A few questions on Polywell facts and figures.

[chrismb]

Also if a zero B field region is important there is no way to get that with a toroid.

Why not? If the idea is that a core of electrons will push back cusped magnetic surfaces until they are smooth, why would they not also push back already smooth surfaces?? The argument was about taking up a surface current that reflects the field, so it would also be with a toroid, if this 'pushing back' idea works.

[Art Carlson]

Also if a zero B field region is important there is no way to get that with a toroid.

Why not? Use whatever method you are planning to use in the polywell. (internal refueling, current, drive, ...) The only difference is that the polywell starts with a field null. It's got zero volume, but maybe you can use it as a seed.

[MSimon]

Exactly.

I am talking about a fast-aimed sphere versus a fast-aimed toroid.

I am NOT talking about Polywell versus tokamak.

The 'wiffleball' seems to be regarded as ideal - why? - because it is a continuous magnetic surface. So why not exploit the best magnetic surface possible for the fast-aimed idea, rather than relying on somethin with holes in it? A toroidal volume enclosed by magnetic curfaces does not HAVE to be a tokamak.

It is too bad Bussard is not alive because I'm sure he could have answered that question. He was a tokamak guy at one time.

All I can tell you from studying the engineering aspects of his designs is that he thought things out very carefully. His engineering stuff is very sweet. I'm not in a good position to evaluate his physics except in a most rudimentary way. So if he chose a box coil system I believe he had a reason.

Maybe Rick Nebel could clarify this.

[chrismb]

But we already know what happens when you put a plasma in a toroidal field without a rotational transform. It accelerates to the outside in short order

As it would in a Polywell. What is the difference? This is a discussion of the mechanism of the process of charge transport. I see no difference whether these things are within a cusped field or a toroidal one. All that matters is that there are surrounding magnetic surfaces.

[Art Carlson]

I don't understand what you mean by this:

And, oh yeah, it [the tokamak] is a globally unstable flow topology.

Or this:

If the wiffleball effect is a true spherical inversion of the magnetic field carried by the plasma, as posited here,
viewtopic.php?t=650&postdays=0&postorder=asc&start=60
then the cusps effectively close, and it is game on with a near perfect field topology for containment being satisfied.

Art, yes, the tokomak is so brilliant it has taken already 50 years to demonstrate that it might be possible to build one that might one day work, given many more billions. ... For now, it has proven to be a blind alley of holy grail proportions, how many more resources does one throw at it to prove such a brilliant idea can actually work?

And that despite the fact that - given only the concepts and a good knowledge of theoretical plasma physics - the tokamak beats the polywell hands down. What does that say about the chances of successfully scaling a polywell up by a factor of a million?

[MSimon]

Also if a zero B field region is important there is no way to get that with a toroid.

Why not? Use whatever method you are planning to use in the polywell. (internal refueling, current, drive, ...) The only difference is that the polywell starts with a field null. It's got zero volume, but maybe you can use it as a seed.

I can see how to do it with three intersecting toroids and two reaction spaces.

It would seem to be simpler to prove the concept in a sphere (even if net energy is not possible) and then go to a more complicated vacuum housing.

[Art Carlson]

I can see how to do it with three intersecting toroids and two reaction spaces.

I don't know why you think it has to be so complex. It would work just fine with a simple torus, e.g. with purely toroidal fields in a perfectly conducting shell. But whatever.

[Art Carlson]

But we already know what happens when you put a plasma in a toroidal field without a rotational transform. It accelerates to the outside in short order

As it would in a Polywell. What is the difference? This is a discussion of the mechanism of the process of charge transport. I see no difference whether these things are within a cusped field or a toroidal one. All that matters is that there are surrounding magnetic surfaces.

There's a big difference. The polywell plasma stays put but loses particles through the cusps. The toroidal plasma moves as a whole across the magnetic field. It's like the difference between putting a leaky balloon in a cage and putting a balloon in a bucket of water. If you estimate the time scales, the plasma is lost from a torus (unless there is a rotational transform) a factor of R/delta_sh ~ 1000 times faster than from a cusp of comparable size.

[bcglorf]

Exactly.

I am talking about a fast-aimed sphere versus a fast-aimed toroid.

I am NOT talking about Polywell versus tokamak.

The 'wiffleball' seems to be regarded as ideal - why? - because it is a continuous magnetic surface. So why not exploit the best magnetic surface possible for the fast-aimed idea, rather than relying on somethin with holes in it? A toroidal volume enclosed by magnetic curfaces does not HAVE to be a tokamak.

From what I've followed from all of Bussard's explanations the difference would be convergence. A sphere would converge on a point but a toroid would converge on a ring, and not nearly as tight. The entire philosophy behind the polywell design was to make a grid-less fusor so you could scale up without burning out the grid and without the grid itself consuming energy while being burnt up. Bussard also always stated that his intent was to work with a non-maxwellian plasma, I think if that can not be done, everything else is a dead end.

[chrismb]

There's a big difference. The polywell plasma stays put but loses particles through the cusps. The toroidal plasma moves as a whole across the magnetic field. It's like the difference between putting a leaky balloon in a cage and putting a balloon in a bucket of water. If you estimate the time scales, the plasma is lost from a torus (unless there is a rotational transform) a factor of R/delta_sh ~ 1000 times faster than from a cusp of comparable size.

The difference is therefore the toroidal plasma will migrate across magnetic surfaces, whereas the Polywell plasma would migrate across the magnetic surfaces AND down the cusps.

I get the impression that so much attention is paid to the cusp losses that it is forgotten that there is also migration straight across the magnetic surfaces, no more nor less than with any other magnetic surface of the same strength.

To say there isn't and to dive into a discussion on cusp losses instead is to confuscate the fact that this is still a magnetic 'confinement' which is a cross-product force and cannot 'confine' with a normal reaction force. This was Bussard's principle objection, but perhaps he should have highlighted the fact that it also applies equally to every steradian of the wiffleball, not just the cusps.

[chrismb]

The entire philosophy behind the polywell design was to make a grid-less fusor so you could scale up without burning out the grid

That's what I thought originally when I started posting a few days ago. But, no, this does not seem to be the case. Some sort of potential gradient is formed by means I have yet to decypher, but I appear to be wrong to have thought there was a big bunch of electrons held at the centre by magnetic fields. So what the replacement of the grid is, I know not.

[TallDave]

And that despite the fact that - given only the concepts and a good knowledge of theoretical plasma physics - the tokamak beats the polywell hands down.

Sure, and it only cost us, what, about $100B to get toks this far? And by "this far" I mean "still no practical power production foreseeable over the next 50 years and $100B spent." Hurrah for toks.

Of course it's quite possible Polywell is a dead end too. But if it is, it will at least probably fail for quite a bit less money and time.

The difference is therefore the toroidal plasma will migrate across magnetic surfaces, whereas the Polywell plasma would migrate across the magnetic surfaces AND down the cusps.

There are not supposed to be ion losses to cross-field transport or through the cusps; the losses are electrons, and those that go through cusps appear to return. The ions aren't supposed to make it to the edge. That's really the whole point of IEC: electrons are much lighter and easy to confine with magnets.

[bcglorf]

The entire philosophy behind the polywell design was to make a grid-less fusor so you could scale up without burning out the grid

That's what I thought originally when I started posting a few days ago. But, no, this does not seem to be the case. Some sort of potential gradient is formed by means I have yet to decypher, but I appear to be wrong to have thought there was a big bunch of electrons held at the centre by magnetic fields. So what the replacement of the grid is, I know not.

I'm a rusty physics minor so just politely point anything ridiculous I might say . From my understanding though, there is in essence a big bunch of electrons contained in the centre. It isn't a tight ball and the confinement leaks, but the main question I believe Nebel is pursuing is if the confinement is 'good enough'. When ions are introduced just inside the magnetic grid, they are on the exterior of the electron cloud loosely contained in the middle and it of course acts much like a traditional fusor on those initial ions. As more ions are introduced, the center region of course contains ions as well, but Bussard always states the intent to only be quasi-neutral. The loosely contained plasma was always meant in my reading of Bussard's view, to have a negative bias outside the core on any new ions being introduced or you simply didn't introduce more until those already in the plasma fused or met some other fate. The trick was to have the ions fuse faster than they(or the plasma as a whole) met some other fate. Again, as I prefaced maybe none of what I've said even applies to the plasma physics level discussion , sorry if that's the case.

[TallDave]

Chris,

This link may be helpful.

http://wwwsoc.nii.ac.jp/aesj/division/f ... hikawa.pdf

[chrismb]

I'm very familiar with the fusor, thanks. I just don't see how it relates to the Polywell [anymore - I thought I did, but no longer].

For DD, the fusor works by colliding fast ions with background neutrals along the beam paths. This is evidentially demonstrated now. For D3He, most fusion tends to go on with embedded neutrals in the grid - which is interesting in itself. I guess the higher coulomb barrier in that reaction is offset by the dense presence of electrons in the solid, but that is speculation.

The fusor doesn't work by colliding fast ions with fast ions at the centre. This just does not happen to any detectable degree. So, if the Polywell was envisaged to replicate the fusor, this fact needs to be understood, I guess.