Abstract In this work, we experimentally and numerically investigated positive and negative diffusive ionization wave characteristics under a double voltage pulse scheme in low-pressure (200 mbar) Nitrogen/Oxygen mixtures. In the experiment, we recorded the characteristics of both first and second discharges. In the simulation, we fully simulated two consecutive discharges and obtained similar results to the experiment with the positive discharge. For the first discharge, positive ionization wave width and length decrease with oxygen concentration, while negative discharge remains consistent but with a worse repeatability. During the second pulse, positive discharge shrinks in morphology but maintains propagation velocity due to the quasi-neutral plasma shielding effect s at the second discharge, which is reproduced and explained through a 2D fluid model. The second negative discharge exhibits pulse-interval-dependent branching probability (increasing then decreasing with pulse interval), which is observed across all tested mixtures. Combined simulation-experiment analysis excluded the effects of residual charge and gas temperature in this branching process: On the one hand, the residual charge density becomes very low and uniformly distributed after the long pulse interval. On the other hand, even under double pulses with the lowest intervals, the gas temperature increase remains limited. Finally, through modeling on the shock wave generated by the first discharge, we attributed negative discharge branching to shockwave-induced gas density gradients near the electrode. The higher gradient surface and lower head electric field of the negative discharge compared to the positive causes localized protrusions, which then grow into filament streamers.
Guo et al. (Tue,) studied this question.