Electrical Characterization of the Cycle-to-Cycle Repeatability of an Atmospheric Pressure Plasma Jet

Atmospheric pressure plasma jets operate by projecting a streamer discharge toward remote substrates. The formation and propagation of streamers is an inherently stochastic process, which leads to cycle-to-cycle variations in streamer properties. The present work quantifies these variations through electrical measurements of a plasma jet striking a conductive substrate. It was found that streamer ignition and magnitude can change substantially from cycle to cycle and thus differ from time-averaged measurements taken over many cycles. For example, the energy required to drive the plasma jet and the amount of charge delivered to the substrate during a given cycle can vary from their respective averages by a factor of 2 or more. While some of this can be due to power supply stability, several other operating characteristics of the plasma jet were found to influence repeatability. It was found that helium and argon produced plasma jets with different levels of repeatability, with the repeatability of argon strongly dependent on the feed gas flow rate. Jets driven with pulsed-DC were notably more repeatable than those driven by a high-voltage sinewave. This is attributed to the difference in voltage rise time, which promotes more consistent ignition times. Increasing the voltage and frequency of the pulsed-DC plasma jet can further improve repeatability, where voltages above 2 kV and driving frequencies above 200 Hz significantly enhance the repeatability of the plasma jet.