Influence of Filament Number on Workability and Critical Current Density of Bi-2212/Ag Superconducting Wires

摘要

The important merit of Bi-2212/Ag high ${rm T}_{rm c}$ superconducting wire is to apply cable as round wire geometry. Bi-2212/Ag wires were fabricated in order to develop Rutherford cable for SMES near the future. Various Ag ratio and various numbers of filaments for PIT (Powder-In-Tube) process were applied to investigate the workability during drawing and to improve critical current property of the wires. In order to find proper working process, we investigated the variation of drawing stress during working. Post-annealing of Bi-2212/Ag wires at various atmospheres was carried out after main heat-treatment in order to increase critical current density. The results of post-annealing in nitrogen were better than that of post-annealing in oxygen. ${rm J}_{rm c}$ of Bi-2212/Ag wire was increased as increased maximum temperature, ${rm T}_{rm m}$ , for partial melting until 890$^{circ}{rm C}$, and highest ${rm J}_{rm c}$ was over than 2000 ${rm A/mm}^{2}$. The shape of grain was observed by SEM to investigate Bi-2212 phase formation in filaments. The critical current density increased in proportion to the increase of Bi-2212/Ag wire''s filaments number.