Developments in the simulation of turbulence and neutral gas with BOUT + +

The performance of the plasma edge region is critical to the design and economic success of future fusion power plants. In particular, the flux of particles and power to material surfaces must be kept within technological limits. This is determined by a nonlinear interplay between parallel and perpendicular turbulent transport, impurities, and neutral gas. Here we report on recent progress towards modelling this complex system in 3D using the BOUT + + framework. Neutral modelling has been carried out using the Monte Carlo kinetic code EIRENE, and a fluid model evolving neutral gas density and momentum. These have been coupled to cold ion electromagnetic drift-reduced plasma turbulence models which evolve density, Te, vorticity, parallel ion momentum, and vector potential. Results in linear geometry show stabilisation of the drift wave turbulence due to neutral interactions, and greater mixing of neutral gas and plasma than would be predicted in the absence of turbulent fluctuations. Progress towards 3D modelling of detachment fronts will be reported. A rigorous verification exercise has also been carried out of BOUT + + using the Method of Manufactured Solutions, showingconvergenceto the exact solution at the expected rate.

This work was supported by the EUROfusion consortium, the UK EPSRC under grant EP/K006940/1, and computing resources under Plasma HEC consortium grant EP/L000237/1.