TRANSPORT AND STABILITY IN SUSTAINED HIGH q_min, HIGH β_N DISCHARGES ON DIII-D

Abstract To address the needs for a fusion pilot plan design, DIII-D/EAST joint experiments on DIII-D have demonstrated high normalized beta βN~4.2, toroidal beta βT~3.3% with qmin>2, q95≤8 sustained for more than six energy confinement times in poloidal beta regime. The excellent energy confinement quality (H98y2~1.8) is achieved with an internal transport barrier (ITB) at high line-averaged Greenwald density fraction fGr > 0.9. Gyrofluid (TGLF) modeling of the transport characteristics shows that the beam-driven rotation does not play an important role in the high confinement quality. The modeling also captures very well several transport features, giving us confidence in using integrated modeling to project these experimental results to future machines. The high-performance phase is terminated by fast-growing modes triggered near the n=1 ideal-wall kink stability limit. New RF capabilities for off-axis current drive could remove the residual ohmic current to achieve a fully non-inductive state, and improve the mode-wall coupling to increase the ideal-wall βN limit, enabling sustainment of the fully non-inductive high performance plasma in stationary conditions.