GB2256080A

GB2256080A - Superconductive electrical conductor.

Info

Publication number: GB2256080A
Application number: GB9110878A
Authority: GB
Inventors: Michael George Clark; Karl Adrian Gehring
Original assignee: GEC Marconi Ltd; Marconi Co Ltd
Current assignee: BAE Systems Electronics Ltd
Priority date: 1991-05-20
Filing date: 1991-05-20
Publication date: 1992-11-25
Also published as: GB9110878D0

Abstract

An electrical conductor (1), for example for use in forming an electromagnetic coil, comprises a tubular core (5) of superconducting material inside a thermally insulating casing (3). Cryogenic fluid e.g. Ar, He, N2, is passed through the core. In an embodiment, a tube (3) of inert ceramic material e.g. yttria stabilised zirconia, has a precursor of superconductive material deposited on an inner surface and is sintered to produce a superconductive phase (5). A sealing layer (7) may be formed over the tube to prevent leakage of cryogenic fluid. The core (5) may be "high temperature" superconducting material e.g. YBCO, BSGCO or TBCCO. <IMAGE>

Description

Electrical Conductors This invention relates to electrical conductors, and particularly to superconductive electrical conductors suitable for forming, for example, energising coils of electromagnets.

Magnets having superconductive energising coils are well-known, and are already widely used. In order to bring the material of such a coil into its superconductive phase it is necessary to cool the coil to a temperature which is far below normal ambient temperature, even if a so-called high temperature" superconducting (HTS) material is used for making the coil. The cooling of the coil is conventionally achieved by providing a cryostat or cryogenic shroud forming an enclosure around the coil and reducing the temperature in the enclosure by passing a cryogenic fluid through the structure of the enclosure. Very effective thermal insulation must be incorporated into the structure to minimise the flow of heat into the enclosure from outside.

Such enclosure impedes, or even renders impossible, the use of superconducting magnets for many applications for which such magnets would otherwise be suitable. This problem results from the need to provide electrical and mechanical access to the high field region within the enclosure, which entails the provision of feedthroughs in the wall of the enclosure. Furthermore, if it is necessary to irradiate materials within the enclosure, one or more windows which are transparent to the radiation at the appropriate wavelength must be provided through the wall of the enclosure.

It is an object of the present invention to provide an improved superconductive electrical conductor.

According to one aspect of the present invention there is provided an electrical conductor comprising a tubular casing of thermal insulation material; and within said casing a tubular core of superconductive material which in use of the conductor carries cryogenic fluid for cooling the material to its superconductive state.

According to another aspect of the invention there is provided a process for manufacturing an electrical conductor, comprising forming a thermally-insulated tubular core of superconductive material for carrying a flow of cryogenic fluid.

Preferably the thermal insulation comprises a tubular ceramic former, and the core is produced by depositing a precursor of superconductive material on the internal surface of the former and sintering said precursor.

Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawing, which is a schematic pictorial view of a portion of an electrical conductor in accordance with the invention.

Referring to the drawing, an electrical conductor 1 in accordance with the invention comprises thermal insulation 3, and a tubular core 5 of a "high temperature" superconducting material, such as YBCO, BSCCO or TBCCO, within the insulation 3. In order to cool the tube 5 to its superconductive state, cryogenic fluid is passed through the bore of the tube 5. The fluid may be, for example, cold helium, argon or nitrogen gas.

In a first embodiment, the core 5 and the insulation 3 are manufactured simultaneously by forming a tube of precursor material and then sintering it to obtain the superconductive phase. The insulation in this case is provided by the superconducting material itself, which is a poor thermal conductor. In operation, the inner part 5 is cold and superconducting, whereas the outer part 3 is warmer and may not be superconducting.

In an alternative, and preferred, embodiment, the insulation 3 is formed as a tube of an inert ceramic material, such as yttria-stabilised zirconia. Precursor of the superconductive material is then deposited on the inner surface of the tube 3 and is sintered to produce the superconductive phase, thereby forming the core 5. The tube 3 provides both mechanical strength and thermal insulation properties.

If necessary, a sealing layer 7 may be formed over the insulating tube 3 to prevent leakage of any cryogenic fluid which may seep through the tube walls.

The transition temperature (which typically is in the range 85K to 125K ) below which the HTS materials are superconductive is high compared with that of normal superconducting materials. It will be apparent that it is possible to use the conductor of the present invention in its superconductive state without the need for an external cryostat or cryogenic shroud.

The conductor may be used for forming an energising coil of an electromagnet. The electromagnet can then be used without the encumbrance of a cryogenic enclosure. It will usually be desired that the ambient atmosphere around the conductor should be free of gases or vapours which might freeze on to the outer surface of the conductor.

Such coil may be used in existing superconducting electromagnet applications and also in other applications where the use of superconducting magnets has previously been inconvenient or impossible. Examples are: 1. The provision of magnetic fields inside vacuum tubes such as magnetrons and CRTs. These fields could be much more easily profiled (to follow the paths of charged particles, to provide a local field gradient or to provide a periodically varying field) than is at present possible.

2. The manufacture of miniature actuators, grippers or motors for use inside vacuum chambers or in space.

3. The provision of fields with complex profiles such as are needed for multipoles or magnetic mirrors.

4. The provision of field volumes in which wide access or multiple path (eg longitudinal as well as transverse) access is required (such access being prevented by conventional designs).

5. The provision of magnetic fields for very small components such as micron valves or micromachined components which have typical feature sizes of a few microns.

Besides the above-described use of the conductor of the present invention for forming a coil for an electromagnet, such conductor might alternatively be used in other applications where extremely low conductor resistance is required, for example in certain transformer, rotating electrical machine and power distribution applications.

Claims

1. An electrical conductor comprising a tubular casing of thermal insulation material; and within said casing a tubular core of superconductive material which in use of the conductor carries cryogenic fluid for cooling the material to its superconductive state.

2. A conductor as claimed in Claim 1, wherein the core is formed by forming a tube of a precursor for the superconductive material and sintering the tube.

3. A conductor as claimed in Claim 2, wherein the casing and the core are formed simultaneously from the same precursor.

4. A conductor as claimed in Claim 1, wherein the casing comprises a tubular former of ceramic material and the core is formed by depositing a precursor of superconductive material on the internal surface of the ceramic former and sintering the precursor.

5. A conductor as claimed in Claim 4, wherein the casing is formed of yttria-stabilised zirconia.

6. A conductor as claimed in any preceding claim, wherein the superconductive material is YBCO, BSCCO or TBCCO.

7. A conductor as claimed in any preceding claim, including a layer around the casing for preventing egress of the cryogenic fluid.

8. A conductor substantially as hereinbefore described with reference to the accompanying drawing.

9. An electromagnet including a conductor as claimed in any preceding claim.

10. A process for manufacturing an electrical conductor, comprising forming a thermally-insulated tubular core of superconductive material for carrying a flow of cryogenic fluid.

11. A process as claimed in Claim 10, comprising the steps of producing a tubular ceramic former; depositing a precursor of superconductive material on the internal surface of the former; and sintering the precursor to form the core.

12. A process as claimed in Claim 10 or Claim 11, wherein the superconductive material is YBCO, BSCCO or TBCCO.