Quiet Periods in Edge Turbulence Preceding the L-H Transition in NSTX

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This paper describes the first observations in NSTX of ‘quiet periods’ in the edge turbulence preceding the L-H transition, as diagnosed by the GPI diagnostic near the outer midplane separatrix. During these quiet periods the GPI Dα light emission pattern was transiently similar to that seen during Hmode, i.e. with a relatively small fraction of the GPI light emission located outside the separatrix. These quiet periods had a frequency of ~3 kHz for at least 30 msec before the L-H transition, and were correlated with changes in the direction of the local poloidal velocity. The GPI turbulence images were also ... continued below

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Zweben, S; Hager, R; Hallatschek, K; Kaye, S M; Munsat, T; Poli, F M et al. April 26, 2010.

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This paper describes the first observations in NSTX of ‘quiet periods’ in the edge turbulence preceding the L-H transition, as diagnosed by the GPI diagnostic near the outer midplane separatrix. During these quiet periods the GPI Dα light emission pattern was transiently similar to that seen during Hmode, i.e. with a relatively small fraction of the GPI light emission located outside the separatrix. These quiet periods had a frequency of ~3 kHz for at least 30 msec before the L-H transition, and were correlated with changes in the direction of the local poloidal velocity. The GPI turbulence images were also analyzed to obtain an estimate for the dimensionless poloidal shearing S =(dVp/dr)(Lr/Lp)τ. The values of S were strongly modulated by the quiet periods, but not otherwise varying for at least 30 msec preceding the L-H transition. Since neither the quiet periods nor the shear flow increased significantly immediately preceding the L-H transition, neither of these appears to be the trigger for this transition, at least for these cases in NSTX.

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191Kb

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  • Report No.: PPPL-4510
  • Grant Number: DE-ACO2-09CH11466
  • DOI: 10.2172/981661 | External Link
  • Office of Scientific & Technical Information Report Number: 981661
  • Archival Resource Key: ark:/67531/metadc1014948

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  • April 26, 2010

Added to The UNT Digital Library

  • Oct. 14, 2017, 8:36 a.m.

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  • Nov. 2, 2017, 3:08 p.m.

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Zweben, S; Hager, R; Hallatschek, K; Kaye, S M; Munsat, T; Poli, F M et al. Quiet Periods in Edge Turbulence Preceding the L-H Transition in NSTX, report, April 26, 2010; (digital.library.unt.edu/ark:/67531/metadc1014948/: accessed December 13, 2017), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.