PPPL-3795 is available in <a href="PPPL-3795.pdf">pdf</a> format (2.8 MB).

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<b>High Speed Imaging of Edge Turbulence in NSTX
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<b>Authors:</b> S.J. Zweben, R. Maqueda, D.P. Stotler, A. Keesee, J. Boedo, C. Bush, S. Kaye, B. LeBlanc, J. Lowrance, V. Mastrocola, R. Maingi, N. Nishino, G. Renda, D. Swain, J. Wilgen, and the NSTX Team 
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<b>Date of PPPL Report:</b> March 2003
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<b>Published in:</b> Nuclear Fusion <b>44</b> (Jan 2004) 134-153</p>


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The two-dimensional radial versus poloidal structure and motion of edge turbulence in NSTX (National Spherical Torus Experiment) were measured by using high-speed imaging of the visible light emission from a localized neutral gas puff. Edge turbulence images are shown and analyzed for Ohmic, L-mode (low-confinement mode), and H-mode (high-confinement mode) plasma conditions. Typical edge turbulence poloidal correlation lengths as measured using this technique are approximately equal to 4±1 cm and autocorrelation times are 40±20 µsec in all three regimes. The relative fluctuation level is typically smaller in H-mode than in L-mode, and transitions from H- to L-mode and can occur remarkably quickly (approximately equal to 30 µsec). The two-dimensional images often show localized regions of strong light emission which move both poloidally and radially through the observed region at a typical speed approximately equal to 10<SUP>5</SUP> cm/sec, and sometimes show spatially coherent modes.




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