Significantly enhanced critical current density in Ag-sheathed (Bi,Pb)2Sr2Ca2Cu3Ox composite conductors prepared by overpressure processing in final heat treatment

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Overpressure (OP) processing otherwise fully treated, commercial Ag-sheathed multifilament (Bi,Pb)2Sr2Ca2Cu3Ox (2223) composite conductors increased the critical current density Jc (0.1 T, 77 K) by 37% to 30.8 kA/cm2 and the self-field Jc (SF, 77 K) to 69.6 kA/cm2. These improvements were obtained on full-size high current conductors such that critical current Ic (0.1 T, 77 K) reached 80.6 A and Ic (SF, 77 K) 181.7 A, even though there was a very strong self-field suppression of Ic. Estimated values for the non-self-field-limited Ic and Jc (0 T, 77 K) reached 235 A and 90 kA/cm2. Scanning electron microscopy and superconducting quantum inference device measurement revealed that OP processing effectively suppressed cracks, porosity, and the volume fraction of the Bi2Sr2Ca1Cu2Oy (2212) phase, which are all major current-limiting mechanisms in present 2223 conductors.