Effect of neutrals on plasma turbulence in simple slab divertor simulations

We present gyrokinetic simulations of a simple slab divertor with MAST Upgrade (MAST-U)

parameters to study the effect of neutral interactions on plasma turbulence. The long leg divertor con-

figuration can be reasonably approximated by simplified geometry as in previous fluid simulations [1],

which showed that turbulence was mainly driven by a Kelvin-Helmholtz mechanism. The fluid model

included a simple recycling source at the divertor plate boundary, but no neutral interactions. In this

work, the gyrokinetic model in the Gkeyll code is used to replicate the simulations to more accurately

model physics such as parallel dynamics. Neutral interactions such as ionization, charge exchange and

endplate recycling are also included to explore their effect on turbulence. We considered several

different scenarios: a baseline case with no neutrals, static neutrals with ionization, static neutrals with

ionization and charge exchange, and a case with dynamic neutrals including both interactions. From

each simulation we calculated the plasma density gradient and E x B shear flow to study the impact of

these different features on interchange- and Kelvin-Helmholtz-driven turbulence. The effect of neutral

interactions on heat flux width is also investigated.

[1] N.R. Walkden et al. Nucl. Mater. Energy 18, 111-117 (2019).