Observation of Edge Plasma Fluctuations with a Fast Camera in Heliotron J

A fast video camera is verified to be a powerful tool for observation of filaments/blobs near the last closed flux surface (LCFS). In order to extract the fluctuation component from the raw data of the fast camera, a pre-processing technique, sliding time window averaging subtraction (STWAS) has been developed to remove the background of slowly varying emission from the bulk plasma. By using this pre-processing technique, the fast camera data are analyzed. A method to identify the filaments in the pre-processed image is also discussed.