Pulsed excitation of low-pressure He-Xe glow discharges

摘要

Theoretical and experimental investigations of the temporal behaviour of the column plasma of square-wave-pulsed low-pressure glow discharges in mixtures of helium and xenon are presented. In the framework of the time-dependent, radially averaged model the equations for the external electrical circuit accounting for an approximate treatment of the electrode regions, rate equations for 13 xenon and 3 helium states and the time-dependent Boltzmann equations of the electrons are self-consistently solved. The experimental studies comprise time-resolved measurements of the electrical characteristics and of the axis densities of the lowest excited states of xenon. The main aspects of the self-consistent model and of the electrical and spectroscopic measurements are given and the results for the He-Xe mixtures containing 2% of xenon in a discharge tube with a diameter of 17.5 mm and an electrode distance of 20 cm at applied voltages between 140 and 250 V and gas pressures between I and 4 Torr are presented. The agreement between experimental and theoretical data is generally good during the entire pulse period. The analysis shows that the velocity distribution function of the electrons is subject to large structural alterations as a result of the periodic change between the on-phase of the discharge, driven by the electric field, and the off-phase when chemo-ionization process gets large importance. However, the chemo-ionization processes are not efficient enough to act as a reservoir of charged particles under the conditions considered. Concerning the excited xenon atoms it is found, in particular, that their temporal behaviour is significantly influenced by their mixing due to electron collision processes for optically forbidden transitions in the afterglow period.