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Title: Barium depletion in hollow cathode emitters

Dispenser hollow cathodes rely on a consumable supply of Ba released by BaO-CaO-Al{sub 2}O{sub 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.
Authors:
; ;  [1] ;  [2]
  1. Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California 91109 (United States)
  2. Graduate Aerospace Laboratories, California Institute of Technology, Pasadena, California 91125 (United States)
Publication Date:
OSTI Identifier:
22494883
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 119; Journal Issue: 2; Other Information: (c) 2016 AIP Publishing LLC; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS; ALUMINIUM OXIDES; BARIUM; BARIUM OXIDES; CALCIUM OXIDES; DEPTH; EQUILIBRIUM; HOLLOW CATHODES; PARTIAL PRESSURE; PLASMA; TRANSPORT THEORY; TUNGSTEN; VAPOR PRESSURE