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Title: Theory of ITG turbulent saturation in stellarators: identifying mechanisms to reduce turbulent transport

Abstract

A three-field fluid model that allows for general three-dimensional equilibrium geometry is developed to describe ion temperature gradient turbulent saturation processes in stellarators. The theory relies on the paradigm of nonlinear transfer of energy from unstable to damped modes at comparable wavelength as the dominant saturation mechanism. The unstable-to-damped mode interaction is enabled by a third mode that for dominant energy transfer channels primarily serves as a regulator of the nonlinear energy transfer rate. The identity of the third wave in the interaction defines different scenarios for turbulent saturation with the dominant scenario depending upon the properties of the 3D geometry. The nonlinear energy transfer physics is quantified by the product of a turbulent correlation lifetime and a geometric coupling coefficient. The turbulent correlation time is determined by a three-wave frequency mismatch, which at long wavelength can be calculated from the sum of the linear eigenfrequencies of the three modes. Larger turbulent correlation times denote larger levels of nonlinear energy transfer and hence smaller turbulent transport. The theory provides an analytic prediction for how 3D shaping can be tuned to lower turbulent transport through saturation processes.

Authors:
 [1];  [1];  [1]
  1. Univ. of Wisconsin, Madison, WI (United States). Dept. of Engineering Physics and Physics
Publication Date:
Research Org.:
Univ. of Wisconsin, Madison, WI (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Fusion Energy Sciences (FES) (SC-24)
OSTI Identifier:
1418997
Alternate Identifier(s):
OSTI ID: 1420362
Grant/Contract Number:  
FG02-99ER54546; FG02-93ER54222; FG02-89ER53291
Resource Type:
Accepted Manuscript
Journal Name:
Physics of Plasmas
Additional Journal Information:
Journal Volume: 25; Journal Issue: 02; Journal ID: ISSN 1089-7674
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; Stellarators; Turbulent Transport; Saturation

Citation Formats

Hegna, Chris C., Terry, Paul W., and Faber, Ben J. Theory of ITG turbulent saturation in stellarators: identifying mechanisms to reduce turbulent transport. United States: N. p., 2018. Web. doi:10.1063/1.5018198.
Hegna, Chris C., Terry, Paul W., & Faber, Ben J. Theory of ITG turbulent saturation in stellarators: identifying mechanisms to reduce turbulent transport. United States. doi:10.1063/1.5018198.
Hegna, Chris C., Terry, Paul W., and Faber, Ben J. Thu . "Theory of ITG turbulent saturation in stellarators: identifying mechanisms to reduce turbulent transport". United States. doi:10.1063/1.5018198. https://www.osti.gov/servlets/purl/1418997.
@article{osti_1418997,
title = {Theory of ITG turbulent saturation in stellarators: identifying mechanisms to reduce turbulent transport},
author = {Hegna, Chris C. and Terry, Paul W. and Faber, Ben J.},
abstractNote = {A three-field fluid model that allows for general three-dimensional equilibrium geometry is developed to describe ion temperature gradient turbulent saturation processes in stellarators. The theory relies on the paradigm of nonlinear transfer of energy from unstable to damped modes at comparable wavelength as the dominant saturation mechanism. The unstable-to-damped mode interaction is enabled by a third mode that for dominant energy transfer channels primarily serves as a regulator of the nonlinear energy transfer rate. The identity of the third wave in the interaction defines different scenarios for turbulent saturation with the dominant scenario depending upon the properties of the 3D geometry. The nonlinear energy transfer physics is quantified by the product of a turbulent correlation lifetime and a geometric coupling coefficient. The turbulent correlation time is determined by a three-wave frequency mismatch, which at long wavelength can be calculated from the sum of the linear eigenfrequencies of the three modes. Larger turbulent correlation times denote larger levels of nonlinear energy transfer and hence smaller turbulent transport. The theory provides an analytic prediction for how 3D shaping can be tuned to lower turbulent transport through saturation processes.},
doi = {10.1063/1.5018198},
journal = {Physics of Plasmas},
number = 02,
volume = 25,
place = {United States},
year = {2018},
month = {2}
}

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Cited by: 4 works
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Figures / Tables:

FIG. 1 FIG. 1: Contours of the peak linear growth rates for the NCSX configuration as predicted by Eq. (54) as a function of kx and ky.

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