Measurement of N+ flows in the high-field side scrape-off layer of ASDEX Upgrade with different degrees of inner divertor detachment

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Journal Title

Journal ISSN

Volume Title

A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä

Date

2017

Major/Subject

Mcode

Degree programme

Language

en

Pages

935-941

Series

Nuclear Materials and Energy, Volume 12

Abstract

Toroidal and poloidal flows of injected N+ ions were measured in the high-field side (HFS) scrape-off layer (SOL) of ASDEX Upgrade by Doppler spectroscopy with different degrees of HFS divertor detachment. In high-recycling conditions, the results suggest reversed parallel N+ flow away from the inner divertor in the near SOL close to the separatrix, while the flow is towards the inner divertor throughout the SOL in detached conditions. The measured poloidal N+ flows were directed away from the HFS divertor in the near SOL for all density cases. Divertor plasma oscillations, characterized by momentary peaking of the HFS target ion flux and decrease of the HFS SOL density, were observed slightly before the roll-over of the ion saturation current to the HFS target and lead to an increase in the N+ flow towards the HFS divertor. SOLPS and ERO simulations of the experiment predict entrainment below 50% between the velocities of N+ and D+ ions, suggesting that N+ ions are quantitatively a limited proxy for measuring D+ flows. ERO simulations show significantly higher entrainment for higher ionization states, e.g., N2+ and N3+.

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Keywords

Impurity migration, Doppler spectroscopy, SOL flow, Divertor detachment

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Citation

Karhunen, J, Groth, M, Heliste, P, Pütterich, T, Viezzer, E, Carralero, D, Coster, D, Guimarais, L, Nikolaeva, V, Hakola, A, Potzel, S & ASDEX Upgrade, T 2017, ' Measurement of N+ flows in the high-field side scrape-off layer of ASDEX Upgrade with different degrees of inner divertor detachment ', Nuclear Materials and Energy, vol. 12, pp. 935-941 . https://doi.org/10.1016/j.nme.2017.02.020