Plasma Transport in Toroidal Confinement Systems

TLDR

Neoclassical plasma transport theory for axisymmetric toroidal confinement systems is developed via a variational principle for irreversible entropy production, highlighting its relevance to recent tokamak experiments. The authors employ a variational principle with the full Fokker‑Planck collision operator to compute neoclassical transport coefficients in the banana regime and combine them with drift‑equation moments to produce a closed set of equations that accurately capture neoclassical predictions. The study provides the diagonal and cross transport coefficients for particle, ion and electron heat, and electric current fluxes in the banana regime.

Abstract

The neoclassical theory of plasma transport in axisymmetric, toroidal confinement systems, is developed by means of a variational principle for the rate of irreversible entropy production. The variational principle derived here employs the full Fokker-Planck collision operator, including both like and unlike species collisions. Using the variational principle, all the relevant neoclassical transport coefficients are systematically evaluated in the “banana” regime of small collisional frequency, to lowest order in the inverse aspect ratio. These results include both the “diagonal” and “cross” coefficients for the particle fluxes, ion and electron heat flux, and electric current. By combining the transport coefficients with appropriate moments of the drift equation, a closed set of equations which accurately summarize the predictions of neoclassical theory in the banana regime is obtained. The significance of these equations, in particular with regard to recent tokamak experiments, is discussed briefly.