Voltage multiplier inside vacuum chamber

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fruitytuter
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Voltage multiplier inside vacuum chamber

Post by fruitytuter »

Question:

Has any one ever constructed a fusor whereby high voltage ac was fed into the vacuum/fusion chamber then multiplied inside the chamber via a Cocroft voltage multiplier? This would involve small form factor capacitors and diodes encased in insulating resin housed inside a glass or acrylic tube. This tube would span from the outside edge of the chamber to the center where it would attach to the electrode.

This design would have some advantages:

The high voltage dc would be in the very center of a grounded metal chamber reducing shock hazard, corona losses outside the chamber, and the size ( cost ) of the high voltage feed through because only the HV ac would need to be insulated.
Say for instance a 4 stage voltage multiplier is inside of the chamber. 40 kv dc can be achieved inside while the feed through only has ~10 kv.
Because the voltage multiplier is inside the chamber it becomes easy to experiment with multiple grids by attaching grids to various stages of the multiplier.

This design would have one disadvantage:

High voltage components are large and building a voltage multiplier inside of the vacuum/fusion chamber would require a large chamber and small HV components. Also run time would be short because of the low heat dissipation of the diodes in a near-vacuum environment.

I am considering this design because very high voltage dc can be achieved inside the grounded chamber with less shock hazard and with a lower voltage feed through, maybe even a spark plug.

Does this design seem practical and are there factors other than those stated above that would effect the feasibility of this design?
Wilfried Heil
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Re: Voltage multiplier inside vacuum chamber

Post by Wilfried Heil »

Hello and yes, something like that has been done. Have a look under "Dynamitron" high voltage generators.
This is not a vacuum chamber, but one filled with an insulating gas like SF6.
http://accelconf.web.cern.ch/Accelconf/ ... 5_0227.PDF

It would be feasible to do this in a fusor, but in general, one would like to keep the chamber as clean as possible, with no plastic parts exposed to the plasma. Like you noted, the components would need to be mounted in such a way that the heat from the multiplier can be dissipated.
fruitytuter
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Re: Voltage multiplier inside vacuum chamber

Post by fruitytuter »

Thank you very much, the dynamitron seems to be a very compact particle accelerator compared to other designs. I am also curious about the use of a van de graff generator as a voltage source. It has the ability to create very high voltage but at very very low amperage. Because the voltage determines the kinetic energy of the ions, a van de graff generator should be able to produce high ion energies at a lower flux because of the low amperage.
Oh and one other question, Has any one ever used lightening as a power source for a fusor? Lightening packs an incredible amount of high voltage electrical power which would be nearly impossible to recreate at those power levels. Of course the reactor would go out with a BANG and have to be rebuilt but it could produce record breaking neutron fluxes and valuable data not found in the current power input levels of 2011 in even the highest energy labs around the world.
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Chris Bradley
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Re: Voltage multiplier inside vacuum chamber

Post by Chris Bradley »

Josh Cherek wrote:
> I am also curious about the use of a van de graff generator as a voltage source.

Thorough searching on the site [use the 'seach' button] will yield the best results, especially as you are very new here. More reading, less questions - for now.

If you had done the search you should've found;

viewtopic.php?f=18&t=7842#p55801

but the first key to a good search is to spell what you are looking for correctly; 'Van de GRAAFF'.

Good luck with your bountiful reading!
fruitytuter
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Re: Voltage multiplier inside vacuum chamber

Post by fruitytuter »

Thanks, I'll use the search feature next time. Also what do you think about the use of lightening as mentioned in my second posting?
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Chris Bradley
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Re: Voltage multiplier inside vacuum chamber

Post by Chris Bradley »

Josh Cherek wrote:
> what do you think about the use of lightening as mentioned in my second posting?

....use... the.... >>search button<< !!
viewtopic.php?f=15&t=7194#p49066


As for coupling a lightning rod to your fusor, or some such, well, a bit Frankenstein-bonkers, really, isn't it? This site is intended for the presentation of practical experiments, not wishful fanatasies.
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Re: Voltage multiplier inside vacuum chamber

Post by Tyler Christensen »

I'm quite curious, how is this not a practical amateur experiment? One would probably want a tall collector rod, then shoot a rocket up with a thin wire attached to the top of the rod (the standard way to induce lightning). If this rod ran through a fusor before getting to the ground, it could make momentary fusion. Total cost, about $30 for a rocket kit, and the cost of a fusor.

I would support someone in trying this if they so desired, however I don't think it would yield many neutrons if any.
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Chris Bradley
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Re: Voltage multiplier inside vacuum chamber

Post by Chris Bradley »

Tyler Christensen wrote:
> I'm quite curious, how is this not a practical amateur experiment?

OK, so I should clarify that this is just my opinion.

If lighting storms overhead are common for you, and you can reasonably anticipate maintaining and readying a live rocket at the same time as preparing your chamber, evacuating it, flowing in the D and getting all the RFI hardened neutrometry ready in anticipation of your rocket launch, all taking place in, presumably, a remote shed that you can operate remotely (for fear of piping in a direct lighting bolt into your house), then I guess it is practical.

...Just seemed a tad towards the impractical side, to me. It's probably a walk in the park for a well seasoned amateur.
fruitytuter
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Re: Voltage multiplier inside vacuum chamber

Post by fruitytuter »

I think the easiest way to perform this experiment would involve creating a vacuum, injecting deuterium to the correct pressure, and then (assuming that the chamber and valves are well sealed) all valves would be shut and the sealed chamber would be unbolted and transported to a suitable location during a storm.
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Richard Hull
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Re: Voltage multiplier inside vacuum chamber

Post by Richard Hull »

I have discussed this ludicrous and dangerous ideal in the main discussion. You have to warrant the proper polarity or no fusion will occur and a lighning rod will operate a small electrostatic motor only. I have done this.

However the fusor requires current in milliamps from such a rod and you will never get it and then there is that polarity thingy.

If lightning hits, you will get the amps alright, but (polarity???) Most of those amps will never go in the fusor though as there are a thousand other sweeter and bekoning lower impedance paths in and around this hypothetical lighting operated fusor.

Stupid, stupid, stupid. How many here have generated and seen real 12 foot arcs crawl all over every thing in sight except where you want the energy to go. No experience just pipe dreams and wild ideas.

My Tesla Magnifier 10E Circa 1996 @ 6KW ten foot arcs one hits my Nikon lens. Bye-Bye Nikon electronics.

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DaveC
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Re: Voltage multiplier inside vacuum chamber

Post by DaveC »

Josh -

On the concept of building an HV multiplier inside a vacuum chamber -
The short answer is "YES" is can be done. A more specific answer is that practically speaking, it depends on the pressure you intend to have in the chamber.

The key to understanding the answer to the question you've asked, is the behavior of the Paschen Curve for the gases of either atmosphere or those in the Fusor - mainly Deuterium. Use the Search function here and/or check out Google for more info.

The Paschen curve plots breakdown voltage between two electrodes vs the product of inter-electrode spacing and pressure. The curves are different for each gas and to some extent, the families of curves will differ depending on electrode shape and material. That said, all the curves exhibit a concave upward shape, although they are by no means either symmetrical or any regular curve.

As to what voltage your internal circuitry could safely withstand without suffering a flashover, it depends on gas type, electrode shapes and pressure, mainly.

At the pressures within a normally operating fusor - 10 to 20 mTorr - breakdown voltages in D2 are obviously in the range of few tens of kV, since those voltages can be sustained across the internal electrodes, with their typical separation and geometries.

An HV multiplier, with its closely spaced electrodes, has a different value for the pressure-separating distance product and hence a different breakdown voltage. This breakdown voltage could be lower than the fusor's breakdown voltage.. because of the higihly curved wires and electrode, or it could be higher because of the close spacing. So, it might work or the multiplier might go into glow discharge be limited to some lower output voltage.

At high vacuum conditions, below 1E-5 Torr, the concept will definitely work well. It has been considered before (reference not available) for high vacuum conditions.

However, construction will be of paramount importance - since outgassing, component failure, overheating and related issues are important but solvable problems. Not trivial, however.

As to the lightning powered fusor.... it IS a way to go out in grand style.. Mostly it's useful for reducing the gene pool... and COULD be a candidate for a DARWIN award, perhaps in some scientific category.

Edit: Removing the "vestigial" Darwin....

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Re: Voltage multiplier inside vacuum chamber

Post by Jeroen Vriesman »

I have given the idea of a voltage multiplier inside the vacuum chamber some thougts in the past.

I had the idea of putting capacitors and diodes in a glass tube, and fill it with heat conducting epoxy, exposing only a minimal area of epoxy on the vacuum side.

The components should be small, so the only way to make it work would be to use a high frequency, the idea was to use a big output transformer from an old audio power tube amplifier and use it at 4kHz (which is already a bit high for a tube amplifier audio transformer, I don't know if the output power is still enough at 4kHz).

The secondary windings (these are primary in the tube amplifier) should be disconnected from each other in order to use one winding for ripple rejection. (make two leads from what was originally the center tap).

The simulation still shows a ripple of about 400V, but that could be compensated by disconnecting the lower secondary winding from ground and using "active ripple rejection" (see http://nuclearfusionreactor.blogspot.co ... ltage.html for an example of active ripple rejection)

For the GI250-4 (any 4kV diode which can handle the current would do) I used:
.model GI250-4 D(Is=5u Rs=3 N=1.2 EG=1.11 XTI=3 BV=4200 IBV=1e-04 Cjo=3p Vj=3.5 M=.5 tt=30n Iave=.25 Vpk=4200 mfg=VISHAY type=silicon)

A transformer with dual 2kV output which works at 4kHz might be a bit hard to find.

But the ceramic 2kV capacitors are small and so are the diodes, they would fit in a not-too-big glass tube.
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DaveC
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Re: Voltage multiplier inside vacuum chamber

Post by DaveC »

Audio power transformers can have a rather high frequency capability. Some of the old high quality tube amplifiers were nearly linear to 100 kHz. (thinking about a McIntosh Professional Audio amplifier, so the output transformers had to be equal to the task. Transformer-less transistor amps, though, sidestepped that issue.

So your idea is certainly viable...since even the low priced equipment was good to 15kHZ or so. HV multipliers typically operate below 50 kHZ because of diode limitations, although some high end gear works at much higher freqs.

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JonathanH13
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Re: Voltage multiplier inside vacuum chamber

Post by JonathanH13 »

>Lightening packs an incredible amount of high voltage electrical power

The 'average' single lightning stroke (100 MV @ 30 kA), has a peak power output of somewhere between one and three trillion watts, but measured estimates have been made as high as 1 GV @ 120 kA.

>a bit Frankenstein-bonkers, really, isn't it?

Yes, definitely.

>practical experiments, not wishful fanatasies.

Not fantasy, and not outside the realm of practical experiments:

I did a series of lightning experiments in South Africa when I was 24. I started with huge meteorological balloons filled with hydrogen. A balloon was attached to a large reel of copper wire (several kilometres in length, 0.2mm diameter). I would wait for the storm to be overhead, and then release the balloon. It would climb rapidly to a few hundred meters, but then the weight of the wire would start to drag it down, and the surface area of the balloon resulted in it being pushed sideways by the storm-front. The balloon does not have to get very high to become the highest point in the area, and at about 100 meters up, the local ground charge profile changes radically, as electrons start to leave the area en masse. This coincides with a 'serious amount' of induced charge in the wire, and the unravelling wire reel literally turns into a ball of blue fire, all your hair stands up on end and you will receive a serious shock off anything metal in the area. This is a good indication that you are standing at ground-zero during leader formation, that you have seconds left to live, and that you should think about being somewhere else.

After several such experiments I switched to large home-made rockets. These are faster and more expensive; they cannot lift as much wire as a balloon, but they have a smaller surface area, so they tend to go straight up into the thundercloud, often breaking the wire on take-off

I initiated several 'controlled strikes', and have had lightning strike as close as 2 meters away from me - knocking me off me feet and leaving a blue glow in the air around me.

>Total cost, about $30

More like $300 per controlled strike.

Using this as a power source for a fusor? Isn't the ultimate aim of a fusor to produce electrical power? So you are converting electrons to neutrons so you can somehow convert them back into electrons?

Seriously though, what you want is to NOT have an actual lightning strike (which destroys everything), but the induced charge off a suitably high (100m) antenna could generate a sufficiently high potential to operate a fusor. You would need to discriminate polarity; lightning can be positive or negative (positive strikes are about 1 out of 10).

>ludicrous and dangerous...Stupid, stupid, stupid.

Experiments involving lightning are always risky and frequently fatal.

One of the most well-known deaths during the spate of Franklin imitators was that of Professor Georg Richmann of Saint Petersburg, Russia. (Wikipedia)

http://www.guardian.co.uk/world/picture ... MP=twt_ipd
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Richard Hull
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Re: Voltage multiplier inside vacuum chamber

Post by Richard Hull »

What makes fusion happen in useful, measurable amounts is ion populations (current) and not specific charge or potential alone. Antenna systems in high fields can't warrant, in general, the 20 ma or more continuous currents at fusor potentials.

This factor would be a surface area issue of the isotropic antenna (net capacitance).

A thunderstorm and local ground referenced, collected electrostatic potential energy is not a fun, stable or safe power source for any fusion device.

Most folks will have enough high adventure trying not to kill themselves with a precision, ultra stable, custom engineered, 60kv mains supply.

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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