Midplane neutral density profiles in the National Spherical
Torus Experiment
Authors: D. P. Stotler, F. Scotti, R. E. Bell, and
B. P. LeBlanc
Abstract: Atomic and molecular density data in
the outer midplane of NSTX [Ono et al., Nucl. Fusion 40, 557
(2000)] are inferred from tangential camera data via a forward
modeling procedure using the DEGAS 2 Monte Carlo neutral transport
code. The observed Balmer-B light emission data from 17
shots during the 2010 NSTX campaign display no obvious trends with
discharge parameters, such as the divertor Balmer- α emission level or edge deuterium ion
density. Simulations of 12 time slices in 7 of these discharges
produce molecular densities near the vacuum vessel wall of 2 to 8
x1017 m-3
and atomic densities ranging from 1 to 7 x 1016m-3
; neither has a clear correlation with other parameters.
Validation of the technique, begun in an earlier publication, is
continued with an assessment of the sensitivity of the simulated
camera image and neutral densities to uncertainties in the data
input to the model. The simulated camera image is sensitive to the
plasma pro files and virtually nothing else. The neutral densities
at the vessel wall depend most strongly on the spatial
distribution of the source; simulations with a localized neutral
source yield densities within a factor of two of the baseline,
uniform source, case. The uncertainties in the neutral densities
associated with other model inputs and assumptions are ≤
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Submitted to: Physics of Plasmas
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