The consequences of quasi-neutrality in the cusps

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

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Postby icarus » Sun Feb 08, 2009 10:32 pm

Last edited by icarus on Mon Feb 09, 2009 1:53 am, edited 1 time in total.

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Ars artis est celare artem.

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Postby Art Carlson » Mon Feb 09, 2009 9:00 am


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high-density quasi-neutral plasma from throat to wall

Postby Art Carlson » Mon Feb 09, 2009 9:30 am

Between the cusp and the wall we have need to drop a few tens of kV. What does the potential profile look like. I think most of us would expect it to be linear or at least a graceful arc. I have decided that can't be the case. You can apply my previous calculation almost unchanged, or you can just look at it this way: Since there is no perpendicular magnetic field, both species will react ballistically to any electric field. That is, one species will roll downhill, getting faster and less dense, the other will run uphill, getting slower and more dense. This would lead to a violation of quasi-neutrality and those MV fields that will spoil your day. If it were any other way, then confinement of a plasma for fusion would be easy.

No, I'm afraid both the electric potential and the plasma density in the flux tube of the cusp will have to be pretty much flat almost all the way out to the wall. You can have a magrid if you like, and it should (in principle) be able to keep the electrons from getting to the wall, but they will get most of the way there before bouncing off the Debye sheath.

This is my next claim: Not only does the cusp throat contain a high-density, quasi-neutral plasma, the entire cusp flux tube from the throat nearly to the wall does as well.

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Postby alexjrgreen » Mon Feb 09, 2009 10:23 am

Ars artis est celare artem.

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Postby Art Carlson » Mon Feb 09, 2009 11:36 am


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Postby alexjrgreen » Mon Feb 09, 2009 12:22 pm

Ars artis est celare artem.

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Re: high-density quasi-neutral plasma from throat to wall

Postby jmc » Mon Feb 09, 2009 6:22 pm


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Postby jmc » Mon Feb 09, 2009 6:24 pm


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Re: high-density quasi-neutral plasma from throat to wall

Postby Art Carlson » Mon Feb 09, 2009 7:53 pm


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Postby Art Carlson » Mon Feb 09, 2009 8:18 pm



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