Publications in Scientific Journals:

U. Stroth, M. Willensdorfer, E. Wolfrum et al.:
"Overview of ASDEX Upgrade results";
Nuclear Fusion, 53 (2013), 1040031 - 1040039.

English abstract:
The medium size divertor tokamakASDEXUpgrade (major and minor radii 1.65mand 0.5 m, respectively, magneticfield
strength 2.5 T) possesses flexible shaping and versatile heating and current drive systems. Recently the technical
capabilities were extended by increasing the electron cyclotron resonance heating (ECRH) power, by installing 28
internal magnetic perturbation coils, and by improving the ion cyclotron range of frequency compatibility with the
tungsten wall. With the perturbation coils, reliable suppression of large type-I edge localized modes (ELMs) could
be demonstrated in a wide operational window, which opens up above a critical plasma pedestal density. The
pellet fuelling efficiency was observed to increase which gives access to H-mode discharges with peaked density
profiles at line densities clearly exceeding the empirical Greenwald limit. Owing to the increased ECRH power
of 4MW, H-mode discharges could be studied in regimes with dominant electron heating and low plasma rotation
velocities, i.e. under conditions particularly relevant for ITER. The ion-pressure gradient and the neoclassical radial
electric field emerge as key parameters for the transition. Using the total simultaneously available heating power of
23MW, high performance discharges have been carried out where feed-back controlled radiative cooling in the core
and the divertor allowed the divertor peak power loads to be maintained below 5MWm−2. Under attached divertor
conditions, a multi-device scaling expression for the power-decay lengthwas obtained which is independent of major
radius and decreases with magnetic field resulting in a decay length of 1mm for ITER. At higher densities and under
partially detached conditions, however, a broadening of the decay length is observed. In discharges with density
ramps up to the density limit, the divertor plasma shows a complex behaviour with a localized high-density region in
the inner divertor before the outer divertor detaches. Turbulent transport is studied in the core and the scrape-off layer
(SOL). Discharges over a wide parameter range exhibit a close link between core momentum and density transport.
Consistent with gyro-kinetic calculations, the density gradient at half plasma radius determines the momentum
transport through residual stress and thus the central toroidal rotation. In the SOL a close comparison of probe
data with a gyro-fluid code showed excellent agreement and points to the dominance of drift waves. Intermittent
structures from ELMs and from turbulence are shown to have high ion temperatures even at large distances outside
the separatrix.

Created from the Publication Database of the Vienna University of Technology.