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Experimental observation of electron-scale turbulence evolution across the L-H transition in the National Spherical Torus Experiment

Publication ,  Journal Article
Ren, Y; Smith, DR; Zweben, SJ; Bell, R; Guttenfelder, W; Kaye, SM; Leblanc, BP; Mazzucato, E; Lee, KC; Domier, CW; Sun, PJ; Yuh, H
Published in: Nuclear Fusion
August 6, 2019

Electron-scale turbulence (for 3 k s12) was measured during the L-H transition in the National Spherical Torus Experiment (NSTX) (Ono et al 2000 Nucl. Fusion 40 557) using a coherent microwave scattering system. The measurements were carried out at a radial region adjacent to the edge transport barrier (ETB) (at smaller radius than ETB). The observed L-H transition occurred during current flattop, which facilitated the measurement of electronscale turbulence. The measured electron-scale turbulence is observed to be quasi-stationary before the L-H transition, and an intermittent phase for electron-scale turbulence is observed after the start of the L-H transition with a gradual decrease in overall turbulence density fluctuation spectral power with intermittent large relative variations (on ~0.5-1 ms time scale) in the total spectral power. A turbulence-quiescent phase is observed following the intermittent phase, and a significant reduction in the electron-scale turbulence spectral power is only observed at lower wavenumbers, namely ks9-10, which is also seen in different operational NSTX scenarios due to different stabilization mechanisms. A recovery phase is seen after the quiescent phase, where the electron-scale density fluctuation power starts to gradually increase. Simultaneous ion-scale turbulence measurements at larger radius than the electron-scale turbulence measurement location show similar temporal behavior in ion-scale turbulence as in the measured electron-scale turbulence. These observations demonstrate that the suppression of turbulence during the L-H transition is not just limited to the ETB region. None of the measured electron-scale turbulence and ion-scale turbulence from edge into core is found to be obviously leading in the response to the L-H transition, and the overall turbulence suppression after the start of the L-H transition at different radii seems to start at the same time and is a gradual process happening on a tens-of-ms time scale. The trend of decrease in electron-scale turbulence during the L-H transition is found to be consistent with a decrease in the maximum electron erature-gradient linear growth rate from linear gyrokinetic stability analysis. However, the observed intermittency in electron-scale turbulence during the intermittent phase cannot be explained by the linear analysis.

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Published In

Nuclear Fusion

DOI

EISSN

1741-4326

ISSN

0029-5515

Publication Date

August 6, 2019

Volume

59

Issue

9

Related Subject Headings

  • Fluids & Plasmas
  • 5106 Nuclear and plasma physics
  • 0202 Atomic, Molecular, Nuclear, Particle and Plasma Physics
 

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Ren, Y., Smith, D. R., Zweben, S. J., Bell, R., Guttenfelder, W., Kaye, S. M., … Yuh, H. (2019). Experimental observation of electron-scale turbulence evolution across the L-H transition in the National Spherical Torus Experiment. Nuclear Fusion, 59(9). https://doi.org/10.1088/1741-4326/ab2f4f
Ren, Y., D. R. Smith, S. J. Zweben, R. Bell, W. Guttenfelder, S. M. Kaye, B. P. Leblanc, et al. “Experimental observation of electron-scale turbulence evolution across the L-H transition in the National Spherical Torus Experiment.” Nuclear Fusion 59, no. 9 (August 6, 2019). https://doi.org/10.1088/1741-4326/ab2f4f.
Ren Y, Smith DR, Zweben SJ, Bell R, Guttenfelder W, Kaye SM, et al. Experimental observation of electron-scale turbulence evolution across the L-H transition in the National Spherical Torus Experiment. Nuclear Fusion. 2019 Aug 6;59(9).
Ren, Y., et al. “Experimental observation of electron-scale turbulence evolution across the L-H transition in the National Spherical Torus Experiment.” Nuclear Fusion, vol. 59, no. 9, Aug. 2019. Scopus, doi:10.1088/1741-4326/ab2f4f.
Ren Y, Smith DR, Zweben SJ, Bell R, Guttenfelder W, Kaye SM, Leblanc BP, Mazzucato E, Lee KC, Domier CW, Sun PJ, Yuh H. Experimental observation of electron-scale turbulence evolution across the L-H transition in the National Spherical Torus Experiment. Nuclear Fusion. 2019 Aug 6;59(9).
Journal cover image

Published In

Nuclear Fusion

DOI

EISSN

1741-4326

ISSN

0029-5515

Publication Date

August 6, 2019

Volume

59

Issue

9

Related Subject Headings

  • Fluids & Plasmas
  • 5106 Nuclear and plasma physics
  • 0202 Atomic, Molecular, Nuclear, Particle and Plasma Physics