Field emission enhanced breakdown in gaseous spark gaps in sub-nanosecond pulsed regime

Sub-nanosecond breakdown of low pressure gaseous spark gaps has been investigated using a combined modeling of the volume discharge in gas and the electron emission at the electrodes. For this purpose, in the gaseous region the continuity equations for the electrons and ions are solved together with the Poisson´s equation. In the electrodes, the thermo-field electron emission current at the surface is used to calculate the current density distribution and the temperature increase in the electrodes; the same method is normally used to simulate the initiation of emission sites on the cathode in vacuum gaps. The resulted emission current density at the electrodes is used as the boundary condition for the volume discharge equations in the gaseous region. Simulation results indicate that depending on the homogeneity of the electrodes, one of two parallel running processes, i.e. the breakdown of the gaseous spark gap due to the volume ionization of the gas and the initiation of the explosive electron emission site on the cathode surface, precedes the other. Simulation results predict minimum breakdown delays of about 400 ps for the geometries considered in this paper. These results are in good accordance with the measurements reported earlier.