Equivalent circuit model for superconductors

We propose an equivalent circuit model that describes the behavior of a superconductor viewed by an external user, for whom the global variables voltage and current are of interest. It is used in time-continuous simulations and it treats well both the subcritical and supercritical current regime. The model is based on Maxwell's equations, measurement results as well as on the physical structure of a superconducting tape. The incorporated circuit elements have been described in mathematical expressions: a nonlinear resistance and a nonlinear inductance (superconducting core) in parallel with a linear resistance and a linear inductance (silver sheath or by-pass material). The simplicity of the model makes it fast and easy to apply compared to existing numerical models of superconductors, based on finite element methods. Furthermore, it is wide-ranging and may represent a superconductor in many different applications depending on parameter values. Examples of applied voltage and current with nonstationary waveforms on a HTS tape are given. Calculated are the hysteresis losses (due to flux pinning) and resistive losses (due to flux creep and flux flow) in the tape in the range 0.1 to 1.8 I/sub c/.