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Title: Intermittent fluctuations in the Alcator C-Mod scrape-off layer for ohmic and high confinement mode plasmas

Abstract

Plasma fluctuations in the scrape-off layer of the Alcator C-Mod tokamak in ohmic and high confinement modes have been analyzed using gas puff imaging data. In all cases investigated, the time series of emission from a single spatially resolved view into the gas puff are dominated by large-amplitude bursts, attributed to blob-like filament structures moving radially outwards and poloidally. There is a remarkable similarity of the fluctuation statistics in ohmic plasmas and in edge localized mode-free and enhanced D-alpha high confinement mode plasmas. Conditionally averaged waveforms have a two-sided exponential shape with comparable temporal scales and asymmetry, while the burst amplitudes and the waiting times between them are exponentially distributed. The probability density functions and the frequency power spectral densities are similar for all these confinement modes. These results provide strong evidence in support of a stochastic model describing the plasma fluctuations in the scrape-off layer as a super-position of uncorrelated exponential pulses. Predictions of this model are in excellent agreement with experimental measurements in both ohmic and high confinement mode plasmas. The stochastic model thus provides a valuable tool for predicting fluctuation-induced plasma–wall interactions in magnetically confined fusion plasmas.

Authors:
ORCiD logo [1]; ORCiD logo [1]; ORCiD logo [1];  [2]; ORCiD logo [2]
  1. Department of Physics and Technology, UiT The Arctic University of Norway, N-9037 Tromsø, Norway
  2. MIT Plasma Science and Fusion Center, Cambridge 02139, Massachusetts, USA
Publication Date:
Research Org.:
Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
1540162
Alternate Identifier(s):
OSTI ID: 1427326
Grant/Contract Number:  
FC02-99ER54512; FC02-99ER54512- CMOD
Resource Type:
Accepted Manuscript
Journal Name:
Physics of Plasmas
Additional Journal Information:
Journal Volume: 25; Journal Issue: 5; Journal ID: ISSN 1070-664X
Publisher:
American Institute of Physics (AIP)
Country of Publication:
United States
Language:
English
Subject:
Physics

Citation Formats

Garcia, O. E., Kube, R., Theodorsen, A., LaBombard, B., and Terry, J. L. Intermittent fluctuations in the Alcator C-Mod scrape-off layer for ohmic and high confinement mode plasmas. United States: N. p., 2018. Web. doi:10.1063/1.5018709.
Garcia, O. E., Kube, R., Theodorsen, A., LaBombard, B., & Terry, J. L. Intermittent fluctuations in the Alcator C-Mod scrape-off layer for ohmic and high confinement mode plasmas. United States. doi:10.1063/1.5018709.
Garcia, O. E., Kube, R., Theodorsen, A., LaBombard, B., and Terry, J. L. Tue . "Intermittent fluctuations in the Alcator C-Mod scrape-off layer for ohmic and high confinement mode plasmas". United States. doi:10.1063/1.5018709. https://www.osti.gov/servlets/purl/1540162.
@article{osti_1540162,
title = {Intermittent fluctuations in the Alcator C-Mod scrape-off layer for ohmic and high confinement mode plasmas},
author = {Garcia, O. E. and Kube, R. and Theodorsen, A. and LaBombard, B. and Terry, J. L.},
abstractNote = {Plasma fluctuations in the scrape-off layer of the Alcator C-Mod tokamak in ohmic and high confinement modes have been analyzed using gas puff imaging data. In all cases investigated, the time series of emission from a single spatially resolved view into the gas puff are dominated by large-amplitude bursts, attributed to blob-like filament structures moving radially outwards and poloidally. There is a remarkable similarity of the fluctuation statistics in ohmic plasmas and in edge localized mode-free and enhanced D-alpha high confinement mode plasmas. Conditionally averaged waveforms have a two-sided exponential shape with comparable temporal scales and asymmetry, while the burst amplitudes and the waiting times between them are exponentially distributed. The probability density functions and the frequency power spectral densities are similar for all these confinement modes. These results provide strong evidence in support of a stochastic model describing the plasma fluctuations in the scrape-off layer as a super-position of uncorrelated exponential pulses. Predictions of this model are in excellent agreement with experimental measurements in both ohmic and high confinement mode plasmas. The stochastic model thus provides a valuable tool for predicting fluctuation-induced plasma–wall interactions in magnetically confined fusion plasmas.},
doi = {10.1063/1.5018709},
journal = {Physics of Plasmas},
number = 5,
volume = 25,
place = {United States},
year = {2018},
month = {5}
}

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Works referenced in this record:

Blob structure and motion in the edge and SOL of NSTX
journal, January 2016

  • Zweben, S. J.; Myra, J. R.; Davis, W. M.
  • Plasma Physics and Controlled Fusion, Vol. 58, Issue 4, Article No. 044007
  • DOI: 10.1088/0741-3335/58/4/044007