Analysis of current and heat transfer in locations with reduced critical current in coated conductor tape

Variation of the critical current along the conductor length is a feature commonly encountered in industrially produced REBCO tapes called coated conductors (CCs). A reduction of the critical current exceeding several percent in portions a few millimetres long can be observed in the data obtained by reel-to-reel characterization provided by manufacturers. Metallic layers in the CC architecture can take over some current in such a ‘weak spot’, and help to keep the local temperature stable, preventing its thermal runaway and conversion to a ‘hot spot’. Understanding this phenomenon is particularly crucial when space and weight limitations do not allow for the addition of a metallic layer with a thickness that would be sufficient to match the lost transport capability of superconductors. For this purpose, we studied a set of samples, representing both standard as well as infrequent profiles of weak spots identified in direct transport experiments. Analytical theory is then utilized as a basic tool for recovering the properties serving as input for numerical modelling. Temperature profiles and current redistribution at weak-spot locations were found, and the effect of cooling conditions and metallic layer thickness on the weak-spot resistance against thermal runaway was analyzed. Quantitative assessment of the possibility to improve the performance of CC tape by adding a Cu stabilizing layer or improving cooling settings could help to optimize the architecture of CCs intended for use in electrical transport.