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Title: Verification of Gyrokinetic (delta)f Simulations of Electron Temperature Gradient Turbulence

Abstract

The GEM gyrokinetic {delta}f simulation code [Chen, 2003] [Chen, 2007] is shown to reproduce electron temperature gradient turbulence at the benchmark operating point established in previous work [Nevins, 2006]. The electron thermal transport is within 10% of the expected value, while the turbulent fluctuation spectrum is shown to have the expected intensity and two-point correlation function.

Authors:
; ; ; ; ; ; ;
Publication Date:
Research Org.:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
942012
Report Number(s):
UCRL-JRNL-230864
Journal ID: ISSN 1070-664X; PHPAEN; TRN: US0807505
DOE Contract Number:
W-7405-ENG-48
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas, vol. 14, no. 8, August 15, 2007, pp. 084501; Journal Volume: 14; Journal Issue: 8
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION; BENCHMARKS; CORRELATION FUNCTIONS; ELECTRON TEMPERATURE; ELECTRONS; FLUCTUATIONS; SIMULATION; TRANSPORT; TURBULENCE; VERIFICATION

Citation Formats

Nevins, W M, Parker, S E, Chen, Y, Candy, J, Dimits, A, Dorland, W, Hammett, G W, and Jenko, F. Verification of Gyrokinetic (delta)f Simulations of Electron Temperature Gradient Turbulence. United States: N. p., 2007. Web.
Nevins, W M, Parker, S E, Chen, Y, Candy, J, Dimits, A, Dorland, W, Hammett, G W, & Jenko, F. Verification of Gyrokinetic (delta)f Simulations of Electron Temperature Gradient Turbulence. United States.
Nevins, W M, Parker, S E, Chen, Y, Candy, J, Dimits, A, Dorland, W, Hammett, G W, and Jenko, F. Mon . "Verification of Gyrokinetic (delta)f Simulations of Electron Temperature Gradient Turbulence". United States. doi:. https://www.osti.gov/servlets/purl/942012.
@article{osti_942012,
title = {Verification of Gyrokinetic (delta)f Simulations of Electron Temperature Gradient Turbulence},
author = {Nevins, W M and Parker, S E and Chen, Y and Candy, J and Dimits, A and Dorland, W and Hammett, G W and Jenko, F},
abstractNote = {The GEM gyrokinetic {delta}f simulation code [Chen, 2003] [Chen, 2007] is shown to reproduce electron temperature gradient turbulence at the benchmark operating point established in previous work [Nevins, 2006]. The electron thermal transport is within 10% of the expected value, while the turbulent fluctuation spectrum is shown to have the expected intensity and two-point correlation function.},
doi = {},
journal = {Physics of Plasmas, vol. 14, no. 8, August 15, 2007, pp. 084501},
number = 8,
volume = 14,
place = {United States},
year = {Mon May 07 00:00:00 EDT 2007},
month = {Mon May 07 00:00:00 EDT 2007}
}
  • The GEM gyrokinetic {delta}f simulation code [Y. Chen and S. Parker, J. Comput. Phys. 189, 463 (2003); and ibid.220, 839 (2007)] is shown to reproduce electron temperature gradient turbulence at the benchmark operating point established in previous work [W. M. Nevins, J. Candy, S. Cowley, T. Dannert, A. Dimits, W. Dorland, C. Estrada-Mila, G. W. Hammett, F. Jenko, M. J. Pueschel, and D. E. Shumaker, Phys. Plasmas 13, 122306 (2006)]. The electron thermal transport is within 10% of the expected value, while the turbulent fluctuation spectrum is shown to have the expected intensity and two-point correlation function.
  • Electron temperature gradient (ETG) transport is conventionally defined as the electron energy transport at high wave number (high-k) where ions are adiabatic and there can be no ion energy or plasma transport. Previous gyrokinetic simulations have assumed adiabatic ions (ETG-ai) and work on the small electron gyroradius scale. However such ETG-ai simulations with trapped electrons often do not have well behaved nonlinear saturation unless fully kinetic ions (ki) and proper ion scale zonal flow modes are included. Electron energy transport is separated into ETG-ki at high-k and ion temperature gradient-trapped electron mode (ITG/TEM) at low-k. Expensive (more computer-intensive), high-resolution, large-ion-scalemore » flux-tube simulations coupling ITG/TEM and ETG-ki turbulence are presented. These require a high effective Reynolds number R{identical_to}[k(max)/k(min)]{sup 2}={mu}{sup 2}, where {mu}=[{rho}{sub si}/{rho}{sub si}] is the ratio of ion to electron gyroradii. Compute times scale faster than {mu}{sup 3}. By comparing the coupled expensive simulations with (1) much cheaper (less compute-intensive), uncoupled, high-resolution, small, flux-tube ETG-ki and with (2) uncoupled low-resolution, large, flux-tube ITG/TEM simulations, and also by artificially turning ''off'' the low-k or high-k drives, it appears that ITG/TEM and ETG-ki transport are not strongly coupled so long as ETG-ki can access some nonadiabatic ion scale zonal flows and both high-k and low-k are linearly unstable. However expensive coupled simulations are required for physically accurate k-spectra of the transport and turbulence. Simulations with {mu}{>=}30 appear to represent the physical range {mu}>40. ETG-ki transport measured in ion gyro-Bohm units is weakly dependent on {mu}. For the mid-radius core tokamak plasma parameters studied, ETG-ki is about 10% of the electron energy transport, which in turn is about 30% of the total energy transport (with negligible ExB shear). However at large ExB shear sufficient to quench the low-k ITG/TEM transport, the high-k tail of the ETG-ki transport survives. Decreasing the trapping to minimize the TEM opens a stability gap between ITG and ETG. High-k ETG transport driven by low-k ITG instability in an ETG linearly stable plasma is demonstrated.« less
  • Recent progress of the gyrokinetic-Vlasov simulations on the ion temperature gradient (ITG) turbulence in tokamak and helical systems is reported, where the entropy balance is checked as a reference for the numerical accuracy. The tokamak ITG turbulence simulation carried out on the Earth Simulator clearly captures a nonlinear generation process of zonal flows. The tera-flops and tera-bytes scale simulation is also applied to a helical system with the same poloidal and toroidal periodicities of L = 2 and M = 10 as in the Large Helical Device.
  • Ion-temperature-gradient turbulence constitutes a possibly dominant transport mechanism for optimized stellarators, in view of the effective suppression of neoclassical losses characterizing these devices. Nonlinear gyrokinetic simulation results for the Wendelstein 7-X stellarator [G. Grieger et al., in Proceedings of the IAEA Conference on Plasma Physics and Controlled Nuclear Fusion Research, 1990 (IAEA, Vienna, 1991) Vol. 3, p. 525]--assuming an adiabatic electron response--are presented. Several fundamental features are discussed, including the role of zonal flows for turbulence saturation, the resulting flux-gradient relationship, and the coexistence of ion-temperature-gradient modes with trapped ion modes in the saturated state.
  • The linear instabilities and nonlinear transport driven by collisionless trapped electron modes (CTEM) are systematically investigated using three-dimensional gyrokinetic {delta}f particle-in-cell simulations. Scalings with local plasma parameters are presented. Simulation results are compared with previous simulations and theoretical predictions. The magnetic shear is found to be linearly stabilizing, but nonlinearly the transport level increases with increasing magnetic shear. This is explained by the changes in radial eddy correlation lengths caused by toroidal coupling. The effect of zonal flows in suppressing the nonlinear CTEM transport is demonstrated to depend on electron temperature gradient and electron to ion temperature ratio. Zonal flowmore » suppression is consistent with the rate of ExB shearing of the ambient turbulence and radial spectra broadening. Strong geodesic acoustic modes (GAM) are generated along with zonal flows.« less