ELECTRICAL CONTACTS ON BISMUTH-BASED BULK HIGH-TEMPERATURE SUPERCONDUCTORS IN HIGH-CURRENT APPLICATIONS

High-current applications of high-temperature superconductor form part s (e.g. plates, rods, tubes) need connections to conventional (copper) current leads of resistivities below 10 muOMEGA cm2. Bismuth-based DS CCO 2212 parts can be contacted by two different methods: (i) the conv entional covering of the surface with gold or silver by sputtering or by vapour deposition, which always needs a post-deposition thermal tre atment, and (ii) applying silver sheet to the superconductor part duri ng its fabrication by a melt casting process. In both cases resistivit ies of 1-3 muOMEGA cm2 at 77 K could be achieved. Experiments and theo retical considerations to localize the partial resistances within the connection demonstrate that the interfacial resistivity of melt proces sed contacts, as well as sputtered or vapour deposited contacts after heat treatment, are lower by about one order of magnitude than the res istivity of the total connection.