Remind me - why 10T field?

[KitemanSA]

Way to go TD!

Hope you don't mind. I did a touch of editing.

By the way, if you have any references for that value, it would be GREAT to include it.

Thanks

Dana

[TallDave]

Feel free to edit away. I added some edits too.

It seems to take about seven edits on average before I actually say what I meant to, in a way that actually makes sense, and actually making a sensible point.

Sorry I don't have a cite for that, Simon might. I'll add it if he shares. I'm probably going to cite Rick a lot, I'm developing a document of all his comments here (am I becoming a stalker? yes), with links, for easy searching and linking.

[KitemanSA]

I'm probably going to cite Rick a lot, I'm developing a document of all his comments here (am I becoming a stalker? yes), with links, for easy searching and linking.

I did a search for all his posts in this forum and have them in a word document. I've gone thru it and marked the most notable statements with highlighter.

Fascinating stuff.

[TallDave]

Hehe, at least I'm not the only one. Mine's in Notepad. I'm about halfway through I think.

Fascinating indeed.

[icarus]

You haven't done anything besides taking Rick's power density scaling number and run it through on like for like basis. (back-fitting)

Now if you'd like to explain how this figures into how the upper density limit on ions, from fusion physics collisional considerations, fits into your beautiful equations? (i.e begin from first principles for once)

Then you'll begin to answer chris's questions.

[D Tibbets]

You haven't done anything besides taking Rick's power density scaling number and run it through on like for like basis. (back-fitting)

Now if you'd like to explain how this figures into how the upper density limit on ions, from fusion physics collisional considerations, fits into your beautiful equations? (i.e begin from first principles for once)

Then you'll begin to answer chris's questions.

I think quoting from authority is a valid tool. If you are suspecious, or disagree, you need to attack the authority (difficult to do as he (Nebel) is not now communicating) or attack the reasoning of the 'back filling.
Other than some personal attacks and comments about mistakes of Bussard by A. Carlson- and without describing the specific mistakes and pointing out where the flaws are, there has not been much discussion here of the fine physics. Quoting people like Rider, is no different than quoting Chacon or Nebel- they are all athorities.
I wonder why I have not seen detailed reviews/ critisisms of the various papers by Bussard, etel. Bussard mentioned that there was reviewers involved with various stages of his research. Are they all fools? Are their motives suspect?

In short, this is a site about Polywells. Some optimism is to be expected and welcome. ChrisMB has raised a number of concerns. Arguing about them is sometime frustrating (I know I am right), but always educational. Arguing about these criticisms and assumptions has taught me alot. Condemning without putting forth the effort to justify your position though is unimpressive.

If you are really determined, then prove the errors. Analyze and refute each (or at least some) of the papers by Bussard, etel that are available publicly.
He and his colleagues cover issuers including, potential wells, magnetic containment, density gradients, limitations, thermalization issues, bremsstrulung, etc. This is most, if not all of the basic physics that you are demanding.

Personally, I am not equipped to argue at this level. Identifying the trends, and seemingly reasonableness of claims, along with some specific analysis and identification of possible reasonable counter arguments to criticisms and seeming misstatements or assumptions is not.
Even A. Carlson admitted that despite opposing theory, the advances in FRC fusion has merit. And he eventually conceded that the effects of quantum mechanics had a potentially useful effect on bremsstrulung radiation in very strong magnetic fields (I don't know if contention over this particular issue is what lead him to ban E. Learner from the Wikipedia site about DPF).

PS: I think I and others have given good arguments about density , and operational issues. As frequently admitted, the lack of available details has been frustrating. There are some uncertain variables that may effect the final efficiencies, but for D-D fusion at least, my impression that the only show stoppers from a theoretical stand point is the existence of the Wiffleball and questions if loss scaling is accurate. Certainly, i seems Bussard had solved all of the issues, except for electron losses, that was claimed to have been solved by WB6. As he said "the physics have been solved" and the earlier papers allows one, if they are qualified and motivated, to evaulate most of the issues that were pointed out in the Valencia paper. He (and associates?) certainly seemed satisfied about the Wiffleball . Nebel was more cautious, though hints are that he is optimistic of the effect even if he did express hesitancy to labil it as a Wiffleball and that performance 'exceeds classical predictions' Crumbs, I know, but a starving man...

[End Rant]

Dan Tibbets

[ladajo]

BTW, a good summary of Polywell there, ladajo. Not many people can write that much about PW without making major errors. I salute you.

Thanks...

[TallDave]

You haven't done anything besides taking Rick's power density scaling number and run it through on like for like basis. (back-fitting)

Shrug. I wasn't claiming I'd done anything more.

Now if you'd like to explain how this figures into how the upper density limit on ions, from fusion physics collisional considerations, fits into your beautiful equations? (i.e begin from first principles for once)

Then you'll begin to answer chris's questions.

I asked if anyone knew what those density limits were, and from principle they were derived. I haven't yet heard any principle invoked to impose such a limit (other than Pauli, which I threw out as a joke), so I guess I don't feel any pressing need to answer an objection not yet given any physical basis.

Unless of course you want a limit based on degeneracy pressure. (I suspect that's an awfully big number though.)

[D Tibbets]

Quote from Patent application, as linked by Aero, which describes some aspects of the pressure question.

http://www.freepatentsonline.com/y2008/0187086.html

"The pressure of particles in the well will be supported by the external magnetic field which confines the electrons, through the inertial effects of conversion of the kinetic energy of in-falling ions to electrostatic dynamic pressure on ions confined in (but moving outward from) the central core of the potential well reacting volume. This well itself is produced by the conversion of the inertial energy of injected electrons to the energy of the well depth at the electrostatic potentials established by the stably-confined electron density. This electrostatic well gives energy to the in-falling ions, which in turn couple their thus-acquired energy of motion (and momentum) into confinement pressure on the core. The kinetic energy of injected electrons thus, through the medium of the electrostatic well, is transformed into the kinetic energy of in-falling ions.

The ratio of momenta of ions and electrons of the same energy is given by the square root of the ratio of their masses, thus this transformation has the effect of producing an ionic “gas” whose (dynamic) pressure is very much larger than the equivalent (dynamic) pressure of the injected electrons. In addition, the convergence of the quasi-spherical geometry of the polyhedral configurations of interest increases the local dynamic pressure by the square of the inverse ratio of radii from the outer (electron injection) radius to the inner (ion dynamic pressure confinement) radius, rc.

As an example of these effects, if the ions are those of deuterium (D= 2 H) and the radius of the inner core is 0.1 that of the inner “surface” of the confinement field region, then the ratio of ion-generated pressure on the core to electron pressure on the (external) confining field will be roughly 6100:1. The physics phenomena invoked in this invention thus have the effect of creating an electrical “gas” inside the magnetic field region whose (dynamic) pressure at large radii is very much less than its “pressure” at small radii within the volume which it occupies.

For this reason, it is possible to contain and confine a high density of reactive ions in a small radius within a larger radius at which a relatively weak magnetic field is placed; it is not necessary for the magnetic field to provide the confining pressure over a large radius to hold the high density plasma together at the pressure at which it operates within the smaller radius core. For example, ion densities of 1.0E15 to 1.0E17 per cm 3 may be sustained in D at 100 kev with surface magnetic fields of only 3 to 10 kG (kilogauss).

Note that scattering collisions in this geometry do not directly increase particle losses, because they occur near the center and their effect of changing the direction of motion still leaves all motion predominantly radial in vector direction. "

Dan Tibbets

[icarus]

TallD:

I asked if anyone knew what those density limits were, and from principle they were derived. I haven't yet heard any principle invoked to impose such a limit

You must not have been reading the earlier posts in the thread.

hanleyp:

As I recall, the density limit on a polywell is from a requirement of a mean free path large relative to the machine size for annealing to work correctly. A matter of ions needing to avoid to many collisions between time in the outer regions being annealed.

TomLignon:

It is important to know that the process Dr. Bussard describes will only work over a fairly narrow range of density. If the density is raised too far, the number of collisions occurring in the wrong places in the machine will, indeed, cause it to thermalize, but if the density is too low, the reaction rate suffers.

Polywell is evidently ion density limited, based on the fusion physics and the mono-energetic requirement. Thus ion pressure limited (albeit in the reaction region) thus linking to upper limit on electron pressure (6100:1? or who knows) and thus upper limit to confining magnetic field (beta=1).

Back to the original question, why 10T? It maybe baseless or 20T may not be so 'slick' either.

How does this fit in with your backfit from the ITER numbers?

[MSimon]

Ideal:

Ion MFP small in the core (center of the reaction space) where you want collisions to take place. Large outside where you don't want collisions.

Electron MFP small where electrons are annealed. Large in the transit volume. Small in the core is OK.

[TallDave]

You must not have been reading the earlier posts in the thread.

I think we're confusing two different questions, edge density (limited by allowable annealing densities, if we want ion convergence) vs core density (limited by ???). I was referring to Chris' objection re density at the core, which is of course not just a function of the electron pressure balanced against the B field, but also of the ion convergence. I still haven't heard any explanation for the objection to the calculated density with ion convergence other than "that density doesn't sound reasonable" which doesn't invoke any particular principle.

The edge density question (re annealing) seems hard to answer, unless someone knows an equation that describes annealing behavior as a function of density, or can derive one from first principles. I think you'd really need a simulation, and I still wouldn't trust the answer very far. Experiment is probably going to be the real arbiter. Does anyone know if Bussard defined such a range? We might be able to infer what he thought the range would be from his proposed WB-100 dimensions.

But of course if you're doing the ITER comparison without convergence, which we may not need anyway, annealing is a moot issue. The plasma can be Maxwellian, as Rick says in the linked post. So some of those edge density questions disappear if you don't care about convergence. This would never work in a fusor, of course, but at higher densities it's not as important. I guess this boils down to: is a power density of ITERx62,500 enough? Or do we need something more like ITERx62.5 billion?

Thus, a Polywell should far outperform a Tokamak even with a constant density Maxwellian plasma. Even if Rider and Nevins were correct (which Chacon has pretty clearly shown they aren’t) this isn’t a show stopper. It has a lot more significance for Hirsch/Farnsworth machines that have low average densities than it does for the Polywell.

Unless I'm misunderstanding Rick here.

(This also illustrates nicely why Rick says the WB is the most important issue.)

That does perhaps raise a new question, though -- is there some value of B past which the loss of ion convergence due to higher density hurts more than the overall density gain helps? And what further increase in B would be required to get back to the peak power available within ion convergence densities? It would be interesting to know.

[TallDave]

Electron MFP small where electrons are annealed. Large in the transit volume. Small in the core is OK.

Do they anneal? I've been under the impression that's what the drive was for (the colder and hotter electrons leave via the Magrid and the wall, and are replaced by new electrons at the "proper" temp).

[BenTC]

I've been under the impression that's what the drive was for (the colder and hotter electrons leave via the Magrid and the wall, and are replaced by new electrons at the "proper" temp).

Why do colder electrons leave via the Magrid?

[KitemanSA]

Why do colder electrons leave via the Magrid?

Its the only place they can go. They don't have the energy to reach either the core virtual cathode or the chamber wall. Eventually they leak thru the B field to the positive MaGrid.