Low-magnetic-field dependence and anisotropy of the critical current density in coated conductors

Many applications of ReBCO-coated conductors operate at low magnetic fields in the superconductor (below 200 mT). In order to predict the critical current and AC loss in these applications, it is necessary to know the anisotropy and field dependence of the critical current density at low magnetic fields. In this paper, we obtain a formula for the critical current density in a coated conductor as a function of the local magnetic field and its orientation. Afterwards, we apply this formula to predict the critical current of a pancake coil that we constructed. We extract the critical current density of the tape from measurements of the in-field critical current at several orientations. Numerical simulations correct the effect of the self-field in the measurements and successfully predict the critical current in the pancake coil. We found that a simple elliptical model is not enough to describe the anisotropy of the critical current density. In conclusion, the analytical fit that we present is useful to predict the critical current of actual coils. Therefore, it may also be useful for other structures made of coated conductor, like power-transmission cables, Roebel cables and resistive fault current limiters.