Validation Studies Of Quasilinear Theory Of Resonant Diffusion In The Ion Cyclotron Range Of Frequencies By Comparison With Exact Integration Results

Abstract

The validity of ICRF quasilinear (QL) diffusion theory is examined in the context of the C‐Mod ICRF experiment by comparison with coefficients calculated from Lorentz orbits in AORSA full‐wave fields, using the DC (Diffusion Coefficient) code. The “exact” Lorentz orbit results largely agree with QL theory, although there are differences in detail. Overall conclusions are that approximation of the excited RF by a single toroidal mode leads, in the Lorentz calculation, to strong correlation pitch angle modification of the RF diffusion; this thereby modifies self‐consistent radial power absorption calculated with the CQL3D Fokker‐Planck code. However, inclusion of a full toroidal mode spectrum results in most, but not all, correlations ceasing to exist. Hence, modeling of ICRF power absorption using a correlation‐less QL theory is reasonably accurate, even with a suitably chosen single toroidal mode. Multi‐mode correlations remain, particularly for neighboring resonances such as when the trapped particles pass successively through resonance. Differences between “exact” and QL theory lead to modification of calculated, perpendicular viewing NPA spectra.