Nonlinear damping of zonal modes in anisotropic weakly collisional trapped electron mode turbulence

Comprehensive spectral analysis of a fluid model for trapped electron mode (TEM) turbulence reveals that marginally stable zonal modes at infinitesimal amplitude become robustly damped at finite amplitude. Zonal-mode structure, anisotropy, excitation, and wave number spectra are shown to result from...

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Bibliographic Details
Published in:Physics of plasmas 2006-02, Vol.13 (2), p.022306-022306-11
Main Authors: Gatto, R., Terry, P. W., Baver, D. A.
Format: Article
Language:English
Subjects:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY
ADVECTION
AMPLITUDES
ANISOTROPY
CHARGED-PARTICLE TRANSPORT
COMPUTERIZED SIMULATION
DAMPING
ENERGY TRANSFER
EXCITATION
FLUCTUATIONS
NONLINEAR PROBLEMS
PLASMA
PLASMA DENSITY
PLASMA DRIFT
PLASMA INSTABILITY
PLASMA SIMULATION
SENSITIVITY
TRAPPED ELECTRONS
TURBULENCE
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Summary:Comprehensive spectral analysis of a fluid model for trapped electron mode (TEM) turbulence reveals that marginally stable zonal modes at infinitesimal amplitude become robustly damped at finite amplitude. Zonal-mode structure, anisotropy, excitation, and wave number spectra are shown to result from interaction of the zero-frequency drift wave with the density advection nonlinearity. Heuristic dimensional balances, closure theory, and simulations manifest the primacy of the interaction, and yield energy transfer rates, fluctuation levels, spectra and finite-amplitude-induced dissipation. Strong sensitivity to the zero-frequency wave induces a marked spectral energy-transfer anisotropy that preferentially drives zonal modes relative to nonzonal modes. Zonal-mode excitation is accompanied by the nonlinear excitation of a spectrum of damped eigenmodes. The mixing of unstable TEM eigenmodes with the damped spectrum subjects zonal modes to finite-amplitude-induced damping. The combination of anisotropic transfer to zonal wave numbers and their nonlinear damping is shown to make this the dominant saturation mechanism for TEM turbulence.
ISSN:1070-664X
1089-7674
DOI:10.1063/1.2167309