A quiver-kinetic formulation of radio-frequency heating and confinement in collisional edge plasmas

Abstract

The near fields in the collisional edge plasma of a radio-frequency-heated tokamak can cause one or more charged species to oscillate in the applied field with a quiver (or jitter) speed comparable to its thermal speed. By assuming the quiver motion dominates over drifts and gyromotion a completely new kinetic description of the flows in an edge plasma is formulated that retains Coulomb collisions and the relevant atomic processes. Moment equations are employed to obtain a description in which only a lowest-order quiver-kinetic equation need be solved to evaluate the slow time particle fluxes and current induced by the applied fields. The electron heating by collisional randomization of their quiver motion (inverse bremsstrahlung) is balanced by impact excitation losses since equilibration with the ions is too weak. A model plasma of electrons, neutrals, and a single cold ion species is considered to illustrate the utility of the quiver-kinetic formulation. The model predicts local electrostatic potential changes and a local E×B convective flux that is of the same magnitude and scaling as would be predicted by Bohm diffusion.