Statistical analysis to the SOL plasma fluctuation in JT-60U

Abstract

Intermittent events and their temporal scale were studied in the L-mode SOL plasma by applying statistical analysis of probability distribution function and conditional average to j s and V f measured with the Mach probes at the HFS and LFS. Fluctuation level was large (20–70%) at the LFS midplane, compared to those near the X-point (4–20%) and the HFS SOL (4–10%). ‘Burst events’ were measured mostly at the LFS midplane, where positive skewness ( S = 0.3–0.8) extended from the separatrix to the far SOL ( r mid < 10 cm). Time scale of the ‘burst events’ was short (∼5 μs). When the divertor plasma was detached up to the vicinity of the X-point, large ‘burst events’ characterized by S ∼ 1.8 and long time scale of 40–80 μs occurred in the outer SOL near the X-point (0.5 < r mid < 1.5 cm). The large ‘burst events’ can therefore be considered as a candidate mechanism to enhance the radial transport and SOL flow in the divertor.