Edge plasma behavior in the GAMMA 10 tandem mirror based on gas puff imaging experiments with a high-speed camera

Abstract Detailed results of edge plasma and neutral particle behavior are described in the gas puff imaging experiments performed in the GAMMA 10 tandem mirror for the first time. Visible imaging measurement by using a high-speed camera (Ultima-SE, Photron Inc.) was recently performed in the central-cell midplane of GAMMA 10. In the standard plasma discharge heated by ICRF wave, a short gas puff of hydrogen (3 ms) was carried out and the time evolution of light emission was visualized precisely. It was found that the time evolution of the emission cloud was similar to that of Hα line intensity measured nearby and was localized close to the gas puff port. Asymmetry in diffusion of the emission cloud is observed radial and axial direction of plasma column in the central-cell. This localization phenomenon of neutrals is qualitatively well explained by a fully 3-dimensional simulation using DEGAS neutral particle transport code.