Criteria for partial LTE in an argon thermal discharge at atmospheric pressure; validity of the spectroscopically measured electronic temperature

A collisional-radiative (C-R) model is used to obtain the population number densities of the excited levels of neutral and singly charged ions in argon for 6000K<T_c<13000K for P=1 atm; radiative processes, atomic and electronic collisions altogether with diffusive phenomena are taken into consideration. The threshold value n_e^th for the electronic density, corresponding to a Saha equilibrium for the lower-lying excited levels, is determined for each T_e value. A simplified model allows evaluation of the influence of each process on the density of the set of metastable and pseudo-metastable atomic excited levels of the 3p⁵ 4s electronic configuration. For the different zones of the discharge, the Saha and Boltzmann temperatures, which can be experimentally obtained, are compared to the electronic temperature T_c.