Influence of ELMs on operation of ICRF antennas in ASDEX Upgrade

Abstract The coupling characteristics of the ion cyclotron range of frequencies antenna during type I edge localized modes (ELMs), asymmetries in the reaction of toroidally distributed antennas to ELMs and arcing phenomena following ELMs are studied for ASDEX Upgrade. The maximum change of the antenna resistance due to ELMs increases with triangularity δL in the on-axis minority heating. In the cases with off-axis heating, the change of the resistance is less sensitive to δL. Time-resolved RF measurements show asymmetries in times of response of the toroidally distributed antennas to the rising edge of ELMs and in the further evolution of this response. Toroidal propagation of ELM perturbations in counter-current direction with times ≈50 μs for one toroidal turn is observed. ELM-induced arcing is observed during ELMs and with delays after ELMs. Conditioning takes place as the arc number during ELMs decreases and time delay between ELM and arc increases.