Studies of improved confinement in JFT-2M

Miura, Yukitoshi; Mori, Masahiro; Shoji, Teruaki; Matsumoto, Hiroshi; Kamiya, Kensaku; Ida, Katsumi*; Kasai, Satoshi*

The improved modes observed in JFT-2M are characterized by the two improvements, i.e. one is the H-mode at the edge, and other modes are core improvement with peaked profiles near the center. The improvement of the pellet injected H-mode was a combination of H-mode and the core improvement. The discovery of limiter H-mode had an impact on the physics understanding of the H-mode and showed the formation of transport barrier at a place without discontinuity of the magnetic field line topology. The appearance of ELMs by applying ergodic fields was investigated and it was clarified that n4 helical components were effective to produce ELMs. A SOL biasing had effects to compress neutrals at divertor region. It would be understood that the compressed neutrals at divertor region might make a situation of low L/H threshold power. High recycling steady (HRS) H-mode could be reproducibly obtained by boronization. It was found that HRS appears at the pedestal collisionality greater than 1.