Using 3D simulations of currents in SPARC conducting structures to improve 2D scenario development and control*

Three dimensional currents induced in the vacuum vessel and other conducting structures in SPARC will impact both the plasma equilibrium and magnetic sensor signals used for equilibrium reconstruction and control. In this study, the thin-wall current modeling tool ThinCurr [1] is employed to accurately model these 3D current structures and to inform reduced 2D models of induced currents for scenario development. These ThinCurr simulations reveal key eddy current eigenmode structures and critical regions where toroidally flowing currents are precluded, while also providing high fidelity models for determining the effects of induced currents on nearby magnetic sensors. The results from the 3D current modeling are used to calibrate the 2D model of SPARC’s vacuum vessel in the free boundary, Grad-Shafranov equilibrium solver TokaMaker [2]. This provides a more accurate description of the vessel currents for time-dependent equilibrium generation and scenario development. It also yields self-consistent results between the 2D and 3D representations of the induced currents in the two codes. This workflow is used to better predict the impact of eddy currents during challenging phases of the discharge, including ramp-up and strike point sweeping.

[1] https://github.com/hansec/OpenFUSIONToolkit

[2] C. Hansen et al. 2024 Comput. Phys. Commun. 298 109111