Details of Neutral Transport in Gas Puff Imaging Experiments
Authors: D.P. Stotler, J. Boedo, B. LeBlanc, R.J. Maqueda, and S.J. Zweben
Date of PPPL Report: June 2006
Submitted to: Journal of Nuclear Materials
Gas puff imaging (GPI) experiments are designed to provide high time and space resolution data on the structure of plasma turbulence in the plane perpendicular to the magnetic field. We first examine the temporal behavior of the helium atoms used as the emitting species for GPI and show that for the time scales of interest (a few micro-seconds), the atomic physics model underlying the conventional interpretation of GPI is valid. Second, we continue the Monte Carlo neutral transport simulations of the GPI diagnostic begun previously. The radial characteristics of the simulated emission clouds match observations to within the estimated errors. The upshot of these two results is that the technique for unfolding the 2-D, time-dependent plasma density and temperature data from helium GPI emission, relying on this atomic physics model and utilizing DEGAS 2's simulated neutral density data, is valid.