O2- and X3-Heating Experiments on ASDEX Upgrade

The improved H-mode in ASDEX Upgrade (AUG) is an operation regime with high confinement and densities near the Greenwald limit. Since the first wall in AUG is completely coated with tungsten, the ECRH is needed to control the tungsten accumulation in H-modes [1], therefore the routinely used X2 mode must be deposited in the plasma centre [2]. For ITER-relevant plasma discharges a safety factor of q₉₅ ≈ 3 must be achieved. At B = 2.5 T plasma currents of > 1.2 MA corresponds to a q₉₅ ≈ 3, which results in densities above the X2 mode cutoff. Another way to decrease q₉₅ is to reduce the magnetic field, but then the X2 mode is not resonant in the plasma centre. For these two cases new ECR heating scenarios using X3 and O2 mode were developed and are presented here.