Electro-thermal quench in metal-insulated nested REBCO coils for magnets over 40 T

TL;DR

This work analyzes electrothermal quench in a high-field magnet design comprising two HTS nested stacks inside an LTS outsert, aiming to exceed $40\,\text{T}$ at the center. Using an in-house MEMEP-FD solver that accounts for screening currents, the authors perform multiphysics simulations to identify weak points and assess mitigation strategies, including voltage limiting and inter-turn resistance optimization. The results consistently point to the bottom inner HTS1 pancake as the most thermally vulnerable region, with quench dynamics strongly influenced by $J_c(B,T,\theta)$ anisotropy and inter-turn contact resistivity; reducing inter-turn resistance below $10^{-7}\ \Omega\cdot\text{m}^2$ improves stability but can slow ramp rates. The study provides actionable guidance for robust high-field magnet design within the SuperEMFL program, balancing thermal stability, mechanical integrity, and operational speed.

Abstract

Superconducting high field magnets have the capability to generate over 40 T, with multiple existing practical applications globally. However, at such high magnetic fields, these magnets are prone to rapid electrothermal quench which can affect the continuous operation of such magnets. A nested stack configuration, with multiple HTS inserts inside a LTS outsert, can be used for better thermal stability and compact design. We have performed detailed multiphysics quench analysis of such a nested stack high field magnet design under SuperEMFL project using our in-house software, which considers screening currents. Through various case studies, we have identified various weak spots in such a magnet, where thermal quench can be the most detrimental for magnet operation, and various ways are suggested to overcome this important issue.

Figures (9)

• Figure 1: (a) Full scale magnet and its cross section, which shows nested HTS1 and HTS2 pancake coil insert stacks inside LTS outsert magnet. (b) Cross section of turns in pancakes, including the isolating Durnomag layer between 2 tapes. The sketches are only for representation and not to scale.
• Figure 2: Hotspot analysis when damage is at the top pancake at HTS1. Figure shows (a) current density profiles, (b) change in temperature, and (c) increase in radial currents up to 1.38 s.
• Figure 3: Hotspot analysis when damage is at the middle pancake at HTS1. Figure shows (a) current density profiles, (b) change in temperature, and (c) increase in radial currents up to 2.88 s.
• Figure 4: Hotspot analysis when damage is at the bottom pancake at HTS1. Figure shows (a) current density profiles, (b) change in temperature, and (c) increase in radial currents up to 2.88 s.
• Figure 5: Nested stack behavior when damage occurs at different parts of the stack. Figures show (a) Total current decay, (b)Average radial current in section, (c) Total power, (d) Power loss due to radial current, (e) Maximum temperature, and (f) Average temperature rise in the nested stacks after the onset of damage. It is seen that maximum temperature rise occurs when the damage is at the bottom of the stack, and hence it is considered as the worst case scenario (or our reference case). All figures use same legend as (a).