Structure identification, tracking and velocimetry in gas-puff imaging measurements*

Field aligned structures play a key role in plasma particle and heat transport, thus, their investigation is of great interest. Intermittent structures such as blobs and transient structures such as ELM filaments have been observed routinely on NSTX by the means of gas-puff imaging (GPI). GPI provides fast temporal (2.5us) and high spatial resolution (1cm) measurement of these structures. Thus far the analysis techniques applied to GPI data has not expoited the high resolution of the measurement to its fullest.

Novel data analysis techniques were developed to analyze the field-eligned structures with the highest possible resolution. A method named spatial displacement estimation was developed to resolve the frame-by-frame velocities of transient structures which was later enhanced for angular velocity estimation, as well. Testing these methods showed that they provide accurate estimates of the translational and angular velocities. To characterize the shape and orientation of the measured structures a watershed algorithm based segmentation method was implemented. The algorithm was ran on a large database of intermittent and transient events to investigate their fast structural dynamics.