Investigation of compatibility of low activation ferritic steel with high performance plasma by full covering of inside vacuum vessel wall on JFT-2M

Low activation ferritic steel plates were installed in the JFT-2M tokamak to fully cover the inside wall of the vacuum vessel (ferritic inside wall; FIW) as a simulation of the blanket wall of the fusion demonstration reactor. After the physics and engineering design concerns with the ripple reduction, the electro-magnetic force and so on, FIW was installed with a tolerance of a few mm. The ripple reduction was confirmed from the detailed measurement. Tokamak discharges were obtained without changing control system, as predicted theoretically. The reduction of ripple loss of fast ions was clearly demonstrated by both experiments and calculations. Compatibility of FIW with high normalized beta plasma up to 3.3 was demonstrated at relatively far wall position. Preliminary investigation showed that the slowdown of the growth rate occurred with closer wall position, which presumably corresponds to wall stabilization effect.