Back to building. Now with a new design.

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jaaz95
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Back to building. Now with a new design.

Post by jaaz95 »

Hi everyone. Been a while.
For those who remember who I am, I was working on a fusor about a year ago. Was going to use magnetic lensing to shift the plasma inside the rector to reduce grid heating and increase fusion. However the design wasn't feasible and the whole project was getting too expensive so I ended up scratching the whole thing. That said, I've regretted giving up on fusion ever since. Anyway, now I'm back with a new design at a reasonable cost. The idea is to essentially aim two small potential drop accelerators at eachother, and use electromagnetic lenses to focus the beam down to a fine point inside the main chamber. I've already started aquiring parts and so far it looks like it may be a feasable plan. I've attached a bunch of pictures of the design. The idea is to run the setup without an inner grid. So really it isn't a fusor anymore. I guess the question would be, what do you guys think? does it seem like an idea that could work? Just looking for thoughts and ideas.
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Richard Hull
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Re: Back to building. Now with a new design.

Post by Richard Hull »

The quadrapole focusers seem cool and the idea is nice but you will need a cathode of sorts in the middle I had posed this sort of device a few years back, using a small wire hoop as the central electrode. However I would imagine a thin sheet of Pd supported on a hoop might give an interesting result provided the beam currents aren't too great. Maybe a tiny sold Pd bead electrode.

Again, you will need a viable cathode at high negative potential in the center.

Richard Hull
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jaaz95
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Re: Back to building. Now with a new design.

Post by jaaz95 »

Why do I need the cathode in the center? I'm not looking for high beam current or for this to be a fusor at all.
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Re: Back to building. Now with a new design.

Post by Jeroen Vriesman »

Your magnets seem a bit strange to me.

The In your design the maximum field strength would be in the gap, an nowhere else...

For a quadrupole the open end of the core needs to point towards the beam, and you need two on both sides to focus the beam, and you need a cathode in the center.

http://en.wikipedia.org/wiki/Quadrupole_magnet

without the cathode in the center there is no ion beam to focus.
jaaz95
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Re: Back to building. Now with a new design.

Post by jaaz95 »

the magnets function the same way they do in an electron microscope. They were just badly and quickly modeled.
http://advressys.com/analytic/maglens.gif

Also realized I misread that. There are two cathodes. One on each of the accelerators. The corona rings are supplied their power via the 2 van de graffs. The last ring's grounded and as such is the cathode. Inside the main chamber there is nothing other than detection equipment. I left out some part in the model because I was having trouble making them.
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Doug Coulter
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Re: Back to building. Now with a new design.

Post by Doug Coulter »

You should be able to get some reactions with this sort of thing - in fact, I'm building one myself (somewhat different design). You might need rather sensitive neutron detectors, but nowdays, that's not that hard to get.

You'll have some issues that have been mentioned, for example, by CarlW - like how to keep the electrons from being back-accelerated in a DC linac, and others - what's going to happen to the vast bulk of ions that *don't* fuse, but merely scatter or just have a clean miss? You'll run into space-charge defocusing as well.

Yes, as some have said, you could put a target in there for beam(s) on target work, but you'll have to actively cool that or it will quickly give up all absorbed D. I've been looking at liquid cooling tubes as used for cooling computers for that as a possible solution to get the heat out of a vacuum. Ti containing D loses it at 250c, Pd loses its D at a much lower temperature. Both of those temperatures are much too low to allow the heat to be simply radiated off the target if you use one - you'll have to find a way to cool it.

One possible idea is to go with a drift-tube RF linac instead, which while more complex, solves some of the electron and other problems, or at least part of them. I've been accumulating the parts to do just that myself (with help from BillF).

Mine is coming along slowly. I plan to start with a single DC linac and build from there, but I'm chasing a leak in my system for it just now. Once I fix that, I will simulate the design in the phillips chapter 8 (borehole tube) mentioned here for initial testing. http://www.coultersmithing.com/data/Dat ... e/Pch8.pdf

In the attached pic, the lower part is a standard pfeiffer turbo pump station. The first "cross" on top of that has ports for a mass spec, a gage (pkr 251), and a valve and extension to allow this station to pump other things down via the tubing coupler pointing down - useful for making discharge tubes, transferring D from one tank to another after pumping down the adapter and the recieving tank etc.

Next is an adapter to 2.75, that also contains a backup gage, and two gas inlet solenoid valves. Yes, these aren't in the right place for a differentially pumped ion source linac (but I have more valves for later use).

The top cross has an 8 pin FT on top for instrumentation, a HF FT on the left (for the target), and provision on the right (tubing coupler) to insert the linac tube. A window in front lets me see a moveable target, which can be adjusted by a magnetic push-pull-turn device I built on the back.

So, you're not alone in having thought of this idea. Focus isn't going to be quite as trivial as what you show, but you knew that anyway - it will be some fun to work out. You'll get some electrostatic focusing too if you design the linac right.

The hope is, this setup will eventually let me play quite a few different games, I have plans....but as we know, many plans never quite make it to reality. I'd like, for example, to experiment with aligning the ion spins this way or that before they interact...hard, but theoretically possible. AFAIK, no one has explored this, but it might allow changing the ratios of the three DD reactions that occur. All existing numbers are based on random spins, but the well known conservation of spin laws indicate that these ratios ought to be modified if you have spin control (no, not the political type).

Another possibility with the 6 way cross on top is to build two beamlines that are really intersecting storage rings - while hard to get working in the first place, this handles that "what happens to the ions that miss interaction at the focus", for one.
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Chris Bradley
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Re: Back to building. Now with a new design.

Post by Chris Bradley »

Doug Coulter wrote:
> You should be able to get some reactions with this sort of thing
Maybe too much optimism in that particular encouragement? I'd like to see some numbers on the probability of a beam-on-beam collision. Would need focussing down to sub-Angstroms of beam width to get any significant percentage of beam particles interacting, would it not?
jaaz95
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Re: Back to building. Now with a new design.

Post by jaaz95 »

I think I'll stick with the regular linac instead of going with an rf design only because I know what my build limits are. Also I'm looking forward to the fun of getting the beams lined up with this. I knew going into this that it'll be hard as hell to get everything lined up. One idea i was toying with was having a virtual cathode in the middle to help direct things. But i realize that would be rather difficult. Also with two ion sources, the amount of particles being accelerated, the amount of interaction shouldn't be that low. Also what's kind of fun is that with minor modification if you invert the direction of one of the accelerators and you can accelerated ions at a solid target instead and get some interactions that way.
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Chris Bradley
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Re: Back to building. Now with a new design.

Post by Chris Bradley »

Justin Atkin wrote:
> I knew going into this that it'll be hard as hell to get everything lined up.
Better to presume 'impossible', perhaps? I suggest you design your kit so it can be easily re-configured to be a beam-target machine afterwards for further experimentation. The probability of getting two ions (especially in amateur-formed beams) to collide is so diminishingly small that you might be in for a shock!!

To a very cursory examination, one might suggest to examine the fusion cross-section for deuterium. Say it is 10 to 100 mbarns in the range of 10's to 100's keV. A millibarn is 10^-28m^2, so that is equivalent to a circle of diameter 2x10^-12mm across. 2 femtometers.

The next conundrum is that for most of the time your particles will scatter off each other in the beams. Scattering has a cross-section of some 10^-20m^2m about 8 oom greater than a fusion event. In a fusor scattered particles do get a bit of a chance to recirculate after losing some scattering energy, but in a beam-on-beam linac they would more likely be lost in the first substantial scatter.

As scattering is so much more likely than fusing, even if you can achieve a beam diameter of atomic dimensions, ions are more likely to be lost in their first lossy scattering collisions than in a fusor.

I'm not trying to dissuade you from your intended build at all, but I am encouraging you to make sure it is re-configurable for beam-target work so that you can aim for results with some fusion going on if you come to find it doesn't work out as you expect.

Good luck!
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Doug Coulter
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Re: Back to building. Now with a new design.

Post by Doug Coulter »

Yes, I think Chris might be being too pessimistic, since after all, fusors that usually seem to have much worse focus than is easily achieved in this sort of thing do work, after all. And in my case (well, my fusor is on the hot side of the ones here), a 3He tube is *too sensitive* to use quantitatively on the fusor at a foot away (an old B10 tube 2-3 feet from the action is just right, or a 1" hornyak at the shell). So it ought to do fine at a lower neutron rate for this. So...we'll find out and report the actuality, not the perhaps "not quite taking everything into account" theory.

And if that doesn't pan out, well, the numbers on that phillips borehole tube (beam on target) are darned impressive vs fusors (in neutrons/ma)...so we just stick a target in there.

I'm starting with DC too, but its troubles might be just as bad or worse than the RF, so I'm working on both, intending to wind up with RF, since it will get me closer to the energy I want without having to deal with super high voltages in air. Electrons won't be accelerated as much in that setup either, since they won't be in sync (different charge/mass ratio) with the drift-tube phase, nor will there be a target at a large negative DC voltage to emit electrons.

Just about anything that hits any metal that's negatively charged re the junk around it is going to emit copious electrons that will be drawn back through the linac - going the wrong way. You might get lucky and defocus or bend them before you use up all your power supply accelerating something you don't even want in there...Of course, if you bend them, you don't want to have them hit any of your insulators and put a charge on that either...electrons are a pain in this work, period.
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jaaz95
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Re: Back to building. Now with a new design.

Post by jaaz95 »

The original plan was that if this doesn't work out, have it re configurable to be a straight linac. Which is really really easy to do. I've wanted to play with a linac for a while but i figured before I do that, See if I can get some research done on how these things work for fusion between two beams. It's almost nice being one of far fewer working on this design because there's more untested territory. Sure that makes it harder but it also makes it more fun. That said I know there are plenty of challenges to work out. I'm very well aware of that. But I have no intention of giving up just because it's hard. If i did I'd be back where I was when I gave up the first time.

I'll probably look into an rf linac but I honestly doubt i'll ever build it. That said, who knows. And for detection I'm not sure what i'll use. I'll see what's viable. Would a bubble dosimeter be too "weak" to detect from this setup? I remember Will working with a very sensitive scintillater that seemed to work well. May give that a go. But the idea is to keep everything as low cost as possible. So the cheapest and most elegant solutions are the ones i'm looking for.
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