Formation and sustainment of ITBs under various heating schemes in JT-60U

Toward the study of steady-state operation of fusion plasma, it is important to assess the confinement characteristics under a condition in which fractional power of electron heating is dominant to the total heating power. In a fusion plasma electron heating by α particles is dominant. Especially, the influence on the internal transport barrier (ITB) is an important issue, since formation of ITB is a key issue in advanced steady-state operation from a viewpoint of both attaining highly improved confinement and larger bootstrap current fraction to the total current. In JT-60U, the influence on ITBs when fractional power of electron heating to the total power is increased has been investigated by using negative-ion based neutral beam injection and electron cyclotron range of frequency (ECRF). It is found that in a reversed magnetic shear plasma of high confinement improvement, still higher over all confinement can be achieved at electron heating powers of 50-60% to the total absorbed power. Reduction of the ion temperature at ECRF injection is observed in an ITB plasma of positive shear. And with intense electron central heating on lower hybrid current drive plasma, high central electron temperature with ITB has been formed.