Field emission, electrostatic ion gun (canal ray)

For the design and construction details of ion guns, necessary for more advanced designs and lower vacuums.
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Richard Hull
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Real name: Richard Hull

Field emission, electrostatic ion gun (canal ray)

Post by Richard Hull »

I was much amused as I studied some of the earliest ion guns used by the Farnsworth team. I attach an image of what I worked up as a simple electrostatic ion gun for the amateur fusor as an experimental device.
One of the great wonderment of the simple fusor is spherical ionization continuously taking place. This points to a relatively large surface electron emission area with a hoped for equivalent possible ionization of local gas in that region to make deuterons.

Ion guns be they powerful of weak warrant an absolutely positive result in the manufacture of deuterons far beyond wall electron emission. The obvious advantage is a certain amount of warranted directional deuteron flow towards a target. In our case it is to the central grid.

Powerful ion guns, (milliamp ion currents), rely on a filament emitter (tens of watts). They also demand an extractor power related to the deuteron current demanded in the design (Often hundreds of watts) and this is for each single gun. All such guns rely on a permanent ring magnet (custom and expensive) or a wound coil around the gun body to electrically create the demanded field. (more watts).

In the gun I show, the chief wattage is whatever voltage and current you wish to apply to the field emitting tungsten needle. The extraction is against ground from a number of largish holes drilled into what is, in effect, the gun's anode. Yes it is a glorified canal ray source, but it is better than a poke in the eye with a sharp stick if you want positive, localized and directed deuterons into a fusor.

Note drawing not to scale. The ideal is a large diameter very short gun less than 1:1 ratio L to D with the needle point rather close to the exit port so that the most deuterons are formed near the exit plate

Richard Hull
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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
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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