AC-loss properties of Bi-2223 multifilamentary taped wires with a central insulation layer

We have been developing twisted Bi-2223 multifilamentary taped wires to suppress the AC losses in perpendicular-field configuration for industrial-production process. It is confirmed that the hysteretic losses in the filamentary region can be reduced by twisting in a same manner as in situ Nb₃Sn multifilamentary ones, while the coupling loss remains in unsatisfactory situation for commercial frequency uses. As one of practical methods for further reduction of the coupling loss, we propose an advanced multifilamentary structure of the taped wires in which an insulation layer is arranged in the central region of the tape to effectively restrict the main part of the coupling current in the perpendicular-field configuration instead of an insulation barrier around each filament that may be not usually suitable to the practical production process. We have designed and fabricated prototype wires with the proposed structure, and measured the AC loss properties in the perpendicular-field configuration. The experimental results suggest that the central insulation barrier has a function to suppress the coupling loss remarkably. We also discuss improvement in the structural design for the further reduction of the AC losses.