Numerical analysis of a.c. losses in superconductors

A two-dimensional computational code to evaluate a.c. losses in superconductors has been developed using the current vector potential method (T-method), where the vector potential T is defined by {down triangle, open} × T = J. The current distributions in both superconductors and normal conductors are calculated while changing the conductivity of the superconductor so that the current density never exceeds the critical current density. The hysteresis and coupling losses evaluated by the numerical code agree with analytical solutions, as far as these are available. In order to verify the validity of the code, an experiment to measure the hysteresis and coupling losses was carried out using Nb-Ti/Cu filaments. The total loss evaluated from the numerical code agrees with that from the experiment. The numerical analysis, however, indicates that the hysteresis loss under quasi-steady magnetic field is less than the loss in the superconductor under transient field.