Experimental study of contamination and cleaning of in-vessel mirrors for ITER optical diagnostics on T-10 and QSPA-T facilities

Abstract ITER-relevant hydrocarbon films deposited under controlled conditions in the SOL of T-10 tokamak during working and cleaning discharges and by using QSPA-T plasma gun at plasma shots onto W and graphite targets were investigated by XPS, XAES and ellipsometry. XPS survey, valence band and C1s, O1s core level spectra showed differences in chemical composition and electronic structure as between T-10 and QSPA-T films and between T-10 films obtained in working and cleaning discharges. Hydrogen content evaluation in the films was made independently by analysis of XPS valence band edge position and ellipsometry data. The Csp 2 carbon content was determined from XAES CKLL spectra. Classification of T-10 and QSPA-T films was undertaken using ternary phase diagram (H, Csp 2 and Csp 3 ). It was shown that all studied hydrocarbon films are positioned between diamond- and polymer-like a-C:H films. The observed difference between XPS and ellipsometry evaluations of hydrogen content may be connected with strong structural non-uniformity of the films along thickness.