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Abstract
A Monte Carlo simulation is developed to model minority ion transport and fundamental-mode (n = 1) ion cyclotron resonance heating (ICRH) in asymmetric magnetic field geometries. A discrete event model is used to superimpose resonance-heated nonadiabatic changes in a test ion’s magnetic moment on a Coulomb pitch angle scattering model. The ion drift orbit equations of motion are set in a magnetic flux coordinate system that separates fast motion along the field lines from slow motion across the lines. The effects of ICRH on minority ion transport are investigated for 3He in stellarator plasmas. The energy distribution functions of these radio-frequency (rf)-heated ions develop high-energy tails as a result of a preferential gain in velocity in the direction perpendicular to the ambient magnetic field. Estimates of neoclassical flux surface diffusion coefficients indicate that ion losses in an rf-heated stellarator plasma can be an order of magnitude larger than non-ICRH losses. This can be attributed to an rf-increased fraction of trapped ions, which results in increased neoclassical transport across the toroidal flux surfaces.