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 al so stiff, as predicted by electron temperature gradient turbulence with str eamers. Accordingly, the core and edge temperatures are proportional to eac h other and the plasma energy is proportional to the pedestal pressure for fixed density profiles. Density profiles are not stiff, and confinement imp roves with density peaking. Medium triangularity shapes (delta < 0.45) show strongly improved confinement up to the Greenwald density n(GW) and theref ore higher beta values, owing to increasing pedestal pressure, and H mode d ensity operation extends above n(GW). Density profile peaking at n(GW) was achieved with controlled gas puffing rates, and first results from a new hi gh field side pellet launcher allowing higher pellet velocities axe promisi ng. At these high densities, small type II ELMs provide good confinement wi th low divertor power loading. In advanced scenarios the highest performanc e 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 tear ing modes (NTMs) at low central magnetic shear (q(min) approximate to 1). T he T profiles axe still governed by ITG and trapped electron mode (TEM) tur bulence, and confinement is improved by density peaking connected with low magnetic shear. Ion internal transport barrier (ITB) discharges - mostly wi th 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 inte rnal and external ideal MHD modes. Turbulence driven transport is suppresse d, in agreement with the E x B shear flow paradigm, and core transport coef ficients are at the neoclassical ion transport level, where the latter was established by Monte Carlo simulations. Reactor relevant ion and electron I TBs with T-e approximate to T-i approximate to 10 keV were achieved by comb ining ion and electron heating with NBI and ECRH, respectively. In low curr ent discharges full non-inductive current drive was achieved in an integrat ed high performance H mode scenario, with (n) over bar (e) = n(GW), high be ta (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 curre nt drive fraction of > 80%. while counter-ECCD leads to negative central sh ear and formation of an electron ITB with T-e(0) > 12 keV. MHD phenomena, e specially fishbones, contribute to achieving quasi-stationary advanced disc harge conditions and trigger ITBs, which is attributed to poloidal E x B sh earing driven by redistribution of resonant fast particles. But MHD instabi lities also limit the operational regime of conventional (NTMs) and advance d (double tearing, infernal and external kink modes) scenarios. The onset b eta (N) for NTM is proportional to the normalized gyroradius rho*. Complete NTM stabilization was demonstrated at beta (N) = 2-5 using ECCD at the isl and position with 10% of the total heating power. MHD limits are expected t o 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 performan ce at higher delta 's and tungsten covering of the first wall is being exte nded on the basis, of the positive experience with tungsten on divertor and heat shield tiles.