Plasma

Influence of rf discharge in Н$_2$–Ne mixture on surface topography and light transmission of sapphire

A. E. Gorodetsky^a, V. L. Bukhovets^a, A. V. Markin^a, R. Kh. Zalavutdinov^a, A. P. Zakharov^a, T. V. Rybkina^a, S. I. Pozin^a, V. A. Kabanova^a, O. Yu. Grafov^a, E. E. Mukhin^b, A. G. Razdobarin<sup>b

a</sup> Institute of Physical Chemistry and Electro Chemistry, Russian Academy of Sciences, Moscow
^b Ioffe Institute, St. Petersburg

Abstract: Three effects of cleaning plasma on the surface topography and transmission stability of a sapphire window are investigated. Firstly, the effect on the surface of long-term exposure to a capacitively coupled RF discharge in a 77% H$_2$–23% Ne mixture is considered. Secondly, changes in the structure of sapphire surface layers formed during long-term exposure to the cleaning plasma after removal of thin Al films are analyzed. Thirdly, changes in the structure of sapphire surface layers after triple deposition and subsequent removal of Al films are studied. The demonstrated transmittance stability of $r$-Al$_2$O$_3$ plates allows the use of an $r$-sapphire window to protect the “first mirror” of the ITER divertor Thomson scattering diagnostic system, as well as in other optical diagnostics in today's fusion research machines and tomorrow's fusion power plants.

Keywords: $r$-sapphire, protective window, AFM surface imaging, Al films, cleaning, iter.

Received: 20.02.2025
Revised: 22.04.2025
Accepted: 24.04.2025

DOI: 10.61011/JTF.2025.11.61594.24-25