Ar metastable kinetics: Role of photoemission in a LF and LF-RF DBD in Ar-NH₃ at atmospheric pressure

The population of metastable argon atoms (1s₃ and 1s₅ in Paschen notation) are recorded in an atmospheric pressure Ar-NH₃ DBD at 50 kHz (LF) and 5 MHz+50 kHz (RF+LF). A 1D fluid model is used to compare the kinetics of Ar_m in these discharges. From the comparison between measurements and calculations, it is shown that the evolution of metastables in the model is too slow and does not fit the temporal evolution measured during a LF cycle. By adding a photoemission process via the dissociation of an argon dimer to the model, the kinetics is improved, and the model reproduces the various physical phenomena experimentally observed in both LF and LF + RF discharges. After a preliminary study, it seems that photoemission is an essential mechanism driving the discharge kinetics in homogeneous DBDs at atmospheric pressure.