The effect of neutrals on intrinsic flows and radial electric fields in the HSX stellarator

The ion parallel flow and radial electric field measured in the HSX stellarator using Charge Exchange Recombination Spectroscopy have been found to be inconsistent with those calculated by the neoclassical code, PENTA. In this work, we show that this discrepancy can in part be explained by including the effect of collisions with background neutrals in the neoclassical calculations. An analytical model, benchmarked with the PENTA code in the linear neoclassical viscosity regime, has been used for this purpose. It has been found that, in the quasi-helically symmetric configuration, the experimental values of ion parallel flow and the radial electric field are in better agreement with the neoclassical calculation if the neutral effects are included. The change in the experimentally measured parallel flow with two plasma density levels in the plasma agrees with the neoclassical calculations when neutral effects are included. In a symmetry degraded configuration, higher neoclassical viscosity makes the viscosity arising from neutrals insignificant.