FEM-calculations on the frequency dependence of hysteretic losses in coated conductors

Calculations based on two different finite-element models have been carried out to investigate the flux flow behaviour of High Temperature Superconductors (HTS), in particular of Coated Conductors (CC) based on 123-HTS. The models allow the simulation of the response of the CC to various experimental operating conditions: e.g. a fast ramping of the transport current typically done in measurements of the critical current Ic or sinusoidal changes of an external magnetic field typically used in AC loss measurements. The models also allow calculating the response to arbitrary combinations of current and field changes. The superconductor is modelled by using either a simple power-law E(J) characteristic or one which also accounts for field and temperature dependences. The obtained results go beyond Bean's approximation, which is mostly employed for interpreting such flux penetration effects. One consequence is that hysteretic losses, which in Bean's model are frequency independent, show a dependence on the time scales of current or field changes. The field and frequency ranges where such deviations from Bean's model should be taken into account are discussed.