Slowing down tail enhanced, neoclassical and classical alpha particle fluxes in tokamak reactors

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Abstract
The classical and neoclassical particle and energy fluxes associated with a slowing down tail, alpha particle distribution function are evaluated for arbitrary aspect ratio ε−1, cross section, and poloidal magnetic field. The retention of both electron and ion drag and pitch angle scattering by the background ions results in a large diffusive neoclassical heat flux in the plasma core. This flux remains substantial at larger radii only if the characteristic speed associated with pitch angle scattering, vb, is close enough to the alpha birth speed v0 so that ε(v0/vb)3 remains less than some order unity critical value which is not determined by the methods herein. The enhanced neoclassical losses would only have a serious impact on ignition if the critical value of ε(v0/vb)3 is found to be somewhat larger than unity.