JPH04282575A - How to connect superconducting wires - Google Patents

Abstract

PURPOSE:To set a resistance value of a connecting part to be less than 10<-14>OMEGA and to provide a connection method for superconductive filament materials themselves in the connection of superconductive wires. CONSTITUTION:The surface of a superconductive filament connecting part which is bared from a stabilized material is irradiated by an ion beam, thereby, the stabilized material and oxides attached to the surface of the filament material are removed. After the connecting part of the filament material is cleaned, supersonic wave connection or pressure connection is performed. Because the resistance of the connecting part of the superconductive wire can be less than 10<-14>OMEGA, the resistance value is stable even in a strong magnetic field for a long time.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a method for connecting superconducting wires, and in particular, a method for connecting superconducting wires in order to obtain a connection that has low electrical resistance and is stable for a long time even in a high magnetic field. Regarding.

0002

2. Description of the Related Art A typical metallic superconducting wire has a structure in which a plurality of superconducting filaments are embedded in a stabilizing matrix of a normal conducting metal such as Cu, Cu--Ni alloy, or Al. When this superconducting wire is actually used, there is a limit to the length of each superconducting wire, and the structure of the device in which the superconducting wire is used requires a complex shape. , the connection between superconducting wires is essential. Due to the characteristics of the superconducting wire, this connection requires that the electrical resistance of the connection be as small as possible.

[0003] As a method for connecting superconducting wires, Japanese Patent Application Laid-open No. 1983-
As shown in Publication No. 16207, after removing the stabilizing material at the connecting part of the superconducting wire and exposing all the superconducting filament material, the superconducting filament materials to be connected are soldered or mechanically crimped. There is a way to do it. However, in soldering, a compound is generated between the filament material and the solder material, deteriorating the characteristics, and the resistance of the connection portion cannot be lowered to 10 −9 Ω or less.

[0004] When using the crimping method, 10-12
Although it is possible to reduce the connection resistance to about Ω, the connection characteristics are greatly affected by slight differences in connection conditions, making it impossible to obtain a stable connection.

[0005] On the other hand, as a connection method for reducing connection resistance and stabilizing the connection portion, JP-A-60-35478 proposes an ultrasonic bonding method for filament materials. This method is quite effective in reducing connection resistance, but when exposing the superconducting filament material embedded in the stabilizing material with a nitric acid solution, it is difficult to use the stabilizing material or oxidized There is a problem that objects are not completely removed. For this reason, ultrasonic bonding or pressure bonding must be performed with a stabilizing material, oxide, etc. attached around the filament material, and there is a problem that the resistance of the connecting portion cannot be lowered to 10-14 Ω or less.

[0006]

[Problems to be Solved by the Invention] As mentioned above, if a superconducting filament material is ultrasonically bonded or pressure welded with a stabilizing material or oxide having poor superconducting properties attached around it, the superconducting filament material The electrical resistance of the conductive wire connection is 10-14 Ω.
There was a problem that it could not be lowered below.

The object of the present invention is to reduce the resistance of the connection part to 10-1.
4. It is an object of the present invention to provide a method for connecting superconducting filament materials as described below.

[0008]

[Means for Solving the Problems] In order to achieve this object, the present invention irradiates an ion beam onto the surface of the connection portion of the superconducting filament material exposed from the stabilizing material, so that the surface of the superconducting filament material adheres to the surface of the filament material. After removing any stabilizing materials and oxides and cleaning the joints, ultrasonic welding or pressure welding is performed.

By the way, since the filament material exposed from the stabilizing material is bundled with multiple filaments, even if the surface of the superconducting filament material is irradiated with an ion beam in this state, the ion beam will not cover the entire surface of the filament material. There is a problem that the irradiation is not uniform. Therefore, in order to solve this problem, multiple filament materials are separated by applying rotation, vibration, or rotation and vibration simultaneously or periodically to the filament material, and the surface of the connection part of all the multiple filament materials is This ensures uniform irradiation with the ion beam.

[0010] The present invention is directed to known alloy-based superconducting wires,
For example, it is applicable to superconducting wires such as Nb-Ti or compound-based Nb3-Sn.

[0011]

[Operation] Experiments have shown that by irradiating the joint surface of superconducting filament material with an ion beam, foreign substances such as stabilizing materials or oxides attached to the surface of the filament material can be removed by the sputtering action of the ion beam. found. That is, the sputtering effect of the ion beam can remove stabilized copper, oxide films, etc. that cannot be removed by chemical etching, and clean the surface of the connection portion of the filament material. With this method, the filament materials can be joined metallically by ultrasonic bonding or pressure welding with the surface of the filament materials sufficiently cleaned, and the resistance of the connection part can be reduced to 10-14.
It can be lowered to below Ω.

Further, in the connection method of the present invention, after removing the stabilizing material such as copper to expose the superconducting filament material, the surface of the exposed joint portion of the filament material is irradiated with an ion beam. Next, the filament materials whose connecting portion surfaces have been cleaned by this method are connected to each other by ultrasonic bonding or pressure welding. Furthermore, if necessary, it is also effective to surround the filament material with an auxiliary connecting wire made of the same material as the filament material, or to bundle the filament material, insert it into a copper sleeve, and press it.

[0013]

[Example] [Example 1] (1) In this example, a bonding example of a superconducting wire in which 100 superconducting filaments made of an Nb-Ti alloy with a diameter of 50 μm are embedded in a copper stabilizing material shows. First, the stabilized copper at the connection portion of the superconducting wire is removed using a nitric acid solution to expose the filament. Next, the exposed surface of the superconducting filament material is irradiated with an argon ion beam to remove the stabilized copper and oxides adhering to the surface of the filament material.

The argon ion beam irradiation conditions in this case are, for example, irradiation at 3×10 −3 Torr for 30 minutes. Further, the argon ion beam is irradiated while imparting rotational motion to the superconducting wire so that the entire surface of the superconducting filament material is uniformly irradiated.

Next, the two filament portions of the superconducting wires whose surfaces have been cleaned by the method described above are bundled, twisted together if necessary, and ultrasonically bonded at three points. The ultrasonic bonding conditions at this time were a pressure of 70 to 120 N, a frequency of 20 kHz, a time of 0.7 to 3 sec, and an amplitude of 20 μm. Next, the filament material joined by the above method is surrounded by auxiliary connecting wires made of the same material as the filament material, further bundled and inserted into a copper sleeve, and an external load of 100 kgf is applied.
Crimp with. As a result of measuring the connection resistance of superconductors connected by this method, the test temperature was 4.2K and the magnetic field was 0.
A resistance value of 10-15 Ω or less was obtained under the conditions of 5T and current of 1000A.

[Example 2] In this example, two superconducting wires similar to those in Example 1 are first cleaned with an argon ion beam in the same manner as in Example 1. The filament portions of the two cleaned superconducting wires are connected by crimping. Next, the connecting portion is surrounded by an auxiliary connecting wire made of the same material as the filament material, further bundled, inserted into a copper sleeve, and crimped from the outside with a load of 100 kgf. As a result of measuring the connection resistance of superconductors connected by this method,
Test temperature 4.2K, magnetic field 0.5T, current 1000A
Under these conditions, a resistance value of 10-14 Ω or less was obtained.

[Example 3] In this example, a material with a diameter of 5 mm made of a Nb3-Sn compound was placed in an aluminum stabilizing material.
This is an example of a superconducting wire in which 100 superconducting filaments of 0 μm are embedded. The stabilized aluminum at the connection portion of the superconducting wire is removed using nitric acid solution to expose the filament material. Next, the exposed surface of the superconducting filament material is irradiated with an argon ion beam to remove aluminum and oxides adhering to the surface of the filament material.

In this case, the etching conditions using argon ions are 3×10 −3 Torr for 60 minutes. Furthermore, the argon ion beam is irradiated while periodically imparting rotational motion and vibration to the superconducting wire so that the entire surface of the superconducting filament material is uniformly irradiated with the argon ion beam.

Next, by this method, the two filament portions of the superconducting wires whose filament surfaces have been cleaned are bundled, twisted together if necessary, and ultrasonically bonded at three points. The ultrasonic bonding conditions at this time are pressure 70-120N.
, frequency 20kHz, time 0.7 to 3s, amplitude 20μ
It is m. The filament materials connected by this method are surrounded by auxiliary connecting wires made of the same material as the filament materials, further bundled, inserted into an aluminum sleeve, and crimped from the outside with a load of 100 kgf.

According to an example of measuring the connection resistance of superconductors connected by this method, the test temperature was 4.2K and the magnetic field was 0.
Under conditions of 5T and current of 2000A, a resistance value of 10-15 Ω or less was obtained.

[0021]

Effects of the Invention According to the present invention, the resistance of the connection portion can be reduced to 10-
The connection resistance can be reduced to 14 Ω or less, and the connection resistance is stable for a long time even in a high magnetic field.

Claims (2)

[Claims] 1. A method for connecting a superconducting wire in which a plurality of superconducting filaments are embedded in a normal conducting metal, wherein after exposing the superconducting filament from the normal conducting metal,
A method for connecting superconducting wires, characterized in that before connecting the superconducting filament materials by ultrasonic bonding or pressure welding, the surface of the joint portion of the superconducting filament materials is irradiated with an ion beam. 2. According to claim 1, rotational motion or vibration is applied to the superconducting wire individually, simultaneously or periodically, and the surface of the connecting portion of the superconducting filament material is irradiated with the ion beam. How to connect superconducting wires.