Decay of Electron-Beam-Generated Argon Plasma upon Outflow into Unexcited Gas

Decay of plasma excited by injection of a quasi-stationary beam of high-energy electrons into argon filling a cylindrical reaction chamber is studied experimentally. Based on the results of analysis of experimentally obtained dependence of the length of the plasma-jet glow region on gas parameters and theoretical estimates, a conclusion is made that plasma decay under studied conditions turns out to be substantially slower relative to decay of plasma containing one type of molecular ions. A kinetic model of decaying electron-beam-generated argon plasma according to which evolution of processes responsible for decay has two stages is proposed. At the first stage, atomic ions of argon transform into molecular ions. The latter recombine with electrons at the second stage. The rate of plasma decay is determined by a relatively slow first stage, while electron-ion recombination occurs on a time scale much shorter than the plasma lifetime.