AC Losses for in Situ Superconducting Microcomposites

Metallurgical linking of the filaments and their proximity coupling through the normal metal matrix in in situ prepared superconducting composites cause greater ac losses than those observed for bronze process materials. Twisting of in situ wire, provided twist length is sufficiently small, results in a limitation of screening supercurrent density by the critical supercurrent density across the filament direction before the twisting. Supercurrent density across the filament direction is determined by both cross-linking and proximity coupling of filaments. Proximity supercurrents between the filaments can be greatly reduced by a high enough magnetic field, so that the separate contribution of metallurgical links can be determined. In fact, this is done by comparison of the magnetization hysteretic curves for the wires before and after twisting.