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- Simple computation of ignition voltage of self-sustaining gas dischargesPublication . Almeida, P. G. C.; Almeida, R. M. S.; Ferreira, N. G. C.; Naidis, G. V.; Benilov, M. S.A robust, fast, and accurate numerical method is proposed for finding the voltage of the ignition of DC self-sustaining gas discharges in a wide range of conditions. The method is based on physical grounds and builds up from the idea that the ignition of a self-sustaining gas discharge should be associated with a resonance that would occur in a non-self-sustained discharge in the same electrode configuration. Examples of the application of the method are shown for various configurations: parallel-plate discharge, coaxial and wire-to-plane corona discharges, and a discharge along a dielectric surface. The results conform to the conventional Townsend breakdown condition for the parallel-plate configuration and are in good agreement with existing experimental data for the other configurations. The method has the potential of providing a reference point for optimization of the hold-off capability of high-power switchgear operating in low-frequency fields.
- A practical guide to modeling low-current quasi-stationary gas discharges: Eigenvalue, stationary, and time-dependent solversPublication . Benilov, M. S.; Almeida, P. G. C.; Ferreira, N. G. C.; Almeida, R. M. S.; Naidis, G. V.The work is concerned with the modeling of low-current quasi-stationary discharges, including the Townsend and corona discharges. The aim is to develop an integrated approach suitable for the computation of the whole range of existence of a quasi-stationary discharge from its inception to a non-stationary transition to another discharge form, such as a transition from the Townsend discharge to a normal glow discharge or the corona-to-streamer transition. This task includes three steps: (i) modeling of the ignition of a self-sustaining discharge, (ii) modeling of the quasi-stationary evolution of the discharge with increasing current, and (iii) the determination of the current range where the quasi-stationary discharge becomes unstable and the non-stationary transition to another discharge form begins. Each of these three steps is considered in some detail with a number of examples, referring mostly to discharges in high-pressure air.
- Computational and experimental study of time-averaged characteristics of positive and negative DC corona discharges in point-plane gaps in atmospheric airPublication . Ferreira, Nuno G. C.; Almeida, Pedro G. C.; Benilov, Mikhail S.; Panarin, Victor A.; Skakun, Victor S.; Tarasenko, Victor F.; Naidis, George V.The use of stationary solvers instead of approximate solution methods or time-dependent solvers, which are standard tools in gas discharge modeling, allows one to develop a very fast and robust numerical model for studying the time-averaged characteristics of dc corona discharges. Such an approach is applied to dc corona discharges in point-plane gaps in ambi ent air. A wide range of currents of both voltage polarities and various gap lengths are investigated, and the simulation results are validated by comparing the computed current–voltage characteristics and spatial distributions of the radiation intensity with experimental results. Specific features of the numerical and experimental results at both polarities are discussed.
- Simulation of pre-breakdown discharges in high-pressure air: II. Effect of surface protrusionsPublication . Ferreira, N. G. C.; Naidis, G. V.; Benilov, M. S.Analysis of deviations from the similarity law, observed at high and very high pressures in experiments on discharge ignition and breakdown in corona-like configurations, can serve as a useful, albeit inevitably indirect, source of information about microprotrusions on the surface of the electrodes. In this work, such analysis was performed by means of 2D numerical modelling. Conical or cylindrical protrusions on the surface of the inner electrode were studied and the kinetic scheme includes the electrons, one species of positive ions, and negative ions O− 2 , O−, and O− 3 . It is shown that the deviations from the similarity law, observed in the experiment, may indeed be attributed to enhanced ionization of air molecules in regions of amplified electric field near the microprotrusions. A qualitative agreement with the experiment in all the cases is achieved for protrusion heights of the order of 50 µm. Such values may appear rather high, however there is no other explanation in sight at present. The enhancement of the field electron emission from the surface of the negative electrode due to the amplification of the electric field on the microprotrusion was estimated and found insignificant in the range of values of the protrusion aspect ratio where the enhanced ionization in the gas phase is already appreciable.
- Comment on “Electric field measurements under DC corona discharges in ambient air by electric field induced second harmonic generation” [Appl. Phys. Lett. 115, 244101 (2019)]Publication . Ferreira, N. G. C.; Almeida, P. G. C.; Benilov, M. S.; Naidis, G. V.