On Zonal flows-Turbulence-Corrugations dynamics in magnetized plasmas

Zonal flows are prevalent in nature and in laboratory experiments. Zonal flow shear breaks up the turbulent eddies, thus reducing the turbulence coherence length and turbulent transport. Zonal flows are often accompanied by corrugations in plasma profiles. Mechanisms of zonal flow and corrugations generation and their effect on feedback processes has been studied. Zonal flows are excited by modulational instability due to negative zonal eddy viscosity and the polarization beat noise. Negative eddy viscosity results from the coherent mode couplings and manifest as inverse cascade of kinetic energy. The beat noise results from the incoherent mode couplings. The synergy of beat noise and modulational effects is stronger than either alone. Polarization beat noise eliminates the power threshold for zonal flow excitation. Thus, zonal flows can exist even below the modulational threshold. Zonal density corrugations are excited by particle advection beat noise, regardless of modulational instability. The zonal density diffusivity is always positive definite. There is no inverse cascade of density corrugations. Cross-correlations between zonal flow shear and density corrugations their implications for staircase structure and turbulence saturation will be discussed in detail.