Simulation of ion generation and breakdown in atmospheric air

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Abstract
Understanding of ion generation in air provides insights to several applications, such as gas sensors, electrohydrodynamic pumping, and air purification. In this paper, ion generation processes in atmospheric air are simulated using a particle-in-cell and Monte Carlo method with emphasis on the prediction of ion generation and breakdown characteristics in microscale gaps. The simulation results are validated through comparison to Townsend’s discharge theory and experiments. The significance of each relevant electron-molecule reaction is characterized to improve understanding of ion generation dynamics. Self-sustaining discharge and ionization are predicted under sufficient voltage bias, and the predicted trends of breakdown voltage are similar to those obtained from Paschen’s curve. Corrections to Paschen’s curve in microscale gaps also are identified and compare well to experiments. Electron field emission produces stable electron current that suggests a controllable ionization device without external electron injection sources.