Extraction of intermittent waveforms associated with the zonal flow at the transition leading to the edge shear flow layer

Abstract

A new technique for the detection of (very) low-frequency oscillations with significant long-range correlation is presented. The technique is applied to Langmuir probe data obtained at the TJ-II stellarator in discharges with spontaneous confinement transitions with and without electrode biasing. A succession of low-frequency and very low-frequency oscillations is observed, preceding the confinement transition.