Experimental study of plasma decay in pulsed microwave discharges of H2, CH4 and their mixtures

Abstract

The results of the experimental investigations of the plasma decay in X-band pulsed microwave discharges produced by surface waves in hydrogen and hydrogen–methane mixtures under pressures of 0.5–5 Torr are presented. The electron density in the decaying plasma was measured by the resonator method using a high-Q quasioptical resonator. These investigations demonstrated a significant influence of ion conversion processes on the composition of ions in a hydrogen–methane plasma. Such conversion processes result in a change in ionization-recombination balance, which, in turn, influences the parameters of the discharge plasma. Ion recharging processes quickly convert the ‘primary’ ions in hydrogen into ions. It was found that the addition of even a few percent of CH4 to hydrogen, after a sequence of ion-molecular reactions, leads to the formation of complex ions Cx. Recombination coefficients and the dominant type of ions in hydrogen and hydrogen–methane plasma are reported.