E-Beam Spreading and Resulting Field Variations in CO2 Laser Plasmas

Abstract

large optical cross sections using e-beam controlled discharges in CO2 and very recently6 with uv initiation of self-sustained discharges. Principal differences between these two methods are in the spatial variations of electron production for the e-beam and the difficulty in obtaining large optical aperture without arc development for the self-sustained discharge. This paper presents a closed form method for rapidly analyzing and predicting e-beam controlled discharges while accounting for the spatial variations of electron production. Predictions obtained from this method are compared to experimental measurements. The e-beam controlled discharge7'10 has been analyzed for CO2 gas mixtures at 1 atm pressure. Previous analytical methods required considerable computer time because they were based on Monte Carlo7'13 calculations for electron scattering to determine spatial source functions of electron energy disposition. Fixed sets of laser cavity configurations, gas compositions, and densities have been successfully modeled. A new and fast computational method for describing the spatial variations of electron energy disposition in e-beam controlled discharges has been developed. Primary electron range enhancement or de-enhancemen t effects are included, but backscattering and electron-runaway effects are neglected. Spatial variations in the resulting drift current density and applied field are easily determined using the streamtube continuity approximation.9 Experiments using a 10-1 discharge volume controlled by a 0.4 A/cm2, 175 kV ebeam were conducted to derive data for correlation. Experimental values of the effective recombination rate, the e