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

Rittner, E. S.; Ahlert, R. H.; Rutledge, W. C.

doi:10.1063/1.1722699

Cited by 63 publications

(6 citation statements)

References 6 publications

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“…With the assumption of the purposed layer structure and using the measured concentration ratios, the BaO coverage is less than a monolayer (∼ 60%). This led us to the conclusion that in the early life of the cathodes the coverage is not homogenous and we found disagreement with Rittner and Jensen's results [4,21].…”

Section: Resultscontrasting

confidence: 85%

“…The emission material that coats the tungsten electrode coils vaporizes by a dissociative process at high operating temperature (1600˚C), generating free Ba at the surface, as a result of the reaction between the polycrystalline tungsten cathode and the emission material [3]. The Ba coverage results in an improved lamp performance by lowering the electron work function ( ) of the tungsten electrodes, and consequently by lowering the operating temperature ( gg= 4,5 eV for clean W surface [4], = 2,0-2,30 eV for BaO monolayer on W at 1000 -1200 K [5][6][7]). …”

Section: Introductionmentioning

confidence: 99%

“…In 1957 Rittner et al [4] found the following three facts: (i) the emitting surface of the cathode consists not only of barium on clean tungsten, (ii) oxygen is an important constituent of the dipole layer throughout the cathode life, and (iii) the oxygen coverage appears to be nearly monoatomic. Based on experimental results, Forman [5] suggested that a barium multilayer is unstable at the operating temperature of cathodes.…”

Section: Introductionmentioning

confidence: 99%

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Investigation of evolved layer structure of Ba-containing emission materials

Beck

Josepovits

Sneider³

2007

Per. Pol. Chem. Eng.

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The emission material in High Intensity Discharge (HID) lamps plays a significant role in lowering the electrode work function and thus the lamps' operating temperature. Bacontaining rare earth-and alkali earth tungstate materials are commonly used as cathode thermionic emission materials because of the production of high intensity discharge.The goal of this present work is to model a cathode tip surface evolved during sintering and to compare the physical and chemical properties of emission materials currently used in the industry. In order to achieve this goal, we investigated and compared the layer structure of Ba-Ca-and Ba-Y-containing emission materials evolved on polycrystalline tungsten foils. Simultaneously, the tendency of the work function was also monitored as a function of Ba/BaO layer thickness. The Ba coverage of cathode is one of the most important factors during the lifetime of HID lamps. The initial Ba diffusion was also examined. We also proposed a layer model, valuable for the structures occurring during the operation of lamps.The chemical composition of the flat samples was analysed by X-ray Photoelectron Spectroscopy (XPS) and the electron emission properties by Work Function Spectroscopy (WFS).

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Section: Resultscontrasting

confidence: 85%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Investigation of evolved layer structure of Ba-containing emission materials

Beck

Josepovits

Sneider³

2007

Per. Pol. Chem. Eng.

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“…This behavior is not present with reservoir cathodes, such as the tungsten-wire cathodes described here. Researchers at Phillips in The Netherlands developed the original reservoir cathode in the late 1940s [21]. Lemmons et al described the L-type cathode in a U.S. patent in 1948 [22].…”

Section: A Work Function Stability and Lifetimementioning

confidence: 99%

Controlled-Porosity Cathodes for High-Current-Density Applications

Ives

Falce²,

Miram

et al. 2010

IEEE Trans. Plasma Sci.

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Controlled-porosity reservoir cathodes that can operate at high current densities with long lifetimes are described. The fabrication process is economical and adaptable to high volume production. The cathodes exhibit superior performance over sintered powdered tungsten cathodes. This paper describes the fabrication, presents measured performance, and compares the results with conventional dispenser cathodes.

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

Abstract: Articles you may be interested inSurface studies of barium and barium oxide on tungsten and its application to understanding the mechanism of operation of an impregnated tungsten cathode

Cited by 63 publications

References 6 publications

Investigation of evolved layer structure of Ba-containing emission materials

Investigation of evolved layer structure of Ba-containing emission materials

Controlled-Porosity Cathodes for High-Current-Density Applications

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

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