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Oct 13 – 18, 2014
Hotel Park Inn Pribaltiyskaya
Europe/Moscow timezone

Experimental Quantification of the Impact of Large and Small Scale Instabilities on Confined Fast Ions in ASDEX Upgrade

Oct 14, 2014, 8:30 AM
4h
Green 8-9 (Hotel Park Inn Pribaltiyskaya)

Green 8-9

Hotel Park Inn Pribaltiyskaya

Saint Petersburg, Russian Federation
Poster Poster 1

Speaker

Dr Benedikt Geiger (Max-Planck-Institut für Plasmaphysik, Garching, Germany)

Description

The transport of fast, suprathermal ions as generated by neutral beam injection (NBI) is an important topic in fusion research. In unperturbed plasmas the fast-ion transport is expected to be neoclassical, i.e. dominated by collisions, while an anomalous transport is observed in the presence of instabilities. This anomalous fast-ion redistribution must be investigated in detail because it may limit the heating and current drive performance in future fusion devices and could even damage the first wall. At the ASDEX Upgrade tokamak, fast ions are generated by up to 8 different NBI sources and their distribution function can be measured by a comprehensive set of diagnostics: A multi-view fast-ion D-alpha (FIDA) spectroscopy diagnostic, neutral particle analyzers, neutron measurements and fast-ion loss detectors (FILD) permit studies in velocity space and real space. A reduction of the central fast-ion density of up to 50% has been measured in experiments with strong sawtooth activity. Outside the q=1 surface, a corresponding increase is observed while the FILDs show no significant fast-ion redistribution to unconfined orbits. Simulations that assume flux aligned transport can explain the radial shape of this measured internal fast-ion redistribution well, but they underestimate its magnitude which could be explained by ExB drifts. Measurements during strong activity of reversed shear Alfvén eigenmodes (RSAE) show significant differences to neoclassical predictions. The observed radial fast-ion profiles are strongly flattened and broadened compared to the predictions. Non-linear simulations of the RSAE-induced fast-ion transport using the HAGIS/LIGKA code will be compared with the experimental data. In MHD-quiescent plasmas, a clear change of the radial fast-ion profiles is measured when replacing on-axis NBI with off-axis NBI. Neoclassical predictions are in very good agreement with this observation while simulations that assume an anomalous transport of 0.5m2/s do not fit the experimental data. This is, however, in contradiction with previous off-axis NBI current drive experiments that related the absence of a measurable fast-ion driven current to a turbulence-induced fast-ion redistribution. New off-axis NBI current drive experiments are, hence, being conducted to resolve this contradiction and the results of this investigation will be discussed.
Paper Number EX/P1-20
Country or International Organisation Germany

Primary author

Dr Benedikt Geiger (Max-Planck-Institut für Plasmaphysik, Garching, Germany)

Co-authors

Dr Christian Hopf (Max-Planck-Institut für Plasmaphysik, Garching, Germany) Dr Francois Ryter (IPP-Garching) Dr Giovanni Tardini (Max-Planck-Institiut für Plasmaphysik, Garching, Germany) Dr Ivo Classen (FOM institute DIFFER) Dr Manuel Garcia-Munoz (Max-Planck Institute for Plasma Physics) Mr Markus Weiland (Max-Planck-Institut für Plasmaphysik, Garching, Germany) Dr Matthias Reich (Max-Planck-Institut für Plasmaphysik, Garching, Germany) Dr Mirjam Schneller (Max-Planck-Institiut für Plasmaphysik, Garching, Germany) Dr Mirko Salewski (Technical University of Denmark) Philip A. Schneider (Max-Planck-Institiut für Plasmaphysik) Dr Philipp Lauber (Max-Planck-Institut für Plasmaphysik) Dr Stefan Nielsen (Technical University of Denmark, Department of Physics, Dk-2800 Kgs. Lyngby, Denmark)

Presentation materials