Quench Protection in Insulated REBCO Conductors: Design Optimization and Fast Detection via REBCO SQD

Abstract

This work was conducted within the framework of the exploratory French project PEPR SupraFusion, which aims to advance the field of fusion energy by developing High-Temperature Superconductor (HTS)-based demonstrators capable of storing significant energy while operating under high magnetic fields and currents. Ensuring a reliable protection during a quench in Insulated REBCO conductors is challenging\,: slow normal-zone propagation and validation delays allow the hotspot's temperature to reach damaging levels. We compare (i) conductor protection via copper-stabilizer optimization and (ii) a co-wound, REBCO superconducting quench detector (SQD) that is electrically isolated yet thermally coupled and intentionally deoxygenated to lower Tc and Ic for an earlier transition. Onedimensional THEA modeling shows that a good choice of stabilizer cross-section makes the protection possible during quench events by keeping the temperature of the hotspot within a safe limit. The simulations also demonstrate that the use of a REBCO SQD enables the quench detection at lower temperatures.

Figures (5)

• Figure 1: Conceptual layout of the co-wound sensor. A lightly stabilized REBCO SQD (top) is thermally coupled to the insulated REBCO conductor (bottom) and electrically isolated from it. Independent voltage taps read $U_{\mathrm{cond}}$ and $U_{\mathrm{SQD}}$. The conductor carries the operating current; the SQD is biased at a small DC current $I_{\mathrm{op,SQD}}$ to enhance its resistive response. A local heater provides a controlled disturbance.
• Figure 2: Sensing principle. Solid lines: hotspot temperatures of the conductor and the SQD; dashed lines: corresponding voltages over a fixed gauge length. The SQD reaches the voltage threshold $U_{\text{threshold}}$ earlier ($t_{\mathrm{det}}(\mathrm{SQD})$) than the conductor ($t_{\mathrm{det}}(\mathrm{cond})$), yielding a cooler hotspot at detection and after the validation delay, relative to the allowable limit $T_{\max}$.
• Figure 3: Stabilizer-only protection results. Evolution of the hotspot temperature (top) and conductor voltage (bottom) for different current densities
• Figure 4: SQD-assisted protection: effect of SQD operating current. The square symbols are the temperatures of the conductor when its voltage $U_{det, cond}$ crosses the threshold. the round symbols are the temperatures of the conductor when the SQD voltage $U_{det, SQD}$crosses the threshold
• Figure 5: SQD-assisted protection: effect of intentional degradation. Larger $\alpha_{\mathrm{deg}}$ (stronger $I_c$/$T_c$ reduction) advances detection on the SQD channel and lowers $T_{\mathrm{HS}}$ at detection for the conductor.