Speaker
Description
See full abstract here
http://ocs.ciemat.es/EPS2019ABS/pdf/P2.1068.pdf
Low frequency edge fluctuations, localized near the last closed flux surface, which show discrete losses of stored energy with each event, are seen especially clearly in specific magnetic configurations in Wendelstein 7-X. While these are certainly ELM-likea, the questions of the cause of these fluctuations is still open, as is any linkage to an H-mode or profile changes (pedestals) with these events. Typically, 1-3% of the diamagnetic stored energy is lost per event, which when summed up over time accounts for ~20% of the overall plasma energy loss. The amplitude of the fluctuations increase with increasing ECRH input power. Bursts of energy and particles are picked up on the divertor. We see toroidal currents at the edge of the plasma (partial Rogowski response), with polarities dependent on magnetic island positions. The crashes, which we name "island localized modes" (ILM's) have a complex poloidal and temporal structure, and if not caused by breaking of islands themselves, are certainly modulated by energy flows to or through the magnetic islands. Using magnetic, visible light (filterscopes and imaging), infrared, microwave, soft x-ray, sodium beam, Thomson, Langmuir probes, and other diagnostics with sufficient time resolution, we will analyse and present further details of the events.
a G. A. Wurden, S. Ballinger, Bozhenkov, et al, "Quasi-continuous low frequency edge fluctuations in the W7-X stellarator", P5.1077, 45th EPS Conference on Plasma Physics, Prague, 2018.
