JPH03116609A - Compound superconducting wire - Google Patents

Abstract

PURPOSE:To increase the critical current of a filament for a magnetic field generated in the longitudinal direction of the cross section of the filament by making the cross section of the filament roughly circular and that of a linear material rectangular. CONSTITUTION:A number of Nb cores are embedded in a bronze matrix 2 consisting of Cu-Sn and a barrier 3 of Nb and a copper stabilizing material 4 are disposed around the number of Nb cores and, after extrusion, wire drawing and annealing are repeated and then a straight angle cross section is obtained by machining process. A filament 1 is made roughly circular by drawing process but is not subjected to rolling process. Thus the filament would not be deteriorated in comparison with a filament flattened by rolling process and so its critical current density is enhanced. In addition, winding of the filament is easy because of its rectangular outer form and then current density as a coil would not be lowered.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to the cross-sectional shape of a compound superconducting wire.

[Conventional technology]

Compound superconducting wires such as Nb, Sn, V, Ga, etc. are used for high magnetic field magnets, but since compound superconductors are weak against strain, so-called wind wires are used in which heat treatment is performed to generate superconductors after coil winding. Coils are often manufactured using the Andreact method.

The cross-sectional shapes of the compound wire used for this include round and rectangular. Round conductors are difficult to coil and require special techniques, and in the case of large conductors, the current density as a coil is low due to wasted space between the wires.

Since rectangular conductors do not have such drawbacks, although they are more expensive than round conductors, they are often more advantageous overall and are often used.

FIG. 1(a), Φ) is a cross-sectional view of a compound superconducting wire having a round and rectangular cross section formed by a conventional bronze method. The round conductor has a structure in which a large number of Nb cores are embedded in a bronze matrix (2) made of Cu5n, a barrier (3) such as Nb or Ta is placed around it, and a copper stabilizing material (4) is placed on the outside. It becomes. By heat-treating this, a filament (1) in which an Nb5Sn superconductor is formed around the Nb core can be obtained.

The rectangular conductor has the same structure, but because it is manufactured by rolling the round conductor, the Nb filament is crushed into a flat shape.

In such a rectangular conductor, the pinning force increases with respect to the magnetic field in the longitudinal direction of the cross section, so it can be expected that the critical current (I,) with respect to the magnetic field in that direction increases.

[Problem to be solved by the invention]

The manufacturing process of Nb3Sn compound superconducting wire by the bronze method consists of extrusion, wire drawing, rolling, and diffusion heat treatment in this order. In the wire drawing process, bronze is work hardened and wire breaks occur, so annealing and wire drawing are repeated. Although the annealing temperature is lower than the heat treatment temperature for Nb3Sn generation and the time is shorter, Nb and Sn are still generated on the Nb surface and destroyed during the next wire drawing. At this time, the surface condition and cross-sectional shape of the Nb filament deteriorate, and further, when severe processing is applied in the rolling process, the deterioration of the filament further progresses. As a result, contrary to expectations, ■ of the rectangular conductor. ■ is a round conductor. There was a problem that it was lower than that.

[Means and actions to solve the problem]

The present invention provides a compound at conductive wire that solves the above problems, and is a compound superconducting wire that has a filament made of a compound superconductor inside and a stabilizing material at the outermost periphery, in which the cross-sectional shape of the filament is approximately It is characterized in that it is circular and the cross-sectional shape of the wire is rectangular.

In compound superconducting wires with the above structure, the filaments are only drawn and have a substantially circular shape, and are not rolled, so they do not deteriorate compared to filaments that are flattened by rolling. , therefore the critical current density also increases. Further, since the outer shape is rectangular, winding is easy and the current density as a coil does not decrease.

〔Example〕

In order to demonstrate the present invention, a small billet was manufactured and compared with a conventional example. As an example of the present invention, a cylindrical billet with an outer diameter of 45φ was prepared, in which a large number of Nb cores were embedded in a bronze matrix made of Cu-3n, and an Nb barrier and a copper stabilizing material were arranged around the core. After extrusion, this wire was repeatedly drawn and annealed to form a round wire of 2.56φ, which was then cut into lengths of about 300 mm. After this, by cutting 2
It had a rectangular cross-sectional shape of m1×1.6-. In this cutting, only the outermost part of the copper stabilizer was cut, so the cross-sectional shape of the barrier, filament part, and bronze remained round, unchanged from before cutting.

In addition, the cross-sectional area of the part excluding the copper stabilizing material at this time is 1.6
As a comparative example, a billet having an outer diameter of 45φ and having the same structure as the billet described above was manufactured. After extrusion, wire drawing and intermediate annealing were repeated to obtain a diameter of 2.19mm, which was then rolled with a roll.
A flat wire of 1.46 am was used. The corner was 0.2R. Therefore, the bronze, Nb filament group, and Nb barrier are also deformed into rectangular shapes. The cross-sectional area of the part excluding the copper stabilizing material at this time was 1.6 as in the previous example.
2- was taken into consideration when assembling the billet.

Five samples each of the above examples and comparative examples were heat-treated simultaneously in an atmospheric furnace to generate Nb and Sn. For these samples, the critical current value (IC) is the current at the time when a voltage of 10 μV per 10 is generated, and the average value of the results of measuring the critical current value of each sample at 4.2 is the first value.
Shown in the table.

From the results shown in Table 1, it can be seen that the I of the sample of the example according to the present invention is increased by about 10% compared to the sample of the comparative example.

〔Effect of the invention〕

As explained above, according to the present invention, since the cross-sectional shape of the filament is approximately circular and the cross-sectional shape of the wire is rectangular, there is an excellent effect of increasing the critical current.

[Brief explanation of drawings]

FIGS. 1(a) and 1(b) are explanatory cross-sectional views of a compound superconducting wire. 1... Filament, 2... Bronze matrix, 3... Barrier 4... Stabilizing material.

Claims (1)

[Claims] A compound superconducting wire having a filament made of a compound superconductor inside and a stabilizing material at the outermost periphery, characterized in that the cross-sectional shape of the filament is approximately circular and the cross-sectional shape of the wire is rectangular. superconducting wire.