Speaker
Thomas Hartl
(E1)
Description
Glow discharge cleaning (GDC) and coating of the plasma facing components (PFC) is still crucial for fusion research machines to reach demands on plasma cleanliness for elaborate investigations. To correspond with latest experimental findings the GDC-system of ASDEX Upgrade (AUG) has been remodeled entirely.After transition to tungsten PFCs it becomes evident that Helium implanted during GDC contaminates subsequent plasma discharges significantly. This can be effectively minimized by alternately switch between short GDC pulses and longer purge phases. Therefore a dependable fast plasma ignition at operational pressure is required.Influenced by the need of space-saving design, enhanced reliability and simplified maintenance a radiation cooled tungsten-coated graphite anode was constructed based on the Wendelstein W7-X GDC electrode. Validated by extensive laboratory investigations a separate surface discharge spark device was developed.Four electrodes have been installed spread evenly around the circumference of the torus midplanes low field side each equipped with a starting device. To ensure high availability for use each single anode is supplied by its individual power supply unit. The starting devices are powered by individual capacities commonly feeded via a high voltage power supply. This enables plasma starting times of less than 100 milliseconds and thereby also efficient pulsed GDCs with an on/off ratio of as less than 10/50 seconds.The paper gives an overview of the technical setup of the AUG GDC-system and summarizes the experiences of the first two operational campaigns.
Co-author
Thomas Hartl
(E1, Max Planck Institute for Plasmaphysics, D-85748 Garching, Germany)
