Generation and stability of zonal flows in ion-temperature-gradient mode turbulence

We address the mechanisms underlying zonal Row generation and stability in turbulent systems driven by the electrostatic ion-temperature-gradient (ITG ) mode. In the case of zonal flow stability, we show the poloidal flows typ ical of numerical simulations become unstable when they exceed a critical l evel. Near marginal stability of the linear ITC mode, the system can genera te zonal Rows that are sufficiently weak to remain stable and sufficiently strong to suppress the Linear ITG mode. This stable region corresponds to t he parameter regime of the nonlinear Dimits up-shift.