Superconducting wire connection structure, superconducting wire connection method, and connection superconducting wire

A superconducting wire connection structure comprises a first superconducting wire and a second superconducting wire, ends of which are arranged across from each other, and a third superconducting wire which spans and connects the first superconducting wire and the second superconducting wire along a longitudinal direction of the first superconducting wire and the second superconducting wire. Each of the first superconducting wire, the second superconducting wire and the third superconducting wire is a tape-shaped superconducting wire which includes a substrate laminated with at least a superconductive layer. The third wire is narrower in at least one portion than the first superconducting wire and the second superconducting wire.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. National Stage application of, and claims priority to, PCT Patent Application No. PCT/JP2013/052734, filed Feb. 6, 2013 and entitled “SUPERCONDUCTING WIRE CONNECTION STRUCTURE, SUPERCONDUCTING WIRE CONNECTION METHOD, AND SUPERCONDUCTING WIRE FOR CONNECTING”; which claims priority to Japanese Patent Application No. 2012-105013, filed May 2, 2012. The entireties of the above-referenced applications are incorporated herein by reference.

TECHNICAL FIELD

The present invention relates to a superconducting wire connection structure, a superconducting wire connection method and a superconducting wire for connecting.

BACKGROUND ART

Conventionally, in order to connect superconducting wires, electrical connection has been carried out as follows. For example, as shown inFIG. 8A,FIG. 8BandFIG. 8C, a superconducting wire100which is cut in a short length for connecting is joined to a portion where ends of superconducting wires10abut on each other by soldering or spot welding such that the superconducting wire100and the superconducting wires10are stuck together.

Such connection structure is also disclosed in Patent Document 1 for example (see FIG. 3 in Patent Document 1).

Also, it is known that a superconducting film is deposited on a portion where ends of superconducting wires abut on each other (see Patent Documents 2 and 3 for example). It is also known that a connection superconducting wire is stuck to a portion of a superconducting wire where a surface metal layer is removed and then the connection superconducting wire is covered with the surface metal layer which was once removed. Thereby the connection superconducting wire is joined to the superconducting wire (see Patent Document 4 for example).

PRIOR ART DOCUMENT

Patent Document

DISCLOSURE OF THE INVENTION

Problem to be Solved by the Invention

However, as shown inFIG. 8BandFIG. 8C, the connection structures according to the above prior arts and Patent Document 1 have a problem that current flow concentration is caused by the skin effect around ends of the connection superconducting wire100(portions enclosed with dotted lines in the figures). A rise in current density can cause heat, and the heat makes the superconducting layer of the superconducting wire deteriorate and thereby superconductivity is lowered.

The connection methods in the above Patent Documents 2 and 3 are not practical because it is hard to bring a deposition apparatus to a work site when the methods are adopted to an applied apparatus (for example, laying of a superconducting wire).

The connection method in the above Patent Document 4 can be adopted to a superconducting wire having a surface metal layer which can be removed, such as a copper tape. However, the method cannot be adopted to a superconducting wire having a surface metal layer which cannot be removed, such as the one formed by plating with copper. Further, superconductivity may be lowered by removal of the surface metal layer which was once formed.

It is an object of the present invention to provide a superconducting wire connection structure, a superconducting wire connection method and a superconducting wire for connecting which make connecting easy and which achieve a stable superconductivity.

Means for Solving the Problem

In order to solve the problems mentioned above, according to the invention of claim1, a superconducting wire connection structure comprises:

a first superconducting wire and a second superconducting wire, ends of which are arranged across from each other; and

a third superconducting wire which spans and connects the first superconducting wire and the second superconducting wire along a longitudinal direction of the first superconducting wire and the second superconducting wire;

wherein each of the first superconducting wire, the second superconducting wire and the third superconducting wire is a tape-shaped superconducting wire which includes a substrate laminated with at least a superconductive layer,

wherein a surface of the third superconducting wire on a side where the substrate is laminated with the superconductive layer faces surfaces of the first superconducting wire and the second superconducting wire on a side where the substrates are laminated with the superconductive layers, and

wherein the third superconducting wire is narrower in at least one portion than the first superconducting wire and the second superconducting wire.

The invention of claim2is the superconducting wire connection structure according to claim1,

wherein the third superconducting wire tapers toward both ends thereof.

The invention of claim3is the superconducting wire connection structure according to claim1or2,

wherein the first superconducting wire and the second superconducting wire are spaced apart from and arranged across from each other.

The invention of claim4is the superconducting wire connection structure according to any one of claims1to3,

wherein the third superconducting wire is widest at a portion corresponding to a space between the first superconducting wire and the second superconducting wire.

The invention of claim5is a superconducting wire connection method for connecting tape-shaped superconducting wires each of which includes a substrate laminated with at least a superconductive layer, comprising:

spanning and connecting the first superconducting wire and the second superconducting wire by a third superconducting wire along a longitudinal direction of the first superconducting wire and the second superconducting wire at a portion where ends of the first superconducting wire and the second superconducting wire are spaced apart from and arranged across from each other, the third superconducting wire having a portion narrower than each width of the first superconducting wire and the second superconducting wire.

The invention of claim6is a superconducting wire connection method, comprising:

spanning and connecting a first area and a second area of a superconducting wire facing each other across a deterioration area by a connection superconducting wire at a portion where the first area and the second area are arranged across from each other, the deterioration area being electrically deteriorated, and the connection superconducting wire having a portion narrower than a width of the superconducting wire.

The invention of claim7is a connection superconducting wire for electrically connecting a first superconducting wire and a second superconducting wire, ends of which are arranged across from each other, comprising:

a center portion in a longitudinal direction of the connection superconducting wire which is a widest portion of the connection superconducting wire,

wherein the connection superconducting wire narrows toward ends from the center portion.

The invention of claim8is the connection superconducting wire according to claim7, wherein the connection superconducting wire has a laminated structure including a superconducting layer, sides of which are covered with an electric conductor.

Advantageous Effect of the Invention

According to the present invention, superconducting wires can be easily connected so that stable superconductivity is achieved.

EMBODIMENT FOR CARRYING OUT THE INVENTION

In the following, preferable modes for carrying out the present invention will be described with reference to the accompanying drawings. Although technically preferable various limitations are added to the embodiments described below in order to carry out the present invention, the scope of the invention is not limited to the following embodiments and shown examples.

FIG. 1is a figure showing a layer configuration of a superconducting wire.

The superconducting wire10is, for example, a tape-shaped superconducting wire provided with a laminated body and a stabilization layer5which surrounds and covers the laminated body as shown inFIG. 1. The laminated body includes a middle layer2, a superconducting layer3and a protection layer4that are piled up in this order on a substrate1.

The substrate1is, for example, a tape-shaped metal substrate made from low-magnetic and non-oriented metal such as hastelloy (registered trademark).

The middle layer2is a layer formed for achieving high in-plane orientation of the superconducting layer3.

The superconducting layer3is, for example, a superconducting layer made of a REBCO superconducting body and is a membrane made by MOCVD method, etc. RE is a rare-earth element such as Y (Yttrium), Sc (Scandium), La (Lanthanum), Ce (Cerium), Pr (Praseodymium), Nd (Neodymium), Pm (Promethium), Sm (Samarium), Eu (Europium), Gd (Gadolinium), Tb (Terbium), Dy (Dysprosium), Ho (Holmium), Er (Erbium), Tm (Thulium), Yb (Ytterbium), Lu (Lutetium), etc.

The protection layer4is, for example, a silver membrane made in the sputtering method, and is formed for protecting the superconducting layer3.

The stabilization layer5is, for example, formed by plating with copper, and consists of an electric conductor which covers sides of the laminated body comprising the substrate1, the middle layer2, the superconducting layer3and the protection layer4. This stabilization layer5is formed for releasing heat generated at limited points and for bypassing current when quenching occurs.

The layer configuration of the superconducting wire10is common to the first superconducting wire11, the second superconducting wire12and the third superconducting wire13which will be explained later.

Next, a superconducting wire connection structure and a superconducting wire connection method according to the present invention will be explained.

FIG. 2illustrates the superconducting wire connection structure and shows, in cross section, a state where the first superconducting wire11and the second superconducting wire12are connected by the third superconducting wire13for connecting.

As shown inFIG. 2, ends of the first superconducting wire11and the second superconducting wire12are spaced apart from and arranged across from each other. The third superconducting wire13is connected to the portion where the first superconducting wire11and the second superconducting wire12are spaced apart from and arranged across from each other via a solder layer6. Preferably, the space between the first superconducting wire11and the second superconducting wire12is approximately 1 mm to 5 mm in view of stiffness.

This third superconducting wire13spans and connects the first superconducting wire11and the second superconducting wire12along a longitudinal direction of the first superconducting wire11and the second superconducting wire12. Preferably, the widths of the first superconducting wire11and the second superconducting wire12are the same and are substantially uniform along the longitudinal direction.

Especially, the third superconducting wire13is characterized by having a portion which is narrower than the first superconducting wire11and the second superconducting wire12. Preferably, the width of the widest portion of the third superconducting wire13is the same as the widths of the first superconducting wire11and the second superconducting wire12.

The third superconducting wire13is, for example, cut in a short length in advance as shown inFIG. 3. The third superconducting wire13is narrower than the first superconducting wire11and the second superconducting wire12throughout the third superconducting wire13along the longitudinal direction, and is substantially rectangle-shaped as seen from above.

In many cases, ends of the first superconducting wire11and the second superconducting wire12are formed after being cut at a work site for laying superconducting cables, etc. for example. However, preferably, the third superconducting wire13is formed, not after being cut at a work site, but after being cut in advance in a desired shape by laser cutting. Since the section cut by laser cutting is fused by heat for sticking, the superconducting layer3included in the third superconducting wire13is prevented from troubles such as peeling. It is preferable because the third superconducting wire13can be cut in a desired shape and in a desired size. Preferably, copper-plating processing, etc. is executed on the third superconducting wire13after laser cutting so that the section is covered with metal.

At this connection portion, the first superconducting wire11and the second superconducting wire12are arranged such that surfaces thereof on the side of the superconducting layer3are arranged across from each other.

Preferably, the melting point of the solder layer6, which connects the first superconducting wire11and the second superconducting wire12to the third superconducting wire13, is no more than 160 C for achieving appropriate superconductivity. Specifically, solder having the melting point of approximately 120 C is preferable (for example, a bismuth alloy, etc.).

According to such superconducting wire connection structure, the length of an edge of the surface of the third superconducting wire13contacting the first superconducting wire11and the second superconducting wire12via the solder layer6is longer than prior art. Therefore current flow concentration by the skin effect is suppressed, and current density around each end of the third superconducting wire13in the longitudinal direction is lowered.

By lowering the current density around each end of the third superconducting wire13in the longitudinal direction, generation of heat caused by current flow concentration is suppressed, and deterioration of the superconducting layer3is reduced.

If the first superconducting wire11and the second superconducting wire12are not spaced apart but are contacted with each other, the first superconducting wire11, the second superconducting wire12and the third superconducting wire13contact with each other at one point. Current flow concentration occurs at this point, and heat caused by the current flow concentration makes the superconducting layer3deteriorate. By keeping a space between the first superconducting wire11and the second superconducting wire12, heat caused by the current flow concentration is suppressed, and thereby deterioration of the superconducting layer3is suppressed.

Thus the third superconducting wire13connects the first superconducting wire11and the second superconducting wire12along a longitudinal direction of the first superconducting wire11and the second superconducting wire12at a portion where ends of the first superconducting wire11and the second superconducting wire12are spaced apart from and arranged across from each other. The third superconducting wire13is narrower in at least one portion than the first superconducting wire11and the second superconducting wire12. This superconducting wire connection structure can suppress generation of heat caused by the current flow concentration at portions where the third superconducting wire13is connected to the first superconducting wire11and the second superconducting wire12. Thereby deterioration of the superconducting layer3is reduced, and stable superconductivity is achieved.

That is to say, the superconducting wire connection structure according to the present invention is a useful technique where the first superconducting wire11and the second superconducting wire12are easily connected to the third superconducting wire13by soldering and which achieves stable superconductivity.

The present invention is not limited to the above embodiments.

For example, as shown inFIG. 4, it is also possible that the third superconducting wire13, which is a connection superconducting wire, is widest at the center portion in the longitudinal direction thereof and narrows toward both ends from the center portion such that the third superconducting wire13is substantially oval-shaped as seen from above.

In the case of such third superconducting wire13substantially oval-shaped as seen from above, the length of an edge of the surface of the third superconducting wire13contacting the first superconducting wire11and the second superconducting wire12via the solder layer6is longer than prior art. Therefore current flow concentration by the skin effect is suppressed, and current density around each end of the third superconducting wire13in the longitudinal direction is lowered. Thereby generation of heat caused by current flow concentration is suppressed, and deterioration of the superconducting layer3is reduced.

The width of the third superconducting wire13substantially oval-shaped is largest at the center portion in the longitudinal direction, wherein the width of the third superconducting wire13is the same as each width of the first superconducting wire11and the second superconducting wire12. The third superconducting wire13is joined such that the center portion, which is the widest portion of the third superconducting wire13, is positioned at a place corresponding to the space between the first superconducting wire11and the second superconducting wire12. Thereby the intensity of the connected portion is maintained appropriately.

As shown inFIG. 5, it is also possible that the third superconducting wire13, which is a connection superconducting wire, is widest at the center portion in the longitudinal direction thereof and narrows toward both ends from the center portion such that the third superconducting wire13is substantially diamond-shaped as seen from above.

In the case of such third superconducting wire13, which tapers toward both ends, the length of an edge of the surface of the third superconducting wire13contacting the first superconducting wire11and the second superconducting wire12via the solder layer6is longer than prior art. Therefore current flow concentration by the skin effect is suppressed, and current density around each end of the third superconducting wire13in the longitudinal direction is lowered. Thereby generation of heat caused by current flow concentration is suppressed, and deterioration of the superconducting layer3is reduced.

The width of third superconducting wire13substantially diamond-shaped is largest at the center portion in the longitudinal direction, wherein the width of the third superconducting wire is the same as each width of the first superconducting wire11and the second superconducting wire12. The third superconducting wire13is joined such that the center portion, which is the widest portion of the third superconducting wire13, is positioned at a place corresponding to the space between the first superconducting wire11and the second superconducting wire12. Thereby the intensity of the connected portion is maintained appropriately.

In order to prevent peeling of this third superconducting wire13, preferably, the substantial diamond shape of the third superconducting wire13is chamfered.

The superconducting wire connection method of the present invention is not limited to the method where the third superconducting wire13for connecting connects the two superconducting wires such as the first superconducting wire11and the second superconducting wire12.

For example, there is a case where one superconducting wire10has a deterioration area R where, for example, superconductivity is lowered by some trouble and thereby critical current is lowered. In such case, the present invention can be applied to electric connection between the first area and the second area facing each other across the deterioration area R using the third superconducting wire13. That is to say, the first area10aand the second area10bin the superconducting wire10spaced apart by the deterioration area R are respectively likened to the first superconducting wire and the second superconducting wire and are electrically connected using the third superconducting wire13.

For example, when the superconducting wire10includes the deterioration area R as shown inFIG. 6andFIG. 7and the first area10aand the second area10bare to be connected with the deterioration area R between them, the third superconducting wire13spans and connects the first area10aand the second area10bat a portion where the first area10aand the second area10bare arranged across from each other. The third superconducting wire13is narrower in at least one portion than the superconducting wire10. In this example, the third superconducting wire13which is substantially oval-shaped as seen from above is joined to the superconducting wire10via the solder layer6.

Thus the third superconducting wire13connects the first area10aand the second area10bin the superconducting wire10which are electrically separated by the deterioration area R, and thereby a superconducting wire connection structure having stable superconductivity is achieved.

In the above embodiments, the third superconducting wires13having substantial shapes of a rectangle, an oval and a diamond as seen from above are exemplified. However, the present invention is not limited to these and any other shapes are possible as long as the third superconducting wire13is narrower in at least one portion than the first superconducting wire11and the second superconducting wire12.

Current density can be more effectively lowered by insulating the periphery of the third superconducting wire13through chemical etching for example.

It goes without saying that specific details, etc. can be changed as the occasion demands.

INDUSTRIAL APPLICABILITY

Since the present invention is configured as above, it can be applied to techniques of connecting superconducting wires as a superconducting wire connection structure, a superconducting wire connection method and a superconducting wire for connecting.

DESCRIPTION OF REFERENCE NUMERALS