Abstract
Gas puff imaging is a two-dimensional diagnostic that measures the edge Dα light emission from a neutral D2 gas puff near the outer midplane of the National Spherical Torus Experiment (NSTX). DEGAS 2 is a three-dimensional Monte Carlo code used to model neutral transport and plasma-neutral interactions in fusion plasmas. In this paper, we compare the measured and modeled Dα light emission for specific NSTX experiments. Both the simulated spatial distribution and the radiance of the Dα light emission agree well with the experimental data obtained during time periods between edge-localized modes (ELMs) in ELMy H-modes.