Improved confinement with plasma profile and shape controls in JT-60U

New improved confinement regimes with reversed shear and high triangularity configurations have been exploited in JT-60U by optimizing the current profile and using shape control. The reversed shear regime was established with the formation of an internal transport barrier (ITB) and enhanced confinement for both ions and electrons. The stored energy was 8.2 MJ at Ip = 2.1 MA where an NB power of 15 MW was applied. The energy confinement time and QDT were 0.71 s and 0.41, respectively. The radial position of the ITB was as large as r/a ∼ 0.65. The ITB manifested in both temperature and density profiles was sustained in the radiative divertor condition. In addition, the reversed magnetic shear configuration has been sustained with LHCD for 7.5 s, which is encouraging for future steady-state operation. The effect of increased triangularity (δ) has also been intensively investigated, particularly regarding the improvement of confinement properties for the H-mode plasmas. The edge density and temperature at the onset of ELMs were improved by factor of 1.3-1.4 for δ ∼ 0.4 and 1.5-2.0 for δ ∼ 0.1. In a high triangularity discharge, a fully non-inductive current drive at 1 MA has been demonstrated for about 2 s in combination with a high bootstrap current and beam current drive fraction with βN ∼ 3, βp ∼ 3 and H = 2.25. A negative-ion-based neutral beam was successfully injected into plasmas for the first time in March 1996. The initial injection power was approximately 100 kW with an energy of 180 keV and D- beam current of 3.2 A. (author)