April 15-17

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Abstracts

Author: Benjamin J Faber
Requested Type: Poster
Submitted: 2019-02-20 15:05:32

Co-authors: C.C. Hegna, P.W. Terry

Contact Info:
University of Wisconsin-Madison
1500 Engineering Drive
Madison, WI   53706
United States of Ame

Abstract Text:
Recent theory and simulation work on turbulence saturation mechanisms in stellarators has highlighted the influence geometry plays on determining turbulence saturation mechanisms [1,2]. In contrast to turbulence saturation in tokamaks, which is mainly mediated by a three-wave interaction between turbulent eddies and a zonal flow, gyrokinetic simulations of turbulence in different stellarator geometries display substantially different turbulence saturation mechanisms. In the low-magnetic-shear quasihelically symmetric HSX configuration, fluid analysis of turbulence saturation through damped eigenmode coupling and tertiary instability analysis suggests turbulence saturation occurs mainly through nonlinear eddy-eddy interactions, bypassing the zonal flow. However, no in-depth study of the nonlinear energy transfer mechanisms in gyrokinetic simulations has been performed for stellarators.

Presented here is the first application of advanced gyrokinetic energy transfer diagnostics to stellarator geometry, focused on the HSX stellarator. Results will be presented using a recently developed diagnostic for the GENE code[3], which calculates the partition of turbulent energy between zonal and non-zonal mediated transfer channels. HSX has some configuration flexibility with the ability to alter key geometric quantities. Nonlinear gyrokinetic simulations suggests turbulent saturation is sensitive to the details of the local magnetic shear. We will employ the GENE diagnostics on a variety of HSX configurations to shed light on the role of geometry in nonlinear energy transfer and turbulence saturation.
[1] G.G. Plunk, P. Xanthopoulos, and P. Helander, Phys. Rev. Lett., 119, 105002 (2017)
[2] C.C. Hegna, P.W. Terry, and B.J. Faber, Phys. Plasmas, 25, 022511 (2018)
[3] G.G. Whelan, M.J. Pueschel, P.W. Terry, J. Citrin, I.J. McKinney, W. Guttenfelder, and H. Doerk., "Saturation and Nonlinear Electromagnetic Stabilization of ITG Turbulence", in preparation.

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