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If polywell fusion is developed, in what ways will the world change for better or worse? Discuss.

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D Tibbets
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Postby D Tibbets » Sun Jun 14, 2009 9:27 pm

MSimon wrote:
93143 wrote:
D Tibbets wrote:And, what about the deuterium contamination in your hydrogen supply?


I don't know - it's his figure, not mine.

Also, the deuterium fraction in seawater is already around 1/6000, resulting in a D-D fusion rate down seven and a half orders of magnitude from pure deuterium even if you do nothing at all to get rid of it. Doesn't sound like much of an issue even with moderate isotopic separation...


I wondered if there was an expotential element to the D-D rate vs relative population portion- looks like there is. Also, any deuterium present would possibly react with the much more common protons to produce He3 and a gamma ray. But the rate may be so low that it is no more significant than the extreamly rare D-D reactions. I briefly looked but I found no mention of possible D- B11 reactions.

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

93143
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Postby 93143 » Mon Jun 15, 2009 4:33 am

For any fusion reaction A+B->something, the reaction rate is proportional to how many ions of type A are flying around smashing into stuff, multiplied by how many ions of type B are present to be smashed into by type A ions.

In other words, density squared.

Unless the cross section for D-p is very high, I can't imagine it being a problem. It's already about four orders down from the main reaction just by virtue of the low D density, even without isotopically pure fuel. This (1e-4) happens to be roughly the odds of p-11B producing a stable 12C and a 16 MeV gamma, so if you purify the fuel at all, the gamma emissions from D-p should drop into the noise floor.

However, according to the Wikipedia article on aneutronic fusion, D does react with 11B to produce 12C and a neutron. So the purity of the fuel may be fairly important depending on the cross section for that reaction.

tombo
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Postby tombo » Mon Jun 15, 2009 7:10 pm

Does reverse osmosis reduce the D fraction? By how much?


RO should not touch the isotope distribution. It is purely physical chemistry. (I work with RO water purifiers these days.)

Even a Palladium hydrogen purifier which makes 99.999995% pure hydrogen sees D pretty much the same as H. Remember the Pons & Fleishmann experiments?
-Tom Boydston-
"If we knew what we were doing, it wouldn’t be called research, would it?" ~Albert Einstein

MSimon
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Postby MSimon » Mon Jun 15, 2009 7:17 pm

tombo wrote:
Does reverse osmosis reduce the D fraction? By how much?


RO should not touch the isotope distribution. It is purely physical chemistry. (I work with RO water purifiers these days.)

Even a Palladium hydrogen purifier which makes 99.999995% pure hydrogen sees D pretty much the same as H. Remember the Pons & Fleishmann experiments?


I would expect some effect due to differential mobility and electric potentials. But I'm not deep enough into that these days to figure out what the likely size of the effect is.
Engineering is the art of making what you want from what you can get at a profit.


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