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Sputtering of polished EUROFER97 steel: Surface structure modification and enrichment with tungsten and tantalum
KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.ORCID iD: 0000-0001-9299-3262
KTH, School of Electrical Engineering and Computer Science (EECS), Fusion Plasma Physics.
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2018 (English)In: Journal of Nuclear Materials, ISSN 0022-3115, E-ISSN 1873-4820, Vol. 508, p. 139-146Article in journal (Refereed) Published
Abstract [en]

Surface structure modification and enrichment with tungsten and tantalum were measured for polished EUROFER97 samples after exposure to a deuterium ion beam. Time-of-flight medium energy ion scattering and time-of-flight elastic recoil detection analysis were implemented for measuring atomic composition profiles. Atomic force microscopy and optical microscopy were used to investigate surface morphology. The deuterium particle fluence was varied between 1021 D/m2 and 1024 D/m2, projectile energy was 200 eV/D and exposure temperatures up to 1050 K were applied. The average fraction of tungsten plus tantalum to total metal content in the 2 nm closest to the sample surface was increased from an initial 0.0046 to 0.12 for the sample exposed to the highest fluence at room temperature. The enrichment was accompanied by an increase in surface roughness of one order of magnitude and grain dependent erosion of the material. The appearance of protrusions with heights up to approximately 40 nm after ion beam exposure at room temperature was observed on individual grains. Samples exposed to 1023 D/m2 at temperatures of 900 K and 1050 K displayed recrystallization and cracking while changes to the total surface fraction of tungsten and tantalum were limited to less than a factor of two compared to the sample exposed to the same fluence at room temperature.

Place, publisher, year, edition, pages
Elsevier, 2018. Vol. 508, p. 139-146
Keywords [en]
AFM, Erosion, EUROFER, Sputtering, ToF-ERDA, ToF-MEIS
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-229259DOI: 10.1016/j.jnucmat.2018.05.031ISI: 000439134500016Scopus ID: 2-s2.0-85047329344OAI: oai:DiVA.org:kth-229259DiVA, id: diva2:1212112
Funder
Swedish Research Council, 821-2012-5144Swedish Foundation for Strategic Research , RIF14-0053EU, European Research Council
Note

QC 20180601

Available from: 2018-06-01 Created: 2018-06-01 Last updated: 2019-01-09Bibliographically approved
In thesis
1. Material characterization for magnetically confined fusion: Surface analysis and method development
Open this publication in new window or tab >>Material characterization for magnetically confined fusion: Surface analysis and method development
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The dream of abundant clean energy has brought scientists and laypeople alike to ponder the possibilities of nuclear fusion since it was established as the energy source of the stars in 1939. Starting from the mid the 20th century, significant effort has been put into overcoming the technological challenges related to the construction of a power plant, but initial optimism has faded somewhat due to a notable absence of practical outcomes. Nevertheless, the research continues and progress is made slowly but surely.

The present work deals with a small part of the fusion puzzle, namely the materials to be used in the first wall surrounding a magnetically confined plasma. Carbon, which has historically been considered as the most viable element for this role, has been ruled out due to issues with plasma-induced erosion, hydrocarbon formation and a buildup of thick deposited material layers on wall components. The latter two lead to an unacceptable accumulation of radioactive tritium, both in the deposited layers and in dust particles. A metal wall, which would alleviate these particular problems but increase the severity of others, is therefore envisioned for a future demonstration reactor.

Three contributions to the overall research effort are made though this thesis. First, an increased understanding of plasma-induced erosion of so-called reduced activation ferritic-martensitic steels and preferential sputtering of light material components is provided. High-resolution ion beam analysis and microscopy methods are used to examine samples of such a steel after exposure to plasma under controlled circumstances. Model films consisting of a mixture of iron and tungsten deposited on silicon substrates are also studied as they constitute simpler systems where the effects of interest may be simulated. The knowledge obtained is necessary for an assessment of the possibility to use reduced activation steel as a plasma-facing material in specific regions of a reactor wall.

The second contribution consists of reports on the composition of deposited material layers on wall components retrieved from the plasma confinement experiments JET and TEXTOR. These provide limited conclusions on the range and rate of material erosion, transport and deposition in two cases.

Finally, a detection system for the ion beam technique elastic recoil detection analysis has been assembled, tested and put into operation. In addition to improving the quality of analyses performed on fusion-related materials, the system has become an established tool available for users of the 5 MV electrostatic pelletron accelerator at Uppsala University’s Tandem Laboratory.

Place, publisher, year, edition, pages
KTH Royal Institute of Technology, 2019. p. 189
Series
TRITA-EECS-AVL ; 2019:4
National Category
Fusion, Plasma and Space Physics
Research subject
Electrical Engineering
Identifiers
urn:nbn:se:kth:diva-241093 (URN)978-91-7873-055-1 (ISBN)
Public defence
2019-02-13, F3, Lindstedtsvägen 26, Stockholm, 09:00 (English)
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Note

QC 20190110

Available from: 2019-01-16 Created: 2019-01-09 Last updated: 2019-01-18Bibliographically approved

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Ström, PetterPetersson, Per

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