Analysis of processes responsible for the memory effect in air at low pressures

Abstract

Listen

Translate article

The memory effect in air at 0.7 and 6.6 mbar pressures, due to post-discharge survival of some species that affect subsequent breakdowns, was analysed using memory curves. In order to complete the analysis of the processes, memory curves for nitrogen have also been monitored, because air is 78% nitrogen. In an early afterglow, the memory effect in air, as well as in pure nitrogen, is a consequence of the same processes, i.e. the presence of and ions, formed by the collision between nitrogen metastable molecules from the previous discharge. The concentrations of nitrogen ions in an air-filled tube are lower than the concentration in a nitrogen-filled tube for a given afterglow period because of their recombination with O, O2 and NO particles which are also present in the early afterglow in air. De-excitation of N2(A) and N2(a′) metastable molecules due to their collision with O2, O and O− particles also contributes to the reduction in the concentration of and ions. In the late afterglow in air and pure nitrogen, N(4S) atoms created during the previous discharge are responsible for the memory effect. In the early air afterglow N(4S) atoms can be formed by the collision of O+ ions with N2(X) molecules. However, because of the relatively small concentration of these ions the most probable process is the recombination of N(4S) atoms with O2, O, NO and NO2 particles. The net effect is that the concentration of N(4S) atoms in the late afterglow is less in air than in nitrogen. When the concentration of N(4S) atoms is sufficiently reduced, the breakdown is initiated by cosmic rays.