PFC / JA - 93 - 27 Alpha Particle Driven Alfven Turbulence and Its Effect on Alpha Transport

Recent developments in computational and theoretical studies of Alpha particle driven Alfven turbulence in both the long (kpi < 1) and short (kpi 1) wavelength regimes are reported. In the long wavelength regime, a hybrid particle-fluid model is solved numerically as well as analytically in a simple slab geometry. The dominant nonlinear interactions are found to be couplings between two Alfven waves to generate a zero frequency electromagnetic convective cell and strong E x B convection of resonant alphas, which result in significant changes in plasma equilibria. The fluctuation energies first increase, then saturate and decay. The alpha transport is convective and significant, but does not necessarily lead to an appreciable alpha loss. A mode coupling theory is developed to explain the simulation results. In the short wavelength regime, a reduced turbulence model describing the coupled nonlinear evolutions of fluctuation spectrum loll and alpha density profile n0 (r, t) in the presence of an alpha source S'(r, t) is solved numerically. A steady state is achieved. The nonlinear saturation is due to ion Compton scattering induced energy transfer to higher wavenumbers. Alpha transport is significant and a diffusion coefficient of Dc t 0.5m 2 /s for ITER-like parameters is obtained. The effect of anomalous alpha diffusion on alpha power coupling to bulk plasmas is also discussed.