Advances in fabrication of Ag-clad Bi-2223 superconductors

Powder-in-tube (PIT) processing was used to fabricate multifilamentary Ag-c lad Bi2Sr2Ca2Cu3Oy (Bi-2223) superconductors for various electric power app lications. The transport current properties of long lengths of multifilamen t tapes were enhanced by increasing the packing density of the precursor po wder, improving the mechanical deformation, and adjusting the cooling rate. The dependence of the critical current density on magnetic field and tempe rature for the optimally processed tapes was measured. J(c) was > 10(4) A/c m(2) at 20 K in magnetic fields up to 3 T and parallel to the c axis, which is of interest for use in refrigerator-cooled magnets. An attempt was made to combine the good alignment of Bi-2223 grains in Ag-sheathed superconduc ting tapes to obtain high Je values at high temperature and low field, with the good intrinsic pinning of YBa2Cu3O7-d (Y-123) thin film, in order to m aintain high J(c) values in high fields. A new composite multifilament tape was fabricated such that the central part contained Bi-2223 filaments, wit h the primary function of conducting the transport current. The central Bi- 2223 filaments were surrounded by Y-123 thin film to shield the applied mag netic field and protect the Bi-2223 filaments. The J(c) values of the compo site tape were better than those of an uncoated tape. In the case of 77 K a pplications, an I-c of approximate to 60 A was obtained in a 150-m-long tap e and zero applied magnetic field. In-situ strain characteristics of the mo no- and multifilament tapes were measured.