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Barium depletion in hollow cathode emitters

Polk, James E. and Mikellides, Ioannis G. and Capece, Angela M. and Katz, Ira (2016) Barium depletion in hollow cathode emitters. Journal of Applied Physics, 119 (2). Art. No. 023303. ISSN 0021-8979. doi:10.1063/1.4938489. https://resolver.caltech.edu/CaltechAUTHORS:20160119-101324573

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Abstract

Dispenser hollow cathodes rely on a consumable supply of Ba released by BaO-CaO-Al_2O_3 source material in the pores of a tungsten matrix to maintain a low work function surface. The examination of cathode emitters from long duration tests shows deposits of tungsten at the downstream end that appear to block the flow of Ba from the interior. In addition, a numerical model of Ba transport in the cathode plasma indicates that the Ba partial pressure in the insert may exceed the equilibrium vapor pressure of the dominant Ba-producing reaction, and it was postulated previously that this would suppress Ba loss in the upstream part of the emitter. New measurements of the Ba depletion depth from a cathode insert operated for 8200 h reveal that Ba loss is confined to a narrow region near the downstream end, confirming this hypothesis. The Ba transport model was modified to predict the depletion depth with time. A comparison of the calculated and measured depletion depths gives excellent qualitative agreement, and quantitative agreement was obtained assuming an insert temperature 70 °C lower than measured beginning-of-life values.


Item Type:Article
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http://dx.doi.org/10.1063/1.4938489DOIArticle
http://scitation.aip.org/content/aip/journal/jap/119/2/10.1063/1.4938489PublisherArticle
Additional Information:© 2016 AIP Publishing LLC. Received 25 July 2015 Accepted. 10 December 2015. Published online 11 January 2016. The authors would like to thank Jim Kulleck for his assistance with the scanning electron microscope. The research described in this paper was carried out by the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise, does not constitute or imply its endorsement by the United States Government or the Jet Propulsion Laboratory, California Institute of Technology.
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NASA/JPL/CaltechUNSPECIFIED
Issue or Number:2
DOI:10.1063/1.4938489
Record Number:CaltechAUTHORS:20160119-101324573
Persistent URL:https://resolver.caltech.edu/CaltechAUTHORS:20160119-101324573
Official Citation:Barium depletion in hollow cathode emitters James E. Polk, Ioannis G. Mikellides, Angela M. Capece and Ira Katz J. Appl. Phys. 119, 023303 (2016); http://dx.doi.org/10.1063/1.4938489
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:63761
Collection:CaltechAUTHORS
Deposited By: Ruth Sustaita
Deposited On:19 Jan 2016 22:52
Last Modified:10 Nov 2021 23:21

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