Overview of ASDEX upgrade results

Ion and electron temperature profiles in conventional L and H mode on ASDEX Upgrade are generally stiff and limited by a critical temperature gradient length delT/T as given by ion temperature gradient (ITG) driven turbulence. ECRH experiments indicate that electron temperature (T-e) profiles are also stiff, as predicted by electron temperature gradient turbulence with streamers. Accordingly, the core and edge temperatures are proportional to each other and the plasma energy is proportional to the pedestal pressure for fixed density profiles. Density profiles are not stiff, and confinement improves with density peaking. Medium triangularity shapes (delta < 0.45) show strongly improved confinement up to the Greenwald density n(GW) and therefore higher beta values, owing to increasing pedestal pressure, and H mode density operation extends above n(GW). Density profile peaking at n(GW) was achieved with controlled gas puffing rates, and first results from a new high field side pellet launcher allowing higher pellet velocities axe promising. At these high densities, small type II ELMs provide good confinement with low divertor power loading. In advanced scenarios the highest performance was achieved in the improved H mode with H(L-89P)beta (N) approximate to 7.2 at delta = 0.3 for five confinement times, limited by neoclassical tearing modes (NTMs) at low central magnetic shear (q(min) approximate to 1). The T profiles axe still governed by ITG and trapped electron mode (TEM) turbulence, and confinement is improved by density peaking connected with low magnetic shear. Ion internal transport barrier (ITB) discharges - mostly with reversed shear (q(min) > 1) and L mode edge achieved HL-89P less than or equal to 2.1 and are limited to beta (N) less than or equal to 1.7 by internal and external ideal MHD modes. Turbulence driven transport is suppressed, in agreement with the E x B shear flow paradigm, and core transport coefficients are at the neoclassical ion transport level, where the latter was established by Monte Carlo simulations. Reactor relevant ion and electron ITBs with T-e approximate to T-i approximate to 10 keV were achieved by combining ion and electron heating with NBI and ECRH, respectively. In low current discharges full non-inductive current drive was achieved in an integrated high performance H mode scenario, with (n) over bar (e) = n(GW), high beta (p) = 3.1, beta (N) = 2.8 and HL-89P = 1.8, which developed ITBs with q(min) approximate to 1. Central co-ECCD at low densities allows a high current drive fraction of > 80%. while counter-ECCD leads to negative central shear and formation of an electron ITB with T-e(0) > 12 keV. MHD phenomena, especially fishbones, contribute to achieving quasi-stationary advanced discharge conditions and trigger ITBs, which is attributed to poloidal E x B shearing driven by redistribution of resonant fast particles. But MHD instabilities also limit the operational regime of conventional (NTMs) and advanced (double tearing, infernal and external kink modes) scenarios. The onset beta (N) for NTM is proportional to the normalized gyroradius rho*. Complete NTM stabilization was demonstrated at beta (N) = 2-5 using ECCD at the island position with 10% of the total heating power. MHD limits are expected to be extended using current profile control by off-axis current drive from more tangential NBI combined with ECCD and wall stabilization. Presently, the ASDEX Upgrade divertor is being adapted ta optimal performance at higher delta 's and tungsten covering of the first wall is being extended on the basis, of the positive experience with tungsten on divertor and heat shield tiles.