Publicação
Investigation of modes of current transfer to cathodes of glow and arc discharges
| datacite.subject.fos | Ciências Naturais::Ciências Físicas | pt_PT |
| dc.contributor.advisor | Benilov, Mikhail | |
| dc.contributor.author | Almeida, Pedro Jorge Gomes Camacho de | |
| dc.date.accessioned | 2017-03-14T11:28:41Z | |
| dc.date.available | 2017-03-14T11:28:41Z | |
| dc.date.issued | 2011 | |
| dc.description.abstract | This 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.abstract | Este 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.tid | 101238444 | pt_PT |
| dc.identifier.uri | http://hdl.handle.net/10400.13/1471 | |
| dc.language.iso | eng | pt_PT |
| dc.subject | Plasma-cathode interaction | pt_PT |
| dc.subject | Self-organization | pt_PT |
| dc.subject | Glow discharges | pt_PT |
| dc.subject | Normal glow discharges | pt_PT |
| dc.subject | Thermionic cathodes | pt_PT |
| dc.subject | Cathodic spots | pt_PT |
| dc.subject | Interacão plasma-cátodo | pt_PT |
| dc.subject | Auto-organização | pt_PT |
| dc.subject | Descargas luminescentes | pt_PT |
| dc.subject | Descarga normal | pt_PT |
| dc.subject | Cátodos termiónicos | pt_PT |
| dc.subject | Manchas catódicas | pt_PT |
| dc.subject | Física | pt_PT |
| dc.subject | . | pt_PT |
| dc.subject | Faculdade de Ciências Exatas e da Engenharia | |
| dc.title | Investigation of modes of current transfer to cathodes of glow and arc discharges | pt_PT |
| dc.type | doctoral thesis | |
| dspace.entity.type | Publication | |
| person.familyName | Almeida | |
| person.givenName | Pedro G C | |
| person.identifier.ciencia-id | D61F-B90C-70B2 | |
| person.identifier.orcid | 0000-0002-8395-2693 | |
| person.identifier.scopus-author-id | 8157100900 | |
| rcaap.rights | openAccess | pt_PT |
| rcaap.type | doctoralThesis | pt_PT |
| relation.isAuthorOfPublication | c7346266-fe94-40ae-aa95-b576b0e1f3a6 | |
| relation.isAuthorOfPublication.latestForDiscovery | c7346266-fe94-40ae-aa95-b576b0e1f3a6 | |
| thesis.degree.name | Doutoramento em Física | pt_PT |
Ficheiros
Licença
1 - 1 de 1
Miniatura indisponível
- Nome:
- license.txt
- Tamanho:
- 1.71 KB
- Formato:
- Item-specific license agreed upon to submission
- Descrição: