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.
Role of isotope mass and evidence of fluctuating zonal flows during the L–H transition in the TJ-II stellarator