JPH0452569B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Application Field] The present invention relates to a wire assembly type compound superconducting conductor,
In particular, the present invention relates to a wire assembly type compound superconducting conductor with an improved wire reinforcement structure. [Prior Art] Compound superconducting conductors inherently have excellent superconducting properties such as critical temperature, critical magnetic field, and critical current density. Therefore, it is promising as a winding for high magnetic fields. By the way, unlike alloy superconducting conductors, compound superconducting conductors have a strain sensitivity in which the superconducting properties significantly deteriorate when subjected to strain, and are usually 0.2 to 0.6
It cannot be used in the strain range of % or more. On the other hand, as a request from the side that uses compound superconducting conductors,
It can be bent to a small radius of curvature, has a large current capacity, is a long continuous large conductor, and has a uniform reinforcement effect in the coil. Fiber aggregate type superconducting conductors are attracting attention as a material that meets these demands. Typical forms of such wire assembly type superconducting wires include twisted wires, braided wires, dislocation wires, and compression molding of a plurality of compound superconducting wires. However, the essential drawbacks of the wire assembly type compound superconducting conductor are that the conductor size changes during winding because it easily stretches in the longitudinal direction and contracts in the radial direction under small tension, and that the conductor size changes during winding. There are many spaces between the wires, so the filling rate of the wires is low, and if the wires are locally restrained, such as by tightening the conductor at a predetermined interval with a reinforcing body, etc.
The strong electromagnetic force generated in the coil causes stress and strain to concentrate on the strands of the wire in the non-tightened portion, resulting in a significant deterioration of superconducting properties. Therefore, there is a need for a reinforced structure for aggregated compound superconducting conductors that overcomes the above-mentioned essential drawbacks. As a conventional wire assembly type compound superconductor,
Six types of structures have been proposed as described below. The first wire assembly type compound superconductor has a structure in which a plurality of superconducting wires 2 are twisted around a reinforcing body 1, as shown in FIG. 1a. The second strand assembly type compound superconductor has a structure in which a plurality of secondary strands 3 in which a plurality of superconducting strands 2 are twisted in advance are twisted around a reinforcing body 1, as shown in FIG. 1b. It is. The third wire assembly type compound superconductor is produced by twisting a plurality of reinforcing wires 1' and a plurality of superconducting wires 2, as shown in FIG. It has a rolled structure. The fourth wire assembly type compound superconductor is produced by twisting a plurality of superconducting wires 2 as shown in FIG. It has a structure made of 50, etc. As shown in FIG. 1e, the fifth strand-aggregated compound superconductor conductor includes secondary strands 3 in which a plurality of superconducting strands have been twisted in advance, as in the second conductor, and a reinforcing body 1. It has a structure in which a plurality of wires are stranded around the ``, and then these are housed in a U-shaped reinforcing body 1 with one side open.The sixth strand assembly type compound superconducting conductor is shown in Figure 1 f. In this structure, a plurality of superconducting strands are twisted in advance to form a secondary strand 3, and the plurality of secondary strands 3 are housed in a tubular reinforcing body 1 having cooling holes 5 on the side surface. [Problems to be Solved by the Invention] However, in the first and second wire assembly type compound superconducting conductors, since the superconducting wire 2 or the secondary prime number 3 is located in the outermost layer, the insulation treatment process and the winding process are difficult. There is a problem in that it is subjected to external stress and strain during processes, etc. In the third wire assembly type compound superconducting conductor,
Since the reinforcing body 1 is arranged discontinuously on the outside of the wire and has unevenness in the longitudinal direction, these unevenness contact randomly between adjacent turns of the coil during the winding process, creating irregular gaps in that part and causing stress. is concentrated,
As a result, there is a problem that current characteristics deteriorate. The fourth to sixth wire assembly type compound superconducting conductors have a protective function against external stress and distortion, but because the reinforcing bodies are manufactured by machining such as cutting and die extrusion, they are thick and lightweight. As a result, the current density of the conductor as a whole decreases accordingly. Furthermore, since the reinforcing body is thick, flexibility during the winding process is poor. Furthermore, there is a limit to how many cooling holes can be densely provided in the reinforcing body by machining, and the cooling holes of adjacent conductors are unlikely to meet each other in the coil after winding, so the refrigerant liquid He
There is a problem that the cooling efficiency is poor because the He gas passages do not communicate with adjacent conductors. Furthermore, in the first to sixth strand aggregate type compound superconducting conductors, the strands constituting the aggregate conductor are not reinforced individually, so the overall stress and strain applied to the conductor is reduced by the reinforcing material. However, it is vulnerable to local stress and strain applied to each strand. For this reason, particularly when superconducting conductors are used in irregularly shaped coils such as racetrack type coils and saddle type coils, there is a problem in that each strand is subjected to local stress and strain. The present invention was made in order to solve the conventional problems, and aims to provide a wire assembly type compound superconducting conductor with improved mechanical strength, flexibility, cooling efficiency, critical current characteristics, etc. It is something. [Means for Solving the Problems] The present invention provides a wire assembly type compound superconducting conductor comprising a desired number of compound superconducting wires having a compound superconductor in a metal matrix.
The strand assembly type compound superconducting conductor is characterized in that a tape-shaped reinforcing body having an inorganic film on at least the inner surface is provided on each of the strands by butt winding. Hereinafter, the wire assembly type compound superconducting conductor of the present invention will be explained in detail with reference to the drawings. FIG. 2 shows an example of a compound superconducting strand used in the strand-aggregated compound superconducting conductor of the present invention, and is a perspective view with a tape reinforcement on the strand partially opened. That is, 2 in the figure is the metal matrix 2
This is a multicore compound superconducting strand in which a large number of compound superconducting filaments 22 are built in. The reinforcing wire 20 is formed by forming a tape-shaped reinforcing body 10 having an inorganic film on at least the inner surface closely around the compound superconducting wire 2 so as to butt wrap it. The abutting portion 23 of the tape-shaped reinforcing body 10 has a thickness of about several μm to about 10 μm. The multicore compound superconducting wire 2 is not particularly limited, but for example, a large number of compound superconducting filaments such as Nb ₃ Sn or V ₃ Ca are embedded in a metal matrix such as a copper-tin alloy matrix or a copper-gallium alloy matrix. There are wires with a structure in which the wires are embedded, and wires with a structure in which a stabilizing metal layer such as high-purity copper or aluminum is provided on the outer periphery or inside the wire with a thin layer of a diffusion prevention barrier such as tantalum interposed therebetween. . The compound superconducting filament may be continuous in the longitudinal direction of the wire in a metal matrix, or may be a discontinuous filament made by the so-called in-centre method or powder method. The cross-sectional shape of the compound superconducting wire is not particularly limited, but usually includes a circular wire shown in FIG. 2, a rectangular flat wire, a trapezoidal irregular wire, and the like. The material constituting the tape-shaped reinforcing body is as follows:
Non-magnetic materials are used, such as stainless steel,
Single or composite materials such as copper alloy, aluminum alloy, and titanium alloy are used. As shown in FIG. 2, it is preferable to provide an inorganic film 24 of Al ₂ O ₃ , MgO, SiO ₂ , CuO, etc. on at least the inner surface of the tape-shaped reinforcing body. This can prevent the stabilized high-purity metal provided on the surface layer of the metal matrix of the wire 2 from being contaminated by the metal of the reinforcing body 10 during the diffusion heat treatment. By providing such a film 24 not only on the inner surface of the reinforcing body 10 but also on the outer surface, it is possible to electrically insulate the strands of the aggregated compound superconducting conductor from each other. Further, the coating provided on the outer surface of the reinforcing body 10 also functions as a separator to prevent sintering between adjacent turns when a coil is manufactured by the wind and react method. In order to provide the tape-shaped reinforcing body on the compound superconducting strand in a butt-wound manner, if the diameter of the strand is relatively large, it can be simply wrapped by taping called butt-wound. In addition, if the wire has a small diameter and low strength, the tape-like reinforcing material can be fed into the die along with the wire vertically and twisted when it exits the die. It can be provided in a double winding. In this case, the strands themselves can be twisted at the same time. In any case, the tape-shaped reinforcement is applied to the wire when the compound superconducting filament has not yet been formed in the wire, that is, before the diffusion heat treatment for forming the compound superconductor is performed. . This is because compound superconductors are susceptible to distortion. The proportion of the reinforcing body in the entire reinforced wire varies depending on the manufacturing household of the wire, current capacity, magnetic field strength received during superconducting, etc., but at least approximately 25% or more of the cross-sectional area of the reinforced wire. It is desirable that The reinforcing strands are assembled as desired and used as a strand-aggregated compound superconducting conductor as shown in FIGS. 1a to 1f. The structure of the strand-aggregated compound superconducting conductor according to the present invention is not specified in any way, such as its aggregated state or shape; for example, a stranded wire, a braided wire, a dislocation wire, or These compression molded wires, or such twisted wires, braided wires, dislocation wires,
These compression-molded wires may further have a wire or strip-shaped reinforcing body in their core, or these wires may be made into two-character wires and stranded wires, braided wires, transposed wires, compression-molded wires, etc. are applied in the same manner as above. Any of the above is acceptable. In addition, the cross-sectional shape of the wire assembly type compound superconductor is not specified at all, but it may be circular, oval,
Generally, they are rectangular or trapezoidal (so-called keystone type) with different lengths for the upper and lower bases. In particular, flat wire conductors with a rectangular cross section are used for large current magnet coils, and conductors with trapezoidal and keystone cross sections are used for irregularly shaped magnet coils. [Function] According to the present invention, in a wire assembly type compound superconducting conductor consisting of a desired number of aggregates of compound superconducting wires having a compound superconductor in a metal matrix, an inorganic film is provided on at least the inner surface of each of the wires. To obtain a wire assembly type compound superconducting conductor with improved mechanical strength, flexibility, cooling efficiency, critical current characteristics, etc., by providing tape-like reinforcement bodies having the same structure by butt winding. Can be done. In other words, an inorganic film such as Al ₂ O ₃ does not become densified by sintering at a heating temperature comparable to the diffusion heat treatment used to generate a compound superconducting conductor, and is porous. It can be expected to act as a buffer material against slight distortions. Therefore, even if local stress or strain is applied to the conductor, the inorganic film on the inner surface of the tape-shaped reinforcement acts as a buffer and absorbs the stress and strain.
It is possible to prevent local stress and distortion from being applied to each strand body, and improve the mechanical strength, critical current characteristics, etc. of the strands. Moreover, by reducing the thickness, or amount, of the tape-shaped reinforcement to the necessary minimum, it is significantly thinner than reinforcement made by conventional machining.
The weight can be reduced and the current density of the entire conductor can be improved. Further, since there is a gap between the abutting portions of the tape-shaped reinforcing body, when each of the wires is bent, this gap opens on the outside of the bend and closes on the inside of the bend.
Therefore, the reinforcing body itself receives almost no bending strain and can be smoothly curved without wrinkles.
Note that if this gap is set at a predetermined interval, the gap on the inside of the bend will be completely closed and serve as a stopper, thereby making it possible to prevent the bending radius from being smaller than the allowable bending radius. Furthermore, the gap between the abutting portions of the tape-shaped reinforcing body can be used as an inlet and an inlet for the helium gas. Therefore, the tape-like reinforcement improves the mechanical strength of the plurality of wires, and also improves the flexibility, cooling efficiency, and critical current characteristics that are incidental to the use of conventional reinforcements. It is possible to obtain a strand-aggregated compound superconducting conductor in which reductions in strands, etc. are improved. [Examples] Examples of the present invention will be described in detail below. Example 1 (Reinforcement body) A reinforcement body was obtained by forming an alumina coating of approximately 10 μm on both sides of a stainless steel tape having a thickness of 0.127 mm and a width of 3.4 mm. (Element wire) 4200 Nb in Cu-Sn bronze matrix
Embed the core and use the outside as a diffusion barrier layer
A Ta tube was coated, and a high-purity copper tube was further coated on the outside as a stabilized copper tube, and the surface was reduced to obtain a wire with an outer diameter of 0.81 mm and a stabilized copper occupation rate of 40%. Next, one of the above-mentioned reinforcing bodies was attached to this single prime, and it was formed into butt winding with a pitch of 35 mm to obtain a reinforced strand with an outer diameter of 1.1 mm (this reinforced strand was subjected to diffusion heat treatment). Since the compound superconducting filament is not coated, there is no built-in compound superconducting filament. (Manufacture of aggregated compound superconducting conductor and coil) Next, a separately prepared stainless steel tape with a thickness of 0.4 mm and a width of 14 mm whose outer periphery is coated with alumina. The above-mentioned reinforced strands of 30 strands are twisted together around the strand, and then compression molded with a roll to form a keystone with external dimensions (upper base 2.0 mm, lower base 2.5 mm, height between both bases 16.5 mm in cross section). A molded stranded wire was obtained.Next, this keystone molded stranded wire was wound on a saddle form with a minimum bending radius of 25 mm, and after being fixed, it was heated at 650℃ for 10
By performing a daily diffusion treatment, an Nb ₃ Sn compound layer was formed at the interface between the bronze matrix and the niobium core in each strand. Thereafter, the outside of this saddle-shaped coil was fixed with a metal collar. Comparative Example 1 30 unreinforced wires with an outer diameter of 0.81 mm similar to those in Example 1 were twisted around a stainless steel tape with a thickness of 0.3 mm and width of 10 mm that had been coated with alumina in advance, and then compression molded with a roll. A keystone-shaped molded stranded wire body with external dimensions (upper base 1.6 mm, lower base 2.0 mm, height 16.2 mm) was obtained. Two layers of alumina-coated stainless steel tape approximately 0.12 mm thick and 5 mm wide are wrapped around the outside of the main body, and the external dimensions (upper base 2.0 mm, lower base 2.5 mm, height 16.5 mm) are keystone shaped. A shaped stranded wire was obtained. Next, in the same manner as in Example 1, this stranded wire was wound around a saddle frame, subjected to diffusion heat treatment, and fixed with a metal collar to produce a coil. Comparative Example 2 In Example 1, a stainless steel tape with a thickness of 0.127 mm and a width of 3.4 mm with an alumina coating of about 10 μm formed on only one side was used as a reinforcing body for reinforcing each strand. Has an inorganic film only on the outer surface (no inorganic film on the inner surface)
A keystone molded stranded wire was obtained in the same manner as in Example 1 except that a tape-shaped reinforcement was provided. Next, in the same manner as in Example 1, this stranded wire was wound around a saddle frame, subjected to diffusion heat treatment, and fixed with a metal collar to produce a coil. After setting the tightening force of the metal collars of the coils of Example 1 and Comparative Examples 1 and 2 in four stages of 5, 10, 15, and 20 Kg/mm ² , the coils were placed in liquid helium (temperature 4.2 K) in a magnetic field. A current test was conducted under 10 Tesla conditions and the critical current value was measured. The results are shown in Table 1 below.

[Table] As is clear from Table 1, the coil of Example 1 is different from Comparative Example 1 in which a tape-shaped reinforcing body was not provided for each strand of wire, and Comparative Example 1 in which a tape-shaped reinforcing body was provided for each strand of wire. Compared to Comparative Example 2 in which no inorganic film was formed on the inner surface of the tape-shaped reinforcing body, the critical current value when the tightening force was increased was increased. In addition, the critical current value (AT10 Tesla) measured for a single Nb ₃ Sn compound superconducting wire with an outer diameter of 0.81 mm, which was produced by performing the same diffusion heat treatment as in Example 1 in addition to the above current conduction test, was 511 A. It can be seen that the value calculated from this measured value (15330A) and the measured value of the coil of Example 1 almost match, and a good critical electric value is obtained. This is because a tape-shaped reinforcing body is butt-wound for each strand of wire, so it has a structure that can withstand stress and distortion caused by localized tightening by metal collars and electromagnetic force. This is due to the fact that Furthermore, in order to find out the cooling characteristics of the superconducting magnet coil of Example 1, the following test was conducted. The coil of Example 1 was impregnated with epoxy resin, filling and sealing all the spaces between all the strands, under the same conditions (liquid helium 4.2K, magnetic field).
10 Tesla) and measured the critical current value, which was 7200A. Therefore, it can be seen that the coil of Example 1 also has extremely excellent cooling properties. In addition, in the above-mentioned Example 1, the superconducting coil is
Although it was created using the wind and react method, it is not limited to this and can also be created using the react and wind method. [Effects of the Invention] As detailed above, according to the present invention, not only can mechanical reinforcement of compound superconducting strands be easily performed with a simple reinforcing body, but also the flexible winding properties and cooling characteristics are significantly improved. Furthermore, since the reinforcement is simple, it is possible to use a reinforcement with the minimum necessary thickness, which increases the current density of the conductor. Since the same characteristics are reliably maintained even when the coil is made into a coil, it is possible to provide a wire assembly type compound superconducting conductor that has extremely excellent advantages such as being able to significantly improve the current density of the coil as a whole. .

[Brief explanation of the drawing]

FIG. 1 shows a conventional wire assembly type compound superconducting conductor, FIG. 1 a, b, d, and e are cross-sectional views, FIG. 1 c, f are perspective views, and FIG. 2 is a wire assembly of the present invention FIG. 2 is a perspective view showing an example of a compound superconducting strand used in a type compound superconducting conductor, with a reinforcing body on the strand partially opened. DESCRIPTION OF SYMBOLS 1... Reinforcement body, 2... Superconducting strand, 3... Secondary strand, 4... Groove, 5... Cooling hole, 10... Tape-shaped reinforcement body, 20... Reinforced strand, 21... ... Metal matrix, 22 ... Compound superconducting filament, 23 ... Butt portion, 24 ... Inorganic film.

Claims (1)

[Claims] 1. In a strand assembly type compound superconducting conductor consisting of a desired number of aggregates of compound superconducting strands having a compound superconductor in a metal matrix, a tape-shaped reinforcing body having an inorganic film on at least the inner surface is pierced onto each of the strands. A wire assembly type compound superconducting conductor characterized in that it is provided by co-winding.