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Title: Quantitative comparison of electron temperature fluctuations to nonlinear gyrokinetic simulations in C-Mod Ohmic L-mode discharges

Abstract

Long wavelength turbulent electron temperature fluctuations (k yρ s < 0.3) are measured in the outer core region (r/a > 0.8) of Ohmic L-mode plasmas at Alcator C-Mod [E. S. Marmar et al., Nucl. Fusion 49, 104014 (2009)] with a correlation electron cyclotron emission diagnostic. The relative amplitude and frequency spectrum of the fluctuations are compared quantitatively with nonlinear gyrokinetic simulations using the GYRO code [J. Candy and R. E. Waltz, J. Comput. Phys. 186, 545 (2003)] in two different confinement regimes: linear Ohmic confinement (LOC) regime and saturated Ohmic confinement (SOC) regime. When comparing experiment with nonlinear simulations, it is found that local, electrostatic ion-scale simulations (k yρ s ≲ 1.7) performed at r/a ~ 0.85 reproduce the experimental ion heat flux levels, electron temperature fluctuation levels, and frequency spectra within experimental error bars. On the other hand, the electron heat flux is robustly under-predicted and cannot be recovered by using scans of the simulation inputs within error bars or by using global simulations. If both the ion heat flux and the measured temperature fluctuations are attributed predominantly to long-wavelength turbulence, then under-prediction of electron heat flux strongly suggests that electron scale turbulence is important for transport in C-Modmore » Ohmic L-mode discharges. Furthermore, no evidence is found from linear or nonlinear simulations for a clear transition from trapped electron mode to ion temperature gradient turbulence across the LOC/SOC transition, and also there is no evidence in these Ohmic L-mode plasmas of the “Transport Shortfall” [C. Holland et al., Phys. Plasmas 16, 052301 (2009)].« less

Authors:
 [1];  [2]; ORCiD logo [3]; ORCiD logo [2];  [4];  [2];  [3];  [5]
  1. University of California, Los Angeles, Los Angeles, California 90095, USA
  2. Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
  3. Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543, USA
  4. University of California, San Diego, La Jolla, California 92093, USA
  5. Ecole Polytechnique Fédérale de Lausanne, SPC, Lausanne 1015, Switzerland
Publication Date:
Research Org.:
Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Fusion Energy Sciences (FES) (SC-24); National Energy Research Scientific Computing Center (NERSC)
Contributing Org.:
Alcator C-Mod Team
OSTI Identifier:
1547042
Alternate Identifier(s):
OSTI ID: 1246539
Grant/Contract Number:  
SC0006419; FC02-99ER54512; AC02-05CH11231; SC006419
Resource Type:
Accepted Manuscript
Journal Name:
Physics of Plasmas
Additional Journal Information:
Journal Volume: 23; Journal Issue: 4; Journal ID: ISSN 1070-664X
Publisher:
American Institute of Physics (AIP)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY

Citation Formats

Sung, C., White, A. E., Mikkelsen, D. R., Greenwald, M., Holland, C., Howard, N. T., Churchill, R., and Theiler, C. Quantitative comparison of electron temperature fluctuations to nonlinear gyrokinetic simulations in C-Mod Ohmic L-mode discharges. United States: N. p., 2016. Web. doi:10.1063/1.4945620.
Sung, C., White, A. E., Mikkelsen, D. R., Greenwald, M., Holland, C., Howard, N. T., Churchill, R., & Theiler, C. Quantitative comparison of electron temperature fluctuations to nonlinear gyrokinetic simulations in C-Mod Ohmic L-mode discharges. United States. doi:10.1063/1.4945620.
Sung, C., White, A. E., Mikkelsen, D. R., Greenwald, M., Holland, C., Howard, N. T., Churchill, R., and Theiler, C. Fri . "Quantitative comparison of electron temperature fluctuations to nonlinear gyrokinetic simulations in C-Mod Ohmic L-mode discharges". United States. doi:10.1063/1.4945620. https://www.osti.gov/servlets/purl/1547042.
@article{osti_1547042,
title = {Quantitative comparison of electron temperature fluctuations to nonlinear gyrokinetic simulations in C-Mod Ohmic L-mode discharges},
author = {Sung, C. and White, A. E. and Mikkelsen, D. R. and Greenwald, M. and Holland, C. and Howard, N. T. and Churchill, R. and Theiler, C.},
abstractNote = {Long wavelength turbulent electron temperature fluctuations (kyρs < 0.3) are measured in the outer core region (r/a > 0.8) of Ohmic L-mode plasmas at Alcator C-Mod [E. S. Marmar et al., Nucl. Fusion 49, 104014 (2009)] with a correlation electron cyclotron emission diagnostic. The relative amplitude and frequency spectrum of the fluctuations are compared quantitatively with nonlinear gyrokinetic simulations using the GYRO code [J. Candy and R. E. Waltz, J. Comput. Phys. 186, 545 (2003)] in two different confinement regimes: linear Ohmic confinement (LOC) regime and saturated Ohmic confinement (SOC) regime. When comparing experiment with nonlinear simulations, it is found that local, electrostatic ion-scale simulations (kyρs ≲ 1.7) performed at r/a ~ 0.85 reproduce the experimental ion heat flux levels, electron temperature fluctuation levels, and frequency spectra within experimental error bars. On the other hand, the electron heat flux is robustly under-predicted and cannot be recovered by using scans of the simulation inputs within error bars or by using global simulations. If both the ion heat flux and the measured temperature fluctuations are attributed predominantly to long-wavelength turbulence, then under-prediction of electron heat flux strongly suggests that electron scale turbulence is important for transport in C-Mod Ohmic L-mode discharges. Furthermore, no evidence is found from linear or nonlinear simulations for a clear transition from trapped electron mode to ion temperature gradient turbulence across the LOC/SOC transition, and also there is no evidence in these Ohmic L-mode plasmas of the “Transport Shortfall” [C. Holland et al., Phys. Plasmas 16, 052301 (2009)].},
doi = {10.1063/1.4945620},
journal = {Physics of Plasmas},
number = 4,
volume = 23,
place = {United States},
year = {2016},
month = {4}
}

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