JPH0721851A - Stabilizer for superconductors - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a stabilizing material for a superconductor, which has a copper clad aluminum structure and can be made to have a composite specific resistance under an extremely low temperature and a high magnetic field, which is close to that of an aluminum material alone. [Structure] A composite material structure in which an aluminum material 22 is covered with a copper material 23, and an alumina layer 27, which is an electrical insulating material, is scattered at the interface between the aluminum material 22 and the copper material 23.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a stabilizer that is used by being attached to a superconductor in order to stabilize the superconductor.

[0002]

2. Description of the Related Art As is well known, large-scale superconducting magnets are required in nuclear fusion reactors, energy storage devices, accelerators and the like. As a superconducting conductor for forming such a large superconducting magnet, from the perspective of ensuring safety when transitioning to the normal conducting state, ensuring continuous operation, and ensuring natural recovery from the normal conducting state to the superconducting state. Usually, a superconductor to which a stabilizing material is joined by solder or the like is used.

As the stabilizing material, a material made of a copper material, an aluminum material or a composite material of copper and aluminum is generally used. Copper is stronger than aluminum, has better workability, and is easier to solder, but has a large specific resistance at extremely low temperatures. On the other hand, although aluminum has a smaller specific resistance at cryogenic temperatures than copper,
It has low strength, is difficult to process, and is difficult to solder.

From the above, as shown in FIG.
Many superconducting conductors 1 use a composite material of a copper material and an aluminum material as a stabilizing material. That is, the superconducting conductor 1 is a high-purity material in which a copper matrix multicore superconducting wire 3 of Nb ₃ Sn or the like is embedded in a copper stabilizing material 2 and the outer surface of the copper stabilizing material 2 is covered with a copper material 4. The aluminum material 5, that is, the composite stabilizing material 6 made of copper clad aluminum is joined by soldering. In this case, the copper material 4 contributes to easy soldering.

However, as described above, the copper clad
Even the composite stabilizer 6 made of aluminum has the following problems. That is, according to the experimental results of the present inventor, the specific resistance of the high-purity aluminum material at 4.2K is significantly smaller than that of the copper material in a zero magnetic field as shown in FIG. 5, and 2 to 6 T (Tesla). Shows a substantially constant value in the range. On the other hand, the specific resistance of copper material is significantly higher than that of high-purity aluminum material at zero magnetic field, and also rises sharply in the range of 2 to 6 T, and is 10 times higher than that of high-purity aluminum material at 6 T high magnetic field. The above specific resistance is shown.

Since the composite stabilizer 6 made of copper clad aluminum has a conductor structure in which a copper material and a high-purity aluminum material are juxtaposed, the specific resistance of the composite stabilizer 6 is calculated in FIG. As shown as a value, it should show a combined specific resistance calculated from the specific resistances of the copper material and the high-purity aluminum material alone, specifically, a value close to that of the high-purity aluminum material. However, the measured combined resistivity is
As shown in FIG. 5, it is extremely large.

As described above, in the conventional composite stabilizer made of copper clad aluminum, there is a problem that the effect obtained by using the aluminum material cannot be effectively obtained.

The reason for this is not clear, but it is presumed as follows. When a magnetic field is applied to a metal in a direction perpendicular to the direction of current flow, an electric field is generated in a direction perpendicular to the current / magnetic field, and an electromotive force appears. This phenomenon is called the Hall effect. The voltage generated by this Hall effect is proportional to the product of the current and the magnetic field. This coefficient is called the Hall coefficient, but the positive and negative of the coefficient are reversed between copper and aluminum. As a result, a current loop is created in the direction perpendicular to the axial direction of the composite stabilizer made of copper and aluminum, which becomes a resistance to the current flow in the axial direction and increases the composite specific resistance. It is expected that

[0009]

As described above, in the conventional composite stabilizer made of copper clad aluminum, the combined specific resistance under extremely low temperature and high magnetic field is much larger than that of aluminum alone. However, there is a problem that the performance as a stabilizing material cannot be fully exhibited.

Therefore, the present invention has a copper clad / aluminum structure, which can bring the combined specific resistance under cryogenic temperature and high magnetic field closer to that of aluminum alone, and can sufficiently exhibit its performance as a stabilizing material. The purpose is to provide a stabilizing material.

[0011]

In order to achieve the above object, a stabilizing material according to the present invention has a composite material structure in which an aluminum material is coated with a copper material, and has an interface between the aluminum material and the copper material. The feature is that the alumina layers are distributed in a scattered manner.

[0012]

[Function] Since the alumina layer, which is an electrical insulating material, is scattered and distributed at the interface between the aluminum material and the copper material, these alumina layers pass through both members along the plane orthogonal to the axial direction due to the Hall effect. The loop current that tends to flow is suppressed to a small value. As a result, the combined specific resistance under cryogenic temperature and high magnetic field can be made closer to that of aluminum alone.

In order to interspersely distribute the alumina layer at the interface between the aluminum material and the copper material, unevenness is formed at the interface when the copper clad / aluminum composite material is formed. Then, after forming a copper oxide film on the surface of this composite material, heat treatment is performed at a temperature of, for example, 600 ° C. or higher. When the heat treatment is performed in this way, oxygen in the copper oxide film formed on the surface of the composite material diffuses in the copper clad and combines with aluminum, forming an alumina layer at the interface.
At this time, the alumina layer is formed in a larger amount at the interface and in a portion close to the surface, and has a form in which it is scattered at the interface.
Therefore, the alumina layer can be formed by simple steps and treatments.

[0014]

Embodiments will be described below with reference to the drawings.

FIG. 1 shows a sectional view of a stabilizing material 21 for a superconductor according to an embodiment of the present invention.

The stabilizing material 21 is formed in a composite structure of a high-purity aluminum material 22 and a copper material 23 provided so as to cover the aluminum material 22.

The interface between the aluminum material 22 and the copper material 23 is formed on the uneven surface 24, and particularly the convex surface 25 and the concave surface 26.
And an alumina (Al ₂ O ₃ ) layer 27 which is an electrical insulating material.
Are formed. The alumina layer 27 is formed thicker by the convex surface 25 closer to the surface than the concave surface 26, and is hardly formed at the boundary portion 28 between the convex surface 25 and the concave surface 26.

Stabilizer 21 for superconductors having such a structure
Is manufactured through the steps shown in FIG. First, the same figure (a)
As shown in FIG. 2, a copper pipe 31 having an outer diameter of 2 mm and a plurality of grooves 30 extending in the axial direction on the inner peripheral surface is prepared, and high-purity aluminum having an outer diameter of 0.3 mm is provided in the copper pipe 31. After inserting many wires, they are drawn and integrated to form a composite material 33 in which the aluminum material 22 is covered with the copper material 23. Due to the presence of the groove 30 described above, the uneven surface 24 is formed at the interface between the aluminum material 22 and the copper material 23.

Next, as shown in FIG. 3B, the composite material 33 is heat-treated at 300 ° C. for 100 hours in the atmosphere to form a copper oxide film 34 on the surface of the composite material 33.

Next, as shown in FIG. 3C, the composite material 33 having the oxide film 34 formed on its surface is heat-treated in argon gas at 600 ° C. for 24 hours. By this heat treatment, oxygen in the copper oxide film 34 diffuses into the copper material 23 and combines with the aluminum material 22 to form an alumina layer 27 at the interface. At this time, the alumina layer 27 is
It is formed more at the interface and in the portion close to the surface, and has a form distributed in the interface.

The stabilizing material 21 thus formed is
When the specific resistance was measured in a high magnetic field at 4.2K, the result close to the characteristics of the high-purity aluminum material was obtained as shown in FIG.

In this way, the aluminum material 22 and the copper material 2
Since the alumina layer 27 which is an electrical insulating material is scattered and distributed at the interface with 3, the alumina layer 27 tries to flow along the plane orthogonal to the axial direction via both members by the Hall effect. Keep the loop current to a small value. As a result, the combined resistivity under extremely low temperature and high magnetic field can be made close to that of the high-purity aluminum material alone. Since the alumina layer 27 is scarcely formed on the boundary portion 28, a current path between the copper material 23 and the aluminum material 22 is secured. Therefore, good performance as a stabilizing material can be exhibited.

In order to diffuse and permeate oxygen in the copper oxide film 34 to form the alumina layer 27 at the interface between the aluminum material 22 and the copper material 23, it is necessary to perform heat treatment at 600 to 750 ° C. High-purity copper has a heat treatment temperature of 600 to 750.
Mechanical strength decreases significantly at ℃. That is, the Vickers hardness Hv decreases from 100 to about 40 at room temperature. Therefore, instead of the copper material 23, alumina dispersion strengthened copper (Hv = 150, 600-750 at room temperature) whose hardness does not easily decrease at 600-750 ° C.
Hv = 130 at 0 ° C may be used. As described above, even when the alumina dispersion strengthened copper is used, the alumina layer can be scattered and formed at the interface, and the synthetic specific resistance can be made closer to that of the high-purity aluminum material alone.

Further, in the above-mentioned embodiment, the stabilizing member has a circular cross section. However, when the stabilizing member has a rectangular cross section, the cross section becomes rectangular in the drawing step shown in FIG. 2 (a). You can draw a line.

[0025]

As described above, according to the present invention, it is possible to contribute to the stability improvement of the superconducting wire under an extremely low temperature and a high magnetic field.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a stabilizer for a superconductor according to an embodiment of the present invention.

FIG. 2 is a view for explaining a manufacturing procedure of the stabilizing material.

FIG. 3 is a diagram showing the specific resistance characteristics of the stabilizing material under a cryogenic temperature and a high magnetic field in comparison with that of a high-purity aluminum material alone.

FIG. 4 is a cross-sectional view of a superconducting conductor in which a stabilizing material made of copper clad aluminum is attached to the superconducting wire.

FIG. 5 is a diagram showing specific resistance characteristics of a conventional stabilizing material made of copper clad aluminum.

[Explanation of symbols]

21 ... Stabilizer for superconductor 22 ... High-purity aluminum material 23 ... Copper material 24 ... Uneven surface 25 ... Convex surface 26 ... Concave surface 27 ... Alumina layer 28 ... Boundary part 33 ... Composite material 34 ... Copper oxide film

Claims (1)

[Claims] 1. A stabilizer for a superconductor, comprising a composite material obtained by coating an aluminum material with a copper material, wherein an alumina layer is scattered and distributed at an interface between the aluminum material and the copper material. Material.