Possible Self-Arresting Screening Current Stress Damage in a REBCO Test Coil At 42.6 T in 31 T Background Field

REBCO coated conductors (CCs) have now been optimized for current-carrying capacity in high magnetic fields. Production-lengthCCsmaycarrymore than 1500Aat 4.2 K/30Tin theB//ab configuration.Such high Ic is essential for the construction of new generations of ultra-high field (B > 40 T) magnets. However, high Ic also increases screening current stresses (SCS) and makes these contemporary tapes vulnerable to mechanical damage during magnet operation. To study this vulnerability, we constructed and tested Little Big Coil #6 (LBC6), one of a series of standardized ultra-high field insert coils operated in a 31 T resistive background field at the National High Magnetic Field Laboratory (NHMFL). LBC6 used contemporary conductor with triple the Ic of the earlier LBCs, so we hypothesized that the coil would be destroyed by SCS during operation. Instead, LBC6 survived multiple quenches from more than 42 T and repeated cycling from 31 T to 41 T. Postmortem analysis revealed plastic deformation throughout the winding pack, but the damage to the REBCO layer was confined to one conductor edge. We propose that this coil exhibited a self-arresting damage mechanism: during the initial energization and quench, SCS damage sufficiently narrowed the superconducting filament width (thus reducing Ic) such that no further SCS damage occurred during subsequent operation. Possible implications for ultra-high-field magnet design are discussed.