Modeling study on different discharge characteristics in pulsed discharges with and without barriers on electrodes

High-pressure nanosecond pulsed discharges (NPDs) have attracted increasing attention in recent years due to their wide potential applications. In this study, a barrier-free NPD in pure helium plasma at 120 Torr was numerically investigated by a one-dimensional self-consistent fluid model, and its current-voltage characteristics show very different behaviors from those in pulsed dielectric barrier discharges (DBDs), indicating an entirely distinctive discharge evolution in pulsed discharges with or without barriers on electrodes. Without the control of barriers, the computational data suggest that the discharge current increases very sharply during the plateau phase of the pulsed voltage and reaches its peak value at approximately the instant when the pulsed voltage starts to drop, together with a gradual reduction in the sheath thickness and an increase in electric field in the sheath region, which is in good agreement with experimental observations. By increasing the voltage plateau width and repetition frequency, the discharge current density from the simulation can be substantially enhanced, which cannot be observed in conventional pulsed DBDs, and the spatial distributions of the electric field and charged particles are given to unravel the underlying physics. From the computational data, the distinctive discharge characteristics in barrier-free NPDs are deeply understood, and could be further optimized by tailoring the waveform of the pulsed voltage to obtain desirable plasmas for applications.