Discharge in Hydrogen-Noble Gas Mixture as the Method to Increase Efficiency of Conditioning of the In-Vessel Components of Large-Scale Fusion Devices

Fusion devices are needed very long wall conditioning time for preparation to experiments with hot plasma. The conditioning procedure is based on chemical reactions when hydrogen atoms and ions of low temperature plasma interact with contaminants coating the walls. With that, the efficiency of removal of carbon atoms is quite small, ～2 − 3%. The possible way to enhance the efficiency of C film cleaning is to use the plasma produced by discharge in mixture of hydrogen with one of heavy rare gases, as was suggested and demonstrated in [1]. This approach is acceptable in fusion reactor projects, where the addition of a rare gas (heavier than helium) is considered as the method to control the periphery plasma parameters. In the present paper we analyze the published data on the most important reactions in a low-temperature plasma produced in mixture of hydrogen with gases: Ne, Ar, Xe, Kr. The peculiarity of such plasma is the appearance of a group of hydride ions, NeH + , ArH + , XeH + , KrH + , which probably are important factor increasing the rate of C film removal compare to pure hydrogen plasma. The comparison of data on cross sections of different reactions demonstrates clearly that among all rare gases the highest concentrations of hydride ions would be in the Ar-H2 mixture plasma.