Comparison of divertor and main wall recycling dynamics during ELMs

Plasma recycling on material surfaces of tokamaks plays essential role in SOL plasma transport via various processes involving neutrals. The plasma-material interfaces are usually described using constant recycling coefficient in tokamak plasma modeling studies. This approach, which ignores the dynamic material response to changing plasma conditions, however, can be insufficient when large plasma transient events, such as ELMs, are considered. In this work, we perform dynamic 2D plasma-wall simulations using coupled plasma transport code UEDGE and wall reaction-diffusion code FACE. The simulations are conducted for different initial states of the divertor plasma and for the material parameters approximating tungsten. The ELMs are emulated by varying in time the edge plasma cross-field transport coefficients and heating power. The obtained results demonstrate that the dynamic plasma recycling at the divertor target and the main wall can have disparate effects during ELM depending on the ELM size, the initial plasma and material conditions. It is shown that in attached divertor plasma regime, large ELMs can lead to desorption of significant amounts of hydrogen from the divertor target, while the hydrogen is simultaneously reabsorbed by the wall material in the far SOL regions. The interplay between the divertor and wall recycling effects on plasma recovery in inter-ELM period will be also examined.