Shining UV-C on a Tungsten wire to increase emittance?

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Sven Andersson
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Shining UV-C on a Tungsten wire to increase emittance?

Post by Sven Andersson » Thu Sep 01, 2016 2:28 pm

On eBay you can buy theses UV-C lamps with a wavelength of 254 nm = 4.88 eV. The work function of Tungsten is approximately 4.5 eV. Say you have a Tungsten filament that is untreated (not treated with Barium or Strontium); then shining that UV-light on it would liberate electrons and the current would increase, wouldn't it?

Again my setup for producing deuterons: UV-C (the bare lamp should be inside the reaction chamber filled with D2 gas) to dissociate the D2 and at the same time increase the emission of electrons from a heated filament cathode. A voltage of several kV between anode and cathode to accelerate electrons, that collide with D2, D, D2+ etc. And also alpha particles from Am-241 buttons, that I scavenged. Should be reasonable population of deuterons then.

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Richard Hull
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Re: Shining UV-C on a Tungsten wire to increase emittance?

Post by Richard Hull » Thu Sep 01, 2016 6:33 pm

I think the alpha emitters are a sad attempt at doing virutally nothing. Forget them. Forget the UV as well. High-field emission is good enough at making deuterons, unless your vacuum is extremely deep. If it is extremely deep, you need a formal properly treated filament in an ion gun or some such arrangement.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
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Sven Andersson
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Re: Shining UV-C on a Tungsten wire to increase emittance?

Post by Sven Andersson » Fri Sep 02, 2016 5:09 pm

Richard Hull wrote:I think the alpha emitters are a sad attempt at doing virutally nothing. Forget them. Forget the UV as well. High-field emission is good enough at making deuterons, unless your vacuum is extremely deep. If it is extremely deep, you need a formal properly treated filament in an ion gun or some such arrangement.

Richard Hull
"High-field emission is good enough at making deuterons"; I don't understand. What do you mean i practice?

1-10 Pa is the vacuum I will use. Probably.

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Re: Shining UV-C on a Tungsten wire to increase emittance?

Post by JohnCuthbert » Sun Sep 04, 2016 12:17 pm

At anything like a decent vacuum, the alpha particles will be emitted from the source, fly across the empty space and hit the wall opposite the source where they will mainly warm it up slightly.
The range of alphas in air is a few cm before they hit something. At a tenth of an atmosphere the range will be long enough that they hit the other side.
They might manage some ionisation on the way.
At lower pressure I don't think you have any real chance of them helping.
But you do introduce the risks associated with an unsealed radioactive source.

Sven Andersson
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Re: Shining UV-C on a Tungsten wire to increase emittance?

Post by Sven Andersson » Sun Sep 04, 2016 2:21 pm

JohnCuthbert wrote:At anything like a decent vacuum, the alpha particles will be emitted from the source, fly across the empty space and hit the wall opposite the source where they will mainly warm it up slightly.
Good point. Of course, you're right.

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Re: Shining UV-C on a Tungsten wire to increase emittance?

Post by Jeroen Vriesman » Wed Sep 07, 2016 9:05 am

Sven,
...a Tungsten filament that is untreated (not treated with Barium or Strontium)...
I think you are mixing the idea of a treated tungsten filament (thoriated and/or carburized) for direct emission with an indirectly heated cathode.
An indirectly heated cathode (which can be heated with any source of heat) is usually coated with BaO, SrO and sometimes some other oxides.

But -for as far as I know- the tungsten wire is never coated with oxides.

And for the original question, the thermionic emission of a heated wire, or the field emission when using HV is several orders of magnitude higher than the photoelectric effect.

For an impression of photocurrent you can take a look at vacuum photocell datasheets, e.g. https://frank.pocnet.net/sheets/030/9/90CV.pdf

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