Maxwell and non-Maxwell behavior of electron energy distribution function under expanding plasma jet conditions: The role of electron-electron, electron-ion, and superelastic electronic collisions under stationary and time-dependent conditions

A stationary and a time-dependent Boltzmann equation including elastic, inelastic, and superelastic terms has been solved for conditions typically met in expanding the Ar-H, plasma jet, i.e., for large ionization degrees and large concentrations of electronically excited states. The results show that the stationary electron-energy distribution functions (EEDFs) in the presence of electron-electron and electron-ion (e-i) Coulomb collisions evolve to the bi-Maxwellian distribution function in which the lower temperature is determined by e-i collisions, and the higher one by superelastic electronic collisions. On the other hand, the time-dependent EEDF clearly shows long plateaus generated by superelastic electronic collisions for times comparable to the expansion ones.