Critical currents and processing of wound coils of Ag-sheathed Bi-2223 high <i>T</i> <i>c</i> tape: Microstructural and pinning effects

Abstract

Using a ‘‘powder-in-tube’’ process long lengths of high Tc prototype tape have been fabricated with high critical currents at liquid-nitrogen temperature and excellent high field properties at liquid-helium temperature. A Pb-doped bismuth-based 2223 powder was initially prepared then packed into silver tubes. Using a combination of cold work and heat treatment, a high degree of texture and good compaction with uniform properties was achieved. Current densities exceeding 10 000 A/cm2 at 77 K and 50 000 A/cm2 at 4.2 K in zero field were measured. At the 4.2 K temperature, the material still carried approximately 14 000 A/cm2 at 8 T. Tests on spirally wound and reacted coils, 52 cm long, have also demonstrated high current carrying capability. Effects of process variations and observed microstructure on superconducting properties are described.