Mechanistic insights into pulsed streamer discharges under seed-electron pre-ionization

Abstract In pre-ionized pulsed streamer discharge, regulating the seed-electron density and its spatial distribution during the pre-ionization stage provides an effective approach to control streamer development and plasma chemical activity. Using electrical measurements, optical diagnostics, and a two-dimensional axisymmetric fluid model, this study systematically analyzes the behavior of pulsed streamer discharges under seed-electron pre-ionization and quantitatively clarifies how seed-electron density and spatial distribution govern the evolution of the primary streamer (PS), the secondary streamer (SS), as well as the generation of reactive species. The results show that ultraviolet pre-ionization enhances the discharge intensity and promotes streamer development. Under the same experimental conditions, simulations indicate that the minimum seed-electron densities required to initiate the development of PS and SS are 10 10 m −3 and 10 12 m −3 , respectively. When the seed-electron density exceeds 10 10 m −3 , PS development is enhanced, leading to increased formation of N 2 (C), N 2 + and O 2 + . Once the density exceeds 10 12 m −3 , SS development is accelerated, and the generation of N and O increases markedly. The spatial distribution of seed electrons is also critical to discharge development. Placing electrons near the anode region accelerates breakdown and promotes PS development, whereas electrons near the cathode region favor SS development, intensifies the radial electric field and electron density near the cathode region, and ultimately leads to a large discharge volume. These findings clarify how seed electrons regulate pulsed streamers and provide guidance for tailoring pre-ionization strategies to optimize plasma reactivity.