Plasma decay in air and N2 : O2 : CO2 mixtures at elevated gas temperatures

Abstract

Plasma decay after a high-voltage nanosecond discharge has been studied experimentally and numerically behind incident and reflected shock waves in high temperature (600–2400 K) air and N2 : O2 : CO2 mixtures for pressures between 0.05 and 1.2 atm. Time-resolved electron density history was measured by a microwave interferometer for initial electron densities in the range (1–3) × 1012 cm−3 and the effective electron–ion recombination coefficient was determined. A numerical simulation was carried out to describe the temporal evolution of the densities of charged and neutral particles under the conditions considered. It was shown that the loss of electrons in this case is determined by dissociative recombination with ions, whereas the effect of complex ions is negligible. Electron attachment to O2 to form negative ions is not important because of fast electron detachment in collisions with O atoms produced in the discharge. In the absence of O atoms the electron density could decay as if the loss of charged particles were governed by electron–ion recombination with the effective rate coefficient being much higher than the dissociative recombination coefficient.