POPS

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

Post by longstreet »

I haven't quite figured out what they are doing. Some grid designs I've seen in the context of POPS has either negative or positive inner grids. Both inject electrons into the chamber and modulate the voltages in some way, but I haven't really understood what these all have in common. At first I thought they were just trying to stabalize the old virtual cathode idea of electron confinement, but it seems there is something different going on.
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Re: POPS

Post by DaveC »

Interesting writeup. In the paper's acknowledgements, there is a mention of thoriated -tungsten wire. This is normally used for filaments, giving good output, at temperatures about 1000K cooler than pure tungsten. Wondering, if they are making grids or cathodes out of the wire.

Dave Cooper
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Re: POPS

Post by longstreet »

I think I understand what they are trying to do. The potential in a normal fusor looks like the bell of a horn. But what they want to do is make the potential into a parabola.

As you know from intro physics, any parabola shaped potential energy curve can cause simple harmonic motion. And this means that frequency is independant of amplitude by definition (meaning it has a natural frequency). So, what they do is create such a parabola shaped potential using a distribution of electrons and then drive the thing at it's natural frequency.

It sounds interesting. But I have questions on the actual dynamics of any ions you put in there since their presence alters the potential well. I'm not 100% convinced you can really maintain a parabolla potential if the net charge density is continually changing with the plasma sphere's size.

edit...

I happened to think now that the harmonic motion is really of the size of the plasma sphere and not of the individual ions. So it does make sense, just not in the sense of a single positive ion flying through a parabola shaped potential well. Equilibrium for the plasma sphere is when the ions are evenly distributed throughout the electron field.

Thanks,
Carter
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Adam Szendrey
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Re: POPS

Post by Adam Szendrey »

And they want to make it modular, with several plasma convergence points. We discussed something like that on these forums aswell. And yes, i have read that too, in a book...it seems there is more truth to it than i thought.

"By applying rf fluctuation to the grid voltage..."
Exactly what i have read...Maybe some of you remember a discussion about modulating the grid voltage in order to trigger an oscillation.

Adam
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Re: POPS

Post by Richard Hull »

Discussions regarding modulating or pulsing the grid in a fusor go back to biblical times on all three fusor sites. Each wave of newbies kick the idea back out onto the playing field.

Lots of ideas, but I have yet to see any one do it, or if they did, they supplied zero data that was of any value in support of the idea.

Hell, someone might actually look into it one day via empirical experiment and report back.

Inquiring minds want to know.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Adam Szendrey
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Re: POPS

Post by Adam Szendrey »

Well if i can get things together in the college lab, i might be able to contribute...But i don't want to make an ass of my mouth, so i just say "maybe"...

Adam
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Re: POPS

Post by DaveC »

I don't know if it applies in this case, but some types of plasma systems oscillate at fairly high natural frequencies, 100 or more KHz. But it is not the plasma that's driving the oscillation, but rather the stray inductance in the power supply, is coming into resonance with the capacitance that usually attends the gas discharge system. For Barrier Discharge lamps, this is how the lamp capacitance is determined when the plasma is formed.

After reading the material posted, it would seem that they are claiming the resonant oscillations tend to bring the ions into some sort of phase coherence..which improves the output.

This could also be a result of oscillation induced compression increase or it could be a resonance with their HVPS. Not easily separated, I wouldn't think.

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Donald McKinley
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Re: POPS

Post by Donald McKinley »

from the web article link in Mike Smiths first post in this thread:

"Tuning the "external" radio-frequency (rf) electric fields to this naturally occurring mode allows the ion motions to be phase-locked."

Sounds like they put a maritime radio tuner up to the fuser, picked up the loudest harmonic, and started amplifying back to the fuser.

They are just attempting to resupply the energy that is lost from coulomb interactions by baking the fuser in a resonant frequency rf oven. They aren't even introducing resonance. The resonance already exists.

It seems that the plasma should already be phase locked, correct me if I'm wrong, otherwise it wouldn't form virtual cathodes and anodes.It looks like the new part is the concern for measuring resonances (a la Tesla) and applying the knowledge to "poke" the fields.

Interesting experiment. This is a very worthy goal. Resonances seem to me to be the right way to go. I would expect the need for a large number of iterations though before designing a monster with thousands of tubes. I would be surprised though if just a single harmonic, and one with such a large wavelength were the most important one. 380KHz has a wavelength of 789 meters. I expect a revision of this seemingly spurious number.

I envision a little more directed approach to the control of resonances. There are quite a few of them. I wouldn't be surprised if there were more than a few which need their own broadcast back into the fuser. Nuclear Magnetic Resonance imaging probably could supply some inspiration on this topic.
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Re: POPS

Post by Conrad Farnsworth »

I have been doing SOME searching around and would like to start "pulsing" my electrical input (for the sake of a science experiment) and since "they supplied zero data that was of any value in support of the idea." Since I'm a newb, POPS goes right over my head (any english explanations?). So, in short, would oscillating or pulsing the input power have any affect at all on the efficiency?
Sorry in advance if this is the wrong section for this.
-Conrad
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Re: POPS

Post by Starfire »

The great advantage of pulses is that you can use more power for a shorter time - beyond that which would distroy apparatus otherwise.

Apparatus may withstand a short burst of power at a level which would distroy it, if continuously applied.

Efficiency remains the same for a given power but remember that power is 'work done in time' - 100 watts for 1 sec is the same power as 100,000 watts for 1 milli sec .
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Re: POPS

Post by Conrad Farnsworth »

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 »

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.
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Re: POPS

Post by Conrad Farnsworth »

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 »

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

Post by UG! »

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 »

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 »

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.
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Re: POPS

Post by Conrad Farnsworth »

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 »

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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Richard Hull
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Re: POPS

Post by Richard Hull »

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
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Re: POPS

Post by Starfire »

Nop - I suggested the sparkgap to keep the cost down and provide a good workable system that can be built on a small budget. It will not allow you much control of pulse width - more the other circuit components and layout.

UHF or Microwave technics are required. Inductance will allow you to extend timing but usually the trick is to shorten it if possible.

As Richard says - it will give microsec timing but good work can be done at these speeds. A sparkgap and a good cap gets you started cheaply.

I use a Radar calibrator to get fast triggering but lose speed with switching loads

A simple sparkgap filled with D2 will get you a Neutron burst when discharged.

The quest continues but room for more workers using pulses.
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Re: POPS

Post by Conrad Farnsworth »

Well, this is a subject that I am continually learning. I would love to try pulses for my next set of experiments!
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Re: POPS

Post by Starfire »

I disaggree with Richard on this one - a 10Ghz Magnetron ( X band ) will give you 50 pico-sec pulses spaced at 50 pico-sec if halfwave rectifyed and shaped ( PFN ) and can be high-powered - well within amateur capabilty and access. - A nice cheap ( Ebay ) oscillator for 50 pico-sec work. Or a 2.4Ghz microwave oven magnetron giving about 200 pico-sec ( there abouts )

Still dreaming.
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Re: POPS

Post by Conrad Farnsworth »

How would one go about shielding the EMF off of the Microwave oven magnetron? Especially from the now necessary camera.
-Conrad
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Re: POPS

Post by Starfire »

Conrad - the need for shielding occurs when the power goes up - low power with low repartation rates generally are not a problem but standard RF shielding will work ok .

With all shielding issues, distance from the source is best.

A camera should not be a problem for low power and proper RF shielding- xray issues more so.
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