Progress in the optimization of wall conditioning techniques for the reliable operation of KSTAR plasmas

KSTAR has developed various kinds of wall conditioning techniques to maintain reliable vacuum environment since its first operation in 2008. Some of them have been applied to recover the vacuum condition immediately after abnormal events that halts the plasma experiment temporarily by deteriorating the vacuum condition. We have selectively chosen appropriate wall conditioning procedures regarding the degree of influence of the event. In this paper, various events we have experienced during more than 10-year KSTAR operation are categorized according to the degree of impact on the vacuum environment.We verified that the initial baking was successfully performed for the long vent of the vacuum vessel, and the effective recovery process of vacuum environment for KSTAR plasma operation very well overcomes against several vacuum interrupt by using the soft-baking and glow discharge cleaning.Various kinds of wall conditioning techniques have been developed in KSTAR to maintain reliable vacuum environment since its first operation in 2008. Some of them have been applied to recover the vacuum condition immediately after abnormal events that halts the plasma experiment temporarily by deteriorating the vacuum condition. We have selectively chosen appropriate wall conditioning procedures regarding the degree of influ-ence of the event. In this paper, various events we have experienced during more than 10-year KSTAR operation are categorized according to the degree of impact on the vacuum environment. The wall recovery procedures applied to some events are described in detail. Assessment of the result of wall recovery procedure in terms of the plasma start-up quality is also introduced.