Electron cyclotron resonance discharge cleaning by using LHRF system on JT-60U

Electron cyclotron resonance discharge cleaning (ECR-DC) has been studied on JT-60U in which the first wall is completely covered by graphite tiles. The radio frequency (RF) waves at 2 GHz band, which are generated by the lower hybrid range of frequency (LHRF) system, are applied to the ECR-DC at the toroidal magnetic field of around 0.06 T. RF power up to ∼125 kW with a pulse length of ∼60 s has been repeatedly injected from the LH current drive launcher. An ECR-DC increases the particle recycling rate on the graphite first wall, and a remarkable desorption of water vapor (mass number of m/e=20) has been observed by the ECR in deuterium gas. Moreover, it is found that the ECR in D2 is effective to desorb tritium from the graphite first wall which are implanted during high power heating in deuterium discharges. This suggests that ECR-DC is one of effective tool to reduce a tritium inventory in a future tokamak fusion reactor.