A New Way to Measure the Thermal Conductance of the ReBCO/Substrate Interface in Coated Conductors

In coated conductors (CC), the quality of the interface between the superconducting layer and the substrate is an important parameter especially for fault current limiter applications. Indeed, it influences the propagation velocity of the normal zone along the CC. We present a new way to measure the thermal conductance of the interface between two electrically isolated layers. The top layer is heated by an ac current and its temperature oscillation is recorded. A simple thermal model consisting of a heater, a substrate, and a thermal bath, all coupled by thermal conductances, was developed to simulate the temperature oscillation and to extract the interface thermal conductance. This model predicts that in a certain frequency range, the oscillation of the temperature is strongly influenced by the thermal conductance of the interface. Measurements performed on CC, produced by Theva, are well fitted by our model assuming a thermal conductance of 320 W/cm² K. This value is confirmed by measurements performed using a dc technique. We also present measurements on another coated conductor (produced by Superpower) having a different architecture, i.e., different interfaces between the superconducting layer and the substrate. These results are the only available values of the thermal conductance of the ReBCO/interface in coated conductors.