Monte Carlo simulation of negative ion kinetics in air plasmas in a time-varying electric field

Abstract

The kinetics of and O− ions was addressed in air plasma in a rapidly time-varying electric field that is typical for nanosecond pulsed surface dielectric barrier discharges. Self-consistent sets of cross-sections for these ions in collisions with O2 and N2 molecules were developed. The Monte Carlo technique was used to calculate ion energy distribution, mean ion energy and reaction rate coefficients in a time-varying electric field at air pressures from 0.1 to 1 atm. Simulations showed that the ion characteristics followed the instantaneous values of the electric field at atmospheric pressure, whereas these characteristics evolved with a noticeable delay at lower pressures. As a result, the rates of electron detachment and ion charge exchange were much lower than those corresponding to the instantaneous values of the electric field at the leading edge of the voltage pulse. The reverse effect was observed for the rates of ion–molecule reactions at the trailing edge of the voltage pulse. Here, the reaction rates decreased with some delay in comparison with electric field variation. An approach was suggested to describe ion rate coefficients in time-varying electric fields on the basis of the Monte Carlo calculation of these coefficients under steady electric field conditions, and the calculation of the mean ion energy in unsteady electric fields.