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Ion beam analysis of tungsten layers in EUROFER model systems and carbon plasma facing components
KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.ORCID iD: 0000-0001-9299-3262
KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.
KTH, School of Electrical Engineering (EES), Fusion Plasma Physics.ORCID iD: 0000-0001-9901-6296
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2016 (English)In: Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, ISSN 0168-583X, E-ISSN 1872-9584, Vol. 371, p. 355-359Article in journal (Refereed) Published
Abstract [en]

The tungsten enriched surface layers in two fusion-relevant EUROFER steel model samples, consisting of an iron-tungsten mixture exposed to sputtering by deuterium ions, were studied by Rutherford backscattering spectrometry and medium energy ion scattering. Exposure conditions were the same for the two samples and the total amount of tungsten atoms per unit area in the enriched layers were similar (2e15 and 2.4e15 atoms/cm2 respectively), despite slightly different initial atomic compositions. A depth profile featuring exponential decrease in tungsten content towards higher depths with 10-20 atomic percent of tungsten at the surface and a decay constant between 0.05 and 0.08 Å-1 was indicated in one sample, whereas only the total areal density of tungsten atoms was measured in the other. In addition, two different beams, iodine and chlorine, were employed for elastic recoil detection analysis of the deposited layer on a polished graphite plate from a test limiter in the TEXTOR tokamak following experiments with tungsten hexafluoride injection. The chlorine beam was preferred for tungsten analysis, mainly because it (as opposed to the iodine beam) does not give rise to problems with overlap of forward scattered beam particles and recoiled tungsten in the spectrum.

Place, publisher, year, edition, pages
Elsevier, 2016. Vol. 371, p. 355-359
Keywords [en]
ERDA, EUROFER, Fusion, MEIS, Tungsten, Atoms, Carbon, Chlorine, Forward scattering, Fusion reactions, Iodine, Ion beams, Ions, Magnetoplasma, Rutherford backscattering spectroscopy, Elastic recoil detection analysis, Exposure parameters, Medium energy ion scattering, Orders of magnitude, Rutherford back-scattering spectrometry
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:kth:diva-177225DOI: 10.1016/j.nimb.2015.09.024ISI: 000373412000071Scopus ID: 2-s2.0-84960241915OAI: oai:DiVA.org:kth-177225DiVA, id: diva2:873938
Note

QC 20171027

Available from: 2015-11-25 Created: 2015-11-17 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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Supervisors
Note

QC 20190110

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

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Ström, PetterRubel, Marek

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