Effect of non-uniform turn-to-turn resistance on quench behavior of nested NI/MI REBCO magnets under open-circuit fault

Abstract

The vulnerability of REBCO insert magnets to extreme mechanical responses during open-circuit faults has caused severe failures in some high-field systems. This work studies the fault behaviors of a nested no-insulation/metal-insulation (NI/MI) REBCO insert in a 30 T magnet using the rotated anisotropic resistivity method. Experimentally calibrated characteristic turn-to-turn resistances of unshunted and InSn surface-shunted coils (4000 and 100 μΩ·cm2) are adopted in the simulation. Results of simulations under radially non-uniform turn-to-turn resistance configurations reveal that electromagnetically coupled quench propagation forces the low-resistance layer to protect the high-resistance layer at the cost of excessive current and stress, failing to reconcile flux compensation and mechanical load. Two complementary strategies are then proposed: an axial graded resistance scheme that synchronizes regional discharge time constants to suppress current amplification, and an external magnetic dam that provides passive flux compensation via co-wound superconducting tapes in the over-banding layer. These reduce peak stress by ∼27%, meeting long-term operational safety thresholds. These findings demonstrate that regulating the spatiotemporal distribution of flux change rate through resistance matching is an effective approach to suppress open-circuit fault damage in nested magnets, offering a theoretical basis for quench protection design in high-field nested REBCO magnets.