Intermittent fluctuations in the Alcator C-Mod scrape-off layer

Journal Article · Wed May 15 04:00:00 EDT 2013 · Physics of Plasmas

DOI:https://doi.org/10.1063/1.4802942· OSTI ID:22228066

Garcia, O. E.; Fritzner, S. M.; Kube, R. ^[1]; Cziegler, I. ^[2]; LaBombard, B.; Terry, J. L. ^[3]

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1. Department of Physics and Technology, University of Tromsø, N-9037 Tromsø (Norway)
2. Center for Energy Research, University of California, San Diego, California 92093 (United States)
3. MIT Plasma Science and Fusion Center, Cambridge, Massachusetts 02139 (United States)

Fluctuations in the boundary region of the Alcator C-Mod tokamak have been analyzed using gas puff imaging data. It is found that the fluctuation amplitudes in the near scrape-off layer follow a normal distribution while the far scrape-off layer fluctuations are dominated by large amplitude bursts due to radial motion of blob-like structures and have a positively skewed and flattened amplitude probability distribution. Conditional averaging of the time series reveals burst wave forms with a fast rise and slow decay and exponentially distributed burst amplitudes and waiting times. Based on this, a stochastic model of the burst dynamics is constructed. The model predicts that fluctuation amplitudes should follow a Gamma distribution and that there is a parabolic relation between the skewness and the kurtosis moments of the fluctuations. This is shown to compare favorably with the gas puff imaging data over a range of line-averaged plasma densities.

• OSTI ID: 22228066
• Journal Information: Physics of Plasmas, Journal Name: Physics of Plasmas Journal Issue: 5 Vol. 20; ISSN PHPAEN; ISSN 1070-664X
• Country of Publication: United States
• Language: English

Related Subjects

70 PLASMA PHYSICS AND FUSION TECHNOLOGY
ALCATOR DEVICE
AMPLITUDES
ASYMMETRY
CHARGED-PARTICLE TRANSPORT
COMPARATIVE EVALUATIONS
FLUCTUATIONS
PLASMA CONFINEMENT
PLASMA DENSITY
PLASMA SCRAPE-OFF LAYER
STOCHASTIC PROCESSES
WAVE FORMS