Engineering design in installation of fully covering ferritic inside wall on JFT-2M

In the JFT-2M tokamak, a low activation ferritic steel, which is a candidate material for a blanket of demo-reactor, has been introduced step by step to investigate the compatibility with plasma. The ferritic plates was installed to cover almost whole inside wall of the vacuum vessel (VV) as a simulate of the blanket wall (ferritic inside wall; FIW). The toroidal field ripple was decreased by adjusting the plate thickness distribution. Prior to the installation, electromagnetic force was calculated. Static force related to ferromagnetism was in the order of 1000 N for each segment (32 pieces in toroidal direction and 7 pieces in poloidal direction). The electromagnetic force is comparable to the static force. The support structure was decided based on this calculation. The most dangerous stress on the support was bending stress. Its maximum value was 170 MPa, which is 2/3 as large as allowable value of M12 bolt. The FIW was installed with a tolerance of a few mm. Tokamak discharges were obtained after the installation and no deteriorative effects have been observed up to now.