Use of electron backscattering for smoothing the discharge in electron-beam-controlled lasers: Computations

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Abstract
The anode material in an electron-beam-controlled gas laser strongly influences the uniformity of the sustainer discharge, because the backscattering of the beam electrons from the anode is different for different atomic numbers. As a result of switching from aluminum to, for instance, uranium, there is a 60% increase in the ionization near the anode, according to Monte Carlo computations for a typical planar laser configuration. This effect can cause a 30–60% drop in the local electric field, depending upon the field dependence of the electron-ion recombination coefficient. As an example for studying this effect, we have considered a 150-keV beam passing through an 0.8-mil Ti window into a 26-cm-wide planar cavity containing a 3:2:1 mixture of He, CO2, and N2 at 1 atm and 293 K, with Eave=4.5 kV/cm. Window power loading, electron attenuation, electron energy distributions, and sustainer field distributions were calculated for the two different anode materials.