Electrical diagnosis of charge relaxation effects on pin-to-water DBD dynamics by Lissajous approaches

This study presents a systematic investigation into the effect of charge relaxation properties on the discharge behavior of a pin-to-water dielectric barrier discharge (DBD) reactor. Potassium chloride (KCl) solutions with concentrations ranging from 10−6 to 100 mol/L were employed to systematically manipulate the charge relaxation time (τe) of the liquid electrode. Our findings demonstrate that the discharge behavior critically depends on the ratio of τe to the characteristic timescale (tc) of the plasma–liquid system, derived from the applied voltage frequency. When τe/tc<0.1, charge transfer on the liquid electrode surface is significantly faster than the applied voltage switching, resulting in near-ideal parallelogram Q–V diagrams indicative of uniform and Townsend discharge. In the transition zone (0.1<τe/tc<1), the discharge shifts from input signal to charge transfer dominance, manifesting as almond-shaped Q–V diagrams attributed to conductivity-restricted plasma region expansion. For τe/tc>1, charge transfer becomes significantly slower than voltage switching, leading to substantial charge accumulation and elliptical Q–V diagram deformation due to charge residual. Furthermore, the non-uniform surface charge distribution, coupled with inherent plasma propagation asymmetry, results in stepped Q–V curves and several individual filamentary discharges during the rising period of applied voltage. These results provide fundamental insights into designing and controlling DBDs with resistive liquid electrodes for diverse applications.