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

The AC longitudinal magnetic field that is parallel to the tape axis couples with the twisted filament bundle in multifilamentary high T-c superconducting tapes to change their current distribution. The temporal evolution of the current distribution in the tape cross-section was calculated numerically to study the influence of the longitudinal magnetic field on AC loss characteristics. The change in the current distribution by the longitudinal magnetic field results in the increase in the AC loss. The AC loss due to the longitudinal magnetic field increases with decreasing twist pitch, while the AC loss due to the transverse magnetic field decreases with decreasing twist pitch. In practical conditions where high T-c superconducting tapes carry their AC transport current in an AC external magnetic field with transverse and longitudinal components, the optimum twist pitch to reduce the total AC loss must be selected. (C) 2000 Elsevier Science Ltd. All rights reserved.