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Description
REBCO has been regarded as one of the most promising high temperature superconductor (HTS) options mainly due to its large in-field current carrying capacity and strong substrate mechanical toughness. Thus, it may not be a surprise that the recent high expectation on compact fusion has been largely relying on REBCO conductor and magnet technologies. Despite the recent notable achievements in some milestone REBCO magnets, however, we are still struggling with even fundamental challenges such as accurate estimation of critical current and understanding of spatial and temporal distributions of currents. Thus, modern REBCO magnets have been designed and operated with lack of confidence in precise estimation of their electrical and mechanical limits. Yet, adequate quench protection for REBCO magnet is still far from success. Firstly reported in 2009, the so-called no-insulation (NI) winding technique enables “current sharing” among adjacent turns, which introduces an alternative quench protection mechanism for REBCO magnets. Despite its “self-protecting” behaviors in small NI REBCO coils, however, failures of protection have been often reported particularly in large stored energy NI REBCO magnets. This paper summarizes protection failures of selected REBCO magnets to date, analyze mechanisms of damages, and suggests alternative vision on quench protection and potential solutions to protect large stored energy REBCO magnets.
