Ionization kinetics of optically excited lithium vapour underconditions of negative electron mobility

Abstract

This work, based on the numerical solution of the Boltzmannequation, analyses the influence of ionization processes onthe shape of the electron energy distribution function (EEDF)in a mixture of molecular nitrogen, heavy inert gases andresonant excited lithium vapour. The convergent close-couplingmethod is used to estimate the singly differential cross sectionsfor the ionization of Li(2S) and Li(2P) atoms byelectron impact. The composition of the three-componentmixture, when the negative electron mobility (NEM)can be observed, is determined. The mixture's ionization degree rangeand the relative density of the resonant excitedlithium atoms favourable for the maximal NEM are found. Itis shown that under optimal conditions the ionization rateis determined by electron-impact ionization of the Li(2P)states. In this case the characteristic time of EEDF formation proved to beshorter than the ionization time. Based on this fact, it is suggested howto realize NEM in a quasi-stationary regime under conditionsof increasing electron density caused by the resonant radiation.