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Research Project
ESTUDO DA ESTABILIDADE DE TRANSFERÊNCIA DE CORRENTE AOS ELÉCTRODOS NAS DESCARGAS DE GÁS
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Multiple solutions in the theory of dc glow discharges
Publication . Almeida, P. G. C.; Benilov, M. S.; Faria, M. J.
Multiple steady-state solutions existing in the theory of dc glow discharges are computed for
the first time. The simulations are performed in 2D in the framework of the simplest
self-consistent model, which accounts for a single ion species and employs the drift–diffusion
approximation. Solutions describing up to nine different modes were found in the case where
losses of the ions and the electrons due to diffusion to the wall were neglected. One mode is
1D, exists at all values of the discharge current, and represents in essence the well-known
solution of von Engel and Steenbeck. The other eight modes are axially symmetric, exist in
limited ranges of the discharge current, and are associated with different patterns of current
spots on the cathode. The mode with a spot at the centre of the cathode exhibits a well
pronounced effect of normal current density. Account of diffusion losses affects the solutions
dramatically: the number of solutions is reduced, a mode appears that exists at all discharge
currents and comprises the Townsend, subnormal, normal and abnormal discharges. The
solutions that exist in limited current ranges describe patterns, and these patterns seem to
represent axially symmetric analogues of the 3D patterns observed in dc glow microdischarges
in xenon.
Study of stability of dc glow discharges with the use of Comsol Multiphysics software
Publication . Almeida, P. G. C.; Benilov, M. S.; Faria, M. J.
Stability of different axially symmetric modes of current transfer in dc glow discharges is
investigated in the framework of the linear stability theory with the use of Comsol
Multiphysics software. Conditions of current-controlled microdischarges in xenon are treated
as an example. Both real and complex eigenvalues have been detected, meaning that
perturbations can vary with time both monotonically and with oscillations. In general, results
given by the linear stability theory confirm intuitive concepts developed in the literature and
conform to the experiment. On the other hand, suggestions are provided for further
experimental and theoretical work.
Simulating different modes of current transfer to thermionic cathodes in a wide range of conditions
Publication . Benilov, M. S.; Cunha, M. D.; Faria, M. J.
Changes in the pattern of steady-state modes of current transfer to thermionic cathodes
induced by variations of the cathode geometry and temperature of the cooling fluid are studied
numerically. For some combinations of control parameters, only one stable mode in a wide
current range exists, which combines features of spot and diffuse modes. This mode, when
attached to an elongated protrusion on the cathode surface, may be identified with the
so-called super spot mode observed in experiments on low-current arcs. There is also
reasonable agreement between the modelling and the experiment on cathodes of high-current
arcs operating in the diffuse mode. The conclusions on existence under certain conditions of
only one stable mode in a wide current range and of a minimum of the dependence of the
temperature of the hottest point of the cathode on the arc current, manifested by this mode,
may have industrial importance and admit a straightforward experimental verification.
Three-dimensional modeling of self-organization in DC glow microdischarges
Publication . Almeida, P. G. C.; Benilov, M. S.; Faria, M. J.
Three-dimensional simulations of self-organization
in dc glow microdischarges are reported. The results describe a
mode with a normal spot and modes with patterns of multiple
spots, qualitatively similar to those observed in experiments with
microdischarges in xenon.
Effect of protrusions on cathodic-arc-attachment mode in high-pressure arc discharges
Publication . Benilov, M. S.; Cunha, Mário D.; Faria, Maria J.
It is shown via computer simulations that a protru sion on a thermionic arc cathode may dramatically change the
pattern of steady-state modes of current transfer. This happens
through a bifurcation of a special type occurring at certain geom etry of the cathode and may play a role in operation of electrodes
of compact high-intensity discharge lamps.
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Funding agency
Fundação para a Ciência e a Tecnologia
Funding programme
PIDDAC
Funding Award Number
SFRH/BD/35883/2007