ECR Discharge Cleaning on JT-60U

Electron Cyclotron Resonance Discharge Cleaning (ECR-DC) was studied on JT-60U whose first wall was composed of graphite tiles. The radio frequency of 2GHz band, which was the original Lower Hybrid Range of Frequency (LHRF) heating system, was applied to the ECR-DC at the toroidal magnetic field of around 0.06T. A high power ECR-DC up to ∼125kW was performed for quasi steady state operation. Though ECR-DC caused the increase in the recycling rate on the graphite first wall, a remarkable desorption of water vapor (mass number of m/e=20) was observed by the ECR in Deuterium gas. Moreover, it was found that the ECR in D2 was effective to desorb Tritium from the graphite first wall. (author)