Zonal profile corrugations and staircase formation: Role of the transport crossphase

TL;DR

This paper develops an analytical theory supported by simulations explaining how turbulence self-organizes into staircase density profiles through transport crossphase modulations, independent of zonal flows.

Contribution

The paper introduces a novel theory for staircase formation driven by crossphase modulations, not relying on zonal flows, supported by collisional drift-wave simulations.

Findings

Density profile corrugations can form independently of zonal flows.

Radial modulations of the transport crossphase drive staircase formation.

Zonal density corrugations feedback to regulate turbulence.

Abstract

Recently, quasi-stationary structures called $E \times B$ staircases were observed in gyrokinetic simulations, in all transport channels [Dif-Pradalier et al. Phys. Rev. Lett. 114, 085004 (2015)]. We present a novel analytical theory - supported by collisional drift-wave fluid simulations - for the generation of density profile corrugations (staircase), independent of the action of zonal flows: Turbulent fluctuations self-organize to generate quasi-stationary radial modulations $\Delta\theta(r,t)$ of the transport crossphase $\theta$ between density and electric potential fluctuations. The radial modulations of the associated particle flux drive zonal corrugations of the density profile, via a modulational instability. In turn, zonal density corrugations regulate the turbulence via nonlinear damping of the fluctuations.