Bifurcation in electrostatic resistive drift wave turbulence

TL;DR

This paper investigates bifurcation phenomena in resistive drift wave turbulence modeled by the Hasegawa-Wakatani equations, revealing how zonal flows can suppress turbulence and the conditions leading to turbulence resurgence.

Contribution

It provides the first numerical observation of an upshift in turbulence onset in resistive drift wave systems, linking bifurcation behavior to zonal flow stability.

Findings

Zonal flows can suppress drift wave turbulence after initial transient.

A parameter tuning can destroy zonal flow dominance, re-establishing turbulence.

The bifurcation is explained via Kelvin-Helmholtz stability analysis.

Abstract

The Hasegawa-Wakatani equations, coupling plasma density and electrostatic potential through an approximation to the physics of parallel electron motions, are a simple model that describes resistive drift wave turbulence. We present numerical analyses of bifurcation phenomena in the model that provide new insights into the interactions between turbulence and zonal flows in the tokamak plasma edge region. The simulation results show a regime where, after an initial transient, drift wave turbulence is suppressed through zonal flow generation. As a parameter controlling the strength of the turbulence is tuned, this zonal flow dominated state is rapidly destroyed and a turbulence-dominated state re-emerges. The transition is explained in terms of the Kelvin-Helmholtz stability of zonal flows. This is the first observation of an upshift of turbulence onset in the resistive drift wave system, which is analogous to the well-known Dimits shift in turbulence driven by ion temperature gradients.