Tuesday, April 16, 2019
Gas-Puff Imaging (GPI) measures the spatially-resolved fluctuations in the plasma edge and SOL by imaging emission from a local gas puff. In August 2018, a GPI system has been installed on TCV in Switzerland. First data were obtained in December 2018 and there is great signal-to-noise ratio for views around the spatial peak of the emission. GPI also captured the propagation of a blob in the SOL. It is typically assumed that the fluctuation in the emission in GPI is correlated with the plasma fluctuations without regarding the neutral density fluctuations. However, according to the GBS simulation result the neutral density fluctuation has significant impacts on the light emission. The neutral fluctuation results in the GPI “shadowing” effect which is expected to be prominent at the distance from the nozzle larger than the neutral mean-free-path. Experiments have been designed to explore the shadowing effect by comparing pairs of cases with different neutral mean-free-path in an identical background plasma.