The anisotropic redistribution of free energy for gyrokinetic plasma turbulence in a Z-pinch

For a Z-pinch geometry, we report on the nonlinear redistribution of free energy across scales perpendicular to the magnetic guide field, for a turbulent plasma described in the framework of gyrokinetics. The analysis is performed using a local flux-surface approximation, in a regime dominated by el...

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Bibliographic Details
Published in:Physics of plasmas 2016-04, Vol.23 (4)
Main Authors: Navarro, Alejandro Bañón, Teaca, Bogdan, Jenko, Frank
Format: Article
Language:English
Subjects:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY
ANISOTROPY
APPROXIMATIONS
Backscattering
Computational fluid dynamics
COORDINATES
ELECTRONS
Energy
ENTROPY
FLUCTUATIONS
Flux
FREE ENERGY
GEOMETRY
GRIDS
MAGNETIC SURFACES
NONLINEAR PROBLEMS
PLASMA
Plasma physics
Plasma turbulence
SIMULATION
TURBULENCE
Variation
WASTE HEAT UTILIZATION
Zeta pinch
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Summary:For a Z-pinch geometry, we report on the nonlinear redistribution of free energy across scales perpendicular to the magnetic guide field, for a turbulent plasma described in the framework of gyrokinetics. The analysis is performed using a local flux-surface approximation, in a regime dominated by electrostatic fluctuations driven by the entropy mode, with both ion and electron species being treated kinetically. To explore the anisotropic nature of the free energy redistribution caused by the emergence of zonal flows, we use a polar coordinate representation for the field-perpendicular directions and define an angular density for the scale flux. Positive values for the classically defined (angle integrated) scale flux, which denote a direct energy cascade, are shown to be also composed of negative angular sections, a fact that impacts our understanding of the backscatter of energy and the way in which it enters the modeling of sub-grid scales for turbulence. A definition for the flux of free energy across each perpendicular direction is introduced as well, which shows that the redistribution of energy in the presence of zonal flows is highly anisotropic.
ISSN:1070-664X
1089-7674
DOI:10.1063/1.4945633