Evaluation of Impacts of Driving Forces on Neoclassical Transport with Weight-Splitting Method

Abstract

Neoclassical transport is caused by the non-equilibrium distribution function produced by the driving forces due to quasi-steady but non-uniform plasma state parameters and electromagnetic fields as well as by the Coulomb interactions. In this article, we present a method to evaluate the impact of each driving force on neoclassical transport by a single global drift-kinetic simulation. This method can be used to evaluate the impacts of each driving force not only in one-dimensional forms as transport coefficients, but also in multidimensional forms as how the impacts of each driving force are distributed over the phase space. As an application of the method, we investigate the impacts of each driving force on particle density variations in an impurity hole plasma and demonstrate that the impact of the outward driving force of the temperature gradient on the radial impurity flux becomes as large as the impact of the inward driving force of the negative ambipolar radial electric field. Further, we show that the variation of electrostatic potential on each flux surface, Φ₁, which is involved in several factors in a drift-kinetic equation, affects the density variations specifically through the radial E × B drift.