Barium depletion in hollow cathode emitters

Articles you may be interested in Barium strontium oxide coated carbon nanotubes as field emitters Appl. Composite-layered solid-state field controlled emitter for a better control of the cathode surface barrier Transition metal carbide field emitters for field-emitter array devices and high current applications Effect of CH 4 on the electron emission characteristics of active molybdenum field emitter arrays Effects of thermal annealing on emission characteristics and emitter surface properties of a Spindt-type field emission cathode Dispenser hollow cathodes rely on a consumable supply of Ba released by BaO-CaO-Al 2 O 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.