Charge-separation velocity shear and suppression of turbulence at a plasmaedge in the gyrokinetic approximation

The existence and time evolution of charge separation at a plasma edge is s tudied using a code in which both ions and electrons are described by gyrok inetic equations that include the finite-Larmor-radius correction and the p olarization drift. The ion finite-Larmor-radius effect allows the existence of charge separation between ions and electrons, and the polarization drif t, which has opposite signs for ions and electrons, has a tendency to accen tuate the charge separation in a time-varying electric field. We compare ou r results with those previously obtained using a code in which the ions wer e described by using a fluid guiding-centre model, and only the electrons w ere treated kinetically. In particular, we present results showing excellen t agreement between the two codes on the transition of the spectrum of the nonlinear solution from a turbulent spectrum to one dominated by the fundam ental mode, where the energy is condensing in the lowest-k modes (inverse c ascade).