Influence of longitudinal magnetic field on current distribution and AC loss in twisted multifilamentary high T-c superconducting tapes

The AC longitudinal magnetic field that is parallel to the tape axis couple s with the twisted filament bundle in multifilamentary high T-c superconduc ting tapes to change their current distribution. The temporal evolution of the current distribution in the tape cross-section was calculated numerical ly to study the influence of the longitudinal magnetic field on AC loss cha racteristics. The change in the current distribution by the longitudinal ma gnetic field results in the increase in the AC loss. The AC loss due to the longitudinal magnetic field increases with decreasing twist pitch, while t he AC loss due to the transverse magnetic field decreases with decreasing t wist pitch. In practical conditions where high T-c superconducting tapes ca rry their AC transport current in an AC external magnetic field with transv erse and longitudinal components, the optimum twist pitch to reduce the tot al AC loss must be selected. (C) 2000 Elsevier Science Ltd. All rights rese rved.