Bending Tests of HTS Cable-In-Conduit Conductors for High-Field Magnet Applications

A high-temperature superconducting (HTS) cable-in-conduit conductor (CICC) suitable for high-field magnet applications and comprised of twisted-stacked coated-conductor tapes arranged around a helically slotted core has been recently proposed and tested, demonstrating full compatibility with existing cabling technologies. To form the desired shape of any coils for high-field magnet applications, any suitable CICC option needs to be bent. For a magnet design, it is then very important to characterize the bending behavior of the CICC and, in particular, to find the smallest bending radius achieved without performance degradation. To this aim, bending tests were carried out on 1-m-long dummy samples of five helical slots in an extruded aluminum core, in which four REBCO tapes and dummy stainless-steel tapes were mounted in each slot. A controlled bending moment has been applied to the HTS CICC samples at room temperature, and each individual superconducting tape has been electrically characterized as a function of bending radius by measuring the critical current and n-index values at 77 K in a self-field condition. Results are analyzed and explained with the help of a three-dimensional cable model implemented in ANSYS and analytical calculations. The experimental and numerical results presented in this paper will demonstrate that the twisted-stack slotted-core technology can meet the bending requirements of high-field magnet designs.