A novel experimental method is applied to localize the initial suppression of turbulence, in the form of density fluctuations, at the transition from the low (L-) to the high (H-) confinement mode in toroidal magnetic fusion plasmas. The high radial and temporal resolution, combined with the unprecedented statistical significance, provided the awaited information on a possible dominant shear layer in L-H transition physics. We show, for the first time, that the H-mode turbulence suppression is initiated at the inner shear layer in the ASDEX Upgrade tokamak possibly shedding light on the causality behind the L-H transition process.
Turbulence link to L-mode, I-mode, and H-mode confinement in the DIII-D tokamak