Sawtooth control experiments on ASDEX Upgrade
In a fusion device, the so-called sawtooth instability can lead to the triggering of confinement limiting neoclassical tearing modes. On the other hand, the existence of sawteeth is desirable for the removal of one fusion product, i.e. helium ash from the plasma core. This has led to great interest in the control of sawteeth. The sawtooth period can be changed drastically by local modification of the q-profile. In this paper, the influence of the beam line geometry of the neutral beam injection in the ASDEX Upgrade tokamak Will be presented as well as the effect of local electron cyclotron current drive. Systematic scans in the electron Cyclotron current deposition from the high-field side to the low-field side resolve areas with sawtooth stabilization and destabilization. These observations will be discussed, including modelling of the main results, with the ASTRA transport code constrained by experimental data.