Modeling of the glow discharge cathode sheath and the cathode surface sputtering in a mixture of argon with mercury vapor

Abstract

A model of the glow discharge cathode sheath in a mixture of argon with mercury vapor used in gas discharge illuminating lamps is developed. It takes into account that at the stage of lamp ignition the mercury atom density is by several orders lower than the argon atom density and depends on the temperature. The cathode sheath characteristics are calculated and it is shown that at a temperature increase, due to growing contribution of the mercury atom Penning ionization, the discharge cathode voltage drop is decreased and the ratio of the mercury and argon ion current densities at the cathode is increased. The energy spectra of the mixture component ion flows bombarding the cathode surface, as well as their corresponding effective sputtering rates and the sputtered atom flow densities, are found. It is shown that at low values of the discharge current density mercury ions practically do not participate in the cathode sputtering because their energies are less than the threshold sputtering energy. However, at its higher values they can make a significant contribution to the sputtering despite the small mercury content in the mixture.