JPH0131244B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a superconducting wire used in a superconducting coil such as a superconducting magnet of a nuclear fusion reactor, and particularly to a type of superconducting wire that is forcedly circulated and cooled by a cooling medium.

Conventionally, as a cooling method for superconducting coils such as superconducting magnets, a cooling medium flow path is formed between each layer or each turn of a superconducting wire wound into a coil, and the superconducting wire is heated with liquid helium, etc. from the outer surface of the superconducting wire. The most common method was to use natural convection of the cooling medium. However, this conventional method has problems in terms of cooling efficiency, mechanical strength of the coil, economic efficiency, etc. In particular, recent large superconducting coils have various inconveniences.

Therefore, recently, so-called hollow superconducting wires with a cooling medium passage formed in the center have been used as superconducting wires, and a cooling medium such as supercritical pressure helium is forced to circulate in the cooling medium passage to forcibly cool the superconducting wire from the inside. Superconducting coils have been proposed. A hollow superconducting wire used in such a superconducting coil is, for example, as shown in FIG. A type in which the strands 3A are embedded, or as shown in Fig. 2, an ultrafine multicore superconducting strand 3B is wound or twisted around the outer surface of a stabilizing base material 2 made of copper or the like, which also has a rectangular cross section. In addition, as shown in FIG. 3, grooves 4 are formed on the outer surface of the stabilizing base material 2 having a rectangular cross section, and molded superconducting wires 3C are fitted and fixed in each groove 4. There are things like that. In all of these hollow superconducting wires, the stabilizing base material 2 such as copper is in direct contact with the cooling medium, and therefore the superconducting material constituting the superconducting wires 3A, 3B, and 3C is made of copper or the like. It will be indirectly cooled via the stabilizing base material 2.

A superconducting magnet using a hollow superconducting wire as described above has the following features compared to a conventional external cooling type magnet using natural convection. That is, since the cooling medium is forced to circulate within the conductor, each part is cooled more evenly than in the case of natural convection cooling. Further, since cooling medium passages between layers and turns of the coil are not required, a compact coil with high mechanical strength can be obtained, and the degree of freedom in the shape of the coil is therefore increased.
Furthermore, since there are no conductor parts directly exposed to the outside for cooling, there is no need to worry about short circuits between turns or layers during manufacturing, and the dielectric strength is increased, and there is no need to cool through an insulator. Large insulators can be used. and again,
Since there is no need to store liquid helium and no helium dewar is required, problems with the shape and strength of the dewar, which have been problems in the past, are alleviated. In addition, the amount of helium contained in the hollow superconducting wire is much smaller than the amount of helium contained in the dewar in the conventional method, making it highly economical. Furthermore, the efficiency of pumping out liquid helium through the transfer tube in the conventional method is poor;
There is the problem that a considerable amount of helium escapes to the outside, and when a large amount of helium is used, it takes a considerable amount of time to pump it out, but it is possible to circulate the cooling medium in a closed circuit using hollow superconducting wires. In this case, this kind of effort is unnecessary, and helium does not escape to the outside.

As mentioned above, superconducting coils using hollow superconducting wires have various advantages over conventional natural convection external cooling type coils, but on the other hand, they also have the following drawbacks. That is,
As mentioned above, since the superconducting wire is indirectly cooled through a stabilizing base material such as copper, the cooling efficiency is lower than that of direct cooling. There is a problem in that when heat spots occur in a part and the superconducting properties are lost, the recovery is slightly delayed.

On the other hand, recently, as shown in FIG. 4, a large number of superconducting strands 3B are housed inside a hollow rectangular cylindrical body 6, and a cooling medium such as liquid helium is filled in the gaps 7 between the superconducting strands. A so-called bundle type superconducting wire that is made to flow has also been proposed, and in this case, a cooling medium is brought into direct contact with the surface of the superconducting strand 3B to perform direct cooling. However, in this type of superconducting wire, it is extremely difficult to allow the coolant to flow smoothly, and the flow of the coolant can locally become stagnant, causing the temperature to rise, creating heat spots, or causing the heat spots to recover quickly. There is a drawback that it is not carried out.

This invention was made in view of the above circumstances, and basically combines the advantages of the hollow superconducting wire and the fourth
By incorporating the advantages of the directly cooled superconducting wire shown in the figure, we have created a structure that has high overall cooling efficiency, good local stability, and can withstand large electromagnetic forces. To provide a superconducting wire having a multilayer structure of two or more layers suitable for large currents and effectively preventing generation of coupling current between each layer of the multilayer structure even when the excitation speed is extremely high as in pulse driving. The purpose is to

In other words, the forced cooling type superconducting wire of the present invention accommodates a plurality of superconducting strands in a hollow stabilizing base material, surrounds the stabilizing base material with an outer sheath through a separator, and connects the outer sheath with the separator. A cooling medium flow path is secured between the stabilizing base material, and a communication path is formed in the stabilization base material to communicate the cooling medium flow path on the outside with the superconducting wire side on the inside,
As a result, the cooling medium flowing in the cooling medium flow path outside the stabilizing base material flows into the gap between the superconducting wires inside the stabilizing base material through the communication path, directly cooling the superconducting wires, and cooling the entire superconducting wire. cooling by the flow of the cooling medium in the outer cooling medium flow path,
Moreover, by arranging the superconducting strands so that they are located at the innermost part (in the center), the structure is such that the superconducting strands are less likely to be damaged by large electromagnetic forces and the effects of bending strain are reduced. In addition to the above-mentioned configuration, the superconducting wire in the stabilizing base material has a multilayer structure of two or more layers suitable for large currents, and a thin tape made of a high-resistance conductive material is interposed between each layer. The tape suppresses the coupling current between each layer.

Hereinafter, the superconducting wire of the present invention will be explained in detail with reference to FIG. 5 and subsequent figures.

FIG. 5 shows an example of the superconducting wire of the present invention, in which a hollow stabilizing base material 1 having a rectangular cross section is shown.
Superconducting wire assemblies 17A and 17B, which are formed by collecting a plurality of superconducting wires 11, are housed inside the superconducting wire 0 in two or more layers stacked one on top of the other. Each of these superconducting wire assemblies 17A, 17B has, for example, a molded stranded wire structure that is compression-molded into a rectangular shape after twisting, a braided structure, or a molded braided structure that is compression-molded after braiding. A thin tape 18 made of a high resistance conductive material such as Cypronickel is interposed between the superconducting wire assemblies 17A and 17B of the superconducting wire assemblies 1 of each layer.
7A and 17B are configured so that they do not come into direct contact with each other. The outside of the stabilizing base material 10 is surrounded by a hollow cylindrical jacket 13 having a rectangular cross section with an appropriate number of spacers 12 interposed between the outer surface of the stabilizing base material 10 and the jacket. A cooling medium flow path 14 is secured between the inner surface of the cooling medium 13 and the inner surface of the cooling medium 13 .
Further, the stabilizing base material 10 is formed with a communication passage 15 that communicates the outer coolant flow path 14 with the inner space. Therefore, the cooling medium flowing through the cooling medium channel 14 flows through the communication path 15 and flows into the gap 16 between the superconducting wires 11 inside the stabilizing base material 10, and the cooling medium flows directly into the superconducting wire 11. will come into contact with each other. And this stabilizing base material 10
A flow of the cooling medium also occurs in the inter-wire gap 16 of the superconducting wire 11 inside the superconducting wire 11 .

In the above-described configuration, steady cooling of the superconducting wire 11 is performed by the cooling medium flowing through the cooling medium flow path 14 outside the stabilizing base material 10.
Cooling at the transition stage, that is, cooling for recovery when a heat spot occurs, is performed through the interline gap 1 in the stabilizing base material 10.
6 cooling medium directly. Then, the inner cooling medium and the outer cooling medium are appropriately exchanged via the communication passage 15 formed in the stabilizing base material 10.

As the superconducting wire 11, Nb-Ti alloy,
Either alloy-based superconducting strands such as Nb-Ti-Ta alloy or compound-based superconducting strands such as Nb ₃ Sn, V ₃ Ga, Nb ₃ Ge, etc. may be used. In addition, the wire diameter of the superconducting wire 11 is arbitrary from about 0.1 to 2.0 mm,
This invention is particularly effective when using a large-diameter superconducting wire with a wire diameter of 1.0 mm or more. Furthermore, regarding the heat treatment to generate superconducting materials such as Nb ₃ Sn that make up the superconducting strands, there are two methods: one is to perform the heat treatment after winding the wire into a coil to make it into a magnet, and the other is to perform the heat treatment in advance before winding the wire. Although the structure of the present invention is basically suitable for the former method, it is of course also applicable to the latter method.

Furthermore, in the structure shown in FIG. 5, since a high-resistance conductive material tape 18 such as Cypronickel is interposed between the superconducting wire assemblies 17A and 17B in each layer, it is possible to prevent a coupling current from flowing between each layer. Therefore, it is possible to prevent deterioration of superconducting properties when the excitation speed is extremely high, such as in pulse drive. In some cases, as shown in FIG.
A thin tape 19 made of a high-resistance conductive material such as Cypronickel may also be inserted between the outer surfaces of A and 17B and the stabilizing base material. In other words, when such a tape 19 is not inserted, the wire is transferred from the outer surface side of the superconducting wire assembly 17A of one layer to the superconducting wire assembly 17B of the other layer via the stabilizing base material 10. Although a coupling current may flow, by interposing the high-resistance conductive material tape 19, such coupling current can be prevented through the stabilizing base material 10. However, although FIG. 6 shows a state where the tape 19 is provided on the entire outer surface of each layer 17A and 17B for the sake of simplicity, in reality, the tape 19 is provided on the entire outer surface of each layer 17A, 17B, but in reality, the tape 19 is provided so as not to obstruct the inflow of the cooling medium from the communication path 15. It is desirable to form a space as appropriate, as will be described later.

The thickness of the high-resistance conductive material tapes 18 and 19 as described above is, for example, when using Cypronickel.
It is desirable to set it to about 0.05 to 0.5 mm. Further, the specific means for interposing the tapes 18 and 19 is arbitrary, but for example, in the case of the tape 18 between each layer, it is placed between the superconducting strand aggregates 17A and 17B in a so-called longitudinally aligned state. It would be better to insert it with Alternatively, the tape may be wound in an open spiral around each superconducting wire assembly 17A, 17B, and in this case, the same tape serves as the interlayer tape 18 and the outer tape 19. Regarding the outer tape 19, both superconducting wire aggregates 17
It may be wound in an open spiral around the entire outside of A and 17B. By winding the coil in an open spiral in this manner, the cooling medium can flow through the spaces between the spirals.

The stabilizing base material 10 is for stabilizing the superconducting wire to bypass the current and prevent the entire superconducting wire from transitioning to normal conduction when a part of the superconducting wire transitions to normal conduction due to some kind of shock. However, in the case of the present invention, in addition to this, it also functions as a reinforcing structural material. That is, stabilizing base material 1
0 serves to protect the internal superconducting wire from damage caused by strong electromagnetic force. This stabilizing base material 1
The material for 0 may be any material as long as it has low resistance on the high magnetic field side and has a certain degree of strength, and oxygen-free copper is usually used, but copper alloys, high-purity aluminum, or various aluminum alloys may also be used. Can be used. Additionally, a communication path 15 formed in the stabilizing base material 10
The shape is arbitrary, and may be, for example, a round hole shape as shown in FIG. 7, or a slit shape as shown in FIG. 8.

The spacer 12 for securing the coolant flow path 14 around the stabilizing base material 10 may be arranged parallel to the longitudinal direction, or may be spirally wound. Moreover, the shape of the spacer 12 is the fifth
It may have a rectangular shape as shown in the figure, a round bar shape as shown in FIG. 9, or a hollow pipe shape as shown in FIG. 10. However, the first
When using pipe-shaped separators 12 as shown in FIG.
It is desirable that the space inside the separator (pipe) 12 also be used as a cooling medium passage. Also separator 1
The material of 2 may be the same as that of the stabilizing base material 10, or stainless steel or the like may be used to ensure strength. Note that the separator 12 is preferably fixed to the stabilizing base material 10 by spot welding or the like.

The outermost jacket 13 must satisfy requirements such as withstanding the pressure of the cooling medium and not being damaged by electromagnetic force, and is made of various metal materials such as steel, stainless steel, titanium, and titanium alloys. It is desirable to use it. Further, as the jacket 13, either a welded pipe or a seamless pipe can be used.

As the cooling medium, supercritical pressure helium is suitable as in the case of the hollow superconducting wire, but normal liquid helium or superfluid helium can of course also be used.

An example in which a superconducting magnet was prepared using the superconducting wire of the present invention and its superconducting properties were investigated will be described below.

The superconducting wire used is an ultra-fine multicore wire with an outer diameter of 1.4 mm.
It is an Nb ₃ Sn wire, and its detailed cross-sectional structure is shown in FIG. In other words, this superconducting wire has a total of 7,735 Nb ₃ Sn filaments 21 with a diameter of 7 μm embedded in a Cu-Sn alloy (bronze) base 20, and
The outer periphery of the Cu-Sn alloy base 20 is covered with a diffusion barrier layer 22 made of Nb.
A stabilizing copper layer 23 made of oxygen-free copper is provided on the outside of the copper layer 2, and the overall ratio of Cu to non-Cu is 0.8. The superconducting property of this superconducting wire itself is the critical current I _c at 4.2K and 10T.
was maximum 550A. Such superconducting wire
The 15 wires are twisted together and formed into a rectangular shape, and the rectangular shaped stranded wires (i.e. superconducting wire aggregates 17A, 17
B) are stacked in two layers, and as shown in Fig. 6, a 0.1 mm thick tape 18 made of Cypronickel is interposed vertically between both layers, and a Cypronickel tape 19 also 0.1 mm thick is placed between the two layers. It was wound in an open spiral around the outside of two layers of superimposed formed stranded wires 17A and 17B. and stabilizing base material 1
Oxygen-free copper rectangular welded pipe with thickness 1.2mm as 0,
A hollow superconducting wire as shown in FIG. 6 was prepared using a rectangular oxygen-free copper wire with a thickness of 1.5 mm as the separator 12 and a rectangular stainless steel pipe with a thickness of 0.8 mm as the jacket 13. However, the overall cross-sectional dimensions of this hollow superconducting wire are 20 mm on the long side and 13 mm on the short side.
It is. Such a hollow superconducting wire (provided that it is in the state of a bronze-Nb filament composite before being heat-treated to generate Nb ₃ Sn filaments)
A length of 35 m was wound into a double pancake coil with an outer diameter of 60 cm, and a Nb ₃ Sn-based forced cooling type superconducting magnet was created by heat treatment to generate Nb ₃ Sn. When we generated a magnetic field of 7T using a backup coil and flowed supercritical helium into the superconducting wire (inside the cooling medium flow path) of the central Nb ₃ Sn forced cooling type magnet, a current of 7000A was generated. We were able to generate a magnetic field with a maximum central magnetic field of 12T. From this result, it is clear that by using the superconducting wire of the present invention, an extremely strong superconducting magnet with excellent superconducting properties can be produced.

As is clear from the above explanation, in the superconducting wire of the present invention, the overall cooling is achieved by the steady flow of the cooling medium flowing through the cooling medium channel outside the stabilizing base material. Uniform cooling is performed in the same way as in the case of wires, and the cooling medium is directly in contact with the superconducting wire itself inside the stabilizing base material, resulting in direct cooling, resulting in high cooling efficiency. Since the cooling medium and the inner cooling medium are exchanged by flowing in and out through the communication path, the inner cooling medium is not locally cooled as in the case of the conventional bundle type directly cooled superconducting wire shown in Fig. 4. There is very little occurrence of heat spots due to temperature rise or delay in the number of heat spots, and therefore, the overall cooling efficiency is excellent, and at the same time, local stability is also extremely excellent. In addition, in the superconducting wire of this invention, when a disturbance occurs and the superconducting state is broken and a magnetic flux flow state occurs, the current is shunted to the stabilizing base material, so that the stabilizing base material also generates heat. However, since the heat generated by this stabilizing base material is also cooled by the cooling medium on the outside, the fourth
Compared to the conventional bundle-type direct cooling method shown in the figure, the superconducting state can be recovered more quickly. Furthermore, as mentioned above, since the cooling medium inside and outside the stabilizing base material flows in and out through the communication path, the collective structure of the superconducting strands in the stabilizing base material allows the cooling medium to flow smoothly in the longitudinal direction. There is no particular problem even if the superconducting wire has a structure that does not easily flow, such as a braided structure or a formed stranded wire structure.Therefore, there is no restriction on the aggregate structure of the superconducting strands, so there is a great degree of freedom in its design. Furthermore, since the superconducting wire is placed in the center of the superconducting wire, there is less deterioration of the characteristics of the superconducting wire due to bending strain when it is wound around a coil such as a magnet. Since the superconducting wire is protected by the material, damage and deterioration of the superconducting wire due to electromagnetic force from the outside can be effectively prevented. As mentioned above, a braided wire or a formed stranded wire can be used as the superconducting wire, and since it is arranged in the center, it is possible to provide a wire with low loss and good characteristics even when used for alternating current. The combined current prevention effect of the high-resistance conductive material tape between each layer of each superconducting wire assembly is combined, and sufficient characteristics can be obtained with low loss when used for alternating current applications.

As described above, the superconducting wire of the present invention has good cooling efficiency and excellent stability, and also has excellent mechanical strength against bending, external force, etc.
In addition to nuclear fusion, the superconducting wire of the present invention is ideal for various applications such as various electrical machines, energy storage, nuclear magnetic resonance absorption, and magnetic separation, especially for large, high-field magnets. Since the superconducting strand assembly is housed in multiple layers and the coupling current between each layer is prevented by a tape made of a high-resistance conductive material, it is ideal for pulse applications using large currents.

[Brief explanation of drawings]

1 to 3 are cross-sectional views showing an example of a conventional hollow superconducting wire, FIG. 4 is a cross-sectional view showing an example of a conventional directly cooled superconducting wire, and FIG. 5 is a cross-sectional view showing an example of a conventional directly cooled superconducting wire. A cross-sectional perspective view showing a first example,
FIG. 6 is a cross-sectional perspective view showing a second example of the superconducting wire of the present invention, and FIGS. 7 and 8 are cross-sectional perspective views showing an example of the stabilizing base material used in the superconducting wire of the present invention, respectively. FIG. 9 is a sectional view showing a third example of the superconducting wire of this invention, FIG. 10 is a sectional view showing a fourth example of the superconducting wire of this invention, and FIG. 11 is a sectional view showing a third example of the superconducting wire of this invention. FIG. 2 is a cross-sectional view showing an example of a superconducting strand. 10... Stabilizing base material, 11... Superconducting wire, 1
2...Spacer, 13...Sheath, 14...Cooling medium passage, 15...Communication path, 16...Gap between superconducting strands, 17A, 17B...Superconducting strand assembly,
18...High resistance conductive material tape.

Claims (1)

[Claims] 1 A plurality of superconducting strands are housed in a plurality of layers inside the hollow stabilizing base material, and a thin tape made of a high-resistance conductive material is inserted between each layer, and the above-mentioned The stabilizing base material is surrounded by a cylindrical jacket with a separator in between, and a cooling medium flow path continuous in the longitudinal direction is formed between the stabilizing base material and the jacket, and the stabilizing base material is surrounded by a cylindrical jacket. A communicating path is formed in the stabilizing base material, and the cooling medium flowing through the cooling medium flow path flows into the gap between the superconducting strands in the stabilizing base material through the communicating path to directly cool the superconducting strands. A forced cooling type superconducting wire characterized in that it is configured so as to be able to