Edge turbulence plays a critical role in anomalous transport within tokamak plasmas, significantly influencing plasma confinement performance. A gas puff imaging (GPI) diagnostic was developed on the J-TEXT tokamak to show the 2D structure of plasma edge turbulence around the last closed flux surface (LCFS). Recent optimizations of the imaging optics and mechanical support have minimized the sightline misalignment with the local magnetic field. An integrated data analysis framework—combining time delay estimation, conditional average sampling, and intermittent structure tracking (IST)—has been established to resolve the dynamics and statistics of boundary turbulent structures. The optimized diagnostic was applied to study ohmic helium plasma discharges. We observe that the flow shear rate at LCFS decreases linearly with increasing plasma density. Concurrently, boundary blob structures evolved to become larger, slower, and longer-lived. The statistical radial velocity of blobs agreed with prior Langmuir probe measurements on J-TEXT. A key finding is the clear separation in shear rate magnitude between pure helium and hydrogen-mixed helium plasmas. These results demonstrate that the upgraded GPI system is a reliable and powerful tool for resolving edge turbulence to the understanding of boundary transport mechanisms.
Sheared flows and turbulence in fusion plasmas