ANALYTICAL APPROACH TO AC LOSS CALCULATION IN HIGH-T-C SUPERCONDUCTORS

Using a linear spline approximation for the E-J characteristic of a su perconductor and representing the solution in form of series, analytic al expressions for AC losses have been obtained. The expression explai ns experimentally observed frequency and magnetic field dependencies o f AC losses. Cases of complete and incomplete magnetic field penetrati on have been distinguished. AC losses per cycle decrease with increasi ng frequency in the case of incomplete penetration, the case relevant to thick slabs and low amplitude magnetic fields, while in thin slabs and large magnetic fields they increase with increasing frequency, the case of complete penetration. The analysis of the analytical solution s obtained has given a simple criterion for the applicability of the c ritical state model (CSM) to the calculations. This criterion involves characteristics of both superconductor and applied magnetic field. Th e physical meaning of the criterion in terms of ratios between the cha racteristic decay times of magnetic field energy in a superconductor a nd the period of applied magnetic field has been established. It has b een shown that the analytical solutions can be applied for various for ms of E-J characteristics by means of defining effective critical curr ent density and flux flow resistivity. (C) 1998 Elsevier Science B.V. All rights reserved.