Supply and loss mechanisms of Ba dispenser cathodes

Gärtner, G.; Geittner, P.; Raasch, D.; Wiechert, Detlef

doi:10.1016/s0169-4332(99)00016-1

Cited by 49 publications

(16 citation statements)

References 21 publications

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“…20,21 The obtained sputter yield is Y ϭ0.62Ϯ0.07. This is in good agreement with previously determined sputter yields by van der Gon et al 14 (Y ϭ0.63) and Gartner et al 22 (Y ϭ0.58), which where deduced directly from ion scattering investigations and indirectly from emission measurement, respectively.…”

Section: ϫ2supporting

confidence: 92%

“…This is in agreement with this one-to-one relation where each dipole is an individual emission site, and does not interact with the neighboring sites. Note that the one-toone relation between emission and coverage has been assumed in previous investigation of the emission degradation of dispenser cathodes under IB, 22 but without actual experimental verification.…”

Section: ϫ2mentioning

confidence: 99%

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Dynamic behavior of thermionic dispenser cathodes under ion bombardment

Cortenraad

Gon

Brongersma

et al. 2001

Journal of Applied Physics

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We have investigated the surface coverage and electron emission of thermionic dispenser cathodes during 3 keV Ar ϩ ion bombardment, thereby simulating the bombardment of the cathodes by residual gases that takes place in cathode-ray tubes as used in television sets. During the ion bombardment at the operating temperature of 1030°C, a dynamic equilibrium is established between the sputter removal and resupply mechanisms of the Ba and O atoms that form the dipole layer on the cathode substrate. We demonstrated that the performance of the cathodes under ion bombardment is governed by the O removal and resupply rates. It was found that the Ba resupply rate is almost an order of magnitude higher than the O resupply rate, but that the Ba can only be present on the surface bound to O atoms. Therefore, the Ba/O ratio is approximately equal to unity during the ion bombardment. Based on the investigations of the removal and resupply processes, we proposed a model that accurately describes the surface coverage and electron emission during the ion bombardment, including the dependence of the ion flux and cathode temperature.

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Section: ϫ2supporting

confidence: 92%

Section: ϫ2mentioning

confidence: 99%

Dynamic behavior of thermionic dispenser cathodes under ion bombardment

Cortenraad

Gon

Brongersma

et al. 2001

Journal of Applied Physics

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“…The initial focus of the modeling is on Ba because this is the dominant species produced by the insert. 11 Ba transport is strongly influenced by the Xe plasma; the electron density and temperature control the ionization of Ba, and the electric field in the Xe plasma and collisions with Xe and Xe þ ions control the diffusion of Ba. However, Ba atom and ion densities are so low they do not significantly modify the charge density or temperature in what is primarily a Xe discharge.…”

Section: A Model Of Barium Depletionmentioning

confidence: 99%

Barium Depletion in Hollow Cathode Emitters

Polk¹,

Capece²,

Mikellides³

et al. 2009

45th AIAA/ASME/SAE/ASEE Joint Propulsion Conference &Amp;amp; Exhibit

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“…The initial focus is on barium because this is the dominant species produced by the insert, 16 although the model will be extended to include BaO flow and chemistry. Barium transport is strongly influenced by the xenon plasma; the electron density and temperature control the ionization of barium and the electric field in the xenon plasma and collisions with Xe neutrals and Xe ions control the diffusion of barium.…”

Section: Barium Transport In the Hollow Cathode Internal Plasmamentioning

confidence: 99%

Tungsten and Barium Transport in the Internal Plasma of Hollow Cathodes

Polk¹,

Mikellides²,

Katz³

et al. 2008

44th AIAA/ASME/SAE/ASEE Joint Propulsion Conference &Amp;amp; Exhibit

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The effect of tungsten erosion, transport, and redeposition on the operation of dispenser hollow cathodes was investigated in detailed examinations of the discharge cathode inserts from 8200 h and 30 352 h ion engine wear tests. Erosion and subsequent redeposition of tungsten in the electron emission zone at the downstream end of the insert reduce the porosity of the tungsten matrix, preventing the flow of barium from the interior. This inhibits the interfacial reactions of the barium-calcium-aluminate impregnant with the tungsten in the pores. A numerical model of barium transport in the internal xenon discharge plasma shows that the barium required to reduce the work function in the emission zone can be supplied from upstream through the gas phase. Barium that flows out of the pores of the tungsten insert is rapidly ionized in the xenon discharge and pushed back to the emitter surface by the electric field and drag from the xenon ion flow. This barium ion flux is sufficient to maintain a barium surface coverage at the downstream end greater than 0.6, even if local barium production at that point is inhibited by tungsten deposits. The model also shows that the neutral barium pressure exceeds the equilibrium vapor pressure of the impregnant decomposition reaction over much of the insert length, so the reactions are suppressed. Only a small region upstream of the zone blocked by tungsten deposits is active and supplies the required barium. These results indicate that hollow cathode failure models based on barium depletion rates in vacuum dispenser cathodes are very conservative.

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Supply and loss mechanisms of Ba dispenser cathodes

Cited by 49 publications

References 21 publications

Dynamic behavior of thermionic dispenser cathodes under ion bombardment

Dynamic behavior of thermionic dispenser cathodes under ion bombardment

Barium Depletion in Hollow Cathode Emitters

Tungsten and Barium Transport in the Internal Plasma of Hollow Cathodes

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