Simulation and Analysis of Field Ionization and Pre-breakdown Processes in Liquid Nitrogen under Pulsed Voltage

Simulation concerning the field ionization and streamer propagation processes in liquid nitrogen under pulsed voltage is performed to investigate the discharging characteristics and the factors that may influence the discharging process. In order to have a better description of field ionization in liquid nitrogen, a computational quantum chemistry method is utilized for obtaining the relations between the ionization potential of nitrogen molecule and the electric field. Results indicate that the pre-breakdown process could be divided into four stages which are initiation, propagation, re-ignition and annealing. In addition, the temperature in liquid nitrogen during the discharging process is investigated which shows that the temperature of liquid nitrogen in a small region near the needle electrode would reach the global maximum close to 120 K whereas along the discharge path there exists an area where the temperature of liquid nitrogen would exceed 85 K after 250 ns under 200 kV pulsed voltage with a 2 mm needle-sphere gap. Finally, several factors that would impact the streamer propagation are discussed.