The problem with ion convergence

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

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The problem with ion convergence

Postby Art Carlson » Sun Jul 06, 2008 7:54 am


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Postby tonybarry » Sun Jul 06, 2008 11:27 am


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Re: The problem with ion convergence

Postby Roger » Sun Jul 06, 2008 5:50 pm

I like the p-B11 resonance peak at 50 KV acceleration. In2 years we'll know.

Art Carlson
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Postby Art Carlson » Sun Jul 06, 2008 7:25 pm


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Postby Roger » Sun Jul 06, 2008 7:45 pm

I like the p-B11 resonance peak at 50 KV acceleration. In2 years we'll know.

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Postby tombo » Mon Jul 07, 2008 6:41 pm

Yes the surface of the well will be "lumpy".
It follows the fields which are "lumpy".
Indrek has an interesting plot of it at

Also it cannot be too spherical. Otherwise the magnetic field would be concave toward the plasma causing an instability.
I think that one of the failure modes is when the plasma pushes the field out far enough to make one of the magnetic arches concave toward the plasma and the well "blows out".

It seems to me that the dodecahedron, the icosahedron and the other higher ordered polyhedrons have more resistance to this failure mechanism than the cube, because they start out with the fields curved more strongly.
-Tom Boydston-
"If we knew what we were doing, it wouldn’t be called research, would it?" ~Albert Einstein

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Postby drmike » Tue Jul 08, 2008 2:18 pm


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Postby Art Carlson » Sun Jul 13, 2008 7:47 pm


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Postby drmike » Sun Jul 13, 2008 8:22 pm


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Postby rnebel » Sun Jul 13, 2008 9:01 pm

First of all, I don't think it is correct to assume that the electrostatic field will collapse into a Debye sheath at the edge. That's an l.t.e. argument applied to a non-l.t.e. plasma. The shape of the potential well depends on the detailed balance of the electrons and the ions in the core. That's one of the peculiar things about these systems.

Secondly, it's worth noting that the power density depends AT MOST linearly on the compression (or convergence) ratio. The Langmuir solutions (no angular momentum) scale like 1/r**2. Unless you have huge convergence ratios (like the Hirsch Poissors) the effect isn't huge. We don't assume huge convergence ratios when we scale the machine.

Finally, the only way to do the "correct" calculation is to do the full bounce-averaged Fokker-Planck like Chacon did. Where the electrons/ions are when they collide makes a huge difference and determines whether or not they gain angular momentum (which is what determines the convergence ratio).

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Postby Art Carlson » Mon Jul 14, 2008 11:33 am


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Postby Art Carlson » Mon Jul 14, 2008 12:02 pm



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