Multi-parameter control of nanosecond-pulsed atmospheric pressure plasma jets: Experiments, turning points, and control guidelines

Control of the operating parameters of atmospheric pressure plasma jets (APPJ) based on pulsed discharge is highly significant for applications in biomedicine and materials processing. Voltage amplitude, pulse width, and gas flow rate strongly influence APPJ discharge characteristics and therefore serve as key regulatory parameters. Here, a helium APPJ generation device was constructed using a high-voltage nanosecond pulse power supply. The effects of changes in voltage amplitude (Va, 4–8 kV) pulse width (tpw, 100–500 ns), and helium flow rate (QHe, 1–5 slm) on APPJ length, development velocity, and discharge stability were experimentally investigated. The results show that APPJ length initially increases and then saturates as tpw increases. Under high voltage and high flow rate, an excessively wide pulse tends to induce plasma instability, causing a reduction in APPJ length. The development velocity rises rapidly in the initial stage of discharge due to electric-field acceleration. As the propagation distance increases, electric-field attenuation and energy dissipation and the velocity fluctuation increase. Stability depends strongly on Va, with tpw and QHe also contributing. Notably, maximum instability occurs at moderate rather than extreme parameter combinations. Using transitions in growth behavior together with increases in the sample standard deviation of length as criteria, we identify turning points marking the onset of nonmonotonic behavior and show that they shift systematically with the other two parameters. These results provide quantitative guidance for coordinated tuning of Va, tpw, and QHe to achieve predictable and stable APPJ operation, and they offer a basis for a predictive, multi-parameter control framework.