Stationary advanced scenarios with internal transport barrier on ASDEX Upgrade

Steady-state discharges with improved core confinement and H-mode edge with edge localized modes (ELMs) are investigated. In plasmas with an upper triangularity top close to zero an H -factor of H ITER89-P = 2.7 and N = 2.2 could be maintained for 1 s and H ITER89-P = 2.4 and N = 2.0 for 6 s, the latter corresponding to 40 confinement times or 2 1/2 resistive time scales for current redistribution, only limited by the duration of the possible discharge length. At a line averaged density of 4 × 10 19 m -3 the central temperatures reach values of T i = 10 keV and T e = 6.5 keV. The stationarity of the current profile is explained by magnetic reconnection driven by strong ( m = 1, n = 1) fishbones, which, in the absence of sawteeth, also expel energy and impurities. Further increasing the pressure, is limited by neoclassical tearing modes. Raising the density by edge gas fuelling and the simultaneous increase of the neutral beam power, H ITER 89- P remained unchanged up to n e = 5.5 × 10 19 m -3 , accompanied by a substantial reduction of Z eff . Increasing top to 0.2, both confinement and -limit improved reaching values of H ITER 89- P = 3.0 and N = 2.4 at densities above n e = 5 × 10 19 m -3 . This resulted in the highest fusion product of n D ,0 T i ,0 E = 0.9 × 10 20 keV s m -3 so far observed in ASDEX Upgrade.