STATIC ELECTRIC-POTENTIAL MEASUREMENTS ON THE SURFACE OF AG/BI-2223 HIGH-TEMPERATURE SUPERCONDUCTING TAPES

By using a fine sliding contact it is possible to measure the surface potential on a superconductor in the flux flow state as a continuous function of position. This method has been applied to the investigation of the current flow distribution in silver-clad Bi-2223 tapes st 77K. A four point sliding contact has been constructed (gauge lengths 1-2mm) which can slide over several cms length of a sample. The probes are arranged in a diamond or square configuration so that the local potential difference can be sampled both along and across the tape simple. Several modes of operation are possible: V-I curves can be measured at several locations along the tape and continuous traces of the transverse and longitudinal surface potential difference can be obtained for fixed values of current and applied field. Deliberately induced defects such as cracks produce characteristic correlating transverse and longitudinal potential signatures from which the local current flow direction can be deduced. Correlations between different local J(c) values and microstructures are discussed.