Start-up of a pulsed plasma jet: from branching to guided streamers

When an atmospheric pressure plasma jet is operated by pulsed voltages with a kHz-range repetition frequency, guided streamers — often called plasma bullets — are typically observed. One of their most notable properties is that these guided streamers follow a predetermined path rather than branch as streamers normally do. This behavior is due to a memory effect where the remnants of previous discharges provide a guiding channel for the new streamer to follow. However, when the plasma jet is first turned on, such guiding channel cannot be present yet and consequently there must be a development phase during which the guiding channel is formed.In this contribution we present a detailed study of the development from branching to guided streamers in a pulsed plasma jet generated in N2 and flowing into open air. During the first voltage pulses after the initial ignition a transition from branching to guided streamers is indeed observed. The length of the guided part of the streamer is determined from individual recordings of the emission with an intensified charge-coupled device (ICCD) camera to examine the transition. This process is repeated for different applied pulse voltages, repetition frequencies and gas flow rates to establish the relation between the development and these parameters. With a numerical calculation of the gas velocity field we show that the development of the guiding channel is closely related to the transport of remnants of previous discharges in the gas flow