Fusor operation pictures, comments on grid designs

For Farnsworth type designs.

Fusor operation pictures, comments on grid designs

Postby Doug Coulter » Tue Dec 28, 2010 8:08 pm

I finally found a way to go though my roughly 3k photos and find some of these, been meaning to put them up here for awhile and comment on the things we've tried, and how well they worked.
So far, it's been a near monotonic rise in "goodness" and I'm going to try to start near where we did and progress to where we are on this thread. Y'all -- add yours too!

I skipped our first nasty looking grid and run that made neutrons, if there's any requests I'll add that one, but it wasn't all that interesting, except perhaps to prove you can make it work "ugly".

spacechargestream.jpg
Shows compression ratio, molecular to viscous flow transition inside grid (or something like it).

This one shows something interesting (this one is in BillF's fusor). Note the stream of ions coming out of the end of the grid, through an insulator with a big length to hole size ratio.
We have, in effect, pressurized the grid center area, and I'm supposing some sort of pressure or Coloumb repulsion is responsible for this. This run was in He gas, not D, which is how we were doing our testing before we got D in a bottle, instead of heavy water we had to deal with. This grid did make neutrons fairly well, it's about 3/4" by 2.5" and will show up in another picture.

slumpedgrid.jpg
Too much power! Bad mechanical design too.

Here's one of our early Ti grids. Trying to brute force things turns out not to be either effective or very wise. Making the end of a bit of Ti rod was dumb, it weighed too much. It took almost yellow heat to make this slump. And by the way -- it still works and makes neutrons just fine.

twogridHe.jpg
Two grids, not right for DC drives, but a good idea worth pursuing.

As we learned, I started focusing on, well, focus, and thought that perhaps something that looked more like an electrostatic lens design would help. Well, sort of. But if you are depending on the normal dynamic equilibrium and whatever ion recycling to happen, it hurts. This is an example of something that will work well with AC drives to make things work out right. This is one vane grid inside another. All is Ti metal, except for some fancy spacers and mountings which need more design work so they don't short when Ti gets sputtered onto them. Very do-able, just wasn't done yet. The idea here was going to be to have the outer grid relatively low voltage -- this way, any ions that hit it haven't had a lot of energy invested in them. Just didn't scale some things right for the conditions. Kept these for later use when I get that nice video amp built up to drive it correctly. Probably the most notable thing in this picture is the window it was taken through. I used the lathe to cut an o-ring slot in a flange adapter, and used a window blank from McMaster (cheap) and a couple of clips to hold the window when vacuum isn't doing that job. Super fast and easy way to get in and out of the tank, and the O ring appeases the tempco force monster just fine.

Spiralgrid.jpg
Spiral grid, NiCr wire, best pic

Because owning the lathe made it easy, we tried a spiral grid. This totally stank, and this is the best picture it ever took. Very few neutrons ever came out of this. It also embrittled so badly that I broke it when removing it.

SpiralAbove.jpg
Shot from above

One of the nicer things about the big tank is that all this runs in a sidearm, and I have a lotta windows, so I can get pictures from various angles that show us things I don't see how we'd learn with the spherical geometry. Note the lack of well defined rays. FWIW -- also lack of neutron output.

More in the next post on this thread.
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Re: Fusor operation pictures, comments on grid designs

Postby Doug Coulter » Tue Dec 28, 2010 8:15 pm

More! We started learning how important it was to have at least decent precision in grids, that Ti was a decent material to make them from, and about what aspect ratio seems best for a good "kernal" for lack of a better word. I still want to try making a really long one and see if I can get more than one kernel, perhaps by dividing it up with a girdle around the middle. But our first try with a girdle wasn't so hot.

TiGrid.jpg
Ti grid, thin endplates, short and fat, large hole, 8 wires, .032" diameter, overall diameter 1".

Now we're cooking for real. This is the one that made the "neutron club" certain, and got us about to the point of equal output to anyone over at fusor.net. Sadly, the camera doesn't show just how good this is -- it blooms on the intensity of the core and doesn't show how fine the focus really is on this one. It's about like a mechanical pencil lead to the human eyeball.

TiAbove.jpg
View from above, same grid.


Here's a shot from above. We don't see this much, but obviously the field at the end of the sidearm is a little different from that deep within it. We have found, and this is pretty interesting, that small changes in how far the grid sticks out towards the main tank has an enormous effect on this, and how many neutrons it makes. As in, the whole range of interest is less than 1/10" inch, there's one heck of a sweet spot in there. The theory, and that's all it is (really, just a guess) is that we are somehow taking some advantage of Paschen's law here with the longer path out to the main tank opposite wall...but only a guess. The supposition is that's why the rays aren't coming out at 90 degrees, which they usually do -- this was one of those "it happened once and I got a picture" kinds of things. It hasn't replicated with other grids or other placements. I am guessing that with a cylinder grid arrangement, active drives will be required to actually get a good linear reaction area of hot neutron production, but I need to test that assumption when I get my one pixel neutron camera going before I'm going to sweat this one much. Right now, as both I and Tyler have noticed, the neutrons aren't coming out isotropic at all, from any of our setups, and his is the standard spherical thingie. So we really don't even know where the reactions are, though U of Wis has some ideas there for their own fusor.

vert.jpg
Vane grid, vertical in the big tank space

I promised a view of that grid that made the space charge stream in the last post. Here it is in different operating conditions, out in the main big tank (14" ID by 26" high tank).
At the time, we didn't realize a few things, but we've since gone to using a grid about where that one is shown as an ion source, very effective at lower pressures, as it has longer paths for Paschen's law. Note lousy focus and poor evident recirculation (not many neutrons either). This one is pretty long and pretty skinny, I'd expected more action along the length of it, but obviously the rays want to be in the middle only. I didn't exercise this through the whole set of operating conditions, so maybe at the right point, things are different. I've kept this one as I plan another use for it later, as well as the larger outer one that it aligns with.

GirdleGrid.jpg
Grid with girdle

Just for giggles, we tried adding a wire girdle to a grid, right where the rays normally are. This is the result. Almost completely killed the neutron output! The same grid sans that girdle works fine.
NoGirdle.jpg
Same grid, no girdle, better operation

And here it is, working fine.

More to come!
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.
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Re: Fusor operation pictures, comments on grid designs

Postby Doug Coulter » Tue Dec 28, 2010 8:38 pm

Of course, once we equaled the best amateur fusor output from fusor.net, we just had to beat that, but didn't want to do it ugly (though I have to say the response we got was fairly unpleasant).
We wanted to do it from a basis of really knowing what was going on, and started to get much more serious about metrology, which is still where our focus lies, as we haven't found out anywhere near enough to please us yet.

PHCam.jpg
Pinhole camera

This helps. We made a pinhole camera, and still have a lot to learn with it yet. I should probably put the details of how it's made on a thread of it's own, but it's pretty simple. We got some ZnS:Ag from Eljen, mixed up some with very dilute sodium silicate, agitated in the beaker, then added about 1 drop of vinegar to make the silicate set, and left it overnight for the ZnS to settle evenly onto the screen, took it out, dried it, baked it, put it in a pipe with lead over one end, and drilled a tiny hole in the lead. It's mounted on a bellows type wiggle stick.

What we don't know that this tool could tell us, is what we are seeing -- charged particles, or X rays -- could be either and is probably both. So I need to add a magnet I can turn on and off to bend any charged particles so we can see what part of the image is what. In real life, this is camera limited again -- the real image is much sharper, but the camera doesn't like this range of contrast. To the eye, the dot from the grid center is much tinier than the one from the ion source seen on the left of the picture (but on the right in the pinhole camera image).
Interesting to say the least. I dumbly soldered on the support wire, and operation melted it off, so it needs repair at this point. Things get real hot in vacuum with no way to lose heat but radiation.

WCGrid.jpg
Getting serious now.

Ok, now we are getting serious. Depending on whose numbers you believe, this grid is the current amateur record holder for output, and by far for Q, and is what's in the tank right now.
This one is made of W welding rods, and graphite ends, and is the most precise one we've made so far (but we're working on that one). The focus seemed to have scaled with the increase in precision -- eg, less mechanical errors, better focus, up to the peak current point where space charge spoils focus, which for this is around 10 ma or so total current (most of which is electrons hitting the tank walls hard and wasting input). Sometime around here is when we discovered the pulsed mode, using inductive ballast and other tricks, that gave us the huge Q improvement -- roughly 1 million neutrons/second but on a mere 0.1 ma indicated on the power supply. Obviously the normal equilibrium is NOT where you want to run a fusor, but it's good for basic tuning of things like focus and so forth. This shot was taken in "photogenic mode" so you could see the rays and so on nicely, the next shot shows how it looks when everything is optimized for max output -- lower pressure, lower current....hint -- this is not going to be about brute force, it's about subtlety, and a big thanks to nature for making sure I figured that out -- hit me on the head real hard a few times, I eventually get it.
WCGoodoperation.jpg
Real operation conditions

Here it is making something on the order of 10 million neutrons/second, which takes silver 2" sq to the couple thousand counts/minute range on a pancake geiger tube with <5 minutes running.
(lots more if we run to what's called "secular equilbrium" but I don't want to be around that many rads that long real often)
At this point, there are so many of those "rare" gammas from the rare DD->4He that are 16 MeV or so in the room, that go right through the lead shielding, we don't run like this much and are looking to scale back.
No point if we don't live through it, or make the whole lab so hot we can't use sensitive detectors anymore. My kitchen is on the floor above this!

To underscore that one, see this:
RawPixels.jpg
Note camera pixels hit by gammas

This is what happens if you're not serious about shielding things. All those noise pixels in under 1/8" second. I got religion after that. You'll have to click this pic to see them, but it kinda got my attention, those CCD's aren't all that sensitive to radiation after all and hot gammas tend to go through matter without leaving much energy behind as well. You could just as well title that one "hoping for hormesis" I suppose. Most of what you see in the pinhole camera here is artifacts, this one was made before we got good at it, and the coating is real non uniform.

FusorInnards.jpg
In normal light (of the bakeout heaters)


This isn't as sexy, being just normal light and all, but it shows pretty much what you'd see if you looked in the tank window right now. That secondary grid out in the middle is used as an ionizer and pulser for the main grid. The effect is awesome when that second grid is driven various ways. For one thing, at some pressure (on the low side) 40kv on that can turn the main grid on (with 53 kv on it) or off, just like a switch, the best Paschen's law demo I've ever seen. Drive it with DC, with or without a normal resistive ballast, and it's a very copius source of ions with about 10 ma input, for the main grid to chew on, but doesn't make squat neutrons itself (note poor accuracy to any particular shape). But when driven with AC, and series inductance, well, "interesting" things begin to happen. During one half cycle (of 60 hz drive), the main grid current and voltage pulse at about a couple of KHz, neutron output goes WAY up, and it's in sync with the pulses. Further, huge voltage pulses show up on the little grid too (enough to cook the NST I was using by internal arcing) -- much higher than any of the voltages applied to the system. I have to believe that this is due to the effect of a big group of charged particles flying past it -- proximity effect of the big bunched charge. Since this is a huge leap ahead of where everyone else reports being, this is the road we are now traveling, hoping to find some more low hanging fruit there. And this is why I proposed the theory I did on another thread, of having two grids to get space-time bunching. This appears to work far better in a non equilibrium mode where you take more active charge of where, well, the charge is. ;) And when.
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Re: Fusor operation pictures, comments on grid designs

Postby Doug Coulter » Tue Dec 28, 2010 11:20 pm

Oops, almost forgot. We did play with the attempt at spherical geometry for awhile, since the sidearm we were running is kinda-sorta not completely unlike a sphere.
Sphere.jpg
Sphere, dupe of Richard Hull's as close as I could

This is as good as it ever got, and I doubt it ever made it to 100k neutrons/second. Trying to push it resulted in the next picture.
HotSphere.jpg
No wonder they burn out at the ends....obvious in hindsight.


The trouble with any attempt at a sphere is that "you can't tile a sphere with any simple set of shapes that give equal spacing" which determines focal length of the effective E lens you're making. And of course, at the end of this one, where the wires all come together....the result is obvious. You'd have to at least make a bucky ball to even get close, that's a bit much for me.
I'll deal with the end effects of a finite cylinder until I learn more.
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Re: Fusor operation pictures, comments on grid designs

Postby chrismb » Wed Dec 29, 2010 7:44 am

I like the pin hole camera. On the topic of the fusion hv's (they are more like 24MeV, I think you'll find!!); d'you think you could run your pin-hole with a lead shield in-front to all but shield the fusion hv's, so that you can image where the fusion is going on?

I am not sure what the reaction rate/dose/safe-distance is for the gammas. I did it for neutrons in another page, so I guess I'd best do the same for gammas... (before I start running my reactor to 10^9! ;) )

On the topic of your cylindrical grid; first off if you want to go for symmetric grid you can always try a geometric-precise dodec or football. I don't think anyone has actually put in the effort for an accurate grid pattern, even Wisconsin or the academics. I seem to recall someone was going to attempt a rapid-prototype grid to get that accuracy, but I don't think it was a well-thoughtout plan.) People seem to always use a 'roughly' somethingorother shape, but I agree with you that the sheer elegance of visual outcome that you have achieved with your improved geometry tolerance is suggestive of benefit from this effort.

That being said, I actually think the cylindrical grid is the way to go. I shall elaborate: In the cylindrical arrangement you have radial and axial ion paths. The radial ones take a short time 'in' the grid (i.e. not under acceleration) whereas the ones axially take longer. I cannot believe this difference has no [beneficial] influence and if the ratio of the cylinder is right then I would expect axial ions to lag the raidal ones such that as one lot leave, it leaves a bigger positive well behind that draws in the other. I think with a cylinder of the right ratio, you should expect some sort of space-charge resonance. I think you are thinking along those lines also.

So my experiment would be to test out different cylinder ratios and see if there is a reaction rate 'delta' between them. And if so, do a parameter-walk of cylinder geometry in the direction of bigger reaction rate! I suspect you may also detect an EM emission according to that space-charge resonance, if it is in the 100k-unitMHz.

This might then achieve what I am trying to do (recover collision losses resonantly), but by analogue means and without the complex electronics I have to contend with.

(Should I delete this quick before it is 'public'? It sounds almost patentable!)
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Re: Fusor operation pictures, comments on grid designs

Postby Doug Coulter » Wed Dec 29, 2010 9:12 am

Yes, the PH camera is nice -- but far from being fully exploited. I was using the book value for the "rare" gamma reaction Q. I have messed around with different scales with this, but slipped up and didn't post the pic yet, which I'll fix directly. Essentially, with the same grid, we can make it relatively "bigger" by making the tank "smaller". In this case by inserting some grounded pipe around the grid, which we have done already. This entire effort has been a trek to map the parameter space, to be sure, but we are finding most of the "surface" to be neither monotonic or differentiable, in other words, there's no (or only a few) gradients you can follow to at best, a local minnima here. The space has enough dimensions that a simple gradient descent only gets to a local best place, not the global best space. The most elegant descriptions of multi-dimensional spaces like this and how to find minima in them is from Timothy Masters Neural Networks books where the relevant math and algorithms are discussed in great detail -- the same math is in play here, and pretty soon I'll be able to show some diminsional slice plots of output vs "whatever" other dimensions I can cram into a visualization. At the moment, the short sweet version is it all works best at lower pressures, higher voltages, less space charge *except* at focus, and how good you do the focus part is the big one until the other factors spoil it (space charge repulsion "blooming" of the focus, like a TV with the brightness turned up too high back in the days of CRT's).

I've been predicting a resonance such as you mention for a few years now, in public, so there goes that patent -- if there was going to be one, I'm not even the most prior art, the subject has been breached by others in our library a few times -- and it's why I'm beginning to work with RF here. Not to worry those things, this publication IS prior art that prevents other, bad people from patenting it and stealing it from us. Or at least would make their patents comparatively easy to challenge if they try it. That's an advantage of having this board off-site and backed up by a (uninterested) third party, complete with time stamps. At any rate, don't miss the point of this open source effort -- we will all get any credit due, and at least for me, the object isn't to get rich (I already am, enough to suit me, and I have money too) -- it's to save (or at least improve) the world. We are trying to pull together the advantages of big science (because we are big, collectively) and small science -- because any of us can go down any path he chooses at any time, following our own noses to the eventual answer(s) -- there may be more than one way that works, after all. So we get advantages of both -- many eyes and minds, but without the strictures of some organization that forces people off the path they favor themselves.

So far, I think one still has to "drive" this resonance actively, though I don't believe it will take a lot of power to do it (but may take some high voltages) as you get most of the energy back from the spring-mass system as things go through the electrodes, same as in say, an ion trap or quadrupole mass spectrometer -- or a particle accelerator. That's the path I'm going down anyway. Here's an example of it happening almost by accident, however -- see the scope traces in my post on that thread. This was our first encounter with the thing being "driven" vs "relaxation oscillation" on which I have a lot of other documentation. It's been a struggle to get posted all we've done in the last few years up here, but we did do it and document it. Now its mainly a job of sorting and collating to get it posted (and either make it public domain or prior art as seems wise).
I've not yet been able to mentally model an oscillator of the magnetron or klystron class with this, since we have two sets of particles that are both moving in both directions, with different transit times, so no obvious way to make a DC to AC converter with it - but obviously, and as we've documented (more to come on that), it can happen for sure. We got our record Q numbers that way, with the thing self oscillating and drawing an indicated .1 ma (100uA) at 50kv with an inductive ballast, and announced that on my main web page long ago. It was met with considerable disbelief (sour grapes?) on fusor.net, but that doesn't mean it didn't happen or isn't replicate-able -- because it did and it is, and has been, with knowledgeable witnesses present and all that legal eagle junk -- that negative reaction is what clued me into the need for that stuff and is part of the reason this site is here.

ScaleExp.jpg
Playing with scale

Reduced outer electrode diameter is easy to try. It's pointed us in the opposite direction, however, at least for DC driven fusors; for active drives, all bets are currently off. At the higher pressures this requires to self-sustain under Paschen's law, things simply do not work as well.

The other part of our "parameter walk" has shown us that in general, electrons are "bad" and waste most of the wasted energy. To the extent we can remove them (see the link above, that AC drive on the second grid does that) things work much better, and as I get better grids built that take that into account, it gets better. I have a pretty neat design I'm working to build now, carved out of graphite billet (yes, Jerry, I know) and using some alumina in critical places to prevent some of the secondary emission, which I have fairly high hopes for. The truth is in tasting the pudding, however. One interesting thing I've found which has been true so far (but may not be always) is that things that improve the classic, static fusor, also improve the "other" mode about the same amount. Since the other mode is "twitchy" when free running, it's easier to perfect things in the static mode, then try the other one, for now. Kind of like the idea that if I can't get gas and air to go bang once, I'm not ready yet to begin building a 4 stroke engine to do it repeatedly and quickly.

The todo list includes getting some better use out of that camera, and by golly, just planting a faraday probe on that wiggle stick and seeing what we see in various places -- even this most-basic stuff hasn't been done yet by any of us. I have to think we'll be in better shape to editorialize once we know some stuff no one else has bothered to find out, which is why I'm doing more actual hours on metrology than anything else right now.
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Re: Fusor operation pictures, comments on grid designs

Postby Doug Coulter » Wed Dec 29, 2010 9:44 am

I'm hoping all this is a wake up call for everyone to get into the lab and DO things to report about. We have been, and are just now taking a break to report it. Y'all get cracking or we'll be so far ahead you'll never catch us ;) I know we have some nice surprises coming soon from this lab...let's see yours too! (scientific version of the game "doctor"?)
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Re: Fusor operation pictures, comments on grid designs

Postby Joe Jarski » Wed Dec 29, 2010 11:00 am

Dang, I wish I was farther along on this so I had something worthwhile to contribute. When I got the fusor bug a few months back I figured the best way to get started is to pick up where everyone else is. Based on the U of W testing, grid geometry didn't deem to matter much, so I figured I wouldn't be too far off if I started out using an icosahedron grid, as it seemed like it had the best chance of setting up some sort of organized recirculation for spherical geometry. That's where I've been headed. Slowly making progress...

I'm still intrigued by the poissor in the cylindrical grid being a ball instead of a rod.
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Re: Fusor operation pictures, comments on grid designs

Postby Doug Coulter » Wed Dec 29, 2010 11:33 am

You'll get there Joe, probably pretty quick. I don't have a particular "religion" on geometry, I'm just repeating what the math guys say. The actual case of what's going on here is so complex it's only a part of it. BTW, the poisser IS a rod when looked at from the side, it's only the rays that come out of a point in the middle. We theorize that the rays are recently neutralized ions from the idea that this is the only thing in there that can make visible light via known physical processes that could be occurring in the conditions. The PH camera pics show that there's action elsewhere too, though. Most of the fusion doesn't do anything one can see, at best the visuals are a kind of semi-related diagnostic. At this point we don't even know conclusively where the neutrons are being generated! I have some plans to test that with a single pixel neutron camera now being worked on. And that Faraday or other probe needs to get in there and do some fishing.

I'm basing my theory of focus on Terman's excellent writeup on electrostatic lensing. And I look at it this way -- when say an optical instrument is way out of focus, for one, you can't necessarily tell which way by looking at the fuzzy image, and for another, small changes won't make much difference to what you see until you get close. I think that's where the sphere guys are at -- so bad they don't see improvements, because, as we've noticed with the cylinders, (where inside the end effects we can be perfect) -- it matters and the difference goes up really fast as the precision gets better, visually and in neutron production. Obviously the net density of colliding beams goes way up as one gets them smaller -- it's an exponential. At the beginning of an exponential, it's flat, but as you get along, it starts going up really quick, which is what we are seeing here in practice, so I think there's a least a little justification to think as I do (but I'm more than willing to be blown away with something that works better). That would explain why they don't see much difference in spherical grids -- the curve is pretty flat when the errors are huge. Bad vs almost as bad. In our case, going from say 1/4" error to 125 mil error didn't do much, but going from 125 mil errors to 30 mils was factor over 10x. Next we'll try and get inside 10 mils (or better, but I know my limits at the lathe/mill on graphite) and see where that puts us.

As the spacing to distance ratio is the determinant of focal length in E lensing, I just don't see how to get there with any relatively simple tiling of a sphere (you'd need to be able to tile it with circles and that's not possible geometrically in this universe). But it might be that a buckyball sort of thing would approximate it close enough, dunno -- it would still have errors bigger than our first lousy cylinder did. Certainly that stuff where all the wires come together is a mistake, as shown above -- that just makes a target for ions to hit the grid, release secondary electrons, and generally waste input power and grid lifetime.

In general, I've given up on the recirculation happening as if by magic. I need more to convince me that will be the main driver in a successful (defined as say scientific break-even energy) attempt, though it clearly happens some. The fact that under our best operating conditions you can turn it on and off instantly with an ion source going on and off tends to indicate that there really isn't very much recirculation at all under the conditions we have here. But I don't see that as an insurmountable obstacle, we can make it happen, instead of hoping for a miracle in step two as the famous cartoon shows. Which is where I personally am heading. The advantage to a bunch of us doing this is we all have different ideas, approaches and capabilities, and we can find out things collectively no one guy could by himself, after all. I'm sure if any of us gets there, there will be plenty of credit (and maybe even money) to go around, that's not a major worry I hold.
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Re: Fusor operation pictures, comments on grid designs

Postby William A Washburn » Wed Dec 29, 2010 1:36 pm

I can't remember who mentioned this but it kicked off a few memory cells:
When I did a year of nuclear lab in school (40 years ago) we never took any special precautions EXCEPT FOR GAMMAS.
These precautions included lead bricks, roving folks in the lab with hand-held real-time counters and the cobolt in our
counters was at one end of the lab bench and our counting electronics was at the other end (where I was with mine).
We stayed as far as possible from the counting module with the cobolt in it. From these precautions I suggest you do
your calculations very carefylly!
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