Zonal flows in plasma—a review

Abstract

A comprehensive review of zonal flow phenomena in plasmas is presented. While the emphasis is on zonal flows in laboratory plasmas, planetary zonal flows are discussed as well. The review presents the status of theory, numerical simulation and experiments relevant to zonal flows. The emphasis is on developing an integrated understanding of the dynamics of drift wave-zonal flow turbulence by combining detailed studies of the generation of zonal flows by drift waves, the back-interaction of zonal flows on the drift waves, and the various feedback loops by which the system regulates and organizes itself. The implications of zonal flow phenomena for confinement in, and the phenomena of fusion devices are discussed. Special attention is given to the comparison of experiment with theory and to identifying directions for progress in future research.

On Imaging of Plasma Turbulence

“…These observations demonstrate that the microscopic fluctuations and the meso-scale perturbation (GAMs) interact through modulational nonlinear coupling. This process has been theoretically pointed out as the driving mechanism of zonal flows in plasma turbulence [4,6,8,30,31]. Further studies have been done for the magnitude of nonlinear coupling, and experiments have given confirmation to the theoretical predictions (within the experimental error) if the convergence study is carefully performed [32].…”

“…4 (b)). The zonal flows in turn suppress the microscopic fluctuations, thus reducing the heat transport from the hot center to the cold periphery [4][5][6][7][8][10][11][12][13][14]. In addition to this coupling between micro fluctuations and zonal flows, there are many nonlinear mechanisms that induce structured flow of plasmas.…”

“…By employing the bipspectral method [3], magnitudes of interactions among excited modes are measured and comparisons with theoretical modeling are performed. Interactions between microscopic turbulence, meso scale fluctuations [4][5][6] and large-scale structures are also demonstrated [1,7,8], providing our understanding of 'how global structures are generated by turbulence'. This is a new step in establishing imaging of plasma turbulence.…”

Fusion Device as an Open System: A New Concept

“…(2) In a symmetric device such as a Tokamak, the pressure profile is a function of magnetic flux function y . The classic concept of a fusion device is to construct a desirable pressure profile p( ) for fusion to take place with sufficiently large energy input and maintain the profile adiabatically until the Lawson criterion is met.…”

“…Recent study of turbulent plasma state indicates possible self-organization and the turbulence spectrum tends to condensate to form zonal flows that is expected to help to confine plasma heat [1,2]. This process is clearly non-adiabatic and involves entropy production.…”