Dielectric barrier discharges in helium at atmospheric pressure: experiments and model in the needle-plane geometry

Abstract

We present an experimental and numerical modelling study of dielectric barrier discharges in pure, flowing helium at atmospheric pressure, in a 3.0 mm length needle-plane gap. Ultra-high speed imaging and synchronous, real-time dual detection (optical–electrical) diagnostics have been carried out. The high-voltage electrode was a hyperboloidal steel needle with a sharp point of 40 μm radius, while the grounded electrode was covered with 1.6 mm of Al2O3. The surface of the latter was either bare (case 1) or coated with ∼20 nm of semiconducting graphite (case 2) or metallic aluminium (case 3), all at floating potential. Axial [z(t)] and radial [r(t)] time-evolutions (⩽2 μs) of discharge propagation across the gap were found to depend very strongly upon surface charging or conduction (cases 1–3). A two-dimensional model of the needle-plane discharge, based on coupled solution of the continuity equations for electrons, ions and excited neutral particles and of Poisson's equation, was found to agree very well with the observed [r,z](t) behaviour.