Ac losses in superconducting parallel conductors in saturation case

Ac loss properties of 2-strand superconducting parallel conductors in the saturation case are quantitatively discussed. The parallel conductors are composed of rectangular cross-sectional multifilamentary strands. In the saturation case, the induced shielding current reaches to the critical current of the strand. The constituent strands in parallel conductors usually need to be insulated and transposed for the sake of low ac loss and uniform current distribution. In the case that the strands are transposed at the optimum position, the interlinkage magnetic flux of the strands is cancelled out and the shielding current is not induced. But in the case that the transposition points deviate from optimum one, the shielding current is induced and the additional ac loss is occurred. We have already investigated the ac loss properties of 2-strand parallel conductors' in the non-saturation case. However, if the field amplitude and/or the deviation in transposition are so large, the saturation condition is satisfied. We derived the expressions of the additional ac loss in the saturation case, and verified them by the experiment with the sample conductors composed of NbTi multifilamentary strands. As a result, the additional ac loss can be much reduced by transposition even in the saturation case.