Introduction The interaction between zonal flows (ZFs) and turbulence is a self-regulating mechanism. Understanding this interaction is crucial to control plasma confinement. The shearing due to ZFs is thought to dominate in regimes when the mean shear flow is modest as before and during the L-H transition [e.g. 1]. This was corroborated by findings in different devices demonstrating the importance of both the oscillating and mean flow shear and their interaction in triggering the transitions [1-4]. While on AUG the sheared flow below the L-H threshold is dominated by Geodesic Acoustic Modes (GAMs) [1], on devices such as DIII-D [2], EAST [3] and HL-2A [4] GAMs do not appear to be important on the way to H-mode. The reported results reveal that no clear picture exists on the relevance of GAMs in the turbulence collapse required for the formation of steep pressure gradients at the transition. This contribution focuses on the characterization of GAMs in JET plasmas when approaching the L-H transition aiming at understanding its possible role in triggering the transition.
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