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@INPROCEEDINGS{Ertmer:891717,
      author       = {Ertmer, Stephan and Marchuk, Oleksandr and Brezinsek,
                      Sebastijan and Dickheuer, Sven Oliver and Mertens, Philippe
                      and Rasinski, Marcin and Kreter, Arkadi},
      title        = {{E}nergy and atomic level distribution of sputtered
                      tungsten determined by high-resolution optical spectroscopy},
      reportid     = {FZJ-2021-01691},
      year         = {2021},
      abstract     = {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)},
      month         = {Jan},
      date          = {2021-01-25},
      organization  = {24th International Conference on
                       Plasma Surface Interactions in
                       Controlled Fusion Devices (PSI 2020),
                       virtuell (virtuell), 25 Jan 2021 - 29
                       Jan 2021},
      cin          = {IEK-4},
      cid          = {I:(DE-Juel1)IEK-4-20101013},
      pnm          = {134 - Plasma-Wand-Wechselwirkung (POF4-134)},
      pid          = {G:(DE-HGF)POF4-134},
      typ          = {PUB:(DE-HGF)1},
      url          = {https://juser.fz-juelich.de/record/891717},
}