Landau-fluid simulations of edge-SOL turbulence with GRILLIX

Abstract

The Landau-fluid closure for parallel heat fluxes is implemented in the edge turbulence fluid code GRILLIX, replacing the previously used collisional Braginskii closure (with limiters). This extends the validity of the model toward lower collisionality, introduces non-local effects, and leads to a more realistic and self-consistent limiting of heat fluxes. Turbulence simulations comparing the Landau-fluid with the Braginskii closure in realistic divertor geometry are carried out. Clear differences between the simulations are observed, most pronounced a spurious up-down ion temperature asymmetry emerges for a strongly limited Braginskii case. For the Landau-fluid case, we demonstrate the presence and relevance of non-local heat fluxes in full-scale turbulence simulations and show that this behavior could only hardly be reproduced with simple flux-limited models. The implementation of the Landau-fluid closure within the flux-coordinate independent approach employed by GRILLIX results in a set of 3D elliptic problems, where magnetic flutter can be incorporated naturally. On reusing the existing solver in GRILLIX, only a moderate additional computational effort is necessary for the higher fidelity Landau-fluid closure.