Effect of Rising Edge on the Dynamics of Nanosecond Positive Diffuse Discharge

In this work, based on the previous published experimental research on the effect of nanosecond pulse rise time on atmospheric diffuse discharge morphology, we try to numerically investigate and explain the same phenonmena. With an ultrafast rise time of 2 ns, the discharge maintains a conical diffuse morphology at different voltage amplitudes (56-85 kV). However, when the pulse rise time is extended to 5.8 ns, the discharge transitions from a diffuse mode to a filamentary streamer. It is not until the voltage amplitude is raised to 85 kV that the filamentary streamer restores a diffuse state.



Through a fluid model, we reproduce the different discharge morphologies under various rise times and investigate the influence of the ionization source term correction factor calculated based on the electron advective and diffusive fluxes, local field approximation (LFA), and local energy approximation (LMEA) on this discharge dynamic process. When LFA is applied, it is observed that although the discharge exhibits a transverse discharge component yet lacks a main discharge channel; introducing an ionization source term correction factor results in the main discharge’s appearance. Conversely, with LMEA, the main discharge is present, but the expected transverse discharge component vanishes.



These results indicate that the transverse discharge component observed in the diffuse discharge within the fluid model is is attributed to a slower rise time, which prolongs the duration of the transverse electric field’s effect This, in turn, corresponds to the experimentally observed filamentary streamers that deviate from the axis. Therefore, when simulating diffuse discharge morphologies generated by fast-rise-time, high-overvoltage pulses at atmospheric pressure, it is necessary to incorporate an ionization source term correction factor within LFA to prevent electrons diffuse across the gradient from generating new ionization.