Optimization of the ASDEX Upgrade glow discharge

• Published in: Fusion engineering and design Vol. 124; pp. 283 - 286
• Main Authors: Härtl, Thomas, Drenik, Aleksander, Kircher, Michael, Rohde, Volker, Stelzer, Franz, Zeidner, Wolfgang
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.11.2017; Elsevier Science Ltd
• Subjects: Anodes; ASDEX upgrade; Carbon; Discharge; GDC; Glow discharge cleaning; Helium; Implantation; Optimization; Plasma; Pulsed GDC; Tungsten; Upgrading; Wall conditioning; Glow discharge cleaning; ASDEX upgrade; GD; Wall conditioning; Pulsed GDC; GDC
• ISSN: 0920-3796; 1873-7196
• DOI: 10.1016/j.fusengdes.2017.04.029

•New glow discharge system.•Ignition of GD within <100ms at glow discharge pressure.•Compact and robust system.•Small footprint.•Pulsed GDC.•Less wall loading with glow gas.•Higher cleaning efficiency. The ASDEX Upgrade (AUG) system for glow discharge (GD) has been revised comprehensively. This was necessary due to technical as well as operational requirements. The available space with in the low field side of the vacuum vessel is strongly limited because it’s the preferred place for diagnostics. The new development based on the design of the W7-X anode now has a smaller footprint, is long term reliable and easier maintainable. Additionally each of the anodes is equipped with a separate starting device. The use of this device now allows the fast ignition of GD at operational pressure without the need of a short-term pressure increase. 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 10s 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.