Transport barrier onset and edge turbulence shortfall in fusion plasmas

TL;DR

This paper investigates the connection between transport barrier formation and edge turbulence in fusion plasmas, revealing that boundary interactions are key to understanding turbulence shortfalls and confinement improvements.

Contribution

It demonstrates, from kinetic equations, that plasma boundary interactions are crucial for explaining turbulence behavior and transport barrier onset in fusion devices.

Findings

Boundary interactions are essential for turbulence regulation.

Transport barrier onset is linked to plasma-boundary interplay.

Predicted turbulence shortfalls are explained by boundary effects.

Abstract

Turbulent plasmas notably self-organize to higher energy states upon application of additional free energy sources or modification of edge operating conditions. Mechanisms whereby such bifurcations occur have been actively debated for decades. Enhanced confinement occurs at the plasma edge, where a shortfall of predicted turbulence intensity has been puzzling scientists for decades. We show, from the primitive kinetic equations that both problems are connected and that interplay of confined plasma turbulence with its material boundaries is essential to curing the shortfall of predicted turbulence and to triggering spontaneous transport barrier onset at the plasma edge. Both problems determine access to improved confinement and are central to fusion research. A comprehensive discussion of the underlying mechanisms is proposed. These results, highly relevant to the quest for magnetic fusion may also be generic to many problems in fluids and plasmas where turbulence self-advection is active.