A gas puff imaging (GPI) diagnostic has been developed and applied to measure edge plasma turbulence on the 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. Statistical characterizations of GPI line emission intensity are calculated, including the probability density functions (PDFs), 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 the original images and the relatively high-frequency (>10 kHz)/ low-frequency (1-10 kHz) component images are illustrated. The observation of the blob's structures and high-speed motions proves the success and high performance of the GPI diagnostic.
Several results based on the Langmuir probes’ data on the HL-2A tokamak are presented. The blob structures’ radial and poloidal drift velocities, estimated by the gradient of floating potential and by time delay evaluation, are compared in different line-averaged density and electron cyclotron resonance heating conditions. A positive correlation is observed in the comparison between blobs’ radial velocity estimated by the two methods mentioned above, regardless of the situation differences mentioned above. Correlation is also observed in the comparison between the blobs’ poloidal velocity estimated by the two methods in different situations, while a shift due to the different line-averaged density is observed. These results imply that the radial gradient of floating potential may have some value as a reference during data analysis in low-parameter discharge.
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