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@ARTICLE{Zhao:891378,
      author       = {Zhao, D. and Yi, R. and Eksaeva, A. and Oelmann, J. and
                      Brezinsek, S. and Sergienko, G. and Rasinski, M. and Gao, Y.
                      and Mayer, M. and Dhard, C. P. and Naujoks, D. and Cai, L.},
      title        = {{Q}uantification of erosion pattern using picosecond-{LIBS}
                      on a vertical divertor target element exposed in {W}7-{X}},
      journal      = {Nuclear fusion},
      volume       = {61},
      number       = {1},
      issn         = {1741-4326},
      address      = {Vienna},
      publisher    = {IAEA},
      reportid     = {FZJ-2021-01467},
      pages        = {016025 -},
      year         = {2021},
      abstract     = {A set of dedicated marker samples consisting of fine-grain
                      graphite as substrate, an interlayer of 0.2–0.4 μm
                      molybdenum (Mo) employed as marker, and a 5–10 μm thick
                      carbon (C) marker layer on top were installed in Wendelstein
                      7-X (W7-X) to investigate locally the C erosion and
                      deposition. In this study, a set of five individual marker
                      tiles, installed in a vertical divertor element of the test
                      divertor unit in half-module 50, and exposed to about 40 min
                      of plasma predominant in the standard magnetic divertor
                      configuration in the first year of divertor operation in
                      W7-X (OP1.2A), were retrieved from the vessel for
                      post-mortem analysis. Picosecond laser induced breakdown
                      spectroscopy (ps-LIBS) was applied on these marker tiles in
                      order to determine the local erosion/deposition pattern
                      caused by plasma impact. The general erosion/deposition
                      pattern on the vertical target element was studied with the
                      aid of depth-profiling by Mo line emission due to ps-LIBS
                      with the number of applied laser pulses (355 nm, 2.3 J
                      cm−2, 35 ps) at one probing location. Several potential
                      asymmetry factors which avoid a perfect layer-by-layer
                      ablation process in the laser ablations are proposed and
                      discussed when a rough layered structure sample with a rough
                      surface is analysed by the ps-LIBS technique. Thereby, a
                      simulation model was developed to correct the measurement
                      error of the ps-LIBS method caused by the non-perfect
                      rectangle profile of the applied laser beam. The depth
                      resolution of the applied ps-LIBS system was determined by
                      quantification of the laser ablation rates of the different
                      layers and the C substrate which were measured utilising
                      profilometry and cross comparison with the thicknesses of
                      the C and Mo marker layers determined by a combined focused
                      ion beam and scanning electron microscopy technique. For the
                      first time, the erosion/deposition pattern on the vertical
                      target was mapped and quantified by ps-LIBS technique. A
                      relatively wide net erosion zone with a poloidal extend of
                      about 200 mm was identified which can be correlated to the
                      main particle interaction zone at the magnetic strike-line
                      of the dominantly applied standard magnetic divertor
                      configuration. At the position of peak erosion, not only 7.6
                      × 1019 C atoms/cm2 but also 2 × 1018 Mo atoms/cm2 which
                      results can be extrapolated to total 15 × 1019 C atoms/cm2,
                      were eroded due to plasma fuel particle (H, He) and impurity
                      (O, C) ion impact.},
      cin          = {IEK-4},
      ddc          = {620},
      cid          = {I:(DE-Juel1)IEK-4-20101013},
      pnm          = {134 - Plasma-Wand-Wechselwirkung (POF4-134)},
      pid          = {G:(DE-HGF)POF4-134},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:000598062900001},
      doi          = {10.1088/1741-4326/abc408},
      url          = {https://juser.fz-juelich.de/record/891378},
}