The experience with JET's combined dc/RF glow discharge cleaning (GDC) system

Abstract The JET Tokamakwas fitted with four new electrodes of novel design, each powered from individual computer controlled dc and RF supplies. Details of enhancements and problems from 15 months experience with the system are outlined. Experiments were performed to assess the effect of RF on the glow dischargecharacteristics, and to establish stable glowat low pressure and high voltage. JET combined RF/dc glow dischargecleaning (GDC) had no significant advantages over pure dc GDC, provided highly stable dc current control was obtained. In fact, the mechanically weak electrode inductor spiral required to allow RF posed a distinct disadvantage. The electrodes were converted to simple plates, following damage caused by halo currents during Tokamakplasma disruptions. The performance of these electrodes was assessed. Future developments in the JET GDC system are outlined.