Modelling of streamer discharges in air-filled sub-millimeter needle-plane electrode gaps under fast-rising field conditions

Streamer discharges are fast ionisation fronts generated under intensive electrical stress. They are a crucial stage in the evolution of an electrical breakdown in gas, and also important to a range of industrial applications. In this work, streamers in sub-millimeter needle-plane gaps in atmospheric air and under fast-rising ramp voltages are modelling using a hydrodynamic approach, using the an open-source finite-element framework. The plasma model used in this study is considerably more advanced than before, now including 7 species partaking in 18 total reactions, including photoionisation. The local mean energy approximation was additionally used to ensure validity over a wider range of electric field. The study of streamers in short gaps and fast-rising voltages helps to inform the design and understanding of HV pulsed power systems, including: the design of plasma-closing switches, understanding electrical breakdown in gas-insulated systems in divergent fields, design of HV diagnostics and discharge detection equipment, and the study of the impact of impulsive fields on plasma composition for chemical processing applications.