Changes in plasma potential and turbulent particle flux in the core plasma measured by heavy ion beam probe during L–H transitions in the TJ-II stellarator

Plasma potential and turbulent particle flux ΓE×B in the plasma core were measured for the first time during L–H/H–L transitions in the TJ-II heliac using a heavy ion beam probe. The L–H transition is characterized by a simultaneous potential drop ∼−100 V over the whole plasma radius, formation of density pedestal and a strong radial electric field Er between −100 to −150 V cm−1 in the edge (0.8 < ρ < 0.9), strong suppression of the broadband density and potential oscillations and of ΓE×B in the edge and core plasma.