Integrated Electrical, Spatial, and Thermal Characterization of Atmospheric-Pressure Ar–O₂ Plasma Jets with Ag and Cu External Ring Electrodes

Abstract

Atmospheric-pressure plasma jets (APPJs) require coordinated control of electrical excitation, gas flow, plume propagation, and thermal output to operate at controlled low temperatures. This study presents an integrated electrical and physical characterization of two geometrically identical Ar–O₂ APPJ systems employing external silver (Ag) and copper (Cu) ring electrodes. The electrical response was evaluated at 5 kHz over a voltage-setting range of 8–11 kV, while plasma-jet length was examined as a function of Ar flow rate and applied voltage. Plasma-effluent temperature was additionally measured as a function of downstream distance and excitation voltage. The measured voltage exhibited an excellent linear relationship with the power-supply setting (R² = 0.9988), with a nearly constant mean voltage-transfer factor of 1.417. Increasing the measured voltage from 11.31 to 15.70 kV increased the current from 7.63 to 9.83 mA and the displayed electrical power from 86.2 to 153.6 W. In contrast, plasma-jet extension showed a non-monotonic dependence on the operating parameters. The maximum visible jet length of approximately 2.5 cm was obtained at an Ar flow rate of 5 L/min and an applied voltage of 10 kV, demonstrating that maximum plume extension did not coincide with the highest electrical input or gas flow. The effluent temperature decreased from approximately 42.0–42.5 °C at the tube outlet to 35.0 °C at 3 cm, while a temperature of approximately 38.5 °C was measured at 2 cm under the 10 kV operating condition. Ag-APPJ and Cu-APPJ exhibited essentially identical plume-length behavior and closely overlapping thermal profiles, with temperature differences not exceeding approximately 0.5 °C. These results demonstrate that, for the investigated external-electrode configuration, the macroscopic APPJ behavior was governed predominantly by the operating conditions rather than by the Ag or Cu electrode material. The combined electrical, spatial, and thermal analysis identifies 10 kV and 5 L/min as a particularly favorable operating regime, providing maximum measured plume extension together with moderate downstream thermal output.