NONLINEAR EVOLUTION OF ALPHA-PARTICLE-DRIVEN ALFVEN TURBULENCE FROM AREDUCED MODEL

The coupled nonlinear evolution of kinetic Alfven turbulence (KAW) and anomalous alpha-particle transport is analyzed using a reduced turbul ence model [Phys. Fluids B 4, 3152 (1992)]. Due to the nonlocal nature of the nonlinear interaction (bulk ion Compton scattering), the satur ated spectrum consists of two well separated peaks, one in the linearl y unstable and one in the stable regime. The two peaks represent the e nergy input from the alphas and energy dissipation to the electrons, r espectively, and are in balance at saturation. Without a particle sour ce, the turbulence-induced anomalous alpha transport leads to a flatte ning of the initial alpha density profile, on a time scale slow compar ed to the fluctuation time scale. In the presence of a particle source , a stationary alpha density profile is built up self-consistently as a result of the competition between the alpha-particle source and anom alous transport. The anomalous alpha diffusivity from the reduced mode l for KAW, using reactor size parameters, is found to be D(alpha)an ap proximately 1 m2/s.