3D modelling of heating of thermionic cathodes by high-pressure arc plasmas

Benilov, M. S.; Carpaij, M.; Cunha, M D

doi:10.1088/0022-3727/39/10/024

Cited by 47 publications

(81 citation statements)

References 21 publications

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“…1 Apart from this S-shape, the current-voltage characteristics shown in Fig. 1 are similar to those calculated for a cathode in the form of a cylindrical rod with a flat top [4]. On the basis of this similarity, one would expect that the mode a is the axially symmetric spot mode, and the mode b is diffuse.…”

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confidence: 56%

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Effect of Protrusions on Cathodic-Arc-Attachment Mode in High-Pressure Arc Discharges

Benilov

Cunha

Faria

2008

IEEE Trans. Plasma Sci.

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Abstract-It is shown via computer simulations that a protrusion 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 geometry of the cathode and may play a role in operation of electrodes of compact high-intensity discharge lamps.Index Terms-Arc attachment, arc cathode, bifurcation of current transfer, bifurcation theory, high-pressure arc. CONSIDERABLE advances in theoretical and experimental investigation of the plasma-cathode interaction in high-pressure arc discharges have been achieved during the last decade [1]. Simulation methods, available at present and validated experimentally, allow one to reliably describe many aspects of operation of thermionic cathodes.A challenging task is to simulate operation of cathodes of complex geometries, which are of practical interest, in particular, those with protrusions [2], [3]. Results of such simulations are reported in this paper.Steady-state modes of current transfer have been calculated with the use of the commercial software COMSOL Multiphysics, as described in [4]. Stability of each of the steady-state modes has been investigated, as described in [5].In Fig. 1, current-voltage characteristics U (I) are shown of axially symmetric steady-state modes of current transfer to an axially symmetric tungsten cathode in the form of a rod of radius R = 750 µm and a height of 12 mm (here, U is the near-cathode voltage drop, and I is the arc current). The cathode has a hemispherical tip. A spherical protrusion with a radius of 200 µm is located at the top of the tip. The arc operates in argon under the pressure of 2 bar. Also shown is the dependence of the maximum temperature of the cathode surface on the arc current. Stable and unstable sections of each mode are shown by solid or dotted lines, respectively.There are two separate modes in Fig. 1 Apart from this S-shape, the current-voltage characteristics shown in Fig. 1 are similar to those calculated for a cathode in the form of a cylindrical rod with a flat top [4]. On the basis of this similarity, one would expect that the mode a is the axially symmetric spot mode, and the mode b is diffuse. However, high values of the maximum temperature in mode b and low values of the maximum temperature on both branches of the mode a do not fit this interpretation.An inspection of distributions of the temperature of the cathode, shown for several states in Fig. 1, disproves such interpretation. While high-current states belonging to the mode b are characterized by smooth temperature distributions typical for the diffuse mode, there is a well-defined spot in lowcurrent states belonging to the mode b. The stable branch of the mode a is diffuse, and there seems to be something that can be identified as a poorly pronounced spot on the unstable branch, although this spot can hardly be seen in Fig. 1. In other words, each of the two modes of steady-state current transfer existing in this geometry embraces diffuse ...

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confidence: 56%

“…Steady-state modes of current transfer have been calculated with the use of the commercial software COMSOL Multiphysics, as described in [4]. Stability of each of the steady-state modes has been investigated, as described in [5].…”

mentioning

confidence: 99%

Effect of Protrusions on Cathodic-Arc-Attachment Mode in High-Pressure Arc Discharges

Benilov

Cunha

Faria

2008

IEEE Trans. Plasma Sci.

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“…for the field distribution near the cathode [132]. From the point of view of 'Nonlinear Dynamics and Pattern Formation' a reasonably complete self-consistent description of the cathode spots in arc discharges can be developed only in special cases [133][134][135].…”

Section: Advances In Physics 525mentioning

confidence: 99%

Dissipative solitons

Purwins¹,

Bödeker²,

Amiranashvili³

2010

Advances in Physics

219

193

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“…with noble gases or mercury. It is on one hand an outcome of intense theoretical studies and on the other hand of experimental investigations, mainly at a model lamp, within the last years [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15]. The description of the dc operation of anodes in HID lamps is less advanced, but at least a qualitative understanding has been achieved for cold and to some extent also for hot HID anodes [16,17,18,19].…”

Section: Introductionmentioning

confidence: 99%

Investigating the dependence of the temperature of high-intensity discharge (HID) lamp electrodes on the operating frequency by pyrometric measurements

Reinelt¹,

Westermeier²,

Ruhrmann³

et al. 2011

J. Phys. D: Appl. Phys.

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Abstract. Phase resolved temperature distributions are determined along a rod shaped tungsten electrode, by which an ac arc is operated within a model lamp filled with argon. Switched dc and sinusoidal currents are applied with amplitudes of several amps and operating frequencies being varied between 10 Hz and 10 kHz. The temperature is deduced from the grey body radiation of the electrode being recorded with a spectroscopic measuring system. Phase resolved values of the electrode tip temperature T tip and of the power input P in are determined comparing the measured temperature distributions with the integral of the one dimensional heat balance with these parameters as integration constants. They are supplemented by phase resolved measurements of the sum of cathode and anode fall called electrode sheath voltage. If a switched dc current is applied it is found that both quantities are within the cathodic phase only marginally higher than for a cathode being operated with a dc current. T tip and P in start to decrease for low currents and to increase for high currents at the beginning of the anodic phase. But with increasing operating frequency the deviations from the cathodic phase are reduced until they cannot be resolved for frequencies of several kHz. A more pronounced modulation but the same tendencies are observed with a sinusoidal current waveform. For 10 kHz a diffuse arc attachment with an almost phase independent electrode tip temperature, which deviates only marginally from that of a dc cathode, and an electrode sheath voltage proportional to the arc current is established with both current waveforms.

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3D modelling of heating of thermionic cathodes by high-pressure arc plasmas

Cited by 47 publications

References 21 publications

Effect of Protrusions on Cathodic-Arc-Attachment Mode in High-Pressure Arc Discharges

Effect of Protrusions on Cathodic-Arc-Attachment Mode in High-Pressure Arc Discharges

Dissipative solitons

Investigating the dependence of the temperature of high-intensity discharge (HID) lamp electrodes on the operating frequency by pyrometric measurements

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