Ionization wave propagation in an atmospheric pressure plasma multi-jet

Abstract

The atmospheric pressure multi-plasma jet produces an array of individual plasma jets which originate from the branching of a single ionization wave (IW). The use of arrays of such plasma jets could enable treatment of larger surface areas than is possible with a single plasma jet. In this paper, we discuss results from a combined experimental and two-dimensional modeling investigation of the behavior of IWs in an atmospheric pressure plasma multi-jet device. In this multi-jet, a rare gas is flowed through a tube having a line of holes, producing gas jets into the ambient from each of the holes. A primary ionization wave (PIW) propagates through the tube which launches a series of secondary ionization waves (SIWs) propagating out each hole through the plumes of the individual gas jets. The propagation of the SIWs is more intense using a positive polarity voltage pulse due to the higher electric field at the ionization front. The diameter of the holes determines the delay of the SIW after passage of the PIW past the hole, with smaller holes resulting in larger delays. The larger delay results from a smaller view angle for photoionization outside the tube from photons originating in the PIW. Higher helium flow rates result in a greater tendency for SIW propagation because the air concentrations in the individual gas jets outside the tube are lower and so the electron temperature is higher. The interaction between SIWs is primarily electrostatic, and is a sensitive function of geometric parameters including proximity of ground planes and the spacing between the holes through which these SIWs emerge.