Focus Fusion On Slashdot

[Art Carlson]

If I try to read Rider very generously, I might be able to gloss over most of his reservations when it comes to a D-T reactor. I think I have been underestimating the seriousness of ion up-scattering, but if I think of the polywell as just another geometry with cusp confinement, I might even be able to put on blinders on that point. In other words, if the model used by Rider and Bussard for cusp confinement is correct (which I doubt) and the parameters of the model are close to the best ones they contemplate, then it might be possible to make a D-T reactor out of a polywell. That could be more or less what the illustrious review panel concluded as well, especially if the secret data Rick showed them was half-way convincing. If, as Betruger suggests, there is "unexpected physics happening in that vacuum chamber", then I think it is most likely related to cusp confinement. The other points, such as the deleterious bremsstrahlung when running p-B11, are just too fundamental to be seriously called into doubt.

[alexjrgreen]

Are you two just babbling? You've got ions and electrons intimately mixed, with separations under a micron and speeds over a meter per microsecond. What geometry can possiblý keep them from running into each other?

The religious fervour with which you express this suggests that you haven't properly thought it through.

The electron geometry and the ion geometry might be completely different, so long as spherical symmetry is maintained.

[Art Carlson]

Are you two just babbling? You've got ions and electrons intimately mixed, with separations under a micron and speeds over a meter per microsecond. What geometry can possiblý keep them from running into each other?

The religious fervour with which you express this suggests that you haven't properly thought it through.

The electron geometry and the ion geometry might be completely different, so long as spherical symmetry is maintained.

<groan> Have I ever mentioned quasi-neutrality?

[alexjrgreen]

Are you two just babbling? You've got ions and electrons intimately mixed, with separations under a micron and speeds over a meter per microsecond. What geometry can possiblý keep them from running into each other?

The religious fervour with which you express this suggests that you haven't properly thought it through.

The electron geometry and the ion geometry might be completely different, so long as spherical symmetry is maintained.

<groan> Have I ever mentioned quasi-neutrality?

You also did a nice calculation to show that the ions overshoot...

[Art Carlson]

The religious fervour with which you express this suggests that you haven't properly thought it through.

The electron geometry and the ion geometry might be completely different, so long as spherical symmetry is maintained.

<groan> Have I ever mentioned quasi-neutrality?

You also did a nice calculation to show that the ions overshoot...

By a Debye length, right? Even if you ask your Maxwell demon to alternate ions and electrons in onion shells, each lambda_D thick, the plasma oscillations will set in and the ions and electrons will inter-penetrate (collide!) on a timescale of 1/omega_pe. What have you gained?

[TallDave]

I think I have been underestimating the seriousness of ion up-scattering,

Rick and Chacon don't believe ion upscattering is an issue in Polywells. Rick talked about this a while back; I'll try to dig it up again. (This is an area where the Chacon paper should apply, is it not?)

The other points, such as the deleterious bremsstrahlung when running p-B11, are just too fundamental to be seriously called into doubt.

I'll be interested to see how Rider's assumptions apply to WB 8.1. Would you care to make a prediction? For sake of argument let's assume we can measure with arbitrary accuracy the alphas and x-rays. (a very rough calc suggests D-D output would be around 8W (assuming 8xB and Rx1), haven't tried for p-B11 yet...)

[alexjrgreen]

<groan> Have I ever mentioned quasi-neutrality?

You also did a nice calculation to show that the ions overshoot...

By a Debye length, right? Even if you ask your Maxwell demon to alternate ions and electrons in onion shells, each lambda_D thick, the plasma oscillations will set in and the ions and electrons will inter-penetrate (collide!) on a timescale of 1/omega_pe. What have you gained?

Suppose, for the sake of argument, that the wiffleball approximates a charged hollow sphere (in short, a virtual grid).

The ions are always going to overshoot, and hardly ever collide...

[TallDave]

Art you are leaving out that while the particles are whizzing passed each other their "point" of maximum interaction is at "1/2 r" where the velocities are equal and opposite. Every where else (if it is a beam machine) the electrons are fast while the ions are slow and vice versa.

In addition you have the "dwell time" at turn around where the slow particles can thermalize at the slow speeds.

At least that is what I have gotten from reading what is out there.

Will it work? TBD.

It all hinges on what the relaxation time to Maxwellian is. And a couple of other things.

Thanks Simon. That illuminates how manipulating anode height and etc could conceivably address brem.

[Art Carlson]

You also did a nice calculation to show that the ions overshoot...

By a Debye length, right? Even if you ask your Maxwell demon to alternate ions and electrons in onion shells, each lambda_D thick, the plasma oscillations will set in and the ions and electrons will inter-penetrate (collide!) on a timescale of 1/omega_pe. What have you gained?

Suppose, for the sake of argument, that the wiffleball approximates a charged hollow sphere (in short, a virtual grid).

The ions are always going to overshoot, and hardly ever collide...

I can read your words, but I don't have any idea what you're talking about.

OK. All the electrons in a relatively thin shell. Then you add hot ions. They'll make an excursion outside by about lambda_D. The excursion on the inside will be determined by the mutual repulsion of the ions (since electrons are by assumption absent), which will also end up being lambda_D. Each ion will go back and forth from inside to out, and each time it passes through the electron layer it will make Coulomb collisions. If there is actually any physics behind what you are thinking, you will have to be less telegraphic in describing it.

[alexjrgreen]

Suppose, for the sake of argument, that the wiffleball approximates a charged hollow sphere (in short, a virtual grid).

The ions are always going to overshoot, and hardly ever collide...

I can read your words, but I don't have any idea what you're talking about.

OK. All the electrons in a relatively thin shell. Then you add hot ions. They'll make an excursion outside by about lambda_D. The excursion on the inside will be determined by the mutual repulsion of the ions (since electrons are by assumption absent), which will also end up being lambda_D. Each ion will go back and forth from inside to out, and each time it passes through the electron layer it will make Coulomb collisions. If there is actually any physics behind what you are thinking, you will have to be less telegraphic in describing it.

I add fairly cold ions, at a distance from the wiffleball, which are then accelerated towards it...

[jmc]

After that slight detour, to get back on the topic of Focus Fusion.

Art, you mentioned the repulsive hoop force preventing the plasmoid in focus fusion from being confined. But prior to the formation of the plasmoid a Z-pinch force causes the plasma to centrally accelerate inward. Could it be that the plasmoid could exist for a period comparable to the time it takes to slow down and start accelerating outward, and if this time equals one burn time, could the dense plasma focus still be a viable concept

[Art Carlson]

I add fairly cold ions, at a distance from the wiffleball, which are then accelerated towards it...

This is like trying to get blood out of a turnip. When you learn to talk in more than a half-sentence at a time, when you have a coherent picture and are ready to explain it in detail, including how it relates to my analysis of collisional energy tranfer, then maybe we can talk. Until then, I've got more important things to do.

[Art Carlson]

After that slight detour, to get back on the topic of Focus Fusion.

Art, you mentioned the repulsive hoop force preventing the plasmoid in focus fusion from being confined. But prior to the formation of the plasmoid a Z-pinch force causes the plasma to centrally accelerate inward. Could it be that the plasmoid could exist for a period comparable to the time it takes to slow down and start accelerating outward, and if this time equals one burn time, could the dense plasma focus still be a viable concept

That's a description of inertial confinement. If you can show that a Z-pinch can drive the compression more efficiently than lasers or other drivers, i.e. to several times solid density without excessive pre-heating, then sure, go for it.

[jmc]

Well the hardware is certainly cheaper.

On another note, if the collective expansion speed of the plasmoid is considerably slower than the thermal velocities of the plasma confined inside it then that would relax the densities required as the confinement time would be larger than that of an exploding pellet. The expansion force of the self-contained plasmoid after all, depends on the hoop force of its own current and might thus be decoupled from the thermal speeds of the particles inside (Any proofs handy to the contrary?)

[Art Carlson]

Well the hardware is certainly cheaper.

On another note, if the collective expansion speed of the plasmoid is considerably slower than the thermal velocities of the plasma confined inside it then that would relax the densities required as the confinement time would be larger than that of an exploding pellet. The expansion force of the self-contained plasmoid after all, depends on the hoop force of its own current and might thus be decoupled from the thermal speeds of the particles inside (Any proofs handy to the contrary?)

Well, since you ask so politely:

http://en.wikipedia.org/wiki/Virial_the ... tic_fields

Thus the lifetime of a plasmoid is expected to be on the order of the acoustic (or Alfven) transit time.