Confinement and beta limit in JT-60U high-βp regime

High-βp regime is becoming a new paradigm of tokamak reactor development, since it has the potential of significantly enhancing the economical attractiveness in a tokamak fusion reactor. The eventual goal of this regime is to maintain a high pressure plasma in a steady state with highly enhanced confinement and stability under a large fraction of bootstrap current. As the pressure and current profiles can strongly be coupled together due to the bootstrap effects, profile optimization is a key issue to make such an advanced tokamak scenario feasible. A centrally peaked profile of the plasma pressure can minimize the plasma energy for a given fusion power output and maintain a large, useful bootstrap current component. Such a peaked profile mode, which was named 'high-βp mode', has been consistently obtained with near-perpendicular neutral beam injection (NBI) in JT-60U high βp regime, where density peaking factors ne(0)/ greater than 3 have been achieved. The combination of the peaked profiles with H-mode characteristics at the edge of the plasma, which was named 'high-βp H-mode', has been recently realized in controlling the edge recycling by the divertor action and boronization of the first wall. The combination of the two improved confinement modes responsible for the core and edge plasmas allows the local pressure gradients to be so moderate that the beta limits can be improved. In the high-βp regime, thus, fusion triple product of 1.1x1021 m-3skeV, neutron rates from DD reactions up to 5.6x1016 /s, peak ion temperature of 40 keV, and energy confinement times up to 3.6 times the predictions of L-mode scaling have been achieved with deuterium NBI powers up to 34 MW. This paper describes the confinement and stability properties achieved with the combined confinement improvement in the JT-60U high-βp regime. (author) 7 refs., 7 figs