Experimental study on AC losses in Ag sheathed PbBi2223 tapes with twist filaments

Experimental measurements of AC losses were carried out on Ag sheathed PbBi 2223 tapes with twisted and untwisted filaments. Losses were measured at 77 K as function of frequency and magnetic field parallel and perpendicular t o the tape surface, using appropriate pick-up loops. Both the first and thi rd harmonics of the signal were measured, in order to distinguish between t he hysteresis loss and other types of loss. The effect of filaments uncoupl ing by twisting was clearly identified. For a tape with a twist pitch of 10 mm and I-c = 40 A (similar to 20 kA cm(-2)) operating at 43 Hz, the filame nts are uncoupled in fields less than 40 mT, which is greater than the full penetration field for both the filaments and the tape. Hence, a reduction in the hysteretic loss of the superconducting core is realised at power fre quency between 10 and 40 mT. Results form the self-field loss measurement i mplies the uncoupling of twisted filaments at relative low transport curren t (I < 0.5I(c)) (C) 1998 Elsevier Science B.V. All rights reserved.