Design and first experimental results of toroidal field ripple reduction using ferritic insertion in JFT-2M

In order to test the effect of the toroidal field ripple on the fast ion losses, ferritic steel boards were inserted between the vacuum vessel and the toroidal field coil in the JFT-2M tokamak. The experimental and computational results show that the ripple amplitude is reduced from 2.2 to 1.1%. The ion losses are monitored from the increase in the wall temperature measured by the infrared TV. The region of the ripple trapped ion losses moves to outer side by about 6 cm and the increment of the wall temperature due to the ion loss of ripple trapped and banana drift is reduced. The ripple loss of the fast ions is reduced by ferritic steel insertion for the first time in the world. No deleterious effect of the ferritic insertion on plasma production and plasma control has been observed so far.