Physical Mechanisms of Negative Corona Current Pulse With Secondary Oscillation

Abstract

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 quasione-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 · 10 −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 .

Non-thermal atmospheric pressure discharges

“…Charged particles are dragged by the weak electric fields from one electrode to another to close the electric circuit. However, in the initial stages, the breakdown circuit in the corona discharge is closed by displacement current rather than charged particle transport [77]. A corona can be observed in air around high voltage transmission lines, around lightning rods, and even masts of ships, where it is called 'Saint Elmo's fire'.…”

Numerical modelling of low-temperature non-equilibrium plasma of pulsing corona and breakdown

“…Differential equations of the continuity for positive and negative ions and electron flows, supplemented with the Poisson equation for electric field in quasi twodimensional space, are put in the basis of numerical calculations [15]:…”

“…where µ is the coefficient of the photon absorption, τ is the lifetime of the exited state, α * is the excitation coefficient, Ω(x) is the solid angle extended at the cathode by the charge at x [15], d is the space length.…”

“…Since positive and negative ions are almost fully separated in space during the pulsation period of the negative corona, and the passing time of electrons through the positive ion cloud (placed in a very narrow cathode sheath) is short in comparison with the pulse duration, we excluded recombination electron-ion and ion-ion processes from consideration. Detailed information about the modelling is possible to find in the work [15].…”

“…In some voltage region, the current pulses have high stable parameters. The main characteristics of low-frequency pulses and high-frequency current pulsation in nitrogen and argon with oxygen admixture were investigated [15][16][17]. This work develops the method of determining the existence region of low temperature non-equilibrium plasma of the discharges.…”