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 f unction 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 1-2m m) which can slide over several cms length of a sample. The probes are arranged in a diamond or square configuration so that the local poten tial 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 transve rse and longitudinal surface potential difference can be obtained for fixed values of current and applied field. Deliberately induced defect s such as cracks produce characteristic correlating transverse and lon gitudinal potential signatures from which the local current flow direc tion can be deduced. Correlations between different local J(c) values and microstructures are discussed.