Optimization of energetic electron energy degradation calculations

Abstract

The optimization of the energy degradation and reapportionment computer algorithms within theoretical computations of the effects and behavior of photoelectrons and other energetic electrons is established within a framework of discrete losses resulting from inelastic collisions with a neutral gas and interactions with the ambient electron gas. The basic method described guarantees energy conservation, while allowing large increases in the energy cell sizes with increasing energy with minimal distortion of the total excitation rates of neutrals and heating of the ambient electrons over what would otherwise be possible. When energy resolution of the spectra can be sacrified, extensions to very large energies are economically feasible using approximately seven cells per decade of energy without significant distortions in the energy reapportionment to other species. The emphasis is not on what particular set of cross sections should be used but rather on how to adapt the energy degradation procedure and the energy grid to the characteristics of the cross sections over the energy range of interest. For example, accurate determination of the ambient electron heating rate in terrestrial applications requires fairly small energy cells at low energies (usually less than 0.2 eV wide below 10 eV), while secondary ionization rates and most neutral excitation rates place no severe limitations on the energy cell sizes. Cell widths much larger than the excitation thresholds are possible and can be large fractions of the mean cell energy. At energies above 30 eV, cell widths that are up to 40% of the mean cell energy appear adequate for some applications not requiring high spectral resolution.