Midplane neutral density profiles in the National Spherical Torus Experiment

Stotler, D. ; Scotti, F.; Bell, R. E. ; Diallo, A. ; LeBlanc, B. P. ; Podesta, M. ; Roquemore, A. L. ; Ross, P. W.
Issue date: 2015
Creative Commons Attribution 4.0 International (CC BY)
Cite as:
Stotler, D., Scotti, F., Bell, R. E., Diallo, A., LeBlanc, B. P., Podesta, M., Roquemore, A. L., & Ross, P. W. (2015). Midplane neutral density profiles in the National Spherical Torus Experiment [Data set]. Princeton Plasma Physics Laboratory, Princeton University. https://doi.org/10.11578/1366462
  author      = {Stotler, D. and
                Scotti, F. and
                Bell, R. E. and
                Diallo, A. and
                LeBlanc, B. P. and
                Podesta, M. and
                Roquemore, A. L. and
                Ross, P. W.},
  title       = {{Midplane neutral density profiles in the
                 National Spherical Torus Experiment}},
  publisher   = {{Princeton Plasma Physics Laboratory, Pri
                nceton University}},
  year        = 2015,
  url         = {https://doi.org/10.11578/1366462}

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-a 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 2–8 􏰁 10^17 m􏰈3 and atomic densities ranging from 1 to 7 􏰁 10^16 m􏰈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 profiles 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 50%.

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