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Talk-Polywell.org • Significance of Electron Recirculation Revisited - Page 7
Page 7 of 10

Re: Dumb question

Posted: Tue Apr 06, 2010 2:03 am
by bcglorf

Posted: Tue Apr 06, 2010 2:15 am
by TallDave

Posted: Tue Apr 06, 2010 8:44 am
by Giorgio

Posted: Tue Apr 06, 2010 9:12 am
by icarus

Beyond me

Posted: Tue Apr 06, 2010 1:57 pm
by bcglorf
I don't think quasineutrality in the cusps is a death knell

I think it is, or is so close as to be hard to distinguish. At the narrowest point in the cusps, the potential voltage must be biased negatively leading back to the center. If it isn't, as Art has pointed out, you have nothing more than basic magnetic confinement, with unacceptable cusp loses. Given that the ions will be at very low energy in the cusps, the potential towards the centre doesn't need to be great, but it absolutely can't be neutral, or worse, drawing ions out where the magrid will slam them into the walls.

If my understanding above is correct, the only real hope I see is reducing the density and volume at the cusps enough that is possible. Bussard and Nebels comments leave me hopeful the WB effect may be doing that, but I'd like to hear more from Art on the hard theoretical limits on that. He seems pretty convinced they are a dead end, but at the same time Nebel doesn't strike me as deliberately deceptive and Art's argument should be elementary enough to Nebel that he has reason to disagree which I wish I knew enough to understand. I've been following in the hopes of a long shot, but also in the belief that nothing about the basic principles in the Polywell violated known physics.

Posted: Tue Apr 06, 2010 2:30 pm
by TallDave
bcglorf,

Well, you can have both quasineutrality and a well or gradient. You just can't have a very large disparity between the electron/ion populations, because that would require MV potentials.

It's true cusp confinement isn't good enough, but we don't really know for sure where the WB effect comes from. Bussard seems to have believed it was a geometric effect resulting from the electron pressure,

Rick seems pretty confident he's seen a WB effect. I'm generally more interested in explanations that don't rule out what Rick and Bussard claim to have measured.

But

Posted: Tue Apr 06, 2010 2:36 pm
by bcglorf

Posted: Tue Apr 06, 2010 2:39 pm
by Giorgio

Re: Dumb question

Posted: Tue Apr 06, 2010 2:51 pm
by Art Carlson

Posted: Tue Apr 06, 2010 3:33 pm
by TallDave

Learning to ask the right question

Posted: Tue Apr 06, 2010 4:07 pm
by bcglorf
But maybe only by enough to balance out the Magrid (what else is there to drive such potentials?).
That is just rephrasing what Art is saying. The limit on volume and density of electron dominated cusps is hard limited by the Magrid potential. What follows is the problem, density in the cusps is related to the density in the core. The question is does the upper limit on cusp density still leave room for viable density in the core? If I understand things at all, this is just a less accurate phrasing of Art's assessment:

Assuming good confinement requires that the cusp plasma contain predominantly electrons (and retaining for the first round the optimistic assumption of point cusps with radius rho_e), what is the maximum permissible density? If this value is not smaller than the density of ITER, for example, one might still have a hope of economic power production.

Thanks for your patience with me Art, I think that's exactly the question I wanted to get at, without knowing enough to even figure out how to ask it :). I don't imagine you have an equally clean answer to go with? Is there any set of circumstances that meet those criteria without violating known physics, even if the window is ridiculously small? I'm searching for the difference between violating the laws of physics, and merely pushing them to the utter edges of what is theoretically possible.

Re: Learning to ask the right question

Posted: Tue Apr 06, 2010 4:47 pm
by Art Carlson

Posted: Tue Apr 06, 2010 6:54 pm
by TallDave

Re: Learning to ask the right question

Posted: Tue Apr 06, 2010 6:55 pm
by bcglorf

Posted: Tue Apr 06, 2010 6:57 pm
by TallDave