Effect of field asymmetry on neoclassical transport in a tokamak

Abstract

The effect on transport of a local increase ("bump") in the confining field of a large aspect ratio tokamak is studied in the small collision frequency regime, in which trapped particles - particles reflected by the bump - make a dominant contribution. From solution of the drift-kinetic equation with boundary conditions appropriate to trapped and untrapped particles, explicit expressions for the cross-field particle and energy fluxes are obtained; the density, temperature, and potential gradients, and a parallel electric field, are considered as driving terms. While the diffusion and energy fluxes have an easily anticipated form, similar to superbanana transport, the influence of the bump on the Ware flux, resulting from the parallel electric field, is surprisingly large.