PREDICTIVE TRANSPORT MODELING OF ICRF-HEATED TOKAMAKS

In tokamaks heated with ICRF power, the time evolution of the resonant minority ion population can have a profound influence on the power de position in the plasma, particularly in the limit when the fast-ion sl owing-down time is comparable with or longer than the period of other time-dependent phenomena in the discharge, such as sawtooth oscillatio ns, which can alter the distribution of the fast ions. In order to pro perly include this effect in transport simulations of ICRF-heated toka mak discharges, a time-dependent predictive transport and heating code has been developed by integrating the WHIST 2D MHD equilibrium/ID flu x-surface-averaged transport code with the RAZE hybrid ray-tracing/Fok ker-Planck ICRF heating code. The package has three distinguishing fea tures: (i) the wave propagation and damping calculations are evaluated using a numerical solution for the instantaneous plasma equilibrium w hich is self-consistently evolved in time, accounting for energy, part icle and magnetic diffusion in the presence of intense auxiliary heati ng; (ii) the wave absorption is calculated on the basis of the combine d effects of RF-driven quasilinear diffusion and collisional thermaliz ation, and therefore includes heating due to all resonant processes in the plasma; and (iii) the time evolution of the minority distribution function is explicitly retained by solving the time dependent Fokker- Planck equation in the isotropic limit. Simulations obtained with the code for high-power ICRF heating experiments in PLT show excellent agr eement between the calculated and measured rate of central electron he ating. Performance projections obtained for ICRF-heated plasmas in BPX indicate that the fusion gain, Q, exceeds 5 even if the best confinem ent achievable in the device is limited to the L-mode regime.