ELMs and sawteeth with ICRF heating on ASDEX upgrade

The ASDEX Upgrade ICRF system has recently been completely equipped with 3-dB couplers. They reduce, in a purely passive way, the sensivity of the ICRF system to fast coupling changes as occur in the presence of ELMs. They also make the matching less critical and allow variations of the plasma conditions, even with fixed matching during a discharge. The 3-dB couplers have operated as expected and permitted full power operation of the system (5.7 MW at the antenna, 6.8 MW generator output) as well as routine operation at 4 MW under a variety of conditions. Using those new capabilities, it was possible to compare, at high power, the ELM and sawteeth behavior of various ICRF heating scenarios (minority heating, direct electron heating and mode conversion heating) and neutral injection heating. Large differences were found in the sawtooth behavior, but no differences in the ELM behavior. The sawteeth are very sensitive to the localization of the power deposition as well as to the distribution of power between electrons and ions, while ELMs seems to be sensitive to the total power only.