Nonlinear kinetic analysis of fluctuations and turbulent transport due to tokamak microinstabilities

Results from comprehensive kinetic eigenmode numerical studies indicate that, for typical TFTR supershot parameters, the dominant microinstabilities are the collisionless trapped electron modes (CTEM). A nonlinear kinetic theory is developed for resonant CTEM in relatively peaked density profile toroidal plasmas with ion and trapped electron E x B nonlinearities treated on an equal footing. The results show that, in the nonlinearly saturated state, the density fluctuation level and the anomalous particle and heat fluxes are smaller than the usual mixing length estimates. Confinement is predicted to improve with higher Ti/Te, more peaked density profile, and larger aspect ratio. These trends are in qualitative agreement with experimental results from TFTR. For flat density profile plasmas, ion temperature gradient acoustic waves are considered which propagate in the electron diamagnetic drift direction and are destabilized by trapped electron inverse dissipation in the presence of electron temperature gradients. A nonlinear analysis of such modes focusing on the ion Compton scattering yields results showing that χe > χi for LTe >> LTi, in rough agreement with DIII-D H-mode results. A set of fluid equations which accurately models ion Landau damping has been derived and used to improve fluid simulations of ion temperature gradient (ITG) driven turbulence. New analytical insight into the nature of the ITG-driven turbulence is gained by analyzing the nonlinear evolution of twisted eddies with very broad radial scale. It is found that, instead of the linear Fourier radial mode width used in most ''mixing length'' estimates of saturation, the appropriate radial scale should actually vary as k-barθ-1. (author). 9 refs