Study of ion kinetics and ion acoustic wave excitation in self-pulsing discharge in argon at atmospheric pressure

Non-thermal plasmas at atmospheric pressure can be efficiently produced using self-pulsing discharges, such as transient sparks. An interesting feature of these discharges is the appearance of weak (≈ 1 mA) and erratic current oscillations (frequency in the MHz range) in the decaying current signal. These oscillations have been attributed to ion acoustic waves (IAW) and used to determine ion densities in argon plasma. Due to the possible practical application of ion density diagnostics, understanding the mechanisms of IAW excitation and determination of the dominant ions is of high importance. To gain insight into ion kinetics, a time-dependent, spatially 1D fluid-Poisson model coupled with an electric circuit equation is used to analyse self-pulsing discharges in atmospheric-pressure argon. The model reproduces a self-pulsing behaviour in the kHz range and the analysis of the charge carriers shows that the Ar₂⁺ ions are dominant in this discharge. The existence conditions of IAW are explored, and their frequencies are determined by solving the dispersion relation using the fluid model results as input.