Improvement in critical current densities of long length AgCu-sheathed Bi-2212 round wires

In order to avoid an injurious effect of release of oxygen gas during heat treatment on critical current densities ( J c ) of AgCu-sheathed Bi-2212 round wires in long length, a modified heat treatment process has been developed. In this modified process, only a schedule of heat treatment for the partial melting and slow cooling process has been changed, instead of increased atmospheric pressures. A transport J c of about 2×10 4 A/cm 2 (critical current of 160 A) at 4.2 K and 10 T has been obtained for a wire 1.5 m in length, using the modified process. This value corresponds to about 80% of J c 's of a few cm long wires, while J c 's of long length wires heat treated by the conventional process are reduced to about 30% of short length wires. Relations between transport J c properties and microstructures such as the size and distribution of voids have been investigated, using X-ray radiography.