Talk-Polywell.org

Ah, thank you drmike!

I should have looked harder.

Yeah. I got the assignment and finished it before writing my latest tirade. Most of what I got out of that paper was confirmation of the gyroradius loss width and the renewed impression that Bussard erroneously thought he could turn a bi-conical cusp into a configuration with only point cusps by adding more coils. Is there something in particular you think I'm overlooking in there?

Art,

I've never worried much about this, because it seems impossible WB-6 could have gotten the neutron counts at those drive depths if WB trapping didn't happen.

It looks like the SCIF device referenced in the paper did provide some experimental data in this regard, but was relatively low-power. I would guess there is better WB trapping data from future models, but I haven't seen it. Maybe someone will share it, if it's not under lock and key.

That seems like a good summary of the concept. So I gather your main contention (at the moment) is that this won't actually produce all point cusps: it will leave line cusps where the coils are nearly tangent to each other. Is that a good summary of what you are saying?

Yes. That's the jist of it.

Gently speaking, have you read Bussard's 2006-9 IAC paper? In which he freely acknowledges the existence of line cusps in WB-6? He points out some other things regarding them and WB-6 but I don't want to misquote him so I point to the paper, its an easy read.

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Aero

Art has already said the IAC paper won't fly because it amounts to a kind of Fermat's Last Theorem if you are feeling charitable ("I have a truly marvellous proof of this proposition which this margin is too narrow to contain"), or "the dog ate my homework" if you aren't.

Well, thats very interesting. Dr. Bussard makes a point and Dr. Carlson agrees with him, now it is up to us to prove that they are both right. Do I correctly understand the issue here?

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Aero

Well, that's the starting point. The actual issue appears to be that Dr. Bussard thought the Polywell would still work even with line cusps, provided recirculation was allowed for, whereas Dr. Carlson thinks it won't, at least once you scale it up.

If we can reduce this to a disagreement about whether or not recirculation happens, we can call the question closed (pending experiment) and move on to recirculation.

I made an attempt here to demonstrate through physical reasoning that Bussard was correct. I'm still waiting for a response. I mention the Valencia paper a few times, but my argument doesn't depend on it.

Art - your question was "what is the difference between regular cusp devices and polywell." If you'd have read Bussard's paper, you would have seen this:


The positions of the "cusps" have nothing to do with his fundamental argument. I think a better way to question this work is to ask how he expects the counter currents to build up into the "wiffle-ball" mode. All the
assumptions are 1-D but to build up these currents requires 3-D analysis.

Oh, good! Have I finally found someone who can explain to me what Bussard was saying? I saw this statement and continued reading in anticipation, but I was not able to figure out why he thought the polywell was so different from (other) cusps. BTW, as I understand Bussard, the reduction of losses from line cusps and point cusps due to high beta effects - i.e., the whiffle ball mode - is also seen in the bi-conical cusp (i.e. 2-d).

Bussard felt that the addition of electrostatics made the polywell sufficiently different from the other cusp confinement systems. I think you need 4 coils in a tetrahedron as a minimum rather than a biconical form because you won't get the pseudo spherical E field portion.

If you try to chop it down from a 3D problem, I don't see how it can work. With just 2 coils, you have a 2D problem and there is no cross current. With "corners" you can have currents flowing opposite of the coil currents, but also coupling the different coils.

The problem I have with Bussard's analysis is that he never states how these currents arise, nor does he really describe where they flow.

Also, when he talks about "recirculation" he means within the coils. My reading of his stuff indicates that anything that gets past the coil radius is "lost". In that sense, it seems very similar to all other cusp systems.

By "electrostatics" do you mean having a plasma with a negative potential? Why shouldn't that be equally possible in a bi-conical cusp machine?

I don't understand. What do you mean by "cross current".

I think your interpretation of what Bussard said is untenable. In the Valencia paper, e.g., he says (my emphasis)

and

and

I think it is clear that Bussard thought the machines operated in a way we just decided was impossible. In fact, he thought they will not work any other way:


Side note: I was feeling a little embarrassed for thinking Bussard was concerned about the electron density outside the machine, when I knew that arcing depended on neutral density. While responding to your post, I found this in the Valencia paper (again, my emphasis):

I was confused about what denstiy was meant because Bussard was confused about it, too.

Personal opinion: Between the fact that we have decided that electrons lost through the cusps cannot recirculate outside the coils, and the fact that Bussard was confused about the dramatic difference between electron density and neutral density, we can pretty much forget everything Bussard thought about polywell physics.

Yeah. I'd love to see the current flow diagram of the plasma. Esp. the electrons. I don't think static analysis can get you the answer. It is a 3-D real time problem. I think that is all implied by the WB effect. It is quite possible that there is no way to do useful simulations until we actually know how the device works. i.e. we know what shortcuts are valid.

There is also the question of the difficulty of getting into the WB state. Is it path dependent? What are the parameters that give you the highest probability of entering the WB state? Or is it "natural"?

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Engineering is the art of making what you want from what you can get at a profit.

I tend to be of a somewhat similar opinion. I don't think you get "recirculation". I think you get oscillation.

It is an oscillating beam machine. The Dietrich paper (MIT) and his lab partner McGuire did some interesting work that tend to point in that direction.

However, the wrong explanation for something interesting is not unusual.

The question at this point is: How good was Dr. B. in the lab? That question will be answered soon.

_________________
Engineering is the art of making what you want from what you can get at a profit.