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

• Published in: arXiv.org
• Main Authors: Kogut, D, Aussems, D, Ning, N, Bystrov, K, Gicquel, A, Achard, J, Brinza, O, Addab, Y, Martin, C, Pardanaud, C, Khrapak, S, Cartry, G
• Format: Paper Journal Article
• Language: English
• Published: Ithaca Cornell University Library, arXiv.org 11.10.2019
• Subjects: Amorphization; Chemical vapor deposition; Dependence; Deuterons; Erosion; Fusion reactors; Hydrogen plasma; Hydrogen-based energy; Ion sources; Molecular dynamics; Optical emission spectroscopy; Organic chemistry; Photoelectrons; Physics - Plasma Physics; Platinum; Polycrystalline diamond; Polycrystals; Raman spectroscopy; Single crystals; Spectrum analysis; Sputtering; X ray photoelectron spectroscopy; Yttrium
• ISSN: 2331-8422
• DOI: 10.48550/arxiv.1910.05155

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)\(\times\)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 \(Y = 9.7\times 10^{-3}\) at/ion at 800\(^\circ\)C was precisely measured ex-situ using a protective platinum mask (5x10x2 \(\mu\)m) 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\(^\circ\)C and 1200\(^\circ\)C, with a maximum yield of ~1.5\(\times\)10-2 at/ion attained at 900\(^\circ\)C. The yields obtained for diamond are relatively high \((0.51.5)\times 10^{-2}\) 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.