Effect of electrons produced by ionization on calculated electron-energy distributions

Abstract

The effects of the form of the distribution in energy of the electrons produced by ionization on electron-energy distributions and transport coefficients are investigated theoretically at high values of the ratio of the electric field to gas density, $\frac{E}{n}$. The calculations are carried out for ${\mathrm{N}}_{2}$ at $\frac{E}{n}$ from 100\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}21}$ to 3000\ifmmode\times\else\texttimes\fi{}${10}^{\ensuremath{-}21}$ V ${\mathrm{m}}^{2}$ using previously determined electron-collision cross sections and secondary-electron energy distributions. As the energy of the secondary electrons and the energy lost by the higher-energy, scattered electrons is increased, the relative numbers of electrons at very low energies and at high energies in the calculated steady-state distributions decreases. These changes are accompanied by decreases in the calculated ionization coefficients, drift velocities, and mean energies and by an increase in the characteristic energy. A simplified secondary-electron energy distribution is proposed which gives distribution functions and transport coefficients in satisfactory agreement with the those obtained using the published experimental distributions.