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TCV mirrors cleaned by plasma

Marot, L. and Coda, S. and Kajita, S. and Moser, L. and Steiner, R. and Meyer, E.. (2017) TCV mirrors cleaned by plasma. Nuclear Materials and Energy, 12. pp. 605-610.

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Abstract

Metallic mirrors exposed in TCV tokamak were cleaned by plasma in laboratory. A gold (Au) mirror was deposited with 185-285 nm of amorphous carbon (aC:D) film coming from the carbon tiles of TCV. Another molybdenum (Mo) mirror had a thicker deposit due to a different location within the tokamak. The thickness measurements were carried out using ellipsometry and the reflectivity measurements performed by spectrophotometry revealed a decrease of the specular reflectivity in the entire range (250-2500 nm) for the Mo mirror and specifically in the visible spectrum for the Au. Comparison of the simulated reflectivity using a refractive index of 1.5 and a Cauchy model for the aC: D gives good confidence on the estimated film thickness. Plasma cleaning using radio frequency directly applied to a metallic plate where the mirrors were fixed demonstrated the ability to remove the carbon deposits. A mixture of 50% hydrogen and 50% helium was used with a -200 V self-bias. Due to the low sputtering yield of He and the low chemical erosion of hydrogen leading to volatile molecules, 20 h of cleaning were needed for Au mirror and more than 60 h for Mo mirror. Recovery of the reflectivity was not complete for the Au mirror most likely due to damage of the surface during tokamak exposure (breakdown phenomena). (C) 2017 The Authors.
Faculties and Departments:05 Faculty of Science > Departement Physik > Physik > Nanomechanik (Meyer)
UniBasel Contributors:Meyer, Ernst
Item Type:Article, refereed
Article Subtype:Research Article
Publisher:Elsevier
ISSN:2352-1791
Note:Publication type according to Uni Basel Research Database: Journal article
Language:English
Identification Number:
Last Modified:15 Jan 2018 12:09
Deposited On:15 Jan 2018 12:09

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