Low energy (<100eV) ion sources

For the design and construction details of ion guns, necessary for more advanced designs and lower vacuums.
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RobertMendelsohn
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Low energy (<100eV) ion sources

Post by RobertMendelsohn » Mon Jul 27, 2020 9:10 pm

Does anyone know of any very low energy ion sources (<100eV)?

Some ideas:

Micro liquid metal ion sources
I have made some liquid metal ion sources that (via very sharp tungsten needles and incredibly close spacing) can operate below 400V, but I'd like to work with even lower energy ions. I've reached my limits in terms of fabrication, otherwise this could be as low as 46eV.

Decelerating lenses
Futrell et. al. (1976) report a decelerating lens that can reduce ion speeds 1400x; this seems to be the basis of all later papers involving low-energy ions.

Surface ionization sources
A surface-ionization based ion source should be able to get a ~0.2eV ion beam , but I am struggling to find a low energy ion source based on that method. Might need to experiment. Something similar to a Q-machine may be a good starting place.

Exploding wire ion sources
On a more exotic note, I have seen references to an exploding wire ion source that produced a pretty massive number of ions at around 100eV, and I may try to implement that and see if I put less energy through it if I can produce a lower energy beam.

If anyone has any ideas, I'm all ears.

Sincerely,

Robert

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Dennis P Brown
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Re: Low energy (<100eV) ion sources

Post by Dennis P Brown » Tue Jul 28, 2020 12:00 am

Rather interesting projects you are conducting; could you explain where you are going with these low ion work?

Cold "plasma's" are a somewhat 'hot' topic currently among some. I have no idea why so posting a bit on that topic would certainly interest me and I am sure other readers as well - sorry for the bad pun.

Maybe some pics of your equipment and descriptions would also be informative.

Aside: UV on a very clean, pure metal under high vacuum will release very low energy electrons if memory serves.

John Futter
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Re: Low energy (<100eV) ion sources

Post by John Futter » Tue Jul 28, 2020 7:05 am

Robert
We made nano-whiskers out of SiC to get field emission and made diodes and triodes that operated at a few tens of volts
end result was around 1 volt per micron spacing some a little better at .7 volts per micron I have put the said paper reference up here many years ago
https://ir.canterbury.ac.nz/bitstream/h ... sequence=1

hope this helps

RobertMendelsohn
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Re: Low energy (<100eV) ion sources

Post by RobertMendelsohn » Tue Jul 28, 2020 2:44 pm

Dennis: thank you for your reply. Your point about UV photoionization is interesting. I will need to look further into whether photoionization ion sources have been realized.

I think cold plasmas are of interest for sanitization and creation of highly-reactive radicals (in the case of so-called cold atmospheric plasmas), and for ion implantation for doping in the case of non-atmospheric, low-energy ion beams.

My interest is for a simpler reason: the slower the ion, the smaller the Larmor radii, so the lower my magnetic fields have to be to prevent the ions from hitting the sides of my vacuum chambers. Even moderate energies result in fairly large magnetic field requirements, or truly massive chambers. Re-building my electromagnets and getting new vacuum chambers are more or less equally odious tasks, but reducing the energy of my ion sources would seem to be the easier approach.

John: what an interesting paper! Thank you for posting this.

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Re: Low energy (<100eV) ion sources

Post by RobertMendelsohn » Thu Jul 30, 2020 8:15 pm

Numerical analysis (COMSOL CPT/plasma) shows that I would be able to get away with a very low energy directed plasma jet as well...

Would anyone happen to know of a plasma source with a low ion kinetic energy (<10eV), ability to use metallic species, and a degree of ionization approaching 100%?

Surface ionization technologies like the Q-machine may work, as may some laser ablation and vacuum arc sources. There must be a term for this, but I simply cannot find it.

Patrick Lindecker
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Re: Low energy (<100eV) ion sources

Post by Patrick Lindecker » Sat Aug 01, 2020 10:47 am

Hello Robert,

>the slower the ion, the smaller the Larmor radii, so the lower my magnetic fields have to be to prevent the ions
I don't know your configuration, but the Larmor radii depends on the initial ions radial speed. If you limit the source emittance by limiting the beam to a very small angle, the Larmor radius will be also very small and consequently the particles diffusion towards the vaccum chamber sides, due to collisions between ions in rotation, will be reduced.

Patrick Lindecker

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Re: Low energy (<100eV) ion sources

Post by RobertMendelsohn » Sat Aug 01, 2020 8:50 pm

Thanks for the reply Patrick. It is precisely that phenomena which I am hoping to exploit. Large chambers and large electromagnets are hassles, not to mention expensive.

-Robert

Patrick Lindecker
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Re: Low energy (<100eV) ion sources

Post by Patrick Lindecker » Sat Aug 01, 2020 10:05 pm

Robert,

Here are some rough ideas. You can:

* force the emittance to a weak value, passing the beam through a calibrated hole. Of course you will lose many ions,

* use a serie of electrostatic lenses to make converge the beam : http://f6cte.free.fr/Electrostatic_lens ... _Rev_B.pdf
This will limit the ions diffusion, even if the Larmor radius is bigger due a relaxation on the magnetic field.
Moreover the electrostatic field can possibly compensate the space charge introduced by the ions and responsible of a part of the ions diffusion.

Patrick Lindecker

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Dennis P Brown
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Re: Low energy (<100eV) ion sources

Post by Dennis P Brown » Sun Aug 02, 2020 12:50 am

The issue you will face with low energy ions is their very short travel time before a neutral collides with them leading to neutralization. You will need a ultra-high vacuum if your ion producion is low.

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