Penetration of an atmospheric pressure plasma jet into a micro-channel: Forward ionization wave and restrike

In this Letter, we reported both experimental observation and 2D fluid modeling on the penetration of an atmospheric pressure plasma jet into a high-aspect-ratio micro-channel in a dielectric substrate. Two distinguished discharges inside the micro-channel, namely, a forward ionization wave (FIW) and a restrike, were identified by streak images and well predicted by the model. The FIW manifested as a bulk streamer, while the restrike appeared as a surface-hugging discharge that propagated along the charged surface with higher velocity and higher plasma intensity. As such, the restrike could affect the plasma treatment of materials with micro-channels such as fibers and structured catalysts. Our results further revealed the formation of the restrike depended on the applied voltage waveform. Thus, the propagating distance of the restrike could be modulated by the width of the voltage pulse, indicating an effective method to control the plasma dose to the treated samples.