Design, manufacture and testing of the glow discharge electrodes for Wendelstein 7-X

The electrodes for the Wendelstein 7-X glow discharge system have been designed, tested and manufactured. The compact design relies on a cooled housing, integrated into the first wall cooling system, and a calotte-shaped graphite anode. The new mounting concept avoids the need of active cooling of the anode due to an improved thermal conduction. Comprehensive tests of a prototype electrode had been carried out in laboratory and in the ASDEX Upgrade Tokamak during two operation campaigns. The electrode showed excellent and reliable long-time discharge behavior and fulfilled all the requirements regarding temperature limits and maintainability resulting from the steady-state operation of W7-X.