Measurements of Thermal Resistance Between Metallic Surfaces for High Current HTS Cable-in-Conduit Conductor

Abstract

High temperature superconductors (HTS) are promising candidates for high current Cable-In-Conduit Conductors (CICCs) for large high-field magnets. In many cases, these CICCs are made from stacks of several HTS tapes. This work focuses on the thermal contact resistance in various metal-to-metal interfaces among tapes and between tapes and surrounding materials. Three main configurations were examined: soldered tapes, unsoldered tapes, and braided copper structures wrapped around the HTS tapes (BRAST). Samples were tested in a controlled cryogenic environment, from 6 K to 300 K, under applied forces ranging from 50 N to 200 N. The analysis reveals that thermal contact resistance plays a prominent role at low temperatures and can be reduced by increasing the applied force. For soldered tapes, an additional reduction in thermal contact resistance was observed after the removal of surface oxides. Unsoldered tapes, by contrast, showed higher sensitivity to contact pressure, pointing to the importance of precise mechanical alignment. These observations highlight the importance of interface quality, contact characteristics, and surface preparation in minimizing thermal contact resistance in HTS cables. By varying the temperature and applied force during measurements, it was possible to characterize the distinct contributions from each interface type, offering valuable insights for improving thermal performance in superconducting systems operating at cryogenic temperatures.