X-point radiation, its control and an ELM suppressed radiating regime at the ASDEX Upgrade tokamak

M. Bernert*, F. Janky, B. Sieglin, A. Kallenbach, B. Lipschultz, F. Reimold, M. Wischmeier, M. Cavedon, P. David, M. G. Dunne, M. Griener, O. Kudlacek, R. M. McDermott, W. Treutterer, E. Wolfrum, D. Brida, O. Février, S. Henderson, M. Komm

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


Future fusion reactors require a safe, steady state divertor operation. The required detached operation is, in tokamaks with metal walls, usually achieved by seeding of impurities, such as nitrogen. With strong seeding levels, the dominant radiation is emitted from a small, poloidally localized volume inside the confined region, in the vicinity of the X-point. The location of the radiating volume is observed to vary relative to the X-point depending on seeding and power levels, i.e. depending on the degree of detachment. At the ASDEX Upgrade tokamak, the position of the radiator relative to the X-point can be controlled in real time by a modulation of the nitrogen puff level. At a certain height of the radiator above the X-point, an ELM-suppressed regime is observed with minimal reduction of confinement. While the control of the X-point radiator already allows operation in full detachment at a dissipated power fraction of around 95 %, which is required for a future reactor and was previously never achieved in a controlled way, such an ELM-suppressed regime additionally eliminates the challenge of the transient, intolerably high heat fluxes by ELMs. Both requirements are met in the presented regime while maintaining a high energy confinement at high density.

Original languageEnglish
Article number024001
JournalNuclear Fusion
Issue number2
Early online date21 Dec 2021
Publication statusE-pub ahead of print - 21 Dec 2021

Bibliographical note

This is the Accepted Manuscript version of an article accepted for publication in Nuclear Fusion. IOP Publishing Ltd is not responsible for any errors or omissions in this version of the manuscript or any version derived from it.

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