possible ion gun design

For the design and construction details of ion guns, necessary for more advanced designs and lower vacuums.
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possible ion gun design

Post by pcfusor » Sat Mar 01, 2008 8:36 pm

This is our ion gun idea. It is somewhat similar to the Carl Jr. design. We decided to try soldering a screen to the end of the copper tube because of what Tom Ligon had said about that design. We deduced that more holes at the end would increase the percentage of ionized deuterium. The whole copper tube and the screen will be held at a positive potential, so that as the neutral gas exits the tube (which should have no electric field inside of it) the gas particles become ionized by the little rings of charge that are the holes in the grid. The particles (now positively ionized) would then be repelled by the field on the screen and the tube towards the center grid, which we will be holding at a negative potential. We were wondering if this idea seems at all feasible. We have created a basic design image to illustrate what we are talking about. Please see below.


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Carl Willis
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Re: possible ion gun design

Post by Carl Willis » Sun Mar 02, 2008 7:14 am

Are you going to use a magnet outside your ion source chamber port? Without some magnetic fields, I don't think this scheme is likely to function as an ion source to any appreciable extent. At typical fusor pressures, the hollow-cathode discharge in the fusor itself is a pretty darn powerful ion source. To make something competitive at this pressure or lower pressures requires a lot of thought and careful implementation.

My ion source, and Jon R.'s similar ion source, use magnetic fields in a magnetron configuration to help trap electrons in the ion source and produce a discharge. They are simple but not very prolific ion sources. I found that my magnetron source is helpful at low fusor current levels and at pressures where the hollow-cathode discharge would go extinct, but when the fusor is running at 75 kV / 1 kW, the ion source barely has an influence at all.

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Re: possible ion gun design

Post by DaveC » Sun Mar 02, 2008 7:53 am

This design it should work alright, at producing ions
You will need a husky ballasting resistor between the postive power supply terminal and the ion source connection. The exact value will depend on the supply voltage and the actual operating pressure. At glow discharge pressures, ion currents can easily be produced in the tens of mAs.

The ionizer supply should be capable of a positive voltage a few hundred volts above the ion energy you want to produce. and be capable of the ion current you want to supply.

When the ionizer "lights off", the ballast resistor will keep the current under control. The ionizer will take on whatever voltage it needs to stay lit, and the ballast resistor will have the rest of the potential across it. The ions produced will have modest energies of a few hundred eV, typically.

If you want the ions to go anywhere other than directly to the chamber walls, a negative electrode at higher potential will be needed to attract them in the desired direction.

Dave Cooper

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