Modification of the turbulence in the plasma boundary of the Wendelstein 7-AS stellarator using electric probes

The fluctuations in the edge plasmas of magnetic fusion experiments are tho ught to play an important role in terms of anomalous energy and particle tr ansport. Experiments on Wendelstein 7-AS were conducted with the primary go al to investigate the performance of influencing and modifying the turbulen ce in the plasma boundary using electrical probes. Two movable poloidal pro be arrays were used for the experiments, one located on the inboard side of the vessel and the other on the outboard side. A subset of probe tips was used for actively driving the plasma by different control signals, the rema ining probes collected fluctuation data in the plasma boundary. Poloidally, we find a significant cross-correlation between active and passive probes. From analysis of the coherency and phases of the passive probe tips, it ca n clearly be seen that the background E x B-rotation of the plasma plays a crucial role for the applied signals. In the case of externally driven wave s by several phase-locked active probes, the direction of the wave propagat ion with respect to the plasma rotation (co- or count er-rotating) is essen tial for a proper coupling to the turbulence. In toroidal direction we find that the propagation of the signals along the magnetic field lines depends on co- or counter-rotation with respect to the background plasma rotation.