Atmospheric pressure plasma jet: Effect of electrode configuration, discharge behavior, and its formation mechanism

Atmospheric pressure plasma jet (APPJ) can protrude several centers into the ambient air; therefore it holds remarkable promise for many innovative applications. The mechanism underlying this nonthermal discharge, however, remains unsettled that it has been often taken as resulting from dielectric barrier discharge or vaguely referred as streamerlike. We generated APPJ by using a quartz capillary tube with three distinct electrode configurations: conventional double dielectric electrodes for making dielectric barrier discharges, single dielectric electrode, and single bare metal electrode attached to the tube orifice. The jets generated by using the double dielectric electrodes were found consisting of three distinct parts and of different origins. The plasma jet starting from the active electrodes is essentially the propagation of streamers induced by corona discharge. With one single electrode, plasma jets can be generated in both downstream and upstream directions simultaneously; and more importantly at a significantly reduced voltage (peak-to-peak value from 3.6 kV on, at 17 kHz), this is particularly the case with the bare metal electrode configuration which also helps promote the jet velocity. The typical jet velocity at 10(4) m/s, the occurrence of a second streamer observed in the optical emission as well as the voltage and/or gas flow dependence of jet length can be reasonably accounted for by a streamer mechanism. These results may help steer the research into the underlying physics and will also facilitate a safer and more flexible implementation of this marvelous cold plasma source.