reddit: We are nuclear fusion researchers, ask us anything

[KitemanSA]

Excellent. Have beams, but no beams.

STARTS WITH beams, doesn't want them, destroys them, gets radial electron flow. Good stuff.

No. Destroyed beam converts to background electrons and getting not radial but chaotic (random) motion interacting then with new portion of electrons entering into reactor zone as a beam.

Chaotic from center is radial.

[Joseph Chikva]

Chaotic from center is radial.

Draw the circle and be convinced that it is possible to spend infinitely many straight lines which are not passing through the center. Radially moving particle once being scattered outside the center will not pass there again. And very unlikely that it will return to radial direction as result of multiple scatterings.

[hanelyp]

I'm of the opinion that electron motion inside the wiffleball is not mostly radial, but more random like a gas. Nor is it needed for the motion to be mostly radial to produce a suitable potential well. Those electrons with a large radial motion component are enough to climb the well as needed.

Nor is uniform electron energy needed for the potential well, though it is of great value for recirculation.

[KitemanSA]

hanelyp, you may be right, but that bodes ill for brem.

Also, I can't help but think that those electrons that are NOT radial will be rflected by the wiffleball holes more toward the center and more often than radial ones will be reflected away. Think of a snooker ball being shot at a skimming angle toward a side hole. It will almost always be reflected more normal to the side than it comes in. Balls that approach that hole normal to the side rail will usually sink. In the Polywell world, that "sunk ball" recirculates. Thus the wiffleball tends to radialize the electrons too. I think.

[TallDave]

Heh, we're still talking about this? Well, not that this will probably help, but...

You have to keep in mind that all along the Polywell was intended as the answer to a question: "how do we make an ETW without a grid that particles will smash into and lose their energy?" If you've never looked at ETWs much I can see how this design would be confusing, but from an IEC perspective it's pretty easy to understand: a virtual "grid" is formed by the electrons magnetically confined by the WB; their average position is the core so that's where the ions see their lowest potential energy (the distribution doesn't have to be beam-like, just isotropic rather than thermal, which is accomplished by the electron drive). That virtual "grid" is then used to accelerate ions to the core where they fuse.

Probably the easiest thing to do with these questions is to just ask why the Magrid is charged, which wouldn't make a lot of sense if you were depending on focused beams. Once you understand that, everything else sort of follows naturally.

[Joseph Chikva]

Heh, we're still talking about this? Well, not that this will probably help, but...

You have to keep in mind that all along the Polywell was intended as the answer to a question: "how do we make an ETW without a grid that particles will smash into and lose their energy?" If you've never looked at ETWs much I can see how this design would be confusing, but from an IEC perspective it's pretty easy to understand: a virtual "grid" is formed by the electrons magnetically confined by the WB; their average position is the core so that's where the ions see their lowest potential energy (the distribution doesn't have to be beam-like, just isotropic rather than thermal, which is accomplished by the electron drive). That virtual "grid" is then used to accelerate ions to the core where they fuse.

Probably the easiest thing to do with these questions is to just ask why the Magrid is charged, which wouldn't make a lot of sense if you were depending on focused beams. Once you understand that, everything else sort of follows naturally.

Once you to undarstand that ions see their will not see their lowest potential energy in the center if there will not the proper potential distribution. And proper potential distribution will not be without proper electron density distribution.
That all motions in Polywell will not pass through the center. Etc., etc., etc.
But good luck. As you are right to believe. And also have a right to speak about conspiracy against Polywell - why TOKAMAK program is heavily financed and Polywell not. Not because decesion making people understand more than you?

[vernes]

Once you to undarstand that ions see their will not see their lowest potential energy in the center if there will not the proper potential distribution.

There isn't?

[Joseph Chikva]

Once you to undarstand that ions see their will not see their lowest potential energy in the center if there will not the proper potential distribution.

There isn't?

They speak about uniform distribution of electron density but at the same time about non-uniform distribution of potential. And that is the nonsense. Vitual cathode was not invented by Dr. Bussard. But for example John Pierce http://en.wikipedia.org/wiki/John_R._Pierce used virtual cathode in his vacuum tubes.

Virtual Cathode Oscillator History

Pierce J. (J.Appl.Phys.,1944) Pierce instability in the diode with positive ion background

Birdsall C.K., Bridges W.B. (J.Appl.Phys. 1963)Virtual cathode demonstrates nonstationary dynamics in electron beam of the diode region (numerical simulation)

Plutto A.I. et al(JETP Lett.,1967)First experimental observation of power microwave generation by virtual cathode in experiments of ions accelerations

Mahaffey R.A. et al, (Phys. Rev. Lett., 1977); Didenko A.N. et al (Sov. Tech. Phys. Lett., 1978)First production of microwaves using virtual cathode oscillations

And virtual cathode is formed with the help of beams. And with nothing else.

Virtual cathode is conditional equipotential plane in the drift space of electron device characterized by the minimal negative potential relative to cathode (emitter of electrons). In wide meaning VC is any equipotential plane across which the part of electron beam cannot pass.

And beams are vulnerable from stream instabilities.

[KitemanSA]

Virtual cathode is conditional equipotential plane in the drift space of electron device characterized by the minimal negative potential relative to cathode (emitter of electrons). In wide meaning VC is any equipotential plane across which the part of electron beam cannot pass.

And beams are vulnerable from stream instabilities.

So your suggestion is that if the Polywell were an "electron device" these conditions (beams and instability) would be an issue.

Well then I guess it is lucky that the Polywell is NOT an "electron device".

[hanelyp]

hanelyp, you may be right, but that bodes ill for brem.

I don't think so. Brem suppression in a polywell depends on 2 factors that come to mind:
- Peak electron energy being ~1/5 of peak boron ion energy.
- While annealing of electron energy isn't needed for a wiffleball, I expect we will still get it, removing the high energy tail responsible for much of the brem.

Also, I can't help but think that those electrons that are NOT radial will be rflected by the wiffleball holes more toward the center and more often than radial ones will be reflected away....

The area presented by the cusp holes in a wiffleball is a small fraction of the total inside area.

[Joseph Chikva]

Virtual cathode is conditional equipotential plane in the drift space of electron device characterized by the minimal negative potential relative to cathode (emitter of electrons). In wide meaning VC is any equipotential plane across which the part of electron beam cannot pass.

And beams are vulnerable from stream instabilities.

So your suggestion is that if the Polywell were an "electron device" these conditions (beams and instability) would be an issue.

Well then I guess it is lucky that the Polywell is NOT an "electron device".

May be you would be surprised but Polywell as well as any other plasma devices is an electrons' and ions' device.

The area presented by the cusp holes in a wiffleball is a small fraction of the total inside area.

So, you think that is posible at the expence of only scattered electrons without beams?

[TallDave]

Once you to undarstand that ions see their will not see their lowest potential energy in the center if there will not the proper potential distribution. And proper potential distribution will not be without proper electron density distribution.
That all motions in Polywell will not pass through the center. Etc., etc., etc.
But good luck. As you are right to believe. And also have a right to speak about conspiracy against Polywell - why TOKAMAK program is heavily financed and Polywell not. Not because decesion making people understand more than you?

You're claiming wells don't form. Sorry, but reality tends to disagree pretty adamantly. If that were the case, WB-5, WB-6, and WB-7 would not have achieved fusion, nor would the Japanese laser measurements have found clear evidence of wells, etc., etc., etc. Nor do any of the simulations agree with your understanding of the physics (Bussard, Chacon, Rogers, etc).

The historical reasons for tokamak funding are well-known and not any kind of conspiracy -- toks had good perfomance early on, and before Polywells there was never much reason to think IEC fusion could ever achieve the proper confinement. For a long time it looked like tokamaks would scale to ignition at much smaller sizes than ITER. Now we know better, and Polywell funding is ramping up in response, even as ITER is delayed again and again and probably ultimately headed for the junk heap of engineering history (if Polywells don't beat them, I bet FRCs or something else will).

[ladajo]

Yup.

Polywell may not work, but it is definately on a short list of "worth tryings".

Joseph, you really do seem to be a bit confused about the actual fucntioning concept, and seem determined to force the round peg into the square hole of other concepts. It is its own thing. Stop with the pre-concieved notions, and free think a little.

Beams are not neccessary.

I get the point you are thinking about how the Fields will make beams (of some sort) through each cusp. But that is not the case. "Spike" in the ball, does not equal "beam" axis.

I think you are also struggling to see how/where the wiffleball itself is formed. Also, I do not think you realize that we keep talking about B=1, purely as a construct of how existing test have been run for the devices. Odds are, an operating machine will function at Beta less than one, but purdy darn close. This will be a function on not exceeeding "1" as a blow out prevention method. To date, all test runs have analyzed data as B "passed" through "1", and the machine blew out. Mostly due to gas buildup driving vacuum to poop.

Your ideas that B has never made it to "1" is just completely wrong in the test devices.

[Joseph Chikva]

You're claiming wells don't form.

I saying that desired well formation will have restrictions caused by instabilities.
Saying "desired well" I mean comparatively small and dense virtual cathode located in the center.

[Joseph Chikva]

Your ideas that B has never made it to "1" is just completely wrong in the test devices.

I see that continuation of this conversation not meaningful.
Thanks.