Boltzmann analysis of electron swarm parameters in CF4 using independently assessed electron-collision cross sections

Abstract

Using independently assessed electron-collision cross sections, electron swarm parameters were calculated via the solution of the Boltzmann equation under the hydrodynamic regime. The cross sections used for the calculations were from a previously published assessment of electron–CF4-collision cross sections that was recently updated. All of the cross sections used are based on published measurements (except those for direct vibrational excitation), and were not modified during the calculations to improve agreement between the calculated swarm parameters and the experimental values. Agreement between calculated and measured values of the swarm parameters was good for the drift velocity in pure CF4 and in mixtures with argon, for the transverse diffusion coefficient in pure CF4, for the longitudinal diffusion coefficient in pure CF4 and in mixtures with argon, and for the electron attachment coefficient in pure CF4. Agreement is poor for the ionization coefficient in CF4 at most electric field-to-gas density ratios. The mostly reasonable agreement between the measured and calculated electron swarm parameters using the independently assessed cross sections validates the cross sections and the model. The use of independently assessed cross sections removes the potential arbitrariness and lack of uniqueness that often characterize cross section sets derived from Boltzmann analyses. Conjectures as to possible reasons for the lack of agreement between the calculated and measured values of the ionization coefficient are discussed.