Comparative study on atmospheric-pressure helium plasma jets driven by pulsed voltage with different polarity

Abstract

A 2D axisymmetric study of the atmospheric pressure plasma jets driven by a trapezoidal pulse voltage with different polarities is performed in this work. The basic properties of the plasma jet in three stages, including the first discharge, the secondary discharge, and the afterglow of the plasma jet, are studied, with emphasis on the influence of voltage polarity on the secondary discharge and the afterglow. For the positive pulse voltage, the plasma jet propagates in the form of a bullet during the first stage. At the falling edge of the pulse, a new ionization wave resulting from the secondary discharge is formed and propagates forward along the preceding jet path in a continuous mode, resulting in a mixing jet propagation mode with the primary bullet and the luminous channel coexist. The plasma jet is finally converted to the continuous mode at the afterglow stage. Meanwhile, the first bullet almost stops propagating after the secondary discharge is ignited due to the rapid reduction of the electric field in the bullet head. In contrast, in the case of negative pulse voltage, a diffusive arrow-like plasma plume is observed during the first stage. The secondary discharge ignition does not completely change the direction of the electric field in the first ionization head and inhibits the propagation of the primary plasma jet. The dominant physics mechanisms associated with these observations are analyzed and discussed. In addition, the dependence of the reactive species on the secondary discharge under different pulse polarities is also compared.