JPH06163140A - Connecting method for superconductor - Google Patents

Abstract

PURPOSE:To suppress heat generation to a fine quantity in a connection part of a superconductor and further to hold dimension to a minimum in the connection part. CONSTITUTION:A filament 6a of fixed length is exposed from a superconducting wire 3a stored in a conduit of one superconductor 1a, and similarly a filament 6b is exposed from a superconducting wire 3b stored in a conduit of the other superconductor 1b. Both the filaments 6a, 6b are made into a suitable number of bundles, piled together with each other and further coated with a connecting piece 7, to solid phase connect the fellow filaments by holding a predetermined temperature and pressure. Hereafter, the periphery of the superconducting wires 3a, 3b in a connection part is coated with a case 10 so as to form air-tight space.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for connecting superconducting conductors of a superconducting coil used in equipment for generating a high magnetic field.

[0002]

2. Description of the Related Art One of the superconducting coils that has been developed in recent years is a forced cooling type superconducting coil. Since this forced cooling type superconducting coil can directly insulate the conductor, it has features such as extremely high strength in terms of structure and excellent insulation characteristics in terms of performance. It is said that application of the method is desirable. Forced cooling method As a superconducting conductor, dozens to hundreds of superconducting wires are twisted together, and the outer circumference is covered with a conduit made of stainless steel or the like to form a cooling passage. -Conduit) type superconducting conductor has been proposed. However, as the size of the superconducting coil has increased, the manufacturing method of the superconducting conductor has recently changed greatly from a seamless method to a method in which superconducting conductors are connected to each other and finished. In this case, it is required that the quality be as stable as a seamless one, and for example, a method of connecting superconducting conductors by soldering is used.

[0003]

The superconducting wire constituting the forced cooling type superconducting conductor has a stabilizing material made of copper or aluminum arranged on the outer peripheral portion of the filament. When this superconducting wire is connected, since the filament is connected through the stabilizing material, a current also flows through the stabilizing material, and heat is generated due to the resistance of the material.

Such an increase in resistance greatly impairs the characteristics of the superconducting conductor, and attempts have been made to reduce the resistance at the connection portion by increasing the connection length, for example. However, with this method, the connecting portion becomes large, and as a result, the superconducting coil must be made larger.

Therefore, an object of the present invention is to provide a method of connecting superconducting conductors, which can suppress a slight amount of heat generation at the connecting portion of the superconducting conductor and can keep the size of the connecting portion to a minimum.

[0006]

In order to achieve the above object, in the connecting method of the present invention, the sheath and the stabilizing material are removed from the superconducting wire contained in one conduit to expose a filament of a certain length. In the same way, expose the filaments from the superconducting wire in the other jets, put a suitable number of both fillers on top of each other, and then cover the overlapped filaments with a connecting piece whose length corresponds to the exposed length. Characterized in that the filaments are solid-phase bonded to each other while maintaining a predetermined temperature and pressure in a vacuum or an inert gas atmosphere, and covered with a case so as to form an airtight space around the superconducting wire at the connecting portion. Is.

[0007]

Each of the superconducting wires contained in the conduit has tens to hundreds of filaments whose periphery is fixed by the stabilizing material. To expose this filament, the stabilizing material is melted with the sheath in the first step. Next, an appropriate number of exposed filaments for joining are bundled and overlapped, and the filaments are covered with a connecting piece having a length corresponding to the exposed length. Next, the process of joining filaments is performed. The joining process using this connecting piece is carried out under vacuum or in an appropriate inert gas atmosphere while maintaining the heating temperature and pressure under the determined conditions.

According to this method, since the filaments are directly bonded to each other without the interposition of the stabilizing material in the connecting portion, it is possible to obtain a good connecting portion which does not generate heat as a superconducting wire.

Following the above steps, the superconducting wire of the connecting portion is covered with a case which forms an airtight space. The space formed by this case is for flowing the cooling medium, and maintains the superconducting state of the filament.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A connection method according to the present invention will be described in detail below with reference to the drawings.

A superconducting conductor according to one embodiment of the present invention shown in FIG. 1 is of a cable-in-conjet type, and superconducting conductors 1a and 1b connected to each other have superconducting wires 3a and 3b, respectively. The superconducting wires 3a, 3b are connected by a connecting piece 7, and the surroundings of the superconducting wires 3a, 3b at the connecting portion are covered with a case 10.

A typical cable-in-conduit type superconducting conductor 1a, 1b has a structure as shown in FIG. That is, a conduit 2 made of a material such as stainless steel and several hundred to several thousand made of copper and Nb-Ti alloy-based materials are contained within the conduit 2 having a diameter of about 1 mm. It consists of a superconducting wire 3. The reason why the conduit 2 is used is to allow a cooling medium to flow inside and to maintain a stable superconducting state.

The structure of the superconducting wire 3 is shown in FIG. This consists of a sheath 4 made of copper with a diameter of 1 mm, a stabilizing material 5 made of copper filling the inside of this sheath 4, and several tens to several hundreds of Nb-Ti-based materials of several μm and several tens of μm. It consists of a filament 6 of a book. The stabilizer 5 is used in a ratio of 3 to 1 to fill the entire circumference of the filament 6.

Details of the connection piece 7 and the case 10 will be described in the description of the connection procedure.

Next, a connecting method using the connecting piece 7 will be described. First, by removing the conduit 2 of the superconducting conductors 1a and 1b connected as shown in FIG. 4, the superconducting wire 3a,
Expose 3b. Next, this exposed superconducting wire 3
The tip portions of a and 3b are immersed in a nitric acid solution or the like to dissolve the sheath 4 and the stabilizing material 5, and the filaments 6a and 6b are exposed as shown in FIG.

Next, as shown in FIG. 6, the superconducting wires 3a, 3
b is made into a bundle of about 5 to 10 and both filaments 6a and 6b are superposed on each other.

Next, the filaments 6a and 6b of the superconducting wires 3a and 3b are connected to each other using the connecting piece 7. As shown in FIG. 7, the connection piece 7 of the present embodiment is composed of a groove-shaped lower member 8 and a flat plate-shaped upper member 9 made of copper foil, and is sufficient to cover the exposed filaments 6a and 6b. The lower member 8 is assembled so that the lower member 8 covers three of the four directions and the remaining one direction is covered by the upper member 9.

Next, the assembled connection piece 7 is placed in a vacuum furnace and the filaments 6a and 6b are solid-phase bonded to each other while maintaining a predetermined temperature and pressure. The joining conditions are adjusted so that the superconducting wires 3a and 3b and the filaments 6a and 6b are not oxidized, the heating temperature is set to 500 ° C. or lower which is the upper limit temperature at which the superconducting characteristics are not deteriorated, and the pressure is set to the filament 6
It is preferable that a and 6b are metallically bonded to each other and are connected within a range of 20 kgf / mm ² or less, which is a range that does not affect superconducting properties.

By the way, the filaments 6a and 6b are bonded together.
In addition to each other, between the lower member 8 and the upper member 9, the connection piece 7
And the filaments 6a and 6b, and further between the connection piece 7 and the superconducting wires 3a and 3b. The shape after completion of the connection by the connection piece 7 is shown in FIG. According to this connection procedure, several tens to several hundreds of superconducting wires 3a, 3b are repeatedly connected, and superconducting conductors 1a, 1b as shown in FIG.
Can be obtained. After this, the cylindrical case 1 shown in FIG. 1 that covers the superconducting wires 3a and 3b so that the cooling medium can flow into the superconducting wires 3a and 3b connected by the connection piece 7
0 is set. The case 10 is formed airtight inside except for the connecting portions with the conduit 2 formed at both ends so as to form cooling passages around the superconducting wires 3a and 3b, and is sealed at the joint with the conduit 2. Welding is done to prevent leakage of the cooling medium.
The appearance of the case 10 after the seal welding is performed is shown in FIG. In the figure, reference numeral 11 is a welded portion. A cooling medium outlet pipe 12 can be connected to the case 10.

Since the filaments 6a and 6b are directly joined to the superconducting conductor produced by the above connecting method, there is no interposition of the stabilizing material 5 of the superconducting wire 3 unlike the case of connecting by soldering, and the filament 6a, A current flows only through 6b, and no heat is generated. If the superconducting state of the filaments 6a, 6b collapses for some reason, a current flows through the stabilizing material 5 and heat is generated, but the superconducting conductors 1a, 1b
Since b and the case 10 are integrated, heat is cooled by the surrounding cooling medium, and the superconducting state of the filaments 6a and 6b is restored. Therefore, the heat generation can be suppressed to a very small amount. Further, since the resistance at the connection portion is close to zero, it is not necessary to take a large connection area, and the size can be reduced.

Although the atmosphere during filament bonding in the above embodiment is described as a vacuum, it may be bonded in an inert gas atmosphere such as an argon gas atmosphere instead.

Next, another embodiment will be described with reference to FIG.

The connection procedure of the above embodiment is the superconducting wires 3a, 3
This is a method in which b is bundled into a plurality of bundles and the filaments 6a and 6b are connected to each other in a predetermined order, but during this connection procedure, heating and pressurizing operations must be repeated. In order to reduce the number of heating and pressurizing operations, the method of simultaneously heating and pressurizing shown in FIG. 11 is used. In this method, a pressure plate 13a and a large number of holding plates 13b are provided so that a bundle of superconducting wires 3a and 3b assembled into a plurality and a bundle are not connected (and pressure is evenly applied between them). The jig 14 is used. The pressurizing direction is the direction indicated by the arrow in the figure.

Further, it is preferable to form a passage for the cooling medium between the bundles of the superconducting wires 3a and 3b, so that the cooling effect can be further improved.

[0025]

As described above, in the present invention, the filament of a certain length is exposed from the superconducting wire contained in the conduit of one superconducting conductor, and the filament is extracted from the superconducting wire contained in the conduit of another superconducting conductor. Similarly, both filaments are put in an appropriate number of bundles and stacked on top of each other, and then the filaments are covered with a connecting piece, and the filaments are solid-phase bonded while maintaining a predetermined temperature and pressure. Since it is covered with a case so as to make an airtight space around it, there is no heat generation at the connection part of the superconducting conductor, or even if there is, it can be suppressed to a very small amount, and the resistance at the connection part is close to zero. Therefore, it is possible to keep the size of the connection portion to a minimum.

[Brief description of drawings]

FIG. 1 is a perspective view of a superconducting conductor made by the connecting method of the present invention.

FIG. 2 is a cross-sectional view of a superconducting conductor.

FIG. 3 is a transverse cross-sectional view of a super transmission line.

FIG. 4 is a diagram showing steps of the connection method of the present invention.

FIG. 5 is a diagram showing steps of the connection method of the present invention.

FIG. 6 is a diagram showing steps of the connection method of the present invention.

FIG. 7 is a diagram showing steps of the connection method of the present invention.

FIG. 8 is a diagram showing steps of the connection method of the present invention.

FIG. 9 is a diagram showing steps of the connection method of the present invention.

FIG. 10 is a diagram showing steps of the connection method of the present invention.

FIG. 11 is a diagram showing a process according to another embodiment of the present invention.

[Explanation of symbols]

 1a, 1b ... Superconducting conductor 3a, 3b ... Superconducting wire 6a, 6b ... Filament 7 ... Connection piece 10 ... Case 13 ... Pressurizing jig

Claims (1)

[Claims] 1. A sheath and a stabilizing material are removed from a superconducting wire contained in one conduit to expose a filament of a certain length, and a filament is similarly exposed from a superconducting wire in another conduit, A suitable number of both fillers are bundled and stacked on top of each other, and the stacked filaments are covered with a connecting piece having a length corresponding to the exposed length, and the filaments are heated to a predetermined temperature under a vacuum or an inert gas atmosphere. And a method of connecting superconducting conductors, which is characterized in that solid-phase bonding is performed while maintaining pressure, and a case is coated so as to form an airtight space around the superconducting wire of the connecting portion.