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research article

Progress from ASDEX Upgrade experiments in preparing the physics basis of ITER operation and DEMO scenario development

Stroth, U.
•
Aguiam, D.
•
Alessi, E.
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April 1, 2022
Nuclear Fusion

An overview of recent results obtained at the tokamak ASDEX Upgrade (AUG) is given. A work flow for predictive profile modelling of AUG discharges was established which is able to reproduce experimental H-mode plasma profiles based on engineering parameters only. In the plasma center, theoretical predictions on plasma current redistribution by a dynamo effect were confirmed experimentally. For core transport, the stabilizing effect of fast ion distributions on turbulent transport is shown to be important to explain the core isotope effect and improves the description of hollow low-Z impurity profiles. The L-H power threshold of hydrogen plasmas is not affected by small helium admixtures and it increases continuously from the deuterium to the hydrogen level when the hydrogen concentration is raised from 0 to 100%. One focus of recent campaigns was the search for a fusion relevant integrated plasma scenario without large edge localised modes (ELMs). Results from six different ELM-free confinement regimes are compared with respect to reactor relevance: ELM suppression by magnetic perturbation coils could be attributed to toroidally asymmetric turbulent fluctuations in the vicinity of the separatrix. Stable improved confinement mode plasma phases with a detached inner divertor were obtained using a feedback control of the plasma beta. The enhanced D- alpha H-mode regime was extended to higher heating power by feedback controlled radiative cooling with argon. The quasi-coherent exhaust regime was developed into an integrated scenario at high heating power and energy confinement, with a detached divertor and without large ELMs. Small ELMs close to the separatrix lead to peeling-ballooning stability and quasi continuous power exhaust. Helium beam density fluctuation measurements confirm that transport close to the separatrix is important to achieve the different ELM-free regimes. Based on separatrix plasma parameters and interchange-drift-Alfven turbulence, an analytic model was derived that reproduces the experimentally found important operational boundaries of the density limit and between L- and H-mode confinement. Feedback control for the X-point radiator (XPR) position was established as an important element for divertor detachment control. Stable and detached ELM-free phases with H-mode confinement quality were obtained when the XPR was moved 10 cm above the X-point. Investigations of the plasma in the future flexible snow-flake divertor of AUG by means of first SOLPS-ITER simulations with drifts activated predict beneficial detachment properties and the activation of an additional strike point by the drifts.

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Type
research article
DOI
10.1088/1741-4326/ac207f
Web of Science ID

WOS:000769721300001

Author(s)
Stroth, U.
Aguiam, D.
Alessi, E.
Angioni, C.
Arden, N.
Parra, R. Arredondo
Artigues, V
Asunta, O.
Balden, M.
Bandaru, V
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Date Issued

2022-04-01

Publisher

IOP Publishing Ltd

Published in
Nuclear Fusion
Volume

62

Issue

4

Article Number

042006

Subjects

Physics, Fluids & Plasmas

•

Physics

•

asdex upgrade

•

confinement

•

ellm-free discharges

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h-mode plasmas

•

alcator c-mod

•

confinement modes

•

upper divertor

•

sol

•

transition

•

turbulence

Editorial or Peer reviewed

REVIEWED

Written at

EPFL

EPFL units
SPC  
Available on Infoscience
March 28, 2022
Use this identifier to reference this record
https://infoscience.epfl.ch/handle/20.500.14299/186759
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