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Investigation of modes of current transfer to cathodes of glow and arc discharges

2011Doctoral thesis Open access
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datacite.subject.fosCiências Naturais::Ciências Físicaspt_PT
dc.contributor.advisorBenilov, Mikhail
dc.contributor.authorAlmeida, Pedro Jorge Gomes Camacho de
dc.date.accessioned2017-03-14T11:28:41Z
dc.date.available2017-03-14T11:28:41Z
dc.date.issued2011
dc.description.abstractThis 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.pt_PT
dc.description.abstractEste trabalho Ø dedicado modelaªo de diferentes modos de transferŒncia de corrente aos cÆtodos de descargas luminescentes e investigaªo experimental da formaªo de manchas transitrias em cÆtodos terminicos de descargas de arco. Mœltiplas soluıes estacionÆrias existentes na teoria da descarga luminescente foram calculadas numericamente pela primeira vez. A modelaªo foi realizada no mbito do modelo bÆsico da descarga luminescente e no mbito de um modelo detalhado. O modelo bÆsico contØm equaıes de conservaªo de uma espØcie inica e dos electrıes, equaıes de transporte dos iıes e electrıes escritas na aproximaªo local e a equaªo de Poisson. O modelo detalhado leva em conta iıes atmicos e moleculares, estados excitados dos Ætomos, dmeros excitados e nªo-localidade dos coecientes de transporte e cinØticos dos electrıes. As mœltiplas soluıes descrevem modos com uma mancha normal e modos com padrıes de vÆrias manchas semelhantes aos observados nas experiŒncias com micro-descargas em xØnon. Demonstra-se que modos com mais que uma mancha podem, em princpio, ocorrer em descargas noutros gases que nªo o xØnon. A formaªo de manchas transitrias em cÆtodos terminicos foi estudada em experiŒncias com lmpadas HID padrªo, COST-529. Existe uma concordncia genØricamente boa entre os resultados experimentais e da modelaªo numØrica. Uma possibilidade de prevenªo do aparecimento de manchas transitrias atravØs da breve reduªo da corrente da descarga logo aps um salto na corrente Ø proposta e justicada. Demonstra-se que o principal mecanismo de escurecimento das lmpadas HID que acompanha a formaªo de manchas catdicas Ø a evaporaªo do material do cÆtodo.pt_PT
dc.identifier.tid101238444pt_PT
dc.identifier.urihttp://hdl.handle.net/10400.13/1471
dc.language.isoengpt_PT
dc.subjectPlasma-cathode interactionpt_PT
dc.subjectSelf-organizationpt_PT
dc.subjectGlow dischargespt_PT
dc.subjectNormal glow dischargespt_PT
dc.subjectThermionic cathodespt_PT
dc.subjectCathodic spotspt_PT
dc.subjectInteracão plasma-cátodopt_PT
dc.subjectAuto-organizaçãopt_PT
dc.subjectDescargas luminescentespt_PT
dc.subjectDescarga normalpt_PT
dc.subjectCátodos termiónicospt_PT
dc.subjectManchas catódicaspt_PT
dc.subjectFísicapt_PT
dc.subject.pt_PT
dc.subjectFaculdade de Ciências Exatas e da Engenharia
dc.titleInvestigation of modes of current transfer to cathodes of glow and arc dischargespt_PT
dc.typedoctoral thesis
dspace.entity.typePublication
person.familyNameAlmeida
person.givenNamePedro G C
person.identifier.ciencia-idD61F-B90C-70B2
person.identifier.orcid0000-0002-8395-2693
person.identifier.scopus-author-id8157100900
rcaap.rightsopenAccesspt_PT
rcaap.typedoctoralThesispt_PT
relation.isAuthorOfPublicationc7346266-fe94-40ae-aa95-b576b0e1f3a6
relation.isAuthorOfPublication.latestForDiscoveryc7346266-fe94-40ae-aa95-b576b0e1f3a6
thesis.degree.nameDoutoramento em Físicapt_PT

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