München 2019 – wissenschaftliches Programm

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P: Fachverband Plasmaphysik

P 17: Helmholtz Graduate School VI

P 17.5: Vortrag

Donnerstag, 21. März 2019, 15:50–16:15, HS 17

Parametric Decay Instabilities in the Electron Cyclotron Resonance Heating Beams at ASDEX Upgrade — •Søren Kjer Hansen1,2, Stefan Kragh Nielsen2, Jörg Stober1, Jesper Rasmussen2, Mirko Salewski2, Morten Stejner2, and the ASDEX Upgrade Team31Max-Planck-Institut für Plasmaphysik, D-85748 Garching b. München, Germany — 2Department of Physics, Technical University of Denmark, DK-2800 Kgs. Lyngby, Denmark — 3See Appendix in Nucl. Fusion 57, 102015 (2017)

In a parametric decay instability (PDI), a large-amplitude pump wave decays to two daughter waves once its amplitude exceeds a nonlinear threshold. PDIs determine the limit of validity of linear theories in quadratically nonlinear media, such as fluids and plasmas. Here, we consider PDIs occurring in connection with injection of high-power mm-waves for electron cyclotron resonance heating (ECRH) of the fusion-relevant plasmas at the ASDEX Upgrade tokamak. We particularly investigate PDIs near the fundamental and second-harmonic upper hybrid resonance (UHR). Near the UHR strong field enhancement leads to the PDI threshold being exceeded at typical ECRH power levels. We have experimentally confirmed theoretical predictions of the PDI threshold and characterised the nonlinear response beyond the threshold for these PDIs. Near the second-harmonic UHR trapping of the daughter waves is required to reduce the PDI threshold to a level accessible with ECRH; this may occur near a local maximum of the electron density. We have investigated such PDIs near the plasma centre, in connection with edge localised modes, and in magnetic islands.

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