Experiments and simulations of an atmospheric pressure lossy dielectric barrier Townsend discharge

A diffuse discharge is produced in atmospheric pressure air between porous alumina dielectric barriers using low-frequency (60 Hz) alternating current. To study its formation mechanism, both the discharge current and voltage are measured while varying the dielectric barrier porosity (0%, 48% or 85%) and composition (99% Al₂O₃,99% SiO₂ or 75% Al ₂O₃ + 16% SiO₂ + 9% other oxides). Time-resolved imaging of the emission is carried out to understand the discharge structure. The results indicate that the ionization is driven by an electron avalanche process. This Townsend discharge is found to persist for quite some time (∼3 ms) when the barriers are alumina with a high porosity (>48%). Micro-streamers are observed for the low porosity alumina barriers as well as for other oxide barriers. This discharge formation with highly porous alumina in air is attributed to a relatively low volume dielectric barrier resistivity (∼10⁵ Ω m). Simulations are carried out, accounting for the surface charge loss due to this porosity, as well as for charge accumulation at the barriers.