# Neutral diffusion and anomalous effects on ion flow shear

## Neutral diffusion and anomalous effects on ion flow shear

Neutral diffusion and anomalous effects on ion flow shear 150 150 Mathew

# Neutral diffusion and anomalous effects on ion flow shear

Bulk ion flow can be modified by ion–neutral interactions in the edge region of tokamaks where neutral atoms are abundant. In this region, the standard neoclassical expression for the ion flow is not consistent with the experimental observations. Previous work in the plateau regime [Valanju et al., Phys. Fluids B 4, 2675 (1992)] suggests that the discrepancy is caused mainly by momentum loss due to ion–neutral charge exchange. In the present work we show that in the absence of neutral diffusion, charge exchange cannot affect the neoclassical transport of the ions significantly if the neutral mean-free path is short and the neutral density is low compared to the plasma density. However, the inclusion of neutral diffusion and anomalous processes in the plateau regime can substantially modify parallel ion flow inside the separatrix as determined by the flux surface averaged momentum constraint. Moreover, the local shear in the flow may be determined by a balance between neutral diffusion and anomalous effects which may then modify the turbulent transport.

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01/09/1998