Kinetic effects on particle and heat fluxes in detached plasmas

Abstract

A model of high recycling scrape-off layer plasmas in tokamaks is presented where both ion and electron species are described by nonlinear kinetic equations. Coulomb and charged-neutral particle collisions are included. The ambipolar electric field and electrostatic sheath potential are evaluated self-consistently. Two models of fluid neutral transport are used to distinguish the neutral density variation for different tokamak divertor geometries. These models are incorporated into a comprehensive three-dimensional (1-D, 2 V) hybrid collisional particle-in-cell–Monte Carlo code W1 [Contrib. Plasma Phys. 34, 436 (1994)]. This code is used to investigate the effects of neutrals on divertor plasma detachment phenomena and on parallel heat and particle fluxes in the presence of strong gradients where fluid descriptions break down. Results are given for simulations of detached and attached divertor plasmas, and comparisons are made with solutions from a one-dimensional fluid model and with experimental observations.