Can gas puff be used for cleaning of the diagnostic first mirrors in ITER?

•It is proposed to use gas puff during the main plasma operation for cleaning of the main chamber diagnostic mirrors in ITER.•It is shown that for Be impurities from the first wall a net cleaning effect is expected.•Two potential issues are identified: (i) the required puffing rate might be too larg...

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Bibliographic Details
Published in:Fusion engineering and design 2017-11, Vol.123, p.834-837
Main Author: Kotov, Vladislav
Format: Article
Language:English
Subjects:
Cleaning
Diagnostic mirrors
Diagnostic systems
Diagnostics
Erosion
Fluxes
Impurities
ITER
Main chamber
Mirror cleaning
Mirror contamination
Neutral particles
Nuclear reactors
Plasma
Port plugs
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Summary:•It is proposed to use gas puff during the main plasma operation for cleaning of the main chamber diagnostic mirrors in ITER.•It is shown that for Be impurities from the first wall a net cleaning effect is expected.•Two potential issues are identified: (i) the required puffing rate might be too large; (ii) contamination by the material of the diagnostic duct wall. Erosion from the first mirrors of optical diagnostics can be enhanced by injecting neutral particles into plasma in the vicinity of the diagnostic entrance aperture. In the present paper feasibility of this method for cleaning from deposits is investigated numerically for conditions of the ITER main chamber diagnostics. Besides erosion on the mirror the local gas puff also increases fluxes of impurities due to sputtering from the neighboring surfaces. Calculations have shown that for external impurities coming from the main chamber (Be) the enhancement of erosion – cleaning effect – by far exceeds the extra deposition. However, two further problems have been revealed which may prevent practical use of the proposed technique. First, the gas puffing rate required for effective cleaning may be too large. Second is the contamination by “internal impurities” – sputtered material of the channels where the mirrors are installed.
ISSN:0920-3796
1873-7196
DOI:10.1016/j.fusengdes.2017.03.166