Ripple reduction and surface coating tests with ferritic steel on JFT-2M

Applicability of the low-activation ferritic steel (F82H), which is one of the candidate materials for next generation fusion devices, has been tested in JFT-2M. Ferritic steel boards (FB) were installed between toroidal field coils (TFC) and the vacuum vessel at all toroidal sections. The experiment and the calculation show that the ripple amplitude decreases from 2.2% to 1.1% by the FB installation at R=1.6 m. The ripple reduction results in the reduction of fast ion loss and in the shift of the ripple loss to the outer region. No undesirable effect to the energy confinement and the plasma control was observed. The FB will be installed inside the vacuum vessel in the near future. In preparation, surface coating tests, mainly concerning with an in situ boron coating, are carried out.