Generation of zonal flows and impact on transport in competing drift waves and interchange turbulence

The generation and radial structure of zonal flows are studied in competing collisional drift waves and interchange turbulence using the reduced flux-driven nonlinear model Tokam1D. Zonal flows are generated in both the interchange dominated and adiabatic regimes with the former favoring radially structured flows and avalanche transport. The distance to the instability threshold proves to be key, with a more stable radial flow structure emerging near the threshold and increased energy stored in the flows for interchange turbulence. The avalanches are shown to perturb zonal flow structures in drift-wave turbulence and to reactivate them in the interchange regime. Finally, the ExB staircases with radially structured, stable in time zonal flows are proved beneficial for the overall confinement.