Chemical sputtering of carbon films by argon ions and molecular oxygen at cryogenic temperatures

Hopf, C.; Schlüter, Michael; Jacob, W.

doi:10.1063/1.2745267

Cited by 17 publications

(16 citation statements)

References 33 publications

(33 reference statements)

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“…It was shown, e.g., in ASDEX Upgrade that removal is very effective, but limited to surfaces with direct contact to the glow discharge [8] and similar results were obtained in TEXTOR [11]. It is known from laboratory experiments, that the ion energy plays a crucial role in the erosion process [12] and that a synergistic interaction between ions and molecular oxygen exists [10,13]. One would therefore expect that removal is only effective when particles with substantial energies reach the surface, which is not expected for deep gaps.…”

Section: Introductionsupporting

confidence: 53%

Carbon removal from tile gap structures with oxygen glow discharges

Schwarz-Selinger

Genoese

Hopf

et al. 2009

Journal of Nuclear Materials

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The removal of redeposited layers from tile gap structures with ITER-like geometries was investigated with various lowtemperature glow discharges in oxygen. The test structure consists of 19 mm deep gaps with widths ranging from 0.5 to 4 mm. Erosion rates inside the gaps are reduced compared with a directly exposed witness surface. Smallest erosion is found for the lowest particle energies. Erosion at the bottom of the gap increases linearly with the gap width. Erosion on the side walls drops nearly exponentially with increasing distance from the top. Side wall erosion dominates the total eroded amount for all cases investigated. The total eroded amount integrated over the whole inner gap surface is larger than the amount that would be eroded on a flat surface with an area identical to the gap opening.

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Section: Introductionsupporting

confidence: 53%

Carbon removal from tile gap structures with oxygen glow discharges

Schwarz-Selinger

Genoese

Hopf

et al. 2009

Journal of Nuclear Materials

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“…Especially for plasma oxidation, e.g. ASDEX Upgrade showed that removal is very effective even at room temperature [10,11] and similar results were obtained in TEXTOR [8] for elevated temperatures. For HT-7 it was reported that at wall temperatures between 400 and 470 K oxygen glow discharge cleaning was more effective than thermal oxidation [7].…”

Section: Introductionsupporting

confidence: 55%

“…However, up to now no dedicated measure-ments were conducted in present fusion experiments to clarify to what extent it is possible to remove co-deposits from nonplasma-wetted and remote areas with oxygen glow discharge cleaning. So far, it is only known from the ASDEX Upgrade cleaning experiment that no substantial erosion was found in remote areas [10,11].…”

Section: Introductionmentioning

confidence: 99%

“…This implies that other reactive species in addition to the energetic ones participate in the erosion process. Hopf et al demonstrated that a synergistic interaction between ions and molecular oxygen exists that can explain such high yields [11,26]. They devised a model that describes quantitatively the measured rates and their dependence on ion energy, ion and neutral fluxes and substrate temperature.…”

Section: Introductionmentioning

confidence: 99%

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Fuel removal from tile gaps with oxygen discharges: reactivity of neutrals

et al. 2009

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Carbon removal in so-called remote areas, where no energetic species can reach the surface, is investigated with low-temperature glow discharges in pure oxygen. Plasma-deposited amorphous hydrogenated carbon thin films are used as a model system for redeposited films. Erosion measurements are performed on flat substrates as well as on two different 3D test structures. One design consists of 19 mm deep gaps with widths ranging from 0.5 to 4 mm to simulate ITER tile gaps. A second design consists of a flat box-like structure where particles can enter only through a narrow slit. Measurements are performed for substrate temperatures ranging from 290 to 580 K. Erosion rates follow an Arrhenius-type dependence on substrate temperature with an effective activation energy of 0.25 eV. While at room temperature the surface loss probability of the dominant eroding species is 50 % it becomes smaller at elevated temperatures. At elevated temperatures the films are not only removed faster but simultaneously erosion penetrates deeper into the gaps.

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“…Vietzke et al [18] first demonstrated the existence of a synergism between energetic ions-in their experiment Ar + -and molecular oxygen. This synergism was recently investigated more thoroughly by Hopf et al [19]. The latter results are an indication that O 2 might be the most important chemically reactive species in low-temperature oxygen plasma erosion of carbon.…”

Section: Introductionmentioning

confidence: 83%

Oxygen glow discharge cleaning in nuclear fusion devices

Hopf

Jacob

Rohde

2008

Journal of Nuclear Materials

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Laboratory experiments were carried out as part of the preparations of an oxygen glow discharge cleaning experiment in ASDEX Upgrade. They aimed at evaluating the effect of mixing the oxygen with helium, the collateral damage caused by the glow discharge, as well as the influence of impurities in the films being eroded. Oxygen concentrations below 20 % in helium are sufficient to achieve high erosion rates. The discharge can lead to the formation of oxide layers on surfaces which-as demonstrated for tungsten-can be rapidly reduced by post-treatment in a hydrogen discharge. For carbon, aluminum and iron the physical sputtering yield may become similar to the erosion yield of redeposited layers, but it is by more than one order of magnitude smaller for tungsten. Using a-B:C:H films with varying boron content, it was found that impurities can cause the erosion rate to drop by orders of magnitude.

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Chemical sputtering of carbon films by argon ions and molecular oxygen at cryogenic temperatures

Cited by 17 publications

References 33 publications

Carbon removal from tile gap structures with oxygen glow discharges

Carbon removal from tile gap structures with oxygen glow discharges

Fuel removal from tile gaps with oxygen discharges: reactivity of neutrals

Oxygen glow discharge cleaning in nuclear fusion devices

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