JPS63192207A - Superconducting coil - Google Patents

Abstract

PURPOSE:To improve reliability and performance by winding and forming a superconducting wire rod with an inorganic insulating thin-film coating layer having good thermal conductivity at a low temperature. CONSTITUTION:A superconducting wire rod having structure having the coating layer of an inorganic insulating thin-film displaying good thermal conductivity at a low temperature is used as a winding wire, and either of diamond, alumina, amorphous diamond or amorphous alumina is employed as the inorganic insulating thin-film. The superconducting wire rod such as a wire rod 1 is manufactured by coating a superconducting wire 2 with the inorganic insulating thin-film 3 consisting of diamond, and the wire rod 1 is wound densely on a bobbin 4, thus completing a solenoid type superconducting coil 5. Accordingly, the possibility of quenching is removed by heat generated in the superconducting coil, and the acceleration of excitation also works to the diffusion of AC heat loss effectively, thus improving reliability, then allowing excitation at high speed and stably displaying expected performance.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a superconducting coil with excellent cooling properties.

The present invention is applicable not only to superconducting coils for magnets but also for other uses such as transformers and generator armatures.

[Conventional technology]

As measures to improve the cooling characteristics of superconducting coils, two methods have become common: providing a cooling channel between the superconducting wires, such as between the eyebrows, through which liquid helium passes, and using a material with good heat conductivity for the spacer between the superconducting wires. This invention belongs to the latter form.

By the way, in the latter type of conventional coil, there are two methods: (1) impregnating commercially available epoxy resin with good thermal conductivity between the wires and using this as a spacer, (2) inserting a metal with good thermal conductivity, such as copper foil, between the eyebrows. method is being adopted.

Method (2) involves impregnating a coil with a resin mixed with fine powder with good thermal conductivity, such as alumina or metal powder, in a vacuum, and forming wires through the resin mixed with the fine powder, which fills the gaps between the wires. The idea is to diffuse heat to the outside.

In addition, method (2) improves the heat conduction between the eyebrows in the same way as above, by wrapping a copper foil insulated with a thin film such as Mylar when winding the tluid coil, for example.

[Problem that the invention seeks to solve]

Superconducting coils that adopt method Therefore, there are problems in that local temperature increases are likely to occur, the coil is unstable, and transition to normal conductivity (quenching) is likely to occur.

In addition, since superconducting wires are wrapped in glass fiber, etc., which easily absorbs resin, and then impregnated with resin to insulate the wires, the insulation layer becomes unnecessarily thick, slowing down the heat transfer rate, and slowing down the manufacturing process. There is also the problem of complicating things.

On the other hand, the coil made by method (2) had problems such as poor heat conduction due to the insulating film on the surface of the copper foil, and if the winding was made too tight to prevent this, a short circuit would occur between the eyebrows through the copper foil. . Note that enamel such as formal is usually used to insulate coil wires, but this is not suitable for superconducting coils.

This invention aims to eliminate the above-mentioned problems and improve the reliability and performance of superconducting coils.

[Means for solving problems]

The superconducting coil of the present invention is characterized by using a superconducting wire having a structure as shown in FIG. 1 or 2, which has a coating layer of an inorganic insulating thin film that exhibits good thermal conductivity at low temperatures for the wire to be wound. can be attached.

A wire 1 in FIG. 1 is a superconducting wire 2 coated with an inorganic insulating thin film 3 such as diamond.
As shown in the figure, if this is densely wound around bobbin 4,
The tluid type superconducting coil 5 is completed.

On the other hand, the wire 1' shown in Fig. 2 is a superconducting wire 2' coated with an inorganic insulating thin film 3 and twisted into a rectangular shape, with an insulating spacer 6 interposed between the eyebrows. When the superconducting coil 5' is wound in layers as shown in FIG. 4, a so-called pancake-wound superconducting coil 5' is completed. 1
0 shows an example of a low-temperature container in which a coil 5' is housed. A heat insulating layer 13 exists between an inner tank 11 and an outer tank 12, and the coil 5' is cooled by liquid helium 14 in the inner tank 11. It is 4 strained to make it.

It should be noted that the superconducting wire to be used may be one having an inorganic insulating thin film 3 on its surface, and various configurations other than those illustrated are possible. The shape of the coil is not limited to that shown in the drawings; for example, it may be a saddle-shaped or racetrack-shaped dipole coil.

Further, the material of the thin film 3 may be alumina, amorphous diamond, amorphous alumina, etc. other than diamond.

[Effect]

The thermal conductivity of diamond, for example, which constitutes the thin film 3, is generally very good at low temperatures, unlike commonly used insulators such as epoxy resin, and is on the same level as copper. Therefore,
Even a small amount of heat is quickly transmitted and diffused, preventing local temperature rises in the coil.

Further, in the case of diamond, the film thickness may be extremely thin compared to the above-mentioned epoxy because it is extremely hard, mechanically strong, and durable. Therefore, heat transfers quickly,
It is difficult for the temperature to rise.

Furthermore, since diamond is an excellent insulator, even if the windings are strengthened, the insulation performance will not deteriorate, and there is no need to worry about interlayer short circuits that occur with copper foil.

In addition, a diamond thin film can be coated relatively easily by CVD (vapor phase growth), and the coil manufacturing process does not become complicated because the coated wire or the twisted wire thereof can be simply wound.

This also applies when alumina or the like is used as the thin film material.

〔Example〕

More specific examples will be described below.

A well-known plasma CVD method or the like may be used to coat the superconducting wire with a thin film of diamond or the like.

That is, first, a supply reel 16 and a take-up reel 17 for continuously feeding out superconducting wire 2 are set in a reaction tube 15 of a plasma CVD apparatus as shown in FIG. supplies raw material gases 18 of H2 and CH4 into the reaction tube.

Under this condition, as shown in the figure (a microwave 20 is emitted from the magnetron 19 and sent from the waveguide 21 to the reaction section to turn the reaction section into a plasma state. 22 is a peephole.

On the other hand, a substrate (not shown) in the reaction tube is heated to maintain the superconducting wire 1 at a temperature of 700 to 1000° C. using radiant heat. Then, a thin diamond film grows on the superconducting wire due to the high-temperature reaction of the source gas.

In the example, a 3 μm thick diamond coating was performed at a growth rate of 1 μm/hr. The gas flow rate at this time was 100 m 17w1n.

Next, the wire thus obtained was used to fabricate a truide-type superconducting coil shown in FIG. 2.

The superconducting wire has a diameter of 0.7 mm, a copper ratio of 1.0, and a length of 3000 m.
The number of layers of the 0 winding wire, which is wound on a stainless steel bobbin, is 27 layers, and the total number of turns is 6500 turns.
The finished diameter of the coil is as shown in Fig. 2: outer diameter D - 140 m, inner diameter d = 100 m, and height H 270 m.

After this, when the completed coil was energized, it reached 6T in 5 minutes without training and without quenching.

Furthermore, the excitation speed was increased and the excitation time up to 6T was shortened to 2 minutes and 1 minute, but no quench occurred at this time either. On the other hand, for comparison, we energized formal insulated coils wound under the same conditions, and found that without training,
Even if the excitation time is 5 minutes, 5. Quench occurs in OT, 6
It didn't reach T. The cause is presumed to be AC loss that occurs during excitation.

The above energization experiment results show that the coil of this invention has better heat dissipation due to the inorganic insulating thin film made of diamond, etc., which quickly diffuses AC loss heat and frictional heat generated between the wires. It can be said that this is clearly expressed.

〔effect〕

As mentioned above, this invention coats the superconducting wire with an inorganic insulating thin film and uses this as a spacer to improve the cooling performance (heat dissipation) of the entire coil. There is no need to worry about the coil being quenched due to heat produced by the coil, such as frictional heat between the wires moved by electromagnetic force.

Furthermore, since it effectively works to diffuse AC loss heat caused by accelerating excitation, reliability in preventing quenching is further increased. Therefore, it is possible to excite at high speed whether it is a DC coil or an AC coil, and the desired performance can be stably exhibited.

The effect on DC coils is due to the above reasons.

On the other hand, AC coils are particularly effective because AC loss greatly affects performance.

As mentioned above, the superconducting wire used is not particularly limited, such as monolithic wires, rectangular stranded wires, etc., but in the case of rectangular stranded wires, the coating film provides electrical insulation between the strands, so there is no coupling loss. (a type of alternating current loss), which reduces heat generation in the conductor, making it particularly suitable for coils for alternating current applications.

[Brief explanation of the drawing]

1 and 2 are cross-sectional views showing an example of a superconducting wire used in the present invention, FIGS. 3 and 4 are cross-sectional views showing an example of a superconducting coil according to the second invention, and FIG. 5 is a cross-sectional view showing an example of a superconducting wire used in the present invention. FIG. 3 is a diagram illustrating a coating process of an inorganic insulating thin film. 1.1'...Superconducting wire, 2.2'...
・Superconducting wire, 3...Inorganic v! A edge thin film, 4
...Bobbin, 5.5'...Superconducting coil, 6...Insulating spacer.

Claims (2)

[Claims] (1) A superconducting coil formed by winding a superconducting wire having an inorganic insulating thin film coating layer with good thermal conductivity at low temperatures. (2) Claim No. 1, characterized in that the inorganic insulating thin film is one of diamond, alumina, amorphous diamond, and amorphous alumina.
) The superconducting coil described in section 2.