High frequency edge coherent modes studied with the ultra-fast swept reflectometer on ASDEX Upgrade

The results on high frequency coherent modes developing at the plasma edge after L-H transitions are presented. These edge coherent modes (ECMs) observed in the I-phase, during ELM-free and ELMy H-mode phases have common characteristics, such as their frequency of 50-200 kHz, radial position and scaling of the frequency with the pressure gradient. The ultrafast swept reflectometer with the sweep time of 1 mu s has provided measurements of the mode dynamics and localisation. The ECMs propagate in the electron diamagnetic direction in the laboratory frame and are localized in the region between the pedestal top and the steepest pressure gradient.