18th IAEA Fusion Energy Conference

Demonstration of Ripple Reduction by Ferritic Steel Board Insertion in JFT-2M

H. Kawashima¹⁾, M. Sato¹⁾, K. Tsuzuki¹⁾, Y. Miura¹⁾, N. Isei¹⁾, H. Kimura¹⁾, T. Nakayama²⁾, M. Abe²⁾, D.S. Darrow³⁾, and JFT-2M GROUP¹⁾
1) Japan Atomic Energy Research Institute, Tokai, Naka, Ibaraki Japan
2) Hitachi Ltd., Hitachi, Ibaraki Japan
3) Princeton Plasma Physics Laboratory, Princeton, New Jersey U.S.A

Abstract.
In the JFT-2M tokamak, application testing of low activation ferritic steel to plasma has been investigated, (so called Advanced Material Tokamak Experiment (AMTEX) program). In the first stage, toroidal field ripple reduction was examined by ferritic steel boards (FBs) insertion between toroidal field coils and vacuum vessel. It is demonstrated that the FB insertion reduced the toroidal field ripple and the losses of fast ions produced by tangential co-NBI. By optimizing the FB thickness, such that the fundamental mode ripple is minimized to be 0.07% at the shoulder part, the ripple-trapped loss is reduced to be almost negligible. It is determined that the reductions of the fundamental mode ripple and the ripple banana diffusion coefficient at the shoulder part are most effective to reduce the ripple ion losses. Ripple loss reduction by FBs is also confirmed with the perpendicular beam injection. The FB insertion gives no undesirable effect on the plasma production and control.