Zonal flow generation and its feedback on turbulence production in drift wave turbulence

TL;DR

This study numerically investigates how zonal flows influence turbulence and particle transport in plasma, revealing a feedback loop that is crucial for understanding the L-H transition in fusion devices.

Contribution

It demonstrates that the Hasegawa-Wakatani equations can serve as a minimal model capturing the drift-wave and zonal-flow feedback mechanism relevant to plasma confinement transitions.

Findings

Low C: turbulence remains isotropic with no zonal flow generation.

High C: turbulence becomes anisotropic with dominant zonal flows.

Zonal flows suppress meridional drift waves and reduce particle transport.

Abstract

Plasma turbulence described by the Hasegawa-Wakatani equations has been simulated numerically for different models and values of the adiabaticity parameter C. It is found that for low values of C turbulence remains isotropic, zonal flows are not generated and there is no suppression of the meridional drift waves and of the particle transport. For high values of C, turbulence evolves toward highly anisotropic states with a dominant contribution of the zonal sector to the kinetic energy. This anisotropic flow leads to a decrease of a turbulence production in the meridional sector and limits the particle transport across the mean isopycnal surfaces. This behavior allows to consider the Hasegawa-Wakatani equations a minimal PDE model which contains the drift-wave/zonal-flow feedback loop prototypical of the LH transition in plasma devices.