Toward the study of steady-state operation of fusion plasma, it isimportant to assess the confinement characteristics under a condition inwhich fractional power of electron heating is dominant to the totalheating power. In a fusion plasma electron heating by αparticles is dominant. Especially, the influence on the internaltransport barrier (ITB) is an important issue, since formation of ITB isa key issue in advanced steady-state operation from a viewpoint of bothattaining highly improved confinement and larger bootstrap currentfraction to the total current. In JT-60U, the influence on ITBs whenfractional power of electron heating to the total power is increased hasbeen investigated by using negative-ion based neutral beam injectionand electron cyclotron range of frequency (ECRF). It is foundthat in a reversed magnetic shear plasma of high confinementimprovement, still higher over all confinement can be achieved at electronheating powers of 50-60% to the total absorbed power. Reduction ofthe ion temperature at ECRF injection is observed in an ITB plasma ofpositive shear. And with intense electron central heating on lowerhybrid current drive plasma, high central electron temperature with ITBhas been formed.
Simultaneous heating by high power lower hybrid waves and neutral beams in the JT-60 tokamak