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@ARTICLE{Brezinsek:826069,
      author       = {Brezinsek, S. and Hakola, A. and Greuner, H. and Balden, M.
                      and Kallenbach, A. and Oberkofler, M. and De Temmerman, G.
                      and Douai, D. and Lahtinen, A. and Böswirth, B. and Brida,
                      D. and Caniello, R. and Carralero, D. and Elgeti, S. and
                      Krieger, K. and Mayer, H. and Meisl, G. and Potzel, S. and
                      Rohde, V. and Sieglin, B. and Terra, A. and Neu, R. and
                      Linsmeier, Ch.},
      title        = {{S}urface modification of {H}e pre-exposed tungsten samples
                      by {H}e plasma impact in the divertor manipulator of {ASDEX}
                      {U}pgrade},
      journal      = {Nuclear materials and energy},
      volume       = {12},
      issn         = {2352-1791},
      address      = {Amsterdam [u.a.]},
      publisher    = {Elsevier},
      reportid     = {FZJ-2017-00329},
      pages        = {575-581},
      year         = {2017},
      abstract     = {Tungsten (W) will be used as material for plasma-facing
                      components (PFCs) in the divertor of ITER and interact with
                      Helium (He) ions either from initial He plasma operation or
                      from Deuterium-Tritium (DT) fusion reactions in the active
                      operation phase. Laboratory experiments reported that in a
                      specific operational window of impact energy, ion fluence,
                      and surface temperature (Ein ≥ 20 eV, ϕ ≥ 1 × 1024 Hem
                      Tsurf ≥ 1000 K) a modification of W surfaces occurs
                      resulting in the formation of He-induced W nanostructures.
                      Experiments in ASDEX Upgrade H-mode plasmas ( T, MA, Paux
                      ≃ 8.0 MW) in He have been carried out to investigate in
                      detail (a) the potential growth of W nanostructures on
                      pre-damaged W samples incorporating He nanobubbles, and (b)
                      the potential ELM-induced erosion of W nanostructure. Both W
                      surface modifications were generated artificially in the
                      GLADIS facility by He bombardment of W samples at keV (a) to
                      ϕ ≃ 0.75 × 1024 He0m at Tsurf ≃ 1800 K and (b) ϕ ≃
                      1 × 1024 He0m at Tsurf ≃ 2300 K prior to exposure in the
                      divertor manipulator of ASDEX Upgrade. Though in part (a)
                      conditions of W nanostructure growth with a total He ion
                      fluence of ϕ ≃ 1.6 × 1024 Hem and peak He ion impact
                      energies above 150 eV were met, no growth could be detected.
                      In part (b) lower density plasmas with more pronounced type
                      I ELMs, carrying energetic He ions in the keV range, were
                      executed with the strike-line positioned on 2 µm thick W
                      nanostructure accumulating a fluence of ϕ ≃ 0.8 × 1024
                      Hem. Post-mortem analysis revealed that co-deposition by
                      predominantly W, and Boron (B), eroded at the main chamber
                      wall and transported into the divertor, took place on all W
                      samples. Erosion of W nanostructure or its formation was
                      hindered by the fact that the outer divertor at the location
                      of the samples was turned under these He plasma conditions
                      into a net deposition zone by W, B and Carbon (C) ions. The
                      surface morphology with large roughness and effective
                      surface area act as a catcher for the impinging impurities.
                      Thus, apart from operation in the existence diagram of W
                      nanostructure with respect to Tsurf, ϕ, and Ein, also the
                      impinging impurity flux contribution needs to be considered
                      in predictions concerning the formation of W
                      nanostructures.},
      cin          = {IEK-4},
      ddc          = {333.7},
      cid          = {I:(DE-Juel1)IEK-4-20101013},
      pnm          = {174 - Plasma-Wall-Interaction (POF3-174)},
      pid          = {G:(DE-HGF)POF3-174},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:000417293300091},
      doi          = {10.1016/j.nme.2016.11.002},
      url          = {https://juser.fz-juelich.de/record/826069},
}