Electrostaic cone traps/lenses for pure beam on beam

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Electrostaic cone traps/lenses for pure beam on beam

Postby Doug Coulter » Wed Aug 25, 2010 2:04 pm

I found some papers on electrostatic cone-trap mirrors that got me a bit fascinated with the idea of beam on beam fusion that solves some of the thermalization and other problems ChrisMcB reminds us of. No one has done fusion with either yet, but it seems like this has some potential with appropriate additions. What's neat about electrostatic-only things such as are described here is that you can have counter-motion beams, particularly in the "loop" configuration. One could add bunching/re-acceleration timed correctly at a point (or two) on the loop to keep things moving and in focus so things that missed would get more chances at recirculation. Even though the beam densities are on the low side here, it looks like it's worth playing with a least a little, as the numbers on how many passes ions can make before being lost to collisions (when they set up to avoid those!) are pretty darn high. Of course, in our case we want collisions, ion on ion, they are mostly worried with storage times and neutrals scattering things out of the beam(s) in these papers. I found a reamer at McMaster that "just happens" to cut the angles they are using in these papers, which I kind of doubt was complete co-incidence, and am starting to make some up for trial in my big tank...why guess when you can know?

ConeTrap.pdf
Cone trap, simple design
(1.47 MiB) Downloaded 636 times


This first paper describes the simplest possible system, maybe not so useful, but it makes the basic understanding needed clear.

electrostatic ion storage ring.pdf
Cone ring, what you need for beam on beam with some control over it all.
(935.86 KiB) Downloaded 632 times


Once you understand the first one, this is what you'd really want to build, but add a couple of bunchers to keep the particle speeds up and refocus them as they go around. Timing would of course be important, but at least with this design you don't need two rings to collide same-charged particles.

More when I know more -- I'm still doing parameter sweeps on fusors at the moment and working on some really serious data acquisition and analysis tools which will be good
no matter the final approach I settle on. Ideas are always far easier to have than real working things ;)
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: Electrostaic cone traps/lenses for pure beam on beam

Postby chrismb » Wed Sep 01, 2010 5:01 pm

Hmmm.... the cone-cone trap is interesting... but only as far as realising this is actually a fusor with a single central loop, as per Wilfred H's experiment on; http://www.fusor.net/board/view.php?bn= ... 1201570293 .

My interpretation of the limited success of Wilfred's fusor is that this arrangement may provide more opportunity for beam-on-beam, but it also increases the likelihood of larger scattering angles. What happens under scattering should be, I think, a primary consideration and not a secondary one to 'likely' ion paths. Energy is sapped from the ions and then they can no longer remain in the beam. And, of course, not forgetting the dreaded 'space charge' limitation.

Maybe this kind of set up might work better with some 'magnetic limiting', with a solenoid added; wrapped around the whole thing long-ways and energised, then particles travelling along the field lines would tend to keep going whereas those not so would slow and drop out. I think both of these set-ups are very lossy and highly selective, as they are, so that the total number of ions that end up 'trapped' from out of the ion injection guns are a very small 'lucky few'. A bit like a cyclotron - very inefficient.

Personally, 'efficiency' is the mantra that I think should enter the mental thinking processes of fusion scientists - and amateurs alike. It's all balls-out power and size that people seem to go for, and though they may have the same ultimate goal of efficiency lurking in the back of their motivations, it is not what drives them and so they drive in the wrong direction! I reckon once folks with a[ny sort of] fusion reactor say "OK, this is my reaction rate, and now I need to see what variables the system is sensitive to where I can keep the reaction rate the same but with less power input". I think it drives a different [and more appropriate] set of questions.
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Re: Electrostaic cone traps/lenses for pure beam on beam

Postby Doug Coulter » Wed Sep 01, 2010 5:50 pm

Nope, you completely missed it on the first para. (Sorry, don't mean to be harsh). The cone trap is not self ionizing, is re-focusing, and runs at at least 3 orders magnitude less pressure than a fusor for low scattering off neutrals. 100% ions, and vacuum pump take the rest. No electrons. It's nothing at all like a fusor in concept, operation, or particle statistics.

I did a similar thing to Wifred (but those are sure nice pix he took) here with two rods (remember, I do cylinders). I got fairly good results, but nothing special at all, not as good as a full grid.
I'm not sure what basis you are using when you say "increased large angle scattering", though. With any number of "beams" you have impact parameters all over the place, thus high angle scattering no matter what, if I understand this correctly. At least until you get beams so tight they are one nucleus across -- good luck with that!

I am talking about (time) bunching, not the continuous flow of ions in all directions discussed in these papers (they just fill the trap and let them re-distribute uniformly from Coulomb repulsion). With bunching the density at the interaction point can be temporarily much higher, and with re-bunching you can keep it that way for a lot of roundy-rounds (of course, all that is "in theory"). Precisely the same idea as a regular storage ring, except it's all electrostatic, so you don't need two to make a beam-collider. In other words, it shares some things with your patent. These want to run well below e-6 millibar for long storage times.

Now, I agree 100% on the efficiency thing. Too many people just want "more" -- even if efficiency is going down as they get it. Heck, if that's all they want, why not go with something proven to get "more" like a borehole tube or some other linac variation? I thought the attraction of a fusor was that it could potentially be more efficient; but no one has gotten one better than a borehole tube yet -- even at my older peak, in a strange operating mode, I only got close, didn't get better than those, at least not for sure. I have seen some things recently that might be gain, in pulses ,though -- and the big enormous question there is: Is the power it draws between the pulses necessary to set up initial conditions? If not, I'm actually at gain now. If so, the question becomes "can we get those conditions some more efficient way"? In this mode, with deliberate perturbation of the fusor normal "equlibrium" I'm at ~3 m n/s, but the duty cycle when they come out is astonishingly low -- many-many thousands to one. I am reduced to using activation to measure that, as the very-sub-uS bursts are far too fierce for any other detector to measure, other than to show they are happening at all. Even a 5ns response phototube/scint doesn't resolve them. You just get one really big pulse per burst.

Efficiency, Q, whatever, is one of the reasons I started this forum, because I want efficiency, or gain, whatever you want to call it -- useful power output? People on that other one seem only to be interested in a neutron source....you never win if you give up right at the start! I just couldn't take that level of defeatism. Surely you can say "yes, this is really-truly-extremely hard" without just giving up completely as many seem to have done there. I am not interested in simply copying someone's recipe and trying to get just the the same results. Sure, I do that to -- replication is at the heart of good science, but only if you then move forward.
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: Electrostaic cone traps/lenses for pure beam on beam

Postby chrismb » Fri Sep 03, 2010 8:15 am

Doug Coulter wrote:Nope, you completely missed it on the first para. (Sorry, don't mean to be harsh). The cone trap is not self ionizing, is re-focusing, and runs at at least 3 orders magnitude less pressure than a fusor for low scattering off neutrals. 100% ions, and vacuum pump take the rest. No electrons. It's nothing at all like a fusor in concept, operation, or particle statistics.


er.. well, clearly if you operate a fusor at the same pressures then the same comments would apply. I was just trying to say that, all else being equal, this is a single loop fusor.

I would suggest you would get the same as is desribed in the paper if you were to operate a single loop fusor at the same pressures.

Point is, as we all know, the space charge in the beam fights the focussing provided by this arrangement of ion-optics, and I don't think you're gonna ever see much in the way of total ion numbers. Pump the ion numbers up, you get more scattering, more ingress of electrons to neutralise the bigger well (Gauss), the generation of a neutral background, &c.... = fusor.

The other thing to 'mind-experiment' on is to then say; OK, we have one beam here. Let's have two beams crossing each other, and maybe a third or fourth. So you add more loops in different axes and.. oops, we've just re-invented the spherical grid fusor!
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Re: Electrostaic cone traps/lenses for pure beam on beam

Postby Doug Coulter » Fri Sep 03, 2010 10:32 am

Yes, but -- and it's a big but, here we can have bunching and short focal length optics that help with the space charge, and since the beam stays focused for such a short bit of time-space, the Coulomb effect of the space charge has less time to act on the beams at the interaction zones. After passing through focus at the interaction point, the beams re-expand (and of course some part is lost to scattering outside the re-collection optics) and are at that point low space charge density and much easier to handle and get collimated again. But this, unlike a fusor, doesn't have loose neutrals and electrons and negative ions in it anywhere, which should be a great help over the normal fusor -- it's a beam colliding device, with regathering of as much of the scattered beams as possible, in other words, a less clever way to do the same thing you've been proposing in nearly all ways -- just simpler to build and test this way.

The key words in my original post are along the lines of adding bunching, focusing optics to the designs in the papers so we have high density at just the point of collisions and we control where and when those are, not just a random fill of ions with random distributions. Left to it's own devices, that cone trap ring winds up with them spread out uniformly and all going the same direction -- no collisions at all. The idea is to get bunches to counter-rotate in there, duplicating your idea, but on a simpler, smaller scale. In your case, the two circular beams don't have to counter rotate, as they "grind" at the edges, like two gears turning the same way -- here we need counter rotation, as the geometry is different. This idea also lacks the "wind the whole thing up into a toroid" that yours has -- it's a walk-before-you-run kind of thing I'm describing here. Probably one heck of a lot easier to do diagnostic measurements on as well -- they show some tricks in the papers on that.

This whole thing is one attempt to limit the bad things about space charge by keeping the beams mostly not-dense except for short time-spaces around the desired interaction zone(s).
With uniform beams, all your objections do apply (more). But that's not the proposal here.

Further, unlike a DC drive fusor, we actively manage the beams as they go around -- we don't depend on them slowing and then falling back in like magic, and in focus, in some hoped for automatic recirculation as fusor proponents do. Every pass around the loop they are re-focused and re-bunched and re-accelerated actively -- again, just like your patent, simply done in a somewhat different way.

You need to get that up here Chris -- establish that it was your idea and get the meme going! I still like it myself. I'm just thinking more along the lines of baby steps on something easier to diagnose troubles with and learn on. If imitation is flattery, you should be feeling a little flattered at this point.
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: Electrostaic cone traps/lenses for pure beam on beam

Postby Jonathan Schattke » Tue Oct 14, 2014 7:19 pm

It was a University of Wisconsin effort, reproducing the Hirsch Six Ion Gun Fusion Experiment, in the last few years.
http://fti.neep.wisc.edu/iec2009/talks/ ... ianegl.pdf
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