Hollow cathode lamp ion gun

[Andrew Seltzman]

Here is a suggestion for an ion gun that I think might be simple and inexpensive to build. The design is based on the utilization of a hollow cathode lamp (about 2” od) as the ion source and body for the gun assembly. The cathode / anode of the lamp (some lamps actually have anodes that are rings in front of the cathode positioned on stand offs) would ionize gas fed in from the rear of the lamp. These lamps have a tubulation at the end for filling them with gas during manufacturing (like on a crt but about 1/4” od) which is sealed, however the tip of the tubulation can easily be cracked off leaving about 1/2” for attaching a tygon tubing for leaking in deuterium, etc. A 1” circle could be cut out from the face allowing the tube to seal up against an o-ring for a 2.75” conflat (with some bracket holding it in place). A conflat adaptor with a 1/8” npt side port could be fashioned into a HV feed through for the extractor cone using a 1/4" swagelok and some glass tubing.

Andrew Seltzman
www.rtftechnologies.org

[Starfire]

Tks Andrew, But two problems arise - the design does not show a gas inlet, which is the purpose of using an Ion gun for fusors, and I dont think a hollow cathode design would give enough Ions -The hot cathode ( filament / heater ) design is necessary for the required Ion current.

[Roberto Ferrari]

John,
Andrew explained how to enter the deuterium opening the sealed tip-off in tha back of the lamp.
I am not sure about the currents needed, but this would not be the first cold cathode ion gun presented in this forum.
See Tim Raney post of 2003-15-02.
Of course, Raney's design is sturder and from high vacuum point of view, better.
Roberto

[Starfire]

Opps! Tks Roberto, I was only considering the drawing as shown. With a normal ( commercial ) Ion gun, the gas stream is feed directly into the Anode via a gas inlet port. The +Ions generated, bypass the Cathode due to the higher neg field beyond. With this design, I am not sure how the +Ions released from the Anode, by the Cathode Electron flow, will proceed toward the higher negative potential of the device. The HV looks like it is on the wrong side of the gun Anode and the +Ions will have to do a 360 through the aperture of the Anode to get there. But it may be the basis of a good design Adam.

[Adam Szendrey]

I think he's name is Andrew . Just a hunch .

Adam

[raneyt]

Hi Guys,

Yes, the hollow cathode is a good idea, but it depends on your execution of the actual design (like anything else). In practice, intense ionization is confined to the cathode's interior and it is capable of high excitation energies. Reference: Fretter, W.B., Introduction to Experimental Physics, Prentice-Hall, Inc., NY, 1954, pg. 243. In this reference, Fretter footnotes two other references that probably go into more depth. As you all have noted, the hollow cathode is used in spectrum tubes for the reasons cited above.

Though I've fabricated an ion gun with the hollow cathode and an x-ray tube, I have not done any quantitative work regarding any comparison between it and using an incandescent filament. So, I'd think this is a fruitful area for experimental efforts. And it is interesting to see the interior of the cathode glow vs. conventional bare electrode as in a simple discharge tube.

Good luck with your experiments!

Warm Regards,

TIM RANEY

[Richard Hull]

As my new vacuum system comes back on line, I hope to test out Tim's glass experimental gun that has been gathering dust in my lab. I hope to make the system versatile enough to allow for a port to be used without disconnecting the fusor.

Richard Hull