Observation of blobs using gas puff imaging diagnostic on HL-2A tokamak

A gas puff imaging (GPI) diagnostic has been developed and applied to measure edge plasma turbulence on HL-2A tokamak. The principle and experimental setup of GPI are described. GPI is applied to investigate blobs in the edge and scrape-off layer (SOL). Statistical characterizations of GPI line emission intensity are calculated, including the probability density functions (PDF), skewness and kurtosis of the intensity, which are found to be consistent with measurements by Langmuir probes. Besides, the track of blob motions is recorded by time sequence of individual frames. The characteristics of original images and the relatively high-frequency (>10 kHz)/low-frequency (1-10 kHz) components images are illustrated. The observation of blob’s structures and high-speed motions proves the success and high performance of the GPI diagnostic.