Because of use of carbon-based wall protection in fusion devices, many surfaces of inner components, remote from plasma, become to be coated with a carbon film. Among components subjected to C film deposition are elements of plasma diagnostics, e.g., in-vessel mirrors and windows of laser and optical methods [1.2]. From time to time these elements have to be cleaned from the contaminating films. One possible method is to use a cleaning discharge with plasma produced of a rather low temperature (T_e≤5 eV) [3]. The mechanism of removing carbon by such plasma is the chemical erosion of C film due to creation of volatile hydrocarbon molecules which can be desorbed from the surface and pumped out from the vacuum vessel. At that the efficiency of hydrocarbon molecules production is quite small, ∼2-3 %. The rate of C film cleaning could be significantly increased by providing discharge in oxygen (with efficiency up to 30% [4]), but this gas is forbidden to use in fusion devices. The possible way to enhance the efficiency of C film cleaning is to use the plasma produced by discharge in mixture of hydrogen with a heavy noble gases, as was suggested in [5]. This approach does not contradict to the general conception of the fusion reactor where the addition of a noble gas (heavier than helium) is considered as a real possibility to control the periphery plasma parameters [6]. In the present paper we analyze the published data on all important reactions in cold low-temperature plasma produced in mixture of hydrogen with noble gases: Ne, Ar, Xe, Kr. The main peculiarity of such plasma is the appearance of ions of hydrides, namely NeH⁺, ArH⁺, XeH⁺, KrH⁺, which practically do not exist as neutrals. It follows from analysis that just these ions are the main factor leading to increase of the rate of C film removing from contaminated surfaces compare to pure hydrogen plasma. With similar plasma characteristics (electron density and temperature), the concentration of hydride ions depends on the kind of a noble gas, and the higher concentration of such ions – the higher has to be efficiency of C film removal. The comparison data on cross sections of different reactions demonstrates clearly that between all noble gases, the highest concentrations of hydride ions would be in the Ar-H₂ mixture plasma. To present day there are no any experimental data on application of Ar-H₂ plasma for conditioning vacuum chambers or cleaning objects from C film (in [5] this mixture was not studied), and the main goal of this presentation is to ground the prospect of such experiment.
Besides, the preliminary comparable results will be presented on efficiency of cleaning of metallic mirrors from the carbon film using low temperature ECR plasma produced in deuterium and in deuterium-argon mixture.

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