Surface-charge-mediated intrapulse discharge-channel reorganization in a nanosecond-pulsed doubly asymmetric coaxial DBD source

Abstract

Nanosecond-pulsed excitation provides rapid voltage transitions that can separate distinct discharge stages within a single pulse, while the internal discharge dynamics of coaxial dielectric barrier discharge (DBD) plasma-jet sources remain difficult to resolve when electrode coverage and dielectric topology are both asymmetric. Here, a two-dimensional axisymmetric fluid model is used to investigate an atmospheric-pressure argon coaxial DBD source with two dielectric barriers, asymmetric axial electrode coverage and a stepped inner dielectric. In the first post-start-up quasi-repetitive pulse at 8000 V, the active region evolves from ionization near the outer dielectric wall during the rising edge, through a plateau dominated by surface-charge memory, to reactivation near the stepped inner dielectric wall during the falling edge. The outer dielectric-gas interface current peaks at approximately 0.197 A at 20.990 μs, whereas a stronger inner-interface peak of approximately 0.319 A occurs at 22.050 μs. Time-resolved plasma quantities, surface charge, boundary-integrated currents, line profiles and regional ionization-rate integration show that the dominant ionization region shifts from the outer interface toward the inner dielectric step. A surface-charge-reset calculation reduces the maximum electric-field magnitude and ionization rate at 22.050 μs to approximately 76.6% and 49.5% of their original values, respectively. The results reveal a stage-resolved reorganization of the internal discharge path governed by the asymmetric geometry, surface-charge memory and pulse timing.