Browsing by Author "Almeida, Pedro Jorge Gomes Camacho de"
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- Investigation of modes of current transfer to cathodes of glow and arc dischargesPublication . Almeida, Pedro Jorge Gomes Camacho de; Benilov, MikhailThis work is dedicated to modelling of di⁄erent modes of current transfer to cathodes of glow discharges and to experimental investigation of formation of transient spots on thermionic arc cathodes. Multiple steady-state solutions in the theory of DC glow discharge have been found for the rst time. The modelling was performed in the framework of the basic model of glow discharges and also in the framework of a more detailed model. The basic model comprises equations of conservation of a single ion species and the electrons, transport equations for the ions and the electrons written in the local approximation, and the Poisson equation. The detailed model takes into account atomic and molecular ions, atomic excited states, excimers, and non-locality of electron transport and kinetic coe¢ cients. These multiple solutions describe modes with a normal spot as well as modes with patterns of several spots similar to those observed in experiments with microdischarges in xenon. It is shown that modes with more than one spot can, in principle, occur not only in xenon but also in other plasma-producing gases. Formation of transient spots on thermionic cathodes was studied in experiments with COST529 standard HID lamps. There is a generally good agreement between experiment and results of numerical modelling. A possibility of prevention of appearance of transient spots by means of a brief reduction of the arc current shortly after the initial current increase is proposed and justied. It is shown that the main mechanism of blackening of burners of HID lamps that accompanies appearance of transient cathode spots is evaporation of the cathode material and not sputtering.