Studies on the Mechanism of Operation of the <i>L</i> Cathode. II

Rutledge, W. C.; Rittner, E. S.

doi:10.1063/1.1722700

Cited by 44 publications

(8 citation statements)

References 8 publications

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“…This transport is expected to take one of two forms: (i) surface diffusion along internal pore surfaces or (ii) vapor flow through pores. Rutledge and Rittner [47] measured the flow rates of inert gases through W pellets of various porosities and found them to be consistent with observed Ba evaporation rates. Therefore, the Ba transportation mechanism was suggested to be Ba vapor flow through the pores as Knudsen flow [46], [47].…”

Section: A Formation and Transport Mechanisms Of Free Metallic Ba And Scmentioning

confidence: 54%

“…Several reactions for the production of atomic Ba have been proposed. In 1957, Rutledge and Rittner [47] studied L-type cathodes, which were comprised of a porous W matrix covering a pocket of Ba compound containing BaO or mixed BaO and SrO. It was proposed that free Ba-that is, Ba not confined to a chemical compound in the Ba reservoir-was generated by the reaction:…”

Section: A Formation and Transport Mechanisms Of Free Metallic Ba And Scmentioning

confidence: 99%

“…During this post-lifetime heating no thermionic emission was detected. Based on these findings, a second stage of Ba generation was proposed to occur via [47]:…”

Section: A Formation and Transport Mechanisms Of Free Metallic Ba And Scmentioning

confidence: 99%

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A Review of Sc-containing "Scandate" Thermionic Cathodes

Seif¹,

Zhou²,

Liu³

et al. 2022

Preprint

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Although thermionic emission has been studied for more than 100 years, recent interest in novel electron devices for military and civilian use has led to a surge in demand for cathodes with enhanced emission properties (e.g. higher current density, more uniform emission, lower operating temperatures, or extended in-service longevity). Sc-containing "scandate" cathodes have been widely reported to exhibit superior emission properties compared to previous-generation thermionic cathodes, including oxide, B-, and M-type cathodes. Despite extensive study spanning several decades, the mechanism by which the addition of Sc enhances cathode emission remains ambiguous, and certain limitations -non-uniform emission, low reproducibility, inconsistent longevity -continue to prevent widespread commercial integration of scandate cathodes into electron devices. This review attempts to survey the literature to-date addressing the fabrication, structure, and properties of scandate cathodes, with particular attention to studies addressing the role of Sc in enhancing emission.

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Section: A Formation and Transport Mechanisms Of Free Metallic Ba And Scmentioning

confidence: 54%

Section: A Formation and Transport Mechanisms Of Free Metallic Ba And Scmentioning

confidence: 99%

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A Review of Sc-containing "Scandate" Thermionic Cathodes

Seif¹,

Zhou²,

Liu³

et al. 2022

Preprint

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“…3 However, oxygen poisoning in discharge cathodes begins to occur at oxygen partial pressures between 10 À6 and 10 À5 Torr, indicating that plasma cathodes are more resistant to oxygen poisoning than vacuum dispenser cathodes. 4 A significant amount of work has been done previously to understand the effects of oxygen poisoning in vacuum cathodes; 2,3,[5][6][7][8][9][10][11][12] however, the xenon plasma adds complexity, and its role during cathode poisoning in discharge cathodes is not completely understood. In this work, we present the results of a material transport model used to predict the oxygen fluxes to the cathode surface that can later be used in kinetics models to understand the dynamics of oxygen poisoning at the plasma-surface interface.…”

Section: Introductionmentioning

confidence: 99%

Oxygen transport in the internal xenon plasma of a dispenser hollow cathode

Capece¹,

Polk²,

Mikellides³

et al. 2014

Journal of Applied Physics

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Articles you may be interested inThe effect of cathode geometry on barium transport in hollow cathode plasmas J. Appl. Phys. 115, 183301 (2014) Reactive gases such as oxygen and water vapor modify the surface morphology of BaO dispenser cathodes and degrade the electron emission properties. For vacuum cathodes operating at fixed temperature, the emission current drops rapidly when oxygen adsorbs on top of the low work function surface. Previous experiments have shown that plasma cathodes are more resistant to oxygen poisoning and can operate with O 2 partial pressures one to two orders of magnitude higher than vacuum cathodes before the onset of poisoning occurs. Plasma cathodes used for electric thrusters are typically operated with xenon; however, gas phase barium, oxygen, and tungsten species may be found in small concentrations. The densities of these minor species are small compared with the plasma density, and thus, their presence in the discharge does not significantly alter the xenon plasma parameters. It is important, however, to consider the transport of these minor species as they may deposit on the emitter surface and affect the electron emission properties. In this work, we present the results of a material transport model used to predict oxygen fluxes to the cathode surface by solving the species conservation equations in a cathode with a 2.25 mm diameter orifice operated at a discharge current of 15 A, a Xe flow rate of 3.7 sccm, and 100 ppm of O 2 . The dominant ionization process for O 2 is resonant charge exchange with xenon ions. Ba is effectively recycled in the plasma; however, BaO and O 2 are not. The model shows that the oxygen flux to the surface is not diffusion-limited; therefore, the high resistance to oxygen poisoning observed in plasma cathodes likely results from surface processes not considered here.

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“…[4][5][6] The work function is lowered as the alkali material trapped in a porous tungsten matrix diffuses to the surface at high temperature. Traditional dispenser thermionic cathodes operate much hotter ͑Ͼ1000°C͒ than the breakdown temperature of high QE films ͑ϳ220°C͒.…”

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confidence: 99%

Prototype dispenser photocathode: Demonstration and comparison to theory

Moody

Jensen

Feldman

et al. 2007

Applied Physics Letters

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A method to significantly extend the operational lifetime of alkali-based photocathodes by diffusing cesium to the surface at moderate temperature is presented and shown to restore the quantum efficiency (QE) of cesiated tungsten. Experimental measurements of QE as a function of surface cesium coverage compare exceptionally well with a recent theoretical photoemission model, notably without the use of adjustable parameters. A prototype cesium dispenser cell is demonstrated and validates the concept upon which long-life dispenser photocathodes can be based.

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Studies on the Mechanism of Operation of the L Cathode. II

Cited by 44 publications

References 8 publications

A Review of Sc-containing "Scandate" Thermionic Cathodes

A Review of Sc-containing "Scandate" Thermionic Cathodes

Oxygen transport in the internal xenon plasma of a dispenser hollow cathode

Prototype dispenser photocathode: Demonstration and comparison to theory

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