Dynamics of plasma–electrode coupling in fluorescent lamp discharges

Garner, R.C.

doi:10.1088/0022-3727/41/14/144010

“…Furthermore, the FPI-derived temperatures during the evaporative regimes of both hot spots agree well with the emission-based diagnostic. This result agrees well with our notion of how electrodes work [5]. The emitter at post 1 presumably has lower work function than the emitter at post 2.…”

Section: Fluorescent Lamp Measurementssupporting

confidence: 91%

“…The notion that barium sputters, not immediately but after some time in the cathode phase, is consistent with our understanding of the phase dependence of the cathode fall [5]. When the electrode first enters the cathode phase, the discharge current is relatively low.…”

Section: Fluorescent Lamp Measurementssupporting

confidence: 81%

Fabry–Perot measurements of barium temperature in fluorescent lamps

Hadrath

¹

,

Garner

²

2010

J. Phys. D: Appl. Phys.

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Abstract.A scanning Fabry-Perot interferometer (FPI) is used to determine the temperature of barium atoms that are liberated from the electrodes of fluorescent lamps during their steady-state operation. Barium, a constituent of the work function lowering emitter material that is placed on the tungsten coil that forms the electrode, is liberated primarily by evaporation from the hot (~1300°K) thermionic electrode. However, there may be situations or modes of operation in which barium is, in addition, sputtered, a condition which may lead to increased end-darkening, shortened life, and increased mercury consumption in the lamp. Using the FPI diagnostic, the occurrence of sputtering is inferred when barium temperatures are much greater than the electrode temperature. The FPI diagnostic senses resonance radiation ( 553 nm λ = ) emitted by barium atoms excited in the low pressure discharge environment, and infers temperature from the Doppler broadened linewidth. The diagnostic has proven to be successful in a number of situations. Measurements have been made on rare gas discharges and on Hg-argon discharges for different discharge currents, gas pressures, and auxiliary coil currents. Measurements are phase resolved for a.c. driven discharges.

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“…For an auxiliary coil heat of 500 mA no barium is sputtered. This is consistent with the fact that cathode fall decreases with increasing heating current [5]. Figure 12 shows a compendium of the coil heat results.…”

Section: Fluorescent Lamp Measurementssupporting

confidence: 82%

Fabry-Perot measurements of barium temperature in fluorescent lamps

Garner

¹

,

Hadrath

²

2009

2009 IEEE International Conference on Plasma Science - Abstracts

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Abstract.A scanning Fabry-Perot interferometer (FPI) is used to determine the temperature of barium atoms that are liberated from the electrodes of fluorescent lamps during their steady-state operation. Barium, a constituent of the work function lowering emitter material that is placed on the tungsten coil that forms the electrode, is liberated primarily by evaporation from the hot (~1300°K) thermionic electrode. However, there may be situations or modes of operation in which barium is, in addition, sputtered, a condition which may lead to increased end-darkening, shortened life, and increased mercury consumption in the lamp. Using the FPI diagnostic, the occurrence of sputtering is inferred when barium temperatures are much greater than the electrode temperature. The FPI diagnostic senses resonance radiation ( 553 nm λ = ) emitted by barium atoms excited in the low pressure discharge environment, and infers temperature from the Doppler broadened linewidth. The diagnostic has proven to be successful in a number of situations. Measurements have been made on rare gas discharges and on Hg-argon discharges for different discharge currents, gas pressures, and auxiliary coil currents. Measurements are phase resolved for a.c. driven discharges.

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“…[4], however with a temporal delay. Due to the quasi-stationary approach of the current model, the electron density is present here in the cathode phase only.…”

Section: Resultsmentioning

confidence: 99%

“…The surface electric field E S at the cathode surface was approximated using a sheath model [4] according to…”

Section: Ba Transport Modelmentioning

confidence: 99%

Barium transport in the hot spot region of fluorescent lamps

Sigeneger¹,

Rackow²,

Uhrlandt³

et al. 2010

J. Phys. D: Appl. Phys.

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Abstract. The transport of barium atoms and ions in the vicinity of the hot spot in fluorescent lamps operating at 25 kHz is investigated by a combined experimental and theoretical approach. By laserinduced fluorescence, the particle densities of barium atoms and ions were measured timeresolved at different distances from the spot center. In addition, the time-dependent cathode fall voltage was measured using an improved band method. The model combines a kinetic part for the electrons with a fluid part for the barium atoms and ions. Both parts are spatially resolved in spherically symmetric geometry. The space-dependent electron Boltzmann equation yields the electron density and the ionization rate coefficient of barium as functions of the cathode fall voltage. These results are used to solve the time-dependent particle balance equations of barium atoms and ions which include the ionization of barium as gain and loss terms, respectively. Good agreement between the measured and calculated particle densities of barium atoms is obtained. A sensitive dependence of the ionization frequency and of the barium particle densities on the cathode fall voltage was found.

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Dynamics of plasma–electrode coupling in fluorescent lamp discharges

Cited by 14 publications

References 22 publications

Fabry–Perot measurements of barium temperature in fluorescent lamps

Fabry–Perot measurements of barium temperature in fluorescent lamps

Fabry-Perot measurements of barium temperature in fluorescent lamps

Barium transport in the hot spot region of fluorescent lamps

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