Hannover 2020 – wissenschaftliches Programm
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P: Fachverband Plasmaphysik
P 10: Poster Session 2
P 10.4: Poster
Dienstag, 10. März 2020, 16:30–18:30, Empore Lichthof
Observation of Alfvénic mode activity at the Wendelstein 7- X stellarator — •Kian Rahbarnia1, Torsten Bluhm1, Matthias Borchardt1, Bernardo B Carvalho2, Ralf Kleiber1, Axel Könies1, Sara Mendes1, Jonathan Schilling1, Christoph Slaby1, Henning Thomsen1, Manfred Zilker1, and Wendelstein 7-X1 — 1Max Planck Institute for Plasma Physics, Wendelsteinstr. 1, 17491 Greifswald, Germany — 2Instituto de Plasmas e Fusao Nuclear Instituto Superior Tecnico, Lisbon, Portugal
During the last divertor campaign at the Wendelstein 7-X stellarator (Greifswald, Germany) no dedicated experiments have been carried out to investigate the excitation mechanism of Alfvén eigenmodes (AE) in the plasma. Nevertheless fairly independent from magnetic configuration and heating scenario (electron cyclotron resonance heating and/or neutral beam injection) broadband fluctuations around 200 kHz have been observed by the Mirnov diagnostic. A complete amplitude and phase calibration of the in total 125 individual probes including all relevant data acquisition system components allows a detailed spectral and mode analysis, using damped multiple signal classification (DMUSIC) and stochastic system identification techniques (SSI). The results are compared with theoretically predicted Alfvén continua calculated with the 3D-MHD continuum code CONTI. The nature of these fluctuations is most likely associated with ellipticity-induced Alfvén eigenmodes in the outer regions of the plasma. The role of density and temperature profiles, as well as iota profiles and Doppler shift effects due to electric fields at the plasma edge are investigated.