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Microanalysis of deposited layers in the inner divertor of JET with ITER-like wall
KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
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2017 (English)In: NUCLEAR MATERIALS AND ENERGY, ISSN 2352-1791, Vol. 12, p. 412-417Article in journal (Refereed) Published
Abstract [en]

In JET with ITER-like wall, beryllium eroded in the main chamber is transported to the divertor and deposited mainly at the horizontal surfaces of tiles 1 and 0 (high field gap closure, HFGC). These surfaces are tungsten coated carbon fibre composite (CFC). Surface sampleswere collected following the plasma operations in 2011-2012 and 2013-2014 respectively. The surfaces, as well as polished cross sections of the deposited layers at the surfaces have been studied with micro ion beam analysis methods (mu-IBA). Deposition of Beand other impurities, and retention of D is microscopically inhomogeneous. Impurities and trapped deuterium accumulate preferentially in cracks, pits and depressed regions, and at the sides of large pits in the substrate (e.g. arc tracks where the W coating has been removed). With careful overlaying of mu-NRA elemental maps with optical microscopy images, it is possible to separate surface roughness effects from depth profiles at microscopically flat surface regions.

Place, publisher, year, edition, pages
2017. Vol. 12, p. 412-417
National Category
Fusion, Plasma and Space Physics
Identifiers
URN: urn:nbn:se:kth:diva-220633DOI: 10.1016/j.nme.2017.02.015ISI: 000417293300062Scopus ID: 2-s2.0-85015310440OAI: oai:DiVA.org:kth-220633DiVA, id: diva2:1173298
Note

QC 20180112

Available from: 2018-01-12 Created: 2018-01-12 Last updated: 2019-02-13Bibliographically approved
In thesis
1. Impact of Surface Structures onDeposition and Erosion in a Tokamak
Open this publication in new window or tab >>Impact of Surface Structures onDeposition and Erosion in a Tokamak
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Fusion is a potentially unlimited and environmentally friendly energy source for human society in the future. However, along the way towards the application of fusion energy there are still unresolved complications. Among them, deposition and erosion are two critical issues. Deposition of fuel and impurities brings potential long-term fuel retention which may generate safety issues and limit the economic efficiency of fusion devices. Moreover, the erosion of the vacuum vessel wall in a fusion device generates impurities which contaminate core plasma and can restrict the life time of plasma facing component. The work in this thesis focuses on deposition and erosion on tiles in the JET-ILW project, which consist of tungsten (or tungsten coating carbon fibre composited) in the divertor and beryllium in limiters.

For the deposition issue, micro ion beam analysis (µ-IBA) was used for observing deuterium and beryllium distributions over tile surfaces. The surface topography was obtained from SEM, optical microscope and confocal laser scan microscope. Distribution maps from IBA were compared with surface topography. To explain experimental results, modelling of ion trajectories was applied on real and artificial surfaces. Micro IBA results show that deuterium and beryllium accumulated in depressed areas, e.g. pits, cracks or craters. Modelling implies that ion gyration, surface roughness and inclination of the magnetic field could to some extent explain this non-uniform distribution of deuterium and beryllium. The same kind of issue, although on different scale length, occurs also for penetration of impurities into artificial castellation grooves, also studied experimentally in the thesis.

For the erosion issue, the thesis includes analysis of a limiter marker tile which is designed for observing material erosion in JET. A new method to acquire erosion data from such marker tiles is proposed, by combining micro IBA and SEM image.  This method could separate the influence on IBA from roughness, a problem in applying IBA on rough surface. Similar Technique is applied to improve the interpretation of IBA measurements of deep penetration of deuterium into layered surface structures.

Abstract [sv]

Fusion är en potentiellt obegränsad och miljövänlig energikälla för det mänskliga samhället i framtiden. Det återstår emellertid vissa problem att lösa. Bland dem är deposition och erosion vid ytor som är i kontakt med plasmat kritiska. Deposition av bränsle och föroreningar ger potentiellt långsiktig ackumulation av bränsle (tritium) som kan ge upphov till säkerhetsproblem och försämra bränsleekonomin. Erosion av vakuumkärlets väggar i in fusionsanläggning alstrar förorenar plasmat och kan begränsa livstiden för väggkomponenter. Arbetet i denna avhandling fokuserar på deposition och erosion på ytor i JET-ILW-projektet, som består av volfram (eller volframbelagd kolfiberkomposit) i divertor och beryllium i limiter.

För depositionsfrågorna användes mikroanalys för att observera hur deuterium och beryllium fördelas över ytorna efter plasmaexponering. Yttopografi erhölls från SEM, optisk mikroskopi och konfokal laserskanmikroskopi. Distributionskartor från IBA jämfördes med yttopografin. För att förklara experimentella resultat användes modellering av jontrajektorior, dels på verklig experimentell topografi, dels på förenklade modellytor. Micro IBA-resultat visar att deuterium och beryllium ansamlas i mikroskopiskt nedsänkta områden, t.ex. gropar och sprickor. Modelleringen visar att joners gyratation delvis kan förklara denna ojämna fördelning av deuterium och beryllium.

För erosionsproblemet gjordes mätningar på markerplattor, konstruerade för att observera materialosion i JET. En ny metod införs för att erhålla erosionsdata, genom att kombinera mikro IBA och SEM-bild. Denna metod kan skilja på inflytande på IBA-resultat från skrovlighet, vilket är annars är ett problem IBA för på skrovlig yta. På samma sätt används mikroanalys för att förbättra tolkningen av analyser av deuterium som trängt in i en skiktad struktur.

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2019. p. 65
Series
TRITA-EECS-AVL ; 2019:11
Keywords
Deposition, erosion, JET, micro ion beam analysis, Deposition, erosion, JET, mikrojonstråleanalys
National Category
Fusion, Plasma and Space Physics
Research subject
Electrical Engineering
Identifiers
urn:nbn:se:kth:diva-244029 (URN)978-91-7873-080-3 (ISBN)
Public defence
2019-03-08, F3, Lindstedtsvägen 26, Stockholm, 14:00 (English)
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Supervisors
Note

QC 20190214

Available from: 2019-02-14 Created: 2019-02-13 Last updated: 2019-02-14Bibliographically approved

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Bergsåker, HenricBykov, IgorPetersson, Per

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