Title: PHYSICAL MECHANISMS OF NEGATIVE CORONA CURRENT PULSE WITH SECONDARY OSCILLATION
Author(s): V.I.Chyhin (National University ``Lvivska Polytechnika'', 12 Bandery Str., 79013 Lviv, Ukraine)

The detailed modelling of the negative corona current pulses including the secondary oscillation (SCO) has been realized, using the continuity differential equations for the fluxes of positive and negative ions and electrons, supplemented by the Poisson's equation for an electrical field in a quasi-one-dimensional space, as the basis for the numerical computation. The analysis of the basic plasma functions behaviour applicable to the pulsing corona in Ar+O$_{2}$ and N$_{2}$+O$_{2}$ mixtures in the concentration region of O$_{2}$ from $2\cdot10^{-3}$\% to $0.04$\% has been carried out and the physical mechanisms of the secondary current oscillation have been grounded for the first time. Moreover, an effect of the photoprocesses on the parameters of the strikingly different pulses in Ar+O$_{2}$ and N$_{2}$+O$_{2}$ mixtures is estimated for the first time. It has been determined that the SCO is caused by the field intensity oscillation in the antiphase in the surface region and in the end of the sheath. The SCO pulse can transfer into the full modes of the Trichel's pulse. Characteristics of the ``precursor'' and the ``step'' in the leading pulse front are determined by the dynamics of the volumetric charges in the sheath, whereas the SCO shape is determined by the variable flow of the positive ions to the cathode. In N$_{2}$+O$_{2}$ the ionization of O$_{2}$ molecules by the N$_{2}^{*}$ emitted photons leads to the adequate current rise. Pulse trailing part duration and current value are operated by the O$_{2}^{-}$ ions collisions with the N$_{2}^{*}$ metastables. Such processes are slowed in Ar+O$_{2}$.

Key words: corona discharge, current pulse, pulse fine structure, secondary current oscillation, photo-processes, numerical modelling
PACS: 52.80.Hc, 52.35.-g, 52.65.-y, 51.50.+v