STRAIN TOLERANCE OF AG-SHEATHED BSCCO(2223) SUPERCONDUCTORS WITH VARIOUS GEOMETRICAL CONFIGURATIONS

Strain tolerance (retained critical current as a function of applied s train) of Ag-sheathed monofilament and wire-in-tube (WIT) Bi-1.8 Pb0.4 Sr2Ca2Cu3Ox tapes sintered for various time periods was evaluated. Str ain tolerance of the WIT tapes sintered for 100 h was significantly lo wer than that of the monofilament tapes. This is attributed to a sharp increase in volume fraction of the superconducting core in WIT tapes (compared with that in monofilament tapes) subjected to a strain value greater than the fracture strain of BSCCO (approximate to 0.2%). This limitation was overcome by fabricating tube-within-tube tapes contain ing an additional BSCCO layer that runs along the neutral plane. Strai n tolerance of these was superior to those of both the monofilament an d the WIT configurations. This improvement is related to crack pinning effects induced by the inner Ag tube and by increased volume fraction of undamaged superconducting core. Experimental evidence indicates th at the effective strain experienced by the current-carrying regions of the cross-section will determine the strain tolerance of the tape. At strains below 1% where there is a significant decrease in the volume fraction of superconducting core within subcritical strain, only a rel atively low decrease in critical current density was observed, indicat ing possible current shunting in all of the tape configurations invest igated.