Computation of ionisation growth at high current densities

A numerical method for integrating the continuity equations describing ionisation growth in gases between parallel-plane electrodes when space-charge distortion is important has been previously described. Simulated streak photographs were obtained showing the propagation of anode and cathode directed streamers in good agreement with experimental observations. The subsequent development of the discharge could not be traced, however, as the numerical errors in the computation led to instability. The present work describes an improved numerical method which allows the later stages of the discharge to be followed. Subsequent to the arrival of the cathode streamer at the cathode, several light fronts are observed crossing the gap before the glow phase of the discharge is established at currents of the order of 10 A. Comparison is made with the measurements in nitrogen of Chalmers et al. and Doran and good agreement is obtained between the computed and experimental values of light output from the discharge and total current flowing between the electrodes.