Wall conditioning effects and boron migration during boron powder injection in ASDEX Upgrade

The efficacy of boron powder injection as a wall conditioning tool method in terms of its ability to create a sufficiently uniform boron layer on plasma-facing surfaces has been studied in ASDEX Upgrade. Boron powder was injected in two series of dedicated plasma discharges at varied injection rates...

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Main Authors: K. Krieger, M. Balden, A. Bortolon, R. Dux, M. Griener, K. Hegele, F. Laggner, V. Rohde, W.R. Wampler
Format: Article
Language:English
Published: Elsevier 2023-03-01
Series:Nuclear Materials and Energy
Subjects:
Online Access:http://www.sciencedirect.com/science/article/pii/S2352179123000133
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author K. Krieger
M. Balden
A. Bortolon
R. Dux
M. Griener
K. Hegele
F. Laggner
V. Rohde
W.R. Wampler
author_facet K. Krieger
M. Balden
A. Bortolon
R. Dux
M. Griener
K. Hegele
F. Laggner
V. Rohde
W.R. Wampler
author_sort K. Krieger
collection DOAJ
description The efficacy of boron powder injection as a wall conditioning tool method in terms of its ability to create a sufficiently uniform boron layer on plasma-facing surfaces has been studied in ASDEX Upgrade. Boron powder was injected in two series of dedicated plasma discharges at varied injection rates and total amount injected. The resulting boron deposition was determined quantitatively by exposure of witness samples followed by ex-situ surface analysis of the retrieved samples. In both experiments, isotopically enriched boron was used to distinguish the deposition of the newly injected material from the residual boron fraction in the machine originating from previous glow discharge boronisations. It could be confirmed that the injected boron is migrating and re-deposited across plasma-facing wall surfaces already within one discharge. At erosion dominated divertor areas, the boron influx from the main chamber results in formation of a mixed tungsten–boron surface layer with a boron area density of O(1nm) whereas at deposition dominated areas closed boron layers grow with ongoing boron injection to a thickness of up to O(1μm). Extrapolating the radial boron deposition profile on the samples exposed in the main chamber to the limiter front yields a similar boron coverage of O(1μm), which is about ten times higher than typical values for glow discharge boronisation. Together with the observed reduction of oxygen level and improved wall pumping, the surface analysis results demonstrate that boron powder injection provides a suitable means to refresh the wall conditioning effect of a preceding glow discharge boronisation.
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spelling doaj.art-0e769cb9d4d84bab8eac879b931017e12023-03-12T04:21:30ZengElsevierNuclear Materials and Energy2352-17912023-03-0134101374Wall conditioning effects and boron migration during boron powder injection in ASDEX UpgradeK. Krieger0M. Balden1A. Bortolon2R. Dux3M. Griener4K. Hegele5F. Laggner6V. Rohde7W.R. Wampler8Max–Planck-Institut für Plasmaphysik, Boltzmannstr. 2, 85748, Garching, Germany; Corresponding author.Max–Planck-Institut für Plasmaphysik, Boltzmannstr. 2, 85748, Garching, GermanyPrinceton Plasma Physics Laboratory University of Princeton, 100 Stellarator Road, Princeton, NJ, 08540, USAMax–Planck-Institut für Plasmaphysik, Boltzmannstr. 2, 85748, Garching, GermanyMax–Planck-Institut für Plasmaphysik, Boltzmannstr. 2, 85748, Garching, GermanyMax–Planck-Institut für Plasmaphysik, Boltzmannstr. 2, 85748, Garching, GermanyNorth Carolina State University, Department of Nuclear Engineering, Raleigh, NC, 27607, USA; Princeton Plasma Physics Laboratory University of Princeton, 100 Stellarator Road, Princeton, NJ, 08540, USAMax–Planck-Institut für Plasmaphysik, Boltzmannstr. 2, 85748, Garching, GermanySandia National Laboratories, 1515 Eubank SE, Albuquerque, NM, 87123, USAThe efficacy of boron powder injection as a wall conditioning tool method in terms of its ability to create a sufficiently uniform boron layer on plasma-facing surfaces has been studied in ASDEX Upgrade. Boron powder was injected in two series of dedicated plasma discharges at varied injection rates and total amount injected. The resulting boron deposition was determined quantitatively by exposure of witness samples followed by ex-situ surface analysis of the retrieved samples. In both experiments, isotopically enriched boron was used to distinguish the deposition of the newly injected material from the residual boron fraction in the machine originating from previous glow discharge boronisations. It could be confirmed that the injected boron is migrating and re-deposited across plasma-facing wall surfaces already within one discharge. At erosion dominated divertor areas, the boron influx from the main chamber results in formation of a mixed tungsten–boron surface layer with a boron area density of O(1nm) whereas at deposition dominated areas closed boron layers grow with ongoing boron injection to a thickness of up to O(1μm). Extrapolating the radial boron deposition profile on the samples exposed in the main chamber to the limiter front yields a similar boron coverage of O(1μm), which is about ten times higher than typical values for glow discharge boronisation. Together with the observed reduction of oxygen level and improved wall pumping, the surface analysis results demonstrate that boron powder injection provides a suitable means to refresh the wall conditioning effect of a preceding glow discharge boronisation.http://www.sciencedirect.com/science/article/pii/S2352179123000133Nuclear fusionPlasma physicsWall conditioningBoronisation
spellingShingle K. Krieger
M. Balden
A. Bortolon
R. Dux
M. Griener
K. Hegele
F. Laggner
V. Rohde
W.R. Wampler
Wall conditioning effects and boron migration during boron powder injection in ASDEX Upgrade
Nuclear Materials and Energy
Nuclear fusion
Plasma physics
Wall conditioning
Boronisation
title Wall conditioning effects and boron migration during boron powder injection in ASDEX Upgrade
title_full Wall conditioning effects and boron migration during boron powder injection in ASDEX Upgrade
title_fullStr Wall conditioning effects and boron migration during boron powder injection in ASDEX Upgrade
title_full_unstemmed Wall conditioning effects and boron migration during boron powder injection in ASDEX Upgrade
title_short Wall conditioning effects and boron migration during boron powder injection in ASDEX Upgrade
title_sort wall conditioning effects and boron migration during boron powder injection in asdex upgrade
topic Nuclear fusion
Plasma physics
Wall conditioning
Boronisation
url http://www.sciencedirect.com/science/article/pii/S2352179123000133
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