Edge plasma electrostatic fluctuation and anomalous transport characteristics in the Sino-united spherical tokamak

In this paper, the edge plasma parameters, including the electron temperature ( T e ), electron density ( n e ), plasma potential (ϕ p ), radial electric field ( E r ) 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 E r × B ϕ 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 v ph r ∼ 0.7 km s −1 in the scrape-off-layer and v ph r ∼ 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.