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@ARTICLE{Coenen:844287,
      author       = {Coenen, J. W. and Matthews, G. F. and Krieger, K. and
                      Iglesias, D. and Bunting, P. and Corre, Y. and Silburn, S.
                      and Balboa, I. and Bazylev, B. and Conway, N. and Coffey, I.
                      and Dejarnac, R. and Gauthier, E. and Gaspar, J. and
                      Jachmich, S. and Jepu, I. and Makepeace, C. and Scannell, R.
                      and Stamp, M. and Petersson, P. and Pitts, R. A. and Wiesen,
                      S. and Widdowson, A. and Heinola, K. and Baron-Wiechec, A.},
      title        = {{T}ransient induced tungsten melting at the {J}oint
                      {E}uropean {T}orus ({JET})174},
      journal      = {Physica scripta},
      volume       = {T170},
      issn         = {1402-4896},
      address      = {Bristol},
      publisher    = {IoP Publ.},
      reportid     = {FZJ-2018-01727},
      pages        = {014013 -},
      year         = {2017},
      abstract     = {Melting is one of the major risks associated with tungsten
                      (W) plasma-facing components (PFCs) in tokamaks like JET or
                      ITER. These components are designed such that leading edges
                      and hence excessive plasma heat loads deposited at near
                      normal incidence are avoided. Due to the high stored
                      energies in ITER discharges, shallow surface melting can
                      occur under insufficiently mitigated plasma disruption and
                      so-called edge localised modes—power load transients. A
                      dedicated program was carried out at the JET to study the
                      physics and consequences of W transient melting. Following
                      initial exposures in 2013 (ILW-1) of a W-lamella with
                      leading edge, new experiments have been performed on a
                      sloped surface (15${}^{\circ }$ slope) during the 2015/2016
                      (ILW-3) campaign. This new experiment allows significantly
                      improved infrared thermography measurements and thus
                      resolved important issue of power loading in the context of
                      the previous leading edge exposures. The new lamella was
                      monitored by local diagnostics: spectroscopy, thermography
                      and high-resolution photography in between discharges. No
                      impact on the main plasma was observed despite a strong
                      increase of the local W source consistent with evaporation.
                      In contrast to the earlier exposure, no droplet emission was
                      observed from the sloped surface. Topological modifications
                      resulting from the melting are clearly visible between
                      discharges on the photographic images. Melt damage can be
                      clearly linked to the infrared measurements: the emissivity
                      drops in zones where melting occurs. In comparison with the
                      previous leading edge experiment, no runaway melt motion is
                      observed, consistent with the hypothesis that the escape of
                      thermionic electrons emitted from the melt zone is largely
                      suppressed in this geometry, where the magnetic field
                      intersects the surface at lower angles than in the case of
                      perpendicular impact on a leading edge. Utilising both
                      exposures allows us to further test the model of the forces
                      driving melt motion that successfully reproduced the
                      findings from the original leading edge exposure. Since the
                      ILW-1 experiments, the exposed misaligned lamella has now
                      been retrieved from the JET machine and post mortem analysis
                      has been performed. No obvious mass loss is observed.
                      Profilometry of the ILW-1 lamella shows the structure of the
                      melt damage which is in line with the modell predictions
                      thus allowing further model validation. Nuclear reaction
                      analysis shows a tenfold reduction in surface deuterium
                      concentration in the molten surface in comparison to the
                      non-molten part of the lamella.},
      cin          = {IEK-4},
      ddc          = {530},
      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:000414120500013},
      doi          = {10.1088/1402-4896/aa8789},
      url          = {https://juser.fz-juelich.de/record/844287},
}