Spectroscopic Diagnostics for Spatial Density Distribution of Plasmoid by Pellet Injection in the Large Helical Device

Abstract

To investigate the behavior of a plasmoid consisting of pellet ablatant ionized by background plasma, two dimensional imaging measurements of high-speed spectroscopy have been developed using a fast camera in the Large Helical Device (LHD). The diagnostic system provides density distribution of the plasmoid. The density distribution is determined using the Stark broadening width of the Balmer-β line. Stark broadening profile can be evaluated from the intensity ratio measured using narrow-band optical filters having different full width at half maximum. Two dimensional images of the plasmoid are obtained by a fast camera connected to a bifurcated fiber scope with two objective lenses. An initial result shows that the plasmoid density is obtained within a factor of 2 by imaging measurements.