Self-consistent plasma-neutrals fluid modeling of edge and scrape-off layer turbulence in diverted tokamaks

Abstract We report on developments in the edge and scrape-off layer turbulence code GRILLIX to self-consistently simulate plasma turbulence coupled to a fluid neutral gas model. The neutrals model is extended from a single fluid moment (neutrals density) to three moments, describing additionally the dynamics of neutrals parallel momentum and neutrals pressure. GRILLIX employs the flux-coordinate-independent (FCI) approach, wherein the mesh is neither conformal to the wall nor the magnetic field. A new flux evaluation method consistent with FCI allows for implementing plasma recycling at the boundaries that preserves particles to high precision. The improved plasma-neutrals model is applied to simulate an ASDEX Upgrade attached L-mode discharge. Diffusion and viscosity of neutrals parallel momentum introduce a loss channel for ion parallel momentum. This increases the plasma-neutrals interaction time, which is expected to facilitate detachment. Evolution of neutrals pressure leads to a smoother neutrals distribution. Through the charge-exchange coupling, fluctuation amplitudes of ion temperature filaments in the divertor region are reduced. When additionally applying self-consistent recycling boundary conditions, neutrals density and ionization rates at the strike-lines further increase, which impacts the heat load distribution on the target plates.