H-mode characterisation for dominant ECRH and comparison to dominant NBI or ICRF heating at ASDEX Upgrade

At ASDEX Upgrade the ECRH system has been upgraded to provide up to 4 MW of heating power at 140 GHz (or 2.2 MW at 105 GHz). The power at 140 GHz exceeds the minimum H-mode power threshold for typical high I-p, B-t conditions by approximately a factor of two. The upgrade allows H-modes with dominant electron heating and significant electron-ion heat exchange to be studied, i.e. the situation expected in ITER. This paper reports on systematic studies varying the heating mix with NBI, ICRF and ECRH and its effect on pedestal parameters and core transport. The H-mode pedestal is hardly affected by the choice of heating mix, but the ion temperature in the plasma center is found to vary significantly. The ion channel dominates heat transport and ion temperature gradient modes (ITG) are found to be the most unstable microinstability in all the scenarios considered. R/L-Ti at half radius reduces by a factor of two when T-e/T-i increases from 0.9 to 1.5. TGLF modelling of the electron and ion temperature and electron density profiles shows very good agreement with the experimental data when applying a realistic sawtooth model.