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

Sung, C.; White, A. E.; Mikkelsen, D. R.; Greenwald, M.; Holland, C.; Howard, N. T.; Churchill, R.; Theiler, C.

doi:10.1063/1.4945620

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

Journal Article · Fri Apr 08 00:00:00 EDT 2016 · Physics of Plasmas

DOI:https://doi.org/10.1063/1.4945620· OSTI ID:1547042

Sung, C. ^[1]; White, A. E. ^[2]; ^[3]; ^[2]; Holland, C. ^[4]; Howard, N. T. ^[2]; Churchill, R. ^[3]; Theiler, C. ^[5]

University of California, Los Angeles, Los Angeles, California 90095, USA; Office of Scientific and Technical Information (OSTI)
Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543, USA
University of California, San Diego, La Jolla, California 92093, USA
Ecole Polytechnique Fédérale de Lausanne, SPC, Lausanne 1015, Switzerland

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-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)].

View Accepted Manuscript (DOE)

Research Organization:: Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)

Sponsoring Organization:: National Energy Research Scientific Computing Center (NERSC); USDOE; USDOE Office of Science (SC), Fusion Energy Sciences (FES) (SC-24)

Contributing Organization:: Alcator C-Mod Team

Grant/Contract Number:: AC02-05CH11231; FC02-99ER54512; SC0006419

OSTI ID:: 1547042

Alternate ID(s):: OSTI ID: 22599118
OSTI ID: 1246539

Journal Information:: Physics of Plasmas, Journal Name: Physics of Plasmas Journal Issue: 4 Vol. 23; ISSN PHPAEN; ISSN 1070-664X

Publisher:: American Institute of Physics (AIP)Copyright Statement

Country of Publication:: United States

Language:: English

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