IMPROVEMENT OF STRAIN-DEPENDENT CRITICAL-CURRENT IN AG-SHEATHED AND AG CU-SHEATHED BI(2223) SUPERCONDUCTING TAPES/

Applications of Bi(2223) tapes in superconducting devices require a re duction of critical current degradation induced by mechanical or therm al stress. Critical currents have been measured dependent on thermocyc les and axial strain. The monofilament Ag-sheathed tapes show a degrad ation of 10% at a critical strain epsilon=0.3%, while multifilament ta pes are nearly stable to epsilon=0.6%. A considerable improvement coul d be reached using Ag90Cu10 sheathes. In opposite to the abrupt irreve rsible degradation in Ag-sheathed tapes the process in Cu hardened tap es is more gradual and the critical E-values are doubled approximately . Micrographs show that microcracks are the reason for the critical cu rrent degradation. Their density is dependent on core properties.