Bulk and surface modifications of metals submitted to hydrogen plasmas : the case of aluminum and tungsten Jury

Abstract : Plasma facing components in fusion reactors are exposed to intense thermal loads, plasma disruptions and high-flux particle bombardment. This leads to a plasma wall interactionthat degrades the overall performance of the materials, limits the lifetime of the components and has a strong influence on the plasma performance. One problem derived from plasmawall interactions is bubble and blister formation in materials. This poses a great concern since it changes the material properties and favors hydrogen isotope (HI) retention. Since tritium, a HI, is radioactive, its inventory is quite limited. Experiments have shown that surface modifications are highly influenced by several parameters such incident ion energy,fluence and crystallographic orientation. This work focuses on analyzing blister and bubble dynamics due to hydrogen plasma exposure in materials with a cubic crystal system and alow hydrogen solubility (i.e. Al and W). This provides a suitable background to understand phenomena related to crystallographic structure in hexagonal systems such as beryllium. In order to perform the experiments, the samples were polished and submitted to a heat treat mentto obtain a well-defined low-roughness base material. Afterwards, they were exposedto a fully characterized hydrogen plasma in which several parameters were varied, such asincident ion energy, fluence and discharge regime. The latter was performed in order to studythe effects stress, relaxation and cooling have on bubble and blister formation given tha tcurrent plasma reactors work in cycles instead of continuous plasma exposure. In addition,the microstructure and crystallographic orientation of the materials was varied during the experiments. The analysis of crystallographic orientation were performed by using {100},{110} and {111} single crystals. This allows studying blister morphology without the effect of grain boundaries and setting the basis to understand hexagonal crystal systems. Finally, in order to understand hydrogen dynamics in materials a 1D macroscopic rate equations model with a code named Hydrogen Isotope Inventory Processes Code (HIIPC) was used. This model allows predicting the amount of retained HI’s in materials and the physical processes involved in this interaction such as HI implantation, migration, depth distribution and their release. The results obtained with HIIPC support the results obtained in the experimental section and contribute in the understanding of hydrogen dynamics in material.
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Catalina Quiros Lara. Bulk and surface modifications of metals submitted to hydrogen plasmas : the case of aluminum and tungsten Jury. Chemical and Process Engineering. Université Sorbonne Paris Cité, 2017. English. ⟨NNT : 2017USPCD057⟩. ⟨tel-02288579⟩

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