Stationary high confinement plasmas with large bootstrap current fraction in JT-60U

摘要

This paper reports the results of the progress in stationary discharges with a large bootstrap current fraction in JT-60U towards steady-state tokamak operation. In the weak shear plasma regime, high-β_P ELMy H-mode discharges have been optimized under nearly full non-inductive current drive conditions by the large bootstrap current fraction (f_(BS) ～ 45%) and the beam driven current fraction (f_(BD) ～ 50%), which was sustained for 5.8 s in the stationary condition. This duration corresponds to ～26τ_E and ～2.8τ_R, which was limited by the pulse length of negative-ion-based neutral beams. The high confinement enhancement factor H_(89) ～ 2.2 (HH_(98y2) ～ 1.0) was obtained and the profiles of current and pressure reached the stationary condition. In the reversed shear plasma regime, a large bootstrap current fraction (f_(BS) ～ 75%) has been sustained for 7.4 s under nearly full non-inductive current drive conditions. This duration corresponds to ～16τ_E and ～2.7τ_R. The high confinement enhancement factor H_(89) ～ 3.0 (HH_(98y2) ～ 1.7) was also sustained, and the profiles of current and pressure reached the stationary condition. The large bootstrap current and the off-axis beam driven current sustained this reversed q profile. This duration was limited only by the duration of the neutral beam injection.