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Quiet periods in edge turbulence preceding the L-H transition in the national spherical torus experiment
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Zweben, S. J., Maqueda, R. J., Hager, R., Hallatschek, K., Kaye, S. M., Munsat, T., Poli, F. M. (Francesca), Roquemore, A. L., Sechrest, Y. and Stotler, D. P. (2010) Quiet periods in edge turbulence preceding the L-H transition in the national spherical torus experiment. Physics of Plasmas, Vol.17 (No.10). Article: 102502. doi:10.1063/1.3476276 ISSN 1070-664X.
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Official URL: http://dx.doi.org/10.1063/1.3476276
Abstract
This paper describes the first observations in the National Spherical Torus Experiment (NSTX) [S. M. Kaye et al., Phys. Plasmas 8, 1977 (2001)] of "quiet periods" in the edge turbulence preceding the low-to-high (L-H) mode transition, as diagnosed by the gas puff imaging (GPI) diagnostic near the outer midplane separatrix. During these quiet periods the GPI D-alpha light emission pattern was transiently similar to that seen during H-mode, i.e., with a relatively small fraction of the GPI light emission located outside the separatrix. These quiet periods had a frequency of similar to 3 kHz for at least 30 ms 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 = (dV(p)/dr)(L-r/L-p)tau. The values of S were strongly modulated by the quiet periods but did not significantly vary during the similar to 30 ms preceding the L-H transition. Since neither the quiet periods nor the shear flow increased immediately preceding the L-H transition, neither of these appears to be the trigger for this transition, at least for these cases in NSTX. (C) 2010 American Institute of Physics. [doi:10.1063/1.3476276]
Item Type: | Journal Article | ||||
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Subjects: | Q Science > QC Physics | ||||
Divisions: | Faculty of Science, Engineering and Medicine > Science > Physics | ||||
Journal or Publication Title: | Physics of Plasmas | ||||
Publisher: | American Institute of Physics | ||||
ISSN: | 1070-664X | ||||
Official Date: | October 2010 | ||||
Dates: |
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Volume: | Vol.17 | ||||
Number: | No.10 | ||||
Number of Pages: | 18 | ||||
Page Range: | Article: 102502 | ||||
DOI: | 10.1063/1.3476276 | ||||
Status: | Peer Reviewed | ||||
Publication Status: | Published | ||||
Access rights to Published version: | Restricted or Subscription Access | ||||
Funder: | U.S. DOE | ||||
Grant number: | DE-AC02-09CH11466, DE-FG02-08ER54995 |
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