Hannover 2020 – scientific programme

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P: Fachverband Plasmaphysik

P 5: Poster Session 1

P 5.14: Poster

Monday, March 9, 2020, 16:30–18:30, Empore Lichthof

Low frequency fluctuations measured by soft X-ray and Mirnov diagnostic at the Wendelstein 7-X stellarator — •Sara Mendes, Christian Brandt, Kian Rahbarnia, Jonathan Schilling, Henning Thomsen, and Wendelstein 7-X Team — Max-Planck-Institute for Plasma Physics, Wendelsteinstr. 1, 17491 Greifswald, Germany

During the last divertor campaign at the Wendelstein 7-X (W7-X) stellarator fluctuations starting at a few kHz up to about 400 kHz have been observed by various diagnostics. Predominantly lower frequency components (<100 kHz) were found in the soft X-ray (SXR) intensities detected by the SXR tomography system XMCTS, a poloidal camera array with 360 lines-of-sight. Similar and slightly higher magnetic broadband fluctuations have been measured by the Mirnov diagnostic, which consists of 125 individual coils located in four out of five modules of W7-X. Part of the observed frequencies fit well into theoretically predicted gaps in corresponding Alfvén continua, but to ensure a precise analysis of the underlaying mode structures, a complete amplitude and phase calibration including all relevant data acquisition components is necessary, as it is performed for the Mirnov diagnostic. The nature of the observed mode activity specifically for the lower frequency components is discussed.