Optimization of the ASDEX Upgrade glow discharge

With the change from carbon to tungsten plasma-facing components (PFCs) an enhanced Helium (He) content at plasma discharges was observed for unboronized walls and the implantation of He during GD could be identified as source. For this reason the use of He GD has to be strongly reduced. It turned out that pulsed GDs of about 10 s length followed by a pumping down phase are sufficient to clean the wall. This mode of operation requires a reliable breakdown of the GD at operating pressure. This paper gives an overview of the technical setup and first measurement results.