Overview of ASDEX Upgrade Results

Full text: The ASDEX Upgrade programme is directed towards physics input to critical elements of the ITER design and the preparation of ITER operation, as well as addressing physics issues foreseen for a future DEMO design. After the finalization of the tungsten coating of the plasma facing components, re-availability of all flywheel-generators allowed high-power operation with up to 20 MW heating power. Implementation of alternative ECRH schemes (140 GHz O2- and 105 GHz X3-mode) facilitated central heating above ne = 1.2x1020 m-3 and low q95 operation at Bt = 1.7 T. ECRH O2-heating was used to maintain low central tungsten concentrations in high P/R discharges with 20 MW total heating power and divertor load control with nitrogen seeding. Improved energy confinement is obtained with nitrogen seeding both for type-I and type III ELMy conditions. The main contributor are increased plasma temperatures both in the core and at the pedestal, no changes of the density profile have been observed. Fast ion losses induced by shear Alfven eigenmodes have been investigated by time-resolved energy and pitch angle measurements. While single Alfven cascades (AC) and toroidal Alfven eigenmodes (TAE) eject resonant fast ions in a convective process, the overlapping of AC and TAE spatial structures was found to lead to a large fast ion diffusion and loss. Doppler reflectometry studies at the L-H transition allowed the disentanglement of the interplay between the oscillatory geodesic acoustic modes (GAMs), turbulent fluctuations and the mean equilibrium E x B flow in the edge negative Er well region just inside the separatrix. The transition of the GAM into low frequency fluctuations is a candidate for the long sought-after trigger for the E x B velocity feedback loop believed to be responsible for the L-H transition. Further improvements of the pedestal diagnostics including the application of integrated data analysis techniques revealed a refined picture of density and temperature profile evolution during an ELM cycle. Different time scales for the recovery of Te and ne gradients after an ELM crash were identified, finally the gradients evolve into a highly fluctuating phase. Currently, the first set of in-vessel coils for ELM control is being installed in ASDEX Upgrade, and first results will be reported if available. (author)