Google Polywell Fusion Counter

[rnebel]

Icarus:

What I think you can surmise from my comments is that confinement theories that rely on ambipolar arguments are incorrect. Polywells are not ambipolar devices for the reasons I stated above. Although some of the posters here may not agree with my comments, the WB-7 does.

[Skipjack]

Although some of the posters here may not agree with my comments, the WB-7 does.

Rick, I am not 100% sure what you are talking about (I am a halfeducated halfidiot), but I think I like what you are saying...

[Munchausen]

Are there any quantitative estimates of electrons lost to ground versus electrons lost to the central positive grid in the Elmore-Watson-Tuck machine?

Are the losses to ground in the Elmore-Watson-Tuck machine tolerable?

Why can we anticipate larger losses to ground of electrons from the central positive grid of a polywell than from the central positive grid of the Elmore-Watson-Tuck machine?

[rnebel]

Electrons in both the Elmore-Tuck-Watson machine and the Polywell are formed at ground. Consequently, if they go back to ground there isn't a significant energy loss. The only way they can do this is if they are upscattered in energy. The major "cost" is that you have to have larger electron sources if a significant number of electrons are lost to ground.

[D Tibbets]

Electrons in both the Elmore-Tuck-Watson machine and the Polywell are formed at ground. Consequently, if they go back to ground there isn't a significant energy loss. The only way they can do this is if they are upscattered in energy. The major "cost" is that you have to have larger electron sources if a significant number of electrons are lost to ground.

OK, another shift in my perspective (perhaps). So, once the need for the round/ conformal magrid shape was identified (greatly increasing the transparancy of the grid), the efficiency of electron containment is less important than the 'containment/ recycling' of the electron kinetic energy. Without the Wiffleball effect, the machine might still work for net power, but you might need electron guns similar in scale to the lasers at the NIF. With a funtional Wiffleball, the scale of the electron guns becomes much more practical, and I'm guessing alot of other associated processes likewise become more practical.

Assuming I'm not totally confused (again), how is the uncontained electron energy recovered? Is it fed into the positively charged magrid? Within the operating conditions, can the magrids absorb/ recycle that energy, and is the recovery of the electron kinetic energy from the electron guns that deterministic for sucessful net energy production, ie- the dominate loss mechanism?

[Edit] Actually, it occurs to me that the electron guns must be low voltage - the high energy comes from the electrons falling twords the high pos. voltage Magrid, so it makes sense that they (the escaped convicts)give back the energy as they climb up the potential well. I guess other options were tested (grounded Magrid with high neg voltage electron guns)but apparently the pos charged Magrid worked best (I have no idea why).


Dan Tibbets

[Art Carlson]

What I think you can surmise from my comments is that confinement theories that rely on ambipolar arguments are incorrect. Polywells are not ambipolar devices for the reasons I stated above. Although some of the posters here may not agree with my comments, the WB-7 does.

You are quite right on the difference between quasi-neutrality and ambipolarity. My personal mantra is quasi-neutrality. I try not to assume ambipolarity, though I may slip from time to time.

Over yonder on the "Recirculation revisited" thread, I re-did my calculation showing that the plasma in the cusp also has to be quasineutral. I assumed neither ambipolarity nor any particular energy distribution. I would appreciate hearing whether you agree with that analysis.

I should give you fair warning though. It took me some time to feel my way into the cusp confinement business. If you once grant be a quasi-neutral plasma with nothing but an electric field between there and the wall, then we're talking sheath physics, and that's my turf. I will haul in Bohm and Child and Langmuir to give me artillery support, and I will deliver carnage from which the polywell will never recover.

Electrons in both the Elmore-Tuck-Watson machine and the Polywell are formed at ground. Consequently, if they go back to ground there isn't a significant energy loss. The only way they can do this is if they are upscattered in energy. The major "cost" is that you have to have larger electron sources if a significant number of electrons are lost to ground.

I am particularly looking forward to showing that even electrons at the wall potential and cold ions at the plasma edge will not save you from massive energy losses.

[chrismb]

If you inject ions and electrons at the same rate, you get the ambipolar result which will likely have small electrostatic potentials and the confinement likely isn't what you desire. On the other hand, if you flood the device with electrons you will get deep potential wells and the ions will be extremely well confined and at very high energy.

I'm not sure I understand how this constitutes "stated reasons". So, exactly how many more electrons do you need to put in than ions before it goes from 'ambipolar' to 'quasi-neutral'?

This sounds to me like some confuscation with tricky technical words. Why does it matter, and how do you differentiate the two anyway?

And if there is no ambipolarity then how come the particle losses are ambipolar losses?

A Polywell is, surely, as ambipolar as you can get! That is to say, if it is to work 'as advertised' (though I am entirely with Art, it would appear far more likely to thermalise into a quasi-neutral state).

Supposedly, regions within a Polywell will contain some net-negative charge at the centre that pulls in ions (that are therefore, by definition, in a region where the net charge is relatively positive). This *is* the definition of ambipolarity, isn't it? Two charge regions that contain charge carriers that react to each others presence over a distance, along lines of (consqeuently evolved) electric field. Is there an alternative definition?

And not forgetting the first question, how far off quasi-neutrality can a region of ions/electrons get before it can be (or isn't) ambipolar? I do not see how you classify these things, and in either case I still don't see why it would make any difference over whether the ions won't happily accompany electrons right through the cusps, especially seeing as the particle losses *are* supposedly ambipolar losses.

best regards,

Chris MB.

[KitemanSA]

WARNING WARNING : TOPIC RECLAMATION IN PROGRESS

Google "Polywell fusion" = 15,900, up from 15,700 yesterday.

THANK YOU : THAT IS ALL .

[TallDave]

Don't these seem contradictory?

On the other hand, if you flood the device with electrons you will get deep potential wells and the ions will be extremely well confined and at very high energy.

the plasma in the cusp also has to be quasineutral.

If you have well-confined ions and non-ambipolar behavior, I don't see how ions make it into the cusp (way out at the edge) at the same rate as electrons. If you're running electron-rich, you have to be losing more electrons than ions.

[Art Carlson]

Don't these seem contradictory?

Good. I see you have been paying attention. I have shown that the potential hump that would keep ions out of the cusps would cost you several MV on the magrids. Once ions get that far, there is nothing to stop them from running to the wall. We can run the numbers later, but that is not going to be what I would want to call "extremely well confined". Flushing electrons through the system might help build up the depth of the central well, but I don't see how it can stop the hemorrhaging of ions. Can't wait to see what Rick has to say.

But I'm not sure I understand exactly what you are trying to say. I showed that ions have to have a significant density in the cusp throats. (Quasi-neutrality is when the ion density and the electron density are equal). We have not yet discussed the question of the ion velocity or flux. (Ambipolarity is when the ion flux and the electron flux are equal.)

[icarus]

Art says:

I showed that ions have to have a significant density in the cusp throats.

Assuming the cusp throats even exist as you describe them.

Is it possible you are looking for sheaths to analyse because that is what you can do? First we have to show that such cusps, having your description of sheaths even exist, how would we do that?

[Art Carlson]

Art says:

I showed that ions have to have a significant density in the cusp throats.

Assuming the cusp throats even exist as you describe them.

Is it possible you are looking for sheaths to analyze because that is what you can do? First we have to show that such cusps, having your description of sheaths even exist, how would we do that?

We could do some simple physics. Better is to go to the literature and so what the real experts have said, both regarding experimental results and theories.

In any case, I duly note that you are also not able to put forth a self-consistent theory of polywell operation. Don't feel bad. Nobody else can either.

(Sheaths are pretty easy in an unmagnetized plasma or when the surface is perpendicular to the field. Sheaths with grazing incidence fields are a bear. Sheaths truly parallel to the field are out of my ken. That's why I listen to people like Haines.)

[rnebel]

Your logic is flawed. Ions do not have to move into the cusp at the same rate as electrons in order to maintain quasi-neutrality. If ions and electrons leave at the same rate that they enter (and this is true anywhere in the plasma) then quasi-neutrality can maintained. They simply have to leave at the same rate they enter, and it doesn't have to be the same for ions and electrons. The ambipolar arguments are not valid, if you inject ions and electrons at different rates. Since people always refuel Tokamaks quasi-neutrally, people from the tokamak community seem to think that ambipolarity is basic physics. It isn't. It's a result of the way they refuel tokamaks. Art, You've got the tail wagging the dog.

[Art Carlson]

Your logic is flawed. Ions do not have to move into the cusp at the same rate as electrons in order to maintain quasi-neutrality. If ions and electrons leave at the same rate that they enter (and this is true anywhere in the plasma) then quasi-neutrality can maintained. They simply have to leave at the same rate they enter, and it doesn't have to be the same for ions and electrons. The ambipolar arguments are not valid, if you inject ions and electrons at different rates. Since people always refuel Tokamaks quasi-neutrally, people from the tokamak community seem to think that ambipolarity is basic physics. It isn't. It's a result of the way they refuel tokamaks. Art, You've got the tail wagging the dog.

I agree with you completely (except maybe the last sentence), so there must be a misunderstanding somewhere. My question is, "Is the plasma in the throat of the cusp (underneath the magrid) quasineutral?" I say it is, and it sounds like you agree with me. Can we move on from there?

[TallDave]

I have shown that the potential hump that would keep ions out of the cusps would cost you several MV on the magrids.

But do you still need that hump given the fact that an electron-rich plasma would be spitting out electrons preferentially anyway?