Self‐organization of plasma edge turbulence in interaction with recycling neutrals

Abstract

Experimental results from several tokamaks suggest a strong impact of divertor density regimes on turbulent transport in the edge plasma. Reciprocally, the change in transverse transport and SOL width affects the access to density regimes, making it a fundamental topic for heat exhaust issue. Such phenomenology is highly nonlinear and can only be approached quantitatively using numerical simulations treating turbulence and neutrals recycling physics self‐consistently. In this study, the SOLEDGE3X edge multi‐fluid code is used to investigate the mutual interaction between edge plasma turbulence and neutrals recycling. A fluid neutrals model based on the assumption of a charge‐exchange‐dominated plasma‐neutral interaction has been implemented. Two simulations in circular geometry are compared: one without neutrals, where the particle flux is driven by a constant in flux from the core region, and the other one with neutrals recycling included in which the particle input to the system is self‐consistently injected by a gas puff from the midplane. The presence of the neutrals triggers three types of perturbations on the plasma: a local and non‐axisymmetric one driven by the gas puff, a global perturbation affecting both profiles and turbulence properties in the whole domain, and a local one in the vicinity of the limiter where recycling occurs. The largest effect of the inclusion of self‐consistent neutrals recycling is a large‐scale reorganization of the plasma profiles and turbulence properties due to the dissociation of particle and energy fluxes. These effects are expected to be more important at higher densities regimes or in diverted configuration.

The effect of divertor particle sources on scrape-off-layer turbulence

“…In this 'high-recycling' regime, the neutral dynamics become more important, as the ionisation acts as a large particle source and the radiation provides an additional energy sink to the system. The full study of plasma and neutral interaction is a very complex problem, and it is challenging to simulate the whole process in realistic tokamaks [5,[16][17][18][19][20]. We could adopt non-self-consistent sources to speed up the calculations.…”