Bremen 2017 – wissenschaftliches Programm

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P: Fachverband Plasmaphysik

P 6: Helmholtz Graduate School I

P 6.10: Poster

Montag, 13. März 2017, 16:30–18:30, HS Foyer

Parametric Decay Instability during Collective Thomson Scattering on ASDEX Upgrade — •Søren Kjer Hansen1,2, Stefan Kragh Nielsen2, Alf Köhn1, Jörg Stober1, and The ASDEX Upgrade Team11Max-Planck-Institut für Plasmaphysik, D-85748 Garching bei München, Germany — 2Department of Physics, Technical University of Denmark, DK-2800 Kgs. Lyngby, Denmark

A parametric decay instability (PDI) is a three-wave interaction where a strong electromagnetic (pump) wave decays into two electrostatic daughter waves. The present work is motivated by observation of such a PDI during collective Thomson scattering (CTS) experiments at the ASDEX Upgrade (AUG) tokamak [Nielsen et al., 2016]. Similar behaviour has been observed during CTS experiments at the LHD stellarator [Kubo et al., 2016]. The PDI, which has been investigated at AUG, is one in which the X-mode pump wave decays into a high-frequency electron Bernstein wave and a low-frequency warm lower hybrid wave. We have obtained estimates of the gyrotron power necessary to excite the PDI and the frequency shift of the electron Bernstein wave relative to the pump wave [Hansen, 2016], generalising the earlier results of [Porkolab, 1982]. Applying these results to an AUG experiment (shot 28286) yielded a gyrotron power threshold well below the one used in the experiment and a frequency shift similar to the one observed, thus validating the existence of a PDI.

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