Experimental investigations of subnanosecond gas breakdown
Short, Brent D.
MetadataShow full item record
The recentiy developed concept of plasma limiters requires breakdown in gas with subnanosecond delays. If subnanosecond breakdown can be achieved in a transmission line or waveguide, most incoming power could be reflected, protecting any circuitry on the other side. This experiment consisted of a study of breakdown in gas using a needle tip to plane geometry with high voltage pulsers, ranging from 1 to 7.5 kV, with a typical risetime of 500 ps. The setup consists of a pulser feeding a 50 U transmission line to a needle-plane test gap inside a vacuum chamber, terminated in a 50Q load line. The needles used have a tip radius of less than 1|xm to produce a high electric field enhancement at the test gap. Measurements were taken from current and voltage sensors on the input transmission line, and the luminosity of discharge was measured with a photomultiplier tube. For voltages of 1.7 kV and below, a minimum breakdown delay of 12 ns was measured. At 15 kV, achieved with a 7.5 kV pulser with the voltage doubling at an open circuit at the test gap, subnanosecond breakdown delays were observed. The pressure was varied from 10^-6 Torr to 600 Torr to obtain breakdown delay characteristics according to pressure. The results of the fastest breakdown observed point toward a vacuum type discharge with field emitted electrons as the dominant breakdown mechanism, with a certain pressure of gas required to sustain the discharge across the test gap.