POPS

It may be difficult to separate "theory" from "application," but let''s see if this helps facilitate the discussion.
Conrad Farnsworth
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Re: POPS

Post by Conrad Farnsworth » Mon Dec 06, 2010 11:28 pm

John,

Thanks for the fast reply! I was looking to use a 5-6kv transistor to modulate and/or pulse my -DC output. Would this work? It is the only way I can think of (besides a spinning wheel with contacts that would only generate a square wave) that i can use to apply a sine wave, and a square wave to via signal generator. Any input? I would also like to add that I can only do this with DEMO mode power since anything at all that has to do with radiation that goes in a science fair has to have oversight throughout the experiment by a qualified nuclear physicist. (Lead, South Dakota).

Thanks!
-Conrad

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Re: POPS

Post by Tyler Christensen » Tue Dec 07, 2010 3:13 am

In principle a transistor (more likely to be transistors in series, hence where a lot of difficulties come in) may work... just a warning that making a 5kv sine wave 10mhz+ amplifier is no easy task, you're in for some decently difficult electrical engineering to make that work based on the voltage (you can't just directly drive transistors in series).

If you just want to pulse, may I suggest a thyratron?

If you plan to use it at only 5-6kv, what are you expecting to see? Visually it will look just like a plain old demo fusor, and there won't be any radiation either way at that voltage.

Conrad Farnsworth
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Re: POPS

Post by Conrad Farnsworth » Tue Dec 07, 2010 3:44 am

Since its a demo, I would like to see the same light levels (peak) as the grid being un-pulsed, but with a lower outgassing rate. Maybe if i get the cajonies (and money) to upgrade to fusion I would hypothesize if X hz is used, then the power to production ratio will be Y.

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Re: POPS

Post by Conrad Farnsworth » Tue Dec 07, 2010 4:07 am

As I have recently learned. Why couldn't I use a vacuum tube?

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Re: POPS

Post by UG! » Tue Dec 07, 2010 10:43 am

I have pondered upon this.

The Fusor is a vacuum tube. Maybe it would be possible to design a grid structure that is self amplifying, like a large amplifying valve, that could be provided with a (heavily decoupled) DC HV and maybe a couple of Watts of RF on a control grid. Using the fusor as its own RF amplifier would remove the need for the complicated HV RF power supplies that I suspect would be the main stumbling block on such an endeavour.

Verifying RF amplification and optimizing grid structure would not require fusion, could be carried out in demo mode and would be a very useful thing to investigate IMO

Oliver

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Re: POPS

Post by Starfire » Tue Dec 07, 2010 12:28 pm

At high voltage a thyratron or a spark gap is the switch of choice - the problem with short pulses ( sub-nanosec pulse width ) is usual getting fast rise or fast fall time which can be difficult to get when using high energy. Keep the impedance as low as possible to achieve high energy fast transfer. Transistors tend to be sluggesh at high voltage avalanche and cost a lot.

Good instrumentation is a must for serious work - a scope capable of 1000mhz+ bandwith and learn how to couple the instrument to read accurately .

I work with pico-sec pulses at 4000+ joules and the transfer bus is 3"x 0.25" pure copper bar on ceramic stand-off insulators - usually with 10kv or 20kv applied from a cap bank which takes a long time to fully charge - and a low repetition of pulses.

Not easy and expensive when amateur funded

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Re: POPS

Post by Starfire » Tue Dec 07, 2010 1:16 pm

Thinking about it - you would be best using a triggered spark-gap ( you can make yourself ) and a cap - it would give you a usefull HV pulse and not cost much - don't try to use a sine - not efficient for energy transfer.

Conrad Farnsworth
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Re: POPS

Post by Conrad Farnsworth » Tue Dec 07, 2010 3:16 pm

Oliver,

That would be cool. Think about using microwaves to amplify or modify the neutron output with changes in frequency. But my experiment doesnt involve that at all, its all about efficiency, so applying an opposing force would require more of it where as pulsing it, would cut down on energy consumption.

-Conrad

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Re: POPS

Post by Conrad Farnsworth » Tue Dec 07, 2010 4:53 pm

John,

I am guessing that to adjust the pulse width, I would adjust the spark gap width? And to measure this in HZ I would hook up my (the schools) oscilloscope to the voltage measurement circuit that the multimeter hooks up to?

Thanks,
Conrad

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Re: POPS

Post by Richard Hull » Tue Dec 07, 2010 5:20 pm

Pulsed high power electronics is a world unto itself. Inductance is the enemy and picosecond pulses are a dream. Nanosecond pulses tough to achieve. Microsecond pulses are more in the casual amateur range. A lot of power can be delivered in a microsecond. (Millions of peak watts).

Hydrogen thyratrons are the switch of choice here and can easily handle 40kv in some tubes. The common tubes that can be found at hamfests surplus top out at 20kv though. (5C22).

Richard Hull
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