Magnetic flux penetration and AC loss in a composite superconducting wire with ferromagnetic parts

The current distribution and the AC loss in a composite superconducting tape containing a layer of magnetic material is calculated and compared with experiments, showing a very good agreement. The situations of an alternating uniform applied field or a transport current are studied. The newly developed numerical model is an approximation to the critical state model, adapted for applicability to commercial finite element codes that solve the vector potential. A substantial feature of this procedure is that it can be carried out in the case when the critical current density in the superconductor depends on the magnetic field and the magnetic layer material is nonlinear. Additionally, the hysteresis loss in the magnetic material is estimated, based on its measured magnetization loops. Measurements on Bi-2223 multifilamentary tapes covered on edges by nickel confirmed our predictions, showing a substantial ac loss reduction in both the investigated regimes.