Reduction of AC loss in Ag sheathed PbBi2223 tapes with twisted filaments in external and self-fields

The hysteretic a.c. losses in multifilament tapes can be reduced by filamen t twisting with a pitch shorter than a critical pitch which is dependent up on the material parameters of the tape and dB/dt. To determine the effectiv eness of twisting, measurements of ac losses have been carried out on Ag sh eathed multifilamentary PbBi2223 tapes with different twist pitches (minimu m 10mm). Self-field loss measurements showed clear uncoupling of filaments for current up to 50% of Ic for a twist pitch shorter than 15mm, In paralle l external fields, the effect of filaments uncoupling by twisting was ident ified with 10mm pitch showed a reduction in the hysteretic loss of the supe rconducting core, at power frequency, between 10mT and 35mT. This correspon ds well with the theoretical predictions for a tape with a twist pitch of 1 0mm and Ic = 40A (similar to 20kAcm(-2)) operating at 43Hz. We also observe d that the losses in the normal matrix are dominant for fields above 30mT a lthough losses in the superconductor are reduced by twisting.