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E. Wolfrum, P. Sauter, M. Willensdorfer, F. Ryter, F. Aumayr, L. Barrera Orte, A. Burckhart, E. Fable, R. Fischer, B. Kurzan, T. Pütterich, S. Rathgeber, W. Suttrop, E. Viezzer, . ASDEX Upgrade Team:
"Recent progress in understanding the L-H transition physics from ASDEX Upgrade";
Plasma Physics and Controlled Fusion, 54 (2012), 1240021 - 1240026.

Kinetic edge profiles are measured with high spatial and temporal resolution and their
behaviour before and after the time of the L-H transition is analysed. It is shown that at low
densities electron and ion channels are strongly decoupled and that the ion kinetic profiles
determine the transition to H-mode.
At medium densities, where electrons and ions are coupled, the H-L back-transition
occurs at the same pressure gradients as the L-H transition. The threshold power for the H-L
back-transition exhibits the same increase at low densities as the L-H transition.
After the L-H transition the density development depends on the available neutral gas
reservoir. Modelling of particle transport indicates that the temporal development of the
density profiles can be reproduced assuming only a reduction in the edge diffusion coefficient.
The influence of magnetic perturbation coils on the L-H transition power threshold
strongly increases with density above a Greenwald factor of about 0.6.