Extensions of the Farnsworth fusor

It may be difficult to separate "theory" from "application," but let''s see if this helps facilitate the discussion.
Post Reply
User avatar
Doug Coulter
Posts: 1312
Joined: Sun May 27, 2007 3:18 pm
Real name: Doug Coulter
Location: Floyd, VA, USA
Contact:

Extensions of the Farnsworth fusor

Post by Doug Coulter »

I wrote this up for another reason, but on the off-chance it helps anyone else here, here goes. paper availabe for download here
Here's the text.


What we are doing in my lab currently does bear quite a bit of similarity to the original Farnsworth fusor, and it seems to be confusing many. We certainly owe the man and a few who came after a serious debt, intellectually. But they never truly succeeded, no one really has yet, although some, including my team, have done far better than the originators have. Some of what people say about "all we make is star-in-jar farnsworth fusors", is like saying we just make fire. Elon Musk's fire gets you to space, though "it's only fire", while yours just lays there - so there.

Or maybe not, in some sense. Going back through history, papers, private communications, it seems many fusor builders report hard-to-repeat huge Q factors (defined as power out divided by power in). Since they are hard to replicate even in the same lab, they have been dismissed as “outliers” or “equipment errors”.

That same attitude would mean that if a modern biologist was brought Fleming's famous contaminated petri dish, some lab assistant would be in trouble, and we'd also not have penicillin. Luckily, Fleming was the sort of guy who paid attention to “outliers” and “equipment failures” - and also luckily, it turned out to be rather easy to reproduce in his case. Not as much so in a fusor, but philosophically speaking, it seems the same attitude would serve well in fusion research, and it's largely absent in other investigators. With ever better data acquisition, storage, and analysis, I've been able to “catch these in the act” a number of times, and now the challenge is simply to understand and reproduce them, as there is no longer any possible doubt that they do happen – bursts of Q many orders of magnitude higher than “normal” such that on an autoscale plot, the Q of regular fusion operation shows as “zero” by comparison to “thousands and higher” when these events occur. This seems worth the chase, the game is clearly worth the candle.

This document will describe what we've done differently here, and what we intend to do that's even more different.

Our setup is a bit unconventional. We are running our main fusor grid, designed to be a very good electrostatic lens (unlike all others we know of) inside a 6” cylindrical side-arm in a much larger tank.
Early on, we found that going to reduced gas pressure improved Q, but had power supply and other limits that prevented the fusor from “lighting off” at the lower pressures with the gas pressures we wanted to explore. We therefore developed various ion sources to allow us to go ever lower in gas pressure (another way of looking at that is “longer mean free path” over which a particle can travel without an accidental wasteful collision). While most of those worked at some level, what we've been doing of late, and which is a “little odd” is simply using another fusor grid (this one not so precise) out in the main body of the larger tank, to take advantage of Paschen's law, which shows that breakdown is a function of p times d – or in other words (counter-intuitively for many), below a certain gas pressure, electricity would prefer to take the longest path, not the shortest one. The reason is obvious in hindsight – if an electron can't get up to ionization energy of the gas before it is slowed down by collision with a gas particle in the extant E field, you get no ionization, and therefore, no discharge.
(put wikipedia link here for Paschen's law – nah anyone worth his salt will just type it into a search box and do their own homework)

Somewhere along the way, we also noticed that our extra grid could not only act as a switch for power draw and discharge on the main grid, but that we had created something that also had a moderately linear gain region, and amplifier, not just a switch. Tiny changes in the input to the “ion source” grid could control large power in the main one. In fact, we'd built a rather complex triode. In fact, it would even go into parasitic oscillations under a variety of conditions, as any amateur radio operator who has built a linear amplifier knows, these parasitics are usually NOT at a desirable frequency. In our setup, the frequency is very high – MHz, which is much faster than would sync with transit times of the various ion species we have in the fields we might reasonably have. The real resonance is beyond actual numeric computation ability at this point, we've asked the simulation software guys and they tell us this and refuse to take our money (and guys, thanks for being honest about that).

Further, we noticed that this happened most often at the edge of stability (the small more or less linear range of power gain between the grids), and while onsets were occurring. The steady state turned out, after quite a lot of data acquisition and analysis, to be the absolutely worst case for Q!

This happened a lot, with these crazy-high-good Q measurements, and I'm convinced that this is what others have reported the entire time, but dismissed. We did not do anything special here – it just “went off” into the mode, presumably tuned by the parasitic capacity, inductance, resistance in the circuits, and the transit times of the various species involved. Remember, this is a complex mix of electrons, D, D2, (and those two can be neutral, positively charged or negatively charged via charge exchanges). That's a lot of “stuff”, and it seems to have emergent behavior – it's quite difficult to do the math here in practice. Who would have imagined such a simple equation in complex numbers, like Z = Z2 + C, would ever have such a complex set of results as the Mandelbrot set, for example? The basic particle in field equations are about as simple as that, with the same idea – iteration – the last output of the system is the next input, except that we have attraction, repulsion, an imposed field, the field generated by the particles themselves, and various spring-mass systems going on, where the spring if the particle's charge and the true field it sees (not what we think we imposed, which is affected by the particles in it), while mass is simply its mass.

Further, armchair theorists have hugely misled the fusion community, without experimental data to back up what they say. They claim recirculation through the grid for example. Well, we don't see it here, and we've looked. Yes, a spring-mass system can have oscillations, but not gain – it always has losses, and with a DC input, there's no (simple or obvious) way to make up for those. It borders on possibility that some of the emergent behavior sometimes does. Further, via charge-exchange (and other things) what we mostly see here is “once through and out”. Not only have we looked for the field fluctuations with the finest gear money can buy – and not found them – we HAVE seen rather large increases in fusion when the tank inner walls were implanted with fuel atoms. No guessing here, careful measurements that lead to facts are preferred. I often feel like the theorists think they know ecology of an anthill because they've studied just one ant. It's not that simple, guys.

Most fusors are build spherical, there's an emotional attraction to that shape, but we don't do it that way for a variety of reasons. Due to our realization that any shape electrode you put in a tank and put voltage on creates not only a field, but a non-uniform one that acts like an optical element for charged particles, we decided to design our “lens” with malice-aforethought to be a good one. Any book on electrostatic lensing will not show example that looks the least bit like all of the spherical grids I've ever seen – and I will note that in 3d space, you cannot tessellate a sphere's surface with uniform circles or anything else that would produce a good point focus. Even a bucky-ball kind of shape or level of complexity would be far too crude to produce the desired “compression ratio” we are looking for here. And with practical materials, you simply can't make even a bucky-ball without making it so opaque it's super-lossy, or simply won't hold up its own weight.

Cylindrical lenses don't have this issue (other than at the ends) and are easy to design and build to generate a line focus. So that's what we do here, and are still making incremental improvements. While we're not even to optical levels of precision, the simpler math would indicate we should (and should be able to) go to levels far more precise – on the order of the wave-function size (At FWHM) of the particles we want to focus would be nice! We are not even within a few orders of magnitude of that at present, so this is one of a few windows for what seems like a very reasonable way to improve.

Of course, at any real density, space charge effects will likely defocus our great lens – something that was worked out long ago by vacuum tube designers – the thing that causes a CRT to lose focus if the brightness is turned up too far. The particles of like charge do repel each other, else we'd not have to force them together in the first place! The one acknowledgment of the fusion community of the space charge issue seems to be when they think they can use it to create a “virtual electrode” that, using electrons, will draw in far heavier ions to collide there.

I hate having to remind people who pretend to be smarter than I that attraction and repulsion are bi-directional, and it's the lighter one that moves the most! That's a pretty huge sin of omission in understanding and only one of them that are widely considered to be “facts”. Anything like a close look into basic physics of course demolishes all such silly arguments. That's just not how it works!

So, it seems we want to go for fairly low power density, short focal lengths to reduce the bad effects of space charge causing “blooming”, and a few other things, like getting actual instead of fictional recirculation of the ions that we had to put in energy to ionize in the first place, that is, if we want Q rather than just a “star in a jar”. We might be able to tolerate very much higher densities if they were “bunched” since by the time the particles “see” one another's fields, they are already “on course for collision” having come from a very diffuse state (2.2 e-2 millibar, or molecular flow) into a much more compressed state at focus – our “compression ratio” if you will let me use that term. We have experimentally witnessed the actual transition from molecular to viscous flow here, many times, but haven't quantified the actual “compression ratio” thus far (it's not trivial to measure with what we have). It is, however visually obvious, particularly if you can then direct that flow through something that would only turn it if it had a very short mean-free-path, as in “high pressure”.
To coin a phrase, “nevertheless, it moves”.

There are some other considerations here. Pauli's exclusion principle (never proven wrong or even a hint of that) says that identical quantum states are excluded (geometrically if I understand correctly) from happening. And D's have spin of =/- 1. Trying to make two fuse that have identical spin would violate this principle, yet to the extent the forces we currently use bring them together, they tend to also align spin in the worst way for fusion – it's only by accident that a collision or something of that nature flips a spin and allows for fusion at all! When we do have them spun correctly we get D+D->He, but sadly, it won't stay that way – this releases about 16 electron mega-volts worth of binding energy, so the resulting He breaks up unless we have a 3 body collision; theres not enough binding energy even in He, which has quite a lot, to hold it together at that energy. A photon can't carry off the extra because photons themselves have spin and there are conservation laws in operation here that prevent cheating on that. Which no one observes being broken, so for now I feel fairly safe standing on the shoulders of the giants of physics past.

I am only one experimenter working in one moderately well-equipped lab, and I can therefore only try so much per run, or do so many runs in a period of time. Theory (and math) has let us down in numerous ways, so it seem the experimental approach is the way to go here. I'm sure some eyebrows will go up over that statement about math. OK, where's my feedforward solution to the very “simple” 3 body gravitational problem? No perturbation and division into tiny time slices allowed, and tell me where Jupiter in a simplified solar system is in say, 100 years or more. I dare ya. Yet that's exactly the sort of math we need to solve this problem without sort of trying everything that may make sense! Has math become merely the princess of science? I'd submit that we're verging on “chambermaid” at this time, for the important questions. I wish I was wrong, but I don't think I am. Even recursive systems (Julia, Mandelbrot) aren't well defined without just trying something, and even though that's well known, Wolfram comes along claiming he invented it (see his book) – years after the real pioneers.
Blind leading the blind in ignorance of history, as far as I can tell.

I'm not claiming to have invented the plasma triode – that seems to have been done by Phillips back in the 50's or so, not the guy 2 years ago who re-invented it and claimed all sorts of interesting applications in what used to be cool – plasma TVs. This was a PhD with no knowledge of things that have happened since my own birth – seems you can get a nice piece of paper without knowing too much these days. Or maybe I should soften that blow by calling it “not enough” these days to actually make a real advance, instead of adding a decimal point to something, or finding something that was already lying there.

But here we have a very interesting use for it. Like any active device with power gain, not only can it sustain oscillations, it can do so at more than one frequency at a time, in several distinct modes, from super-regeneration to reflex oscillations. And here we have a situation where those properties could be extremely useful. We might find that having the electrons bouncing back and forth at one fast frequency, yet controlled by bigger external fields than they alone generate might actually act as a useful virtual electrode for deuterium ions going a lot slower, but oscillating in space themselves. And have this drive them both! Of course, if that turns out to be impractical, we can always just drive this thing like the triode it is, with whatever arbitrary waveform we can generate - a little harder, takes an arb wave-function generator, but we have one of those too.

So, since I have to prioritize or dither endlessly, the next try is going to be taking advantage of this active device to see if we can't pull off something pretty elegant – using its own gain to drive particles around, flip spins, and make a nice transition from the lowest energy state (ions evenly spread throughout the tank) to a lower entropy state – ions of the correct spin all striking at the focus.

This seems to require no actually-new science, or violate any of the “laws”. Yet it would result in fusion Q numbers extremely larger than have been experienced so far – even in those “outliers”.

It's worth a shot, so that's what I'm doing next. I'll shortly have a youtube video up of what it all looks like, if it will upload in less than a lifetime.

Edit: youtube link added.
Last edited by Doug Coulter on Mon Mar 17, 2014 1:49 am, edited 1 time in total.
Why guess when you can know? Measure!
Doug Browning
Posts: 156
Joined: Sat Mar 10, 2012 9:19 pm
Real name: Doug Browning

Re: Extensions of the Farnsworth fusor

Post by Doug Browning »

How about using two opposed short focus electrostatic lenses (one at each end of the cylinder) to bring an electron pulse and an ion pulse together at the same time and focal point between. The strong electrostatic attraction between the two groups at the focus should help concentrate the collision area.

Another possible enhancement might be to put a small dipole coil (electromagnet) just over the focal point, axis aligned with the beam axis. By keeping it small, its stray dipole field lines should spread similarly to the particle paths from the two electrostatic lenses (particle travel along the field lines tends to compress with the field, beams will twist some along the axis). The concentrated B field at the focus beneath the coil might help the e- and +ion pulses stay aligned and compress to a small point when transiting the focal point.

Alternately, there is a so called solenoid B focusing effect along a coil axis. Since the ions and electrons differ in mass so much, the electromagnetic solenoid would need to be offest along the axis to bring both species to the same focal point. Solenoid length would conflict with a short electrostatic focus however.
User avatar
Doug Coulter
Posts: 1312
Joined: Sun May 27, 2007 3:18 pm
Real name: Doug Coulter
Location: Floyd, VA, USA
Contact:

Re: Extensions of the Farnsworth fusor

Post by Doug Coulter »

I've looked into some of that. I feed my grid from one end, FWIW, you have to feed it somewhere, and any other place seems to be much worse in terms of exposed stuff in the field wasting power by attracting ions that hit it, as well as field warping the ruins focus and whatever circulation there might be. Magnets of reasonable (achievable) field strength don't have much effect on the ions, though they do on electrons. There isn't a focal point with a cylinder grid, there's a focal LINE along the axis. It does waste some ions spewing out the open end, but those make more ions out in my bigger tank, so they're not utterly wasted, just mostly. Closing that end is worse, they all hit the closure instead (from both sides!), melting it and being totally wasted. This is why I reccomend putting a hole in the end of the spherical grids people mostly use, on the far side from the feedthrough, FWIW. Tried it both ways, the hole makes it work better.

I'm fairly sure I don't want all the species at the same spot at the same time. I don't want to turn my ions back into neutrals, which are for one thing, much too large to let the nuclei get within fusion tunneling range. I don't think I usually want charge-exchange, though we've found here that quite a few D+ become D- (dual electron pickup) in some modes, and are therefore accelerated into the tank walls at near double the power supply voltage. Proved this by putting a D laden titantium target at the tank walls and seeing tons of fusion right there with a point detector (hornyak button + phototube). Has a little better spatial resolution compared to a big moderated He3 or boron detector...and plenty of sensitivity when you get to the multiple millions neutrons/second generation range, which we are solidly in here.
Why guess when you can know? Measure!
Doug Browning
Posts: 156
Joined: Sat Mar 10, 2012 9:19 pm
Real name: Doug Browning

Re: Extensions of the Farnsworth fusor

Post by Doug Browning »

It would seem unlikely that the two particle species would combine significantly at a (good) focal collision point due to the high opposing velocities involved. Any bonding attempt would just fly apart after a brief helical encounter.

It appears that the real problem is to produce a point focus of short focal length. Electron microscope lenses are all long focus. One might want to look at the composite quadrupole lense approach used by Tektronix years ago for shorter HV oscilloscope tubes.
Last edited by Doug Browning on Tue Mar 18, 2014 5:31 am, edited 5 times in total.
User avatar
Chris Bradley
Posts: 2930
Joined: Fri May 02, 2008 7:05 am
Real name:

Re: Extensions of the Farnsworth fusor

Post by Chris Bradley »

There is a fundamental question that does not appear to be addressed in your dissertation, Doug. Where do you think the fusion is happening? Sure, there may be a number of mechanisms, but if you want the optimum efficiency, you have to figure out which is the most efficient mechanism and get the kit doing that to the exclusion of the less efficient mechanisms.

So just getting the 'soup' to mix better is only one step, you also have to start nailing down where/when in the soup the fusion is happening.

You know my thoughts on this - after several years honing an experiment to increase the fast ion/background collisions I got a negative result. As it can't be fast ion/fast ion (too low a probability for what is seen) I reluctantly concluded my experiment was, in its original configuration, a dead end because I now believe a fusor works by charge exchanged neutrals all focussed and hammering a particular target spot where the beams intersect the shell. This was, funnily enough, a conclusion also supported by my null experiment because I was finding I was losing most of the fast ions to charge exchange.
User avatar
Richard Hull
Moderator
Posts: 14991
Joined: Fri Jun 15, 2001 9:44 am
Real name: Richard Hull

Re: Extensions of the Farnsworth fusor

Post by Richard Hull »

Understanding how interstitial hydrides are formed via electrolysis or bombardment has long lead me to a conclusion that in our simple fusors, a significant fraction of our fusion was occuring as beam on target fusion as fast neutrals slammed into D loaded shell walls. Fusion in velocity space within the fusor of all stripes is the remainder with little due to recirculation. The old and now rather discredited idea of recirculation is a relic of earlier theroetical dreams.

Chris has a point. Regardless of mechanization, artifice or other factors: where is the largest segment of fusion taking place in any design or methodology? Realizing at the outset that real fusion energy will never be achieved by the processes involved here is one of the first tenets to accept. Significant improvements will be ultra cheap and easy to impliment or they will prove unworthy and perhaps undoable by the simple amateur standards, which is the goal that this site caters to. An order of magnitude increase in continuous, unrelenting output, if purchased at a doubling of costs, may or may not break the amateur's back. All is a question of where you want to be and what your final goal is.

Most here just want to do fusion and most of those who try, never get there. This is why the plasma club list grows disproportionately to the neutron club. There is no shame in failing to get fusion or in making a successful demo fusor and then moving on to cars or women or whatever. Most everyone who has ever done fusion here is no longing either doing it or have scrapped their fusors and will never fuse again as long as they live. They can say, "Fusion?...Yes, I've been there, done that." That success can never be taken from them.

The scientific questions and mysteries are many and litter the path to improvements in the amateur fusor and any answers gained are a plus, regardless.

Any future results that are positive and definitive are welcomed

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
Stephen_Hill
Posts: 3
Joined: Wed Mar 19, 2014 1:41 pm
Real name: Stephen_Hill

Re: Extensions of the Farnsworth fusor

Post by Stephen_Hill »

Hi, Richard,

As you stated, in our simple fusors, a significant fraction of our fusion was occurring as beam on target fusion as fast neutrals slammed into D loaded shell walls, do you see a possible method for the amateur to experiment with this using differently saturated samples? Perhaps an ion gun directed at a sample plate... Hydrides are fascinating and it hadn't occurred to me that there would of course be a deuterium analog. Thanks for your time!
User avatar
Richard Hull
Moderator
Posts: 14991
Joined: Fri Jun 15, 2001 9:44 am
Real name: Richard Hull

Re: Extensions of the Farnsworth fusor

Post by Richard Hull »

Sure! Linear acceleration, via beam on target is possible and is already commonly used extensivley in neutron generators (real fusion). The fusor has an advantage is some respects as the plate can have a giant surface area with a lot more bombardment with far less heating for the same power input. Implantation is rather continuous as is "knock out" A saturation point is easily imagined though in this process. I hope to investigate palladium plating of a fusor shell at some point. Also lining the walls with vanadium or titanium foils might be worth looking at. Much awaits free time after retirement.

Edit - side note: All forms of amateur, demonstrable fusion are welcomed here even though we are mainly fusor based. Any devices that do fusion, especially those that are simple, like the fusor and can be fully demonstrated to actually do fusion on the cheap are especially welcome in discussions.

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
Stephen_Hill
Posts: 3
Joined: Wed Mar 19, 2014 1:41 pm
Real name: Stephen_Hill

Re: Extensions of the Farnsworth fusor

Post by Stephen_Hill »

Sounds fascinating, Richard! Looking forward to hearing about it. Thanks again!
User avatar
Doug Coulter
Posts: 1312
Joined: Sun May 27, 2007 3:18 pm
Real name: Doug Coulter
Location: Floyd, VA, USA
Contact:

Re: Extensions of the Farnsworth fusor

Post by Doug Coulter »

We have measured what looks like beam-target fusion at the walls. U of Wis - about the only other guys who seem to be measurement rather than speculation based, claim to have measured it in the "rays" as well as at the focus and walls. I'll believe them, they haven't told me any lies so far.

I'm only speculating so far, but I am also building the gear and putting the details on my own site for now - I'll report the results of actual tests, not guesses, when I have them.

I've always thought that in a multi-species enviornment, where one weighs a lot more than the other (eg, D+ weighs much more than an e-) that trying to use the lighter one as a "virtual electrode" is pure hogwash. Yes, it works in electron tubes, but if I magnetize a bb and a bowling ball and set them down, which moves again? Why does no one think of the obvious?

On the other hand, driven flows, perhaps using more than one frequency, look in my models like I might just pull that kind of thing off for just long enough, in pulses. In other words, the electrons go back and forth a lot of times per fusion pulse, but are "there" at just the right moment to help supress space charge defocusing. Up to the space charge limit, the focus I get is far better than in that movie - they couldn't capture it in the dyn range of their camera, so left it out of focus. It's about human hair seen on end size now at reasonable current, and blooms just like a CRT if I try to go too high in flux, as you'd expect. Probably this is why my Q plots show a peak at lower currents than I run for max total neutrons - I'm actually getting good enough focus to get significant fusion at the core in that case. The limit appears to be the accuracy with which I can make grids if I'm willing to run at the lower currents. I'm not to optical grade yet, much less wavefunction FWHM grade.
But I'm already doing better than tektronix wildest dreams...on focus and current density (luminosity).

This movie shows the effect: https://www.youtube.com/watch?v=-58gdiLNIqc
As does this one, which is a more or less full parametric sweep. https://www.youtube.com/watch?v=WJe0YBAXwPw

Sadly, the audio and video are a little out of sync on that one, but all runs were done with identical gear on the last vid. If you squint just so, it looks like there's a high Q bulge starting a little below my top voltage, and going up in current as the voltage also goes up - exactly as space-charge limited focus should behave theoretically.

I will of course not post further results on a theory thread. This isn't the right place for that. But I'll post'em when I got'em.
Why guess when you can know? Measure!
User avatar
Doug Coulter
Posts: 1312
Joined: Sun May 27, 2007 3:18 pm
Real name: Doug Coulter
Location: Floyd, VA, USA
Contact:

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.
Why guess when you can know? Measure!
Dan Tibbets
Posts: 578
Joined: Thu Apr 17, 2008 1:29 am
Real name:

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.


Dan Tibbets
User avatar
Doug Coulter
Posts: 1312
Joined: Sun May 27, 2007 3:18 pm
Real name: Doug Coulter
Location: Floyd, VA, USA
Contact:

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.
Why guess when you can know? Measure!
Dan Tibbets
Posts: 578
Joined: Thu Apr 17, 2008 1:29 am
Real name:

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.

Dan Tibbets
User avatar
Dave Xanatos
Posts: 108
Joined: Tue Apr 22, 2014 1:59 pm
Real name: Dave Xanatos
Location: Western Massachusetts, USA
Contact:

Re: Extensions of the Farnsworth fusor

Post by Dave Xanatos »

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
User avatar
Richard Hull
Moderator
Posts: 14991
Joined: Fri Jun 15, 2001 9:44 am
Real name: Richard Hull

Re: Extensions of the Farnsworth fusor

Post by Richard Hull »

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.

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
User avatar
Dave Xanatos
Posts: 108
Joined: Tue Apr 22, 2014 1:59 pm
Real name: Dave Xanatos
Location: Western Massachusetts, USA
Contact:

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
Post Reply

Return to “Fusor and/or General Fusion Theory (& FAQs)”