Materials for superconducting magnets

Abstract

The major construction materials for the magnet area, as they are the superconductor, the stabilizer, solders, electric and thermal insulations are reviewed concerning the optimal data achieved so far for the specific use in fusion. The magnet technology for fusion is already well advanced, so that sufficient material data are available for design purposes, but with one important exception, the irradiation damage behaviour. The paper tries to review the state of the art specifically in this resp'ect. Irradiation data on the superconductors have in most cases not been measured in a fusion project relevant manner, e.g. in-situ 4 K measurements of prototype conductors with stabilizer and solder bond are missing. For the wide spread amount on organic insulations, polyimide based systems show better irradiation resistance than epoxy based materials, but the later are the major ones used in magnet technology. The interpretation of all data available so far allows still both an optimistic and a conservative point of view on irradiation limits for the magnet materials. Not underestimated should be the importance of a very high strength low temperature steel for the conductor/winding structure, because it occupies a large fraction of the overall cross section and implies a good potential for savings or current density increase.