Electrical breakdown of gases II. Spark mechanism in nitrogen

The growth of pre-breakdown ionization currents I in uniform fields in nitrogen has been measured over a range of the spark parameters E/p from 41 to 45 V/cm/mm Hg and pd up to 810 mm Hg cm with sparking potentials up to 38 kV, where p is the gas pressure and d the electrode separation. The graphs of log I against d were initially linear, but at separations near the sparking distance the graphs curved upwards, indicating the existence of both primary α and secondary (ω/α) ionization mechanisms. The sparking potentials and distance here measured were found to be exactly in accordance with those predicted by the growth of current equation I = I0exp (αd)/[1 – (ω/α) {exp(αd) –1 }]. There were strong indications that the secondary ionization was, in fact, a cathode process. Possible effects of space charge were also considered, and the spark mechanism discussed.