JPH0789455B2 - Superconductor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application] The present invention relates to a superconductor in which a large number of insulated superconducting element wires are housed in a metal tube of a refrigerant passage.

(Prior Art) At present, as a superconducting magnet, various studies are being made to apply a forced cooling method to a large magnet for a fusion reactor, a large magnet such as an accelerator magnet, and a specially shaped magnet.

As a superconductor applied to such a system, a forced cooling type superconductor, in which a large number of superconducting element wires are twisted and housed in a stainless steel tube that serves as a refrigerant passage, is excellent in cooling efficiency and mechanically. It is being used a lot because of its high strength.

The forced cooling superconducting hollow conductor, for example Nb ₃ multiple superconducting wire of a multi-filament structure for Sn formed in accordance twisted this wound pressing the outer periphery of a stainless tape, and further vertically served with the stainless sheet at its outer periphery It is manufactured by welding the butt portion and roll-forming it into a rectangular shape, and then performing heat treatment for forming Nb ₃ Sn.

By the way, in this superconductor, when an alternating magnetic field is applied, an AC loss occurs due to the coupling between the wires, which increases the loss of helium in the refrigerant that maintains the superconducting state, and in some cases, changes to the normal conducting state. It may lead to an accident of transfer. When the superconducting wire is a compound-based superconducting wire made of Nb ₃ Sn, for example, Nb ₃
During the heat treatment for forming Sn, there is a problem that the superconducting wires are fused to each other and helium is less likely to flow, which lowers the cooling efficiency. Therefore, in this type of superconductor, it has been proposed to apply an insulating coating such as an oxide film or an inorganic polymer coating film to the surface of the superconducting element wire at the stage of the element wire.

(Problems to be Solved by the Invention) However, such an insulating coating has a problem that it is easily peeled off in a subsequent twisting process or when the whole is processed into a rectangular shape after being accommodated in a stainless pipe. . In particular superconductor elements are compound-based, for example, in the case of superconducting wire, such a Nb ₃ Sn is oxidized film for heat treatment for Nb ₃ Sn formation is performed a long time at 600 to 800 ° C. is thermally decomposed insulation There is a drawback that defects are likely to occur, resulting in an increase in AC loss.

The present invention has been made to solve such a conventional problem, and the insulation performance is improved without the insulating coating peeling off due to heat treatment at high temperature for a long time or external force, whereby a superconductor with a small AC loss is obtained. The purpose is to provide.

[Structure of the Invention] (Means for Solving Problems) That is, the superconductor of the present invention is a forced cooling type or immersion cooling type superconductor in which a large number of superconducting element wires are twisted and inserted into a metal tube. In the above, the surface of the superconducting wire is coated with a Cr film by electroplating 1 to 5 μm as an insulating film.
It is characterized in that it is formed by m.

In the present invention, the surface of the superconducting wire before twisting, Cr is attached by electroplating, then twisted in the same manner as in the conventional method, covering the stainless tube, roll forming and heat treatment through each step of the superconductor can get.

In the present invention, the thickness of the insulating film is set to 1 to 5 μm because when the thickness is less than 1 μm, the dielectric strength is insufficient and is easily worn by an external force, and when it exceeds 5 μm, the flexibility becomes poor and the twisting process is performed. This is because the insulating film is peeled off and heat generated in the wire conductor cannot be quickly transferred to the refrigerant.

In addition to Nb ₃ Sn, Nb ₃ V and Nb ₃ Al can be used as superconducting wires.
Compound based superconducting wire may be used.

The superconductor of the present invention is applicable not only to the forced cooling type but also to the immersion cooling type superconductor. In the case of the immersion cooling type, a metal tube having a large number of holes formed on the wall surface is used.

(Operation) In the present invention, since the insulating thin film of Cr is firmly adhered to the superconducting wire by electroplating, it does not easily peel off even when bending or external force is applied to the wire, and Nb ₃ Sn etc. It is stable without peeling even at the heat treatment temperature for generation. Also Cr plating
Since there is no diffusion of Cr into Cu even at the heat treatment temperature for Nb ₃ Sn formation, the residual resistance ratio (RRR)
The value of o) can be maintained and the level value of pure copper can be maintained.

Further, since the thickness of the insulating coating is as thin as 1 to 5 μm, when the refrigerant flows through the space inside the metal tube, the heat generated in the wire conductor can be quickly transferred to the refrigerant.

(Example) Next, the Example of this invention is described.

FIG. 1 is a sectional view of an embodiment of the present invention. In this superconductor 1, as shown in FIG. 2, a Cr insulating film 3 having a thickness of 1.5 μm is formed on the outer circumference of a 0.61φ superconducting wire 2 by electroplating. And this Nb ₃ Sn superconducting element wire 2 is 3 × 3 × 3
× 4 = 108 strands are twisted together, and the outer circumference of the stainless steel tape 4 is clamped and wound, and the outer circumference of the stainless steel tape is vertically attached and the rectangular stainless pipe 5 is welded.

A cylindrical stainless steel tube is used instead of the rectangular stainless steel tube 5 described above, and the outer diameter is 8.82 so that the void ratio is 32.3%.
mm, an inner diameter of 7.70 mm, wire drawing, and heat treatment at 700 ° C. for 2 hours, and then the vertical specific resistance was determined. The results are shown in the graph of FIG.

As can be seen from FIG. 3, the insulating coatings of the examples have a higher level of vertical specific resistance than other insulating materials, and are excellent as insulating materials.

[Effects of the Invention] As described above, in the superconductor of the present invention, since a thin film of Cr having a thickness of 1 to 5 μm is adhered on the superconducting element wire by electroplating, the superconducting element wire is strong and external force is applied to the superconducting element wire. It is possible to apply an insulating coating that does not easily peel off and that can withstand heat treatment, thereby improving the insulating performance of the insulating coating and reducing the AC loss of the superconductor.

[Brief description of drawings]

FIG. 1 is a sectional view of an embodiment of the present invention, FIG. 2 is an enlarged sectional view of a Nb ₃ Sn superconducting wire, and FIG. 3 is a kind of a film including a superconductor of the embodiment after heat treatment and a vertical specific resistance. It is a graph showing the relationship of. 1 …… Superconductor 2 …… Nb ₃ Sn superconducting wire 3 …… Cr insulating film 4 …… Stainless tape 5 …… Stainless steel tube

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Susumu Shimamoto 576-46 Funaishikawa, Tokai-mura, Naka-gun, Ibaraki Prefecture (72) Inventor Eimoto Suzuki 2-1-1 Oda Sakae, Kawasaki-ku, Kanagawa Prefecture Showa Densen Denwa (72) Inventor Nobuo Aoki 2-1-1 Oda Sakae, Kawasaki-ku, Kawasaki-shi, Kanagawa Showa Electric Cable Co., Ltd. (72) Masamitsu Ichihara 2-1-1 Oda, Kawasaki-ku, Kawasaki-shi, Kanagawa No. 1 Showa Densen Denki Co., Ltd. (72) Inventor Yoshimasa Yoshimasa 2-1-1 Oda Sakae, Kawasaki-ku, Kawasaki-shi, Kanagawa Prefecture No. 1 Showa Densen Denki Co., Ltd. (72) Inventor Tomoyuki Kumano Sakae Oda, Kawasaki-ku, Kanagawa Prefecture 2-1-1 No. 1 Showa Electric Wire & Cable Co., Ltd.

Claims (3)

[Claims] 1. A forced-cooling type or immersion-cooling type superconductor in which a large number of superconducting element wires are twisted and inserted into a metal tube, and a Cr film formed by electroplating as an insulating coating on the surface of the superconducting element wires. 1 to 5 μm is formed. 2. The superconductor according to claim 1, wherein the superconducting element wire is a compound-based superconducting element wire such as Nb ₃ Sn or Nb ₃ Al. 3. The superconductor according to claim 1 or 2, wherein the metal tube is a stainless tube.