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Proud Mary

Sun Sept 11 2011, 08:57PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Microwatt wrote ...

I am experimenting with ionized gas. A very fast rise time and short pulse width will allow a uniform glow discharge to form.

Uniform glow discharges are usually associated with space-charge limited current flow through an ionised gas.

It's not easy to put all the different statements made about the characteristics of the device being discussed in this thread into a coherent picture.

Pinky's Brain

Sun Sept 11 2011, 10:53PM

Registered Member #2901 Joined: Thu Jun 03 2010, 01:25PM
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Posts: 837

Dr. Kilovolt wrote ...

why not build a small VTTC with a 1-3 MHz secondary, with a horizontal output tube? The circuit can run from rectified or voltage multiplied mains and has very few components. The voltage can be regulated with a variac.

Won't the sparks taking energy out of the Tesla coil reduce the spark frequency to well below the resonance? (ie. it rings up for a few cycles, sparks, rings up for a few cycles, sparks, etc etc.) A problem for any low coupling ratio transformer approach. The original description was rather inaccurate ... what he is looking for is a very high rep rate pulse generator.

I'd consider a flyback.

Microwatt

Sun Sept 11 2011, 11:06PM

Registered Member #3282 Joined: Wed Oct 06 2010, 05:01PM
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An ideal wave shape would be a pulse lasting less than 50 nanoseconds. beyond that the gas has trouble making streamers according to paschens(sp?) law. How could i find out the Z of a gas discharge in open air?

Pinky's Brain

Mon Sept 12 2011, 12:14AM

Registered Member #2901 Joined: Thu Jun 03 2010, 01:25PM
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I assume you mean more than 50 ns, to give time for the streamers to form ... Paschen's law is essentially for DC.

AFAICS barrier discharge is a far easier way to accomplish what you want ... with exposed electrodes riding that fine line between streamer/glow discharge and arcing (inefficient and destructive for your electrodes) is complex.

Microwatt

Mon Sept 12 2011, 01:51AM

Registered Member #3282 Joined: Wed Oct 06 2010, 05:01PM
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i don't want streamers to form. The faster the pulse the close you can bring the electrodes together before you have a discharge. Does anybody have any clue how to build the circuit found here? this looks very promising.
]10123.pdf[/file]

Proud Mary

Mon Sept 12 2011, 11:04AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Microwatt wrote ...

i don't want streamers to form. The faster the pulse the close you can bring the electrodes together before you have a discharge.

These authors have a different view of streamer formation and suppression in DBD, that does not involve fast pulses or high frequencies:

Yongho Kim, Min Suk Cha,y Wan-Ho Shin and Young-Hoon Song Characteristics of Dielectric Barrier Glow Discharges with a Low-Frequency Generator in Nitrogen Journal of the Korean Physical Society, Vol. 43, No. 5, November 2003, pp. 732-737

Pinky's Brain

Mon Sept 12 2011, 04:46PM

Registered Member #2901 Joined: Thu Jun 03 2010, 01:25PM
Location:
Posts: 837

Microwatt wrote ...

i don't want streamers to form. The faster the pulse the close you can bring the electrodes together before you have a discharge. Does anybody have any clue how to build the circuit found here? this looks very promising.

You could try PMing Cedric, he actually prototyped a magnetic switch pulser and tried to research the availability of SOS diodes. That said, SOS diodes are exotic and likely expensive, also I sincerely doubt you could scale these circuits to MHz range pulse rates OR make them produce a nicely distributed plasma.

BTW, with a magnetic switch alone you can get 100 ns FWHM pulses which is enough to prevent arcing :

The microdischarges in barrier discharge aren't really streamers ... AFAICS barrier discharge is by far the simplest atmospheric pressure plasma generation technique, and popular in research both for pollution control and ignition.

Forty

Mon Sept 12 2011, 05:04PM

Registered Member #3888 Joined: Sun May 15 2011, 09:50PM
Location: Erie, PA
Posts: 649

so hv ac + glass/pyrex plate between two copper bars + nitrogen atmosphere => plasma generator? I'm missing something, where does the plasma form exactly? sounds like something i could try b/c i have tons of pyrex plates and nitrogen here in my lab.

Pinky's Brain

Mon Sept 12 2011, 05:38PM

Registered Member #2901 Joined: Thu Jun 03 2010, 01:25PM
Location:
Posts: 837

AFAIK the microdischarges simply strip the electrons from the molecules creating a "cold" non equilibrium plasma (ie. the electrons are far hotter than the ions).

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