PSI in fusion devices. Function and perspective of wall conditioning

Wall conditioning techniques for fusion wall surfaces are surveyed. Focused on the wall conditioning by low-Z film coating, its effect on the reduction of impurity and on the hydrogen recycling is described. Guidelines we suggested for uniform coating of the wall in boronization, which has been shown to aid in the suppression of the impurities in wall materials. The reduction of the oxygen impurity by low-Z film conditioning, such as boronization or lithium conditioning, is described. The reduction of the hydrogen retention by helium discharge conditioning is also mentioned. (author)