Removing W-contaminants in RF plasma to maintain optical performance of the ITER UWAVS first mirror
other
The PBS 55 GA Upper Wide Angle Viewing System (UWAVS) provides real-time, simultaneous visible and IR images of the ITER diverter region via optical systems located in the upper port plugs of the ITER vacuum vessel. Optical performance is expected to deteriorate due to mirror contamination from plasma operations and imaging and temperature measurements are expected to reach unacceptable error levels. In the UWAVS design, a first mirror (FM) cleaning system will be implemented to maintain / restore optical performance. The Front End Optical Tube (FEOT) is schematically illustrated in Fig. 1. Since the UWAVS FM looks at the diverter region contamination with tungsten is expected. Tungsten is not expected to be a main contaminant, yet removing it with ion sputtering becomes challenging due to the high atomic mass. 10 nm levels of contamination degrade FM optical performance. The proposed radio-frequency (RF) plasma cleaning was demonstrated in a prototyping RF plasma setup. Cleaning of various materials is discussed in a separate paper.
TNO Identifier
961358
Publisher
TNO
Source title
13th International Symposium on Fusion Nuclear Technology, ISFNT-13, 25-29 September 2017, Kyoto, Japan
Collation
1 p.
Place of publication
Delft, The Netherlands
Files
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