JPH06349357A - Manufacture of superconductor - Google Patents

Abstract

PURPOSE:To simply form a rigid insulating film on the surface of each superconductive wire by bundling superconductive wires on each of which a copper oxide film is formed, by heat treating, then by exposing in an oxygen- containing high temperature gas. CONSTITUTION:An intermetallic compound family superconductive wire 21 is heat treated in the air to form a copper oxide film 26a. The superconductive wire is conducted with wire forming treatment and inserted into a pipe 28. The pipe 28 into which a superconductive wire bundle 27 is inserted is heat treated at high temperature to form a superconductive layer in each superconductive wire 21. By this heat treatment, oxygen in the copper oxide film 26a is diffused in a stabilized copper layer, and the copper oxide film 26a disappears to form gaps. When high temperature air is passed through the pipe 28, the high temperature air flows through the gaps, and a copper oxide film 26b is formed on the surface of each superconductive wire to fill the gaps. A superconductor whose each superconductive wire 21 is electrically insulated with the copper oxide film 26b is obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a superconducting conductor having a superconducting wire bundle in which a plurality of intermetallic compound superconducting wires are bundled.

[0002]

2. Description of the Related Art A magnetic field generator for a fusion reactor requires a superconducting conductor capable of passing a large current and having a small AC loss. One of the superconducting conductors satisfying such a demand is a cable-in-conduit type conductor.

In this cable-in-conduit type superconducting conductor, as shown in FIG. 7 (a), several hundred superconducting wires 1 each having a wire diameter of about 1 mm are formed into a bundle, and this superconducting wire bundle 2
Is inserted in a pipe 3 made of stainless steel or the like. An insulating coating 4 for reducing AC loss is provided on the surface of each superconducting wire 1 as shown in FIG. 7 (b). Then, the refrigerant is caused to flow into the gap between the superconducting wires or the gap with the pipe 3 so as to cool the superconducting wire 1 to the superconducting transition temperature or lower.

When the superconducting wire 1 is made of an alloy such as Nb.Ti, an organic insulating material such as formal is used as the insulating coating 4. However, the superconducting wire 1 is N
In the case of intermetallic compounds such as b ₃ Sn and Nb ₃ Al, the heat treatment temperature at the time of forming the superconducting layer is 600 to 750 ℃ or 800.
Since it is as high as ~ 1000 ° C, organic insulating materials cannot be used. That is, when the superconducting wire 1 is an intermetallic compound system, if the superconducting layer is subjected to a linearizing treatment after the superconducting layer is formed, the superconducting layer generated by the mechanical strain during the treatment is divided and the superconducting characteristics are deteriorated. Therefore, it is necessary to provide the insulating coating before the stranding. For this reason, when the superconducting wire 1 is made of an intermetallic compound, the insulating coating film 4 should be formed of a chromium oxide plating layer that is highly heat resistant and less likely to contaminate the stabilized copper layer of the superconducting wire 1. I have to.

However, since the insulating coating film 4 formed of the chromium oxide plating layer has poor adhesion to the stabilized copper layer forming the outer layer of the superconducting wire 1, it becomes more linear and forms a superconducting wire bundle. There is a problem in that it easily peels off and lacks reliability as an insulating layer.

[0006]

As described above, in a superconducting conductor provided with a superconducting wire bundle in which a plurality of intermetallic compound-based superconducting wires are bundled, an insulating coating composed of a chromium oxide plating layer is provided on the surface of each superconducting wire. However, the insulating coating easily peels off at the stage of forming the superconducting wire bundle, which causes a problem of lack of reliability as a conductor.

Therefore, the present invention is directed to a superconducting conductor having a superconducting wire bundle in which a plurality of intermetallic compound superconducting wires are bundled, and a superconducting conductor capable of forming a strong insulating coating on the surface of each superconducting wire in a simple process. It is intended to provide a manufacturing method.

[0008]

In order to achieve the above object, the present invention provides a method for producing a superconducting conductor comprising a superconducting wire bundle comprising a plurality of intermetallic compound superconducting wires having a stabilized copper layer. A first step of exposing each superconducting wire before formation of the superconducting layer to a high temperature gas atmosphere containing oxygen to form a copper oxide film on the surface of each superconducting wire, and a copper oxide film on the surface by the first step. A plurality of formed superconducting wires are bundled, and the superconducting wire bundle is subjected to a heat treatment at a temperature necessary for forming an intermetallic compound-based superconducting layer, and then the superconducting material is placed in a high temperature gas atmosphere containing oxygen. A third step of exposing the wire bundle to re-form a copper oxide film on the surface of each superconducting wire.

[0009]

In the first step, a copper oxide film as an electric insulating material is formed on the surface of each superconducting wire. This copper oxide film is formed by oxidizing the surface portion of the stabilized copper layer. Therefore, in the second step, the copper oxide film is not peeled off even when bending distortion is applied to the copper oxide film or when the copper oxide films are rubbed with each other when the superconducting wire bundle is formed. In the second step, after forming the superconducting wire bundle, the superconducting wire bundle is subjected to heat treatment at a temperature necessary for forming an intermetallic compound-based superconducting layer, whereby the copper oxide film formed on the surface of each superconducting wire Oxygen diffuses into the stabilized copper layer and the copper oxide film disappears. As a result, a gap corresponding to the thickness of the copper oxide film is formed between the superconducting wires. And
When the superconducting wire bundle is exposed to a high-temperature gas atmosphere containing oxygen in the third step, the high-temperature gas containing oxygen flows through the gaps and a copper oxide film is formed again on the surface of each superconducting wire. The superconducting wires are surely electrically insulated by this newly formed copper oxide film.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the manufacturing method according to the present invention will be described below with reference to the drawings. First, several hundreds of superconducting wires 21 of intermetallic compound system before heat treatment (before formation of superconducting layer) as shown in FIG. 1 (a) are prepared. These superconducting wires 1 are
For example, a Nb ₃ Sn system with a wire diameter of about 1 mm
As shown in (b), the niobium material 23 is contained in the copper-tin alloy material 22.
A plurality of barrier layers 24 are arranged along the axis, and the barrier layer 24 is made of a tantalum material (a niobium material can also be used) for preventing the tin material from diffusing toward the outside.
Is arranged, and the stabilizing copper layer 25 is further arranged outside thereof.

Each superconducting wire 1 having such a structure is heat-treated in the atmosphere at 200 ° C. for 20 hours to form a copper oxide film 26a of about 0.5 μm on the surface of the superconducting wire 1 as shown in FIG. did.

Next, these superconducting wires 1 were linearized as shown in FIG. 3, and this superconducting wire bundle 27 was inserted into a stainless steel pipe 28 as shown in FIG. 4 (a). The ratio of the sectional area of the superconducting wire bundle 27 to the spatial sectional area of the pipe 28 was about 40%. At this time, each superconducting wire 21 is in a state of being electrically insulated from each other by the copper oxide film 26a formed on the surface.

Next, the pipe 28 in which the superconducting wire bundle 27 is inserted is placed in argon gas and heat-treated at 725 ° C. for 20 hours to make Nb which is a superconducting layer in each superconducting wire 21.
_{A 3} Sn layer was generated. When high-temperature heat treatment is performed to generate the superconducting layer in this way, oxygen in the copper oxide film 26a formed on the surface of each superconducting wire 1 diffuses into the stabilized copper layer 25, and the copper oxide film 26a is formed. Disappears. As a result, a gap 29 corresponding to the thickness of the copper oxide film 26a is formed between the superconducting wires 1 as shown in FIG.

Next, the atmosphere at 200 ° C. was passed through the pipe 28. As a result, high-temperature air flows through the gap 29, and as shown in FIG. 6, a 0.53 μm-thick copper oxide film 26b is formed on the surface of each superconducting wire 1 so as to fill the gap 29. A superconducting conductor in which each superconducting wire 21 is electrically insulated by the newly formed copper oxide coating 26a can be obtained.

When high-temperature heat treatment is performed to form the superconducting layer, oxygen in the copper oxide film 26a diffuses into the stabilized copper layer 25 as described above. This diffused oxygen is
When combined with the tantalum that constitutes the barrier 24, Ta ₂ O
Generates ₅ . In the above example, since the thickness of the copper oxide film 26a was as thin as 0.5 μm, the amount of oxygen diffused into the stabilized copper layer 25 and combined with tantalum was small, and the thickness of Ta ₂ O ₅ was 0.1 μm.

In order to investigate the influence of the Ta ₂ O ₅ layer on the superconducting stability, the critical current (Ic) was measured and the degree of voltage generation with respect to the current was observed. It turns out that there is no difference. That is, a tantalum oxide layer having such a thickness does not cause instability in the superconducting state.

For comparison, the thickness of the copper oxide film 26a is set to 10
When the sample having a thickness of 5 μm and subjected to the same treatment as in the example was investigated, the thickness of the tantalum oxide layer formed on the barrier 24 was 5 μm, and the voltage generation during the critical current measurement became rapid. This means that when an attempt is made to transition from the superconducting state to the normal conducting state due to some disturbance, when a current flows through the stabilized copper layer, the tantalum oxide layer with high resistance heats up and becomes an unstable factor. Is shown. Therefore, the thickness of the copper oxide coating 26a is preferably 1 μm or less.

However, in the case of a wire having a large number of Nb filaments in a copper matrix such as Nb ₃ Al superconducting wire or Nb ₃ Sn superconducting wire formed by the Nb tube method, copper oxide is used. There is no influence of the thickness of the coating film 26a. This is for the following reasons. That is, in these wires, the shape of the Nb filament located at the outermost side is rich in undulations. When a copper oxide film is formed on the surface of such a wire and then heat treatment is performed to generate Nb ₃ Al or Nb ₃ Sn, oxygen in the copper oxide film diffuses into the copper matrix and the outer surface of the Nb filament is Part reacts with a part having a short diffusion distance to generate NbO. That is, NbO is not formed in the place where the diffusion distance is long. Therefore, in such a wire, when the transition from the superconducting state to the normal conducting state is attempted, a current flows from the portion where NbO is not generated to the stabilized copper layer, and the stability as the superconducting wire is secured. Therefore, in the case of such a wire rod, the thickness of the copper oxide film 26a may be 1 μm or more.

[0019]

As described above, according to the present invention,
A strong insulating coating can be formed on the surface of each superconducting wire in a simple process.

[Brief description of drawings]

FIG. 1 is a diagram showing an appearance and a cross section of a superconducting wire prepared for carrying out a manufacturing method according to the present invention.

FIG. 2 is a diagram for explaining an embodiment of a manufacturing method according to the present invention.

FIG. 3 is a view for explaining an embodiment of a manufacturing method according to the present invention.

FIG. 4 is a diagram for explaining an embodiment of a manufacturing method according to the present invention.

FIG. 5 is a view for explaining an embodiment of a manufacturing method according to the present invention.

FIG. 6 is a diagram for explaining an embodiment of a manufacturing method according to the present invention.

FIG. 7 (a) is a sectional view of a cable-in-conduit type superconducting conductor, and FIG. 7 (b) is a sectional view of a superconducting wire incorporated in the same superconducting conductor.

[Explanation of symbols]

21 ... Superconducting wire 22 ... Copper / tin alloy material 23 ... Niobium material 24 ... Barrier 25 ... Stabilized copper layer 26a, 26b ...
Copper oxide film 27 ... Superconducting wire bundle 28 ... Pipe 29 ... Gap

Claims (2)

[Claims] 1. When manufacturing a superconducting conductor comprising a superconducting wire bundle comprising a plurality of intermetallic compound-based superconducting wires having a stabilized copper layer, each superconducting material before forming a superconducting layer in a high temperature gas atmosphere containing oxygen. A first step of exposing a wire to form a copper oxide film on the surface of each superconducting wire, and bundling a plurality of superconducting wires having a copper oxide film formed on the surface by the first step, with respect to this superconducting wire bundle A second step of performing a heat treatment at a temperature necessary for forming an intermetallic compound-based superconducting layer, and thereafter exposing the superconducting wire bundle to a high-temperature gas atmosphere containing oxygen to form a copper oxide film on the surface of each superconducting wire again. And a third step of forming the superconducting conductor. 2. A high-temperature gas containing oxygen for producing a cable-in-conduit type superconducting conductor in which a superconducting wire bundle comprising a plurality of intermetallic compound-based superconducting wires having a stabilized copper layer is inserted into a pipe. A first step of exposing each superconducting wire before formation of the superconducting layer to an atmosphere to form a copper oxide film on the surface of each superconducting wire, and a superconducting wire having a copper oxide film formed on the surface by this first step. And a second step of inserting the superconducting wire bundle into a pipe, and a third heat treatment of the superconducting wire bundle inserted into the pipe at a temperature necessary for forming an intermetallic compound-based superconducting layer. A superconducting conductor, which comprises a step and a fourth step of thereafter exposing the superconducting wire bundle to a high temperature gas atmosphere containing oxygen to re-form a copper oxide film on the surface of each superconducting wire. of Production method.