skip to main content

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

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 neutralmore » gas puff, and BES normalized fluctuation levels for frequencies between 1 and 10 kHz are observed to increase during the GPI puff.« less
Authors:
;  [1] ;  [2] ; ;  [3]
  1. Department of Physics, University of Colorado, Boulder, Colorado 80309 (United States)
  2. Department of Engineering Physics, University of Wisconsin-Madison, Madison, Wisconsin 53706 (United States)
  3. Princeton Plasma Physics Laboratory, Princeton, New Jersey 08540 (United States)
Publication Date:
OSTI Identifier:
22410313
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physics of Plasmas; Journal Volume: 22; Journal Issue: 5; Other Information: (c) 2015 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
70 PLASMA PHYSICS AND FUSION TECHNOLOGY; CORRELATION FUNCTIONS; DEUTERIUM; DISTRIBUTION FUNCTIONS; EDGE LOCALIZED MODES; EMISSION SPECTROSCOPY; FLUCTUATIONS; H-MODE PLASMA CONFINEMENT; IMAGES; KHZ RANGE; MAGNETIC FIELDS; NSTX DEVICE; PLASMA SCRAPE-OFF LAYER; PROBABILITY DENSITY FUNCTIONS