Numerical and Analytical Interpretation of Rotation and Radial Electric Fields in Collision Dominated Edge Plasmas

Abstract

Finite Larmor radius effects and inertia become important in the edge region, where the scale lengths of the plasma parameters are intermediate between the ion Larmor radius and the connection length. In contrast to standard neoclassical theory the ambipolarity constraint and the parallel momentum equation of the revisited neoclassical theory [2] allow to predict the parallel and poloidal flow speeds and therefore the radial electric field E r via the usual radial momentum balance equation. The crucial parameter A entering both equations measures the ratio of the contributions arising from perpendicular viscosity to those from the parallel viscosity. The theory also accounts for the friction with the recycled neutral gas due to charge exchange. The solution method of the second order equation obtained in this case is validated by comparing with analytical results obtained at vanishing neutral gas density. Indeed, the deviations of the maxima of the flow velocities and of the minima of the electric field are smaller than 10%. Comparison of the analytical and numerical results with the measurements at ALCATOR C-MOD shows good agreement.