PIC Simulation Study of Heat Transport Kinetic Factors in Scrape-Off Layer Plasmas

Abstract

An accurate calculation of heat load on the divertor plates in a tokamak must take into account kinetic effects, present when the electron velocity distribution function (EVDF) in the plasma column departs from a thermal distribution. In this work PARASOL-1D, a particle-in-cell code with a Monte-Carlo binary collision model, is used to find and explain the electron heat flux-limiting factor αe and the heat transmission coefficient (HTC) γe in the complex SOL. We develop and test two simple models for these kinetic factors that take as input the temperature of the SOL and the temperature of the electrons striking the divertor plates. Both models assume a piecewise EVDF, with a symmetric bulk electron population and a high-energy tail of electrons moving only in the direction of the nearest diverter plate. The model EVDF are fit to the simulation-derived EVDF by allowing the variables for the densities and temperatures in the bulk and tail to vary independently. The block model, which assumes a bulk population of infinite parallel temperature in the bulk, is found to reproduce the kinetic factors for a wide range of conditions in the complex SOL much better than both the classical and Gaussian models. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.