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Deep deuterium retention and Be/W mixingat tungsten coated surfaces in the JETdivertor
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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2016 (English)In: Physica Scripta, ISSN 0031-8949, E-ISSN 1402-4896Article in journal, Editorial material (Refereed) Published
Abstract [en]

Surface samples from a full poloidal set of divertor tiles exposed in JET through operations2010–2012 with ITER-like wall have been investigated using SEM, SIMS, ICP-AES analysisand micro beam nuclear reaction analysis (μ-NRA). Deposition of Be and retention of D ismicroscopically inhomogeneous. With careful overlaying of μ-NRA elemental maps with SEMimages, it is possible to separate surface roughness effects from depth profiles at microscopicallyflat surface regions, without pits. With (3He, p) μ-NRA at 3–5 MeV beam energy the accessibledepth for D analysis in W is about 9 μm, sufficient to access the W/Mo and Mo/W interfaces inthe coatings and beyond, while for Be in W it is about 6 μm. In these conditions, at all plasmawetted surfaces, D was found throughout the whole accessible depth at concentrations in therange 0.2–0.7 at% in W. Deuterium was found to be preferentially trapped at the W/Mo andMo/W interfaces. Comparison is made with SIMS profiling, which also shows significant Dtrapping at the W/Mo interface. Mixing of Be and W occurs mainly in deposited layers.

Place, publisher, year, edition, pages
2016.
National Category
Fusion, Plasma and Space Physics
Identifiers
URN: urn:nbn:se:kth:diva-243916OAI: oai:DiVA.org:kth-243916DiVA, id: diva2:1287570
Note

QCR 20190312

Available from: 2019-02-11 Created: 2019-02-11 Last updated: 2019-03-12Bibliographically 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)
Opponent
Supervisors
Note

QC 20190214

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

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