GB1569983A

GB1569983A - Super conductor

Info

Publication number: GB1569983A
Application number: GB52001/76A
Authority: GB
Original assignee: BBC Brown Boveri AG Switzerland; BBC Brown Boveri France SA
Current assignee: BBC Brown Boveri AG Switzerland; BBC Brown Boveri France SA
Priority date: 1975-12-15
Filing date: 1976-12-13
Publication date: 1980-06-25
Also published as: DE2602734A1; DE7602013U1; CH604332A5; DE2602734C2

Description

(54) IMPROVED SUPERCONDUCTOR (71) We, BBC BROWN BOVERI & BR< COMPANY LIMITED, a Swiss company of BADEN, Switzerland., do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed to be particularly described in and by the following statement: This invention relates to a superconductor including a plurality of wires forming a cable, in which at least some of which wires each comprises a large number of filaments of superconductive material embedded in a matrix consisting of a normally electrically conductive material and also to a method for the manufacture of this superconductor.

By way of example, for the generation of the magnetic fields necessary for nuclear fusion, with fields strengths up to 12 Tesla, superconductors for currents of up to 50,000 Amperes and more are required. The superconductive materials appropriate for such high electrical currents consisting of intermetallic compounds of A15 structure (as described in Handbook of Lattice Spacing and Structures of Metals by W.B. Pearson (Pergamon, New York, 1958) at page 79), such for example as Nb,Sn, V3Ga or V3 Si, however, exhibit the disadvantage that they are very brittle after undergoing the reaction heat and must be bent or strained only slightly if their superconductive properties are not to be deleteriously affected.

In addition, with such high currents the forces acting on the superconductor are much higher than has formerly been usual, so that high demands are made of the mechanical strength of the superconductors.

The object of the invention is to provide a superconductor for which the danger of damage to the filaments consisting of superconductive material during its manufacture, processing and installation, is reduced to a minimum.

According to the present invention there is provided a superconductor, comprising a plurality of wires stranded or braided together or transposed with one another to form a cable, at least some of which wires each comprise a multiplicity of filaments consisting of a superconductive intermetallic Al 5 alloy embedded in a matrix of material of normal electrical conductivity, and a support structure extending lengthwise of the cable and serving at least two different main fuunctions, the wires forming the cable being connected together and to the support structure by means of a soft solder which is plastically deformable, and connections between different members of the support structure having a mechanical strength, at the operating temperature of the superconductor, not substantially less than the corresponding mechanical strength of said members themselves.

If now such a superconductor is bent, for example to manufacture a coil, then the wires forming the cable can give with respect to one another and to the adjacent portions of the supporting structure, although the superconductor regarded as a whole exhibits and extraordinary strength as regards external forces operating upon it, so that damage to the filaments consisting of superconductive material during winding of a coil is reduced to a minimum. This is very important, since the detection of damage to the superconductor only when the completely installed magnet is first put into operation represents a substantial loss, regarded economically.

It is advantageous if the wires forming the cable are soft-soldered together and to the adjacent members of the support structure and said connections between the different members of the support structure, which connections affect the strength of the final superconductor, are formed by brazing or welding.

In order so far as possible to avoid the danger of damage to the filaments consisting of superconductive material upon bending of the superconductor, it is advantageous for the cable containing the superconductive wires to be flat and lie parallel to the neutral surface that results upon bending of the superconductor.

In order to be able to cool the superconductor to its working temperature, it is advantageous for the support structure to be provided with at least one cooling duct or cooling tube running in the longitudinal direction of the cable.

It is also advantageous for electrical stabilisation of the superconductor, for the support structure to be provided with at least one stabilising member extending along the cable and consisting of normally conductive material, for example copper or aluminium.

To increase the mechanical strength of the superconductor it is advantageous for the support structure to be provided with at least one strengthening member of a material of greater tensile strength than that of the stabilising material, preferably by 50%.

For the further protection of the filaments consisting of superconductive material against damage during the manufacture and processing of the superconductor, it is advantageous for the cable containing the superconductive wires to contain at least one stabilising and/or reinforcing wire running parallel to the longitudinal axis of the superconductor.

In order to ensure that a minimum of eddycurrents result when the superconductor is inserted in very rapidly altering magnetic fields, it is advantageous for the stabilising material to be divided into several wires and for these to be separated by a layer of a high-resistance material, consisting for example of a coppernickel alloy.

The intermetallic A15 alloy, which enables the conduction of very large electrical currents, comprises for example Nb3 Sn, V3Ga or V3 Si.

The invention will now be further described with reference to the accompanying drawings, in which: Figure 1 shows a cross-section through a first embodiment of a superconductor in accordance with the invention; Figure 2 shows a cross-section through a second embodiment of superconductor; Figure 3 shows a cross-section through a third embodiment; Figure 4 shows a cross-section through a fourth embodiment; Figure 5 shows a cross-section through a fifth embodiment; Figure 6 shows a cross-section through yet another embodiment;; In the embodiment represented in Figure 1, the superconductor is provided with a plurality of superconductive wires 2 forming a cable 1, the wires each consisting of a large number of filaments of an intermetallic A15 compound embedded in a matrix consisting of a material of normal electric conductivity at the operating temperature of the superconductive material of an alloy such as Cu-Sn for Nb Sn filaments or Cu-Ga for V3Ga filaments, and so on. For stabilisation, this matrix may also include a highly conductive material such as, for example, copper or aluminium and/or a reinforcing material.

In addition to the superconductive wires 2 the cable 1 contains also wires 3 consisting of a stabilising material and reinforcing wires 4 consisting of steel, the reinforcing wires 4 running parallel to the longitudinal axis of the cable to produce minimum extensibility.

For the electrical stabilisation of the superconductor, stabilising and support members 5 and 6 are arranged running along the cable and consisting of electrically highly conductive material, for example copper or aluminium, the stabilising and support member 6 being additionally provided with a cooling channel 7 for conducting a flow of cooling medium.

In order additionally to increase its mechanical strength, the superconductor is completely ensheathed externally by a steel sheath 8, this latter being welded along the seam 9.

The stabilising and support members 5, 6 and also the steel sheath 8 are fixedly secured to one another by hard solder, for example a Cu-Ag hard solder, and thus form a unitary component which is throughly suitable as regards rigidity for the manufacture of the magnet coils required for carrying out nuclear fusion.

In the manufacture of the superconductor illustrated in Figure 1, the flexible cable 1 containing the cable, stranded, braided or mutually transposed wires 2, 3 and 4 is arranged in the interior of a support structure consisting of the members 5, 6 and 8, the individual members 5, 6 and 8 of the latter are fixed together by brazing. The steel sheath 8 is welded together along the seam 9 between openings 10 provided in the member 5 and then the wires 2, 3 and 4 forming the cable 1 are soft-soldered together and with the enclosing members 5 and 6 of the support structure by the introduction of soft solder through the openings 10 spaced along the superconductor.

The support structure members 5, 6 and 8, brazed or welded together, form a mechanically unitary support structure which has the advantage that when the superconductor is bent , for example in the winding of a magnet coil, the flexible arrangement and construction of the cable 1 allows a small displacement of the soft-soldered superconductor wires 2 with respect to one another, and with respect to the stabilising and support members 5 and 6, because the soft solder is to a degree plastically deformable, so that the danger of damage to the filaments consisting of superconductive material is very slight. The soldering time and the melting point of the soft solder employed are chosen in a range such that the superconductive characteristics of the filaments consisting for example of Nb3 Sn are not deleteriously affected.

In order to keep the tensile forces acting on the superconductive wires 2 as small as possible during bending of the superconductor the cable 1 is arranged so that in bending the neutral surface of the bending lies parallel to and between the major surfaces of the cable 1.

In the embodiment illustrated in Figure 2, in contrast to the embodiment illustrated in Figure 1, two cooling tubes 13 and 14 running symmetrically with respect to the cable 1 are introduced into the corresponding formed support and stabilising members 5 and 6.

In this embodiment the superconductive wires 2 forming the cable 1 are soft soldered together and to the two members 5 and 6 forming the support structure. To produce the mechanically rigid structure the steel sheath 8 completely surrounding the exterior of the superconductor is brazed or welded to the exterior of the support and stabilising members 5 and 6.

The embodiment illustrated in Figure 3 differs from the embodiment shown in Figure 2 especially in that the cooling channels intended for the cooling medium are formed by two reinforcing members consisting of seamless drawn steel tubes.

In order to keep to a minimum eddy-current losses arising on installation of the superconductor, the support and stabilising members 5 and 6 made of a material that is normally electrically conductive at the operating temperature of the superconductor, such as for example copper or aluminium, are divided into a plurality of wires 5a, 5b, 5c, 5d and 6a, 6b, 6c, 6d running parallel to one another and these wires 5a to 5d and 6a to 6d are individually separated by high-resistance layers consisting for example of a copper-nickel alloy.

In addition the individual superconductive wires 2 may also each be surrounded by a respective high-resistance layer.

To produce a certain flexibility of the cable 1 upon bending of the superconductor, that is, to reduce the risk of damage to the filaments of brittle superconductive material, such as for example Nb3 Sn, V3Ga or V3 Si, here also the superconductive wires 2 are soft-soldered together and to the adjacent members 5, 6, 13 and 14. To produce as rigid as possible a supporting structure the support and stabilising members 5 and 6, the steel tubes 13 and 14 and also the steel sheath 8 are brazed or welded together.

In the embodiment illustrated in Figure 4 the cable 1 consisting of a plurality of superconductive wires 2 is arranged in a recess in a support, stabilising and cooling member 6, consisting of copper and provided with two cooling channels 11 and 12. To strengthen the support structure a strong steel channelsection member 15 is secured by hard soldering to the outer surface of the support, stabilising and cooling member 6, so that a very strong and rigid assembly is formed.

In order to avoid damage to the superconductive filaments during manufacture and subsequent handling of the superconductor, the superconductive wires 2 are soldered together and to the adjacent members 6 and 15 of the mechanically stable support structure with a soft solder so as to produce a small flexibility of the superconductive wires, and the cable 1 is so arranged, considered over the cross-section of the superconductor, that it is concentric about the neutral surface when the superconductor is bent.

It is obviously also possible to choose the geometric arrangement and the materials in this and in the other described embodiments, so that in the finished and bent superconductor the cable 1 is situated in the region subjected to compression.

In the embodiment illustrated in Figure 5 the support structure is formed by a seamless drawn cooling tube 16 that consists of an electrically highly conductive stabilising material, such as for exampe copper or aluminium. To increase its mechanical rigidity the cooling tube is internally reinforced by a reinforcing tube 17 consisting of steel. The two tubes 16 and 17 are hard soldered together to produce the highest possible mechanical rigidity. Alternatively, an external steel tube may be used.

The cable 1 consistng of superconductive wires 2 is arranged on the outer surface of the tube 16 consisting of stabilising material, the superconductive wires 2 being plastically connected together and to the adjacent tube 16 to produce slight flexibility of the superconductive wires 2, for example by means of a soft solder.

In the embodiment of a superconductor illustrated in Figure 6 the cable 1 is enclosed by two identical sections 19, serving for electrical stabilisation and for supporting the cable and consisting of copper or aluminium. To increase the mechanical rigidity of the two sections 19, reinforcing wires 18 consisting for example of a copper-aluminium bronze are embedded in the sections 19 and metallurgically united with them. The superconductive wires 2 of the cable 1 are plastically connected with the adjacent sections 19, e.g. by soft solder.

The soft solder may be introduced into the interior of the superconductor after the hard soldering of the two section 19 through openings 20 provided in the latter. The embedding of the reinforcing wires may be affected for example by laying bronze rods in grooves and subsequent rolling or drawing or by extrusion in common with the sections 19, a metallurgical connection of the reinforcing and the stabilising material being produced by thermal diffusion.

In all the embodiments the reinforcing member or members may be of alloy steel or a Cu-Al-, Cu-Ga-, Cu-Sn- or Cu-Ni- based alloy.

It is preferred that the cross-section and material of the reinforcing member or members shall be so chosen that in the manufacture, processing and use of the superconductor the longitudinal extension of the superconductive filaments shall not exceed 0.2%.

WHAT WE CLAIM IS: 1. A superconductor, comprising a plurality of wires stranded or braided together or transposed with one another to form a cable, at least some of which wires each comprising a multiplicity of filaments consisting of a superconductive intermetallic A15 alloy embedded in a matrix of material of normal electrical conductivity, and a support structure extending lengthwise of the cable and serving at least two different main functions, the wires forming the cable being connected together and to the support structure by means of a soft solder which is plastically deformable, and connections between different members of the support structure having a mechanical strength, at the operating temperature of the superconductor, not substantially less than the corresponding mechanical strength of said members themselves.

2. A superconductor in accordance with Claim 1 wherein said connections between the different members of the support structure are formed by braizing or welding.

3. A superconductor is accordance with any one of the preceding claims, wherein the cable containing the superconductive wires is flat and lies parallel to the neutral surface of the superconductor when bent.

4. A superconductor in accordance with any one of the preceding claims, wherein the support structure is provided with at least one cooling duct or cooling tube extending in the longitudinal direction of the cable.

5. A superconductor in accordance with any one of the preceding claims, wherein the support structure is provided with at least one stabilising member consisting of normally electrically conductive material extending in the longitudinal direction of the cable.

6. A superconductor in accordance with Claim 5, wherein said stabilising member consists of copper or aluminium.

7. A superconductor in accordance with any one of the preceding claims, wherein the support structure includes at least one reinforcing member extending in the longitudinal direction of the cable.

8. A superconductor in accordance with Claim 7, wherein the reinforcing member has a tensile strength at least 50% higher than that of the stabilising material.

9. A superconductor in accordance with any one of the preceding claims, wherein the matrix for the superconductive filaments consists of reinforcing and/or stabilising material.

10. A superconductor in accordance with Claim 9, wherein the reinforcing member is embedded in the stabilising material.

11. A superconductor in accordance with Claim 10, wherein the reinforcing members are metallurgically joined to the stabilising material.

12. A superconductor in accordance with any one of the preceding claims, wherein said cable contains at least one stabilising and/ or reinforcing wire running paralle to the axis of the superconductor.

13. A superconductor in accordance with any one of the preceding claims, wherein the cable is situated in that part of the cross-section of the superconductor that is subjected to compression when bent.

14. A superconductor in accordance with any one of the preceding claims, wherein the support structure is formed by a cooling tube, arranged to conduct a cooling medium, that consists of a good electrical conductor and wherein the cable is arranged about the exterior of the cooling tube.

15. A superconductor in accordance with Claim 14, wherein the cooling tube is strengthened by an internal or external reinforcing tube, preferably of steel.

16. A superconductor in accordance with any one of the Claims 1 to 15, wherein said cable is completely enclosed by the support structure.

17. A superconductor in accordance with any one of the preceding claims, wherein the superconductive wires are surrounded by layers of high-resistance material.

18. A superconductor in accordance with any one of Claims 1 to 16, wherein layers of high-resistance material are provided between the filaments.

19. A superconductor in accordance with Claim 5, wherein the stabilising member is divided into a plurality of wires which are separated by layers of a high-resistance material.

20. A superconductor in accordance with Claim 17, wherein the high-resistance material is a copper-nickel alloy.

21. A superconductor in accordance with any preceding claim, wherein the A15 alloy is Nb3 Sn, V3Ga or V3 Si.

22. A superconductor in accordance with Claim 7, or in accordance with any one of Claims 8 to 21 as dependent upon Claim 7, wherein the reinforcing member consists of alloy steel or of an alloy with a copperaluminium, copper-gallium, copper-tin or copper-nickel base.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. subsequent rolling or drawing or by extrusion in common with the sections 19, a metallurgical connection of the reinforcing and the stabilising material being produced by thermal diffusion. In all the embodiments the reinforcing member or members may be of alloy steel or a Cu-Al-, Cu-Ga-, Cu-Sn- or Cu-Ni- based alloy. It is preferred that the cross-section and material of the reinforcing member or members shall be so chosen that in the manufacture, processing and use of the superconductor the longitudinal extension of the superconductive filaments shall not exceed 0.2%. WHAT WE CLAIM IS:

1. A superconductor, comprising a plurality of wires stranded or braided together or transposed with one another to form a cable, at least some of which wires each comprising a multiplicity of filaments consisting of a superconductive intermetallic A15 alloy embedded in a matrix of material of normal electrical conductivity, and a support structure extending lengthwise of the cable and serving at least two different main functions, the wires forming the cable being connected together and to the support structure by means of a soft solder which is plastically deformable, and connections between different members of the support structure having a mechanical strength, at the operating temperature of the superconductor, not substantially less than the corresponding mechanical strength of said members themselves.

23. A superconductor in accordance with

Claim 7 wherein the material and cross-section of the reinforcing member are such that during manufacture, processing and operation of the superconductor the superconductive filaments are not stretched longitudinally by more than 0.2%.

24. A method of manufacturing a superconductor as claimed in Claim 16, wherein said wires are soft soldered together and to said support structure after said members of the support structure are hard soldered or welded together.

25. A superconductor in accordance with Claim 1 and substantially as described with reference to any one of Figures 1 to 6 of the drawings.

26. A superconductor made by the method of Claim 24, and substantially as described with reference to any one of Figures 1 to 6 of the drawings.