Bremen 2017 – wissenschaftliches Programm
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P: Fachverband Plasmaphysik
P 13: Magnetic Confinement
P 13.12: Poster
Dienstag, 14. März 2017, 16:30–18:30, HS Foyer
Origin of radiative fluctuations close to the X-point during detachment in ASDEX Upgrade — •Peter Manz1, Steffen Potzel1, Marco Wischmeier1, Sergei Krasheninnikov2, and the ASDEX Upgrade Team1 — 1Max-Planck-Institut für Plasmaphysik, Garching, Germany — 2University California San Diego, La Jolla, USA
The dynamics of radiative fluctuations in the divertor region close to the X-point during the fluctuating state of detachment are studied in ASDEX Upgrade. In this state the inner divertor is detached and the outer divertor is still attached. The X-point fluctuations appear at a frequency of a few kHz, which is at rather low frequency for plasma instabilities, but also at a rather high frequency for equilibrium related phenomena. Two possibilities will be discussed. The first one equates the X-point fluctuations with the dynamics of the ionization front. Fluctuations arise due to geometric restrictions on the propagation of the ionization front. The divertor nose constitutes an obstacle for the perpendicular neutral flux from the target to the region above the X-point. Passing into this shadow the ionization front fades away. A cyclic reformation of the ionization front propagating from below to above the X-point occurs. Another possibility for the X-point fluctuations is the current convective instability caused by the large temperature difference between the inner and outer divertor and a radial gradient in the resistivity.