Study of the dark phase in the initial stage of the positive column formation in an argon glow discharge

The initial stage of the positive column formation in an argon glow discharge is investigated both experimentally and theoretically. A decrease in the plasma radiation intensity (the so-called “dark phase”) was observed experimentally over a time period of about 1 ms. A similar dip was also observed in the time dependence of the electric field strength. The time evolution of the population of the lowest metastable state of Ar was measured. A relevant theoretical model has been developed and used to perform calculations for the actual experimental conditions. A comparison between the numerical and experimental results shows that the model adequately describes the processes that occur during the formation of the positive column in an argon glow discharge. Experimental and theoretical study shows that the dark-phase effect is related to an excessive amount of metastable Ar atoms at the beginning of a discharge and, consequently, to high rates of stepwise ionization and chemionization.