Transient Development of Nanosecond Gas Discharges

The development of cufrent in gaseous spark gaps has been investigated in the context of a transmission-line pulse system. A simple model, which utilizes the electron continuity equation, provides a description of the formative period as well as the current buildup during the resistive phase. The E-field in the gap is assumed to be spatially uniform and dependent on time through temporal variations in the applied field. We have employed this simple model in analyzing the dependence of the formative time on the initial parameters of the discharge. At the end of the breakdown formation process, space-charge and secondary ionization effects become important. A two-dimensional time dependent model has been developed to include these effects. Current waveforms obtained from both models have been compared with experimental waveforms. Experimental measurements were performed in a 50-Ω pulse transmission-line system. Incident voltage waveforms of approximately rectangular shape were applied between large electrodes in a nitrogen filled test gap. Incident voltage and transmitted current waveforms were monitored with capacitive dividers and recorded by a fast transient digitizer.