Formation of Internal Transport Barriers and Lts Lmpact on the Jt-60u Plasmas Ide Shunsuke+ and the Jt-60 Team

Formation of internal transport barriers (ITBs) in a plasma is a key to access to improved confinement. In JT-60U, there are two types of plasmas which are accompanied with ITB. One is a high Bo plasma and the other one is a reversed magnetic shear (RS) plasma. In RS plasmas, interesting features can be seen in spatial profiles of plasma parameters. For example, the location of the ITB can be strongly related to the location where the safety factor (4) becomes minimum, and the radial electric field (8,) has strong spatial variation at the ITB. These features can be related to the physics mechanisms of confinement improvement at the ITB. On JT-60U RS plasmas, experiments to modify the toroidal current density or the toroidal rotation profiles, which are expected to influence the ITB structure directly or indirectly, have been carried out. And these modifications were fond to cause chanses in the ITB structure. The results are shown in this paper.