Extensions of the Farnsworth fusor

It may be difficult to separate "theory" from "application," but let''s see if this helps facilitate the discussion.
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Doug Coulter
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Re: Extensions of the Farnsworth fusor

Post by Doug Coulter »

OK, I lied. Here's a teaser bit of data on the fusor in dynamic mode.
Inset is neutrons vs volts and amps, larger plot is Q in neutrons counter/watt.  980 n/s counted is one million n/s produced.
Inset is neutrons vs volts and amps, larger plot is Q in neutrons counter/watt. 980 n/s counted is one million n/s produced.
And of course, the movie:
https://www.youtube.com/watch?v=8rSnaE0 ... l009sYggjA

This was without using the secondary for anything, just a relaxation oscillator, I suppose, since the series L in the main HV is much too small (3.5 mh) for this rate.

Yes, we break 7m neuts/second in the high power (but lower Q) mode now - 50kv, 23 ma or thereabouts.
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Re: Extensions of the Farnsworth fusor

Post by Dan Tibbets »

As for focus of charge, a virtual cathode if you will, the work of George Miley may be pertinent. He used two dish shaped (parabolic?) cathodes that focuses electrons towards a common center. He further impeded beam spread by magnetically focusing the beams. This ring magnet around the center did result in a virtual cathode but the effect was weak(?). It was helped by biasing the surface of the magnet positive to combat the space charge effects of the concentrated electrons. The details are buried in papers but I believe he did have significant if modest gains.

http://nextbigfuture.com/2011/01/review ... ed-in.html


As for spherical versus cylindrical shapes.I believe the cylinder may be easier (away from the ends as mentioned) to achieve significant beam focus. You are essentially trading 2 degrees of freedom for three. Small errors in geometry are less painful. The spherical focus will be more concentrated, but the cylindrical focus might make up for this by being longer in axial axis (line down the center).
Where losses are not the paramount concern the cylinder may be the best compromise. Losses scale generally as the surface area of the containing structure- eg magnetic fields. The surface area of a sphere is less than the same diameter cyclinder. If there is a no or minimal containment this may be irrelevant.

I do think there is containment in fusors- multiple passes of ions in a cathode gridded fusor. This containment of ions is modest with only perhaps 10-20 passes at best. The electrons of course, are not contained at all. Electrostatic grids can contain ions (positively charged) or electrons, but not both. As such, input energy costs may be similar for a cylinder versus a sphere. If the cylinder has benefits in geometry error tolerance, not to mention various possible wave like or resonance conditions, I could see the cylindrical shape outperforming 'near' spherical shapes. This is just my perspective with beam beam fusion.When you add beam background and beam target contributions, which probably dominate, the questions change.

Using both electrostatic and magnetic properties you can theoretically confine both charged species, and by having a virtual cathode, you eliminate the grid impact problems. As for creating a virtual cathode, I think work by Japanese and other researchers, including Miley, have demonstrated this well. Magnetic confinement of electrons have also been well demonstrated. The difference in momentum between electrons and ions has also been understood. Ions tend to drag electrons much more readily than the opposite when they pass close together. This may actually be beneficial within limits.

For raw fusion power, at least at relatively small scale, it is difficult to beat beam target fusion - accelerating deuterium ions towards a stationary wall of deuterium at high density (deuterium ice or deuterium embedded in a metal hydride). For the best Q, power out / power in, beam beam fusion has the best characteristics.


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Re: Extensions of the Farnsworth fusor

Post by Doug Coulter »

I have Miley's book - Dr Sleeper suggested it, and we got it. It's an interesting mix of tested theories and utterly unsubtantiated (complete with unstated and dead-wrong assumptions) guesses that have zero experimantal or even intuitive backing. It's a mixture of great and terrible. I do suggest it as an excercise in critical thinking - it'll give you a real workout seeing what's real and what's imaginary.

I have doubts about (much) more than once through and out (OK, you can have 10, but I can't even see that on real test equipment), and will contrinue to have them until I see actual experimental evidence otherwise, and I've looked VERY HARD for it. I'm not saying it's impossible, just that you don't see it much (way below the noise, if any) in a DC-drive fusor. It's at best a spring-mass system (And it's only even that at super high vacuum, else you start having to pay attention to electrons) with nothing to make up for scattering losses, so at best, any intitial impulse just rings down like any tuned circuit. We checked for this from DC to 2.5 ghz with probes and saw - nothing. Not guessing or armchair theory, real actual get in there and check, kinda data. Put an impulse on the main grid, measure with faraday/langmuir probes, and you don't even see one full cycle of ringdown - and what you do see is fully atributable to other effects of inductance and capacity of the drive and probes and "makes no sense" as to the timing - far too fast (ns) compared to how fast anyone thinks anything in there is going. I can and have measured transit times of charge across the tank this way - and they are in the microseconds, not nanoseconds, but when our probe is right in the fusion space - we see no lag at all - just capacitive coupling between main grid and probe.

Yes, with a cylinder, obviously neglecting end effects, you can do better with focus, mixed species or not - and I'm proving that also with real data - 2m neuts/second with under 5ma@50kv is now normal here, and the Q tracks very closely with grid-build precision. It's simply not possible (even in theory) to tesselate the surface of a sphere with circles, or anything else that would make a point focus, and the crossed loops, while the best of the spherical grids (as far as I can tell) are simply warped, closed end cylinders in a spherical tank as regards the focus issue. Since the wires come together at a point at both ends, it's not really doing anything much spherical, and lacks the equidistant rod spacing you can have if you start out thinking of a cylinder. You guys doing spherical stuff should at least try putting a 1/2" or so hole in the end away from the HV stalk. It'll work better and not get as hot in the bargain.

We measure beam on target fusion on our tank walls with a point (hornyak, 1") detector, and proved it very easily by coating the walls with Ti and loading D into them - you can see just how much you get there by heating the walls and driving the D back out. Over half the total fusion is at the walls, even with plain SS walls and much more than half with the D-loaded Ti - and if you let it get to a couple hundred degrees C, it's all gone.
All my early data taking shows this reduction in fusion as the tank walls heat up. No exceptions, and in fact, that was the motivation to find this out. John Futter was here to see it just before HEAS 2013, in fact, and agrees that this is the correct interpretation of what's going on.

This again tosses the (magic and automatic) "recirculation" idea pretty much out the window as far as I'm concerned - stuff hitting the walls hard enough to make fusion after losing some energy to metal is recirculating? Further, the neutrons are mainly emitted where the "rays" strike the walls, as tested by moving the small hornyak around the cylinder and noting the readings. If anything, we're seeing charge exchange and making a rather efficient (by comparison to what the Van De Graff guys use) tandem accelerator here. It would be easier to convnice me I was seeing recirculation if I was actually measuring more fusion at the core, and there was a reasonably understandable thing driving it, than it is now, with zero evidence, despite looking, and no theoretical basis for it whatever.

Simple accuracy seems to eliminate most of the grid impact issues, if you judge by how hot the wires get. This last one will eat a kilowatt of input and not even glow red, though the ends get hot where it's not really acting like a good lens anymore. It is: 2" long active area, graphite ends, pure tungsten TIG rods (.020" diameter), total of 8 at 45 deg angles, at a 1" (actually about .98") diameter. One end closed, where the HV stalk mount is, the other open - a graphite ring about 1/8" in cross section to hold the other ends of the rods.

I have serious doubts about virtual electrodes of electrons in a static situation - you might pull that off dynamically, kind of "as they pass through" if the momentum is just so as well as the timing, and if there are many thousands times more of them (eg similar total mass) than ions present. But really - magnetize a bb and a cannonball - or even a bunch of bb's, put them on the floor - which moves? Most of that is pure fantasy - even a cursory examination of Newton's laws says, no way. Yes, you can have a virtual cathode in a beam power tube - those are in fact the only guys who've worked out that math...fusor people tend to ignore that sort of thing, but charged particles is charged particles - only e/m changes - and it only takes a single, very comparatively light electron, to totally cancel the charge on a proton. No one has worked it out for our situation with mixed species present. All of e-, D-, D2-, D, D2, D+, D2+, - are present here. That's a lot of charge/mass ratio balls to juggle, and I suspect it's going to take more than static fields to have any real effect on what happens (in a postive way, that is, almost anything will mess stuff up). I know when I described this set of conditions to the guys at SIMION, they said "no way, we won't take your money because our code can't do that complex a set of conditions with enough particles present to be realistic on any computer that exists on this planet". I thought it was nice of them to be that honest, I really did have my checkbook out.

In fact, simply adding an inductor (roughly 3.5 mh, but with a very high self resonant frequency) in series with the main DC power and letting noise impulse things - just two days ago, is now showing me Q 2800 times larger than my recent "static" fusor records. I'm working now with a transformer, using that inductor as the primary, driving the ion source grid to make an oscillator - I had previously measured power gains in excess of 100 with this as a "PNP tube", and I will be doing a parametric sweep of that space to see what I see, but initial results are nothing short of amazing. I am only seeing about 3-4x more total neutrons (putting me in reach of 10 million/second) at high powers, but the neutrons don't fall off at lower powers nearly as quickly as the power inputs do - resulting in lower net neutrons (say a few million/second) but with next to no input power. Since this is an N dimensional parameter space, it's going to take a little while (perhaps all summer) to sweep it and find the good places - that 2800x was "first light"!

I wish more people would go beyond just making a fusor to a recipe, and stick in some probes like pinhole cameras, faraday probes, and whatever else you can dream up - even scope things - it seems only a few do this, main among us are U of Wis and myself it seems - not exactly as robust a research program as one might wish. You learn things that make sense just fine in hindsight, and it tosses a bunch of extant armchair theories in the trash, where they belong.
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Re: Extensions of the Farnsworth fusor

Post by Dan Tibbets »

Doug Couter, your efforts are impressive and it looks like you are systematically addressing important issues.

I think the 10-20 pass (90-95% transparancy) for one species only of course, is mostly based on theoretical surface area comparisons. This is even with some guiding- Star mode effects in fusors. Of course this is profoundly changed in the Polywell, if you accept their claims..
I apologize for not including the references, but I believe there has been some efforts that has improved transparency, admittedly by only tiny amounts by a doctoral student at U. Missouri, Rollo(?).

As for fusion type the location within the fusor for fusion reactions has been reported by a Japanese group. With D-D they reported 10%of the fusions occuring within the cathode grid despite the relative small volume (later uptaded to 50%). This suggests that beam beam fusions were common. With D-He3 fusions the grid was the dominate location- suggesting Beam target fusion. I'm uncertain why there is this difference though I could speculate on several.

Certainly in most fusors with pressures above a few microns, the beam neutral collisions and charge exchange interactions complicates things considerably. Then there are wave like effects. With R. Nebel's work with POPS at Los Alamos Labs, it would be interesting to see results obtained(?) later than when they were designing the test machine~ 1999. I've done Google searches but found no articles later than this early work. Was it abandoned or was it suppressed?

There have been multiple reports, primarily by Japanese researchers of virtual cathode formation and structure- from IEC conferences. In the Polywell there is extensive claims of deep virtual cathode potential well formation( Bussard did like to stress the dynamic processes rather than static snapshots, and lessens learned with vacuum power tubes). I don't know how much experimental data has been accumulated, but comments by Tom Ligon suggests that probe data has been collected.

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Re: Extensions of the Farnsworth fusor

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This discussion brings me to a conversation with Jake Hecla I had today in which he specifically mentioned an interest in the community with possibly plating the interior surfaces of the chamber with Pd or other hydrogen or deuteron absorbing materials. (For those who don't know, metals like Pd absorb 950 times their volume of H or D). In current LENR/CF research, Pd co-deposition via plating with PdCl in heavy water is yielding some very promising results by pre-loading the cathode surfaces with D. The same could be reasonably applied to any beam incidence point on any surface where accelerated D ions impact, even a fusor chamber wall or bulkhead plate.

Am I understanding the foregoing correctly? Would this indeed be of any value?

Dave
It would take decades of work, by thousands of scientists, in a particle accelerator powered by dump trucks of flaming grant money! - Professor Farnsworth/FUTURAMA
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Re: Extensions of the Farnsworth fusor

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I am sure it would be valuable. I and others have posted on this in the distant past. It is no new idea. I would not just plate point of beam incidence points, but the entire inside chamber. I do not know if this would significantly or even measurably increase the results. It has been claimed there is a measurable increase, something I would suspect to be the case. Worth trying to any and all degrees. Titanium might be a bit cheaper, hydrogen absorption is even higher in many other metals like niobium and thorium. Lots of possibilities here, but not likely to be a world beater or lift the fusor by orders of magnitude.

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Re: Extensions of the Farnsworth fusor

Post by Dave Xanatos »

Richard Hull wrote:...not likely to be a world beater or lift the fusor by orders of magnitude...

Richard Hull
Probably nothing we do here will, of itself, be any sort of world beater, but every new little poke we take at the fusion phenomenon yields just a tiny bit more of the nature of the animal, and who knows which one, when combined with other new discoveries, will be the one that helps us over the threshold. :)

But for the moment, I'll be content to get demo plasma going... one step at a time! :)

Dave
It would take decades of work, by thousands of scientists, in a particle accelerator powered by dump trucks of flaming grant money! - Professor Farnsworth/FUTURAMA
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