Oxidation for deposits removal and hydrogen release on HT-7

Oxidation experiments at wall temperatures of 400–470 K, including O-ICR, O-GDC conditioning and thermal-oxidation have been carried out for removal of deposits and hydrogen in HT-7. Thermal-oxidation seems ineffective to remove co-deposited layers and hydrogen at these temperatures. O-GDC oxidation appeared to be the most efficient on HT-7. However O-ICR was almost as good and could be applied with the magnetic field in ITER. Both O-ICR and O-GDC have a deposits removal rates ∼20 times that of He-ICR and He-GDC cleaning. Higher pressures and conditioning power during oxygen wall conditioning are favorable for removal of deposits and hydrogen. The oxygen retention after O-GDC oxidations was much higher than that after O-ICR oxidations. High power low oxygen pressure and He in O-ICR oxidation are beneficial for reducing oxygen retention. To remove the retained oxygen on walls both He-ICR and He-GDC were found to be effective. Plasma discharges could be recovered after a few tens of disruptive plasmas.