JPH0821272B2 - 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 pipe 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.

This forced cooling type superconducting hollow conductor is obtained by, for example, twisting many superconducting wires having a multi-filament structure for forming Nb ₃ Sn, winding the outer circumference with a stainless tape and winding the stainless sheet vertically around the outer circumference. 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 system, for example, a superconducting wire made of Nb ₃ Sn, the N
During the heat treatment for b ₃ Sn formation, there is a problem that the superconducting wires are fused and helium is less likely to flow, which lowers the cooling efficiency. Therefore, in this type of superconductor, it has been proposed to provide an insulating coating such as an oxide film or an inorganic polymer coating film on 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 a superconducting wire consisting of Nb ₃ Sn is heat treatment for Nb ₃ Sn formation 600 to 800 ° C.
Since it is carried out for a long time, the oxide film is likely to be thermally decomposed to cause insulation failure, resulting in an increase in AC loss.

In order to solve such conventional problems, the present inventors applied for a superconductor having high insulation performance, that is, a small AC loss, without the insulation coating peeling off due to heat treatment at high temperature for a long time or external force ( Japanese Patent Application 61-227799
issue). This is one in which a Cr film layer was formed by electroplating on the surface of a superconducting element wire.After that, as a result of diligent research, it was found that the insulation performance was significantly improved depending on the state of the Cr film layer. . It is an object of the present invention to provide a superconductor having such an improved Cr insulating layer.

[Structure of the Invention] (Means for Solving the 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. The body is characterized in that a porous Cr plating layer is formed on the surface of the superconducting element wire as an insulating coating in a thickness of 1 to 5 μm.

In the present invention, on the surface of the superconducting element wire before twisting,
Cr is attached by electroplating, and then twisted in the same manner as in the conventional method, and the superconductor is obtained through the steps of coating the stainless tube, roll forming and heat treatment. Since the Cr layer is made porous, the current density during plating is set to be several times higher than in the case of forming an ordinary plating layer.

In the present invention, the thickness of the insulating coating 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. This is because the insulating coating is peeled off in the above step and the heat generated in the wire conductor cannot be quickly transferred to the refrigerant.

Furthermore, as superconducting element wires, in addition to Nb ₃ Sn, V ₃ Ga and Nb ₃
A compound-based superconducting element wire such as Al 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.

(Function) In the present invention, since the porous Cr insulating thin film 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 It is stable and does not peel even at the heat treatment temperature for producing Sn and the like. Also
Since Cr plating does not diffuse Cr into Cu even at the heat treatment temperature for generating Nb ₃ Sn, the residual resistance ratio (RRR; Residual Resista
It is possible to maintain the level value of pure copper without lowering the nce ratio).

Furthermore, 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 porous Cr insulating film 3 having a thickness of 1.5 μm is formed on the outer periphery of a 0.61 mmφ superconducting wire 2 by electroplating at a current density five times higher than usual. This Nb ₃ Sn superconducting element wire 2 is twisted in 3 × 3 × 3 × 4 = 108 pieces, and a stainless tape 4 is press-wound around its outer circumference. The shaped stainless tube 5 is covered.

A cylindrical stainless tube is used in place of the rectangular stainless tube 5 described above, and the outer diameter is set to 82.3 so that the void ratio is 32.3%.
After drawing wire to 82 mm and inner diameter of 7.70 mm and heat-treating at 700 ° C. for 2 hours, the vertical specific resistance was determined. The results are shown in the graph of FIG.

The term "chrome coating" in the figure refers to the case where the Cr plating layer is formed at a current density of 1/5 of that in the above embodiment.

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, since the superconductor of the present invention has the porous Cr plating layer having a thickness of 1 to 5 μm formed on the superconducting element wire, the superconducting element is strong and even if an external force is applied to the superconducting element wire. An insulating coating that does not easily peel off and that can withstand heat treatment can be applied, whereby the insulating performance of the insulating coating can be improved and the AC loss of the superconductor can be reduced without increasing the thickness of the plated layer.

[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 front page (72) Inventor Hidemoto Suzuki 2-1-1, Oda Sakae, Kawasaki-ku, Kawasaki-shi, Kanagawa Prefecture Showa Cable Denki Co., Ltd. (72) Masamitsu Ichihara, Sakae Oda, Kawasaki-ku, Kawasaki-shi, Kanagawa 2-1-1 No. 1 Showa Cable Denki Co., Ltd. (72) Inventor Shiroo Nagaoka 2-1-1 1-1 Showa Densen Denki Co., Ltd. (72) Inventor Mitsuhisa Harada Kawasaki Kanagawa 2-1-1 Oda Sakae, Kawasaki-ku, Showa Electric Wire & Cable Co., Ltd. (72) Inventor Nobuo Aoki 2-1-1, Odae Sakae, Kawasaki-ku, Kawasaki-shi, Kanagawa (56) References Special Kai 63-81709 (JP, A) JP-A 64-21826 (JP, A)

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, wherein porous Cr plating is applied as an insulating coating on the surface of the superconducting element wires. A superconductor characterized by forming a layer of 1 to 5 μm. 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.