A kinetic model for neoclassical transport in EBT with enhanced ion tail

The best currently available transport coefficients for neoclassical transport of ions in EBT i n the plateau regime are based on the assumption of a lowest-order ion velocity distribution function that is Maxwellian. Experimental evidence, however, suggests the presence of an enhanced high-energy tail on the ion distribution function, and a simple theoretical analysis indicates that an enhanced tail may be a major contributor to neoclassical losses. For a study of these effects, a kinetic model for neoclassical transport is developed assuming isotropic velocity distributions. Three coupled non-linear integrodifferential equations i n one velocity dimension are solved numerically; this includes, for the first time, a self-consistent solution for the lowest-order ion distribution function which proves to be non-Maxwellian and has an enhanced high-energy tail due to electron-ion collisions. It is shown that this non-Maxwellian lowest-order solution leads to higher core ion temperatures and to much larger ion diffusion rates than those obtained when a Maxwellian distribution is assumed.