The breakdown fields and risetimes of select gases under the conditions of fast charging (～20ns and less) and high pressures (20-100 atmospheres)

摘要

An interest in wide-band impulse radar systems has brought about the need to develop phased antenna arrays that can focus and steer an electromagnetic pulse in the far field. To produce useful radiated signal levels in the farfield, these arrays will need to be driven by high voltage, high power sources that at least in the short term may rely on pulsers using gas spark gap technology. To produce the high frequencies necessary, an array must be driven by sources with a risetime in the range of 100-200 picoseconds or even faster. Since multiple pulsers will have to be used to drive a large array, a suitable pulser design will most importantly have to have ultra-low triggering jitter (the standard deviation in the switch closure delay after trigger arrival). The jitter will have to be some relatively small fraction of this risetime to accurately synchronize the array to steer and preserve the risetime. This implies a jitter ideally in the 10's of pico-second range. Although risetimes can routinely be achieved in the desired range, the jitter requirement represents a breakthrough in spark gap technology. A preliminary gas characterization investigation preceded the development of such a fast risetime, ultra-low jitter triggered spark gap based pulser. This paper describes the results of this investigation that looked at the breakdown fields and risetimes for a variety of commonly used gases in the field of pulse power. The gases studied included SF6, air, 15 and 30% SF6/Air mixes, nitrogen, and hydrogen. The goals of this investigation were to: ·Characterize the breakdown field vs. pressure and examine the effects of: ·Polarity ·Varying stress times ·Uniform field vs. point-plane ·Compare the actual measured resistive phase risetimes to calculations