Validation of runaway electron mitigation coil electromagnetic modeling in the HBT-EP tokamak

Abstract The electromagnetic design and modeling process for the HBT-EP Runaway Electron Mitigation Coil (REMC) is validated through comparison with experimental results, confirming the accuracy of predictions for disruption-driven REMC currents. ThinCurr, a thin-wall, 3D electromagnetic modeling code, predicts currents and fields in the coupled REMC, plasma, vacuum vessel, and operational coil system. The REMC design process utilizing ThinCurr is discussed, demonstrating the ability to quickly iterate over possible coil designs. REMC induced current and perturbed field predictions are then compared to experimental data to validate numerical models. Initial testing is performed without plasma by driving current in the REMC directly with a high-power amplifier or inductively with the central solenoid or poloidal field coils. Experimental measurements and model predictions for the REMC current are in good agreement. Following these tests, plasma disruptions are observed to inductively drive current, as intended for REMC applications. Approximately 14% of the pre-disruption plasma current is driven in the REMC by the current quench and operational coils, consistent with modeling. The results highlight that accurate predictive modeling depends on careful treatment of conducting pathways and self-inductance uncertainties. The calculated REMC field perturbation is then validated against Mirnov probe array readings, showing good agreement and confirming that the field prediction accuracy is within 23%. The validation provides confidence in the analogous workflow used for electromagnetic predictions for REMCs in other devices.