STATUS OF HTS SUPERCONDUCTORS - PROGRESS IN IMPROVING TRANSPORT CRITICAL CURRENT DENSITIES IN HTS BI-2223 TAPES AND COILS

More than five years have passed since the first demonstrations by Bednorz and Muller1, Chu2 and others of bulk materials having high T(c) (HTS) characteristics. While a level of uncertainty still exists concerning the theoretical and physical conduction mechanism involved, reasonable progress has been made in process technology, thereby obtaining current densities that approach usefulness in several areas of application. Though these encouraging results have mainly been achieved in very small samples, there is increasing confidence that over the next few years one can look forward to the further development of process technology toward long lengths of HTS superconducting wires and tapes. We have focused on silver-clad, Pb-doped, Bi-2223 (T(c) 105 K) high-temperature superconducting tapes fabricated by the powder-in-tube technique. Short and long lengths of mono- and multicore conductors have been characterized by measuring critical current densities (J(c)) at 77 K, 20 K and 4.2 K in applied magnetic fields up to 20 T. Thermomechanical process parameters have been optimized to obtain J(c)s in the superconductor core of 3.3 x 10(4) A cm-2 at 77 K, zero field and 1.5 x 10(5) A cm-2 at 4.2 K, zero field. We report here on measurements in high applied field, for both short samples and small pancake-wound coils. Requirements are outlined for the development of preprototype coils for motor and generator applications.