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Title: The role of zonal flows in the saturation of multi-scale gyrokinetic turbulence

Abstract

The 2D spectrum of the saturated electric potential from gyrokinetic turbulence simulations that include both ion and electron scales (multi-scale) in axisymmetric tokamak geometry is analyzed. The paradigm that the turbulence is saturated when the zonal (axisymmetic) ExB flow shearing rate competes with linear growth is shown to not apply to the electron scale turbulence. Instead, it is the mixing rate by the zonal ExB velocity spectrum with the turbulent distribution function that competes with linear growth. A model of this mechanism is shown to be able to capture the suppression of electron-scale turbulence by ion-scale turbulence and the threshold for the increase in electron scale turbulence when the ion-scale turbulence is reduced. The model computes the strength of the zonal flow velocity and the saturated potential spectrum from the linear growth rate spectrum. The model for the saturated electric potential spectrum is applied to a quasilinear transport model and shown to accurately reproduce the electron and ion energy fluxes of the non-linear gyrokinetic multi-scale simulations. The zonal flow mixing saturation model is also shown to reproduce the non-linear upshift in the critical temperature gradient caused by zonal flows in ion-scale gyrokinetic simulations.

Authors:
;  [1];  [2];  [3]
  1. General Atomics, San Diego, California 92186 (United States)
  2. Oak Ridge Institute for Science Education (ORISE), Oak Ridge, Tennessee 37831 (United States)
  3. University of California San Diego, San Diego, California 92093 (United States)
Publication Date:
OSTI Identifier:
22598922
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 23; Journal Issue: 6; Other Information: (c) 2016 Author(s); Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; AXIAL SYMMETRY; CRITICAL TEMPERATURE; DISTRIBUTION FUNCTIONS; ELECTRIC POTENTIAL; ELECTROMAGNETIC FIELDS; ELECTRONS; GEOMETRY; MIXING; NONLINEAR PROBLEMS; SATURATION; SIMULATION; SPECTRA; TEMPERATURE GRADIENTS; TOKAMAK DEVICES; TRANSPORT THEORY; TURBULENCE; VELOCITY

Citation Formats

Staebler, G. M., Candy, J., Howard, N. T., and Holland, C.. The role of zonal flows in the saturation of multi-scale gyrokinetic turbulence. United States: N. p., 2016. Web. doi:10.1063/1.4954905.
Staebler, G. M., Candy, J., Howard, N. T., & Holland, C.. The role of zonal flows in the saturation of multi-scale gyrokinetic turbulence. United States. doi:10.1063/1.4954905.
Staebler, G. M., Candy, J., Howard, N. T., and Holland, C.. Wed . "The role of zonal flows in the saturation of multi-scale gyrokinetic turbulence". United States. doi:10.1063/1.4954905.
@article{osti_22598922,
title = {The role of zonal flows in the saturation of multi-scale gyrokinetic turbulence},
author = {Staebler, G. M. and Candy, J. and Howard, N. T. and Holland, C.},
abstractNote = {The 2D spectrum of the saturated electric potential from gyrokinetic turbulence simulations that include both ion and electron scales (multi-scale) in axisymmetric tokamak geometry is analyzed. The paradigm that the turbulence is saturated when the zonal (axisymmetic) ExB flow shearing rate competes with linear growth is shown to not apply to the electron scale turbulence. Instead, it is the mixing rate by the zonal ExB velocity spectrum with the turbulent distribution function that competes with linear growth. A model of this mechanism is shown to be able to capture the suppression of electron-scale turbulence by ion-scale turbulence and the threshold for the increase in electron scale turbulence when the ion-scale turbulence is reduced. The model computes the strength of the zonal flow velocity and the saturated potential spectrum from the linear growth rate spectrum. The model for the saturated electric potential spectrum is applied to a quasilinear transport model and shown to accurately reproduce the electron and ion energy fluxes of the non-linear gyrokinetic multi-scale simulations. The zonal flow mixing saturation model is also shown to reproduce the non-linear upshift in the critical temperature gradient caused by zonal flows in ion-scale gyrokinetic simulations.},
doi = {10.1063/1.4954905},
journal = {Physics of Plasmas},
number = 6,
volume = 23,
place = {United States},
year = {Wed Jun 15 00:00:00 EDT 2016},
month = {Wed Jun 15 00:00:00 EDT 2016}
}