Behavior of high Z impurities and its impact on core plasmas

Since the 10th PSI conference in 1992, studies on high Z impurity behavior have been restarted in tokamaks such as TEXTOR, ASDEX-Upgrade, FTU, Alcator C-Mod, DIII-D. According to these experimental studies, it has been found that destructive impact of radiation loss due to high Z impurities can be seen only in limited cases, which suggests that rather wide operation regimes including H-modes could be compatible with the high Z plasma facing components (PFC). Impurity transport and atomic processes of highly charged ions are playing key roles in the core plasma. Compatibility of high Z PFC with 'radiative divertor' is new concern, which should be investigated more quantitatively. Number of efforts have been made to evaluate deuterium retention on tungsten samples, of which some recent results are reported. A viewpoint for the long term research and development for high Z PFC is briefly discussed. (author)