SUPERCONDUCTOR WITH TWISTED STRUCTURE

Abstract

A superconductor (10, 30) has a twisted structure and is adapted to form windings in a superconducting coil. The superconductor (10, 30) comprises at least one superconductor wire. The superconductor further comprises at least one elongated electrical insulation element (18, 37). The elongated electrical insulation element(s) (18, 37) is/are twisted with or around the superconductor wire(s) in order to create a separation distance with an adjacent superconductor wire in a neighbouring winding. The elongated electrical insulation element(s) (18, 37) and the superconductor wire(s) may be twisted in one and the same twisting operation.

Claims

1. A superconductor having a twisted structure and adapted to form windings in a superconducting coil, said superconductor comprising at least one superconductor wire, said superconductor further comprising at least one elongated electrical insulation element, wherein said at least one elongated electrical insulation element is twisted with or around said at least one superconductor wire in order to create a separation distance with an adjacent superconductor wire in a neighbouring winding.

2. The superconductor according to claim 1, wherein said superconductor has only one superconductor wire.

3. The superconductor according to claim 1, said superconductor being a superconductor cable and comprising at least two superconductor wires that are twisted with each other and with said at least one elongated electrical insulation element.

4. The superconductor according to claim 3, wherein said at least two superconductor wires are twisted with each other with a first twist step, wherein said at least one elongated electrical insulation element has a second twist step, said first twist step being equal to said second twist step.

5. The superconductor according to claim 1, wherein said at least one elongated electrical insulation element is made of a polymer or of glass.

6. The superconductor according to claim 1, wherein said separation distance ranges from 30 μm to 300 μm.

7. The superconductor according to claim 1, said superconductor further comprising a thermally and electrically conducting material.

8. The superconductor according to claim 7, wherein said superconductor has a core+n+m structure, n and m being integer numbers, said core being formed by said thermally and electrically conducting material or by a superconductor wire, n superconductor wires being twisted around said core, m elongated electrically insulating elements being twisted with said n superconducting wires around said core.

9. The superconductor according to claim 8, wherein n is equal to m, wherein n and m are greater than three, and wherein each elongated electrically insulating element faces two superconductor wires.

10. The superconductor according to claim 1, wherein said superconductor wires comprise MgB.sub.2 as superconducting material.

11. The superconductor according to claim 5, wherein said at least one elongated electrical insulation material is made of heat resistant glass fibres.

12. The superconductor according to claim 11, wherein said heat resistant glass fibres are S-glass fibres.

13. The superconductor according to claim 5, wherein said at least one elongated electrical insulation material is incorporated in a tape, said tape having a radially inner side and a radially outer side after twisting, the radially outer side being the electrical insulation material.

14. The superconductor according to claim 13, wherein the radially inner side is a thermally and electrically conducting material.

15. A method of manufacturing a superconductor that is adapted to form windings in a superconducting coil, said method providing the following steps: a) providing at least one superconductor wire; b) providing at least one elongated electrical insulation element; c) twisting said at least one elongated insulation element with or around said at least one superconductor wire in order to create a separation distance with an adjacent superconductor wire in a neighbouring winding.

Description

BRIEF DESCRIPTION OF FIGURES IN THE DRAWINGS

[0054] FIG. 1 shows a cross-section of a first embodiment of a superconductor;

[0055] FIG. 2 shows a longitudinal view of this first embodiment of a superconductor;

[0056] FIG. 3 is a cross-section of a second and preferable embodiment of a superconductor.

MODE(S) FOR CARRYING OUT THE INVENTION

[0057] FIG. 1 shows a cross-section of a first embodiment of a superconductor 10 according to the present invention and FIG. 2 shows a longitudinal view of this first embodiment of a superconductor 10.

[0058] A first winding 12 is shown in full lines.

[0059] The superconductor 10 has a core 14 with superconductive material, e.g. with MgB.sub.2 and some dopants. The core 14 is surrounded by a sheath or tube 16 out of copper. Six polyester filaments 18 are wrapped around the sheath. As is clearly shown in FIG. 2, the polyester filaments 18 do not cross each other and thus avoid to create pressure points.

[0060] Part of a cross-section of a second adjacent winding 19 is shown in dash lines in FIG. 1.

[0061] By selecting the diameter and the number of the polyester filaments 18, the separation distance between two windings may be determined.

[0062] FIG. 3 is a cross-section of a second and preferable embodiment of a superconductor 30 cable. Superconductor cable 30 has a core 31 of copper that functions as thermally and electrically conducting material in case of an increase in temperature. The copper core 31 has a sheath 32 of tin. The function of tin is to enhance temperature and current transfer between superconductor wires in case of a fracture of a wire or in case of a quench of one or more wires in the superconductor. Another advantage of tin is that tin consolidates the structure. Six superconductor wires are twisted around the copper core 31. Each superconductor wire has a core 34 with superconducting material, e.g. MgB.sub.2 and a metallic sheath 35. The metallic sheath 35 can be made of iron or can be made of copper. The six superconductor wires with the sheath 34-35 form a circumscribed circle 36, that is shown in dash lines. Six S-glass yarns 37 are also twisted around the around the copper core 31 with the same twist step and in the same direction as the superconductor wires. Each S-glass yarn 37 faces two superconductor wires. Each S-glass yarn 37 protrudes out of the circumscribed circle 36 to create the separation distance. The six S-glass fibres 37 form a circumscribed circle 38, that is shown in a dot and dash lines. The distance between the circumscribed circle 36 and the circumscribed circle 38 is the separation distance. By their positioning the six S-glass fibres 37 fill part of the empty space that is created radially outside and between two superconducting wires leaving only small voids 39. The six S-glass fibres 37 provide stability to the twisted construction of the superconductor 30. In addition, the six S-glass fibres 37 function as distance holder between neighbouring windings so that resin can infiltrate. The diameter or thickness of the S-glass yarns 37 is greater than the separation distance. This means that thicker and stronger elongated electrically insulating elements can be used and still have a limited separation distance between windings. Thicker elongated electrically insulated elements are stronger and more robust and will allow faster twisting and production.

[0063] Typical dimensions for the superconductor cable 30 are: [0064] diameter of the superconductor wire 34 with sheath 35: 750 μm; [0065] diameter of the S-glass fibre 37: 200 μm.

[0066] In general for MRI applications, the diameter of the superconductor wires may range between 250 μm and 1000 μm, as long as the total diameter of the superconductor does not exceed 3.0 mm, preferably does not exceed 2.5 mm.

[0067] For use as power transmission, the dimensions may be much greater.

[0068] FIG. 3 shows a 1+6+6 superconductor cable 30. However, any 1+n+m superconductor with n and m ranging from three on, has the same advantages as long as the superconductor wires and the elongated electrical insulating elements have the same twist direction and twist step.

[0069] A superconductor according to the invention is preferably used in a superconducting magnet of a magnetic resonance imaging apparatus. A superconductor according to the invention may also be applied in magnetic levitating vehicles, superconducting electromagnetic propulsion ships, nuclear fusion reactors, superconducting generators, accelerators, electron microscopes, energy storing apparatus, magnetic separators and power cables.

LIST OF REFERENCE NUMBERS

[0070] 10 first embodiment of a superconductor

[0071] 12 one winding of superconductor 10

[0072] 14 core with superconducting material

[0073] 16 metal tube or sheath

[0074] 18 insulating polymer fibre

[0075] 19 adjacent winding

[0076] 30 second embodiment of a superconductor

[0077] 31 copper core of superconductor

[0078] 32 sheath of tin around copper core 31

[0079] 34 core of superconducting material of superconductor wire

[0080] 35 copper sheath around core of superconducting wire

[0081] 36 circumscribed circle formed by superconducting wire

[0082] 37 insulating S-glass yarn

[0083] 38 circumscribed circle formed by S-glass yarns

[0084] 39 voids inside twisted structure of superconductor