Neoclassical transport theory for tokamak plasmas with large radial gradients

Abstract

A steep-radial-gradient (finite-banana-width) correction to the neoclassical ion thermal conductivity is obtained in a tokamak plasma under the conventional assumption that the particle flow parallel to magnetic field lines dominates the trapped particle's orbital dynamics. It is found that the steep-radial-gradient effect makes ion thermal conductivity itself be function of radial plasma density gradient and magnetic shear. Negative radial gradients in plasma density and/or safety factor can reduce the neoclassical ion thermal conductivity when the banana width is a significant fraction of the gradient scale length.