Speaker
Dr
Joerg Stober
(IPP Garching)
Description
Since 2007 the tokamak ASDEX Upgrade (AUG) successfully operates with fully W-coated
plasma facing components. Operation in this environment is facilitated using high levels of
deuterium puff to minimize W erosion of the out-board limiters by ELMs and by seeding impurities
in order to control divertor temperature at a low level to protect especially the W-coatings
of graphite tiles. These measures effectively mitigate W erosion and accumulation, but are
incompatible with operation at collisionalities low enough to obtain significant global current
drive with the available means, i.e. NBCD and ECCD at high power levels. As a consequence
advanced tokamak studies relying on the modification of current profiles by external current
drive made poor progress in the first years following full W coverage. Additionally, polarized
reflections of Halpha-light from W-coated surfaces distort the current profile measurement based
on the Motional Stark Effect, as it turned out several years later. This contribution reports on
how these multiple operational restrictions have been overcome in AUG with a variety of measures
including optimization of shape and gas puff timing, change to a full-W divertor with
better pumping and optimization of the heating schemes. In parallel current profile diagnostics
have been significantly improved, including polarimetry. Equilibrium reconstruction has been
included into the concept of integrated data analysis, allowing a direct analysis of the influence
of stochastic and systematic errors in the data on the estimated current profiles. Improved
H-mode operation at moderate collisionality could be recoverd and studies of H-modes with
centrally elevated q-profiles could be successfully extended making use of the extended ECRH
capapilities. A non-inductive scenario at q95 = 5.5 could be obtained, which does not depend
on q-profile tayloring during the current ramp-up phase and its successive diffusion. These high
beta plasmas are also compared to results with the TGLF modell.
| Country or International Organization | Germany |
|---|
Primary author
Dr
Joerg Stober
(IPP Garching)
Co-authors
Dr
Albrecht Herrmann
(Max-Planck_Institut für Plasmaphysik, Garching, Germany)
Dr
Alexander Bock
(Max-Planck-Institut für Plasmaphysik)
Dr
Alexander Mlynek
(Max-Planck-Institut für Plasmaphysik)
Dr
Arne Kallenbach
(Max-Planck-Institut f. Plasmaphysik)
Dr
Christian Hopf
(Max-Planck-Institut für Plasmaphysik)
Dr
Clemente Angioni
(Max-Planck-Institut fuer Plasmaphysik, EURATOM Association, D-85748 Garching, Germany)
Mr
David Rittich
(Max-Planck-Institut für Plasmaphysik)
Dr
Dietmar Wagner
(Max-Planck-Institut für Plasmaphysik)
Dr
Emiliano Fable
(Max-Planck-Institut für Plasmaphysik)
Prof.
Hartmut Zohm
(Max-Planck-Institut für Plasmaphysik)
Dr
Jörg Hobirk
(Max-Planck-Institut für Plasmaphysik)
Dr
Martin Schubert
(Max-Planck-Institut für Plasmaphysik)
Dr
Matthias Reich
(Max-Planck-Institut für Plasmaphysik, Garching, Germany)
Dr
Rainer Fischer
(Max-Planck-Institut für Plasmaphysik)
Prof.
Rudolf Neu
(Max-Planck-Institut für Plasmaphysik)
Dr
Thomas Pütterich
(Max-Planck-Institut für Plasmaphysik)
