Carl, thank you for the advice.
I will be doing a brief bit of research and get back to all of you with the geometry that I will eventually submit to SIS and my contact there so long as there is enough support.
I was considering spherical cages, so the example will most like be of this species.
James
SimIon and Fusor Simulation
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James Parkin
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- Real name:
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Dan Tibbets
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Re: SimIon and Fusor Simulation
A few links that may or may not have useful information themselves or in their bibliographies
http://ssl.mit.edu/publications/theses/ ... chCarl.pdf
http://fti.neep.wisc.edu/static/TALKS/1 ... anmeye.pdf
http://fti.neep.wisc.edu/static/TALKS/1 ... hnkipr.pdf
Pessimistic discussion of IEC devices from an energy balance perspective.
http://fsl.ne.uiuc.edu/IEC/Nevins,%20Ph ... 995%29.pdf
http://fsl.ne.uiuc.edu/IEC/Rider,%20Phy ... as1995.pdf
A more optimistic analysis.
http://www.mendeley.com/research/a-boun ... n-devices/
and
http://www.sciencedirect.com/science/ar ... 9199963945
The abstract of this article explains things clearly
Dan Tibbets
http://ssl.mit.edu/publications/theses/ ... chCarl.pdf
http://fti.neep.wisc.edu/static/TALKS/1 ... anmeye.pdf
http://fti.neep.wisc.edu/static/TALKS/1 ... hnkipr.pdf
Pessimistic discussion of IEC devices from an energy balance perspective.
http://fsl.ne.uiuc.edu/IEC/Nevins,%20Ph ... 995%29.pdf
http://fsl.ne.uiuc.edu/IEC/Rider,%20Phy ... as1995.pdf
A more optimistic analysis.
http://www.mendeley.com/research/a-boun ... n-devices/
and
http://www.sciencedirect.com/science/ar ... 9199963945
The abstract of this article explains things clearly
Dan Tibbets
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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
- Contact:
Re: SimIon and Fusor Simulation
I think what you run into is a matter of sheer scale, like peeing into the ocean and expecting to see the level rise.
I gave you the standard dimensions, surprised no one else did. Chamber, sphere, 6" ID. Grid, three circular loops, about 1" OD, some are a little smaller, down to 3/4" or so. Grid in the center of course, and perhaps a small stalk from the chamber edge up to it -- some insulate that, some don't.
The issue is, it's not that there's a collision or two during a simulation. There are perhaps thousands per pass of a particle in some cases, and unless you can simulate it all, you can't trust the results for "any". Things get not-linear quick if for example, a bunch of neutralized ions gather in the grid center, as it appears they do from some other experiments. It's an all or nothing thing. If you can't do it at the real gas/ion density, you just can't do it, you're not simulating a fusor, but something else we don't (or can't) build.
The reason for the skepticism is experience. Many simulations have been done, then the gear built based on those predictions didn't work anything like the simulation predicted, not close, not in the same ballpark, not in the same universe. It's been going on for years -- some of it is mentioned here if you search (which would also have found you a lot of info on dimensions, gas pressures, voltages, grid geometries, you name it, it's here).
It got so bad, that most who do simulations just write papers, but never build anything, because even they know by now it's pointless. And those who build things, and spend time and money and effort making them work are rightly suspicious when they see all these simulations that seem to closely match things they've tried for real and in person -- but don't correctly predict what they actually saw when they did the real build. It's just the sorry state of the art at this point. No one's going to put you down if you do a simulation that indicates that changing this or that would improve things, then you build it and prove you were right. There's just so very little of that that's ever actually happened.
In fact, I can't think of a single case. I don't think it's impossible, just very difficult, and most aren't that willing to waste yet more time on it -- it's a "you first" kind of thing at this point.
I know my own practical lab experience has overwhelmed my own understanding so many times that I no longer depend on it so much. What seems "it's obvious how it ought to be" has been flat wrong too many times. Emergent behavior in this system is fierce and only tends to be obvious in hindsight.
Since some of us have "simulators" that run in real time, with the real stuff, warts and all, we just do that these days. If SIMION improves to the point where it can be trusted, that would be great news indeed -- but we're not there yet, or so I think. Take those numbers above (they are from Richard's fusor) and see what you get! We already know what he gets. That would be the first, necessary baby step to moving forward.
Then you can try my setup, which is a cylinder grid, 8 eqispaced .040" diameter rods 2.5" long, 7/8" OD, with graphite endcaps, fed HV from one end, the other endcap with a 3/4" hole in it, in a long 6" ID pipe, with one end open to a much larger tank -- and depth to the big tank is critical adjustment, the grid end being a little recessed working the best. It seems to work a little bit better than most of the spherical ones do, but not a lot. If your trajectories match what I see with various probes, I'll be real impressed, because I was quite surprised myself when I actually measured some things (and I have a lot more to measure before I spout any useless theories about that).
I gave you the standard dimensions, surprised no one else did. Chamber, sphere, 6" ID. Grid, three circular loops, about 1" OD, some are a little smaller, down to 3/4" or so. Grid in the center of course, and perhaps a small stalk from the chamber edge up to it -- some insulate that, some don't.
The issue is, it's not that there's a collision or two during a simulation. There are perhaps thousands per pass of a particle in some cases, and unless you can simulate it all, you can't trust the results for "any". Things get not-linear quick if for example, a bunch of neutralized ions gather in the grid center, as it appears they do from some other experiments. It's an all or nothing thing. If you can't do it at the real gas/ion density, you just can't do it, you're not simulating a fusor, but something else we don't (or can't) build.
The reason for the skepticism is experience. Many simulations have been done, then the gear built based on those predictions didn't work anything like the simulation predicted, not close, not in the same ballpark, not in the same universe. It's been going on for years -- some of it is mentioned here if you search (which would also have found you a lot of info on dimensions, gas pressures, voltages, grid geometries, you name it, it's here).
It got so bad, that most who do simulations just write papers, but never build anything, because even they know by now it's pointless. And those who build things, and spend time and money and effort making them work are rightly suspicious when they see all these simulations that seem to closely match things they've tried for real and in person -- but don't correctly predict what they actually saw when they did the real build. It's just the sorry state of the art at this point. No one's going to put you down if you do a simulation that indicates that changing this or that would improve things, then you build it and prove you were right. There's just so very little of that that's ever actually happened.
In fact, I can't think of a single case. I don't think it's impossible, just very difficult, and most aren't that willing to waste yet more time on it -- it's a "you first" kind of thing at this point.
I know my own practical lab experience has overwhelmed my own understanding so many times that I no longer depend on it so much. What seems "it's obvious how it ought to be" has been flat wrong too many times. Emergent behavior in this system is fierce and only tends to be obvious in hindsight.
Since some of us have "simulators" that run in real time, with the real stuff, warts and all, we just do that these days. If SIMION improves to the point where it can be trusted, that would be great news indeed -- but we're not there yet, or so I think. Take those numbers above (they are from Richard's fusor) and see what you get! We already know what he gets. That would be the first, necessary baby step to moving forward.
Then you can try my setup, which is a cylinder grid, 8 eqispaced .040" diameter rods 2.5" long, 7/8" OD, with graphite endcaps, fed HV from one end, the other endcap with a 3/4" hole in it, in a long 6" ID pipe, with one end open to a much larger tank -- and depth to the big tank is critical adjustment, the grid end being a little recessed working the best. It seems to work a little bit better than most of the spherical ones do, but not a lot. If your trajectories match what I see with various probes, I'll be real impressed, because I was quite surprised myself when I actually measured some things (and I have a lot more to measure before I spout any useless theories about that).
Why guess when you can know? Measure!
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James Parkin
- Posts: 25
- Joined: Thu Sep 22, 2011 8:37 am
- Real name:
Re: SimIon and Fusor Simulation
Cheers, for your time and the dimensions you've given me.
I have had a good long look at your forums and have found many a design, but I felt I wasn't experienced enough to pick a particular setup for the simulator and didn't want to make a mistake or pick an option that would be pointless to simulate, etc.
I am aware of the issues involved with fusors and their complexity and I'm not naive enough to know that I can easily simulate a fusor's operation, I'm just trying to help provide some tools that *might* help, or be a good place to start to understand fusors.
As I have never built a fusor, I thought it would be ridiculous to give schematics representative of the fusor community. Fortunately I might actually be able to rectify this in the near future as I have been accepted to study at Imperial College London, at which there is a chance I might be lucky enough to have access to a fusor.
If SimIon add the fusor example swiftly I will get back to you with the results.
Regards
James Parkin
I have had a good long look at your forums and have found many a design, but I felt I wasn't experienced enough to pick a particular setup for the simulator and didn't want to make a mistake or pick an option that would be pointless to simulate, etc.
I am aware of the issues involved with fusors and their complexity and I'm not naive enough to know that I can easily simulate a fusor's operation, I'm just trying to help provide some tools that *might* help, or be a good place to start to understand fusors.
As I have never built a fusor, I thought it would be ridiculous to give schematics representative of the fusor community. Fortunately I might actually be able to rectify this in the near future as I have been accepted to study at Imperial College London, at which there is a chance I might be lucky enough to have access to a fusor.
If SimIon add the fusor example swiftly I will get back to you with the results.
Regards
James Parkin
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James Parkin
- Posts: 25
- Joined: Thu Sep 22, 2011 8:37 am
- Real name:
Re: SimIon and Fusor Simulation
Hi, I have spent a bit of time looking through all his simulations.
They are very intriguing and I have already, asked him about what interactions he simulates and in what way he simulates them, for example using Laplace, etc. He is actually harnessing a particle engine and using graphic card based processing, but I'm not sure how accurately he is simulating the particles till I found out exactly what he is doing, as I have seen some simulations that look good but it turns out that sometimes the physics/maths is nonsense and this has turned me into a bit of a skeptic as to where people draw the line between simulation and graphic representation of a system.
Regards
James Parkin
They are very intriguing and I have already, asked him about what interactions he simulates and in what way he simulates them, for example using Laplace, etc. He is actually harnessing a particle engine and using graphic card based processing, but I'm not sure how accurately he is simulating the particles till I found out exactly what he is doing, as I have seen some simulations that look good but it turns out that sometimes the physics/maths is nonsense and this has turned me into a bit of a skeptic as to where people draw the line between simulation and graphic representation of a system.
Regards
James Parkin