Chaos in the magnetic field structure governs the plasma edge and divertor fluxes in resilient stellarator divertors

We explore fundamental features of non-resonant divertors (NRDs) in the Compact Toroidal Hybrid (CTH) and the Helically Symmetric eXperiment (HSX). In NRDS, the plasma core is separated from the plasma facing components (PFCs) by chaotic structures in the plasma edge. The resulting field line intersection pattern on the PFCs is resilient to plasma equilibrium effects which can expand operational flexibility for optimized stellarator configurations. In CTH, an open chaotic layer has channels of longer connection length (L_C) which deposit localized heat flux on the PFC. The magnetic footprint pattern calculated for varying inductive currents shows that this pattern on the PFC is resilient [1]. Recently, similar structures have also been shown in HSX simulations where the plasma edge is composed of tangles and other structures from chaotic formalism. EMC3-EIRENE simulations of the divertor heat and particle flux demonstrate that the link between the plasma core and the resilient footprint is through finger-like flux tubes of long L_C. Results for CTH and HSX are compared. The analysis supports future design efforts for a NRD mechanical structure and influences the understanding of resilient stellarator divertors.

[1] K.A. Garcia, et al., 2023 Nucl. Fusion 63 126043