Anisotropic Inverse Cascade toward Zonal Flow in Magnetically Confined Plasmas

TL;DR

This paper introduces a novel mechanism for generating zonal flows in magnetically confined plasmas, emphasizing a conservation law that directs turbulent energy into zonal flows without relying on scale separation.

Contribution

It presents a new conservation law and mechanism for zonal flow generation, expanding understanding beyond traditional modulational instability theories.

Findings

Conservation law focuses inverse cascade into zonal flows.

Mechanism operates without scale separation.

Supports continuous energy transfer to zonal flows.

Abstract

We propose a new mechanism for the generation of zonal flows in magnetically confined plasmas, complementing previous theories based on a modulational instability. We derive a new conservation law that operates in the regime of weakly nonlinear dynamics, and show that it serves to focus the inverse cascade of turbulent drift wave energy into zonal flows. This mechanism continues to operate in the absence of the separation of dynamical scales typically assumed in instability calculations.