JPS6115534B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a superconducting wire with low AC loss. Superconducting wires are currently being developed for use in electromagnets for nuclear fusion reactors and particle accelerators.
In the above-mentioned applications, an alternating magnetic field is applied to the superconducting wire, causing alternating current losses in the superconducting wire. The heat generated by the AC loss evaporates the refrigerant liquid helium, increasing the load on the refrigerator, or in severe cases, the temperature of the superconducting wire increases excessively, causing a normal conduction transition and burning out the electromagnet. Sometimes.

The present invention has been made in order to reduce AC losses that cause such adverse effects.The present invention has been made to improve multilayer stranded superconducting wires that have small AC losses caused by magnetic field components perpendicular to the superconducting wires, and to improve The present invention aims to provide a superconducting wire structure that also reduces AC loss caused by magnetic field components.

The present invention embeds a superconducting core wire in a stabilizing material and twists a plurality of wires as necessary.
In a multilayer stranded superconducting wire consisting of two or more layers twisted together, the twist pitch of each layer is proportional to the area surrounded by the projected locus formed on the cross section by the plurality of wires constituting each layer. This is a superconducting wire characterized by:

In the present invention, superconducting core wires include Nb-Ti,
Alloys consisting of Nb-Zr, etc., or V ₃ Ga, Nb ₃ Sn,
Refers to a core wire made of a superconducting material such as an intermetallic compound such as Nb ₃ Ge.

First, the principle of the present invention will be explained.

In order to reduce AC loss caused by magnetic field components perpendicular to the superconducting wire, the wire itself, which is made by embedding the superconducting core wire in a stabilizing material, is also twisted, and the superconducting wire is composed of multiple wires. It is well known that in some cases, the plurality of wires are twisted together. However, when a plurality of wires are twisted together, alternating current loss occurs due to magnetic field components parallel to the superconducting wires, for reasons explained below with reference to FIG. FIG. 1A is a sectional view showing an example of the arrangement of strands of a multilayer stranded superconducting wire. Now the outermost layer 1
Attention is paid to two strands 2 and one strand 1 in the inner layer. When looking at the strands 1 and 2 from the side, the first
The conductors 3 and 4 have a twist pitch length τ _p as shown in FIGS. The magnetic field parallel to the superconducting wire is the first
As shown by arrow B in the figure, the area interlinking with the magnetic field of conductors 3 and 4 is the area of conductors 3 and 4 seen from arrow C.
This is the area surrounded by the projection loci 5 and 6 on the cross section of . According to the law of electromagnetic induction, both ends of the conductor 3,
That is, the voltage generated between terminal A ₂ and terminal A′ ₂ is V ₁ = S ₅・B〓・n ……(1) The voltage generated between both ends of the conductor 4, that is, between terminal A ₁ and terminal A′ ₁ is given by V ₂ =S ₆・B〓・n (2).

However, S ₅ : Area surrounded by the projected locus 5 of the conductor 3 S ₆ : 〃 4 〃 6 〃 B〓 : Magnetic flux density change rate n : Number of turns = L/τp L : Wire length τp : Stranded wire pitch Figure 1 As is clear from , b, the area S 5 surrounded by the projected locus ₅ of the conductor 3 and the area S ₆ surrounded by the projected locus 6 of the conductor 4 are different, so from equations (1) and (2), the voltage V ₁
and V ₂ are different, and a potential difference occurs between conductor 3 and conductor 4, causing AC loss.

Now, if the twist pitch of conductor 3 and conductor 4 is S ₅ and S ₆
If the number of turns n in equations (1) and (2) is
is different between conductor 3 and conductor 4, and equations (1) and (2) become equations (3) and (4), respectively.

V ₁ =S ₅・B〓・L/a・S ₅ =B〓L/a ...(3) V ₂ =S ₆・B〓・L/a・S ₆ =B〓L/a ...( 4) However, a: proportionality constant From equations (3) and (4), V ₁ = V ₂ , and in this case, no AC loss occurs.

Next, the present invention will be explained using examples and drawings. FIG. 2 is a diagram illustrating an embodiment of the present invention.

In the figure, reference numeral 8 indicates a superconducting core wire 9 made of a niobium-titanium (Nb-Ti) alloy or a niobium-tin (Nb ₃ Sn) compound, embedded in a stabilizing material 10 made of copper, aluminum, or an alloy thereof. It is a strand of wire that has been twisted itself. The superconducting wire 14 is 1
The strand 13 that is the center of the book and the 6 strands 1 of the first layer
It is composed of 2 and 12 second layer strands 11.

In the present invention, the ratio of the twist pitch of the first layer to the twist pitch of the second layer is determined by the area surrounded by the projected locus 15 formed by the strands 12 on the cross section and the projected locus formed by the strands 11 on the cross section. 16.

FIG. 3 is a diagram illustrating another embodiment of the present invention.

In the figure, reference numeral 20 denotes a wire formed by embedding a superconducting core wire 21 made of a superconducting material such as a niobium-titanium alloy or a niobium-tin compound in a stabilizing material 22 made of copper, aluminum, or an alloy thereof, and twisting the core wire 21 itself. be. The superconducting wire 28 is 25-1,
25-2, 25-3, 25-4, 25-5, 25
-6 strands of the first layer shown by 6 and the 14 strands 24 of the second layer outside the strands, and a lead-tin alloy, a silver-tin alloy, or indium filled between the strands. - It is a rectangular stranded wire made of solder 23 made of a tin alloy or the like.

In the present invention, the ratio of the twist pitch of the first layer to the twist pitch of the second layer is set as follows:
2, 25-3, 25-4, 25-5, and 25-6 are surrounded by the projected locus 26 formed on the cross section, and the projected locus 27 formed by the second layer strands 24 on the cross section. It matches the ratio of the area covered.

As described above, the present invention provides a multilayer stranded superconducting wire consisting of two or more layers twisted together, in which the twist pitch of each layer is surrounded by the projected locus formed on the cross section by the plurality of wires constituting each layer. Since the superconducting wire is formed in proportion to the area of the superconducting wire, it is possible to reduce not only the AC loss due to the magnetic field component perpendicular to the superconducting wire, but also the AC loss due to the parallel magnetic field component, and prevent heat generation due to AC loss. This has the advantage of providing stable operation of the superconducting electromagnet and reducing the load on the refrigerant refrigerator.

[Brief explanation of the drawing]

Figure 1, A is a cross-sectional view showing an example of the arrangement of strands of a multilayer stranded superelectric wire, and Figure 1, B is a diagram showing the relationship between the wires and the magnetic field parallel to them in the arrangement of Figure A. be. FIG. 2 and FIG. 3 are diagrams each explaining an embodiment of the present invention. 1, 2, 8, 11, 12, 13, 20, 24,
25-1, 25-2, 25-3, 25-4, 25
-5,25-6...Element wire, 3,4...Conductor, 5,
6, 15, 16, 26, 27... Projection trajectory onto the cross section of the conductor, 9, 21... Superconducting core wire, 10,
22... Stabilizing material, 23... Solder, 28... Superconducting wire.

Claims (1)

[Claims] 1. In a multilayer stranded superconducting wire formed by twisting together two or more layers of a plurality of wires each having a superconducting core wire embedded in a stabilizing material, the twist pitch of each layer is such that the plurality of wires constituting each layer are A superconducting wire characterized in that its shape is proportional to the area surrounded by a projected locus formed on a cross section.