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Diagnostic performance of the beam emission spectroscopy system on the National Spherical Torus Experiment.

Authors
  • Smith, D R
  • Fonck, R J
  • McKee, G R
  • Thompson, D S
Type
Published Article
Journal
Review of Scientific Instruments
Publisher
American Institute of Physics
Publication Date
Oct 01, 2012
Volume
83
Issue
10
Identifiers
DOI: 10.1063/1.4728094
PMID: 23126846
Source
Medline
License
Unknown

Abstract

The beam emission spectroscopy system on the National Spherical Torus Experiment measures localized density fluctuations on the ion gyroscale. Optical sightlines provide core to edge radial coverage, and the sightlines are aligned to typical pitch angles to maximize cross-field spatial resolution. Sightline images are 2-3 cm, and point spread function calculations indicate image distortion from pitch angle misalignment and atomic state finite lifetimes is minor with a 15% increase in the image size. New generation photodetectors achieve photon noise limited measurements at frequencies up to 400 kHz with refrigerant cooling at -20 °C. Measurements near the pedestal show broadband turbulence up to 100 kHz, and poloidal correlation lengths are about 10 cm. Plasma turbulence signals can be 2-3 orders of magnitude above photon noise and amplifier thermal noise.

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