Nonlinear effects in velocity space and drift wave transport in tokamaks

It is pointed out that the use of kinetic models for drift wave transport in general makes it necessary to treat consistently the transport in both real space and velocity space. For a broad class of collisionless or marginally collisionless plasmas, nonlinear effects in velocity space will effectively remove the dissipative kinetic type wave–particle resonances, leaving only a type of fluid two-stream resonance. At the same time a two-dimensional treatment of the turbulence becomes realistic. This is important for explaining the magnitude and radial profiles of diffusion coefficients in tokamaks and may also have important consequences for low-k damping and pinch effects.