AC losses to be reduced by twisting filaments in a silver-sheathed Bi-2223 multifilamentary tape

An investigation is carried out to manifest types of AC losses in silver-sheathed Bi-2223 multifilamentary tapes that can be reduced by twisting filaments. The AC losses, in external magnetic fields parallel to the tape surface, consist mainly of the AC losses due to macroscopic screening currents in the multiple filaments and the AC losses due to the microscopic screening currents in the grains. The former loss depends greatly on the filament twist pitch, while the latter does not. Below the critical changing rate of a magnetic field at which screening currents at the outer filaments begin to saturate, the inter-filament coupling losses are added to the hysteresis losses for the equivalent filament size. Consequently, an analytical model can successfully explain experimental results that the macroscopic AC losses are considerably reduced by twisting filaments.