JPH08138821A - Junction structure and end structure of superconducting conductor - Google Patents

Abstract

(57) [Summary] (Modified) [Purpose] To obtain a superconducting conductor joint having a compact connection and a highly reliable joint having low connection resistance and small variation in characteristics. [Structure] When the superconducting conductors 1 are butt-joined, the superconducting element wires 4'constituting each conductor are joined so as to have a one-to-one correspondence on the butt surfaces. This makes it possible to obtain a highly reliable superconducting junction having low connection resistance. [Effect] It is possible to obtain a superconducting junction that has low connection resistance and is capable of conducting high current, which makes it possible to manufacture a coil for generating a high magnetic field or a coil using a permanent current mode without attenuation (loss). , The field of superconducting application can be expanded significantly.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an end structure of a superconducting conductor formed by bundling a plurality of superconducting element wires, a method for forming the end, and a joined body and a joining structure of the superconducting conductors.
In particular, the present invention relates to a conductor end portion structure, an end portion forming method, and a joining method for obtaining a joined body of superconducting conductors having a small connection resistance and capable of conducting a large current. Further, the present invention relates to a highly reliable superconducting conductor joining method applicable to various superconducting conductors.

[0002]

2. Description of the Related Art When a superconducting wire is used as a large magnet, there is a limit to the length of the superconducting wire that can be manufactured as a superconducting wire without variations in characteristics or breakage in the manufacturing process of the superconducting wire. is there. Also, it is necessary to connect the superconducting wires to each other due to the structure of the device used. However, the superconducting wire joint has various problems such as temperature rise and current capacity decrease due to generation of connection resistance. It is essential to establish a reliable joining technology with low connection resistance.

As a method for joining superconducting wires, it is considered that butt joining is effective because it can form a direct contact interface between superconductors (superconducting filaments). Examples of butt welding include butt resistance welding as described in Japanese Patent Laid-Open No. 3-40382, as well as welding methods such as diffusion welding, cold pressure welding and hot pressure welding.

In the case of a superconducting wire and a conductor which are composite materials, the correspondence between each wire or conductor end structure on the butt face is greatly involved as one of the factors governing the connection characteristics. In particular, in the joining of superconducting conductors formed by bundling a plurality of superconducting element wires, the arrangement state of the superconducting element wires on each conductor end face to be joined is not constant. When they are joined, there is a problem that there is no correspondence between the superconducting element wires in the joined portion and the joined interface becomes a discontinuous plane of current, resulting in an increase in resistance of the connecting portion. Further, due to the uncertainties of the butt surfaces corresponding to the strands, there is a large variation in the characteristics among the bonded bodies, which is a problem in reliability.

[0005]

In the above-mentioned prior art, in the butt-joining method for superconducting conductors, there is no positional correspondence between the superconducting element wires on the butt surface, and therefore, partial current concentration or constant current flow at the joining interface. There is a problem that the superconducting current is attenuated due to the connection resistance due to the passage of the conduction region. Also, due to the contingency of the butt faces, it is not possible to make the joint structure constant for each joint body, and not only the connection characteristics of the conductors vary, but also the current non-uniformity occurs between the wires that form the conductors. There was a problem in reliability and conductor performance.

An object of the present invention is to solve the above-mentioned problems of the prior art, to provide a superconducting conductor joined body having an extremely low connection resistance, and a method for obtaining the joined body with high reliability. To do.

[0007]

In order to achieve the above object, in the present invention, a superconducting conductor end face composed of a bundle of superconducting element wires has a structure having a constant strand arrangement, and a conductor end portion having a regular array structure is formed. It is characterized in that the wires of the butt joint surfaces are made to correspond to each other one to one by joining them. That is, in the joining structure of the superconducting conductor of the present invention, the end portions of the structure in which the strands on the opposing conductor end faces have the same arrangement are abutted with each other, and the strands have a one-to-one correspondence on the abutting faces. Is characterized by.

As an example of the conductor end structure, the entire cross section of the conductor has a rotational symmetry of 6th order and is divided into small blocks arranged in a rotational symmetry of 6th order. Each block constitutes a conductor. There is a case where the superconducting element wires are arranged in a rotational symmetry of sixth order. A flow path for a coolant may be formed in the small block, and the flow path and the strands may be arranged in a sixth-order rotationally symmetrical shape. Further, the small blocks arranged in the 6th order rotationally symmetrical shape may have their peripheries covered with a high resistance metal material, and the respective blocks may be electrically separated by a high resistance layer.

Further, in the conductor end structure of the present invention, the conductor cross section may have a rotational symmetry of a lower order than the first order. For example, even if the strand cross section is rectangular, the opposing end structures may be symmetrical to each other.

The joining method, conductor end structure and end forming method of the present invention include (Nb, Ti) in addition to the compound superconducting conductor formed by bundling Nb ₃ Sn superconducting wires among known superconducting wires.
₃ Sn, Nb ₃ Al, can be applied to a superconducting conductor made by bundling V ₃ Ga superconducting wire. It can also be applied to a superconducting conductor formed by bundling alloy-based superconducting wires such as Nb-Ti.

[0011]

When a conductor such as a certain type of forced cooling type conductor that does not have a constant conductor cross section is arranged to be joined by abutting the end faces of each other, the superconducting of one conductor is performed at the abutting face. When the region comes into contact with the void between the strands of the other conductor, the superconducting current flowing in the filament must flow into the other side through the matrix portion at the bonding interface. Also, even if one superconducting filament does not contact the superconducting filament on the other side at all, but only contacts the matrix, the superconducting current will flow through the normal conducting region in the same manner as above, Increase resistance. By making the superconducting wires correspond one-to-one with the butt surfaces, the connection resistance based on the above reason can be reduced. Further, by butt-joining the conductor end portions having a constant array structure, the contact area between the superconductors can be widened and the variation thereof can be reduced, so that the variation of the connection characteristics due to the difference of the contact area can be reduced.

Further, if the conductor end face has a 6th order rotational symmetry, each time the conductor is rotated by 60 °, the wires can be brought into contact with each other in a one-to-one correspondence, which is more advantageous in the joining process. Further, when the small blocks, which are composed of the wires arranged in the 6th order rotationally symmetrical shape, are electrically insulated from each other by the high resistance metal material, the AC loss due to the coupling current can be reduced.

Further, by providing a coolant passage in a part of the 6th-order rotationally symmetric small block, a superconducting joint having high stability can be obtained without hindering the supply of the refrigerant at the joint. be able to.

[0014]

【Example】

(Example 1) As shown in FIG. 2, the superconducting conductor 1 used in this example contains N in a Cu-Sn alloy matrix 2.
A composite conductor with an outer diameter of about 11 mm, in which 49 wire bundles with an outer diameter of about 1 mm having a structure in which about 10,000 filaments 3 of b are embedded are bundled and covered with SUS conduits 5. ₃ Sn Can form superconductors. The conduit at the end of the composite conductor before heat treatment for superconducting was stripped off with a length of about 200 mm, and the internal wire was taken out. The individual strands 4 thus taken out were processed by a processing roll as shown in FIG. 3 over 150 mm from the end under processing conditions of a pressure of about 5 kg and a drawing speed of 300 mm / min. The processed wires 4'are each inserted into a frame made of oxygen-free copper having a shape as shown in FIG. 4 and a wall pressure of 0.3 mm, a width of 2.5 mm, and a length of 150 mm, and each of them is inserted into the block of FIG. Was formed. 7 blocks are made in this way, and this 7 blocks
Two blocks were inserted into a copper pipe with an outer diameter of about 11 mm and a wall pressure of 1 mm, and swaged into a regular hexagonal shape. As a result, a sixth-order rotationally symmetric composite conductor end surface was formed. The whole terminal-treated composite conductor was heat-treated in an inert atmosphere at about 700 ° C. for 200 hours to produce an Nb ₃ Sn superconducting conductor having a 6th order rotationally symmetric end face shown in FIG.

In order to connect the above-mentioned superconducting conductors, first, each conductor was cut at a right angle with respect to the axial direction of the conductor, leaving the end processed to the 6th order rotational symmetry with a length of about 50 mm. . The cut surface was polished with a No. 1000 emery paper, and further finish-polished with a 10 μm alumina abrasive. The end faces were abutted against each other, and they were connected by resistance welding with the vertex positions of the regular hexagon aligned. As a result, as shown in FIG.
To obtain a joined body 6 of superconducting conductors corresponding to each other.

As a result of conducting a tensile test on the joined portion of this joined body, the base material fractured at a maximum tensile strength of 800 kgf. Moreover, when the connection resistance in liquid helium was measured by the four-terminal resistance method for the bonded body manufactured under the same conditions, it was found that no voltage was generated by applying a current of 4 kA in a magnetic field of 4 T applied perpendicularly to the bonded body. It was below the detection limit, and no occurrence of connection resistance was observed.

On the other hand, as a comparison, the composite conductor of FIG. 2 is heat-treated into a superconductor without treatment of terminals to form a compound superconducting conductor, and the strand positions of the end faces are not the same, and the compatibility of the strands at the butted faces is high. A joined body was prepared. The joint surface was similarly polished by the above method. The welding conditions are the same,
The amount of axial deformation of the joint was set to be the same as that of the conductor joined body subjected to the terminal treatment. When the connection resistance of this joined body was measured (in a 4.2 K, 4 T vertical magnetic field, 4 kA energization), a connection resistance of 1 nΩ was generated.

From the above, it was found that the joint obtained by this method has very excellent electrical characteristics.

(Second Embodiment) This embodiment is basically the same as the first embodiment. Here, a compound superconducting conductor having a 6th order rotationally symmetrical end face was formed by using Cu-Ni which is a high resistance metal material in a block frame (FIG. 4) into which the wires are inserted. By joining the superconducting conductors by abutting the six-fold symmetrical end faces to each other, the superconducting element wires constituting each conductor have a one-to-one correspondence in the abutting surfaces, and there is a small gap between the element wires in the same plane. A superconducting conductor assembly, which is electrically separated for each block, was obtained.

With respect to this bonded body, the connection resistance in a constant vertical applied magnetic field of 4T and the heat generation amount of the bonded portion when an alternating magnetic field was applied were measured. With respect to the connection resistance, the voltage generation was less than the detection limit when a current of 4 kA was applied, and the connection resistance generation was not observed. In addition, the amount of heat generated at the junction was 1 W when the magnetic field changed at 2 T / s.

From the above, it was found that the joint obtained by this method has very excellent electrical characteristics.

(Third Embodiment) This embodiment is basically the same as the first embodiment. As shown in FIG. 2, the superconducting conductor used here has a structure in which about 10000 Nb filaments are embedded in a Cu—Sn alloy matrix, and a wire rod having an outer diameter of about 1 mm is used as an element wire. It is a composite conductor with an outer diameter of about 10 mm that is bundled and covered with a SUS conduit to form a Nb ₃ Sn superconductor by heat treatment.
The conduit end portion of the composite conductor before heat treatment for forming a superconductor was stripped off in a length of about 200 mm, and the internal wire was taken out.
Each of the drawn wires was processed by a processing roll as shown in FIG. 3 from the end to 150 mm under the processing conditions of a pressure of about 5 kg and a drawing speed of 300 mm / min. The processed wire was divided into six wires, and six wires were placed around the hexagonal copper pipe for a refrigerant channel (FIG. 6) and combined with each other. This is meat pressure 0.3m
A block was formed by inserting it into a frame made of oxygen-free copper having a size of m, a width of 2.5 mm, and a length of 150 mm. In this way, 7 blocks are made, and these 7 blocks are
It was inserted into a copper pipe with a meat pressure of 1 mm and swaged. As a result, a sixth-order rotationally symmetric composite conductor end face having a coolant passage in the center of each block was formed. Approximately 70% of the entire composite conductor that has been subjected to this termination is processed in an inert atmosphere.
By heat treatment at 0 ° C. for 200 hours, an Nb ₃ Sn superconducting conductor having a sixth-order rotationally symmetric end face was produced.

In order to connect the above-mentioned superconducting conductors, first, each conductor was cut at a right angle with respect to the axial direction of the conductor, leaving the end processed to the 6th order rotational symmetry with a length of about 50 mm. . The cut surface was polished with a No. 1000 emery paper, and further finish-polished with a 10 μm alumina abrasive. The end faces were abutted against each other, and they were connected by resistance welding with the vertex positions of the regular hexagon aligned. As a result, a joined body of superconducting conductors in which the strands of the butt face corresponded to each other one by one was obtained.

The connection resistance of this bonded body in liquid helium was measured by the four-terminal resistance method, and it was found to be 4 kA in a magnetic field of 4 T applied perpendicularly to the bonded body.
The voltage generation was below the detection limit and the connection resistance was not detected by the energization of No. 1, and the connection resistance of several nΩ was better in the joined body in which the wires did not correspond to each other at the butt surfaces. It showed excellent electrical characteristics.

(Fourth Embodiment) This embodiment is basically the same as the third embodiment. Here, in joining superconducting conductors, a guide pin is formed on the joining end face and the joining is performed by using it in order to more reliably and simply form the correspondence at the abutting surfaces. . In the same manner as in Example 3, an Nb ₃ Sn superconducting conductor having an end face of a 6th order rotationally symmetric type and having flow passages for the refrigerant was produced. In order to connect these superconducting conductors with each other, as shown in Fig. 7, a pin of hexagonal hexagonal shape (distance between the opposite sides of 1 mm) having a hole with a diameter of 0.5 mm and a length of 10 mm and made of oxygen-free copper is used. , The superconducting conductor to be joined was fitted into the refrigerant passage hole on one end face. The protrusions on this end face are inserted into the refrigerant flow passage holes on the other conductor end face, but the conductors are butted against each other,
Welded under pressure and electricity. As a result, similar to Example 3, it was possible to more easily manufacture a joint between superconducting conductors having excellent electrical characteristics and high mechanical strength.

[0026]

According to the present invention, it is possible to obtain a joint in which superconducting element wires constituting a superconducting conductor composed of a bundle of superconducting wires are made to correspond one-to-one, and the connection resistance is low and the current density is high. It is possible to obtain a joined body of superconducting conductors capable of conducting electricity. As a result, a large coil for generating a high magnetic field can be manufactured, and a coil with low AC loss can be realized.
In addition, it is possible to reduce the heat load on the coil cooling system that accompanies it, which is also useful from the economical point of view.

[Brief description of drawings]

FIG. 1 is a structural diagram of a superconducting conductor joint portion of the present invention.

FIG. 2 is a cross-sectional view of a composite conductor, which becomes a compound superconducting conductor by the heat treatment of the present invention, before the heat treatment.

FIG. 3 is a schematic view of a wire processing jig according to an embodiment of the present invention.

FIG. 4 is a perspective view of a block frame used in an embodiment of the present invention.

FIG. 5 is a perspective view after the block is assembled according to the embodiment of the present invention.

FIG. 6 is a schematic view of a refrigerant channel pipe used in an embodiment of the present invention.

FIG. 7 is a perspective view of an end surface of a block according to an embodiment of the present invention.

FIG. 8 is a structural view of an end face of a superconducting conductor according to an embodiment of the present invention.

[Explanation of symbols]

1 ... Superconducting conductor, 2 ... Cu-Sn matrix, 3 ... N
b filament, 4, 4 '... Superconducting element wire, 5 ... SUS conduit, 6 ... Superconducting conductor assembly, 7 ... Block frame, 8
… Copper pipes.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Ryuyoshi Takahashi 7-1, 1-1 Omika-cho, Hitachi City, Ibaraki Hitachi Ltd. Hitachi Research Laboratory (72) Inventor Yoshihide Wadayama 7-chome, Omika-cho, Hitachi City, Ibaraki Prefecture No. 1 in Hitachi Research Laboratory, Hitachi, Ltd. (72) Inventor Katsuo Takaki 7-1-1, Omika-cho, Hitachi City, Hitachi, Ibaraki Prefecture (72) In Hitachi Research Laboratory, Hitachi, Ltd. (72) Asano ▲ Katsu ▼ ▲ Hiko ▼ 3-1-1, Sachimachi, Hitachi, Ibaraki Pref., Hitachi, Ltd., Hitachi Factory (72) Inventor, Akira Shigenaka 3-1-1, Sachimachi, Hitachi, Ibaraki, Hitachi, Ltd., Hitachi, Ltd.

Claims (12)

[Claims] 1. A superconducting conductor formed by bundling a plurality of superconducting element wires each having a structure in which a plurality of superconducting filaments are embedded in a metal matrix, wherein the superconducting element has a cross section at a butt joint portion of the superconducting conductors. A superconducting conductor characterized in that the two-dimensional arrangement of lines is the same at the joint. 2. A superconducting conductor formed by bundling a plurality of superconducting element wires each having a structure in which a plurality of superconducting filaments are embedded in a metal matrix, wherein the cross-sectional shape of the superconducting element wires is a secondary or higher rotation. A superconducting conductor characterized by being symmetrical. 3. A superconducting conductor formed by bundling a plurality of superconducting element wires having a structure in which a plurality of superconducting filaments are embedded in a metal matrix, the superconducting element wires having a cross section at a joint portion of the superconducting conductors. The superconducting conductor is characterized in that the two-dimensional arrangement of is composed of an assembly of rotationally symmetric small blocks of secondary or higher order. 4. A superconducting conductor formed by bundling a plurality of superconducting element wires having a structure in which a plurality of superconducting filaments are embedded in a metal matrix, the superconducting element wire having a cross section at a joint portion of the superconducting conductors. The superconducting conductor has a two-dimensional or more two-dimensionally arranged outer shape of rotational symmetry and has an outer shape of rotational symmetry of the same order as the outer shape, and is composed of an assembly of the superconducting element wires. 5. A superconducting conductor formed by bundling a plurality of superconducting element wires having a structure in which a plurality of superconducting filaments are embedded in a metal matrix, the superconducting element wires having a cross section at a joint portion of the superconducting conductors. Is a six-dimensional rotationally symmetric outer shape, and is composed of an assembly of the superconducting element wires having a sixth-order rotationally symmetric outer shape. 6. A twisted-wire superconducting conductor manufactured by repeating several times a step of bundling a plurality of superconducting element wires having a composite multi-core structure composed of a superconducting filament and a metal matrix, wherein a cross section of a joint portion of the twisted-wire superconducting conductor is formed. The two-dimensional arrangement of the superconducting wires is composed of 6-order rotationally symmetric small blocks, and the strands of the smallest twisted wire unit in the small blocks are arranged in 6th-order rotationally symmetrical form. A superconducting conductor having a different structure. 7. The superconducting conductor according to claim 1, wherein a refrigerant passage is formed between the superconducting element wires. 8. The superconducting conductor according to any one of claims 1 to 7, wherein a high resistance metal material is arranged between the superconducting element wires. 9. A superconducting conductor formed by bundling a plurality of superconducting element wires having a structure in which a plurality of superconducting filaments are embedded in a metal matrix, wherein the superconducting section of the cross section at the joint portion of the stranded superconducting conductor is The two-dimensional arrangement of the strands is divided into blocks arranged in a 6th order rotational symmetry, and a high resistance metal material is interposed between the blocks. A joined body of superconducting conductors, characterized in that the end faces of a structure arranged in a sixth-order rotational symmetry are butted against each other, and the positions of the opposing strands at the butted faces correspond. 10. A method of butt-joining superconducting conductors formed by bundling a plurality of superconducting element wires each having a structure in which a plurality of superconducting filaments are embedded in a metal matrix, the superconducting element wires constituting the conductors being bonded together. After dividing into multiple groups, inserting into each group a copper pipe, swaging, then inserting the entire group into a copper pipe and swaging again, the conductor end face of the structure having a regular strand arrangement is formed. A method for joining superconducting conductors, characterized in that after forming them, they are opposed to each other and the superconducting element wires constituting each conductor are connected so as to have a one-to-one correspondence at the abutting surfaces. 11. A structure of a conductor end portion of a superconducting conductor formed by bundling a plurality of superconducting element wires each having a structure in which a plurality of superconducting filaments are embedded in a metal matrix. An end structure of a superconducting conductor, which is the same at the joint and has a regular array of strands. 12. The superconducting conductor end structure according to claim 11, wherein when these end faces are abutted with each other, a convex portion and a concave portion are provided so as to be fitted with each other at the abutting faces. End structure of conductor.