Is there a vacuum pumping technology availible that can...

Discuss the technical details of an "open source" community-driven design of a polywell reactor.

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KitemanSA
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Post by KitemanSA »

Yeah. What he said.

D Tibbets
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Post by D Tibbets »

What is ECR?
Electron Concentrated Region, Energy Conserving Reality, Entirely Confusing Relationship...?
:D

Dan Tibbets
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93143
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Post by 93143 »

http://en.wikipedia.org/wiki/Electron_c ... _resonance

This was mentioned a long while back by knowledgeable people, possibly actual Polywell researchers (I can't remember). I'm not an expert in this field, but the claim was that the mean free path of a neutral would be x, where x was impressively small... possibly the main application here would be to prevent recombination, since there are so many fast electrons already... or perhaps the dual-electron-population idea comes into play, and this works on the cold one, for cross-section reasons? Anyway, that's what that means...

ohiovr
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Post by ohiovr »

93143, If in 10 years I learn 1/10th as much as you I will be a very happy man.

chrismb
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Post by chrismb »

93143 wrote:
chrismb wrote:I'm certainly in no position to say yes or no, but the collisions are meant to happen mostly in the centre of the reaction voulme, and the free electrons constrained further to the interior (I thought). Why would ionisation happen more where the ion density is less, and further away from the region of slightly-over-net electrons?
It sounds like you've misunderstood the proposed geometry of the wiffleball. The idea of ions being accelerated towards a small central magnetically-confined electron-rich region, which they are initially outside, is wrong. That's what it sounds like you are describing.
The issue is that there are electrons and ions, and they are mobile in the waffleball. So, as they transit that ball, so their density will increase as they all converge in the centre. Nothing to do with where the acceleration and/or charge regions are, this is just plain congestion of the particles on the surface of a sphere all passing down to a central focus.

If the argument is now, also, that the electrons stay hanging around the edge and don't transit through the waffleball, then why would the ions at the edge head towards the centre when there is a locally higher negative charge at the edge? That seems to me to be just plain stretching the idea of 'space charge' far too far.

If all this were so, then why doesn't it already happen with a toroidal confined volume? Surely if it were likely to happen, then why don't electrons gather around the outer magnetic surfaces of a tokamak core, with ions being pulled in by some sort of space-charge? The electrons in a tokamak are perfectly well confined within a diamagnetic volume, just like you appear to be describing. Does this mean that with just a quick spurt of electrons injected into a tokamak volume that it might start operating along the lines of a Polywell? I don't see the different, short of the actual shape and the electron/ion injection - excepting that a toroidal magnetic field has no cusps.

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Post by MSimon »

Don't forget the electrons added by the electron guns. They will have (Grid voltage)eV of energy as they enter the reaction space.
Engineering is the art of making what you want from what you can get at a profit.

93143
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Post by 93143 »

chrismb wrote: The issue is that there are electrons and ions, and they are mobile in the waffleball. So, as they transit that ball, so their density will increase as they all converge in the centre. Nothing to do with where the acceleration and/or charge regions are, this is just plain congestion of the particles on the surface of a sphere all passing down to a central focus.
Yes. That is quite true. But it is also true that for a globally-circulating system like this, assuming steady-state operation, the areas with the highest fractional residence time per pass will tend to have the highest particle density. Combine this with the inverse-square effect and you find that the density of the ions has two maxima - the edge region and the core.

As a matter of fact, it occurs to me that there may be an excess of ions at the edge due to the higher fractional residence time there as compared with the electrons (which are fast at the edge, and don't slow down during magnetic deflection). [This means that what I read you as describing is not quite as wrong as I thought it was, but it's still wrong.] The electrons have their slowest point much lower down, with the smaller radius at that point accentuating the traffic congestion (perhaps some electron annealing takes place there?)...
If the argument is now, also, that the electrons stay hanging around the edge and don't transit through the waffleball, then why would the ions at the edge head towards the centre when there is a locally higher negative charge at the edge? That seems to me to be just plain stretching the idea of 'space charge' far too far.
No, I specifically noted that since the electrons are high-energy and radially-directed at the edge, they do NOT form a sheath; rather they penetrate deeply into the wiffleball. There may actually be two electron density maxima, now that I think about it; one at the edge of the virtual anode where the electrons are at their slowest (or rather slightly further in because of the inverse-square effect), and one at the centre. Perhaps this is related to the "multiple well" referenced in that Japanese paper I never bothered reading...?

Anyway, in this scheme an ion will definitely see a net negative charge below it for a considerable portion of its transit.


Ionization was expected to happen very quickly in the edge region. This may be due to the sometimes-referenced secondary population of electrons (the ones from ionization are much slower than the drive electrons, and they will probably form some sort of sheath) combined with ECR, or some other effect I'm not thinking of. I'm not sure how this lines up with the idea of using ion guns, but I'm sure we'll eventually find out how, exactly, they intend to fuel a power reactor, and why...

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