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

Variation of critical current along the conductor length is the feature commonly encountered in industrially produced REBCO tapes called coated conductors (CC). Reduction of critical current exceeding several percent in the portions few millimetres long can be observed in the data obtained by reel-to-reel characterisation provided by manufacturers. Metallic layers in the CC architecture can take over some current in such „weak spot”, and help to keep the local temperature stable, preventing its thermal runaway and conversion to a “hot spot”. Understanding the phenomenon is particularly crucial when the space and weight limitations do not allow to add metallic layer with the thickness, that would be sufficient to match the lost transport capability of superconductor. 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 was then utilised as basic tool for recovering the properties serving as input for numerical modelling. Temperature profiles and current redistribution in the weak spot locations were found, and the effect of cooling conditions and metallic layer thickness on the weak spot resistance against thermal runaway analysed. Quantitative assessment of the possibility to improve the performance of CC tape by adding Cu stabilising layer or improving cooling settings could help to optimise the architecture of coated conductor intended for use in electric transport.