Energy deposition and species generation in nanosecond pulsed diffuse discharges: A numerical study on voltage parameters and pressure regimes

The generation of reactive species and the associated energy efficiency (G-value) are critical metrics for plasma applications ranging from surface modification to plasma-assisted combustion. In this work, a comprehensive 2D axisymmetric fluid model incorporating a detailed chemical kinetic scheme for air is employed to investigate the energy deposition and chemical reactivity in nanosecond pulsed diffuse discharges. The model is rigorously validated against benchmark literature and experimental discharge current measurements. The study systematically explores the influence of voltage characteristics at atmospheric pressure and discharge polarity at low pressure (200 mbar). At atmospheric pressure, a critical trade-off is identified regarding voltage amplitude: while increasing amplitude (from 56 to 85 kV) significantly enhances total species production and energy deposition, it drastically reduces energy efficiency. Conversely, shortening the voltage rise time simultaneously enhances both the production yield and the energy efficiency (G-values) of key reactive species—such as reactive atomic species O(3P), N(4S), electronically/vibrationally excited states N2(v), and nitrogen oxide species (NO, N2O)—suggesting that rapid energy injection is key to optimizing diffuse discharges. At low pressure, the discharge polarity plays a dominant role; When the voltage amplitude is kept around 18 kV, at negative polarity discharges are found to outperform positive ones in both production volume and energy efficiency due to stronger ionization and wider spatial distribution. Furthermore, a comparative analysis reveals that low-pressure diffuse discharges generally exhibit higher G-values for atomic N and O production compared to atmospheric cases for a more favorable energy channeling at optimal reduced field and larger discharge volume.