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

Journal Article · Fri Apr 15 00:00:00 EDT 2016 · Physics of Plasmas

DOI:https://doi.org/10.1063/1.4945620· OSTI ID:22599118

White, A. E.; Greenwald, M.; Howard, N. T. ^[1]; Mikkelsen, D. R.; Churchill, R. ^[2]; Holland, C. ^[3]; Theiler, C. ^[4]

---

1. Plasma Science and Fusion Center, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139 (United States)
2. Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543 (United States)
3. University of California, San Diego, La Jolla, California 92093 (United States)
4. Ecole Polytechnique Fédérale de Lausanne, SPC, Lausanne 1015 (Switzerland)

Long wavelength turbulent electron temperature fluctuations (k{sub y}ρ{sub 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{sub y}ρ{sub 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. In contrast, 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. In addition, 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)].

• OSTI ID: 22599118
• Journal Information: Physics of Plasmas, Vol. 23, Issue 4; Other Information: (c) 2016 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA); ISSN 1070-664X
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
ALCATOR DEVICE
COMPARATIVE EVALUATIONS
CYCLOTRONS
ELECTRON TEMPERATURE
ERRORS
FLUCTUATIONS
HEAT
HEAT FLUX
ION TEMPERATURE
IONS
L-MODE PLASMA CONFINEMENT
NONLINEAR PROBLEMS
PLASMA
SIMULATION
SPECTRA
TEMPERATURE GRADIENTS
TRANSPORT THEORY
TRAPPED ELECTRONS
TURBULENCE
WAVELENGTHS