Uniform nanosecond gas breakdown of negative polarity: Initiation from electrode and propagation in molecular gases

The charge density per unit length, the longitudinal component of the electric field and the electron concentration behind the front of fast ionization wave, initiated by a nanosecond voltage pulse of negative polarity in air, N₂ and H₂, are reconstructed in the pressure range of 1-24 Torr. The breakdown initiation from the high-voltage electrode is investigated. The accumulation of the positive charge in the vicinity of the cathode at the initial moment of the time of discharge development is revealed; and the time dependence of the conduction current through the cathode is determined. Energy branching in the discharge is analyzed in various gases. It is shown that the greater part of the energy (40-60%) in the whole range of parameters passes to excitation of electronic states of molecules, that a part of the energy input into high-energy degrees of freedom (ionization, dissociation) monotonically decreases with the pressure and that a part of low-energy ones (rotation, vibration) monotonically increases.