In this paper, the edge plasma parameters, including the electron temperature (Te), electron density (ne), plasma potential (ϕp), radial electric field (Er) and the corresponding fluctuations in the Sino-united spherical tokamak (SUNIST) have been systematically measured using Langmuir probe arrays. The characteristics of the edge electrostatic fluctuations and the turbulence-induced transport are experimentally investigated. The results show that a naturally formed Er × Bϕ poloidal velocity shear layer (VSL) exists near the radial location of the limiter. Wavenumber spectrum analyses show that edge fluctuations have a radial propagation character of the drift wave turbulence, with a characteristic radial phase velocity vphr ∼ 0.7 km s−1 in the scrape-off-layer and vphr ∼ 0.9–1.4 km s−1 at plasma edge, suggesting that the edge turbulence may originate from the core and propagate to the edge in an intermittent pattern. A radial profile of the toroidal flow velocity Mach number has been observed whose maximum is just located at the VSL position, which may imply a possible relation between the poloidal shear flow and the toroidal plasma flow in SUNIST.
Inward and outward propagation of the floating potential fluctuations in the plasma edge of the TJ-II stellarator