Formative time lags in nitrogen and dry air

Abstract

Formative time lags have been measured in uniform-field gaps of up to 3 cm in air and nitrogen at pressures of 300 and 500 Torr. Recorded time lags were in the range 20 ns<or=tf<or=1.7 mu s for overvoltages Delta V of up to 50%. For each pressure and gap spacing, a discontinuity was found in the log-log plot of tf against Delta V for air but not for nitrogen. Consideration has been given to the possibility of a change in the breakdown mechanism as the overvoltage is increased. Observations of the form of voltage collapse at breakdown and comparison of measured and calculated time lag data suggest that the same basic breakdown mechanism, involving the production of photosecondary electrons at the cathode, exists over the entire overvoltage range of the present study. At high overvoltages, however, this mechanism is probably strongly influenced by distortion of the applied electric field due to the space charge produced in the early stages of ionization growth.