Modelling quench in fusion magnets protected by an internal dump

This work presents a numerical model for quench simulation in the non-planar superconducting magnets of the GIGA stellarator reactor (Gauss Fusion), which stores energies on the order of 100 GJ. The study focuses on the development and application of a predictive multi-physics model for an innovative active protection concept that eliminates external dump resistors by using the structural steel plates of the winding pack as distributed resistive elements for energy dissipation. The approach is based on an integrated simulation model coupling the THEA code, specialized in one-dimensional thermo-electro-hydraulic modelling of superconducting cables, with a dedicated electrical circuit model. The THEA component resolves the transient behavior of the conductor in both LTS (Nb₃Sn) and HTS (REBCO) configurations, including quench initiation and propagation, helium coolant dynamics, and current redistribution. The circuit model represents the current paths through the structural steel plates, which run parallel to the conductor but are connected in series with it, and evaluates their electro-thermal response. The model simulates quench initiation mechanisms through localized thermal disturbances and critical current degradation and implements different quench detection logic based on voltage and temperature thresholds. Following quench detection, the coupled model captures the transient transfer of current from the superconductor to the resistive steel plates and the associated Joule dissipation of magnetic energy. Owing to the one-dimensional description of the conductor and the lumped description of the plates, a complete quench transient of 200 s is simulated in a few minutes on a laptop-class computer, and the same framework handles LTS and HTS conductors, different quench initiation mechanisms and both voltage- and temperature-based detection. A systematic parametric study is performed using the model to assess sensitivity to geometric, thermal, and electrical design parameters, conductor characteristics, and quench detection strategies. The simulation results demonstrate the capability of the model to predict the thermal, hydraulic and electric transient response of the coil, a useful aid to achieve successful mitigation of hot-spot temperature and terminal voltage, and a quantitative guidance for the design of the magnet and associated systems.