Thermo-oxidative erosion of amorphous hydrogenated carbon films

Haasz, A.A.; Chiu, S.; Pierre, J.; Gudimenko, Y.

doi:10.1116/1.579916

Cited by 64 publications

(51 citation statements)

References 16 publications

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“…The scheme for thermal oxidation of hydrocarbon polymers provides a plausible reaction mechanism leading to the emission of D20, C02 and CO. This mechanism is consistent with the observed surface complexes [71].…”

Section: Haasz Et Al E711 Concluded That Essentially All Of the D Issupporting

confidence: 81%

“…Surface analysis after "02 exposure using X P S and SlMS revealed the appearance of carbonyl groups and an increase of hydroxyl groups due to surface oxidation [71]. The scheme for thermal oxidation of hydrocarbon polymers provides a plausible reaction mechanism leading to the emission of D20, C02 and CO.…”

Section: Haasz Et Al E711 Concluded That Essentially All Of the D Ismentioning

confidence: 99%

See 1 more Smart Citation

In-vessel tritium retention and removal in ITER

Federici

Anderl

Andrew

et al. 1999

Journal of Nuclear Materials

234

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Invited Review Paper -R2 CEI SUN 3 0 O S T ITritium retention inside the vacuum vessel has emerged as a potentially serious constraint in the operation of the International Thermonuclear Experimental Reactor (ITER). In this paper we review recent tokamak and laboratory data on hydrogen, deuterium and tritium retention for materials and conditions which are of direct relevance to the design of ITER. These data, together with significant advances in understanding the underlying physics, provide the basis for modelling predictions of the tritium inventory in ITER.We present the derivation, and discuss the results, of current predictions both in terms of implantation and codeposition rates, and critically discuss their uncertainties and sensitivity to important design and operation parameters such as the plasma edge conditions, the surface temperature, the presence of mixed-materials, etc. These analyses are consistent with recent tokamak findings and show that codeposition of tritium occurs on the divertor surfaces primarily with carbon eroded from a limited area of the divertor near the strike zones. This issue remains an area of serious concern for ITER. The calculated codeposition rates for ITER are relatively high and the in-vessel tritium inventory limit could be reached, under worst assumptions, in approximately a week of continuous operation.We discuss the implications of these estimates on the design, operation and safety of ITER and present a strategy for resolving the issues. We conclude that as long as carbon is used in ITER, the efficient control and removal of the codeposited tritium is essential. There is a critical need to develop and test in-situ cleaning techniques and procedures that are beyond the current experience of present-day tokamaks. We review some of the principal methods that are being investigated and tested, in conjunction with the R&D work still required to extrapolate their applicability to ITER. Finally, unresolved issues are identified and recommendations are made on potential R&D avenues for their resolution.

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Section: Haasz Et Al E711 Concluded That Essentially All Of the D Issupporting

confidence: 81%

Section: Haasz Et Al E711 Concluded That Essentially All Of the D Ismentioning

confidence: 99%

In-vessel tritium retention and removal in ITER

Federici

Anderl

Andrew

et al. 1999

Journal of Nuclear Materials

234

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“…4.7.3.1) [205][206][207][208][209], so they are considered at risk under ITER accident conditions, and their accumulation need to be strictly controlled on safety grounds. The released hydrogen is mainly in the form of water [210]. A precautionary operating limit of 1000 g was set for mobilisable in-vessel tritium in the 1998 ITER design, based on safety considerations due to the release from postulated accident sequences (more than a factor of two lower, i.e., about 350 g, is set for the design of the smaller ITER-FEAT).…”

Section: Insert Tablementioning

confidence: 99%

Plasma-material interactions in current tokamaks and their implications for next step fusion reactors

et al. 2001

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The major increase in discharge duration and plasma energy in a next step DT fusion reactor will give rise to important plasma-material effects that will critically influence its operation, safety and performance. Erosion will increase to a scale of several centimetres from being barely measurable at a micron scale in today's tokamaks. Tritium co-deposited with carbon will strongly affect the operation of machines with carbon plasma facing components. Controlling plasma-wall interactions is critical to achieving high performance in present day tokamaks, and this is likely to continue to be the case in the approach to practical fusion reactors. Recognition of the important consequences of these phenomena stimulated an internationally co-ordinated effort in the field of plasma-surface interactions supporting the Engineering Design Activities of the International Thermonuclear Experimental Reactor project (ITER), and significant progress has been made in better understanding these issues. The paper reviews the underlying physical processes and the existing experimental database of plasma-material interactions both in tokamaks and laboratory simulation facilities for conditions of direct relevance to next step fusion reactors. Two main topical groups of interaction are considered: (i) erosion/redeposition from plasma sputtering and disruptions, including dust and flake generation and (ii) tritium retention and removal. The use of modelling tools to interpret the experimental results and make projections for conditions expected in future devices is explained. Outstanding technical issues and specific recommendations on potential R&D avenues for their resolution are presented.

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“…As a consequence of the removal from vacuum, the surface of the a-CH x is exposed to air prior to application of the lubricant [26]. Exposure of a-CH x films to air or O 2 generates partially oxidized carbon species such as C-O-C, C-OH, and C=O on the a-CH x surface [34,35]. In our experiments using oxidized a-CH x surfaces either air or O 2 was introduced into the chamber immediately after a-CH x film preparation and prior to (CF 3 CF 2 ) 2 O and CF 3 CH 2 OH adsorption.…”

Section: Molecular Adsorption and Desorption Of Fluorocarbons On Fresmentioning

confidence: 99%

Electron stimulated decomposition of fluorocarbons on amorphous hydrogenated carbon (a-CHx) overcoats used in data storage media

2007

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The electron-induced surface chemistry of perfluoropolyalkylether (PFPE) lubricants on a-CH x films has been probed by studying the impact of free electrons on perfluorodiethylether, (CF 3 CF 2 ) 2 O, and 2,2,2-trifluoroethanol, CF 3 CH 2 OH, as models of the chemical functionality of PFPE lubricants such as Fomblin Zdol. Electron-stimulated decomposition of (CF 3 CF 2 ) 2 O and CF 3 CH 2 OH on fresh and oxidized a-CH x is observed when the sample is unbiased and in the presence of 70 eV free electrons. Electron-induced decomposition is indicated by the deposition of fluorine onto the surface of the a-CH x film following desorption of molecular (CF 3 CF 2 ) 2 O and CF 3 CH 2 OH by heating in front of a mass spectrometer. Biasing the sample to )80 V successfully eliminates the decomposition by preventing the impingement of electrons onto the surface. The electron-stimulated decomposition of PFPE lubricants may contribute to lubricant decomposition during normal drive operation.

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Thermo-oxidative erosion of amorphous hydrogenated carbon films

Cited by 64 publications

References 16 publications

In-vessel tritium retention and removal in ITER

In-vessel tritium retention and removal in ITER

Plasma-material interactions in current tokamaks and their implications for next step fusion reactors

Electron stimulated decomposition of fluorocarbons on amorphous hydrogenated carbon (a-CHx) overcoats used in data storage media

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