Collisional damping of zonal flows due to finite Larmor radius effects

The collisional damping of seeded E X B zonal flows on the ion Larmor radius scale is studied using a gyrokinetic model. The focus is on flow damping due to finite Larmor radius effects, which cause a nu(parallel to)/nu anisotropy of the ion distribution function that is damped by ion-ion collisions. The gyrokinetic equations are solved in a slab geometry with no gradients or curvature, and a gyroaveraged Lorentz collision operator that conserves particle number, momentum, and energy is used. The solution of the gyrokinetic equations explores the dependence of the damping rate on the wavelength of the flows and the impact of the collisions on the ion distribution function. These numerical results can be used as a benchmark test during the implementation of finite Larmor radius effects in the collision operator of gyrokinetic codes. (C) 2010 American Institute of Physics. [doi:10.1063/1.3447875]