Inception and growth of an electrodeless atmospheric double-headed streamer

Gas discharge physics is particularly helpful to study many spectacular aspects of atmospheric electricity, e.g., lightning and sprite streamers. However, the observations of double-headed streamers (DHS) in nature-formed after the breakdown-remain an open question. Considering that the topic of DHS has been studied exclusively through theoretical and numerical models, this Letter presents the very first experimental model of DHS. Here, a primary plasma jet device operated at ground pressure is used to ignite a DHS in laboratory-scale experiments. This fundamental experimental model employs a noble gas flow (helium or neon) that expands freely and mixes with ambient air. The growth of the positive and the negative head was observed to originate from an isolated ionized column, directly confirming the previously published theoretical study. The high predictability and stability of the discharge allow advanced characterization diagnostics such as the Stark effect from which the electric field was measured along the discharge axis. This investigation indicates that a DHS can ignite in subbreakdown conditions and reveals the crucial role of the preionization phase. The consistency of these findings with some modeling studies on the topic will shed light on fundamental elementary processes in atmospheric electricity.