Effect of ion-neutral charge exchange on radial electric fields in the edge plasma

A fluid treatment of the perpendicular plasma conductivity is extended to include the effects of arbitrary ion-neutral collision frequency ν and large perpendicular drifts. It is shown that ion-neutral friction (charge-exchange) can give a nonmonotonic relationship between the nonambipolar radial current and the radial electric field, leading to a bifurcated plasma equilibrium. This bifurcation may influence the properties of the low-to-high-confinement (L-H) transition in the presence of neutrals. The physical origin of this effect is an interplay between the surface-averaged equilibrium drifts and the small poloidal variations in the pressure and parallel flow around the flux surface generated by the geodesic curvature.

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