Fabrication of thin-filament Bi-2223/Ag superconducting tapes

Abstract

The use of high-temperature superconductors (HTS) in some power utility applications requires long lengths of conductors with low AC losses and good mechanical properties. This is typically obtained by making multifilamentary wires with thin filaments. In Powder-In-Tube (OPIT) process, the fabrication of thin filaments is limited by the development of non-uniformities due to sausaging, shear fracture, and 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 formation of these types of defects in terms of the stress-dependent mechanical properties of the superconducting powder. Experimental results verify that small roller size and low reduction rates during flat rolling (two factors that reduce die hydrostatic stress component in the powder core) improve the uniformity of these filaments. Tapes with core thicknesses of down to 12-18 /spl mu/m have been manufactured, which exhibit values of critical current density of 31-36 kAcm/sup -2/ (at 77 K and 1 /spl mu/V/cm) for heat treatments of 70-200 h.