Carbon removal in stainless steel wall and graphite sheet by using oxygen glow discharge

In ITER, oxygen glow discharge cleaning (He/O2-GDC) is proposed as a method for removal of a-C:H co-deposited layer. In this study, graphite was irradiated by this method, and its erosion rate was quantitatively estimated from the CO and CO2 desorption during the discharge. With He/O2(7%)-GDC, the erosion rate was estimated to be 4.1 × 10−6 g cm−2 h−1, which corresponds to 23 nm h−1. This erosion rate increased with O2 mixture ratio in its discharging gas. However, the rate was not proportional to the oxygen mixture ratio because of an O2 retention in graphite. From TDS, it is found that graphite exposed to He/O2(7%)-GDC retained 3.1 × 1016 O atoms/cm2.