Observations on the electrical breakdown of gases at 2800 Mc/s. Part 2: Relative breakdown stresses, statistical lags and formative lags

Gas confined in a nosed-in-cavity type of resonator is subjected to individual pulses of electric stress of frequency 2 800 Mc/s, and the variation of the field amplitude with time is recorded oscillographically. The study of the oscillograms deals with the statistical and formative time-lags preceding breakdown and with the relative breakdown stresses of various gases. In all experiments the gas in the resonator is irradiated by means of an auxiliary spark fired just before the beginning of the microwave pulse. The effect on the time-lags of the flux of radiation and, separately, of the distance between the irradiating spark and the resonator are examined. The formative time is found to be zero, within the limits of experimental error, for air, nitrogen, oxygen and hydrogen in all conditions examined. It is appreciable, however, in neon, argon and helium. The statistical time-lags are much greater in air and nitrogen than in oxygen and hydrogen. A study of these time-lags suggests that electrons are present in the gap throughout the pulse and that break down occurs as a consequence of a single event in the life of an electron, rather than by a progressive growth of ionization. The formative times in neon agree with the hypothesis that in this gas electrons are not removed during the pulse.