Nonlinear entropy transfer via zonal flows in gyrokinetic plasma turbulence

Nakata, M.; Watanabe, T.-H.; Sugama, H.

doi:doi:10.1063/1.3675855

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Simulation studies of positron acceleration in a shock wave in a nonuniform external magnetic field

Positron acceleration in a shock wave in an electron-positron-ion plasma is studied with one-dimensional, fully kinetic, electromagnetic particle simulations, with particular attention paid to the effect of inhomogeneity of external magnetic field B0. First, acceleration to γ ∼ 104, where γ is the Lorentz factor, is demonstrated for a shock wave in a uniform B0 with the shock speed νsh close to c cos θ, where c is the speed of light and θ is the angle between B0 and the wave normal. The acceler...

Nonplanar electron acoustic shock waves in a plasma with electrons featuring Tsallis distribution

The properties of cylindrical and spherical electron acoustic shock waves (EASWs) in an unmagnetized plasma consisting of cold electrons, immobile ions, and hot electrons featuring Tsallis statistics are investigated by employing the reductive perturbation technique. A Korteweg-de Vries Burgers (KdVB) equation is derived and its numerical solution is obtained. The effects of electron nonextensivity and electron kinematic viscosity on the basic features of EA shock waves are discussed in nonplan...

Nonlinear entropy transfer processes in toroidal ion temperature gradient (ITG) and electron temperature gradient (ETG) driven turbulence are investigated based on the gyrokinetic entropy balance relations for zonal and non-zonal modes, which are coupled through the entropy transfer function regarded as a kinetic extension of the zonal-flow production due to the Reynolds stress. Spectral analyses of the “triad” entropy transfer function introduced in this study reveal not only the nonlinear interactions among the zonal and non-zonal modes, but also their effects on the turbulent transport level. Different types of the entropy transfer processes between the ITG and ETG turbulence are found: the entropy transfer from non-zonal to zonal modes is substantial in the saturation phase of the ITG instability, while, once the strong zonal flow is generated, the entropy transfer to the zonal modes becomes quite weak in the steady turbulence state. Instead, the zonal flows mediate the entropy transfer from non-zonal modes with low radial-wavenumbers (with contribution to the heat flux) to the other non-zonal modes with higher radial-wavenumbers (but with less contribution to the heat flux) through the triad interaction. The successive entropy transfer processes to the higher radial-wavenumber modes are associated with transport regulation in the steady turbulence state. In contrast, in both the instability-saturation and steady phases of the ETG turbulence, the entropy transfer processes among low-wavenumber non-zonal modes are dominant rather than the transfer via zonal modes.

Article Outline

INTRODUCTION
THEORETICAL MODEL AND LINEAR STABILITY ANALYSIS
NONLINEAR SIMULATIONS
1. Entropy balance relation
2. Comparison of flow structures and heat-flux spectra
NONLINEAR ENTROPY TRANSFER VIA ZONAL MODES
CONCLUDING REMARKS

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KEYWORDS and PACS

Keywords

plasma flow, plasma instability, plasma nonlinear processes, plasma thermodynamics, plasma transport processes, plasma turbulence

PACS

52.35.Ra

Plasma turbulence
52.25.Fi

Transport properties
52.25.Kn

Thermodynamics of plasmas
52.35.Bj

Magnetohydrodynamic waves (e.g., Alfven waves)
52.35.Mw

Nonlinear phenomena: waves, wave propagation, and other interactions (including parametric effects, mode coupling, ponderomotive effects, etc.)
52.35.Qz

Microinstabilities (ion-acoustic, two-stream, loss-cone, beam-plasma, drift, ion- or electron-cyclotron, etc.)

ARTICLE DATA

Digital Object Identifier

http://dx.doi.org/10.1063/1.3675855

PUBLICATION DATA

ISSN

1070-664X (print)

1089-7674 (online)

Publisher

$abstract.society.value is a Member of CrossRef

American Institute of Physics

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