Print Email Facebook Twitter Removing W-contaminants in helium and neon RF plasma to maintain the optical performance of the ITER UWAVS first mirror Title Removing W-contaminants in helium and neon RF plasma to maintain the optical performance of the ITER UWAVS first mirror Author Ushakov, A. Verlaan, A.L. Ebeling, R.P. Rijfers, A. O'Neill, R. Smith, M. Stratton, B. Koster, N.B. van der List, J.F.M. Gattuso, A. Lasnier, C.J. Feder, R. Maniscalco, M.P. Verhoeff, P. Publication year 2018 Abstract First metallic mirrors used in optical diagnostics such as the Upper Wide Angle Viewing System (UWAVS) in ITER may undergo contamination with beryllium and tungsten. Contamination levels of 10 nm can significantly degrade mirror performance. A UWAVS first mirror cleaning system prototype uses radio-frequency (RF) gas discharge to remove contaminants. Although tungsten is not expected to be a main contaminant, removing it with ion sputtering may become challenging due to the high atomic mass. Cleaning tests were focused on 10–20 nm tungsten layers removal from various substrates using a tailored RF circuit in He and Ne. W-coatings were also produced on an existing single-crystal (SC) Mo-mirror 105mm diameter. He and Ne were chosen for many tests due to their effectiveness and suitability for ITER operations. Sputtering conditions were determined through ion energy measurements. Ion energies of 100–150 eV and currents of 0.5–0.8 A/m2 were found to be optimum for 30–40 MHz RF discharges. The cleaning rate in He was 0.3–0.5 nm/hour for W-deposits. Etching rate of 1 nm/hour was observed for the Mo-mirror. No surface roughness degradation was determined with SEM and optical interferometry after mirror material was removed. Overall exposure time of the SC Mo-mirror was 100 h. Subject First mirrorIon sputteringPlasma cleaningRadio-frequency dischargesHigh Tech Systems & MaterialsIndustrial Innovation To reference this document use: http://resolver.tudelft.nl/uuid:25cba1e8-6a59-4535-bfaa-0f6293b90f47 DOI https://doi.org/10.1016/j.fusengdes.2018.02.082 TNO identifier 954954 Publisher Elsevier, Amsterdam ISSN 0920-3796 Source Fusion Engineering and Design, 136 (136), 431-437 Document type article Files To receive the publication files, please send an e-mail request to TNO Library.