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Single-crystal and polycrystalline diamond erosion studies in Pilot-PSI

Abstract : Diamond is a promising candidate for enhancing the negative-ion surface production in the ion sources for neutral injection in fusion reactors; hence evaluation of its reactivity towards hydrogen plasma is of high importance. High quality PECVD single crystal and polycrystalline diamond samples were exposed in Pilot-PSI with the D + flux of (4-7)·10 24 m-2 s-1 and the impact energy of 7-9 eV per deuteron at different surface temperatures; under such conditions physical sputtering is negligible, however chemical sputtering is important. Net chemical sputtering yield Y = 9.7·10-3 at/ion at 800°C was precisely measured ex-situ using a protective platinum mask (5x10x2 µm) deposited beforehand on a single crystal followed by the post-mortem analysis using Transmission Electron Microscopy (TEM). The structural properties of the exposed diamond surface were analyzed by Raman spectroscopy and X-ray Photoelectron Spectroscopy (XPS). Gross chemical sputtering yields were determined in-situ by means of optical emission spectroscopy of the molecular CH AX band for several surface temperatures. We observed a bell shape dependence of the erosion yield versus temperature between 400°C and 1200°C, with a maximum yield of ~1.5·10-2 at/ion attained at 900°C. The yields obtained for diamond are relatively high (0.51.5)·10-2 at/ion, comparable with those of graphite. XPS analyses show amorphization of diamond surface within 1 nm depth, in good agreement with molecular dynamics (MD) simulation. MD was also applied to study the hydrogen impact energy threshold for erosion of [100] diamond surface at different temperatures.
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Submitted on : Thursday, October 10, 2019 - 3:29:12 PM
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D. Kogut, D. Aussems, N. Ning, K. Bystrov, A. Gicquel, et al.. Single-crystal and polycrystalline diamond erosion studies in Pilot-PSI. Journal of Nuclear Materials, 2018, 500, pp.110-118. ⟨10.1016/j.jnucmat.2017.12.028⟩. ⟨hal-02310941⟩



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