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@ARTICLE{Zammuto:852579,
      author       = {Zammuto, I. and Giannone, L. and Herrmann, A. and Houben,
                      A. and Kallenbach, A. and Schuhbeck, K. H. and Sieglin, B.
                      and Vorbrugg, S.},
      title        = {{I}mplementation of ferritic steel as in vessel wall:
                      {L}essons learnt and follow up},
      journal      = {Fusion engineering and design},
      volume       = {124},
      issn         = {0920-3796},
      address      = {New York, NY [u.a.]},
      publisher    = {Elsevier},
      reportid     = {FZJ-2018-05491},
      pages        = {297 - 301},
      year         = {2017},
      abstract     = {ASDEX Upgrade (AUG) is the only tokamak in Europe to have
                      low activation ferritic steel as the inner vessel wall
                      facing component. Together with the massive tungsten tiles
                      in the lower divertor, AUG is the tokamak with the closest
                      DEMO wall. The project is a first step towards the extensive
                      use of ferritic steel in future fusion reactors. For
                      example, the test blanket module of ITER is planned to have
                      a ferritic steel wall and thick tungsten tiles as a plasma
                      facing component.The ‘ad hoc’ ferritic steel built with
                      low activation capability is known as Eurofer. As the low
                      activation property is not a requirement for AUG, the
                      material selected for the project is the martensitic steel
                      P92 which is the most similar material to Eurofer from a
                      magnetic point of view. The purpose of the project is to
                      improve understanding of the magnetic perturbation of the
                      ferritic steel both on the plasma and magnetic probes,
                      evaluating and controlling these effects. Additionally, the
                      effect of the additional forces on the supporting structure
                      has been addressed.Bearing this in mind, in 2013 a step wise
                      program has been started and part of the W coated graphite
                      tiles in the region of the inner column were replaced by
                      steel tiles [1]. The first campaign did not suffer any
                      particular issue related to the new material. According to
                      the calculations, the plasma was almost unperturbed, thanks
                      also to the toroidal symmetry of the tiles inside the
                      vessel, and the magnetic probe measurements were properly
                      corrected [2].Inspection of the machine pointed out some
                      hardware problems. The graphite tiles adjacent to the steel
                      tiles were damaged. The graphite tiles had broken edges in 5
                      from 64 positions and notches in many others. The coating of
                      the graphite and steel tiles, made of tungsten and TiO
                      respectively, was damaged. At first glance it was clear that
                      the steel tiles were moving but it was definitely
                      unexpected. In understanding the process, the location of
                      the damage was the crucial hint. In fact all failures were
                      located at the boundary between 2 vacuum vessel octants. To
                      justify this failure mode inside the vessel, a hypothesis
                      (about current flowing in the heat shield supporting
                      structure) was made and FEM analyses were carried out in
                      this direction. With extreme caution, in 2015 just one
                      additional row of steel tiles was added together with
                      diagnostics that confirmed the hypothesis. Now that a clear
                      understanding of the problem has been reached, the project
                      to add further rows of steel tiles can be continued. For the
                      next campaign it is planned to replace all the tiles in the
                      middle region of the heat shield together with stiffening
                      and modification of the supporting structure.In this paper
                      the learning process from the damage of the tiles and its
                      causes, from the FEM analysis results to the data
                      diagnostics will be reported. The future plans for steel
                      tiles in AUG will be discussed.},
      cin          = {IEK-4},
      ddc          = {620},
      cid          = {I:(DE-Juel1)IEK-4-20101013},
      pnm          = {113 - Methods and Concepts for Material Development
                      (POF3-113)},
      pid          = {G:(DE-HGF)POF3-113},
      typ          = {PUB:(DE-HGF)16},
      UT           = {WOS:000419411900063},
      doi          = {10.1016/j.fusengdes.2017.04.016},
      url          = {https://juser.fz-juelich.de/record/852579},
}