Recent results in JT-60 experiments

Emphases in recent JT-60 experiments are placed on 1) lower-hybrid (LH) current drive characteristics with a multi-junction type launcher and 2) the confinement study with combination of neutral beam injection, LH current drive and pellet injection. The current drive efficiency and the radial distribution of high energy electron production show clear correlation with injected N||; the current drive efficiency has the maximum at low N||(∼1.3) while flattening of plasma current is more effective in large N||. A broad radial distribution of high energy electron current and ∼30% reduction in sawtooth inversion radius were obtained by high N|| (∼2.5) LH injection. In order to fully suppress the sawtooth activity, low N|| (∼1.3) injection was found to be more effective. Improved energy confinement has been obtained with hydrogen pellet injection. Energy confinement time was enhanced up to 40% relative to usual gas fuelled discharges. When large, (3mm,4mm) and fast (2.2km/s) pellets were injected, 30% energy confinement improvement was obtained even during the NB heating of 14MW. Further investigations of improved divertor confinement (IDC) characteristics have been made. Most of the IDC characteristics are totally different from that of H-mode, although there are some similarities i.e., gas puff degrades the confinement, both have the same favorable BT direction. (author)