NUMERICAL SIMULATIONS OF ICRF HEATED TOKAMAK PLASMA

Several computer models are used to examine ICRF heating in PLT and the conceptual tokamak reactor NUWMAK. A O-D transport code which uses trapped particle scaling finds that (TURN)240 MJ of RF energy is required to ignite the 660 MW(,e) NUWMAK reactor.;The complete multi-species 3 x 3 hot plasma dispersion tensor, accurate for any temperature, for ion cyclotron harmonics up to five is derived. The dispersion relation which is obtained is then coupled to a Fokker-Planck code and a 1-D transport code.;Using a 2-D in velocity space, time-dependent Fokker-Planck code, in which charge exchange, radial losses, radiation and Ohmic heating are included, we find that over 90% of the RF power is absorbed through fundamental minority damping by the protons (n(,H)/n(,e)(TURN)0.1). The spatially-averaged deuterium temperature doubles while the protons become nonMaxwellian with a high energy tail of 18 keV. In NUWMAK, both deuterium and tritium remain Maxwellian with T(,D)(TURNEQ)T(,T)(TURNEQ)T(,e). There is little ICRF Q enhancement when fundamental or second harmonic damping is the dominant heating process.;A WKB slab model is coupled to a 1-D time-dependent transport code to investigate the spatial aspects of ICRF heating. In PLT, over 90% of the RF power is absorbed near the center by the protons, over a heating width of 12-14 cm. In both PLT and NUWMAK, a plane fast wave launched from the low field side is almost completely absorbed before the mode conversion layer is reached. The occurrence of mode conversion, near the ion cyclotron resonance layer, does not alter the density and temperature profiles. Due to the high reactor densities and temperatures, the dominant heating processes in the ICRF startup of NUWMAK are electron Landau and transit time damping when the RF frequency f = nf(,cD) near the plasma center with n = 1,2,3. Using "PLT empirical" scaling, 150-300 MJ of RF energy is needed to ignite NUWMAK.;For PLT, both the Fokker-Planck and space-time simulations agree with the experiment. For NUWMAK, direct electron heating dominates and no high energy ion tails are produced. In both devices the RF power is deposited close to the plasma core. Therefore, ICRF heating appears to be an attractive auxiliary heating scheme for tokamaks.