JPH0462765A - Connection of superconductive wire of nb3sn - Google Patents

Abstract

PURPOSE:To prevent deterioration in performance caused by influence of distor tion by producing Nb3Sn layer simultaneously at a connection part at the time of heat treatment of a complex wire. CONSTITUTION:A complex wire 1 has a plurality of Nb pipes 4 in its Cu matrix 3, and in each pipe 4 a Cu pipe 5 and an Sn wire 6 are stored. After heat treat ment the Cu pipe reacts to the Sn wire to form a Cu-Sn alloy 7, and at the same time, inside the Nb pipe 4' Nb3Sn layer 8 is generated to form a superconductive wire 2. Then by the use of HF mixture liquid the outer circum ference of the Nb pipes 4a, 4b are melted to have a small outer diameter. A pair of complex wires 1, 1' are arranged in a face-to-face manner and the Nb filaments 4a', 4b' are arranged to overlap each other in the axial direction. A Cu sleeve 9 is thereafter put over the outside and the Cu part at the opposed ends and compressed to bring the Nb pipes into close contact with each other, and they are heat-treated to form a connection part.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for connecting superconducting wires, and in particular, Nb3Sn which is suitable for forming superconducting coils by the Wind and React method using superconducting wires by the tube method.
Related to a method of connecting superconducting wires.

[Prior Art] A tube method is known as one of the methods for manufacturing Nb3Sn superconducting wire.

In this method, a plurality of composite wires in which the outer periphery of an Sn rod is sequentially coated with Cu tubes and Nb tubes are arranged in a Cu matrix to form a composite, and after cold working this composite, heat treatment is performed. By applying Nb3 Sn to the inside of the Nb tube
It generates layers.

Compared to the bronze method using Cυ-8n alloy as a matrix, the above method has advantages such as being able to process without requiring intermediate annealing and having a high critical current density (Tc) value. It is widely used in wire rods for high-field magnets, etc.

When manufacturing high-field magnets using superconducting wires using the tube method, grading technology is employed to reduce the size, performance, and cost of the coils. This grading technology uses wires with different wire diameters and critical current values (Tc) depending on the strength of the external magnetic field on the inside (high magnetic field side) and outside (low magnetic field side) of the coil. It is something to be manufactured.

The above grading technology is applied to Wind and Rea.
When adopting the ct method (a method of applying heat treatment to generate Nb3Sn after coil formation), React and W
It is impossible to perform the solder connection employed in the ind method (a method of forming a coil after heat treatment to generate Nb3Sn) or when forming a coil using NbTi alloy wire.

The reason for this is that in the case of the Wind and React method,
For example, since it is necessary to perform a heat treatment at 700° C. for 50 to 100 hours after forming the coil to generate Nb3Sn, the solder is melted during this heat treatment.

Therefore, conventionally, a method has been adopted in which the ends of the wire are drawn out of the flange plate of the coil winding frame and the ends are connected after heat treatment.

[Problem to be solved by the invention] However, in the above connection method, both ends of the wires to be connected are susceptible to bending strain, especially in the case of compound-based superconducting wires whose characteristics tend to deteriorate due to strain. has become a problem.

In addition, it is not known until the coil is energized that the connection is complete, so if the connection is incomplete, it requires a great deal of labor and cost, such as rewinding the coil.

Furthermore, in the case of Nb3Sn superconducting wire made by the tube method using a high-resistance material such as CuNi alloy for the matrix (for example, superconducting wire for persistent current switch-PC8), the connection resistance increases due to soldering, and the PC8 There was a problem in that the performance was significantly degraded.

The present invention was made to solve the above problems, and
The object of the present invention is to provide a connection method that can reduce the influence of distortion and connection resistance when connecting Nb3Sn superconducting wires using the tube method. The present invention is particularly suitable for a connection method when forming a grading coil by the vind and rear method.

[Means for Solving the Problems] In order to achieve the above object, the present invention arranges a plurality of Nb-based metal tubes in a matrix made of copper-based metal, and in this metal tube, copper-based metal and tin-based metal are placed. In a method for connecting superconducting wires manufactured by heat-treating a cold-worked composite wire containing a composite wire, the method includes: (a) removing the copper-based metal forming the matrix at both ends of the pair of composite wires; (b) reducing this filament to a predetermined thickness by chemical means; and (c) making the filaments overlap each other in the axial direction. (d) placing a sleeve made of a copper-based metal around the outer periphery of the filament and then compression molding; (e) then performing heat treatment to generate Nb3Sn. It consists of

In the present invention, from the viewpoint of workability, it is preferable to use a tin-based metal coated with a copper-based metal, such as a Cu-coated Sn rod, as the copper-based metal and tin-based metal accommodated in the Nb-based metal tube. In addition, a composite wire with a multi-core structure has, for example, Cu inside.
It can be manufactured by placing Cu on the outside of a Nb tube containing a coated Sn rod, processing this, and then storing a plurality of the rods in the Cu tube and processing them.

In the above invention, the filament coated with Nb-based metal is reduced to a predetermined thickness by exposure machine chemical means, and the thickness is reduced to the inside of the filament coated with Nb-based metal in the composite wire after heat treatment. It is preferable that the thickness be approximately the same as the thickness of the Nb3Sn layer to be produced. This allows almost the entire amount of the filament in the connection portion to react with the Nb3Sn layer. It is also possible to react almost the entire amount to the Nb3Sn layer without reducing the thickness of the filament, but in this case, S in the matrix within the composite wire is
This gives rise to the possibility that n is diffused.

It is preferable that the heat treatment when forming the above-mentioned connection portion is performed after forming a coil using a pair of composite wires mechanically joined by a sleeve. This makes it possible to eliminate the influence of distortion during coil formation.

[Function] In the method for connecting superconducting wires according to the present invention, since a superconducting layer is formed at the connection part during heat treatment of the composite wire, that is, heat treatment for Nb3Sn generation, the mechanically connected composite wire is By molding it into the shape of , deterioration of characteristics due to the influence of distortion can be prevented. Furthermore, since the connecting portion can be directly connected through the Nb3Sn layer, an increase in the connection resistance of the connecting portion can be prevented, and the superconducting properties thereof will not be deteriorated.

[Example code] An embodiment of the present invention will be described below.

FIG. 2(a) is a sectional view of the composite wire 1 before heat treatment by the tube method, and FIG. 2(b) is a sectional view of the superconducting wire 2 after the heat treatment.

The composite wire 1 includes a plurality of Nb tubes 4 in a Cu matrix 3.
It has a structure in which a Cu tube 5 and a Sn wire 6 are housed inside this Nb tube, and after heat treatment,
The Cu tube and the Sn wire react to form a Cu--Sn alloy 7, and at the same time, an Nb3Sn layer 8 is formed inside the Nb tube 4' to form the superconducting wire 2.

First, as shown in FIG. 3, a pair of compound lines 1.
The Cu matrix at both ends of 1′ was removed with nitric acid to form Nb
The tubes 4a and 4b are exposed.

Next, as shown in FIGS. 4(a) to 4(c), the outer peripheries of the Nb tubes 4a and 4b are melted using an HF mixture to reduce their outer diameters. At this time, the thickness of the Nb tube 4a'4b' is melted so as to be approximately equal to the thickness of the Nb3Sn layer formed on the composite wire during heat treatment.

Due to this dissolution, the S inside the Nb tube 4a'4b'
Since n may have been removed, it is preferable to cut both ends of the Nb tube.

The pair of compound lines 1.1' obtained in this way are
As shown in Figure (a), the Nb filaments 4a' and 4b' are arranged facing each other in the axial direction so as to overlap each other, preferably intertwined, and then the Nb filaments 4a' and 4b' are intertwined with each other, and then the Nb filaments 4a' and 4b' are intertwined with each other so as to overlap each other in the axial direction. A Cu sleeve 9 is placed over the tube, and this sleeve portion is compression molded to bring the Nb tubes into close contact with each other, and then a predetermined heat treatment is performed, for example, heating at 755° C. or lower to form a connection portion.

In this case, as shown in FIG. 5(b), the above-mentioned pair of composite wires 1.1' are arranged in parallel to form the Nb filament 4a'.
, 4b', the Cu on the outside and both ends
It is also possible to cover the Cu sleeve 9' over the section and then compression mold this sleeve section.

As shown in FIG. 1, the connection portion 10 after heat treatment has a cross-sectional structure in which an Nb3 Sn layer 12 is formed within the Cu7 matrix 11 on the outside of the Cu--Sn alloy 13.

In addition, to maintain stability, Nb is added inside the Cu sleeve.
It is also possible to arrange a tape made of or Ta.

[Effects of the Invention] As described above, according to the method for connecting Nb3Sn superconducting wires of the present invention, an Nb3Sn layer is simultaneously generated at the joints during heat treatment of the composite wire, so that the mechanically connected joints are By applying heat treatment to the composite wire after forming the composite wire, deterioration of characteristics due to the effects of distortion can be prevented. Further, it is possible to prevent the connection resistance of the connection portion from increasing, and its superconducting properties are also good. The method of the present invention is particularly suitable for forming grading coils by the Wind and React method.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view of a connection formed by the method of the present invention, FIG. 2(a) is a cross-sectional view of a composite wire before heat treatment by the tube method, and FIG. 3 is a schematic diagram showing the end portions of a pair of composite wires after removing the Cu matrix, and FIG.
Side view of the filament, Figure 5(b) is its AA' cross-sectional view, Figure 5(c) is its B-B' cross-sectional view, and Figures 5(a) and 5(b) are the connection portion before compression molding. FIG. 1.1'...Composite wire 3...Cu matrix 4.4a, 4b-Nb tube 5...Cu tube 6...Sn wire 9... ......Cu sleeve 0...Connection part 1 after heat treatment...
...Cu matrix 2...Nb3
Sn layer 3...Cu-Sn alloy

Claims (2)

[Claims] (1) By arranging a plurality of Nb-based metal tubes in a matrix made of copper-based metal, and applying heat treatment to a composite wire that is cold-worked by accommodating copper-based metal and tin-based metal within the metal tube, A method for connecting manufactured superconducting wires includes (a) a step of removing a copper-based metal forming a matrix at both ends of the pair of composite wires to expose a filament coated with an Nb-based metal; ) reducing the filament to a predetermined thickness by chemical means; (c) arranging a pair of composite wires so that the filaments overlap each other in the axial direction; and (d) the outer periphery of the filament. Nb characterized by comprising a step of placing a sleeve made of a copper-based metal on the surface and then performing compression molding, and (e) then a step of performing heat treatment to generate Nb_3Sn.
_ How to connect 3Sn superconducting wire. (2) The method for connecting Nb_3Sn superconducting wires according to claim 1, wherein the pair of mechanically connected composite wires after compression molding are formed into a coil shape before heat treatment.