Extra invariant and plasma inhomogeneity to improve zonal flow

Abstract

Zonal flows are known to diminish turbulent transport in magnetic fusion. Interestingly, there is an adiabatic invariant that implies the emergence of zonal flow. This 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 in the adiabatic invariant. A simple condition for such decrease is found.