Transport control by coherent zonal flows in the core/edge transitional regime

3D Braginskii turbulence simulations show that the energy flux in the core/edge transition region of a tokamak is strongly modulated-locally and on average-by radially propagating, nearly coherent sinusoidal or solitary zonal flows. Their primary drive is the anomalous transport together with the Stringer-Winsor term. The transport modulation and the flow excitation are due to wave-kinetic effects studied for the first time in turbulence simulations. The flow amplitudes and the transport sensitively depend on the magnetic curvature acting on the flows, which can be influenced, e.g., by shaping the plasma cross section.