Effect of twisting on microstructure, critical current, and AC losses of Bi-2223 superconductor tape

We evaluated the effect of twisting on microstructure, critical current, and AC losses of Bi-2223 superconductor tapes. It was observed that grain size and grain alignment were reduced with decreasing twist pitch probably due to the formation of an irregular interface between Ag and filaments. The critical current of the tapes decreased with decreasing pitch. For the tape having a twist pitch of 10 mm, ≈50% of the critical current was maintained compared to that of the non-twisted tape. The reduction of critical current is believed to be due to irregular interface, poor grain alignment, small grain size, and existence of second phases, etc. In addition, it was observed that AC losses of the tapes were reduced as the pitch decreased probably due to the combined effect of lower critical current and electrically decoupled filament of twisted tape.