Overview of JT-60U Results toward Establishment of Advanced Tokamak Operation

Recent JT-60U experimental results toward establishment of advanced tokamak operation are reviewed with emphasis on the further expansion of the operational regime of AT plasmas using improved flexibility of NBIs by the modification of power supply and on the investigation of important issues for the establishment of steady-state AT operation using new diagnostics and improved heating systems. In PS plasma, high βNHH98(y,2) of 2.6 with βN ~ 2.6 and HH98(y,2) ~ 1 is sustained for 25 s significantly longer than the current diffusion time (~14τR) without NTMs. High G-factor (βNHH98(y,2)/q95) of 0.25 and high bootstrap current fraction (fBS) > 0.43 under the ITER-like small toroidal rotation condition is suitable for ITER hybrid operation scenario. In WS plasma, high βN ~ 2.8 exceeding the ideal MHD limit without conducting wall (βN) is sustained for ~5 s with RWM stabilization by a toroidal rotation at q = 2 surface. A combined external current drivers of negative-ion based NB and lower-hybrid waves together with high fBS of 0.5 could sustain whole plasma current of 0.8 MA for 2s (1.5τR). In RS plasma, high βN ~ 2.7 (βp ~ 2.3) exceeding βN with qmin ~ 2.4 (q95 ~ 5.3), HH98(y,2) ~ 1.7 and fBS ~ 0.9 was obtained with wall stabilization. Based on PS plasma for ITER hybrid operation scenario, the high βN of 2.1 with good thermal plasma confinement of HH98(y,2) > 0.85 was sustained for more than 10 s at⎯ne/nGW > 0.7 and frad > 0.77 using stored energy feedback system and radiation feedback system. Physics studies for AT plasmas, H-mode and pedestal physics, and studies on impurity transport, SOL/divertor plasmas and plasma wall interactions are also progressed. The active NTM stabilization system using modulated ECCD, which is synchronized to rotating island, has been developed and the efficiency of modulated ECCD in m/n = 2/1 NTM stabilization was demonstrated. The intrinsic toroidal rotation driven by the ion pressure gradient and the ECH has been confirmed and its direction is counter direction in both cases. The dedicated H-mode and pedestal experiments indicated two scalings, H-factor evaluated for the core plasma as H89core ∝ li and pedestal width scaling of Δped = 0.315aρpolβpol. New fast diagnostics with high spatial and temporal resolutions reveals the different structure of pedestal pressure between coand counter-rotating plasma, resulting different ELM size. The tungsten accumulation becomes more significant with increasing the toroidal rotation in the counter-direction.