Comparison of Quasi-linear and Exact Ion Cyclotron Resonant Heating Diffusion, with and without Finite Width Ion Orbits

Full text: These studies investigate the validity of ICRF quasilinear (QL) diffusion theory by comparison of coefficients calculated with Lorentz orbits in full-wave fields. In addition, we investigate finite-orbit-width effects of ICRF power absorption. Results are obtained within the context of the C-Mod ICRF experiment. QL theory is examined using the new, parallelized, diffusion coefficient code, DC, which calculates RF diffusion by suitable average of results of direct numerical integration of the Lorentz force equation for ion motion in the combined equilibrium fields and the RF full wave EM fields from the AORSA full-wave code. The overall conclusions are that approximation of the excited RF by a single toroidal mode leads to strong correlation pitch angle modification of the RF diffusion, which thereby modifies self-consistent radial power absorption as calculated with the CQL3D Fokker-Planck code. However, inclusion of a fully toroidal mode spectrum results in most of 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. Results are presented for the sMC ('simple Monte Carlo') guiding center orbit code comparing ion effects with and without finite-orbit-width effects turned on, using a single toroidal mode representation of the ICRF fields. For minority H heating in C-Mod, the inclusion of finite ion orbits is shown to give a broader collisional power deposition profile and evidence of rf-induced radial transport. In addition, since sMC utilizes the AORSA diffusion coefficients, up-shift in parallel wave number due to the poloidal field is included allowing the present approach to be extended to high harmonic and beam heating on devices including DIII-D and NSTX. (author)