Characteristics of spatiotemporal variations of primary and secondary streamers under pulsed-voltage in air at atmospheric pressure

A pulsed positive streamer discharge was simulated using a two-dimensional axisymmetric model to investigate the characteristics of primary and secondary streamers in air at atmospheric pressure and ambient temperature. The spatiotemporal variations of the reduced electric field and the electron density during propagation of the primary streamer were clarified, and their relationships with the applied voltage were discussed. The phenomenon of the secondary streamer was introduced according to the previously developed "attachment instability" theory, and the spatiotemporal variations of the net-attachment frequency were presented to validate the theory. The results indicated that variations in the reduced electric field and electron density can be approximately estimated by the theory even in conditions involving a pulsed voltage and non-uniform Laplacian field. Because the primary and secondary streamers have spatiotemporal characteristics related to the chemical reactivity in the streamer discharge, understanding these characteristics is valuable for the development of atmospheric-pressure plasma applications.