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 deposition in the plasma, particularly in the limit when the fast-ion slowing-down time is comparable with or longer than the period of other time-dependent phenomena in the discharge, such as sawtooth oscillations, which can alter the distribution of the fast ions. In order to properly include this effect in transport simulations of ICRF-heated tokamak discharges, a time-dependent predictive transport and heating code has been developed by integrating the WHIST 2D MHD equilibrium/ID flux-surface-averaged transport code with the RAZE hybrid ray-tracing/Fokker-Planck ICRF heating code. The package has three distinguishing features: (i) the wave propagation and damping calculations are evaluated using a numerical solution for the instantaneous plasma equilibrium which is self-consistently evolved in time, accounting for energy, particle and magnetic diffusion in the presence of intense auxiliary heating; (ii) the wave absorption is calculated on the basis of the combined effects of RF-driven quasilinear diffusion and collisional thermalization, 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 agreement between the calculated and measured rate of central electron heating. Performance projections obtained for ICRF-heated plasmas in BPX indicate that the fusion gain, Q, exceeds 5 even if the best confinement achievable in the device is limited to the L-mode regime.