Oxygen glow discharge cleaning in nuclear fusion devices

Hopf, C.; Jacob, W.; Rohde, V.

doi:10.1016/j.jnucmat.2007.10.001

Cited by 27 publications

(18 citation statements)

References 31 publications

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“…in an ECR plasma with rf-biased sample holder on the erosion rate of a-C:H films [18]. The erosion rate saturates between R = 0.1 and 0.2, because with increasing supply of molecular oxygen erosion becomes limited by the ion-induced creation of reactive sites.…”

Section: Introductionmentioning

confidence: 99%

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Oxygen glow discharge cleaning in ASDEX Upgrade

Hopf

Rohde

Jacob

et al. 2007

Journal of Nuclear Materials

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Oxygen-containing glow discharges have been proposed for the removal of redeposited hydrocarbon films in fusion experiments. After the 2004/2005 experimental campaign a 49 hours He/O 2 glow discharge experiment was performed in ASDEX Upgrade. A total of 25 g of carbon was removed as CO and CO 2 . In order to probe erosion in various locations in the vessel 48 well defined laboratory-deposited a-C:H film samples were distributed poloidally and toroidally. In principle, the films were successfully removed on all types of surfaces directly facing the discharge. Additionally, two sets of tungsten-coated tiles were removed from the vessel, one prior to and one after the cleaning discharge. Analysis of films on the tiles revealed that they consisted mainly of boron with only little carbon and deuterium. Neither erosion of these films nor any further reduction of their carbon and deuterium content due to the glow discharge could be detected.

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Section: Introductionmentioning

confidence: 99%

“…We have studied the erosion of redeposited layers from AUG in laboratory experiments [18]. Complete removal of the layers was demonstrated on collector samples as well as on tiles, which had been removed in 2002.…”

Section: Introductionmentioning

confidence: 99%

Oxygen glow discharge cleaning in ASDEX Upgrade

Hopf

Rohde

Jacob

et al. 2007

Journal of Nuclear Materials

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“…Therefore, the erosion behavior of such mixed layers needs to be investigated. Moreover, a reduction of the chemical erosion of carbon by doping has been reported, but is still not fully understood [13][14][15] (for a review of this field see [16]). Hence, metal-doped carbon films represent a model system to investigate the erosion of redeposited carbon films by oxygen plasmas.…”

Section: Introductionmentioning

confidence: 99%

Erosion of tungsten-doped amorphous carbon films in oxygen plasma

Wang

Jacob

Balden

et al. 2012

Journal of Nuclear Materials

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Abstract:Tungsten-doped amorphous carbon films with 0-9 at.% W concentration were produced by magnetron sputtering and eroded in oxygen plasmas applying different bias voltages and substrate temperatures. The partial C and W erosion rates were determined from the C and W areal density changes measured by Rutherford backscattering spectrometry (RBS). The initial C removal rate increases with increasing ion energy and temperature and decreases with increasing W concentration. For W-doped films the erosion rate decreases with increasing plasma exposure duration. At low bias voltages the erosion process stops after W accumulation at the surface, which protects the carbon underneath from further erosion. RBS and X-ray photoelectron spectroscopy suggest that the Wrich layer at the surface is carbon free and consists of porous WO 3 . Biasing to 200 V leads to removal of W by physical sputtering and, therefore, inhibits the formation of the protecting W oxide layer and the C erosion proceeds.

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“…A disadvantage that leads to its replacement in the designs of new fusion devices is, however, the high erosion yield that would seriously limit the lifetime of plasma-facing components. Furthermore, the eroded carbon is redeposited along with hydrogen from the plasma in locations with no or little erosion, producing layers that can have a high hydrogen content like soft a-C:H [13,14] or can structurally resemble hard a-C:H [15,16] and can contain substantial amounts of other elements [17]. In an all-carbon machine operating with a D/T mixture this redeposition can be a dominant mechanism of the retention of radioactive tritium [18].…”

Section: Introductionmentioning

confidence: 99%

Characterization of temperature-induced changes in amorphous hydrogenated carbon thin films

Hopf¹,

Angot²,

Aréou³

et al. 2013

Diamond and Related Materials

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Hard hydrogenated amorphous carbon thin films were heated in vacuum to different temperatures and held at these for at least 30 min. Afterwards, the cooled-down samples were analyzed by various techniques. Strict and reproducible correlations were found between all the determined parameters and the annealing temperature. Single-wavelength ellipsometry shows that the real part of the refractive index of the films at 633 nm wavelength decreases with temperature while the extinction coefficient increases. It also shows swelling of the films with a thickness increase of about 50 % for films heated to ≈ 1000 K. The associated decrease of mass density is proportional to the decrease in refractive index. Ion beam analysis shows that hydrogen is released from the films during heating with only about 5 % of the initial H remaining after annealing at 1300 K while no significant loss of carbon can be detected. The losses of hydrogen during heating are monitored by temperature programmed desorption and they are in good agreement with the ion-beam-analysis results. Raman spectroscopy delivers evidence of aromatization of the films under heat treatment. Indication of first structural changes is found already at 600 K while the quickest changes of the refractive index, thickness, and hydrogen content with temperature occur around 850 K.

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Oxygen glow discharge cleaning in nuclear fusion devices

Cited by 27 publications

References 31 publications

Oxygen glow discharge cleaning in ASDEX Upgrade

Oxygen glow discharge cleaning in ASDEX Upgrade

Erosion of tungsten-doped amorphous carbon films in oxygen plasma

Characterization of temperature-induced changes in amorphous hydrogenated carbon thin films

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