JPS63245885A - Connection of superconductive wires - Google Patents

Abstract

PURPOSE:To realize a connection of sufficiently low resistance without reducing current capacity by providing with a coating layer of material with a hardness higher than that of filament materials or an oxide layer existing on them, and connecting the superconductive filament materials with each other through the coating layer by pressure-welding them. CONSTITUTION:Stabilizing base material 2 at the end of superconductive wires 1a, 1b is removed to expose superconductive filament materials 3 for a predetermined length respectively, and a coating layer 4 of material with a hardness higher than that of the superconductive filament materials 3 such as tungsten is formed on their surface by deposition. Parts if the filament materials 3 coated by the coating layer 4 are collected and contained in a sleeve of copper, and pressure is applied to the sleeve 5 from outside to cause plastic deformation. The coating layer 4 is crushed by this, so the surface parts of the superconductive filament materials 3 are pulled out, and noncontaminant faces of the filament materials 3 are pressed-welded and connected with each other, thereby a connection of low resistance can be obtained without reducing current capacity.

Description

[Detailed Description of the Invention] [Object of the Invention] (Technical Field of the Invention) The present invention relates to a method of connecting superconducting wires, and in particular, to a method of connecting superconducting wires, in which the resistance value of the connecting portion is reduced as much as possible without causing a decrease in current capacity. This relates to a connection method that allows for smaller size.

(Prior art) When trying to obtain a magnetic field that is stable for one hour when continuously generating a magnetic field with a superconducting coil.

Usually, a method is adopted in which the superconducting coil is operated in persistent current mode. In this case, the attenuation of the current in the persistent current loop is determined by the resistance value of the connection between the superconducting wires that are present to constitute the persistent current loop and the inductance value of the superconducting coil. That is, in order to reduce the attenuation of the current, it is necessary to make the resistance value of the connection part as small as possible.

By the way, a typical superconducting wire has a plurality of superconducting filaments embedded in a stabilizing base material such as copper or aluminum. For this reason, it is recommended as a means of connecting superconducting wires.

Conventionally, a method has been adopted in which stabilizing base materials are connected to each other by soldering or the like. With this connection method, the resistance value at the connection part can be reduced by lengthening the connection part. However, since the stabilizing base material is a normal conducting material and is not essentially superconducting, the resistance value at the connection part is set to 10.
It was not possible to reduce the resistance to about 9Ω or less.

In addition, a connection method called diffusion bonding is being considered as a method of shortening the connection length and realizing a very small connection resistance value. This is a method of connecting superconducting filament materials by heating them in a vacuum and applying pressure. In this connection method, 10-
A connection of 12Ω or less can be achieved. However, when connected in this manner, the current capacity of the connected portion is usually reduced by more than 50% compared to the case of a bare wire. This is thought to be caused by the surface of the superconducting filament material being contaminated by oxidation, or the processing state of the superconducting filament material changing due to the heat applied during pressurization.

On the other hand, it is a simpler connection method than diffusion bonding.

Attempts have been made to use cold welding, but the reality is that a satisfactory resistance value has not yet been achieved.

(Problems to be Solved by the Invention) As described above, with the conventional connection method, it is difficult to realize a connection of about 10-12 Ω or less without reducing the current capacity with a simple process.

Therefore, the present invention aims to provide a method for connecting superconducting wires that can realize a connection of about 1042 Ω or less without reducing the current capacity and that has a simple process. After providing a coating layer made of a material harder than the filament material or the oxide layer existing on it on the surface of the superconducting filament material located in the part used for connection, the superconducting filament materials are connected to each other through this coating layer. They are connected by pressure welding.

(Function) The hard coating layer provided on the surface of the superconducting filament material collapses when subjected to pressure and is rolled in the direction of weak pressure. At this time, the surface of the superconducting filament material is torn off.

This action removes oxides, etc. on the surface of the superconducting filament material, revealing the surface of pure filament material, and these clean surfaces are pressure-welded to each other.See the drawings below for an embodiment of the connection method of the present invention. I will explain while doing so.

First, as shown in FIG. 1('a), superconducting wires 1a and lb to be connected are prepared. In the case of this embodiment, the superconducting wires 1a, lb are constructed by embedding a plurality of superconducting filament materials 3 made of NbTi in a stabilizing base material 2 made of copper.

The stabilizing base material 2 at the ends of these superconducting wires 1a and lb to be connected is removed to expose a predetermined length of each superconducting filament material 3. Next, as shown in FIG. 3B, a coating layer 4 made of a material harder than the superconducting filament material 3, such as tungsten, is formed on the surface of the exposed portion of each superconducting filament material 3 by vapor deposition.

Next, as shown in the same figure (c), each superconducting wire la, lb
The portion of the superconducting filament material 3 covered with the coating layer 4 is placed together in a copper sleeve 5, and a pressure of about 100,100 O' is applied to this sleeve 5 from the outside.
This is plastically deformed to complete the connection work.

When the superconducting filament material 3 is connected under pressure in this manner, the coating layer 4 covering the surface of the superconducting filament material 3 is crushed and rolled in the direction of the weaker pressing force as shown in FIG.

At this time, the fact that the coating layer 4 has a higher hardness than the filament material effectively acts to tear off the surface portion of the superconducting filament material 3. This tearing reveals surfaces of pure, uncontaminated filament material, which are then welded together as shown in FIG.

With such a connection method, the superconducting filament material 3
Since a contamination layer such as an oxide layer existing on the surface of the electrode can be reliably removed, the connection can be made with a resistance of about 10-12 Ω or less without reducing the current carrying capacity. In addition, with this connected blade method, there is essentially no need to perform pressure welding in a vacuum or to heat it, so
Connection work can be extremely simplified.

Note that the present invention is not limited to the embodiments described above. That is, in the embodiment described above, each superconducting wire 1a, lb
The stabilizing base material 2 of the part used for connection is removed to expose a predetermined length of the superconducting filament material 3, and these are connected in a switchback manner using a sleeve.
The superconducting filament materials may be brought together and bonded under pressure. Further, pressure welding work is sufficient in the atmosphere, but there is no problem even if it is performed in a vacuum or in a high temperature atmosphere.

[Effects of the Invention] As described above, according to the present invention, it is possible to provide a superconducting wire connection method that can realize a sufficiently low resistance connection with only a simple culm without reducing the current capacity.

[Brief explanation of the drawing]

FIGS. 1A to 1C are diagrams for explaining an embodiment of the connection method of the present invention in the order of steps, and FIG. 2 is a diagram for explaining the connection principle of the connection method of the present invention. la, lb...superconducting wire, 2...stabilizing base material, 3.
...Superconducting filament material, 4...Covering layer, 5...
sleeve. Applicant's agent Patent attorney Takehiko Suzue (a) Person (b) 1,:I Figure 2

Claims (2)

[Claims] (1) When connecting superconducting wires to each other, the surface of the superconducting filament material located in the part used for connection of each superconducting wire is coated with a material harder than the filament material or the oxide layer existing thereon. 1. A method for connecting superconducting wires, characterized in that after a layer is provided, superconducting filament materials are connected by pressure welding through the coating layer. (2) The method for connecting superconducting wires according to claim 1, wherein the coating layer is formed by any one of electroplating, vapor deposition, and sputtering.