You might read the forum title explanation in its forum box. The forum exists only for ion gun discussions related to advanced designs and for work where folks wish to work at reduced fusor pressures in possible differentially pumped designs. This is an advanced fusor device. Thus far, no one has reported neutron numbers using any ion gun that tops the common simple fusor's best reported record.
Accomplished fusioneer researchers need a forum to discuss possible improvements and deuteron sources to advance upon what they have already mastered in the simple fusor device.
Richard Hull
Ion gun fusor
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Richard Hull
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- Real name: Richard Hull
Re: Ion gun fusor
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
Fusion is the energy of the future....and it always will be
The more complex the idea put forward by the poor amateur, the more likely it will never see embodiment
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Doug Coulter
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- Joined: Sun May 27, 2007 3:18 pm
- Real name: Doug Coulter
- Location: Floyd, VA, USA
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Re: Ion gun fusor
Well, I'm one of those microscopic fraction that DOES use ion guns, and I've designed a few with differing results on the actual fusion process. My ECR microwave ion source will take you to very low pressures (e-6 millibar!), but it's hard to get the ions out of at any real current. Pretty reliable as these things go, though.
What I do now is silly, but due to my strange setup, it works great and is even more reliable. I'm doing my main grid fusion in a 6" sidearm of a much larger tank (cylinder grid 1" dia, 2" length). I added another tiny fusor grid right out in the middle of the bigger (14" by 26") part, and it will "light off" at far lower pressures and voltages than the main grid. I can literally control/modulate the main grid current with it. If I set the pressure below what the main grid will "light off" at, I can tun its current on and off and modulate how much by varying what I put into the little one out in the middle of the tank quite nicely. AC also has interesting effects here, and it only takes 10-20kv on the little grid to light things off when 50kv on the main grid will not...since it has a better PxD for Paschen's law out there - a lot better. Watching what voltage the little power supply I have on grid #2 current limits at is a more precise and repeatable indication of conditions than my PKR-251 gas pressure gage...
I do find I can get higher Q and more neutrons both with an ion source, but it's not a huge multiplier (so far, I haven't tried everything I've thought of there yet).
No question it makes it easier to run the main fusor, as it gives you another knob to control the current with, fairly smoothly, so things aren't as touchy about precise gas pressure or other variables when this is in use.
But I can also run without it just fine too - mainly things are a lot pickier re getting all the other conditions just so.
What I do now is silly, but due to my strange setup, it works great and is even more reliable. I'm doing my main grid fusion in a 6" sidearm of a much larger tank (cylinder grid 1" dia, 2" length). I added another tiny fusor grid right out in the middle of the bigger (14" by 26") part, and it will "light off" at far lower pressures and voltages than the main grid. I can literally control/modulate the main grid current with it. If I set the pressure below what the main grid will "light off" at, I can tun its current on and off and modulate how much by varying what I put into the little one out in the middle of the tank quite nicely. AC also has interesting effects here, and it only takes 10-20kv on the little grid to light things off when 50kv on the main grid will not...since it has a better PxD for Paschen's law out there - a lot better. Watching what voltage the little power supply I have on grid #2 current limits at is a more precise and repeatable indication of conditions than my PKR-251 gas pressure gage...
I do find I can get higher Q and more neutrons both with an ion source, but it's not a huge multiplier (so far, I haven't tried everything I've thought of there yet).
No question it makes it easier to run the main fusor, as it gives you another knob to control the current with, fairly smoothly, so things aren't as touchy about precise gas pressure or other variables when this is in use.
But I can also run without it just fine too - mainly things are a lot pickier re getting all the other conditions just so.
Why guess when you can know? Measure!
Re: Ion gun fusor
Doug Coulter, I find this an very interesting comment. I dont have a 6" sidearm, so this is not really applicable to me, but I wonder, why you make the sidearm grid your main grid, when the small grid at the center of the big chamber works so well and starts so easily.
Can you explain this a little more?
Can you explain this a little more?
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Doug Coulter
- Posts: 1312
- Joined: Sun May 27, 2007 3:18 pm
- Real name: Doug Coulter
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Re: Ion gun fusor
I kind of wish I *could* explain this better than I have, but that's why we get in the lab and "play".
In my case, it was just the natural thing - I had this big tank (BillF found it in a scrapyard for the weight of the stainless steel, where the workers had been using it as a urinal, talk about a cleaning job), and it had this sidearm that was 6" - the same size most of the people here were telling me to shoot for, so....it just worked out that way - my first work was just trying to duplicate what others here have done. Just basic science to make sure everyone is getting the same results, as if you're not, something is wrong somewhere.
At first, when I wasn't making many neutrons, the advantage of getting the detector in a lot closer was important, now it's not so much, and in fact, my big 3He tube now gets into pulse pileup issues and won't count correctly past about 1m neuts/second (and I've seen 6-10 million). I'm now using a fast-only neutron detector (Hornyak button and phototube) and an old B10-lined detector, mostly, since both are on the "numb" side and very stable, particularly the Hornyak, since it only sees fast neutrons and thus isn't shifted when a big moderator (me) moves around.
I keep talking about Paschen's law, which CarlW actually put me onto. Here's some decent reading on it: http://en.wikipedia.org/wiki/Paschen%27s_law
I can find some other links (on my site) if that's not enough. Some of them are huge downloads, though (whole books, scanned as images). At least one of those is all about designing gas tubes (thyratrons, indicators, and so forth).
The deal is, at higher pressures, an electron can't gain enough energy between collisions with atoms to ionize them, given a certain field, and there's a magic pressure times distance where things are "just so" at that dip in the chart at the link. We run fusors way over on the left hand side of that plot, so yes, this works quite well having an ion source that sees a long electrical path, and a main grid that sees a shorter one. This makes the P x D a lot bigger for the grid out in the middle of the big tank, since D is bigger. It's lighting off at 5-10kv when the main grid won't at 50!
This is in general, the issue with trying to make a good ion gun. You're usually thinking it's going to be smaller - but then it's hard to get it to "light off" without a fairly huge magnetic field, which makes D bigger by making the electrons spiral around the H field lines. And even then it's hard, and most sources need a rebuild inside 100 hours use - sputtering of the metal parts messes them up.
In fact, my homebrew feedthrough is quartz, shielded by a grounded copper pipe right up to the back of my grid, maybe 1/4" clearance, and this doesn't discharge, arc, or draw much current! This is only true while the pressure is such that we are at the left hand side of the Paschen curve, however, it wouldn't have worked for me at first as I dumbly tended to turn on power and then pump down. Now I get everything else just so before turning power on, and "walk" that up slowly to get into the good part of a run.
I wound up shielding the internal quartz as it's something that fast D ions can reduce into conductive silicon, and I like not to have to replace the glass so often.
This isn't to say I might not start using the grid in the big part of the tank as the main grid sometime.
But this isn't broken, so for now, I'm not fixing it. I think JonR gets more neutrons than I do, but is using a lot more volts to get there, so this meets my definition of "works really well". At least compared to other fusors, that is. I want gain!
Frankly, my own research is going in another direction anyway - trying to influence the ratio of the 3 possible DD reactions via controlling spin of the reactants, for which I'll be injecting some RF on the little grid or another antenna in there to try and accomplish, along with some magnets here and there....we'll see what I can find out with that. As far as I know, no one has even tried to alter the thermal DD reaction ratios by using non-thermal preparation of the reactants. It's not Nobel turf - conservation of spin in all nuclear reactions was figured out IIRC, in about the 1930's, but it's interesting that the entire fusion community has utterly ignored this very basic and known-true aspect of things (it also explains in a way why DT has a larger cross section - the odd number of nucleons makes conservation of net spin easier). So if/when it works, I expect snarky comments from physicists who have themselves missed this for most of a century.
You have to wonder - to the extent a fusor affects spin - it's in precisely the wrong way to get to fusion, or at least the DD->He reaction (spin 2 in if the D's are aligned, zero out for 4He - I want + and - one spin going in here, no neutrons, more gain). Now I've got to figure out how to even measure the ratios so I can tell if it works! I am thinking I might find out some things with a gamma spectrometer if I can get one going here...The 16 mev gamma from that one ought to sort of stand out...you'd think. And I'd bet that you can tell between the other two as well, since they don't put the same energy into the results. But that's getting into guessing, and the lab will tell all, when I get there.
The trouble there is most big gamma spec heads are NaI:Tl, which will activate under neutron flux, so no one here with one has been willing to look, so far. I have one I'm willing to put at risk, but no MCA at the moment - and they count many thousands of times faster on a fusor run than the PRA software/hardware can handle.
The last picture is what it looks like in the light of the quartz "stab in" bakeout heaters. When things are running, the poisser on the little grid doesn't look too great, but it has rays. The main grid has such sharp focus that things disappear if you get aligned right to them. Note, you're looking at this through 2 pieces of 3/8" thick borosilicate glass, followed by 1/2" of lead glass scrounged from a hospital rad room. Else you'd be fried by the X rays in use. I just like to use my mark 1 eyeballs, which have far better resolution than any camera (and which don't bloom on high contrast ratios).
In my case, it was just the natural thing - I had this big tank (BillF found it in a scrapyard for the weight of the stainless steel, where the workers had been using it as a urinal, talk about a cleaning job), and it had this sidearm that was 6" - the same size most of the people here were telling me to shoot for, so....it just worked out that way - my first work was just trying to duplicate what others here have done. Just basic science to make sure everyone is getting the same results, as if you're not, something is wrong somewhere.
At first, when I wasn't making many neutrons, the advantage of getting the detector in a lot closer was important, now it's not so much, and in fact, my big 3He tube now gets into pulse pileup issues and won't count correctly past about 1m neuts/second (and I've seen 6-10 million). I'm now using a fast-only neutron detector (Hornyak button and phototube) and an old B10-lined detector, mostly, since both are on the "numb" side and very stable, particularly the Hornyak, since it only sees fast neutrons and thus isn't shifted when a big moderator (me) moves around.
I keep talking about Paschen's law, which CarlW actually put me onto. Here's some decent reading on it: http://en.wikipedia.org/wiki/Paschen%27s_law
I can find some other links (on my site) if that's not enough. Some of them are huge downloads, though (whole books, scanned as images). At least one of those is all about designing gas tubes (thyratrons, indicators, and so forth).
The deal is, at higher pressures, an electron can't gain enough energy between collisions with atoms to ionize them, given a certain field, and there's a magic pressure times distance where things are "just so" at that dip in the chart at the link. We run fusors way over on the left hand side of that plot, so yes, this works quite well having an ion source that sees a long electrical path, and a main grid that sees a shorter one. This makes the P x D a lot bigger for the grid out in the middle of the big tank, since D is bigger. It's lighting off at 5-10kv when the main grid won't at 50!
This is in general, the issue with trying to make a good ion gun. You're usually thinking it's going to be smaller - but then it's hard to get it to "light off" without a fairly huge magnetic field, which makes D bigger by making the electrons spiral around the H field lines. And even then it's hard, and most sources need a rebuild inside 100 hours use - sputtering of the metal parts messes them up.
In fact, my homebrew feedthrough is quartz, shielded by a grounded copper pipe right up to the back of my grid, maybe 1/4" clearance, and this doesn't discharge, arc, or draw much current! This is only true while the pressure is such that we are at the left hand side of the Paschen curve, however, it wouldn't have worked for me at first as I dumbly tended to turn on power and then pump down. Now I get everything else just so before turning power on, and "walk" that up slowly to get into the good part of a run.
I wound up shielding the internal quartz as it's something that fast D ions can reduce into conductive silicon, and I like not to have to replace the glass so often.
This isn't to say I might not start using the grid in the big part of the tank as the main grid sometime.
But this isn't broken, so for now, I'm not fixing it. I think JonR gets more neutrons than I do, but is using a lot more volts to get there, so this meets my definition of "works really well". At least compared to other fusors, that is. I want gain!
Frankly, my own research is going in another direction anyway - trying to influence the ratio of the 3 possible DD reactions via controlling spin of the reactants, for which I'll be injecting some RF on the little grid or another antenna in there to try and accomplish, along with some magnets here and there....we'll see what I can find out with that. As far as I know, no one has even tried to alter the thermal DD reaction ratios by using non-thermal preparation of the reactants. It's not Nobel turf - conservation of spin in all nuclear reactions was figured out IIRC, in about the 1930's, but it's interesting that the entire fusion community has utterly ignored this very basic and known-true aspect of things (it also explains in a way why DT has a larger cross section - the odd number of nucleons makes conservation of net spin easier). So if/when it works, I expect snarky comments from physicists who have themselves missed this for most of a century.
You have to wonder - to the extent a fusor affects spin - it's in precisely the wrong way to get to fusion, or at least the DD->He reaction (spin 2 in if the D's are aligned, zero out for 4He - I want + and - one spin going in here, no neutrons, more gain). Now I've got to figure out how to even measure the ratios so I can tell if it works! I am thinking I might find out some things with a gamma spectrometer if I can get one going here...The 16 mev gamma from that one ought to sort of stand out...you'd think. And I'd bet that you can tell between the other two as well, since they don't put the same energy into the results. But that's getting into guessing, and the lab will tell all, when I get there.
The trouble there is most big gamma spec heads are NaI:Tl, which will activate under neutron flux, so no one here with one has been willing to look, so far. I have one I'm willing to put at risk, but no MCA at the moment - and they count many thousands of times faster on a fusor run than the PRA software/hardware can handle.
The last picture is what it looks like in the light of the quartz "stab in" bakeout heaters. When things are running, the poisser on the little grid doesn't look too great, but it has rays. The main grid has such sharp focus that things disappear if you get aligned right to them. Note, you're looking at this through 2 pieces of 3/8" thick borosilicate glass, followed by 1/2" of lead glass scrounged from a hospital rad room. Else you'd be fried by the X rays in use. I just like to use my mark 1 eyeballs, which have far better resolution than any camera (and which don't bloom on high contrast ratios).
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Why guess when you can know? Measure!