Turbulence in the near scrape-off layer towards the L-mode density limit in ASDEX-Upgrade

The L-mode density limit in ASDEX Upgrade is investigated with focus on the scrape-off layer. We observe a chain of events that involves the collapse of the E×B outer shear layer (just outside the separatrix), widening of the electron pressure fall-off length, outer divertor detachment, density shou...

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Bibliographic Details
Published in:Nuclear materials and energy 2022-10, Vol.33, p.101277, Article 101277
Main Authors: Grenfell, G., Manz, P., Conway, G.D., Eich, T., Adamek, J., Brida, D., Komm, M., Nishizawa, T., Griener, M., Tal, B., Stroth, U.
Format: Article
Language:English
Subjects:
Density limit
Detachment
Electrostatic probes
Scrape-off layer
Tokamaks
Turbulence
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Summary:The L-mode density limit in ASDEX Upgrade is investigated with focus on the scrape-off layer. We observe a chain of events that involves the collapse of the E×B outer shear layer (just outside the separatrix), widening of the electron pressure fall-off length, outer divertor detachment, density shoulder formation, reduction and flattening of the parallel Mach number, and enhanced turbulent cross-field transport. The latter effect was associated with higher amplitude density fluctuations at low frequencies, where the turbulent cross-phase between density and velocity fluctuations pointing radially outward was favourable.
ISSN:2352-1791
2352-1791
DOI:10.1016/j.nme.2022.101277