Kharkiv, Ukraine
Kharkiv, Ukraine

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Eren B.,University of Basel | Marot L.,University of Basel | Ryzhkov I.V.,IPP NSC KIPT | Lindig S.,Max Planck Institute for Plasma Physics (Garching) | And 7 more authors.
Nuclear Fusion | Year: 2013

Optical diagnostic systems of ITER are foreseen to include metallic, plasma-facing, electromagnetic radiation reflecting components called first mirrors (FMs). Molybdenum coatings are important candidates for these components. Depending on the local plasma parameters of the reactor, the mirrors may be under net erosion or deposition conditions. In this work, we exposed molybdenum coatings to a high-flux deuterium plasma in order to test their roughening limits under erosion conditions. The high energy of deuterium ions (500 eV on average) results in more vigorous roughening of the surface compared with lower energy ions (200 eV). Longer exposure (3 × 1020 ions cm-2) of the 200 eV ions results in only a slightly increased roughness compared with shorter exposure (6.8 × 1019 ions cm-2). Both phenomena match to the theory regarding roughening dynamics of physical sputtering. A comparison of results in this work with previous studies gives support to the hypothesis that roughening is flux and temperature dependent. Partial delamination of the coatings is observed upon exposure at room temperature, but not at an elevated temperature (200 °C). In summary, Mo coatings will remain functional in the ITER environment under the expected conditions. However, changes in the expected conditions such as 500 eV mean energy of impinging charge exchange neutrals or <100 °C surface temperature of the mirrors can lead to gradual or sudden failure of the coatings. © 2013 IAEA, Vienna.

Voitsenya V.S.,IPP NSC KIPT | Balden M.,Max Planck Institute for Plasma Physics (Garching) | Bardamid A.F.,Taras Shevchenko National University | Bondarenko V.N.,IPP NSC KIPT | And 6 more authors.
Nuclear Instruments and Methods in Physics Research, Section B: Beam Interactions with Materials and Atoms | Year: 2013

The characteristics of surface microrelief that appear in sputtering experiments with polycrystalline metals of various grain sizes have been studied. Specimens with grain sizes varying from 30-70 nm in the case of crystallized amorphous alloys, to 1-3 μm for technical tungsten grade and 10-100 μm for recrystallized tungsten were investigated. A model is proposed for the development of roughness on polycrystalline metals which is based on the dependence of sputtering rate on crystal orientation. The results of the modeling are in good agreement with experiments showing that the length scale of roughness is much larger than the grain size. © 2013 Elsevier B.V.All rights reserved.

Bardamid A.F.,Taras Shevchenko National University | Bondarenko V.N.,IPP NSC KIPT | Davis J.W.,University of Toronto | Konovalov V.G.,IPP NSC KIPT | And 6 more authors.
Journal of Nuclear Materials | Year: 2010

The reflectance of Be mirrors due to impact by ions from a deuterium plasma has been studied under several bombardment conditions. Analysis of the resulting surface films has been performed using various diagnostic techniques, with the conclusion that the primary factor leading to the decrease in reflectance following bombardment with energetic ions is the conversion of the surface oxide layer, composed of BeO, to the hydroxide, Be(OD)2, with a corresponding increase in the optical extinction coefficient. The increase in the thickness of the layer is also important. Modifications to the surface layer are thought to involve a balance between the ion-induced diffusion of Be atoms to the surface where they may react with incident D and O atoms, and physical and chemical sputtering processes. For incident ion energies less than ∼50 eV, chemical reactions leading to disoxidation of the oxide-hydroxide film dominate, while keV-range ions (primarily D, but with some O impurities) lead to the formation of hydroxide, and an increase in the surface layer thickness. © 2010 Elsevier B.V. All rights reserved.

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