Extra invariant and plasma inhomogeneity to improve zonal flow

TL;DR

This paper investigates how plasma inhomogeneity can enhance zonal flow by decreasing an adiabatic invariant, potentially improving turbulence suppression in magnetic fusion devices.

Contribution

It introduces a new understanding of how plasma inhomogeneity affects the adiabatic invariant and consequently the strength of zonal flows.

Findings

Plasma inhomogeneity can decrease the adiabatic invariant.

Decreasing the invariant leads to stronger zonal flows.

A simple condition for the decrease is derived.

Abstract

Zonal flows are known to diminish turbulent transport in magnetic fusion. Interstingly, there is an adiabatic invariant that implies the emergence of zonal flow. The paper shows that if this invariant is decreasing (due to some external factors) then the emerging zonal flow is better. It is also shown that the plasma inhomogeneity can lead to the decrease of the adiabatic invariant. A simple condition for such decrease is found.