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Registered Member #1451
Joined: Wed Apr 23 2008, 03:48AM
Location: Boulder, Co
Posts: 661
When smoothing high voltage the output tends to dump all at once into an arc creating the sparkgap like discharge (if not using ballast). Now, from experience, when that same supply is discharged into a vacuum, the discharge is continuous. Why is this? Is it due to the resistance of the gas in the vacuum? I would think that that would go to zero as soon as a discharge is started as the plasma is a very good conductor.
Registered Member #2372
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When you say vacuum, that indicates less than atmospheric pressure, but when you say there is still a plasma I assume you dont mean a hard vacuum of the type used in tubes (<10^-6 Torr) where the current pulled out of the cathode is due to field emission. It could be that you were operating at a pressure where there was sufficient background gas such that some ionization occurred, allowing you to see light, but the density of the plasma was very low so the conductivity was low. Without knowing the actual pressures,voltages, and current you were operating at it is pure conjecture (and it might still be even if those are known).
Registered Member #1451
Joined: Wed Apr 23 2008, 03:48AM
Location: Boulder, Co
Posts: 661
Sorry for not including all those factors, sorry.
The vacuum was less than 1000 mTor and more than 100 mTor. Voltage at about 20kV (from good ol' flyback). Current not measured but flyback was not run at high powers.
Registered Member #1225
Joined: Sat Jan 12 2008, 01:24AM
Location: Beaumont, Texas, USA
Posts: 2253
Well, i think it has something to do with a constant load on the LOPT... Once plasma ignites, the resistance is surprisingly low.
With my plasma experiments in a SoBe drink bottle, i first used about 50 watts, and the voltage with no load was probably 30kv. I got a column of plasma, about 8 inches long, and at least 1 inch in diameter. When i used more like 600 watts, there was no difference. Also, if i used another homewound transformer with maybe 4kv out and around 600 or more watts, it is the same.
I guess once the arc strikes, the resistance was falling to almost nothing (considering the voltage) and it pulled enough current to drop the voltage way down. Kind of like an arc at atmospheric pressure with normal air.
The resistance is high enough to keep the capacitor from discharging at many amps or whatever, but still short enough pulse to prevent you from seeing any difference... Then, once the voltage drops, it does not rise to charge the capacitor because duh, the resistive load of the plasma :P
I might be tired and i may not be making sense. Good luck
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HV pulse discharge in vacuum
