MICROSTRUCTURE AND Jc IMPROVEMENTS IN MULTIFILAMENTARY Bi-2212∕Ag WIRES FOR HIGH FIELD MAGNET APPLICATIONS

Abstract

Bi‐2212/Ag conductor is one of the most promising materials for extending the field strength of superconducting magnets over present low temperature superconductor systems. From the view point of practical application, Bi‐2212/Ag round wires have significant advantages over more typical HTS tape conductors, such as no anisotropy, and easier handling and coil winding, which allows considerable flexibility in the magnet design. Recent development efforts at Oxford Superconducting Technology have been aimed at manufacturing high quality multifilamentary Bi‐2212/Ag round wires with the varied sizes to fabricate HTS insert coils for high field magnet applications. However, further improvement of critical current density (Jc) and engineering current density (JE) in larger diameter wires is desirable for practical applications. Recent results show a strong dependence of the wire JE and Jc performance on its microstructure, in particularly, the interface of Bi‐2212/Ag. Significant improvements of microstructure and Jc have resulted from the optimization of wire size and filament numbers, but not obviously on starting powder fill factors. The highest JE of 320 A/mm2 (non‐Ag Jc of 1103 A/mm2) at 4.2 K, 25 T was obtained in 1.15 mm wire with 85×19 filament configuration.