THE EXTENDED E-J CHARACTERISTICS OF FLUX DIFFUSION AND THEIR ROLE IN THE SELF-FIELD AC LOSSES IN AG-SHEATHED PBBI2223 TAPES

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