Double Casing Conductor Designed for High Mechanical Stress in Fusion Devices

Abstract

The demand for stronger magnetic fields in fusion devices necessitates robust conductors capable of withstanding greater loads. High-temperature superconducting (HTS) cables using REBCO tapes have demonstrated practicality by carrying high currents even in magnetic fields up to 20 T. Several projects have been initiated to demonstrate the feasibility of using HTS twisted stacked-tape cable (TSTC) conductors. However, these challenges, particularly those associated with soldering defects leading to cavities, failures, and cable cracking, have been effectively addressed, significantly enhancing load resistance and structural reliability when making REBCO tapes into cables. In this study, we conducted experiments on a double casing cable (DCC), a round HTS strand designed following the TSTC approach. We improved soldering quality using vacuum pressure impregnation: an inner casing provides additional tape support, reducing mechanical issues from weak solder strength, while an outer casing facilitates solder flow channels, preventing inner casing cracking under direct stress. Direct current (DC) tests on transverse electromagnetic characteristics demonstrate the DCC strand's potential for high-current cables and fusion magnet applications. Notably, the strand sustained transverse load amplitudes up to 1250 kN/m without degradation of critical current (I$_{c}$). We present experimental results and discuss structural optimizations based on visual inspection and analysis.