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Comparison of beam emission spectroscopy and gas puff imaging edge fluctuation measurements in National Spherical Torus Experiment

Publication ,  Journal Article
Sechrest, Y; Smith, D; Stotler, DP; Munsat, T; Zweben, SJ
Published in: Physics of Plasmas
May 1, 2015

In this study, the close physical proximity of the Gas Puff Imaging (GPI) and Beam Emission Spectroscopy (BES) diagnostics on the National Spherical torus Experiment (NSTX) is leveraged to directly compare fluctuation measurements, and to study the local effects of the GPI neutral deuterium puff during H-mode plasmas without large Edge Localized Modes. The GPI and BES views on NSTX provide partially overlapping coverage of the edge and scrape-off layer (SOL) regions above the outboard midplane. The separation in the toroidal direction is 16 °, and field lines passing through diagnostic views are separated by ∼ 20 cm in the direction perpendicular to the magnetic field. Strong cross-correlation is observed, and strong cross-coherence is seen for frequencies between 5 and 15 kHz. Also, probability distribution functions of fluctuations measured ∼ 3 cm inside the separatrix exhibit only minor deviations from a normal distribution for both diagnostics, and good agreement between correlation length estimates, decorrelation times, and structure velocities is found at the ±40% level. While the two instruments agree closely in many respects, some discrepancies are observed. Most notably, GPI normalized fluctuation levels exceed BES fluctuations by a factor of ∼ 9. BES mean intensity is found to be sensitive to the GPI neutral gas puff, and BES normalized fluctuation levels for frequencies between 1 and 10 kHz are observed to increase during the GPI puff.

Duke Scholars

Published In

Physics of Plasmas

DOI

EISSN

1089-7674

ISSN

1070-664X

Publication Date

May 1, 2015

Volume

22

Issue

5

Related Subject Headings

  • Fluids & Plasmas
  • 5109 Space sciences
  • 5106 Nuclear and plasma physics
  • 0203 Classical Physics
  • 0202 Atomic, Molecular, Nuclear, Particle and Plasma Physics
  • 0201 Astronomical and Space Sciences
 

Citation

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Sechrest, Y., Smith, D., Stotler, D. P., Munsat, T., & Zweben, S. J. (2015). Comparison of beam emission spectroscopy and gas puff imaging edge fluctuation measurements in National Spherical Torus Experiment. Physics of Plasmas, 22(5). https://doi.org/10.1063/1.4921215
Sechrest, Y., D. Smith, D. P. Stotler, T. Munsat, and S. J. Zweben. “Comparison of beam emission spectroscopy and gas puff imaging edge fluctuation measurements in National Spherical Torus Experiment.” Physics of Plasmas 22, no. 5 (May 1, 2015). https://doi.org/10.1063/1.4921215.
Sechrest Y, Smith D, Stotler DP, Munsat T, Zweben SJ. Comparison of beam emission spectroscopy and gas puff imaging edge fluctuation measurements in National Spherical Torus Experiment. Physics of Plasmas. 2015 May 1;22(5).
Sechrest, Y., et al. “Comparison of beam emission spectroscopy and gas puff imaging edge fluctuation measurements in National Spherical Torus Experiment.” Physics of Plasmas, vol. 22, no. 5, May 2015. Scopus, doi:10.1063/1.4921215.
Sechrest Y, Smith D, Stotler DP, Munsat T, Zweben SJ. Comparison of beam emission spectroscopy and gas puff imaging edge fluctuation measurements in National Spherical Torus Experiment. Physics of Plasmas. 2015 May 1;22(5).

Published In

Physics of Plasmas

DOI

EISSN

1089-7674

ISSN

1070-664X

Publication Date

May 1, 2015

Volume

22

Issue

5

Related Subject Headings

  • Fluids & Plasmas
  • 5109 Space sciences
  • 5106 Nuclear and plasma physics
  • 0203 Classical Physics
  • 0202 Atomic, Molecular, Nuclear, Particle and Plasma Physics
  • 0201 Astronomical and Space Sciences