Bismuth sphere in the center of a polywell?

Discuss how polywell fusion works; share theoretical questions and answers.

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JoeOh
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Bismuth sphere in the center of a polywell?

Post by JoeOh »

I was thinking about the diamagnetic properties of bismuth and a thought came to me regarding the polywell reactor. How strong would the magnetic field(s) have to be in order to levitate the bismuth sphere in the center. And also would the diamagnetic property of bismuth also repel the electron cloud to keep the bismuth from melting?

Assuming the sphere can maintain it's solid state in the center, will this help combat thermalization by keeping the electron cloud as a thin shroud around the sphere?

Also, has this been considered before? I seem to keep coming up with ideas (even though I do a forum search) that have been fooled around with.
I'd trade it all, for a little more :)

Nik
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Why bismuth ?

Post by Nik »

According to Wiki... ( Care: your mileage may vary)

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

... pyrolytic graphite will do it at room temperature with super-magnets.

Note, superconducting mags NOT required in this case...

===
Added: see...
http://www.davidwyatt.me.uk/maglev/

...which mentions that the ~3% tin in bismuth 'shot' cripples the diamagnetism.

kunkmiester
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Post by kunkmiester »

The sphere will give you the same trouble the grid gives a regular fusor--solid stuff in the middle absorbs too many ions.
Evil is evil, no matter how small

JoeOh
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Post by JoeOh »

What if the pure bismuth was coated in a thin layer of ceramic?
I'd trade it all, for a little more :)

KitemanSA
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Post by KitemanSA »

Why would you want a lump of cold material right in the middle of where you want your fusion to be? Not making sense to me.

JoeOh
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Post by JoeOh »

KitemanSA, for the diamagnetic property that Bismuth has to repel the electron cloud into a thin shroud to combat central thermalization.
I'd trade it all, for a little more :)

KitemanSA
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Post by KitemanSA »

Still not getting it. Diamagnetism repels magnetic fields which are nil at the center anyway. Certainly it WON'T be strong enough to repel the ions which means they will collide with the lump and lose all their energy. Nope, don't get it at all.

KitemanSA
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Post by KitemanSA »

JoeOh wrote:...combat central thermalization.
By the bye, check out the FAQ about annealing.

kunkmiester
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Post by kunkmiester »

What if the pure bismuth was coated in a thin layer of ceramic?
Not going to help--the ions fly through the center of the system. The sphere is in the center. Unless it itself is magnetic enough to deflect the ions without absorbing their energy, they will impact, and be removed from the system. It might even be worse than with the grid of a fusor.
Evil is evil, no matter how small

Nanos
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Post by Nanos »

> has this been considered before?

viewtopic.php?t=309

And perhaps related:

viewtopic.php?t=599

D Tibbets
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Post by D Tibbets »

Daniel Whitmire was involved in developing the theory of the CNO fusion cycle in hot stars. I don't know how bismuth fits into the picture.
P-P fusion is very slow and the rate increases only moderately as the temperature goes up (shallow crossection curve). This fusion rate in the Sun is ~ 20 orders of magnitude slower than D-D fusion at perhaps 10,000 eV. I don't know the actual scaling rate for P-P fusion, but I believe it is in the neighborhood of perhaps 10X for each doubling of temperature. At the Sun's temperature of ~ 15,000,000 degrees C (~ 1200 eV) the CNO cycle fusion rate is even slower (accounts for ~ 1 % of the fusion in the Sun. But, as the temperature goes up the CNO fusion rate increases extreamly fast. If the Sun was 2 million degrees hotter the CNO cycle would catchup with the P-P reaction and then leave it in the dust. This is why larger hotter stars burn mostly through the CNO cycle. The scaling rate for CNO fusion is ~ 16,17,18,or 19th power of the temperature increase I've seen all those numbers). If temp increased from 1200 eV to 2400 eV (doubling of temperature) The CNO fusion rate would increase by 2^18th power ( or ~ 250,000 times) Double the temperature to 48,000eV and the rate would go up a corresponding amount. One source I saw described the hydrogen fusion through the CNO cycle reaching peak levels of ~ 1% of the D-D fusion rate at several hundred KeV. That is about as good as it can do (and even further behind the P-B11 reaction at those energies).
As suggested by Chrismb, using Nitrogen 13 as a feed stock with hydrogen may be somewhat faster, though I dought it could catch deuterium. This would not be a catalytic process (as the nitrogen is not recycled), but it could avoid several slower steps that are involved in the overall CNO cycle, and who cares if you have plenty of nitrogen 13 around.
I once looked for how bismuth enters into this picture, but I didn't find anything. It is not directly listed as a nessisary ingrediant in either branch of the CNO reaction. Perhaps (vigerous hand waving) it modifies one of the rate limiting steps (involving one of the intermediate oxygen isotopes I believe) and therefor accelerates the recycling of the carbon , making it available for the next cycle). This would certainly help an interstellar ram scoop space craft, as only small amounts of carbon (and bismuth) would be needed so long as you could reclaim and recycle it.And, just like starting with N13, if you continually feed in new carbon, presumably the rate could be pushed to higher levels. The Sun does not have this advantage as it is stuck with the relative small amount of carbon that it started with. If the carbon was not recycled, it would quickly (in stellar time scales) be consumed and the reaction would grind to a halt.

Dan Tibbets
To error is human... and I'm very human.

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