Reincrease in electron density in the current-decaying phase of pulsed-discharge of argon-hydrogen mixture

A noticeable reincrease in electron density was observed during the current-decaying phase of a pulsed Ar+H₂(10%) discharge in a pressure range of 133∼800 Pa. It was experimentally verified by using laser-induced fluorescence and self-absorption methods that the reincrease appeared concurrently with the increase in a population density of the first excited state of H atoms. This phenomenon can be reasonably explained by a mechanism that such excited atoms increase due to dissociative recombination of ArH⁺ ions generated in the ionizing phase of the discharge and they are reionized by electron collisions. A proposed model, which was expressed both by rate equations of H atoms on the ground and excited states and three kinds of ions such as H⁺, H₃⁺ and ArH⁺ and by a quasi-neutral equation of the plasma, can qualitatively explain these experimental results.