A computer approach to the nonlinear hysteretic problem of electromagnetic field computation in hard superconductors for loss evaluation

The computation of the losses in superconducting wires requires the solution of electromagnetic problems with a complicated constitutive equation of the superconducting material, which is nonlinear with hysteresis, under time-varying conditions. Analytical and numerical procedures which can be found in the literature about this problem present a very limited application range and cannot be applied to cases of practical interest. In the paper a procedure is presented, by which most of the drawbacks are eliminated. The critical state model developed by Bean, Kim et al is used, in both the forms with constant critical current density and with critical current density function of the magnetic field. In this model the magnetic field penetrates the superconductor entering from the boundary by fronts. These fronts cannot reverse their velocity and represent interfaces with unknown geometric shapes. A package has been implemented to solve this problem, some example of field solution are given and the results are discussed.