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@PHDTHESIS{Wirtz:133850,
      author       = {Wirtz, Marius Oliver},
      title        = {{T}hermal {S}hock {B}ehaviour of {D}ifferent {T}ungsten
                      {G}rades under {V}arying {C}onditions},
      volume       = {161},
      school       = {RWTH Aachen},
      type         = {Dr.},
      address      = {Jülich},
      publisher    = {Forschungszentrum Jülich GmbH Zentralbibliothek, Verlag},
      reportid     = {FZJ-2013-02241},
      isbn         = {978-3-89336-842-6},
      series       = {Schriften des Forschungszentrums Jülich : Energie $\&$
                      Umwelt / Energy $\&$ Environment},
      pages        = {100 S.},
      year         = {2012},
      note         = {RWTH Aachen, Diss., 2012},
      abstract     = {Thermonuclear fusion power plants are a promising option to
                      ensure the energy supply for future generations, but in many
                      fields of research enormous challenges have to be faced. A
                      major step on the way to the prototype fusion reactor DEMO
                      will be ITER which is build in Cadarache, southern France.
                      One of the most critical issues is the field of in-vessel
                      materials and components, in particular the plasma facing
                      materials (PFM). PFMs that will be used in a device like
                      ITER have to withstand severe environmental conditions in
                      terms of steady state and transient thermal loads as well as
                      high particle fluxes such as hydrogen, helium and neutrons.
                      Candidate wall materials are beryllium, tungsten and carbon
                      based materials like CFC (carbon fibre composite). Tungsten
                      is the most promising material for an application in the
                      divertor region with very severe loading conditions and it
                      will most probably also be used as PFM for DEMO. Hence, this
                      work focuses on the investigation of the thermal shock
                      response of different tungsten grades in order to understand
                      the damage mechanisms and to identify material parameters
                      which influence this behaviour under ITER and DEMO relevant
                      operation conditions. Therefore the microstructure and the
                      mechanical and thermal properties of five industrially
                      manufactured tungsten grades were characterised. All five
                      tungsten grades were exposed to transient thermal events
                      with very high power densities of up to 1.27 GWm$^{−2}$ at
                      varying base temperatures between RT and 600 °C in the
                      electron beam device JUDITH 1. The pulse numbers were
                      limited to a maximum of 1000 in order to avoid immoderate
                      workload on the test facility and to have enough time to
                      cover a wide range of loading conditions. The results of
                      this damage mapping enable to define different damage and
                      cracking thresholds for the investigated tungsten grades and
                      to identify certain material parameters which influence the
                      location of these thresholds and the distinction of the
                      induced damages. Furthermore the grain structure and the
                      recrystallisation of the material have a significant
                      influence on the thermal shock damage, especially the
                      cracking pattern and surface roughening. Beside the thermal
                      shock damage mapping tungsten was also successively exposed
                      to steady state high flux hydrogen-plasma and to cyclic
                      thermal shock events simulated with an electron beam. The
                      induced damages were investigated to determine if the
                      exposure to hydrogen-plasma has an influence on the thermal
                      shock response of tungsten. Special attention was paid to
                      the thermal shock crack parameters such as distance, width
                      and depth. The investigations showed that there is a
                      significant influence on the damage behaviour of tungsten,
                      especially if the tungsten targets are pre-loaded with
                      hydrogen plasma. Beside the sequence of the exposure also
                      the surface temperature during the plasma loading shows a
                      clear influence on the thermal shock [...]},
      keywords     = {Dissertation (GND)},
      cin          = {IEK-2},
      cid          = {I:(DE-Juel1)IEK-2-20101013},
      pnm          = {133 - Fusion technology for ITER (POF2-133)},
      pid          = {G:(DE-HGF)POF2-133},
      typ          = {PUB:(DE-HGF)11},
      url          = {https://juser.fz-juelich.de/record/133850},
}