Growth of ionization currents in dry air at high values of E/N

Uniform field steady-state ionization currents were measured in dry air as a function of N at constant E/N (E is the electric field strength and N the gas number density) and constant electrode separation d for 14·13 × 10⁻¹⁶ less-than-or-eq, slant E/N less-than-or-eq, slant 282·5 × 10⁻¹⁶ V cm². Uniform field sparking potentials were also measured for Nd range 1·24 × 10¹⁶ less-than-or-eq, slant Nd less-than-or-eq, slant 245 × 10¹⁶ cm⁻². The ratio of the Townsend primary ionization coefficient α to N, α/N, was found to depend on E/N only. The secondary coefficients were also evaluated for aluminium and gold-plated electrodes for the above range of E/N. Measurements of the sparking potentials showed that Paschen's law is not obeyed in air at values of Nd near and below the Paschen minimum.