Discharge modes of self-pulsing discharges in argon at atmospheric pressure

Abstract Self-pulsing discharges are an intriguing method to generate non-thermal plasma using DC high voltages. However, the sophisticated interaction between the electrical circuit and the actual plasma characteristics is still not well explored. Therefore, this study presents a modelling study on self-pulsing discharges in pure argon at atmospheric pressure in a 1.5 mm gas gap. A time-resolved, one-dimensional fluid-Poisson model coupled to an equivalent circuit with variable parameters is applied to analyse the impact of circuit parameters like resistance and applied negative DC high voltage on basic discharge properties. This includes the analysis of the spatio-temporal development of the densities of charge carriers and excited species, the electric field and ionisation rates in combination with the synchronised electrical quantities like discharge current, discharge voltage and self-pulsing frequency. In particular, three distinct periodic self-pulsing modes of the discharge are found, i.e. a transient spark, a transient glow and a modulated DC glow mode. The transition between these modes is related to different recharging times of the circuit capacitance for different external resistances in series with the gas gap. It leads to changes in the predominance of the different ionisation processes together with the crucial impact of pre-ionisation on the discharge inception. These insights provide essential knowledge on tunability within a selection of self-pulsing DC discharge modes for generating non-thermal plasma with desired effects, e.g. for material processing and environmental or medical applications.