Calculation of neoclassical fluxes in the plateau regime for nonaxisymmetric toroidal plasmas

An analytic calculation of the neoclassical fluxes in the plateau regime in the absence of momentum and energy sources is carried out with a general model field, B=B0[1+∑iεi cos(liθ−miζ)], following the moment-equation approach. It is shown that the radial particle and heat fluxes resulting from each harmonic (εi) are additive and have the same sign. Consequently, the neoclassical fluxes in a stellarator in the plateau regime are larger than those in the corresponding ‘‘equivalent’’ tokamak (same aspect ratio and rotational transform). Numerical calculations performed with a drift kinetic equation solver agree to within 10% with the analytic results for the examples considered.