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

The hysteretic AC losses in multifilament tapes can be reduced by filament twisting with a pitch shorter than a critical pitch which is dependent upon the material parameters of the tape and dB/dt. To determine the effectiveness of twisting, measurements of AC losses have been carried out on Ag sheathed multifilamentary PbBi2223 tapes with different twist pitches (minimum 10 mm). Self-field loss measurements showed clear uncoupling of filaments for current up to 50% of Ic for a twist pitch shorter than 15 mm. In parallel external fields, the effect of filaments uncoupling by twisting was identified with 10 mm pitch showing a reduction in the hysteretic loss of the superconducting core, at power frequency, between 10 mT and 35 mT. This corresponds well with the theoretical predictions for a tape with a twist pitch of 10 mm and Ic=40 A (/spl sim/20 kAcm/sup -2/) operating at 43 Hz. We also observed that the losses in the normal matrix are dominant for fields above 30 mT although losses in the superconductor are reduced by twisting.