Effective fabrication practices for Ag-sheathed Bi-2212 superconductors

The powder-in-tube (PIT) process has been widely used to fabricate long superconducting wires However, the irregular shape of the wire cross sections has not been adequately addressed. In this investigation, Ag-clad Bi2Sr2CaCu2O8 superconductors were formed using different wire drawing and tape rolling schedules, The effects of the drawing direction and annealing on geometric characteristics of the round wires were determined. Also, the impact of the reduction in thickness per pass and the roll configuration on the tape properties was studied. This paper shows that geometrical uniformity and core dimensional stability are strongly influenced by the rolling parameters chosen, A combination of a small roll diameter and a small reduction per pass reduces dimensional variations. This practice also leads to higher critical current densities at cryogenic temperatures in the resulting superconducting tapes. Recommendations for optimum fabrication schemes for wires and tapes are presented.