Runnin with AC drive, re-circulation seen, likely

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Runnin with AC drive, re-circulation seen, likely

Postby Doug Coulter » Sat Dec 16, 2017 9:23 pm

Running with AC drive on the main grid - actually AC coupled via a 750 pf capacitor, which results in a 30/70 +/- waveform symmetry as any positive voltage on the grid attracts electrons very well. - the fusor acts like a diode to ground for positive voltages - so we have kind of a not-very-good half wave voltage doubler with no output filter. This run is with "around" 14kv P-P at around 68khz sine wave. It's been problematic to measure the real AC voltage as anything near the HV probe moves the reading around hugely - just a handwave near it changes it 50% - so any number I would relate would be pretty suspicious anyway. I could measure what showed up as charge on the series capacitor with some confidence - around 7kv. This resulted in a few neutrons, not tons, but at a lower threshold than with DC by a good bit, and it was easier to light off and stay lit even with this much lower than usual voltage. No ion grid drive was used.

What is interesting here is what we see on the faraday probe channel. We see short positive pulses, as though the D+ ions were being bunched up, and then repelled by the main grid when it went positive. We saw what looked like a beating kind of behavior, where some sort of ion oscillation would build up around once a second or so, and neutrons would be produced along with some "interesting" changes on the scope looking at the faraday probe. If we triggered on detected fast neutrons, we saw this multi-pulse on the Faraday probe 100% of the time. Triggering on just the drive - never saw it.

This might be the first time this has been seen or measured. What might be significant is that we got neutrons well under our normal DC threshold voltage for a detectable output, and with DC anyway, things scale up a heck of a lot faster than linear with increased potential - 3rd power maybe, or maybe a lower power but with (volts-threshold)some exponent. If this turns out to also be true with the AC drive, and of course, there's just about no way that what I tested with here was the magic ideal parameters - then it's going to get exciting when we get louder and get closer to the right frequency, which looks like it's going to be a function of the voltage itself - it seems to be in the traces shown in the video - lower voltages seem to have more phase lag to the neutron output. This is consonant with the existing math for ion traps and mass spectrometers, so perhaps I'm not in left field. But you never know for sure till it's all measured and repeatable. This at least seems really repeatable. More to test and measure. This was for sure a "hmm, that's funny" moment in the lab - we know what that means here.
Thanks to BillF for the help and motivation - and some of the parts.
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Re: Runnin with AC drive, re-circulation seen, likely

Postby Doug Coulter » Sun Dec 17, 2017 6:07 pm

A friend mentioned he couldn't quite read the scope in the video, so I thought I'd go ahead and just upload most of the slideshow here - the originals aren't too bad.

This one is kind of the baseline, what we saw most of the time.
This is what we see with a free running trigger.

Now, when we switched to triggering on fast neutrons, as detected by the numb but time-accurate Hornyak detector, we saw more interesting things.
Moe than one burst of + going by the probe






The filenames of these contain the timestamps for when they were taken. They're in reverse order here.
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Re: Runnin with AC drive, re-circulation seen, likely

Postby Doug Coulter » Sun Dec 17, 2017 6:13 pm

Avoiding the attachment limit on the board...





The top view inside the tank (power off, just a flashlight shining in the front window).
Inside the tank.

The final drive stuff. A FET H-bridge not shown is driving a 4 turn primary on a ferrite slug inside the big coil shown here. I'll have to design and build another if I want a lot more biggie, but it'll take time.
Some of the drive stuff.
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Re: Runnin with AC drive, re-circulation seen, likely

Postby Jake Gray » Mon Dec 18, 2017 4:57 pm

A few thoughts. Please excuse my limited understanding. I tend to know just enough to be dangerous.

What are you using to drive the H-bridge? I assume you're going to push the Transformer a little out of it's range to get some more of the parameter sweep before going to the tube beast.

I guess the lump of ferrite isn't a particularly efficient core so cranking the frequency up is likely to cook it, while dropping it down will leave you saturated and heat up the primary. So wondering what a flyback is going to look like that you can drive with the tube setup? I guess you just make it bigger so it doesn't have to be very efficient.

I'm a bit confused how there can be recycling while the grid is still positive. I understand some multi bumps inside the positive half of the wave form as there could be some "ringing" of the ions inside the focus of the grid. The one that is baffling to me is the one with two clear bumps on either side of the sine wave. It's almost as if on the initial ramp up some ions are blasted away while many others are trapped inside the focus of the lens of the grid, then as the voltage drops they are still repelled but those on the inside of the grid can now escape. Or perhaps you are hitting a resonant frequency where the first blip is the initial ions being blasted away while the other group is focused to the center, bounces off the focus and just happens to line back up with the other side of the sine wave on the way down. I suppose the resonant frequency of the ions "bouncing" is also going to change with voltage so a few rebuilds of the transformer are likely?

Interesting results indeed!
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Re: Runnin with AC drive, re-circulation seen, likely

Postby Doug Coulter » Mon Dec 18, 2017 9:00 pm

Interesting indeed, hopefully not as in the Chinese curse...
I'm currently driving the H bridge with an IRS 2453 - it's about the simplest H bridge driver out there, but it has some limitations on speed and gate drive current. I'm looking to put together something a little more sophisticated soon. This setup is near the limit on speed as is, already wasting some input power due to slow turn on and off times.

You pretty much called out the issues on the stepup transformer situation...but for research, we can force it some (more than I thought at first). Once we know what we want, I can do a redesign and hit the numbers a lot better, but anything with this turns ratio isn't going to do octaves of bandwidth decently - and for the arbitrary waveform I suspect we'll need in the end, it'll probably take two in series, one for the fast part and one for the slower part.
As is, it only has to be efficient enough to not go up in smoke in the time it takes to get data, which can be pretty fast - and pulsed operation is a side benefit of all the remote control stuff I've put in.

As to interpreting that data...a few things to keep in mind. And don't forget, I'm guessing too - I might be on a better perch to do it, but that just increases the stress to get it right.
Things to note:
1. The geometry of the tank. What we want eventually is for all the ions to be inside that side arm pipe, stay in there, recirculate through the focus, and not bash the tank walls while outside the grid.
2. The Faraday probe isn't in the sidearm, and is far enough away that if it sees anything, it might mean we failed #1 - or just that the fields out there are weaker so things flew further in that direction.
3. The probe doesn't say a thing about how far a burst of ions was away at nearest approach (other than how loud the signal was) or how many (also how loud the signal was) or what direction - no indication at all. It's pretty limited information. That said, no one else ever even bothered to get that much.
4. The neutron detector, while time accurate and low latency, is deaf as a hammer. Calibration is a million neutrons a second gives us 980 counts per *minute*, Numb. But the ones we get we have very high confidence in.

The Matheiu math describes what you need to put on some electrodes, a mix of AC and DC, to restrain charged particles (ideally, just one at a time) inside some limits - eg stay in the trap or between the electrodes of a quadrupole mass spectrometer. The "just one" is because even that fairly hairy math (to me anyway) doesn't take into account any mutual repulsion of the like charged particles, and of course takes no account of any opposite charged paricles that might be flying around (in our case, electrons mostly). This stinks, but it's the only math that even addresses what we have at all, it's just going to need some more terms to handle that stuff. Know any super hot math guys we could hire? What I did discover just now is that it's not as bad, or at least all the time and everywhere, as I'd feared. For most of the cycle things are so not-dense the original math is pretty close, or should be based on some other measurements of transit times and trajectories I made earlier. Whew....Here's a little background that might seem a bit off topic at first, but the good stuff is in this very expensive book Bill bought and it'd take a long time to scan all that in with nice pix of trajectories and so on. This is a start, anyway:
Normally in an ion trap, the residual small forces between the few ions tend to drive it toward an end state where they keep maximum distance between themselves. That's not what we want, but that equilibrium takes time, and if we can get this done on the first few cycles...that won't matter. There's more - a lot, but I only have ten fingers and this much time. For short, when things are slow and low energy, near the tank walls, if they get uniform due to mutual repulsion - we've already gotten our energy back while slowing them down, and this creates a nice uniform start for the next cycle without costing us in energy investment. (when the grid is biased to slow things down, we get energy back into the power supply!).

Now, why did we see what we saw? Well, I have a theory, let's call it a guess.

Remember, most of the time all we see is stuff flying past the faraday probe (lower left in the picture) at some point after the grid has passed its negative peak. We'd expect that even if we just drove it negative and it sat there, though the timing would be different. After being attracted in from all over the tank, they'd go through focus and go back out the other side, slowing down, but...eventually going out as far as they came in from, more or less.
Having the grid go positive while they're flying away would just make that happen faster.

Now, suppose that with the alternating grid potential, we have the ions doing big old loops through the big part of the tank - we don't have it "right" to keep them in the sidearm, and even if we did, there's that open end...
After some of this, some will find a happy place - a distance or loop size - where they get into near sync with the drive signal. Call it "selection from random data" - which is dreaded when scientists use it to cheat, but here it's jut that the ones that don't hit the tank walls and are lost - so we only see the lucky ones. BUT! There's more than one set of speed-size parameters that would accomplish this, and in this data we see up to around that aren't always in phase. The other two in this sense might just be from previous roundy-rounds, we have no way of knowing. (in guessing, it's important to know what you don't know - known unknowns and all that).

As an example of abusing that one - I noticed that when we have the multiple peaks they aren't as large as when we had the one...which could mean that the total ion current has divided itself up into these guessed-at loops.
Or it could mean anything, actually. We have no way to know from this data. Rigor isn't as much fun when guessing, but it gets you there quicker, usually ;) .

But this is of course, just guessing - hopefully limited to the things that are possible, but still, a lot of things are possible. I do note that all those with the multiple peaks were seen while triggering on that numb neutron detector - there could have been neutrons on every drive cycle (I assume there were, it's fairly safe, the thing is truly numb) - and when we free-ran - we didn't see neutrons on the scope, there weren't common enough, nor were the multiple peaks. Just didn't see them, and yes we looked.

So, what could have made that come and go? Those dreaded missing terms in what will be the real math describing this is my best guess. We have a lot of stuff sloshing around in there - it's not pure D+ or even D+ and e-.
We have D2, D2+ D and D2- (yup - measured that once), and various contaminants sloshing around in there. It's a ten gallon reservoir with bumps and warts and...the part we're interested in is 6" diameter and 6" long hanging off one side - with an end open to all the rest.. The Mathieu math only gives confinement and re-circulation for one charge to mass ratio at a time...and there's about zero chance we hit the right set of numbers here. In looking at the plots in the expensive book on Quadrupole Mass Spectrometry, some of the orbit types and shapes for off resonance particles would easily account for what we saw. It's my best guess at this moment, anyway.

Here's a few scans from Peter Dawson's "Quadrupole Mass Spectrometry and its Applications" so you can see what we're dealing with, kind of. It's the only extant math for this. Yes, what he describes is a different geometry (but the same math works for a few he does describe) and under somewhat different conditions - but for part of our cycles they are about the same - but it's all we really have to go on, it's just the implications of the equations of motion (Newton) for charged particles in a field imposed externally. It does NOT take into account the fields created by the particles themselves - that's the extension we have to make. And it'd be nice to have it feedforward as in "what do I do to get a result" rather than feedback "this is the result if you do this" form, but hey. If it was easy someone else would have done it. And if the conditions were common, we'd see it out there in the sky with our telescopes. (Feynmann and others).

Note one thing not obvious to people who haven't spent a lifetime looking at scopes. A low frequency thing - even just a delay (due to a path time) can look just like something high frequency thing if the delay causes a "re-play" of the high frequency thing later on, perhaps almost on top of the other high frequency thing. I suspect strongly that's what we're seeing - a pulse from a previous roundy round whose trajectory eventually brought it back by the sensor.
Note in these scans that the X and Y are synthetic variables that take into account amplitude and frequency of the AC and amplitude of the DC. The search space we're interested in is that plot that looks like a spider - the intersections are where things go round and round and don't hit the wall.
(sorry the board doesn't seem to want to preview gifs today - click on them)

The inputs

the spider

Some possible trajectories

This will all of course be a little different for us - our geometry and goals are different. But the equations of motion are what they are. Pretty scary stuff, juggling charged particles with an attempt at applying fields that will always be imperfect, and affected by the tank, and by the particles themselves - and in our case, the density of the particles changes as they go from diffuse out in the tank where this math is pretty close, to compressed (yeah, we have a compression ratio, but that's not what people think) at the focus - when things are at the focus, which isn't all the time.

Further, what I'm pretty sure we want - and I was surprised that a simple sine did bunching that well - that was amazing - is a slow onset to negative, but a quick reversal to positive when the ions are inside the grid, then back to negative to slow them down again before they hit the tank walls and are lost (they cost energy to create...we want our nickel's worth here).
The idea behind the reversal is to drive them in further, but mainly to draw in the much faster moving electrons to get between the ions and promote fusion, much like a meson would do. At some relative speed, they become effectively "small" compared to a deuterium nucleus wave-function...which should allow some of the Coulomb force to be neutralized and allow lingering long enough for tunneling into fusion to happen...that's my theory.

It pays to know that other things being equal, electrons move ~60 times as fast in the same electrostatic field, so we can hustle them around before a deuterium ion notices much. This is the square root of the charge/mass ratio ratio. If that makes sense.

Since strong force kinds of things are 1020 or 22 per second, and this is more like 10-9 of a second near focus...well, that's a relative eternity for luck to give us fusion, eh? Both are fast, but you have to have a sense of proportion (H/T Hitchhiker's guide to the galaxy),
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Re: Runnin with AC drive, re-circulation seen, likely

Postby Doug Coulter » Mon Dec 18, 2017 9:28 pm

To add to my theory, I should note that such luminaries as T Rider and C McDonald-Bradley (and quite a few others) have noted that since the scattering cross section is bigger than the fusion one under current measurement conditions, this can't work. I've in fact modeled our approach carefully to avoid Rider's objections, because it's obvious (to me) that under his assumptions, he's right.

So...why bother?
Because scattering is elastic - no energy is lost, just how it's arranged. If all your collisions/scattering happen near the focus (or the huge bulk of them) and if there's any fudge around slowing things down for another pass before they hit the tank walls - we are golden! Think about it. When you're in the middle of a circle, all directions are "out". So it doesn't matter much if things scatter a bit, the net result is that what came in, went out, more or less as it would have if there was no scattering! Momentum and energy are conserved, the velocity distribution will be disturbed some of course. If we have some fudge there due to getting our trap parameters forgiving, we might have a few "dead slow" ions floating around, but those will already have given up all the energy we invested in them to another one - we didn't lose diddly. If Coulomb repulsion causes the D ions to get uniform out there when they're at the tank walls, away from the grid, that actually helps us by providing a uniform starting place for the next cycle!

(Do I hear walls of previous assumptions falling down? Well, I hope I'm right and not being foolish here.)

This drove the selection of the cylindrical architecture, along with the idea that we wanted a decent electrostatic lens and a central focus for that "effective compression ratio". Coupled with the knowledge that the focal length is determined by element spacing and there's no way to tesselate a sphere...I figured we could live with the end effects, and in this case it seems we are getting data precisely because some stuff is free to be "lost" out of one of the ends.

The other thing my theories bring to the party is the possibility that a relatively fast moving electron can get between two D ions for long enough - sub nanosecond - to let them be close enough to promote fusion. Dunno - the deBroglie wavelength gets commensurate with the Schrodinger wavelength of a D at around 50kev on the electron, relative to the D. Which, since one is coming in and at least some of the others are going out - is head on for a lot of cases. So, achievable.

I just couldn't think of anything else that would decently explain what it seemed actually happened in my "lab accident" that didn't require a boatload of completely new physics. This only requires looking at the same old laws a little differently, doesn't need anything new, really. If it's true, it remains to make it happen on purpose, which is what I'm trying to do.
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Re: Runnin with AC drive, re-circulation seen, likely

Postby Paul Fontana » Wed Dec 20, 2017 2:34 pm

Preliminary congratulations on your interesting preliminary results, Doug! Being able to drive the thing with AC is indeed a milestone - now some real physics can get going.

Is your Faraday probe signal showing current or voltage? Also, is it surprising to you that it only shows positive signal and never negative? Is it rectified (other than by the plasma)? As you probably know, there's a limit to how much a floating probe can tell you about what's actually going on, due precisely to the shielding effects from the electrons you've described. Down the road it might be worth building a proper double- or triple-probe, but even in the short term since the ion grid is not in operation, I wonder if you could use that as a second probe just to get more information on how the charge is moving in the tank. (Biasing it relative to the Faraday probe you have now and measuring the differential current might also be very informative.)

The fact that your Faraday probe signals are not obviously periodic relative to your drive is puzzling and is bound to make any interpretation difficult. It's going to be awfully hard to construct a model that explains a signal that's different every time you look at it. If this is chaotic dynamics and if you've been living right, it might turn out to have a periodic attractor at some amplitudes or frequencies (IF you can stumble into them). It's always hard in science to know when it's time to start speculating and when premature speculation is going to lead you down the garden path with self-imposed blinders on, but if I can throw in my $0.02 it does seem like the Faraday probe may be picking up signs of a soliton structure in the ion density. The multiple echoes might indicate rotation of that structure, but again, hard to make any inferences without something repeatable (like time between echo pulses or time from some driving voltage threshold to the Faraday probe peaks). Having even one more probe to compare the signals in time and space would be valuable.

Keep it up, and keep us posted! I'm on pins and needles, and I'm sure I'm not the only one.
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Re: Runnin with AC drive, re-circulation seen, likely

Postby Doug Coulter » Wed Dec 20, 2017 4:09 pm

I'm looking at the probe shown in the picture, which is loaded with a 100k resistor to ground (plus parasitic C from the structure shown and a scope probe), so I suppose some of both potential and current. Yes, the ion grid could also be pressed into service, though it's almost equidistant and geometrically symmetric and might not tell us much more. There are, however, some other things sticking into the tank, mostly near the far walls of the big part, that might be looked at. I'm trying to avoid opening it up - it's been under hard vacuum (10-8 mbar) when not in use for almost 2 years now, and that kinda gives confidence about contamination - and has definitely improved repeatability of a lot of things....Yeah, I have a door, and more already-installed feedthroughs, and as a last resort...It's kind of gratifying how long that Pfeiffer turbo has been continuously running...a lot longer than they say it should between bearing replacements. Lucky so far.

Yes, it's surprising that I don't see negative on that probe, very. I normally see quite a lot, due I think to excess electrons that are likely secondaries emitted when things strike the grid electrode. This theory is slightly bolstered by the fact that it has tended to be less when I used grid materials with higher work functions, limiting with what I have now - pure tungsten and pure carbon. It was far worse when the grid rods were thoriated or lanthanated tungsten (I'm using TIG welding rods for this), and the ends something other than graphite. After all, we have an endless supply of electrons available, they go through wires nicely, unlike nucleons, and we have a pretty decent pump for them in DC modes. Still, you'd think that due to some of the above, I'd see an excess of electrons and for sure not an excess of positive (well, maybe my eyes aren't good at integrating a tiny long period negative against a few short positive pulses to see the net accurately) here. Always more to learn. I suppose it might be due to the power supply in this case being AC coupled and things balancing out in the coupling capacitor.

I'm really not sure about the rest at this point. Yes, we could have soliton like behavior, migma like, strange attractors, or phenomenon that could be described in several ways. What I do note here is that this is nearly the first time we've been able to measure anything much dynamic going on at all - while also getting neutrons. Just pulsing the main grid with a big negative pulse didn't show us anything like transit time on the Faraday probe - just capacitive coupling - and also - no neutrons modulated by the pulse. Just getting any kind of transit time took a couple years of trying this and that, and what finally showed us something we could take to the bank was modulating the ion source grid. FWIW, the numbers we got still approximately agree with what we're seeing here. Going backwards though the math (I wrote a perl program called speedvolt to do some of that for me and checked it against transit times in electron tubes for that e/m ratio and sizes) it seems we're getting insanely low energies on our D ions...which would kind of explain why existing fusors are so lousy. Partly because Richard was right about most of the ions being created near the bottom of the potential well (such as that is - it's not a pure function of the applied potential) - where the cross sections are favorable for ionizing stuff. In fact, one valid way of starting to analyze the old fusor is to think "why is this so terrible, it would seem it ought to work better than that?". In explaining things, maybe the best way is to attack this from both ends - why is that so terrible as one end, and how could it be really good from the other - maybe we meet in some decent middle.

There's plenty unexplained to look at! I'm trying to live right, and yes, we do have the necessary (and maybe sufficient) conditions for chaotic dynamics - it's certainly fractal in the sense that this is all recursive - the input state is the previous output state. I'm hoping that there's a simpler solution to the dynamics than a pimply snowman on it's side, of course. We could hope for a strange attractor.

In fact, it's been my observation (mentally) that the dynamic equilibrium achieved in a DC operated fusor is one such attractor, and it's the one that makes the least fusion - when everyone makes their rig stable, it's worst case in actuality. We've noticed repeatedly that just about anything that knocks it off that perch momentarily increases neutron output, which is part of why we are doing this now.

I do strongly suspect that when we see those multiple pulses on the faraday that what we're really seeing is the results from more than one previous cycle, almost time-aligned at the probe position - and probably better aligned at the grid focus (which I don't show here as it's pretty dim at this power level, but it qualitatively looks about the same as with high power inputs of DC).

Right now I'm awaiting some parts from good old DigiKey to build a coil driver that'll get to around 1 mhz...and hoping for our Baker Street Dozen to find us some more type 61 ferrite to replace the type 77 that's now in that coil (for higher frequency performance)...and related issues, like weather that makes it worth trying to heat the lab to work over there...(I have a separate electronics workspace, one of many, here in the warm, in the meanwhile). Above around 1 Mhz, I'm going to have to go to the tube amp, which is fraught with consequences if I mess up - many of those parts are "million dollar collectables"...and easy to make the magic smoke come out of. This is hard to do if you have to do fully qualified specialist design and testing on a ton of subsystems, even if in theory you know how to do it all and have done it before - there's just a lot of it. Having it all at least automatically do safe shutdown for all edge cases anticipated or not - is kind of a crap shoot - it ain't my first rodeo, but even the best get thrown. Fingers crossed.
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