Effect of collisional transitions on the population distributions of excited atoms in a plasma

The effect of collisional transitions on the population distribution of excited atoms has been studied by considering a plasma in which the electron density varies with time. It has been found that for highly excited states, for which the ionization rate is much larger than that of electron-density variations, the collisional transitions are not important compared with the collisional ionization and recombination processes. However, for intermediate and lower excited states, they play an important role in making the population distribution approach Saha equilibrium with the electrons.