Physical mechanisms of negative corona current pulse with secondary oscillation

摘要

The detailed modelling of the negative corona current pulses including theudsecondary oscillation (SCO) has been realized, using the continuity differentialudequations for the fluxes of positive and negative ions and electrons,udsupplemented by the Poisson’s equation for an electrical field in a quasione-dimensionaludspace, as the basis for the numerical computation. Theudanalysis of the basic plasma functions behaviour applicable to the pulsingudcorona in Ar+O₂ and N₂+O₂ mixtures in the concentration region ofudO₂ from 2 · 10−3% to 0.04% has been carried out and the physical mechanismsudof the secondary current oscillation have been grounded for theudfirst time. Moreover, an effect of the photoprocesses on the parameters ofudthe strikingly different pulses in Ar+O₂ and N₂+O₂ mixtures is estimatedudfor the first time. It has been determined that the SCO is caused by theudfield intensity oscillation in the antiphase in the surface region and in theudend of the sheath. The SCO pulse can transfer into the full modes of theudTrichel’s pulse. Characteristics of the “precursor” and the “step” in the leadingudpulse front are determined by the dynamics of the volumetric chargesudin the sheath, whereas the SCO shape is determined by the variable flowudof the positive ions to the cathode. In N₂+O₂ the ionization of O₂ moleculesudby the N₂∗emitted photons leads to the adequate current rise. Pulse trailingudpart duration and current value are operated by the O₂−udions collisions withudthe N₂∗ metastables. Such processes are slowed in Ar+O₂.