Collisional Effects on Drift Wave Microturbulence in Tokamak Plasmas

Collisional effects on the microturbulence, excited by the electrostatic drift-wave instability, are investigated through first-principle large scale gyrokinetic particle simulations using the realistic discharge parameters of the DIII–D Tokamak. In the linear simulations, the growth rates of the drift waves are decreased by the collisions compared to the collisionless simulations in the lower and higher T_\rm e plasmas. In the lower T_\rm e plasma, the collisions can promote the transition of the drift wave regime from the TEM-dominant instability to the ITG-dominant instability. The zonal flows are excited by the microturbulence and work as a modulation mechanism for the microturbulence in the nonlinear simulations. Microturbulence can excite high frequency zonal flows in the collisionless plasmas, which is in agreement with the theoretical work. In the lower T_\rm e plasma, the collisions decrease the microturbulence in the nonlinear saturated stage compared to the collisionless simulations, which are beneficial for the plasma confinement. In the higher T_\rm e plasma, the final saturated microturbulence shows a slight change.