Light Transmission and Surface Topography of KU-1 Optical Quartz After Sputtering and Cleaning from Al Films in RF Discharge of H2(D2)–Ne Mixturesстатья
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Дата последнего поиска статьи во внешних источниках: 6 октября 2021 г.
Аннотация:In plasma devices, in which plasma–wall interaction and material migration are significant, thediagnostic-window transmission may decrease due to the contamination of plasma-cleaning components bysputtered materials. We discuss the cleaning of KU-1 fused silica, which simulates the diagnostic window,from aluminum films in RF plasma generated in pure H2(D2) and Ne and in H2(D2)–0.23Ne mixtures. Aluminum is used as a chemical analogue of Be, which is the main material of the International ThermonuclearExperimental Reactor (ITER) first wall. The morphology of the plasma-treated surface is investigated byatomic force microscopy, the chemical composition is analyzed by X-ray photoelectron spectroscopy, andthe transmission spectra in the range 400−1000 nm shows that plasma cleaning is accompanied by the slightreduction of quartz to suboxides and a simultaneous decrease in roughness Rq from 1.3 up to 1.0 nm. Afterplasma treatment of the quartz surface, a decrease in light transmission by 1.5–2% in the wavelength range400–750 nm is observed. Further sputtering of the purified quartz surface with the removal of a layer with athickness of more than 300 nm is accompanied by gradual smoothing of the surface and a decrease in Rq to1 nm, but with the retention of reduced light transmission. All investigated gases, hydrogen isotopes, neonand D2(H2)–Ne mixtures, are suitable for removing Al films from the quartz surface at a RF power of severalW/cm2 and temperatures of 20–100°C.