Transport Barrier generation at the interface of regions with different zonal flows dynamics

TL;DR

This paper presents a new understanding of how transport barriers form spontaneously in turbulent systems, linking their emergence to spectral gaps and zonation regimes, with implications for fusion plasma confinement.

Contribution

It introduces a generic transition paradigm explaining barrier formation at interfaces of different zonal flow regions, unifying various experimental observations.

Findings

Transport barriers form at interfaces of zonal flow regions due to spectral gaps.

Barrier relaxation involves turbulence bursts regenerating zonal flows.

The duration of quiescent phases is governed by viscous damping processes.

Abstract

A novel and generic understanding of spontaneous generation of transport barriers and zonation regimes in turbulent self-organization is presented. It associates the barrier onset to the development of a spectral gap between large scale flows and turbulence modes leading to a zonation regime. A robust barrier builds-up at the interface of such a region and a neighboring one with reduced zonal flow generation. This more complex and generic transition paradigm could fit the numerous and sometimes conflicting observations as in fusion plasma experiments. Barrier relaxation by bursts of turbulence regenerate the zonal flows that are eroded by viscous (collisional-like) damping. The duration of the quiescent phase between the quasi-periodic relaxation events is governed by this damping process, hence the barrier collision frequency for fusion plasmas.