On the Discharge Modes of 10-ns Atmospheric Pressure Helium Plasma Jets

Three discharge modes—guided streamer, transient spark, and low-impedance spark—were investigated here using a hollow needle-to-plate electrode configuration driven by 10-ns voltage pulses with a helium flow at 70 sccm at atmospheric pressure. The criteria of the discharge modes were assessed using energy deposition as well as spatiotemporally resolved rotational temperatures, which were determined by measuring the rotational temperature of the second positive system of $N_{2}$ . Guided streamer has the lowest energy deposition per pulse and the lowest rotational temperature among the three modes. As the discharge transitions from a streamer to a transient spark, then to a low-impedance spark, both the energy deposition and rotational temperature increase significantly. In addition, during the first 20 ns of the discharge, the mean energy of the excited states was strongly correlated with the external electric field and modes of the discharge; higher mean rotational energy was observed near the high-voltage needle electrode for streamers but closer to the ground plate for sparks.