Wall conditioning of the KSTAR vacuum vessel

The wall conditioning of the KSTAR vacuum vessel has been performed in order to remove various kinds of impurities including H2O, carbon and oxygen for the first plasma. The first step of the wall conditioning was baking to 100 by hot pressurized water which circulates through the water channels between inner and outer wall of the vacuum vessel. The baking process continued for more than 200 h. Next step of the wall conditioning was the R-GDC with both hydrogen and helium. The R-GDC was operated in low level of 10−3 mbar range. The partial pressure analysis showed that the R-GDC in the baking process is satisfactory and efficient and the outgassing rate is remarkably reduced. In addition to the R-GDC, the ICRH discharge cleaning under 1.5 T of the toroidal field is performed between plasma shots.