase due to wire drawing is suppressed, and damage to the barrier phase due to inhomogeneous deformation is prevented.

[0007] JP 2016-126950 A

[0008] MgB ２ There is a demand for superconducting wires to be thinner and longer. ２ When making superconducting wires thinner and longer, the MgB ２ For the filament, MgB ２ It is desirable to more reliably prevent damage to the barrier layer covering the core. In Patent Document 1, a plate-shaped hard metal member is placed between adjacent single-core superconducting wires. However, this technology has room for improvement in terms of the arrangement of the member, the degree to which non-uniform deformation is prevented, and the uniformity of the thickness of the barrier layer.

[0009] Therefore, the present invention provides MgB ２ In the filament, MgB ２ By increasing the uniformity of the thickness of the barrier layer covering the core, MgB２ MgB filament is suitable for thinning and elongating filaments. ２ Superconducting wire and MgB ２ The present invention aims to provide a method for manufacturing a superconducting wire, a superconducting coil using the same, and a magnetic field generator including the same.

[0010] In order to solve the above problems, the MgB ２ The superconducting wire comprises a central member disposed at the center of the wire, and a plurality of superconducting wires disposed to surround the central member. ２ A plurality of MgB cores covered with a barrier layer ２ a filament and a plurality of the MgB ２ A multi-filamentary MgB wire having a metal sheath covering the filaments. ２ A superconducting wire, ２ The filament is the MgB ２ The thickness of the barrier layer on the outer periphery of the superconducting wire is ２ The thickness is three times or less the thickness of the barrier layer on the central side of the superconducting wire.

[0011] Furthermore, the MgB ２ The method for manufacturing a superconducting wire comprises: a central material disposed at the center of a wire; and a superconducting wire having MgB ２ A plurality of MgB cores covered with a barrier layer ２ a filament and a plurality of the MgB ２ A multi-filamentary MgB wire having a metal sheath covering the filaments. ２ A method for producing a superconducting wire, comprising: ２ a step of forming a plurality of embedded single-core wires in which the raw material is filled in a metal barrier tube that forms the barrier layer; a step of forming a recess in the outer surface of the central material; a step of arranging the plurality of embedded single-core wires in the recess, incorporating the central material and the plurality of embedded single-core wires into a metal sheath tube that forms the metal sheath, and incorporating a spacer into a gap surrounded by the plurality of embedded single-core wires and the inner surface of the metal sheath tube to form an embedded material; a step of processing the embedded material to reduce its area; and a step of heat-treating the processed embedded material to form MgB ２and generating the MgB ２ a step of forming a plurality of embedded single-core wires in which a core material is filled in a metal barrier tube that forms the barrier layer; a step of incorporating the central material and the plurality of embedded single-core wires into a metal sheath tube that forms the metal sheath, and incorporating an inner spacer into a gap surrounded by the plurality of embedded single-core wires and the outer surface of the central material, and incorporating an outer spacer into a gap surrounded by the plurality of embedded single-core wires and the inner surface of the metal sheath tube to form an embedded material; a step of processing the embedded material to reduce its area; and a step of heat-treating the processed embedded material to form MgB ２ and generating

[0012] The superconducting coil according to the present invention is also made of the above-mentioned MgB ２ The magnetic field generating device according to the present invention is formed by winding a superconducting wire. ２ It is equipped with a superconducting coil wound with superconducting wire.

[0013] According to the present invention, MgB ２ The thickness of the barrier layer covering the core is highly uniform, and MgB ２ MgB filament has reduced defects and is suitable for thinning and lengthening. ２ Superconducting wire and MgB ２ It is possible to provide a method for manufacturing a superconducting wire, a superconducting coil using the same, and a magnetic field generator including the same.

[0014] MgB according to an embodiment of the present invention ２ 1 is a cross-sectional view schematically illustrating an example of a precursor of a superconducting wire according to an embodiment of the present invention. ２ 2A is a cross-sectional view schematically illustrating an example of a superconducting wire. ２ 1 is a cross-sectional view schematically illustrating an example of a precursor of a superconducting wire according to an embodiment of the present invention. ２ 1 is a cross-sectional view schematically illustrating an example of a superconducting wire according to a comparative example; ２ 1 is a cross-sectional view schematically illustrating a superconducting wire according to an embodiment of the present invention. ２It is a diagram showing an example of a superconducting coil using a superconducting wire.It is a cross-sectional view showing an example of a magnetic field generating device according to an embodiment of the present invention.

[0015] Hereinafter, MgB according to one embodiment of the present invention will be described. ２ Superconducting wire and MgB ２ A method for manufacturing a superconducting wire, a superconducting coil using the same, and a magnetic field generator including the same will be described with reference to the drawings. In the following drawings, common components will be assigned the same reference numerals and redundant explanations will be omitted.

[0016] MgB according to this embodiment ２ The superconducting wire is manufactured by the powder-in-tube (PIT) method. ２ The superconducting wire may be produced by either the ex situ method or the in situ method, but is preferably produced by the in situ method. ２ can be produced by a relatively low-temperature heat treatment. In the following description, MgB ２ A configuration for manufacturing a superconducting wire by an in situ method will be exemplified.

[0017] FIG. 1 is a diagram illustrating an MgB ２ 1 is a cross-sectional view showing a schematic example of a precursor of a superconducting wire according to the present embodiment. ２ 1 shows a cross-sectional structure of an embedded material 100, which is an example of a precursor of a superconducting wire before heat treatment. ２ The superconducting wire is made by subjecting the precursor, ie, the embedded material 100, to area reduction processing and heat treatment to form a plurality of MgB ２ It can be manufactured as a multifilamentary wire structure made up of filaments.

[0018] As shown in Fig. 1, the embedded material 100 is composed of a central material 110 arranged at the center of the embedded material 100, a plurality of embedded single-core wires 120 arranged so as to surround the central material 110, a metal sheath tube 130 that covers the plurality of embedded single-core wires 120, and a spacer 140. The embedded material 100 shown in Fig. 1 is made of MgB ２ Superconducting wire MgB ２In order to improve the uniformity of the thickness of the barrier layer covering the core, a central material 110 having a recess 110a formed on its outer surface is used, and spacers 140 are incorporated into the gaps between the embedded single-core wires 120.

[0019] The embedded material 100 is formed as a multi-billet by incorporating a central material 110, multiple embedded single-core wires 120, and a spacer 140 into a metal sheath tube 130. The central material 110 is incorporated at the center of the embedded material 100. The embedded single-core wires 120 are incorporated around the central material 110 so as to be located in recesses 110a formed in the outer surface of the central material 110. The spacer 140 is incorporated into gaps between the embedded single-core wires 120 that are located radially outward of the embedded material 100 and are surrounded by the multiple embedded single-core wires 120 and the inner surface of the metal sheath tube 130.

[0020] 1 , the central material 110 is formed by an inner central material 111 disposed at the center of the embedded material 100 and an outer central material 112 disposed toward the outside of the center of the embedded material 100. The inner central material 111 is provided as a cylindrical billet. The outer central material 112 is provided in a tubular shape. The outer central material 112 is disposed so as to accommodate the inner central material 111 therein and cover the outer surface of the inner central material 111.

[0021] The inner core material 111 can be made of copper, such as oxygen-free copper, phosphorus-deoxidized copper, or tough-pitch copper, or iron. The inner core material 111 is preferably made of oxygen-free copper. The inner core material 111 made of copper is preferably made of MgB after area reduction and heat treatment. ２ In the superconducting wire, the inner core material 111 functions as a stabilizer that stabilizes superconductivity. The stabilizer is made of a good conductor with low electrical resistivity and high thermal conductivity. When the stabilizer is incorporated, the superconductivity is thermally and electromagnetically stabilized, suppressing quench propagation and thermal runaway in the event of loss of cooling, etc. When the inner core material 111 is made of iron, it is preferable to place the stabilizer on the outside of the metal sheath tube 130.

[0022] The outer core material 112 can be made of, for example, iron. The outer core material 112 made of iron is made of MgB after area reduction processing and heat treatment. ２In superconducting wires, MgB ２ It constitutes a part of the base material that supports the filaments, etc. The outer core material 112 is preferably formed of a material that is harder than the material of the inner core material 111. The high hardness of the outer core material 112 improves the workability of the embedded single-core wire 120, particularly the side that contacts the core material 110, during the area reduction process of the embedded material 100. After the heat treatment of the embedded material 100, the dense MgB ２ Therefore, MgB2 has good superconducting properties such as critical current density. ２ A superconducting wire is obtained.

[0023] The embedded single-core wire 120 is composed of raw material powder 121 that constitutes the superconductor and a metal barrier tube 122 that accommodates the raw material powder 121. The embedded single-core wire 120 is formed by filling the raw material powder 121 into the metal barrier tube 122. The embedded single-core wire 120 can be formed as a single billet that is a round wire, and subjected to area reduction processing to adjust it to a predetermined wire diameter.

[0024] The embedded single-core wire 120 is made of MgB ２ In superconducting wires, MgB ２ MgB with a core covered by a barrier layer ２ When the embedded material 100 is produced, a plurality of embedded single-core wires 120 are embedded inside the metal sheath tube 130. By incorporating a plurality of embedded single-core wires 120, the embedded material 100 is produced to form a multi-core wire structure made up of a plurality of filaments.

[0025] The raw material powder 121 is MgB ２ When the superconducting wire is manufactured by the in situ method, a mixed powder of magnesium powder and boron powder is prepared. When the built-in material 100 is heat-treated at about 600° C. or higher, the magnesium and boron react to produce MgB ２ The raw material powder 121 is MgB after surface reduction processing and heat treatment. ２ In superconducting wires, MgB ２ Become the core.

[0026] The metal barrier tube 122 is made of MgB２ The barrier material functions as a barrier to prevent reactions between magnesium and components other than boron during the heat treatment to produce MgB. ２ The metal barrier tube 122 can be made of iron, niobium, tantalum, or an alloy thereof. The metal barrier tube 122 is made of MgB after surface reduction and heat treatment. ２ In superconducting wires, MgB ２ It becomes a barrier layer that covers the core, and MgB ２ MgB with core ２ Constitutes a filament.

[0027] 1 , the metal sheath tube 130 is formed by an inner sheath tube 131 arranged radially inside the embedded material 100, and an outer sheath tube 132 arranged radially outside the embedded material 100. The inner sheath tube 131 accommodates a plurality of embedded single-core wires 120 therein and is arranged so as to surround the plurality of embedded single-core wires 120. The outer sheath tube 132 accommodates the inner sheath tube 131 therein and is arranged so as to cover the outer surface of the inner sheath tube 131.

[0028] The inner sheath tube 131 can be made of iron, niobium, tantalum, an alloy thereof, or the like. The inner sheath tube 131 is preferably made of a material that is harder than the copper used for the inner core material 111. If the hardness of the inner sheath tube 131 is high, a large processing force can be applied to the embedded single-core wire 120 from the outside in the radial direction of the embedded material 100 during the area reduction processing of the embedded material 100. After the heat treatment of the embedded material 100, the dense MgB ２ Therefore, MgB2 has good superconducting properties such as critical current density. ２ The inner sheath tube 131 is preferably made of the same material as the metal barrier tube 122. If the inner sheath tube 131 is made of the same material as the metal barrier tube 122, the direction and magnitude of the processing force acting on the metal barrier tube 122 is less likely to vary when the embedded material 100 is subjected to area reduction processing. ２ Thermal strain due to differences in thermal expansion coefficients is less likely to occur in the base material of the superconducting wire.

[0029] The outer sheath tube 132 can be made of a nickel-copper alloy, stainless steel, low-carbon steel, or the like. Examples of nickel-copper alloys include Monel, which has a Cu content of 20% by mass or more and 35% by mass or less. Examples of low-carbon steel include carbon steel, which has a carbon content of 0.01% by mass or more and less than 0.25% by mass. The outer sheath tube 132 is preferably made of a material that is harder than the material of the inner sheath tube 131. If the hardness of the outer sheath tube 132 is high, a large processing force can be applied from the outside in the radial direction of the embedded material 100 during the surface reduction process of the embedded material 100. The surface reduction of each embedded single-core wire 120 can be highly uniform. Therefore, MgB, which has good superconducting properties such as critical current density, is preferred. ２ Superconducting wire can be manufactured.

[0030] 1, a plurality of recesses 110a are formed on the outer surface of the central material 110. The recesses 110a are recessed in a circumferential direction of a portion of the outer surface of the central material 110, recessed toward the center of the central material 110. The plurality of recesses 110a are formed at predetermined intervals around the entire circumference of the central material 110. The recesses 110a are formed in a groove shape along the longitudinal direction of the embedded material 100.

[0031] The recess 110a is a position where the embedded single-core wire 120 is placed. A plurality of recesses 110a are provided, the number corresponding to the number of embedded single-core wires 120 to be placed around the central material 110. The embedded single-core wires 120 are embedded along the recesses 110a when the embedded material 100 is produced. In a cross-sectional view, at least a portion of the embedded single-core wire 120 is housed in the recess 110a. By fitting along the recess 110a, the gap around the embedded single-core wire 120 is reduced.

[0032] The depth of the recess 110a is preferably 50% or less, and more preferably 25% or less, of the diameter of the embedded single-core wire 120. Also, it is preferably 5% or more of the diameter of the embedded single-core wire 120. When the depth is 25% or less of the diameter of the embedded single-core wire 120, it is relatively easy to form the recess 110a by drawing. Also, when the depth is 5% or more of the diameter of the embedded single-core wire 120, the gap around the embedded single-core wire 120 can be significantly reduced.

[0033] The depth of the recess 110a can be calculated as the difference between the maximum and minimum radii of the central material 110. The maximum radius of the central material 110 can be measured as the radius of the central material 110 at the side edge of the recess 110a or the radius of the central material 110 at a portion where the recess 110a is not formed. The minimum radius of the central material 110 can be measured as the radius of the central material 110 at the bottom of the recess 110a, which is the shortest distance from the center of the central material 110.

[0034] 1 , among the gaps around the embedded single-core wires 120, spacers 140 are embedded in gaps that are surrounded by a plurality of embedded single-core wires 120 and the inner surface of the metal sheath tube 130. The spacers 140 are provided as columnar billets so as to extend in the longitudinal direction of the embedded material 100. A plurality of spacers 140 are embedded in each embedded material 100 so as to fill each of the gaps aligned in the circumferential direction of the embedded material 100.

[0035] The spacer 140 can be made of iron, niobium, tantalum, alloys thereof, or metals having a hardness equivalent to these. The spacer 140 is preferably made of a material having a higher hardness than the copper used for the inner core material 111. If the spacer 140 has a high hardness, a large processing force can be applied to the embedded single-core wire 120 from the outside in the radial direction of the embedded material 100 during the area reduction processing of the embedded material 100. After the heat treatment of the embedded material 100, the dense MgB ２ Therefore, MgB2 has good superconducting properties such as critical current density. ２ The spacer 140 is preferably made of the same material as the metal barrier tube 122. If the spacer 140 is made of the same material as the metal barrier tube 122, the direction and magnitude of the processing force applied to the metal barrier tube 122 and the core material 110 are less likely to vary when the embedded material 100 is subjected to area reduction processing. ２ Thermal strain due to differences in thermal expansion coefficients is less likely to occur in the base material of the superconducting wire.

[0036] The spacer 140 is inserted into a gap surrounded by the plurality of embedded single-core wires 120 and the inner surface of the metal sheath tube 130 when the embedded material 100 is produced. The insertion of the spacer 140 reduces the gap around the embedded single-core wires 120. The spacer 140 is made of MgB ２ In superconducting wires, MgB ２ It forms part of the base material that supports the filaments, etc.

[0037] In Fig. 1, the spacer 140 has a triangular cross-sectional shape. However, the cross-sectional shape of the spacer 140 may be other shapes, such as a fan shape, a trapezoidal shape, a rectangle, or a circle. The cross-sectional shape of the spacer 140 is preferably similar to the general shape of the gap. With such a shape, the gap around the embedded single-core wire 120 can be significantly reduced. The spacer 140 may be configured so that multiple pieces of the spacer 140 are inserted into one gap.

[0038] Generally, if there are many gaps inside the built-in material, the MgB ２ This makes it easier for the filament to deform unevenly. The embedded single-core wire embedded in the embedded material may shift position, or the embedded single-core wire may undergo uneven plastic deformation toward the gap. As a result, the thickness of the metal barrier tube that forms the embedded single-core wire may also become uneven, making the barrier tube more susceptible to breakage. If the metal barrier tube breaks, it loses its function of isolating the raw material powder, which causes the problem of the formation of a different phase due to a reaction between magnesium and components other than boron during heat treatment after the area reduction process. In addition, magnesium is consumed by the formation of the different phase, and this leads to the formation of MgB ２ This results in a problem of a decrease in the amount of

[0039] One possible method for preventing the metal barrier tube from breaking is to increase the thickness of the metal barrier tube. However, if the thickness of the metal barrier tube is increased, the thinned MgB ２ Since the core area ratio per cross section of the superconducting wire becomes small, it may become difficult to obtain necessary superconducting properties such as critical current density. ２ The core symmetry is reduced and disconnection occurs, resulting in a healthy MgB２ There is a risk that the core may not be formed easily, and MgB ２ It becomes difficult to make long superconducting wires.

[0040] In contrast, when a recess 110a is formed on the outer surface of the central material 110, the gap around the embedded single-core wire 120 is reduced on the radially inner side of the embedded material 100. Furthermore, when a spacer 140 is incorporated into the gap surrounded by the multiple embedded single-core wires 120 and the inner surface of the metal sheath tube 130, the gap around the embedded single-core wire 120 on the radially outer side of the embedded material 100 is reduced.

[0041] As a result, in the initial stage of the area reduction process, the adhesion between the components that make up the embedded material 100 is increased, reducing variations in the direction and magnitude of the processing force acting on the embedded single-core wire 120. Misalignment of the embedded single-core wire 120 and uneven plastic deformation of the embedded single-core wire 120 toward the gaps are suppressed. Therefore, during the area reduction process of the embedded material 100, the thickness of the metal barrier tube 122 of the embedded single-core wire 120 becomes more uniform, making the metal barrier tube 122 less likely to break.

[0042] FIG. 2A shows an MgB ２ 2A and 2B are cross-sectional views showing an example of a superconducting wire. Fig. 2B is an enlarged view of a portion of Fig. 2A (the portion within the thick dashed frame indicated by the symbol A). Figs. 2A and 2B show MgB2 superconductors obtained by subjecting the built-in material 100 having the structure shown in Fig. 1 to area reduction processing and heat treatment. ２ 2 shows a cross-sectional structure of a superconducting wire 200.

[0043] As shown in FIG. 2A, MgB ２ The superconducting wire 200 comprises a central material 210 disposed at the center of the wire, and a plurality of MgB ２ filament 220 and a plurality of MgB ２ The MgB 200 includes a metal sheath 230 that covers the filament 220 and a filler layer 240. ２ Superconducting wire 200 includes core material 210 derived from core material 110 having recess 110 a formed on the outer surface thereof, and filling layer 240 derived from spacer 140 .

[0044] 2A, the core material 210 is formed by an inner core material 211 arranged at the center of the wire material and an outer core material 212 arranged toward the outside of the center of the wire material. The outer core material 212 is provided so as to cover the inner core material 211. The inner core material 211 is formed by subjecting the inner core material 111 constituting the embedded material 100 to area reduction processing. The outer core material 212 is formed by subjecting the outer core material 112 constituting the embedded material 100 to area reduction processing. The inner core material 211 made of copper functions as a stabilizer that stabilizes superconductivity. The outer core material 212 is made of MgB ２ It constitutes a part of the base material of the superconducting wire 200 .

[0045] MgB ２ The filament 220 is made of MgB ２ Core 221 and MgB ２ The barrier layer 222 covers the core 221. ２ The filament 220 is MgB ２ The core 221 is covered with a barrier layer 222. ２ The core 221 is formed by subjecting the raw material powder 121 that constitutes the embedded material 100 to area reduction processing and heat treatment. The barrier layer 222 is formed by subjecting the metal barrier tube 122 that constitutes the embedded material 100 to area reduction processing. The barrier layer 222 is made of MgB ２ It constitutes a part of the base material of the superconducting wire 200 .

[0046] 2A, the metal sheath 230 is formed by an inner sheath 231 arranged inside the wire in the radial direction and an outer sheath 232 arranged outside the wire in the radial direction. The inner sheath 231 is made of a plurality of MgB ２ The inner sheath 231 is provided so as to cover the filament 220. The inner sheath 231 is formed by subjecting the inner sheath tube 131 constituting the embedded material 100 to area reduction processing. The outer sheath 232 is provided so as to cover the inner sheath 231. The outer sheath 232 is formed by subjecting the outer sheath tube 132 constituting the embedded material 100 to area reduction processing. The metal sheath 230 is made of MgB ２This contributes to protecting the core 221 and dispersing the current.

[0047] As shown in Fig. 1, the embedded material 100 has a plurality of recesses 110a formed on the outer surface of the core material 110, and a spacer 140 is embedded in the gap surrounded by a plurality of embedded single-core wires 120 and the inner surface of the metal sheath tube 130. Therefore, as shown in Fig. 2, the MgB ２ The superconducting wire 200 has a recessed portion 210a formed on the outer surface of the core material 210 by subjecting the recessed portion 110a to area reduction processing. ２ The space surrounded by the filament 220 and the inner surface of the metal sheath 230 has a filling layer 240 formed by subjecting the spacer 140 to area reduction processing. The filling layer 240 is made of MgB ２ It constitutes a part of the base material of the superconducting wire 200 .

[0048] Such an embedded material 100 is used as a precursor to MgB ２ When superconducting wire 200 is manufactured, the thickness of barrier layer 222 on the outer periphery of the wire can be limited to three times or less the thickness of barrier layer 222 on the center side of the wire, across the longitudinal direction of the wire. In other words, the thickness of barrier layer 222 on the center side of the wire can be ensured to be one-third or more of the thickness of barrier layer 222 on the outer periphery of the wire, across the longitudinal direction of the wire.

[0049] 2B is an enlarged view of a part of FIG. 2A, i.e., part A enclosed by a thick dashed line in FIG. 2A. In FIG. 2B, when the thickness of the barrier layer 222 on the outer periphery of the wire is Tout and the thickness of the barrier layer 222 on the center side of the wire is Tin, the thickness Tout is thicker than the thickness Tin, and the ratio of the thicknesses is 3 times or less. That is, 1<Tout / Tin≦3. In FIG. 2B, the dashed line indicates the distance between the center of the wire and the MgB ２ A diameter line C is shown passing through the center of the filament.

[0050] MgB ２ The filament 220 is MgB ２ The thickness of the barrier layer 222 on the outer periphery of the superconducting wire 200 is ２The thickness of the barrier layer 222 on the central side of the superconducting wire 200 is preferably 1 to 3 times (1≦Tout / Tin≦3), and more preferably 1.5 to 3 times (1.5≦Tout / Tin≦3). That is, the thickness of the barrier layer 222 on the central side of the wire is preferably 1 / 3 to 1 time (1 / 3≦Tout / Tin≦1) and more preferably 1 / 3 to 2 / 3 (1 / 3≦Tout / Tin≦2 / 3) of the thickness of the barrier layer 222 on the outer periphery of the wire. With such a thickness, the thickness of the barrier layer 222 becomes more uniform, and the amount of MgB per cross section of the wire becomes ２ On the other hand, if the thickness on the outer periphery exceeds three times the thickness on the center side, the thickness on the center side becomes less than one-third of the thickness on the outer periphery side, and the metal barrier tube 122 and the barrier layer 222 may be broken, or the MgB ２ This makes it easier for the filament 220 to become asymmetric or break, making it difficult to obtain good superconducting properties.

[0051] MgB ２ The thickness of the barrier layer 222 on the outer periphery of the superconducting wire 200 and the MgB ２ The ratio of the thickness of the barrier layer 222 at the center of the superconducting wire 200 can be adjusted more precisely by changing the shape and size of the recess 110a, the shape, size and number of the spacers 140, the shape and size of the embedded single-core wire 120, the area reduction rate of the area reduction process applied to the embedded material 100, the thickness of the metal barrier tube 122 that constitutes the embedded single-core wire 120, etc. in the embedded material 100 having the structure shown in Figure 1.

[0052] The thickness of the barrier layer was measured using MgB ２ Any cross section of the superconducting wire is cut out and any MgB ２ Any MgB filament observed in any cross section can be used. ２ Regarding the filament, the center of the wire and MgB ２ The thickness of the barrier layer at the center of the wire can be compared with the thickness of the barrier layer at the outer periphery of the wire on a diameter line passing through the center of the filament (see the dashed line in Figure 2B). The ratio of the barrier layer thickness at the outer periphery to the barrier layer thickness at the center can be calculated for any MgB ２The average value of the measurement results for the filament can be obtained. The number of samples for measurement is, for example, 5 or more.

[0053] The thickness of the barrier layer is measured after cutting out an arbitrary cross section and polishing the cross section. If the interface of the barrier layer is unclear, the thickness can be measured after performing a process to clarify the interface. An example of a process to clarify the interface is chemical etching. It is also effective to distinguish the interface based on component analysis. An example of component analysis is energy dispersive X-ray spectroscopy (EDX).

[0054] Such MgB ２ According to the superconducting wire 200, the thickness uniformity of the metal barrier tube 122 and the barrier layer 222 is improved, and the metal barrier tube 122 and the barrier layer 222 are less likely to break, so that a thinner metal barrier tube 122 can be used when manufacturing the embedded material 100. Using a thinner metal barrier tube 122 can reduce the material costs and processing costs of the embedded single-core wire 120 and the embedded material 100. In addition, the MgB ２ Since the area ratio of the core is increased, the superconducting properties such as the critical current density can be improved.

[0055] Furthermore, the uniformity of the thickness of the metal barrier tube 122 and the barrier layer 222 is increased, and the metal barrier tube 122 and the barrier layer 222 are less likely to break. Therefore, when the embedded material 100 is heat-treated, formation of a different phase and MgB ２ In addition, the geometrically asymmetric MgB ２ Filament and MgB ２ This makes it difficult for the filament to break, etc. This prevents a decrease in the critical current (Ic) and makes it easier to make a long wire.

[0056] Therefore, such MgB ２ According to the structure of the superconducting wire 200, MgB ２ Multiple MgB cores ２ A multifilamentary wire structure composed of filaments, ２The thickness of the barrier layer in the circumferential direction of the filament is highly uniform, and MgB ２ MgB is suitable for thinning and lengthening wires, with reduced core defects. ２ Since the barrier layer can be made thin, the MgB ２ The area occupation rate, critical current density, etc. of the core material 110 can be improved. The structure in which the recess 110a is formed on the outer surface of the core material 110 makes it easy to arrange the embedded single-core wire 120 relative to the core material 110, making it easy to manufacture a long wire.

[0057] FIG. 3 shows an MgB ２ 3 is a cross-sectional view showing a schematic example of a precursor of a superconducting wire according to the present embodiment. ２ 1 shows a cross-sectional structure of an embedded material 300, which is an example of a precursor of a superconducting wire before heat treatment. ２ The superconducting wire is made by subjecting the precursor, ie, the embedded material 300, to area reduction processing and heat treatment to form a plurality of MgB ２ It can be manufactured as a multifilamentary wire structure made up of filaments.

[0058] As shown in Fig. 3, the embedded material 300 is composed of a central material 310 arranged at the center of the embedded material 300, a plurality of embedded single-core wires 320 arranged so as to surround the central material 310, a metal sheath tube 330 covering the plurality of embedded single-core wires 320, and a spacer 340. The embedded material 300 shown in Fig. 3 is made of MgB ２ Superconducting wire MgB ２ To improve the uniformity of the thickness of the barrier layer covering the core, spacers 340 are incorporated into the gaps between the embedded single-core wires 320. The spacers 340 are incorporated into the gaps on both the outer periphery and the center of the embedded material 300.

[0059] The embedded material 300 is formed as a multi-billet by incorporating a central material 310, multiple embedded single-core wires 320, and a spacer 340 into a metal sheath tube 330. The central material 310 is incorporated at the center of the embedded material 300. The embedded single-core wires 320 are incorporated around the central material 310. The spacers 340 are incorporated into gaps between the embedded single-core wires 320 that are located on the radially outer side of the embedded material 300 and are surrounded by the multiple embedded single-core wires 320 and the inner surface of the metal sheath tube 330, and into gaps that are located on the radially central side of the embedded material 300 and are surrounded by the multiple embedded single-core wires 320 and the outer surface of the central material 310.

[0060] In Figure 3, the central material 310 is formed by an inner central material 311 located at the center of the built-in material 300 and an outer central material 312 located toward the outside of the center of the built-in material 300. The inner central material 311 is provided as a cylindrical billet. The outer central material 312 is provided in a tubular shape. The outer central material 312 accommodates the inner central material 311 and is disposed so as to cover the outer surface of the inner central material 311. The inner central material 311 and the outer central material 312 can be formed using the same materials and methods as the inner central material 111 and the outer central material 112 described above. The central material 310 can be one without a recess formed on its outer surface.

[0061] The embedded single-core wire 320 is formed by raw material powder 321 that constitutes the superconductor and a metal barrier tube 322 that accommodates the raw material powder 321. The embedded single-core wire 320 is formed by filling the raw material powder 321 into the metal barrier tube 322. The embedded single-core wire 320 can be formed as a single billet that is a round wire, and subjected to area reduction processing to adjust to a predetermined wire diameter.

[0062] The embedded single-core wire 320 is made of MgB ２ In superconducting wires, MgB ２ MgB with a core covered by a barrier layer ２ When the embedded material 300 is manufactured, a plurality of embedded single-core wires 320 are embedded inside the metal sheath tube 330. By incorporating a plurality of embedded single-core wires 320, a plurality of MgB ２An embedded material 300 for forming a multifilamentary wire structure made up of filaments is produced. The raw material powder 321 and the metal barrier tube 322 can be formed using the same materials and methods as the raw material powder 121 and the metal barrier tube 122 described above.

[0063] 3, the metal sheath tube 330 is formed by an inner sheath tube 331 arranged radially inside the embedded material 300, and an outer sheath tube 332 arranged radially outside the embedded material 300. The inner sheath tube 331 houses a plurality of embedded single-core wires 320 therein and is arranged so as to surround the plurality of embedded single-core wires 320. The outer sheath tube 332 houses the inner sheath tube 331 therein and is arranged so as to cover the outer surface of the inner sheath tube 331. The inner sheath tube 331 and the outer sheath tube 332 can be formed using the same materials and methods as the inner sheath tube 131 and the outer sheath tube 132 described above.

[0064] 3 , an inner spacer 341 is incorporated into a gap surrounded by the plurality of embedded single-core wires 320 and the outer surface of the core material 310. An outer spacer 342 is incorporated into a gap surrounded by the plurality of embedded single-core wires 320 and the inner surface of the metal sheath tube 330. The inner spacer 341 and the outer spacer 342 are provided as columnar billets so as to extend in the longitudinal direction of the embedded material 300. A plurality of inner spacers 341 and outer spacers 342 are incorporated into one embedded material 300 so as to fill each gap lined up in the circumferential direction of the embedded material 300.

[0065] The inner spacer 341 and the outer spacer 342 can be made of iron, niobium, tantalum, alloys of these, or metals having a hardness equivalent to these. The inner spacer 341 and the outer spacer 342 are preferably made of a material having a higher hardness than the copper used for the inner core material 311. If the hardness is high, a processing force can be applied to the embedded single-core wire 320 from the outside toward the center in the radial direction of the embedded material 300 when the embedded material 300 is subjected to area reduction processing. After the embedded material 300 is heat-treated, the dense MgB ２ Therefore, MgB2 has good superconducting properties such as critical current density. ２The inner spacer 341 and the outer spacer 342 are preferably made of the same material as the metal barrier tube 322. If they are made of the same material as the metal barrier tube 322, the direction and magnitude of the processing force acting on the metal barrier tube 322 during the area reduction processing of the embedded material 300 are less likely to vary. ２ Thermal strain due to differences in thermal expansion coefficients is less likely to occur in the base material of the superconducting wire.

[0066] The inner spacer 341 is inserted into a gap surrounded by the multiple embedded single-core wires 320 and the outer surface of the core material 310 when the embedded material 300 is produced. The outer spacer 342 is inserted into a gap surrounded by the multiple embedded single-core wires 320 and the inner surface of the metal sheath tube 330 when the embedded material 300 is produced. By inserting the inner spacer 341 and the outer spacer 342, the gap around the embedded single-core wire 320 is reduced. The inner spacer 341 and the outer spacer 342 are made of MgB after area reduction processing and heat treatment. ２ In superconducting wires, MgB ２ It forms part of the base material that supports the filaments, etc.

[0067] In Fig. 3, the inner spacer 341 and the outer spacer 342 have a circular cross-sectional shape. However, the inner spacer 341 and the outer spacer 342 may have other cross-sectional shapes, such as a triangular shape, a sector shape, a trapezoidal shape, or a rectangular shape. The cross-sectional shapes of the inner spacer 341 and the outer spacer 342 are preferably similar to the general shape of the gap or have contours parallel to the wall surfaces of the gap. Such shapes can significantly reduce the gap around the embedded single-core wire 320. The inner spacer 341 and the outer spacer 342 may be configured so that multiple pieces are inserted into one gap.

[0068] When the inner spacer 341 is incorporated into the gap surrounded by the multiple embedded single-core wires 320 and the outer surface of the core material 310, the gap around the embedded single-core wires 320 is reduced on the radially inner side of the embedded material 300. Furthermore, when the outer spacer 342 is incorporated into the gap surrounded by the multiple embedded single-core wires 320 and the inner surface of the metal sheath tube 330, the gap around the embedded single-core wires 320 is reduced on the radially outer side of the embedded material 300.

[0069] As a result, in the initial stage of the area reduction process, the adhesion between the components that make up the embedded material 300 is increased, reducing variations in the direction and magnitude of the processing force acting on the embedded single-core wire 320. Misalignment of the embedded single-core wire 320 and uneven plastic deformation of the embedded single-core wire 320 toward the gaps are suppressed. Therefore, during the area reduction process of the embedded material 300, the thickness of the metal barrier tube 322 of the embedded single-core wire 320 becomes more uniform, making the metal barrier tube 322 less likely to break.

[0070] FIG. 4 shows an MgB ２ 4 is a cross-sectional view showing an example of a superconducting wire. ２ 4 shows a cross-sectional structure of a superconducting wire 400.

[0071] As shown in FIG. ２ The superconducting wire 400 includes a central material 410 disposed at the center of the wire, and a plurality of MgB ２ filament 420 and a plurality of MgB ２ The MgB ferrite core shown in FIG. ２ Superconducting wire 400 includes, as filling layer 440 derived from spacer 340 , inner filling layer 441 derived from inner spacer 341 and outer filling layer 442 derived from outer spacer 342 .

[0072] In Fig. 4, the core material 410 is formed by an inner core material 411 arranged at the center of the wire material and an outer core material 412 arranged toward the outside of the center of the wire material. The outer core material 412 is provided so as to cover the inner core material 411. The inner core material 411 is formed by subjecting the inner core material 311 constituting the embedded material 300 to area reduction processing. The outer core material 412 is formed by subjecting the outer core material 312 constituting the embedded material 300 to area reduction processing. The inner core material 411 made of copper functions as a stabilizer that stabilizes superconductivity. The outer core material 412 is made of MgB ２ It constitutes a part of the base material of the superconducting wire 400 .

[0073] MgB ２ The filament 420 is made of MgB ２ Core 421 and MgB ２ The barrier layer 422 covers the core 421. ２ The filament 420 is MgB ２ The core 421 is covered with a barrier layer 422. ２ The core 421 is formed by subjecting the raw material powder 321 that constitutes the embedded material 300 to area reduction processing and heat treatment. The barrier layer 422 is formed by subjecting the metal barrier tube 322 that constitutes the embedded material 300 to area reduction processing. The barrier layer 422 is made of MgB ２ It constitutes a part of the base material of the superconducting wire 400 .

[0074] 4, the metal sheath 430 is formed by an inner sheath 431 arranged inside the wire in the radial direction and an outer sheath 432 arranged outside the wire in the radial direction. The inner sheath 431 is made of a plurality of MgB ２ The inner sheath 431 is provided so as to cover the filament 420. The inner sheath 431 is formed by subjecting the inner sheath tube 331 constituting the embedded material 300 to area reduction processing. The outer sheath 432 is provided so as to cover the inner sheath 431. The outer sheath 432 is formed by subjecting the outer sheath tube 332 constituting the embedded material 300 to area reduction processing. The metal sheath 430 is made of MgB ２ This contributes to protecting the core 421 and dispersing the current.

[0075] As shown in Fig. 3, the embedded material 300 has an inner spacer 341 embedded in a gap surrounded by the plurality of embedded single-core wires 320 and the outer surface of the core material 310, and an outer spacer 342 embedded in a gap surrounded by the plurality of embedded single-core wires 320 and the inner surface of the metal sheath tube 330. Therefore, as shown in Fig. 4, the MgB ２ The superconducting wire 400 is made of a plurality of MgB ２ The inner spacer 341 has an inner filling layer 441 formed by subjecting the inner spacer 341 to area reduction processing in the space surrounded by the filament 420 and the outer surface of the core material 410. ２ The outer spacer 342 has an outer filling layer 442 formed by subjecting the outer spacer 342 to area reduction processing in the space surrounded by the filament 420 and the inner surface of the metal sheath 430. The inner filling layer 441 and the outer filling layer 442 are made of MgB ２ It constitutes a part of the base material of the superconducting wire 400 .

[0076] Such an embedded material 300 is used as a precursor to MgB ２ When superconducting wire 400 is manufactured, the thickness of barrier layer 422 on the outer periphery of the wire can be limited to no more than three times the thickness of barrier layer 422 on the center side of the wire, across the longitudinal direction of the wire. In other words, the thickness of barrier layer 422 on the center side of the wire can be ensured to be no less than one-third the thickness of barrier layer 422 on the outer periphery of the wire, across the longitudinal direction of the wire.

[0077] MgB ２ The filament 420 is MgB ２ The thickness of the barrier layer 422 on the outer periphery of the superconducting wire 400 is ２ It is preferable that the thickness of the barrier layer 422 at the center of the superconducting wire 400 is 1.5 to 3 times the thickness of the barrier layer 422 at the center of the wire. That is, it is preferable that the thickness of the barrier layer 422 at the center of the wire is 1 / 3 to 2 / 3 the thickness of the barrier layer 422 at the outer periphery of the wire. With such a thickness, the thickness of the barrier layer 422 becomes more uniform, and the amount of MgB per cross section of the wire is ２On the other hand, if the thickness of the outer periphery exceeds three times the thickness of the center, the thickness of the center becomes less than one-third of the thickness of the outer periphery, which may cause breakage of the metal barrier tube 322 or the barrier layer 422, or the formation of MgB ２ The filament 420 becomes more susceptible to becoming asymmetric or breaking, making it difficult to obtain good superconducting properties.

[0078] MgB ２ The thickness of the barrier layer 422 on the outer periphery of the superconducting wire 400 and the MgB ２ The ratio of the thickness of the barrier layer 422 at the center of the superconducting wire 400 can be adjusted more precisely by changing the shape, size and number of the spacers 340, the shape and size of the embedded single-core wire 320, the area reduction rate of the area reduction process applied to the embedded material 300, the thickness of the metal barrier tube 322 that constitutes the embedded single-core wire 320, etc. in the embedded material 300 having the structure shown in Figure 3.

[0079] Such MgB ２ According to the superconducting wire 400, the thickness of the metal barrier tube 322 and the barrier layer 422 is highly uniform, and the metal barrier tube 322 and the barrier layer 422 are less likely to break, so that a thinner metal barrier tube 322 can be used when manufacturing the embedded material 300. Using a thinner metal barrier tube 322 can reduce the material costs and processing costs of the embedded single-core wire 320 and the embedded material 300. In addition, the MgB ２ Since the area ratio of the core is increased, the superconducting properties such as the critical current density can be improved.

[0080] Furthermore, the uniformity of the thickness of the metal barrier tube 322 and the barrier layer 422 is increased, and the metal barrier tube 322 and the barrier layer 422 are less likely to break. Therefore, when the embedded material 300 is heat-treated, formation of a different phase and MgB ２ In addition, the geometrically asymmetric MgB ２ Filament and MgB ２ Filament breakage and the like are less likely to occur. As a result, the critical current (Ic) is less likely to decrease, and the wire can be easily made longer.

[0081] Therefore, such MgB ２ According to the structure of the superconducting wire 400, MgB２ Multiple MgB cores ２ A multifilamentary wire structure composed of filaments, ２ The thickness of the barrier layer in the circumferential direction of the filament is highly uniform, and MgB ２ MgB is suitable for thinning and lengthening wires, with reduced core defects. ２ Since the barrier layer can be made thin, the MgB ２ In comparison with the case where the embedded single-core wire 120 is disposed in the recess 110a formed on the outer surface of the core material 110, the manufacturing process can be simplified because there is no need to form the recess 110a.

[0082] FIG. 5 shows a comparative example of MgB ２ 5 is a cross-sectional view showing a schematic diagram of a superconducting wire. ２ The cross-sectional structure of the superconducting wire 500 is shown. ２ The superconducting wire 500 is obtained by increasing the thickness of the metal barrier tube 122 shown in FIG. 1 to 1.5 times that of the metal barrier tube 122 shown in FIG.

[0083] As shown in FIG. ２ The superconducting wire 500 comprises a central material 510 disposed at the center of the wire, and a plurality of MgB ２ filament 520 and a plurality of MgB ２ The MgB ferrite core shown in FIG. 5 includes a metal sheath 530 that covers the filament 520 and a filler layer 540. ２ Superconducting wire 500 includes core material 510 derived from a core material having a recess formed on the outer surface thereof, and filling layer 540 derived from a spacer.

[0084] In FIG. 5, the core material 510 is formed by an inner core material 511 disposed at the center of the wire and an outer core material 512 disposed toward the outside of the center of the wire. ２ The filament 520 is made of MgB ２ Core 521 and MgB ２The wire 521 is formed of a barrier layer 522 that covers the core 521. The metal sheath 530 is formed of an inner sheath 531 that is disposed radially inside the wire and an outer sheath 532 that is disposed radially outside the wire.

[0085] As shown in Fig. 1, the embedded material 100 has a plurality of recesses 110a formed on the outer surface of the core material 110, and a spacer 140 is embedded in the gap surrounded by a plurality of embedded single-core wires 120 and the inner surface of the metal sheath tube 130. Therefore, as shown in Fig. 5, the MgB ２ The superconducting wire 500 has a recessed portion 510a formed on the outer surface of the core material 510 by subjecting the recessed portion 110a to area reduction processing. ２ The space surrounded by the filament 520 and the inner surface of the metal sheath 530 has a filling layer 540 formed by subjecting the spacer 140 to area reduction processing. The filling layer 540 is made of MgB ２ It constitutes a part of the base material of the superconducting wire 500 .

[0086] Such an embedded material 100 is used as a precursor to MgB ２ When superconducting wire 500 is manufactured, because a thick metal barrier tube is used, the thickness of barrier layer 522 on the outer periphery of the wire is not limited to be three times or less the thickness of barrier layer 522 on the center side of the wire along the longitudinal direction of the wire. In other words, the thickness of barrier layer 522 on the center side of the wire is not ensured to be one-third or more of the thickness of barrier layer 522 on the outer periphery of the wire along the longitudinal direction of the wire.

[0087] If the ratio of the thickness of the barrier layer on the outer periphery of the wire to the thickness of the barrier layer on the center of the wire is too large, the MgB ２ Since the area ratio of the core becomes small, superconducting properties such as critical current density deteriorate. Therefore, in order to improve the uniformity of the thickness of the barrier layer, it is preferable to adjust the thickness of the metal barrier tube constituting the embedded single-core wire so that the thickness of the barrier layer on the outer periphery of the wire is three times or less the thickness of the barrier layer on the center side of the wire over the longitudinal direction of the wire.

[0088] Next, the above-mentioned MgB２ A method for manufacturing a superconducting wire will be described below. In the following description, the MgB ２ An example of a method for producing a superconducting wire by an in situ method will be described.

[0089] MgB according to this embodiment ２ The method for manufacturing a superconducting wire includes a preparation step for forming a built-in single-core wire, an assembly step for forming a built-in material as a precursor, an area reduction step for reducing the area of ​​the built-in material, and a heat treatment of the area-reduced built-in material to form MgB ２ and a heat treatment step to produce MgB ２ When manufacturing the superconducting wire 200, a recess forming step is performed to form a recess on the outer surface of the core material before the assembly step, and a spacer is also prepared. ２ When manufacturing the superconducting wire 400, an inner spacer and an outer spacer are prepared before the assembling step.

[0090] In the preparation process, MgB ２ The core material is filled into a metal barrier tube that forms a barrier layer to form a plurality of embedded single-core wires. ２ The core material is MgB ２ The magnesium powder and boron powder used as raw materials are weighed out so that the molar ratio of Mg to B is approximately 1:2, and then crushed and mixed to prepare the powder.

[0091] MgB ２ The raw material for the core may include MgB ２ A carbon source can be added to perform element substitution. When a carbon source is added, MgB ２ During the heat treatment to generate MgB ２ Some of the boron atoms in MgB can be replaced with carbon atoms. ２ The critical current and critical magnetic field of the superconducting wire can be improved. ４ Inorganic carbon compounds such as C and SiC, hydrocarbons such as benzene, naphthalene, coronene, and anthracene, organic acids such as stearic acid, magnesium salts of organic acids, and the like can be used.

[0092] MgB ２The core raw material is preferably handled in a non-oxidizing atmosphere such as an inert gas atmosphere of nitrogen, argon, or the like, or a vacuum atmosphere. The oxygen content in the atmosphere is preferably 10 ppm or less. The moisture content in the atmosphere is preferably 10 ppm or less. MgB ２ The raw material powder for the core can be pulverized and mixed using a ball mill, a planetary mixer, a V-type mixer, a mortar, or the like.

[0093] Also, MgB ２ The core raw materials can also be crushed and mixed by mechanical milling. In mechanical milling, the particles constituting the powder are violently collided with media such as zirconia balls or the inner wall of a pot, and crushed and mixed while being subjected to intensive processing. In mechanical milling, MgB ２ It is preferable to apply a collision energy that is not enough to clearly generate MgB. ２ The formation of MgB ２ This can be confirmed by the substantial presence or absence of a peak.

[0094] By using the mechanical milling method, boron particles penetrate into magnesium particles, and a powder structure with a high degree of mixing is obtained in which boron is finely dispersed and encapsulated in a magnesium matrix. When such a powder structure is heat-treated, MgB ２ This allows for the formation of a core with many bonds and few voids, resulting in a high critical current density.

[0095] As the embedded single-core wire, a plurality of wires are prepared to form a multi-core structure. ２ The embedded single-core wire, in which the core material is filled in the metal barrier tube, can be adjusted to a predetermined wire diameter by performing area reduction processing. The area reduction processing of the embedded single-core wire can be performed by an appropriate number of passes. The area reduction processing is preferably performed at an area reduction rate of 8 to 12% per pass.

[0096] The area reduction process for the embedded single-core wire can be performed by drawing, extrusion, swaging, cassette roll processing, groove roll processing, etc. As the processing device, a draw bench, a hydrostatic extruder, a wire drawing machine, a swager, a cassette roller die, a groove roll, etc. can be used.

[0097] In addition, the MgB structure shown in FIG. ２ When manufacturing a superconducting wire, a recess forming step is carried out before the assembly step, in which a recess is formed on the outer surface of the core material used to produce the assembly material. The method for forming the recess is not particularly limited. For example, a method of drawing the core material using a predetermined die can be used to form the recess. The die can be one equipped with a die hole in which a convex portion having a shape that is the inverse of the concave portion is formed. Furthermore, when the length of the assembly material is short, cutting, grinding, beam machining, electric discharge machining, etching, etc. can also be used.

[0098] Next, in the assembly process, the assembled single-core wire and the core material are assembled into a metal sheath tube, and MgB ２ An embedded material, which is a precursor of the superconducting wire, is formed. The core material can be a cylindrical inner core material covered by a tubular outer core material. The metal sheath tube can be a double tube in which an outer sheath tube is placed over an inner sheath tube to form the inner sheath.

[0099] The MgB shown in FIG. ２ When manufacturing the superconducting wire 200, in the assembly process, a plurality of embedded single-core wires 120 are placed in a recess 110a formed on the outer surface of the central material 110, the central material 110 and the plurality of embedded single-core wires 120 are assembled into a metal sheath tube 130, and a spacer 140 is assembled into the gap surrounded by the plurality of embedded single-core wires 120 and the inner surface of the metal sheath tube 130.

[0100] The MgB shown in FIG. ２ When manufacturing the superconducting wire 400, in the assembly process, the central material 310 and the multiple embedded single-core wires 320 are assembled into the metal sheath tube 330, an inner spacer 341 is assembled into the gap surrounded by the multiple embedded single-core wires 320 and the outer surface of the central material 310, and an outer spacer 342 is assembled into the gap surrounded by the multiple embedded single-core wires 320 and the inner surface of the metal sheath tube 330.

[0101] Next, in the area reduction process, the built-in material with the built-in single-core wire or the like incorporated is subjected to area reduction. By applying area reduction to the built-in material at a predetermined area reduction rate, the built-in material is drawn to be elongated and thinned to a predetermined wire diameter. The area reduction of the built-in material can be performed with an appropriate number of passes. The area reduction of the built-in material can be performed, for example, so that the wire diameter is 0.3 to 2.0 mm.

[0102] The area reduction of the embedded material can be performed by drawing, extrusion, swaging, cassette roll processing, groove roll processing, etc. Processing equipment that can be used includes a draw bench, hydrostatic extruder, wire drawing machine, swager, cassette roller die, groove roll, etc.

[0103] During the area reduction process, the built-in material may be annealed to remove residual stress and soften the processed structure. Furthermore, the built-in material processed to a predetermined wire diameter may be twisted into a spiral. Twisting into a spiral reduces the coupling current between the cores. The twist pitch may be, for example, 10 to 100 mm.

[0104] In the heat treatment process, the thinned embedded material is heat treated to form MgB ２ When the embedded material is heat-treated at a predetermined temperature, the magnesium and boron filled in the barrier tube react to produce MgB ２ A core is formed.

[0105] The heat treatment atmosphere is preferably a non-oxidizing atmosphere such as an inert gas atmosphere of nitrogen, argon, or the like, or a vacuum atmosphere. The oxygen content in the atmosphere is preferably 10 ppm or less. The moisture content in the atmosphere is preferably 10 ppm or less. The heat treatment may be performed after the thinned embedded material is wound into a coil or the like, or may be performed before the winding. If the material is wound before the heat treatment, an insulating coating can be applied using a heat-resistant insulating material such as glass fiber.

[0106] The heat treatment temperature is, for example, 550 to 800° C., preferably 560 to 700° C., and more preferably 580 to 620° C. The higher the heat treatment temperature is above 550° C., the more the MgB ２The lower the heat treatment temperature is below 800°C, the more easily the reaction to generate MgB ２ Since grain growth is difficult, the density of grain boundaries that act as pinning centers increases, resulting in a high critical current density.

[0107] The heat treatment time is, for example, several tens of minutes to several tens of hours, preferably 2 to 16 hours, and more preferably 3 to 12 hours. When the heat treatment time is 3 hours or more, the MgB ２ Furthermore, if the heat treatment time is 12 hours or less, MgB ２ Since grain growth is difficult, the density of grain boundaries that act as pinning centers increases, resulting in a high critical current density.

[0108] More than MgB ２ According to the method for manufacturing a superconducting wire, the gap around the embedded single-core wire is reduced because it includes a step of forming a recess on the outer surface of the core material and a step of incorporating a spacer into the gap around the embedded single-core wire. Variation in the direction and magnitude of the processing force acting on the metal barrier tube is reduced, and positional deviation of the embedded single-core wire and uneven plastic deformation of the metal barrier tube toward the gap are suppressed. This increases the uniformity of the thickness of the metal barrier tube during area reduction processing, making the metal barrier tube less likely to break. It becomes possible to use a thinner metal barrier tube, thereby reducing the material costs and processing costs of the embedded single-core wire. Furthermore, the formation of heterophases and the formation of MgB ２ Therefore, the generation of geometrically asymmetric MgB ２ Filament and MgB ２ Filament breakage is less likely to occur, the critical current (Ic) is less likely to decrease, and the wire can be easily made longer. ２ Multiple MgB cores ２ A multifilamentary wire structure composed of filaments, ２ The thickness of the metal barrier layer in the circumferential direction of the filament is highly uniform, and MgB ２ MgB filament has reduced defects and is suitable for thinning and lengthening. ２ Superconducting wire can be produced efficiently.

[0109] Next, the above-mentioned MgB ２Superconducting coils using superconducting wires and the above-mentioned MgB ２ A magnetic field generating device equipped with a superconducting coil using superconducting wire will be described with reference to the drawings.

[0110] FIG. 6 shows an MgB ２ 6 is a diagram showing a schematic diagram of an example of a superconducting coil using a superconducting wire. FIG. 6 shows a cross-sectional view of a superconducting coil 600 cut parallel to the coil axis. As shown in FIG. 6, the above-mentioned MgB ２ The superconducting wire can be used as a winding of a superconducting coil 600. The superconducting coil 600 includes a bobbin 601, a winding portion 602, and a cooling vessel 603.

[0111] The superconducting coil 600 is a coil formed of a superconductor capable of superconducting transition, and constitutes a superconducting magnet device that generates a magnetic force. The superconducting coil 600 can be provided in, for example, an MRI (Magnetic Resonance Imaging) device, an NMR (Nuclear Magnetic Resonance) device, etc.

[0112] The superconducting coil 600 may be formed by either a wind-and-react method or a react-and-wind method. The wind-and-react method is a method in which a precursor of a superconducting wire is wound into a coil and then heat-treated. The react-and-wind method is a method in which a heat-treated superconducting wire is wound into a coil.

[0113] The bobbin 601 can be made of a metal with high thermal conductivity. The bobbin 601 is preferably made of copper, and particularly preferably made of oxygen-free copper. The bobbin 601 is covered with an insulating material (not shown). When the wind and react method is used, a heat-resistant material that can withstand the heat treatment temperature is used as the insulating material. An example of a heat-resistant insulating material is a glass braid made of glass fiber.

[0114] The winding section 602 is made of the above-mentioned MgB ２When the winding and react method is used, the winding section 602 is made of MgB ２ Before the heat treatment to generate MgB, it can be insulated with a heat-resistant insulating material. ２ After the heat treatment to generate MgB, the insulating resin may be impregnated. ２ After the heat treatment to generate the insulating resin and after winding the wire into a coil, the wire may be impregnated with an insulating resin.

[0115] The cooling vessel 603 is a vessel with a sealed structure, and contains MgB ２ The superconducting wire 602 is accommodated in the MgB ２ The cooling vessel 603 cools the superconducting wire 602. The cooling vessel 603 is provided in a vacuum insulation structure or a structure insulated from the inside and outside by a heat insulating material, a heat shield, etc. The cooling vessel 603 may be filled with a cooling medium such as liquid helium, or may be cooled by conduction using a refrigerator.

[0116] According to the superconducting coil 600, the MgB ２ MgB that constitutes the multi-core structure of the superconducting wire ２ The ratio of the thickness of the barrier layer on the outer periphery of the wire to the thickness of the barrier layer on the center of the wire is limited, and the thickness of the barrier layer is highly uniform, making it difficult for the barrier layer to break. ２ Superconducting wires can be made thinner and longer than ever before, making it possible to provide superconducting magnet devices that are suitable for miniaturization and high magnetic force.

[0117] 7 is a cross-sectional view showing a schematic example of a magnetic field generating device according to an embodiment of the present invention. FIG. 7 shows an MRI device 700 as an example of a magnetic field generating device. As shown in FIG. 7, the above-mentioned MgB ２ The superconducting coil 600 having a winding made of superconducting wire can be provided in an MRI device 700 .

[0118] The MRI apparatus 700 includes a pair of static magnetic field generating units 701, an imaging region 702, and a gradient magnetic field generating unit 703. The static magnetic field generating units 701 are arranged above and below each other so as to face each other with the imaging region 702 in between. The static magnetic field generating units 701 are connected to each other via connecting members (not shown). The gradient magnetic field generating units 703 are arranged between the static magnetic field generating units 701 and the imaging region 702, respectively.

[0119] The MRI apparatus 700 also includes a bed 705 on which a subject 704 is placed, and a transport mechanism 706 that transports the bed 705. The bed 705 is provided so as to be movable toward and away from the imaging region 702. When the bed 705 is transported by the transport mechanism 706, the subject 704 placed on the bed 705 moves toward and away from the imaging region 702.

[0120] The static magnetic field generating unit 701 generates a static magnetic field that is constant over time in the imaging region 702. The static magnetic field generating unit 701 includes a coil unit and a persistent current switch. The coil unit can be formed by the superconducting coil 600. The persistent current switch can be formed by the MgB ２ The static magnetic field generating unit 701 can be formed of a superconducting wire. The circuit of the static magnetic field generating unit 701 is electrically connected to a power supply (not shown) via a normal conductor.

[0121] An excitation current flows through the coil section of the static magnetic field generating section 701 when the persistent current switch is in the OFF state. When the persistent current switch is switched to the ON state, a persistent current flows. The persistent current flowing through the coil section generates a static magnetic field with high temporal stability in the imaging region 702. The stronger the static magnetic field, the higher the nuclear magnetic resonance frequency, and therefore the frequency resolution of the MRI apparatus 700 can be improved.

[0122] The gradient magnetic field generator 703 receives a time-varying current and generates a gradient magnetic field with a spatial distribution in the imaging region 702. When an oscillating magnetic field at a nuclear magnetic resonance frequency is applied to the imaging region 702, a resonance signal is emitted from the subject 704. The resonance signal is received by a receiving coil (not shown). The received resonance signal is converted into a spectrum by Fourier transform. The spectral information is visualized as a magnetic resonance tomographic image of the subject 704. The subject 704 can be examined by imaging, such as a two-dimensional contrast image.

[0123] According to the MRI device 700, MgB used in the coil section and the persistent current switch ２ MgB that constitutes the multi-core structure of the superconducting wire ２ Regarding the filament, the ratio of the thickness of the barrier layer on the outer periphery of the wire to the thickness of the barrier layer on the center side of the wire is limited, and the thickness of the barrier layer is highly uniform, making it difficult for the barrier layer to break. Therefore, it is suitable for MgB ferrites used in coils and persistent current switches. ２ Superconducting wire can be made thinner and longer than before, which makes it possible to form a static magnetic field generator that is suitable for miniaturization and high magnetic force, thereby enabling magnetic generators to be made smaller and take up less space than before.

[0124] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the present invention. For example, the present invention is not necessarily limited to those having all of the configurations of the above-described embodiments. Part of the configuration of an embodiment can be replaced with another configuration, part of the configuration of an embodiment can be added to another form, or part of the configuration of an embodiment can be omitted.

[0125] For example, the above-mentioned MgB ２ As shown in Figs. 1 to 5, the superconducting wire is made of 10 MgB ２ The filaments are arranged in a single layer in the radial direction of the wire, but MgB ２ The superconducting wire may be multi-layered in two or more layers in the radial direction of the wire, or may be composed of an appropriate number of MgB ２In the case of a multi-layer structure of two or more layers, the MgB ２ For the filament, the ratio of the thickness of the barrier layer on the outer periphery of the wire to the thickness of the barrier layer on the center of the wire is limited.

[0126] The present invention will be specifically described below with reference to examples, but the technical scope of the present invention is not limited to these examples.

[0127] Example 1 In Example 1, an embedded material 100 having the structure shown in FIG. 1 was fabricated, and the embedded material 100 was subjected to area reduction processing and heat treatment to form an MgB ２ A superconducting wire 200 was produced.

[0128] First, a precursor for the embedded single-core wire was prepared by the following procedure. ２ The magnesium powder and boron powder, which are raw materials for the core, were weighed so that the molar ratio of Mg to B was approximately 1:2, and the magnesium powder and boron powder were pulverized and mixed in a ball mill to prepare a mixed powder. The obtained mixed powder was then filled into a metal barrier tube formed of a barrier material to form a precursor for an embedded single-core wire. The precursor for the embedded single-core wire was then subjected to area reduction processing to produce an embedded single-core wire. The precursor for the embedded single-core wire was reduced in area to a predetermined wire diameter by drawing using a die, and was then drawn.

[0129] Next, a double-structure core material with a recess formed on its outer surface was produced. An outer core material was placed over the outside of an inner core material that had been processed to a specified wire diameter. Then, a recess was formed on the outer surface of the outer core material that covered the inner core material by drawing using a specified die. The die used had a die hole with a projection shaped like the inverse of the recess, and the same number of die holes as the number of single-core wires. Copper was used for the inner core material. A metal tube made of the same material as the metal barrier tube was used for the outer core material.

[0130] Next, MgB ２An embedded material, which is a precursor of a superconducting wire, was fabricated. Ten embedded single-core wires were arranged around the central material, each fitted along the recess of the central material. The central material and the embedded single-core wires were then inserted into an inner sheath tube, which was then inserted into an outer sheath tube. A billet-shaped spacer was inserted into each gap surrounded by the embedded single-core wires and the inner surface of the inner sheath tube.

[0131] Next, the assembled material was subjected to area reduction processing. The area reduction processing was repeated using a drawing die until the assembled material had a predetermined wire diameter. Then, the thinned assembled material was subjected to heat treatment to form MgB ２ A superconducting wire was produced.

[0132] Subsequently, the obtained MgB ２ The cross section of the superconducting wire was observed. ２ A cross section perpendicular to the longitudinal direction of the superconducting wire was cut out and polished. Furthermore, chemical etching was performed to distinguish the boundaries between the components, and then the cross section was observed using an optical microscope. As a result, as shown in Figure 2A, 10 MgB ２ Filaments were confirmed. MgB ２ The filament was surrounded by an inner sheath and an outer sheath. ２ A filling layer originating from the spacer was confirmed in the space surrounded by the filament and the inner surface of the metal sheath.

[0133] Subsequently, the obtained MgB ２ In the cross section of the superconducting wire, MgB ２ The thickness of the barrier layer of the filament was measured. ２ The thickness of the barrier layer on the outer periphery of the superconducting wire is MgB ２ It was confirmed that the thickness was limited to 2.2 times the thickness of the barrier layer at the center of the superconducting wire. No heterogeneous phases due to reactions between magnesium and copper, etc. were observed, and it was confirmed that no breakage of the barrier layer had occurred.

[0134] Example 2 In Example 2, an embedded material 300 having the structure shown in FIG. 3 was fabricated, and the embedded material 300 was subjected to area reduction processing and heat treatment to form an MgB ２ A superconducting wire 400 was produced.

[0135] First, a precursor for the embedded single-core wire was prepared by the following procedure. ２ The magnesium powder and boron powder, which are raw materials for the core, were weighed so that the molar ratio of Mg to B was approximately 1:2, and the magnesium powder and boron powder were pulverized and mixed in a ball mill to prepare a mixed powder. The obtained mixed powder was then filled into a metal barrier tube formed of a barrier material to form a precursor for an embedded single-core wire. The precursor for the embedded single-core wire was then subjected to area reduction processing to produce an embedded single-core wire. The precursor for the embedded single-core wire was reduced in area to a predetermined wire diameter by drawing using a die, and was then drawn.

[0136] Next, a double-layered core was fabricated. The inner core, which had been processed to a specified wire diameter, was covered with an outer core. The inner core was made of copper. The outer core was made of a metal tube made of the same material as the metal barrier tube.

[0137] Next, MgB ２ An embedded material, which is a precursor of a superconducting wire, was produced. Ten embedded single-core wires were arranged around a central material. The central material and the embedded single-core wires were then inserted into an inner sheath tube, and the inner sheath tube was then inserted into an outer sheath tube. An inner spacer was inserted into each gap surrounded by the multiple embedded single-core wires and the outer surface of the central material. An outer spacer was also inserted into each gap surrounded by the multiple embedded single-core wires and the inner surface of the inner sheath tube.

[0138] Next, the assembled material was subjected to area reduction processing. The area reduction processing was repeated using a drawing die until the assembled material had a predetermined wire diameter. Then, the thinned assembled material was subjected to heat treatment to form MgB ２ A superconducting wire was produced.

[0139] Subsequently, the obtained MgB ２ The cross section of the superconducting wire was observed. ２A cross section perpendicular to the longitudinal direction of the superconducting wire was cut out and polished. Furthermore, chemical etching was performed to distinguish the boundaries between the components, and then the cross section was observed using an optical microscope. As a result, as shown in Figure 4, 10 MgB ２ Filaments were confirmed. MgB ２ The filament was surrounded by an inner sheath and an outer sheath. ２ An inner filling layer originating from the inner spacer was confirmed in the space surrounded by the filament and the outer surface of the core material. ２ An outer filling layer originating from the outer spacer was confirmed in the space surrounded by the filament and the inner surface of the inner sheath.

[0140] Subsequently, the obtained MgB ２ In the cross section of the superconducting wire, MgB ２ The thickness of the barrier layer of the filament was measured. ２ The thickness of the barrier layer on the outer periphery of the superconducting wire is MgB ２ It was confirmed that the thickness was limited to three times the thickness of the barrier layer at the center of the superconducting wire. No heterogeneous phases due to a reaction between magnesium and copper or the like were observed, and it was confirmed that no breakage of the barrier layer occurred. MgB ２ It has been confirmed that when an inner spacer is disposed in the gap surrounded by the filament and the outer surface of the core material, the same effect as when a recess is formed in the outer surface of the core material can be obtained.

[0141] Comparative Example 1 As Comparative Example 1, an MgB ２ A superconducting wire was produced. ２ The superconducting wire was fabricated with a metal barrier tube thicker than that of the embedded material having the structure shown in FIG.

[0142] First, in the same manner as in Example 1, MgB ２ The superconducting wire was then drawn to a predetermined diameter and finally heat-treated to form the MgB ２A superconducting wire was produced, except that the metal barrier tube used was about 1.5 times thicker than the metal barrier tube used in Examples 1 and 2.

[0143] Subsequently, the obtained MgB ２ The cross section of the superconducting wire was observed. ２ A cross section perpendicular to the longitudinal direction of the superconducting wire was cut out and polished. Furthermore, chemical etching was performed to distinguish the boundaries between the components, and then the cross section was observed using an optical microscope. As a result, as shown in Figure 5, 10 MgB ２ Filaments were confirmed. MgB ２ The filament was surrounded by an inner sheath and an outer sheath. ２ A filling layer originating from the spacer was confirmed in the space surrounded by the filament and the inner surface of the metal sheath. ２ It was confirmed that the degree of deformation of the core shape along the radial direction of the wire rod was increased compared to Examples 1 and 2.

[0144] Subsequently, the obtained MgB ２ In the cross section of the superconducting wire, MgB ２ The thickness of the barrier layer of the filament was measured. As a result, it was confirmed that the thickness of the barrier layer on the outer periphery of the wire was four times that of the barrier layer on the center of the wire. It is thought that if the thickness of the metal barrier tube is increased, the proportion of metal that plastically deforms toward the outside in the radial direction of the wire during area reduction processing increases.

[0145] Subsequently, the obtained MgB ２ The critical current value of the superconducting wire was measured. ２ The superconducting wire was cooled to 4.2 K and then energized. ２ The critical current value of the superconducting wire was about 20% lower than that of Example 1. It is effective to limit the thickness of the barrier layer on the outer periphery of the wire to at least four times the thickness of the barrier layer on the center side of the wire.

[0146] Example 3 As Example 3, an MgB ２A superconducting wire was produced. ２ The superconducting wire was fabricated by making the thickness of the metal barrier tube thinner than that of the embedded material having the structure shown in FIG.

[0147] First, in the same manner as in Example 1, MgB ２ The superconducting wire was then drawn to a predetermined diameter and finally heat-treated to form the MgB ２ A superconducting wire was produced, except that the metal barrier tube used had a thickness about 0.6 times that of the metal barrier tube used in Examples 1 and 2.

[0148] Subsequently, the obtained MgB ２ The cross section of the superconducting wire was observed. ２ A cross section perpendicular to the longitudinal direction of the superconducting wire was cut out and polished. Furthermore, chemical etching was performed to distinguish the boundaries between the components, and then the result was observed using an optical microscope. Ten MgB ２ Filaments were confirmed. MgB ２ The filament was surrounded by an inner sheath and an outer sheath. ２ A filling layer originating from the spacer was confirmed in the space surrounded by the filament and the inner surface of the metal sheath.

[0149] Subsequently, the obtained MgB ２ In the cross section of the superconducting wire, MgB ２ The thickness of the barrier layer of the filament was measured. As a result, it was confirmed that the thickness of the barrier layer on the outer periphery of the wire was limited to three times or less the thickness of the barrier layer on the center side of the wire. It is thought that by reducing the thickness of the metal barrier tube, the proportion of metal that plastically deforms toward the outside in the radial direction of the wire during area reduction processing is reduced. It can be said that the thickness of the metal barrier tube can be reduced by about 40%.

[0150] Comparative Example 2: As Comparative Example 2, an MgB ２ A superconducting wire was produced. ２The superconducting wire was fabricated without forming a recess on the outer surface of the core material and without incorporating an inner spacer into the gap surrounded by the plurality of embedded single-core wires and the outer surface of the core material.

[0151] First, in the same manner as in Example 1, MgB ２ An embedded material, which is a precursor of a superconducting wire, was produced. However, the metal barrier tube used had a thickness about 0.6 times that of the metal barrier tube used in Examples 1 and 2. MgB ２ The embedded material, which is a precursor of the superconducting wire, was fabricated by arranging 10 embedded single-core wires around the core without forming any recesses on the outer surface of the core. Then, it was drawn to a predetermined wire diameter and finally, it was heat-treated to form MgB ２ A superconducting wire was produced.

[0152] Subsequently, the obtained MgB ２ The cross section of the superconducting wire was observed. ２ A cross section perpendicular to the longitudinal direction of the superconducting wire was cut out and polished. Furthermore, chemical etching was performed to distinguish the boundaries between the components, and then the result was observed using an optical microscope. Ten MgB ２ Filaments were confirmed. MgB ２ The filament was surrounded by an inner sheath and an outer sheath. ２ A filling layer originating from the spacer was confirmed in the space surrounded by the filament and the inner surface of the metal sheath. ２ It was confirmed that the degree of deformation in the radial direction of the wire was greater in the core than in Example 3. Some of the barrier layers had tears near the center of the wire. A heterogeneous phase was formed around the tears due to a reaction between magnesium and copper.

[0153] Subsequently, the obtained MgB ２ In the cross section of the superconducting wire, MgB ２The thickness of the barrier layer of the filament was measured. As a result, it was confirmed that the thickness of the barrier layer on the outer periphery of the wire was more than three times that of the barrier layer on the center of the wire. It is thought that the presence of gaps surrounded by the multiple embedded single-core wires and the outer surface of the core material reduced the proportion of metal on the radially inner side of the wire during the area reduction process.

[0154] Subsequently, the obtained MgB ２ The critical current value of the superconducting wire was measured. ２ The superconducting wire was cooled to 4.2 K and then energized. ２ The critical current value of the superconducting wire was about 40% lower than that of Example 3. The metal barrier tube used was about 0.6 times thicker than the metal barrier tubes used in Examples 1 and 2, but the presence of gaps surrounded by the multiple embedded single-core wires and the outer surface of the core material made the wire more susceptible to breakage during the wiredrawing process, which is thought to have resulted in the formation of heterophases, etc.

[0155] Example 4 As Example 4, an MgB ２ A superconducting coil having the structure shown in FIG. 6 was fabricated using the superconducting wire.

[0156] First, a built-in material was prepared using the same procedure as in Example 1, and the built-in material was subjected to area reduction processing. Then, the built-in material thinned by the area reduction processing was covered with glass fiber, which is an insulating material. Also, a metal bobbin was covered with glass fiber, which is an insulating material. Then, the insulated built-in material was wound around the bobbin and subjected to heat treatment at a predetermined temperature to form MgB ２ Then, the coiled MgB ２ The gaps between the superconducting wires are impregnated with insulating resin, and MgB ２ A superconducting coil with a superconducting wire fixed thereto was obtained.

[0157] The resulting superconducting coil was then placed in a cryostat and electrically connected to a power supply. The superconducting coil was then cooled below its critical temperature and excited by passing current from the power supply to confirm the magnetic field stability of the superconducting coil.

[0158] Example 5 As Example 5, an MgB ２ An MRI device equipped with a superconducting coil using superconducting wire was fabricated.

[0159] The MRI apparatus includes a pair of static magnetic field generating units and a gradient magnetic field generating unit. The static magnetic field generating units are connected via a connecting member and arranged above and below each other so as to face each other. The gradient magnetic field generating units are arranged between the static magnetic field generating units so as to sandwich the imaging region. A transport mechanism is also provided for transporting the bed so that it can be moved toward and away from the imaging region.

[0160] MgB ２ A superconducting coil made of superconducting wire was housed in a cryocontainer. The cryocontainer housing the superconducting coil was placed in a static magnetic field generator. The superconducting coil was electrically connected to a power source. The superconducting coil was able to generate a stable static magnetic field when excited by passing current through the power source.

[0161] 100, 300 Built-in material 110, 310 Center material 110a Recess 111, 311 Inner center material 112, 312 Outer center material 120, 320 Built-in single-core wire 121, 321 Raw material powder 122, 322 Metal barrier tube 130, 330 Metal sheath tube 131, 331 Inner sheath tube 132, 332 Outer sheath tube 140, 340 Spacer 341 Inner spacer 342 Outer spacer 200, 400, 500 MgB ２ Superconducting wire 210,410,510 Center material 210a, 510a Recess trace 211,411,511 Inner center material 212,412,512 Outer center material 220,420,520 MgB ２ Filament 221, 421, 521 MgB ２ Core 222, 422, 522 Barrier layer 230, 430, 530 Metal sheath 231, 431, 531 Inner sheath 232, 432, 532 Outer sheath 240, 440, 540 Filling layer 441 Inner filling layer 442 Outer filling layer Tin Thickness of barrier layer at center Tout Thickness of barrier layer at outer periphery

Claims

1. A core material is arranged at the center of the wire, and MgB ２ A plurality of MgB cores formed by the method described above are covered with a barrier layer. ２ a filament and a plurality of the MgB ２ A multi-filamentary MgB wire having a metal sheath covering the filaments. ２ A superconducting wire comprising: ２ The filament is the MgB ２ The thickness of the barrier layer on the outer periphery of the superconducting wire is ２ The thickness of the barrier layer at the center of the superconducting wire is three times or less than that of the MgB ２ Superconducting wire.

2. The MgB according to claim 1 ２ A superconducting wire comprising: ２ The filament is the MgB ２ The thickness of the barrier layer on the outer periphery of the superconducting wire is ２ The thickness of the MgB barrier layer at the center of the superconducting wire is 1.5 times or more and 3 times or less. ２ Superconducting wire.

3. The MgB according to claim 1 ２ The superconducting wire is characterized in that the metal sheath is made of the MgB ２ An MgB filament having an inner sheath covering the filament and an outer sheath covering the inner sheath. ２ Superconducting wire.

4. MgB according to claim 3 ２ A superconducting wire, wherein the inner sheath is made of iron, niobium, or tantalum, and the outer sheath is made of nickel-copper alloy, stainless steel, or low-carbon steel. ２ Superconducting wire.

5. The MgB according to claim 1 ２ A superconducting wire, wherein the core material is the MgB ２ An MgB superconducting wire having an inner core disposed at the center of the superconducting wire and an outer core covering the inner core. ２ Superconducting wire.

6. MgB according to claim 5 ２ A superconducting wire, wherein the barrier layer is made of iron, niobium, or tantalum, the inner core material is made of copper or iron, and the outer core material is made of the same material as the barrier layer, such as MgB ２ Superconducting wire.

7. A core material arranged at the center of the wire, and MgB ２ A plurality of MgB cores formed by the method described above are covered with a barrier layer. ２ a filament and a plurality of the MgB ２ A multi-filamentary MgB wire having a metal sheath covering the filaments. ２ A method for producing a superconducting wire, comprising: ２ forming a plurality of single-core wires in which the raw material is filled in a metal barrier tube that forms the barrier layer; forming a recess in the outer surface of the central material; arranging the plurality of single-core wires in the recess, incorporating the central material and the plurality of single-core wires into a metal sheath tube that forms the metal sheath, and incorporating a spacer in a gap surrounded by the plurality of single-core wires and the inner surface of the metal sheath tube to form an embedded material; reducing the area of ​​the embedded material; and heat-treating the embedded material that has been subjected to the area reduction process to form MgB ２ and generating MgB ２ A method for manufacturing superconducting wire.

8. A core material arranged at the center of the wire, and MgB ２ A plurality of MgB cores formed by the method described above are covered with a barrier layer. ２ a filament and a plurality of the MgB ２ A multi-filamentary MgB wire having a metal sheath covering the filaments. ２ A method for producing a superconducting wire, comprising: ２ a step of forming a plurality of single-core wires in which the raw material is filled in a metal barrier tube that forms the barrier layer; a step of incorporating the core material and the plurality of single-core wires into a metal sheath tube that forms the metal sheath, and incorporating an inner spacer into a gap surrounded by the plurality of single-core wires and the outer surface of the core material, and incorporating an outer spacer into a gap surrounded by the plurality of single-core wires and the inner surface of the metal sheath tube to form an incorporated material; a step of reducing the area of ​​the incorporated material; and a step of heat-treating the area-reduced incorporated material to form MgB ２ and generating MgB ２ A method for manufacturing superconducting wire.

9. MgB according to any one of claims 1 to 6 ２ A superconducting coil made of wound superconducting wire.

10. MgB according to any one of claims 1 to 6 ２ A magnetic generator equipped with a superconducting coil wound with superconducting wire.

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