Approximate Formulae Representing Effective-Charge-Number Dependence of Collisional Relaxation Coefficients for Electron Fluid Moment Equations in Open Magnetic Field System

Abstract

We study the collisional relaxation processes of electron fluid moments in open magnetic field systems, such as scrape-off layer and divertor plasmas, by using a simplified Fokker-Planck equation. Anisotropies in temperature and heat flux in directions parallel and perpendicular to the magnetic field are taken into account. The thermal force is not given by the temperature gradient but by the heat flux damping. The relaxation of heat-flux anisotropy is found to play a role in the heat flux transport. For the convenience of plasma fluid simulations, approximate formulae are devised to represent the dependence of relaxation coefficients on the effective charge number.