Would a heated Barium oxide filament survive in a deuterium environment?

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Sven Andersson
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Would a heated Barium oxide filament survive in a deuterium environment?

Post by Sven Andersson » Tue Sep 25, 2018 7:06 pm

Let's say that I try to ionize deuterium gas at 1 mBar or lower, with electron bombardment from a heated cathode. Would a Barium oxide filament (treated that way to increase emittance) survive in a such an environment? Or would the oxide be reduced chemically by the deuterium? Picture from Wikipedia.

Thermionic_filament.jpg

Roberto Ferrari
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Re: Would a heated Barium oxide filament survive in a deuterium environment?

Post by Roberto Ferrari » Tue Sep 25, 2018 8:48 pm

Sven
That is almost the situation inside a deuterium discharge lamp, used in spectrometers.

ian_krase
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Re: Would a heated Barium oxide filament survive in a deuterium environment?

Post by ian_krase » Thu Sep 27, 2018 5:32 am

I would worry more about residual air every time you go to to air. Barium is mostly used in vacuum tubes that are never ever vented. A better idea might be yttrium as used in ion gauges - or just bare tungsten, it works and is vastly simpler.

I'm curious at this choice of ion gun - it's my impression that if you're trying to get a lot of ions as is the case in a fusor, glow discharge ion sources may be more practical than thermionic.


Keep also in mind the electric field right around the filament heavily affects emission.

Dan Knapp
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Re: Would a heated Barium oxide filament survive in a deuterium environment?

Post by Dan Knapp » Thu Sep 27, 2018 11:40 am

Some university IEC researchers (e.g. the University of Wisconsin group) routinely use filaments in their reactors, but I don’t recall seeing anyone use a barium oxide coated filament. Bare tungsten is commonly used, and a convenient source is light bulb filaments.

Roberto Ferrari
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Re: Would a heated Barium oxide filament survive in a deuterium environment?

Post by Roberto Ferrari » Thu Sep 27, 2018 12:50 pm

I see several points to mention:
Barium oxide-coated filaments do well in D2 atmosphere. The coating is intended to enhance electron emission.
Yttria coating in filaments enhances electron emission and also filament life, being able to be exposed to atmosphere.
Barium oxide-coated filaments are able to be recovered from atmosphere exposition, at least as the attached paper states.
Of course, I agree that glow discharge ion source is simple and good enough for fusor purposes.
pre activation.pdf
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