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Fuel inventory and deposition in castellated structures in JET-ILW
KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.ORCID iD: 0000-0001-9901-6296
KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
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2017 (English)In: Nuclear Fusion, ISSN 0029-5515, E-ISSN 1741-4326, Vol. 57, no 6, article id 066027Article in journal (Refereed) Published
Abstract [en]

Since 2011 the JET tokamak has been operated with a metal ITER-like wall (JET-ILW) including castellated beryllium limiters and lamellae-type bulk tungsten tiles in the divertor. This has allowed for a large scale test of castellated plasma-facing components (PFC). Procedures for sectioning the limiters into single blocks of castellation have been developed. This facilitated morphology studies of morphology of surfaces inside the grooves for limiters after experimental campaigns 2011-2012 and 2013-2014. The deposition in the 0.4-0.5 mm wide grooves of the castellation is 'shallow'. It reaches 1-2 mm into the 12 mm deep gap. Deuterium concentrations are small (mostly below 1 × 1018 cm-2). The estimated total amount of deuterium in all the castellated limiters does not exceed the inventory of the plasma-facing surfaces (PFS) of the limiters. There are only traces of Ni, Cr and Fe deposited in the castellation gaps. The same applies to the carbon content. Also low deposition of D, Be and C has been measured on the sides of the bulk tungsten lamellae pieces. Modelling clearly reflects: (a) a sharp decrease in the measured deposition profiles and(b) an increase in deposition with the gap width. Both experimental and modelling data give a strong indication and information to ITER that narrow gaps in the castellated PFC are essential. X-ray diffraction on PFS has clearly shown two distinct composition patterns: Be with an admixture of Be-W intermetallic compounds (e.g. Be22W) in the deposition zone, whilst only pure Be has been detected in the erosion zone. The lack of compound formation in the erosion zone indicates that no distinct changes in the thermo-mechanical properties of the Be PFC might be expected.

Place, publisher, year, edition, pages
Institute of Physics Publishing , 2017. Vol. 57, no 6, article id 066027
Keywords [en]
beryllium limiters, castellation, deposition, fuel inventory, ITER-like wall, JET, Beryllium, Carbon, Deuterium, Erosion, Facings, Fighter aircraft, Fusion reactor divertors, Intermetallics, Jets, Magnetoplasma, Tungsten, Tungsten compounds, X ray diffraction, Experimental campaign, Fuel inventories, Morphology of surfaces, Plasma facing surfaces, Plasma-facing components, Thermomechanical properties, Tokamak devices
National Category
Fusion, Plasma and Space Physics
Identifiers
URN: urn:nbn:se:kth:diva-216517DOI: 10.1088/1741-4326/aa6864ISI: 000425870600001Scopus ID: 2-s2.0-85019426928OAI: oai:DiVA.org:kth-216517DiVA, id: diva2:1161883
Note

QC 20171201

Available from: 2017-12-01 Created: 2017-12-01 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)
Opponent
Supervisors
Note

QC 20190214

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

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