FABRICATION OF THIN-FILAMENT BI-2223 AG SUPERCONDUCTING TAPES/

The use of high-temperature superconductors (HTS) in some power utilit y applications requires long lengths of conductors with low AC losses and good mechanical properties. This is typically obtained by making m ultifilamentary wires with thin filaments. In the Oxide-Powder-In-Tube (OPIT) process, the fabrication of thin filaments is limited by the de velopment of non-uniformities due to ''sausaging'', shear fracture, an d tensile fracture in the oxide core. This work analyses factors that control the uniformity of thin filaments of Bi-2223/Ag superconducting tapes. Some simple theoretical considerations have explained the form ation of these types of defects in terms of the stress-dependent mecha nical properties of the superconducting powder. Experimental results v erify that small roller size and low reduction rates during flat rolli ng (two factors that reduce the hydrostatic stress component in the po wder core) improve the uniformity of these filaments. Tapes with core thicknesses of down to 12-18 mu m have been manufactured, which exhibi t values of critical current density of 31-36 kAcm(-2) (at 77 K and 1 mu V/cm) for heat treatments of 70-200 h.