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 lowfield
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. |