0.7996 mm dia., Ic = 209A (at 5T, 4.2K)

1. 250 filament Bi-2212 wire ~ 0.8 mm dia. Round Wire Bi-2212 – A New High Field Superconductor TechnologyGregory S. Boebinger, Florida State University, DMR 0654118 Bi-2212 is the only cuprate superconductor that can be made in round wire with high critical current density Jc; however, to date, its use in superconducting magnets is restricted because gas bubbles form during heat treatment, causing wire expansion, leakage and superconducting filament de-densification that greatly reduces Jc in coil-length wires. This year we have developed over pressure (OP) processing and have shown that the critical current for wires processed at 25 bar is more than five times higher than samples processed at 1 bar with closed ends, a geometry that mimics a coil-length wire. Our results demonstrate a wire-fabrication process for Bi-2212 round wire that avoids the long-length loss of Jc. This process has raised Jc to ~500 A/mm2 at 20 T, very attractive values for high field magnets, and about 5 times higher than Nb3Sn at 20 T. Six fold increase in critical current when processed in 25 bar overpressure (OP) to prevent internal gas bubbling. At left are shown the problems – only for short wires (upper image) could expansion be prevented (see next page too), while long lengths expanded and often split. OP avoids expansion. Open end short wire 0.7996 mm dia., Ic = 209A (at 5T, 4.2K) Closed end short wire splits open 0.8444 mm dia., Ic = 72 A (at 5T, 4.2K)