OVERVIEW OF THE RECENT EXPERIMENTAL RESULTS IN JT-60 AND JFT-2M

The recent experimental results on H-mode in JT-60U and JFT-2M are reported. The enhanced confinement mode with the edge transport barrier (H-mode) in JT-60U is characterized by the high edge ion temperature. The confinement improvement is well correlated with the edge ion temperature. The H-mode at low magnetic field (approximately 2 T) in JT-60U has similar feature to the H-mode in JFT-2M: rapid reduction of D(alpha) emission. However, in the H-mode at high magnetic field (approximately 4 T) and at low density, no clear transition is observed in JT-60U, although the confinement is still improved with the edge transport barrier. Collisionality and the width of the transport barrier are also investigated in both tokamaks, and are compared with Shaing's theory. Improvement of the high-betap mode discharge with the H-transition was demonstrated in JT-60U. Owing to this improvement, the record value of the fusion triple product (1.1x10(21) m-3 s keV ) has been achieved. Quasi-steady H-mode operation with H-factor of approximately 1.8 has been also demonstrated in JT-60U by controlling the repetition rate of edge localized modes (ELMs). In JFT-2M, ELM activity has been successfully induced by a new and active method using helical magnetic field perturbation, and as a result, steady H-mode has been achieved.