Water Impurity Removal by Different Wall Conditioning Methods

The major impurity among gas species in the 2009 KSTAR campaign is water, up to 6.91 % of total pressure in the vacuum vessel. Various wall conditioning methods such as GDC, ICWC, and boronization are conducted to reduce water impurity which affects the plasma initiation. GDCs reduce water pressure to 1 × 10^-9 mbar while several minutes of inter-shot ICWCs suppress water pressure around 3 × 10^-9 mbar. Compared with the results from the KSTAR boronization, routinely performed inter-shot ICWCs would have similar effect as boronization for water removal from the vacuum vessel.