1-Hour Ion Gun

For the design and construction details of ion guns, necessary for more advanced designs and lower vacuums.
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Tyler Christensen
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1-Hour Ion Gun

Post by Tyler Christensen » Fri Jul 03, 2009 9:01 am

I just built an ion gun today to help since I haven't been able to get measurable fusion with a neutron detector. It is basically just a copper tube centered down a 1/4" npt nipple with a negative voltage fed onto that copper tube (from an NST). Gas flows between the copper tube and the 1/4" npt pipe.

At around 1500 volts, the plasma formation disappeared and a pink formation formed coating all of the metal in the chamber. This change is instant, at a certain voltage around 1500 the plasma completely disappears and turns purple. What exactly is this other formation? I have never seen anything like it before.

Also there is a very high RF field coming off of it, my tube-amplifiers across the room were going crazy and I couldn't even hear my music over the static noise. Normal plasma operation on the grid doesn't make anywhere near this much noise. It knocked out my vacuum gauge for about 5 minutes, I have no way of explaining why it suddenly started working again after a few minutes but at least it saved me some money.

I wish I could power up the grid with this installed but I need to get another variac to do this because I need one on the ion gun.
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Re: 1-Hour Ion Gun

Post by Quantum » Fri Jul 03, 2009 10:27 am

I can only hazard a guess here, but if, for example, an arc occurred, vapourizing some copper, this would coat things pink.

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Doug Coulter
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Re: 1-Hour Ion Gun

Post by Doug Coulter » Fri Jul 03, 2009 2:34 pm

Without seeing your wiring I can't speak to the RF you're seeing, but it's real easy to build a relaxation oscillator with gas and voltage at some pressures, and they can have fast enough edges to drive other stuff nuts.

Your conditions look ideal for sputtering, so that's probably what you're seeing or at least some of it.
Unless you design around it carefully, sputtering is going to coat insulators with conductive stuff, so watch for that.

I too have seen bizarre glow structures like you describe hopping around the tank and changing color as the tank conditions change -- and sputtering can change them by itself. That was with just an electrode going into the tank with medium HV on it from an NST/rectifier setup. Everything from the entire tank volume seeming to glow, to glow only in little pockets where flanges are welded in, to the normal cathode glow on surfaces -- but not necessarily where you'd think the field would be best for that.

Many people have done entire careers on the dynamics of glow discharges, there's a lot going on here, and some not obvious, even in a simple glass tube with electrodes at the ends (wall conductivity/recombination effects, the various dark spaces and stripes and so on). Places where you see no glow might be places where the voltage drop is either greatest or least, and varying ionization densities can give some sort of emergent behavior due to varying conductivity of the plasma in different places helping set up non-uniform fields that either change it back, or get to some odd equilibrium.

Fun to be sure, and maybe something to learn on. Magnets and plasma are fun to mess with.

Of course anything you see in a fusor is loss! Human vision is in the low single digit eV range only.
And photons are emitted by electrons in mostly neutral atoms falling from one energy level to another, not nuclear reactions.
Why guess when you can know? Measure!

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Re: 1-Hour Ion Gun

Post by Dustinit » Mon Jul 06, 2009 11:06 pm

Sounds to me that you have electron multipaction within the ion source.
Farnsworths patents have a good description of what may be happening.

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