Oxygen removal with D2-ICR cleanings after oxidation experiment in HT-7

The effectiveness of D2-ICR cleaning with a pressure up to 0.18 Pa was surveyed on hot walls of 400–470 K for oxygen removal after oxidation experiment in the HT-7 superconducting tokamak. The oxygen removal rate in D2-ICR cleaning was about (7–9) × 1021 O-atoms/h, about 5–10 times higher that that He-ICR cleanings before and after the D2-ICR cleaning. In about 130 min He-ICR and D2-ICR cleanings, about 8 × 1021 O-atoms were removed. After the cleanup, a lot of water still retained in HT-7 vessel and 67 disruptive plasmas were required before obtaining normal plasma. In present experiment, the recovered plasmas were easily controlled and much better than previous report in HT-7 oxidation experiments.