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Title: Flow and shear behavior in the edge and scrape-off layer of L-mode plasmas in National Spherical Torus Experiment

Abstract

Fluctuations in the edge and scrape-off layer (SOL) of L-mode plasmas in the National Spherical Torus Experiment (NSTX) as observed by the gas puff imaging (GPI) diagnostic are studied. Calculation of local, time resolved velocity maps using the Hybrid Optical Flow and Pattern Matching Velocimetry (HOP-V) code enables analysis of turbulent flow and shear behavior. Periodic reversals in the direction of the poloidal flow near the separatrix are observed. Also, poloidal velocities and their radial shearing rate are found to be well correlated with the fraction of Dα light contained in the SOL, which acts as a measure of turbulent bursts. The spectra of GPI intensity and poloidal velocity both have a strong feature near 3 kHz, which appears to correspond with turbulent bursts. This mode exhibits a poloidal structure with poloidal wavenumber of 7.7 m-1 for GPI intensity and 3.4 m-1 for poloidal velocity, and the poloidal velocity fluctuations near 3 kHz remain coherent over length scales in excess of the turbulent scales. Furthermore, recent SOL Turbulence (SOLT) simulations find a parameter regime that exhibits periodic bursty transport and shares many qualitative similarities with the experimental data. Strong correlations between the shearing rate and the turbulent bursts are observedmore » for time periods of ~ 2 ms, but the relationship is complicated by several factors. Finally, measurements of the radial profiles of the Reynolds shear stresses are reported. These radial profiles exhibit many similarities for several shots, and a region with positive radial gradient is seen to be coincident with local flow shear.« less

Authors:
 [1];  [1];  [2];  [3];  [2];  [2];  [3]
+ Show Author Affiliations
  1. Univ. of Colorado, Boulder, CO (United States)
  2. Lodestar Research Corp., Boulder, CO (United States)
  3. Princeton Plasma Physics Lab. (PPPL), Princeton, NJ (United States)
Publication Date:
Research Org.:
Univ. of Colorado, Boulder, CO (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
1076474
Grant/Contract Number:  
AC02-09CH11466; FG02-08ER54995; SC0001966
Resource Type:
Accepted Manuscript
Journal Name:
Physics of Plasmas
Additional Journal Information:
Journal Volume: 18; Journal Issue: 1; 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

Sechrest, Y., Munsat, T., D’Ippolito, D. A., Maqueda, R. J., Myra, J. R., Russell, D., and Zweben, S. J. Flow and shear behavior in the edge and scrape-off layer of L-mode plasmas in National Spherical Torus Experiment. United States: N. p., 2011. Web. doi:10.1063/1.3533435.
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Sechrest, Y., Munsat, T., D’Ippolito, D. A., Maqueda, R. J., Myra, J. R., Russell, D., & Zweben, S. J. Flow and shear behavior in the edge and scrape-off layer of L-mode plasmas in National Spherical Torus Experiment. United States. https://doi.org/10.1063/1.3533435
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Sechrest, Y., Munsat, T., D’Ippolito, D. A., Maqueda, R. J., Myra, J. R., Russell, D., and Zweben, S. J. Sat . "Flow and shear behavior in the edge and scrape-off layer of L-mode plasmas in National Spherical Torus Experiment". United States. https://doi.org/10.1063/1.3533435. https://www.osti.gov/servlets/purl/1076474.
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@article{osti_1076474,
title = {Flow and shear behavior in the edge and scrape-off layer of L-mode plasmas in National Spherical Torus Experiment},
author = {Sechrest, Y. and Munsat, T. and D’Ippolito, D. A. and Maqueda, R. J. and Myra, J. R. and Russell, D. and Zweben, S. J.},
abstractNote = {Fluctuations in the edge and scrape-off layer (SOL) of L-mode plasmas in the National Spherical Torus Experiment (NSTX) as observed by the gas puff imaging (GPI) diagnostic are studied. Calculation of local, time resolved velocity maps using the Hybrid Optical Flow and Pattern Matching Velocimetry (HOP-V) code enables analysis of turbulent flow and shear behavior. Periodic reversals in the direction of the poloidal flow near the separatrix are observed. Also, poloidal velocities and their radial shearing rate are found to be well correlated with the fraction of Dα light contained in the SOL, which acts as a measure of turbulent bursts. The spectra of GPI intensity and poloidal velocity both have a strong feature near 3 kHz, which appears to correspond with turbulent bursts. This mode exhibits a poloidal structure with poloidal wavenumber of 7.7 m-1 for GPI intensity and 3.4 m-1 for poloidal velocity, and the poloidal velocity fluctuations near 3 kHz remain coherent over length scales in excess of the turbulent scales. Furthermore, recent SOL Turbulence (SOLT) simulations find a parameter regime that exhibits periodic bursty transport and shares many qualitative similarities with the experimental data. Strong correlations between the shearing rate and the turbulent bursts are observed for time periods of ~ 2 ms, but the relationship is complicated by several factors. Finally, measurements of the radial profiles of the Reynolds shear stresses are reported. These radial profiles exhibit many similarities for several shots, and a region with positive radial gradient is seen to be coincident with local flow shear.},
doi = {10.1063/1.3533435},
journal = {Physics of Plasmas},
number = 1,
volume = 18,
place = {United States},
year = {Sat Jan 01 00:00:00 EST 2011},
month = {Sat Jan 01 00:00:00 EST 2011}
}
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https://doi.org/10.1063/1.3533435
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    Works referencing / citing this record:

    Edge transport studies in the edge and scrape-off layer of the National Spherical Torus Experiment with Langmuir probes
    journal, April 2014

    • Boedo, J. A.; Myra, J. R.; Zweben, S.
    • Physics of Plasmas, Vol. 21, Issue 4
    • DOI: 10.1063/1.4873390

    Observation of quasi-coherent edge fluctuations in Ohmic plasmas on National Spherical Torus Experiment
    journal, April 2016

    • Banerjee, Santanu; Diallo, A.; Zweben, S. J.
    • Physics of Plasmas, Vol. 23, Issue 4
    • DOI: 10.1063/1.4946871

    Invited Review Article: Gas puff imaging diagnostics of edge plasma turbulence in magnetic fusion devices
    journal, April 2017

    • Zweben, S. J.; Terry, J. L.; Stotler, D. P.
    • Review of Scientific Instruments, Vol. 88, Issue 4
    • DOI: 10.1063/1.4981873
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