Sherwood 2015

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approvedabstract_bf-1.pdf2015-01-19 14:15:51Benjamin Faber

Nonlinear gyrokineitc simulation of long wavelength microturbulence in HSX

Author: Benjamin J Faber
Requested Type: Poster Only
Submitted: 2015-01-19 14:14:26

Co-authors: M.J.Pueschel,P.W.Terry,C.C.Hegna

Contact Info:
University of Wisconsin-Madison
1150 University Ave.
Madison, WI   53706

Abstract Text:
Nonlinear gyrokinetic simulation of long wavelength microturbulence in HSX
B.J. Faber, M.J. Pueschel, P.W. Terry and C.C. Hegna
University of Wisconsin-Madison, Madison, WI 53706
Nonlinear, gyrokinetic, flux tube simulations of Helically Symmetric eXperiment (HSX) plasmas are presented. Two-species linear and nonlinear simulations show that the Trapped Electron Mode (TEM) is the dominant linear and nonlinear microturbulence mode for plasmas with parameters similar to experimental HSX parameters (Te > Ti, ∇Ti ≈ 0)[1,2]. Nonlinear simulations show the development of zonal flows that may serve as the saturation mechanism for the TEM. HSX has small averaged magnetic shear with s ≤ 0.1 for r/a < 0.9, where a is the plasma minor radius. This low shear requirement complicates flux tube simulations, as the minimum numerical box size in the radial direction is set by lx= 1/(s*kymin) and a reasonable choice of kyminρs = 0.1 leads to lx ~ 222ρs for a flux tube on the half toroidal flux surface. Gyrokinetic simulations indicate that the low shear has a significant influence on the physics of the longest wavelength modes, where kyρs < 0.2 and ion scale turbulence is usually dominant. Linear simulations show the emergence of a large scale, slab-like mode as the density gradient is increased. While the linear growth rate of these modes is small compared to the peak TEM growth rate at kyρs = 2.1, nonlinear simulations show the mode eventually dominates the nonlinear transport as the density gradient is increased. In particular, the growth of the mode leads to the destruction of the zonal flows and subsequently increases transport. However, the physics of the long wavelength mode is sensitive to choice of flux tube within the same flux surface.
[1] Faber, B.J. et al. “Gyrokinetic studies of trapped-electron mode turbulence in HSX.” In preparation.
[2] Weir, G.M. et al. “Comparison of Measurements of Profile Stiffness in HSX to Nonlinear Gyrokinetic Calculations.” Invited talk at APS-DPP 2015.


March 16-18, 2015
The Courant Institute, New York University