Computer modelling of a short-pulse excited dielectric barrier discharge xenon excimer lamp (λ∼172 nm)

Abstract

A detailed rate-equation analysis has been used to simulate the plasma kinetics in a pulsed-excited dielectric barrier discharge in xenon, under operating conditions where the discharge structure is spatially homogeneous. The one-dimensional model, incorporating 14 species and 70 reaction processes, predicts results that are in good agreement with experimental measurements of the electrical characteristics, and optical (vaccum-ultraviolet (VUV) and visible) pulse shapes. The model reveals that electrical breakdown of the discharge gap occurs via a fast-moving ionization/excitation wavefront that starts close to the anode dielectric and propagates towards the cathode at ∼3×105 m s−1. The wavefront appears as a result of successive avalanches of electrons that propagate across the discharge gap after release from the cathode dielectric. During breakdown, the mean electron energy in the bulk plasma is close to optimum for preferential excitation of the Xe* 1s4,5 states that feed the VUV emitting Xe2* excimer states. Calculations suggest that the overall conversion efficiency from electrical energy to VUV output in the plasma is greater than 60%, with >99% of the light output emitted in the VUV. Parasitic processes that act to reduce the key Xe* 1s4,5 and Xe2* populations are found to be essentially negligible. For pulsed excitation, the longer-term spatio-temporal behaviour of the electron/ions during the afterglow or inter-pulse period is important, resulting in a remnant `pre-pulse' ion density of ∼1015 m−3 close to the cathode dielectric. These ions bombard the cathode during the subsequent excitation period to release the secondary (seed) electrons required to achieve electrical breakdown.