Performance optimisation in ASDEX upgrade with ECRH and ECCD

In the ASDEX Upgrade tokamak we use localised electron cyclotron beating and current drive at 140 GHz. Both confinement and stability properties of the plasmas can be favourably altered. Particle transport can he modified with central ECRH. Linear gyrokinetic studies indicate that the transport is determined by collisionality and by the kind of turbulence which is dominant. A similar result is obtained for the electron heat transport. At higher collisionality the turbulent contribution to the diffusivity decreases. With central ECRH accumulation of high Z impurities can be prevented. Trace impurity injection experiments show that this is due to strongly increased impurity diffusion. Stability improvement can he achieved by controlling the sawtooth instability and thus the generation of seed islands for neoclassical tearing modes, by triggering their frequent interruption with ECCD, or by their complete suppression with ECCD on the resonant flux surface.