Reduction of the a.c. losses in Ag sheathed PbBi2223 tapes with twisted filaments

Measurements of the total a.c. losses in an applied parallel a,c. magnetic field have been measured for Bi2223/Ag tapes with twisted and untwisted fil aments. The measurements were undertaken using suitable pickup loops and a lock-in amplifier. For all frequencies (37-200 Hz) and field amplitudes use d (< 45 mT) the tape with untwisted filaments behaved as if its filaments w ere fully coupled. For this situation, the total losses were accurately des cribed using the Bean model for a 1D slab (assuming the tape acts as a mono block). In contrast, the losses for the tape with twisted filaments (10-mm pitch) were considerably less than for the tape with untwisted filaments ov er the entire frequency and field amplitude range. The loss behaviour indic ated that the filaments were partially decoupled, and the total losses in t his tape were best described by adding the filament hysteresis losses to th e coupling current losses. The filament losses were calculated using the Be an model for a slab with dimensions of an individual filament and the coupl ing current losses predicted from existing theory for a tape geometry in pa rallel field. (C) 1999 Elsevier Science B.V. All rights reserved.