This work investigates the role of superimposed positive direct current (DC) bias on the discharge regime dynamics of radio frequency (RF) driven atmospheric-pressure plasma jets (APPJs). A variable positive DC bias ranging from 0 to 1600 V was applied to the powered electrode during RF excitation to examine its influence on plasma stability and ionization behavior. The discharge evolution was studied under three different RF power increment rates (1 W/10 s, 1 W/3 s, and 3 W/1 s) using electrical characterization and optical emission spectroscopy. The application of DC bias was found to mitigate abrupt current transitions associated with normal-to-abnormal glow regime switching and to reduce the saturation current in the abnormal glow regime. The electron density and excitation temperature exhibited a non-monotonic response, showing an initial enhancement at low DC bias followed by a reduction at higher bias levels, indicating bias-dependent modulation of plasma energetics. Analysis of floating potential fluctuations indicates that positive DC bias modifies the local electric field near the powered electrode, leading to a reduction in discharge instabilities consistent with suppressed electrode-driven electron emission. Overall, this study provides new insight into electric-field-assisted control of discharge regime behaviour in APPJs, offering a pathway toward improved plasma stability and controlled modulation of discharge regimes and plasma parameters, which is a prerequisite for tailoring plasma operation in advanced material processing and biomedical applications.
P. et al. (Thu,) studied this question.