Modeling the effect of MHD activity on runaway electron generation during SPARC disruptions

Abstract Magnetohydrodynamic (MHD) instabilities and runaway electrons (REs) interact in several ways, making it important to self-consistently model these interactions for accurate predictions of RE generation and the design of mitigation strategies, such as massive gas injection (MGI). Using M3D-C1—an extended MHD code with a RE fluid model—we investigate the effects of 3D nonlinear MHD activity, material injection, and 2D axisymmetric vertical displacement events (VDEs) on RE evolution during disruptions on SPARC—a high-field, high-current tokamak designed to achieve a fusion gain Q > 1. Several cases, comprising different combinations of neon (Ne) and deuterium ( D 2 ) injection, are considered. Our results demonstrate key effects that arise from the self-consistent RE + MHD coupling, such as an initial increase in RE generation due to MHD instability growth, decreased saturation energies of the m / n = 1 / 1 mode driving sawteeth-like activity, RE losses in stochastic magnetic fields, and subsequent RE confinement and plateau formation due to re-healing of flux surfaces. Large RE plateaus (>5 MA) are obtained with Ne-only injection (2– 5 × 10 21 atoms), while combined D 2 + Ne injection ( 2 × 10 21 Ne atoms; 1.8 × 10 22 D 2 molecules) produces a lower RE current (