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

L. Moser, R.P. Doerner, M.J. Baldwin, C.P. Lungu, C. Porosnicu, M. Newman, A. Widdowson, E. Alves, G. Pintsuk, J. Likonen, A. Hakola, R. Steiner, L. Marot, E. Meyer, JET Contributors

Research output: Contribution to journalArticleScientificpeer-review

8 Citations (Scopus)

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.
Original languageEnglish
Article number086019
JournalNuclear Fusion
Volume57
Issue number8
DOIs
Publication statusPublished - 23 Jun 2017
MoE publication typeA1 Journal article-refereed

Fingerprint

beryllium
cleaning
contaminants
tungsten
mirrors
helium
reflectance
molybdenum
argon
plasma composition
vacuum chambers
toxicity
x ray spectroscopy
vessels
coating
ion beams
deposits
photoelectron spectroscopy
scanning electron microscopy
ions

Keywords

  • ITER
  • plasma cleaning
  • reflectivity
  • surface analysis

Cite this

Moser, L., Doerner, R. P., Baldwin, M. J., Lungu, C. P., Porosnicu, C., Newman, M., ... JET Contributors (2017). Investigation and plasma cleaning of first mirrors coated with relevant ITER contaminants: beryllium and tungsten. Nuclear Fusion, 57(8), [086019]. https://doi.org/10.1088/1741-4326/aa73e2
Moser, L. ; Doerner, R.P. ; Baldwin, M.J. ; Lungu, C.P. ; Porosnicu, C. ; Newman, M. ; Widdowson, A. ; Alves, E. ; Pintsuk, G. ; Likonen, J. ; Hakola, A. ; Steiner, R. ; Marot, L. ; Meyer, E. ; JET Contributors. / Investigation and plasma cleaning of first mirrors coated with relevant ITER contaminants: beryllium and tungsten. In: Nuclear Fusion. 2017 ; Vol. 57, No. 8.
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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.",
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author = "L. Moser and R.P. Doerner and M.J. Baldwin and C.P. Lungu and C. Porosnicu and M. Newman and A. Widdowson and E. Alves and G. Pintsuk and J. Likonen and A. Hakola and R. Steiner and L. Marot and E. Meyer and {JET Contributors}",
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Moser, L, Doerner, RP, Baldwin, MJ, Lungu, CP, Porosnicu, C, Newman, M, Widdowson, A, Alves, E, Pintsuk, G, Likonen, J, Hakola, A, Steiner, R, Marot, L, Meyer, E & JET Contributors 2017, 'Investigation and plasma cleaning of first mirrors coated with relevant ITER contaminants: beryllium and tungsten', Nuclear Fusion, vol. 57, no. 8, 086019. https://doi.org/10.1088/1741-4326/aa73e2

Investigation and plasma cleaning of first mirrors coated with relevant ITER contaminants: beryllium and tungsten. / Moser, L.; Doerner, R.P.; Baldwin, M.J.; Lungu, C.P.; Porosnicu, C.; Newman, M.; Widdowson, A.; Alves, E.; Pintsuk, G.; Likonen, J.; Hakola, A.; Steiner, R.; Marot, L.; Meyer, E.; JET Contributors.

In: Nuclear Fusion, Vol. 57, No. 8, 086019, 23.06.2017.

Research output: Contribution to journalArticleScientificpeer-review

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T1 - Investigation and plasma cleaning of first mirrors coated with relevant ITER contaminants: beryllium and tungsten

AU - Moser, L.

AU - Doerner, R.P.

AU - Baldwin, M.J.

AU - Lungu, C.P.

AU - Porosnicu, C.

AU - Newman, M.

AU - Widdowson, A.

AU - Alves, E.

AU - Pintsuk, G.

AU - Likonen, J.

AU - Hakola, A.

AU - Steiner, R.

AU - Marot, L.

AU - Meyer, E.

AU - JET Contributors, null

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N2 - 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.

AB - 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.

KW - ITER

KW - plasma cleaning

KW - reflectivity

KW - surface analysis

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