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Investigation and plasma cleaning of first mirrors coated with relevant ITER contaminants: beryllium and tungsten

Moser, L. and Doerner, R. P. and Baldwin, M. J. and Lungu, C. P. and Porosnicu, C. and Newman, M. and Widdowson, A. and Alves, E. and Pintsuk, G. and Likonen, J. and Hakola, A. and Steiner, R. and Marot, L. and Meyer, E. and Contributors, J. E. T.. (2017) Investigation and plasma cleaning of first mirrors coated with relevant ITER contaminants: beryllium and tungsten. Nuclear Fusion, 57 (8). 086019.

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Official URL: http://edoc.unibas.ch/58439/

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Abstract

In order to extend the investigation of the plasma cleaning of ITER first mirrors, a set of molybdenum mirrors was coated in a laboratory with ITER-relevant contaminants, namely beryllium and tungsten. Different coating techniques as well as several contaminant compositions were used to ensure a large variety of films to clean, completing a previous study conducted on mirrors exposed in the JET ITER-like wall (tokamak deposits) [ 1]. Due to the toxicity of beryllium, the samples were treated in a vacuum chamber specially built for this purpose. The cleaning was performed using capacitively coupled RF plasma and evaluated by performing reflectivity measurements, scanning electron microscopy, x-ray photoelectron spectroscopy and ion beam analysis. The removal of all types of contaminants was achieved by using different plasma compositions (argon, helium and mixtures of the two) with various ion energies (from 200-600 eV) and in some cases the mirror`s reflectivity was restored towards initial values. Pure helium discharges were capable of removing mixed beryllium/tungsten layers and oxidized molybdenum. In addition, no significant increase in the diffuse reflectivity of the mirrors was observed for the helium cleaning, though this was the case for some samples cleaned with argon. Helium is therefore appropriate for cleaning all mirrors in ITER leading to a possible cleaning regime where the entire vessel is filled with He and all mirrors are cleaned simultaneously without damaging their surfaces.
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:IOP Publishing
ISSN:0029-5515
e-ISSN:1741-4326
Note:Publication type according to Uni Basel Research Database: Journal article
Identification Number:
Last Modified:15 Jan 2018 12:18
Deposited On:15 Jan 2018 12:18

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