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RF plasma cleaning of water-cooled mirror equipped with notch filter based on shorted λ/4 line

: Dmitriev, A.M.; Pflug, A. et al.


Fusion engineering and design 146 (2019), Pt.A, S.1390-1393
ISSN: 0920-3796
Fraunhofer IST ()
RF discharge; mirror cleaning; mirror cooling; RF notch filter; λ / 4 line; first diagnostic mirrors; physical sputtering

Physical and engineering aspects of RF plasma cleaning developed for actively cooled first mirror serving as grounded DC-coupled electrode are under consideration. Feasibility of the water-cooling lines implemented as the coaxial notch filter for ITER in-vessel diagnostic mirrors was demonstrated for Capacitively Coupled Radio Frequency (CCRF) discharge in neon at 1–10 Pa. The impinging ions energy as a function of absorbed RF power was measured for both the DC-coupled and -decoupled schemes. Sputtering yield variation over rectangular surface of stainless steel mirror was studied experimentally. The measured sputtering yield profiles were found to be in qualitative agreement with the RF plasma numerical simulations. It was demonstrated that Al/Al2O3 used as Be/BeO proxy can be removed from the water cooled mirror surface by 100 eV neon ions with the use of the notch filter. The 14 h plasma exposure didn’t affect the mirror reflectivity.