Post-processing method for extracting the resistivity of Rare-Earth Barium Copper Oxide (REBCO) coated conductors in over-critical current conditions from ultra-fast V-I pulsed current measurements

This paper presents a simple but rigorous method to extract correctly the resistivity of the superconducting Rare-Earth Barium Copper Oxide (REBCO) layer of High Temperature Superconductor coated conductors, when the latter are characterized in over-critical current conditions using ultrafast V-I pulsed current measurements. The pulsed current measurement method is used to reduce the amount of heat generated by the strong current flowing in the sample, but it cannot prevent it completely at current levels well above the critical current. In order to estimate accurately the temperature rise, we developed the so-called Uniform Current (UC) model, which consists in a static current sharing model coupled with a 2D thermal solver. The model assumes that the electric field is uniform over the sample cross section. It has been shown that this hypothesis works fine at high currents, but for lower current levels, although still higher than the critical current, one must wait until the magnetic relaxation effects disappear before using the outputs of the UC model. We also derived a theoretical bound for the error related to magnetic relaxation, which can be estimated experimentally by using a rectangular pick-up coil located just above the sample surface. After applying the UC model on an experimental set of data, one obtains a whole set of data points defining the resistivity rho(J, T) of the REBCO superconductor being characterized.