Edge pedestal structure

Abstract

The hypothesis is advanced and it is investigated that, in between or in the absence of edge-localized modes, the structure of the edge pedestal is determined by the transport requirements of plasma particle, momentum and energy balance, and by recycling neutral atoms. A set of “pedestal equations” following from this hypothesis are presented and applied to calculate the edge density, temperature, rotation velocity, and radial electric field profiles in a DIII-D H (high)-mode plasma. It is found that a pedestal structure in the density profile and sharp negative peaks in the radial electric field and poloidal velocity just inside the separatrix are predicted as natural consequences of the conservation of particle and momentum, in qualitative and quantitative agreement with measured values. Detailed examination of the calculation reveals a sequence of mechanisms by which the ionization of recycling neutrals affect the structure of the density profile in the edge pedestal.