Monte Carlo Simulation of the Ion and Fast Atom Energy Spectra at the Cathode Surface in Low-Current Discharge in a Mixture of Argon with Mercury Vapor

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Simulation of ion and fast atom motion in the low-current discharge in an argon-mercury mixture used in gas discharge illuminating lamps is performed with the Monte Carlo method. As at the stage of discharge ignition mercury relative content in the mixture is small, only collisions of fast particles with slow argon atoms are taken into account. The energy spectra of the ion and fast atom flows bombarding the cathode surface are calculated. The energy distribution of mercury ions is shown to differ considerably from that found previously from analytical model based on the approximation of mercury ion continuous slowing down in argon. The effective rates of tungsten cathode sputtering by ions and fast atoms are calculated, as well as the flow densities of sputtered atoms, as functions of the reduced electric field strength in the discharge gap. At small mercury content in the mixture of the order of 10^–3, the cathode is found to be sputtered mainly by mercury ions. Their contribution to sputtering process decreases with increasing in the reduced electric field strength and decreasing in the mixture temperature.