This title appears in the Scientific Report :
2021
Energy and atomic level distribution of sputtered tungsten determined by high-resolution optical spectroscopy
Energy and atomic level distribution of sputtered tungsten determined by high-resolution optical spectroscopy
Energy and atomic level distribution of sputtered tungsten determined by high-resolution spectroscopy S. Ertmer, O. Marchuk, S. Dickheuer, S. Brezinsek, Ph. Mertens, M. Rasinski, and A. KreterForschungszentrum Jülich GmbH - Institut für Energie- und Klimaforschung -Plasmaphysik, Partner of the Trila...
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Personal Name(s): | Ertmer, Stephan (Corresponding author) |
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Marchuk, Oleksandr / Brezinsek, Sebastijan / Dickheuer, Sven Oliver / Mertens, Philippe / Rasinski, Marcin / Kreter, Arkadi | |
Contributing Institute: |
Plasmaphysik; IEK-4 |
Imprint: |
2021
|
Conference: | 24th International Conference on Plasma Surface Interactions in Controlled Fusion Devices (PSI 2020), virtuell (virtuell), 2021-01-25 - 2021-01-29 |
Document Type: |
Abstract |
Research Program: |
Plasma-Wand-Wechselwirkung |
Publikationsportal JuSER |
Energy and atomic level distribution of sputtered tungsten determined by high-resolution spectroscopy S. Ertmer, O. Marchuk, S. Dickheuer, S. Brezinsek, Ph. Mertens, M. Rasinski, and A. KreterForschungszentrum Jülich GmbH - Institut für Energie- und Klimaforschung -Plasmaphysik, Partner of the Trilateral Euregio Cluster (TEC), 52425 Jülich, Germanys.ertmer@fz-juelich.deTungsten (W) is proposed as plasma-facing material (PFM) in the divertor and in the main chamber of future fusion devices. The lifetime of the PFM is mainly determined by erosion; passive spectroscopy is a very powerful, reliable and cheap in-situ diagnostic tool to monitor the W gross erosion. One of the unresolved problems related to physical sputtering of W by ion impact in the energy range of 100-200 eV remains the initial energy level population distribution of the W atoms. A further unresolved problem is that until now there are considerable deviations between the modelled and experimentally observed energy and angular distribution of sputtered W [1,2]. Both problems are addressed in this work using spectroscopy with high spatial and spectral resolution in the linear plasma device PSI-2 [3].For measurements of the population distribution of sputtered W atoms within the ground state (5D0) and the first excited levels, e.g. the quintet 5DJ (J=1,..4) and the metastable level 7S3, a target was exposed to an argon plasma (electron temperature Te = 2 eV; electron density ne = 1∙1012 cm-3). The ions were accelerated via applying a bias voltage onto the target to kinetic energies Ei between 100 and 200 eV. The line intensities in front of the target for neutral W I lines were investigated by an imaging spectrometer in the Czerny-Turner configuration (resolving power λ/Δλ ≈ 3∙104) with a high spatial resolution of 50 µm/px [4]. The development of the emission of W I lines in front of the target was tested against the lifetime of W I levels populated by electron impact. It was found that for a target at room temperature the W atoms are sputtered in the ground state 5D0, whereas the other levels 5DJ>0 and 7S3 get populated deeper in the plasma. The energy distribution function of sputtered W atoms is obtained from the Doppler shift affected line shape of the W I line (5D0-7F1) detected perpendicularly to the target surface by a high resolution Echelle spectrometer (λ/Δλ ≈ 7∙105). The model of the Doppler-shifted emission at the surface [5] was extended to take into account the Zeeman splitting and instrumental broadening of spectral lines [6]. The data for W is in a very good agreement with the Thompson energy distribution function featuring an increase in the high energy tail with increasing impact energy of the incident Ar+ ions. Moreover, this method determines in-situ the optical reflectance of the target at specific wavelengths, which impacts the measured net emission. We demonstrate here for the first time that high spectral resolution spectroscopy of sputtered atoms in combination with polarisation measurements close to the pseudo-Brewster angels can be used for surface morphology studies independently of other diagnostics.[1] Stepanova M et al, 2001 J. Vac. Sci. Technol. A 19 2805[2] Nishijima D et al, 2011 J. Nucl. Mater 415 96–99 [3] Kreter A et al, 2015 Fusion Sci. Technol. 68 8–14 [4] Marchuk O et al, 2018 J Phys B: At. Mol. Opt. Phys. 51 025702 (19pp)[5] Dickheuer S et al, 2019 Physics of Plasmas 26, 073513 [6] Ertmer S. et al, Phys. Scr. B (to be published) |