Sub-nanosecond breakdown in argon and air

Sub-nanosecond gaseous breakdown is of key importance in several areas including high-speed switching for pulsed power applications, fast breaking plasma limiters for RADAR protection, and the development of Ultra-Wideband (UWB) RADAR sources. This paper summarizes research done to expand the traditionally accepted range for E/p plots of similarity laws describing breakdown. Experiments were carried out using a variety of rounded electrode gap geometries and spacing combinations with over-voltages up to a factor of 35. This paper also describes modifications to the existing test set-up, which were performed in order to minimize rise time and reduce impedance mismatches.

All experiments performed in this research used a pulse delivery system with short coaxial transmission lines feeding an axial or radial spark gap inside a vacuum chamber. The gap geometry, whether it was axial or radial, incorporated a conical inner and outer conductor designed to maintain a constant impedance as the transition was made from transmission line to gap.

The electric field distribution at the gap in these experiments is more homogenous than that created using the tip-plane geometry of previous research. The data in this paper encompasses a relatively wide range of voltages and pressures. At each relevant combination of voltage and pressure where breakdown occurred, the conduction current was calculated. Minimum voltage - current delay times on the order of 200 ps were calculated for high E/p and compared to previously published results.