JPH06150993A - Nbti alloy superconducting wire with connection section - Google Patents

Abstract

PURPOSE:To provide a superconducting wire with a connection section having the stable superconducting characteristic of the connection section by covering NbTi alloy filaments of the connection section with a Cu stabilizer, and preventing pinning centers in the NbTi alloy filaments from disappearing by the heat treatment when the Cu stabilizer is coupled with the NbTi alloy filaments. CONSTITUTION:A continued superconducting wire contains a connection section of NbTi alloy superconducting wires 1, and the superconducting wires 1 contain Ta artificial pining centers in NbTi alloy filaments 2. The filaments 2 exposed at the end sections of the superconducting wires 1 are twisted, the portion is covered with a Cu tube 4, Cu powder 5 is filled in the Cu tube 4, and the whole is compressed, heat-treated, and integrated to form the connection section.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a NbTi-based alloy superconducting wire containing a connecting portion including a connecting portion between NbTi-based alloy superconducting wires.

[0002]

2. Description of the Related Art Generally, a superconducting wire has a structure in which a superconducting filament made into an ultrafine wire is embedded in a matrix having low resistance and excellent thermal conductivity based on the stabilization theory. As a result, electromagnetic instability such as magnetic flux jumping is suppressed, and a stable current can flow.

When a magnet or the like is formed of superconducting wires, it is often necessary to connect the superconducting wires to each other because the length of the superconducting wires is finite. Conventionally, Nb
When connecting a Ti-based alloy superconducting wire, N that should be connected
The filaments exposed at the end of the bTi-based alloy superconducting wire were gathered together, and indium or solder was melted into the part at a relatively low temperature for connection.

The reason why the low melting point metal such as solder is used for the connection is as follows. That is, in the NbTi alloy superconducting wire, the pinning center for pinning the magnetic flux is α-precipitated in the NbTi alloy filament.
This is because it is Ti, and this α-Ti dissolves and disappears as a solid solution when heated to about 450 ° C. or higher, so that it cannot be heated to a very high temperature during connection.

[0005]

However, in the superconducting wire having the above connecting portion, solder or the like having a higher resistance than a stabilizing metal such as copper or aluminum is provided around the NbTi alloy filament in the connecting portion. Since it exists, the stability against disturbance is poor, and there are problems such as sudden quenching at the connection.

[0006]

In order to improve the stability of the connecting portion, it is effective to dispose a stabilizing metal such as copper or aluminum around the NbTi alloy filament of the connecting portion. However, it is necessary to dispose a stabilizing metal in the connection portion and to perform a metal bonding between the filament and the stabilizing metal in order to exert its function, and for that purpose, heat treatment at a high temperature is required. When heat treatment is performed at high temperature, α-Ti is solid-dissolved as described above and the pinning center disappears, so the Jc of the connection part decreases, the operating current exceeds Jc at the connection part, and the result of normal conduction transition occurs. Becomes

Therefore, in the present invention, an artificial pinning center made of, for example, Ta or Au is introduced into the NbTi-based alloy filament as a superconducting wire so that the pinning center does not disappear even when heat-treated at a high temperature during connection. The filaments exposed at the end of the NbTi alloy superconducting wire to be connected are assembled (twisted, bundled, or braided), and the connecting part is made of metal. The structure is such that the metal tube is covered with a tube, the powder of the stabilizing metal is filled in the metal tube, and then the whole is compressed and heat-treated to form an integrated structure.

[0008]

By doing so, the NbTi-based alloy filament in the connecting portion is covered with the stabilizing metal, and the electromagnetic stability of the connecting portion is enhanced. Further, since the artificial pinning center introduced into the NbTi alloy filament does not disappear at the temperature of the heat treatment for binding the stabilizing metal to the NbTi alloy filament, the pinning center remains in the filament of the connecting portion, and the superconducting characteristic The decrease is extremely small.

[0009]

Embodiments of the present invention will now be described in detail with reference to the drawings. FIG. 1 shows the ends of two NbTi-based alloy superconducting wires 1 to be connected. Each superconducting wire 1 has a large number of Nb
The Ti-based alloy filament 2 is embedded in a Cu matrix 3. Further, each filament 2 is introduced with Ta as an artificial pinning center, and α-Ti which is a conventional precipitation type pinning center does not exist. The superconducting wire 1 has an outer diameter of 0.5 mm, the filament 2 has an outer diameter of 5 μm, and the number of filaments 2 is 6,270.

At the time of connection, first, as shown in FIG. 1, the matrix 3 at the end of the superconducting wire 1 is removed by etching,
The filament 2 is exposed. Next, as shown in FIG. 2, the filaments 2 exposed at the ends of the superconducting wire 1 are twisted together. After that, as shown in FIG. 3, a Cu tube 4 is covered from the twisted portion of the filament 2 to the end of the Cu matrix 3, and Cu powder (rrr = 200) 5 is filled therein. As a result, the filament 2 is embedded in the Cu powder 5. Next, compress it from the outer circumference in a vacuum,
The filament 2, the Cu powder 5, and the Cu tube 4 are metal-bonded and integrated by heating to 00 ° C. Thereby, as shown in FIG. 4, it is possible to obtain the connecting portion 7 in which the filament 2 is embedded in the Cu stabilizing material 6.

The superconducting wire 1 including the connecting portion 7 obtained as described above is immersed in liquid helium (4.2 K) as shown in FIG. 5 and an electric current is applied to the superconducting wire 1 on both sides of the connecting portion 7. The voltage tap 8 was taken to examine the voltage-current characteristics. For comparison, the same method was used to examine the voltage-current characteristics of the superconducting wire having no connection part and the conventional superconducting wire having a solder connection part. The result is shown in FIG. According to this, in the conventional product by solder connection, quenching occurs due to magnetic flux jump due to some disturbance, but in the product of this example, voltage is generated due to minute resistance due to contact bonding of filaments, It can be seen that the magnetic flux jump is suppressed and a stable current is flowing.

Next, a one-turn coil of 0.3 μH was made from the superconducting wire including the connecting portion of the above-mentioned embodiment, cooled to 4.2 K, and the decay of the persistent current was measured. For comparison, the same coil was made with the conventional superconducting wire having the solder connection portion, and the same measurement was performed. The result is shown in FIG. 7. according to this,
In the conventional product with solder connection, there is a resistance after the normal conduction transition that occurs due to the magnetic flux jump, so the current is abruptly attenuated at a certain point (the point when an external disturbance occurs). It is understood that is only the attenuation due to the minute resistance due to the filament contact, and does not occur due to the magnetic flux jump and the rapid resistance generation due to the normal conduction transition.

[0013]

As described above, according to the present invention, the NbTi-based alloy filament in the connection portion is covered with the stabilizing metal, and the NbTi-based alloy is heat-treated when the stabilizing metal is combined with the NbTi-based alloy filament. Since the pinning center in the filament does not disappear, it is possible to obtain a superconducting wire with a connecting portion in which the superconducting characteristics of the connecting portion are stable.

[Brief description of drawings]

FIG. 1 is an NbTi with a connecting portion according to an embodiment of the present invention.
The top view which shows the 1st step which manufactures a system type alloy superconducting wire.

FIG. 2 is a plan view showing the next step of FIG.

FIG. 3 is a plan view showing the next step of FIG.

FIG. 4 is a cross-sectional view showing a NbTi-based alloy superconducting wire with a connecting portion according to an embodiment of the present invention manufactured by the method of FIGS. 1 to 3.

FIG. 5 is an explanatory view showing a test method of a NbTi-based alloy superconducting wire containing a connection part.

FIG. 6 is a graph showing voltage-current characteristics of the example product of the present invention and other comparative products in a superconducting state.

FIG. 7 is a graph showing permanent current attenuation characteristics of an example product of the present invention and a conventional product.

[Explanation of symbols]

 1: NbTi-based alloy superconducting wire 2: NbTi-based alloy filament 3: Cu matrix 4: Cu pipe 5: Cu powder 6: Cu stabilizing material 7: Connection part

Claims (1)

[Claims] 1. A continuous NbTi-based alloy superconducting wire including a connecting portion between NbTi-based alloy superconducting wires, wherein the superconducting wire comprises an artificial pinning center in an NbTi-based alloy filament. The filaments exposed at the end of the NbTi-based alloy superconducting wire to be connected are gathered, the portion is covered with a metal tube, and the metal tube is filled with powder of stabilizing metal, and the whole is compressed and heat treated to be integrated. Nb with connection part characterized by comprising
Ti-based alloy superconducting wire.