Electron energy distributions in e-beam generated Xe and Ar plasmas

Abstract

Calculations have been performed to determine the time evolution of electron energy distributions in e-beam generated Xe and Ar plasmas. In these calculations, we have included electron-neutral elastic and inelastic collisions, electron-electron collisions, and electron-ion dissociative recombination. Our results indicate that in equilibrium the distributions can be reasonably approximated by a Maxwellian below the thresholds for inelastic electron-neutral processes. However, above these thresholds, the inelastic processes dominate so that the high-energy tails of the distributions are largely missing. As a result, a model which takes the distribution to be Maxwellian everywhere somewhat underestimates the average energy of the electrons or overestimates the ionization and direct-impact excitation rates. At very early times and after the removal of the e-beam, there can be significant departures from a Maxwellian distribution. Following removal of the e-beam, the electrons equilibrate with the gas; however, this equilibration occurs on a time scale that is long compared to many other processes in noble-gas eximer laser systems.