Scaling of radial propagating structures in the scrape-off layer of the National Spherical Torus Experiment (NSTX)

The radial propagation of spatiotemporal turbulent structures in the scrape-off layer of the National Spherical Torus Experiment [M. Ono, M.G. Bell, R.E. Bell, et al. Plasma Phys. Control. Fusion 45, A335 (2003)] is investigated. Two-dimensional spatiotemporal imaging of the Dα emission intensity is used to observe the fluctuation structures in the poloidal plane perpendicular to the ambient magnetic field. Turbulent structures are extracted and the individual properties such as velocity, spatial scale and amplitude are determined. The typical poloidal scale of the structures is kϑ = 0.5 cm−1. The poloidal and radial structure velocities are < 5 km/s and 1 km/s, respectively. The radial velocities do not vary significantly with their spatial size within this set of data