The extended E-J characteristics of flux diffusion and their role in the self-field AC losses in Ag-sheathed PbBi2223 tapes

Abstract

The interplay between the flux pinning of the critical state and flux diffusion has an important effect on the hysteresis losses at high frequencies (>200Hz). This interplay between the two mechanisms has been seen in the dB/dt dependence of the magnetization and AC losses in a varying external field. In order to study this effect in the self-field situation we have separated the eddy current losses and hysteresis losses, of an Ag-sheathed PbBi2223 tape, by making measurements of the 1st and 3rd harmonics of the electric field, at various frequencies. These measurements show as expected that the hysteresis loss per cycle decreases for increasing frequency. Our data shows that, for a given frequency and transport current, there exists an equivalent critical current, which when plotted against the corresponding loss electric field is coincident with the DC E-J characteristics of the tape. This demonstrates that the hysteresis losses are determined by the extended E-J characteristics of the tape.