Significance of Electron Recirculation Revisited

[Art Carlson]

Sorry, I just don't find analyses that contradict what the experimenters are telling us very interesting. If Art wants to assume Rick hasn't actually seen WB confinement, fine, he's certainly entitled to do that given that nothing is published. I'm much more interested in analyses that would tend to explain what we're told has been measured, and how those might scale in larger machines.

Here's where I'm coming from. Obviously, I know what's in the data and I know what it is consistent with. We've known that for several months. However, just because a piece of data is consistent with one model doesn't mean that it's inconsistent with another model. When you compare data and theory, the best you can say is "it's consistent with...." .

(emphasis added)

[TallDave]

Grasping at straws there, Art. He strongly implied your model didn't conform with what they're seeing (now, if someone has a model which explains WB-7 results as implied by Rick, I am interested in what it says about prospects for WB-100 (looking in Joel's direction)). I'm not all that interested in why you may be wrong or proving it; that will come out in due time. Meanwhile feel free to prove it's all impossible for our amusement

Really back to work now.

[Art Carlson]

And I'm afraid your referenced post is the point where you lose me. Rather, more accurately, where I get lost. My physics isn't strong enough to follow through your argument and understand it properly. I'm afraid there probably isn't any way to dumb it down enough for someone at my level to grasp, so just let me know if my question simply doesn't make sense to the problem. If I really want the answers I can take the time to school myself back up on the physics.

I've no problem with people who are trying to follow the physics and need help. What gets my goat is people who pretend they understand some physics and then talk nonsense.

I can't follow how/where you map the density of the main plasma to the density in the cusp cylinder. If I'm not mistaken, Bussard seemed rather confident in claiming the density varied by as much as a factor of 4 from inside to outside the magrid, or is that my misunderstanding? Is there not any rational reason to expect a significant density decrease in the cusp cylinders the further you are from the main plasma? Again, if these questions are all irrelevant or foolish if you can follow the math you've already given just let me know that too. At least I know then where to start with my own study.

I think Bussard's idea that the density in the cusp outside the magrid is very much lower than inside is based on (wrongly) neglecting quasi-neutrality in the cusps. My working picture of the cusps is just holes (or more precisely a straw or a slit between two parallel plates) that let plasma out. In fluid dynamics you usually don't get more than a factor of 2 drop in the density in those circumstances. A somewhat more sophisticated way to look at, that is also found in the literature, is that there is a "sheath" around the plasma ball that gets bled off into the cusps, whereby the flux tubes have a constant magnetic field, at least as long as they run along the plasma ball. This would also lead to a cusp density close to the density in the plasma ball, again dropping by a factor of 2 or less.

In the theory of plasma-wall interactions, including Langmuir probes, the density drop would be called the "pre-sheath". The value can depend on various conditions, particularly on how the plasma is replenished, but a drop by a factor of 2 is very typical.

[Art Carlson]

He strongly implied your model didn't conform with what they're seeing

His statement, directed to me, that "just because a piece of data is consistent with one model doesn't mean that it's inconsistent with another model", strongly implies that his data does not contradict my model. But go ahead and believe what you want. I don't care anymore.

[TallDave]

Oh Art, read on to the next sentence.

I know that the confinement in the WB-7 is much, much better than ballistic. I also believe that the dominant energy flowthrough is in the electrons, not the ions. Glen Wurden (whom you probably know from LANL) has taken some fast framing pictures of the plasma, and the hot spots are on the coils, not the walls. While this isn't a proof, it's a pretty strong indicator.

I find your efforts sometimes amusing, sometimes interesting, and often insightful, but not ultimately convincing. I don't particularly care about who is more expert in anything, as much as in how well what they're saying jibes with reality. I'm not sure anyone really has a good model of PW behavior. You're free to advance your model, I'm free to not care about your model, you're free to not care about my not caring.

[D Tibbets]

Nice find Dan, do you have a link or do I have to kill a tree for that?

I think I found it from a link by M. Simon (?). At that time it was a free download, but no longer.

Another lecture/ text that is a little harder to read (for me) is:

http://farside.ph.utexas.edu/teaching/p ... tures.html

Dan Tibbets

[Art Carlson]

Oh Art, read on to the next sentence.

I know that the confinement in the WB-7 is much, much better than ballistic. I also believe that the dominant energy flowthrough is in the electrons, not the ions. Glen Wurden (whom you probably know from LANL) has taken some fast framing pictures of the plasma, and the hot spots are on the coils, not the walls. While this isn't a proof, it's a pretty strong indicator.

Uh, yees. I read that. It is one of the most amazing statements Rick has ever made. "Ballistic confinement" means the plasma just blows apart as if nothing was there. No magnetic fields. No electric fields. Nothing. That he would choose ballistic confinement as his benchmark speaks volumes about the performance of his polywell. Or it means nothing at all. Rick has never stated anything outright. That's why you and I can disagree so exquisitely about what he has "strongly implied". Anyway, my model predicts "confinement much, much better than ballistic", so I'm right in line with everything we know about WB-7.

[TallDave]

Thanks Dan, I'll have to struggle through that at some point this week. BTW in case you didn't see, Simon left another link which may be helpful.

Art -- Sure, except you predict ion currents and the hot spots are on the casings, not the wall. But you don't care, and neither do I, so...

bcglorf -- here's the point I was trying to make, probably not very well:

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

At the cusps the electrons are near the bottom of their potential well and highly energetic, the ions near their top and sluggish. Electrons bounce around the bottom, recirculating and being lost to cross-field diffusion, while relatively few ions make it over the top. Bussard deliberately set out to build a machine in which electron losses would dominate. Did he succeed? Maybe. Rick seems to think so. Does it scale well? Who knows. Rick has said he doesn't know how cross-field diffusion scales in these machines.

There's a lot that seems to be poorly understood. Frankly, I won't be shocked if they never get WB-8 past arcing problems.

[Giorgio]

Uh, yees. I read that. It is one of the most amazing statements Rick has ever made. "Ballistic confinement" means the plasma just blows apart as if nothing was there. No magnetic fields. No electric fields. Nothing. That he would choose ballistic confinement as his benchmark speaks volumes about the performance of his polywell. Or it means nothing at all. Rick has never stated anything outright. That's why you and I can disagree so exquisitely about what he has "strongly implied". Anyway, my model predicts "confinement much, much better than ballistic", so I'm right in line with everything we know about WB-7.

Considering that we know practically nothing about WB-7 than yes, you are perfectly in line with nothing.

This whole discussions based on "I think", "he has strongly implied", "I belive he means", "he never stated", really bring us to Nothing.

[icarus]

Giorgio:

Quite the opposite, it's a compression in the directions perpendicular to the magnetic field and a traction parallel to the field (notice the negative sign in the Maxwell Tensor)

Where and when are talking about applying this in the Polywell?

Generalised sketches of magnetic pressure principles are practically useless for the purposes of this discussion, if you could be more specific of what you are talking about. Are you implying that there is a surface tension on the edge of the plasma wiffle-ball?

[Giorgio]

Giorgio:

Quite the opposite, it's a compression in the directions perpendicular to the magnetic field and a traction parallel to the field (notice the negative sign in the Maxwell Tensor)

Where and when are talking about applying this in the Polywell?

Generalised sketches of magnetic pressure principles are practically useless for the purposes of this discussion, if you could be more specific of what you are talking about. Are you implying that there is a surface tension on the edge of the plasma wiffle-ball?

You probably didn't read carefully my original post, I repost it with added enphasis:

As a pure example, one of the factor that I never see anyone considering is that while the increase in magnetic field gives life to an increase in magnetic pressure (B^2/2*u_0) in the two directions "perpendicular" to the magnetic field, it also gives a decrease in pressure equal to the same amount in "parallel" direction, i.e. a Magnetic Tension.
How (if at all) will this tension influence the behavior of our fluid-Plasma inside the geometric confinement of a polywell?
This is of course just a rhetoric question, no need to try to answer it.
It's just to point out that first of all we should question if all the various hypothesis and the related formula that we try to apply do have any meaning and validity in a machine like Polywell.

My guess is NO. After all all of they come from observations done on machines and systems completely different from Polywell.

I am not implying anything, I am just stating that most of the ideas proposed or exposed here not only are based on hypothesis that MIGHT NOT apply to the Polywell, but also DO NOT keep in due consideration all the system forces forces that are a part of the very hypothesis they are basing their assumption on.

And lastly, yes, the Pressure Tensor shows that also a Magnetic Tension value is present when there is an increase in magnetic pressure.
If this has any effect is something no one at this moment can probably prove or disprove, but it exist and should enter the model.

[icarus]

Giorgio:

If this has any effect is something no one at this moment can probably prove or disprove, but it exist and should enter the model.

If every effect that exists that no-one can prove/disprove goes into the model you are not doing physics ... I thought you knew what you were talking about but you have come here to spout off like so many others .... haven't you?

Maybe we should create a Theory for Time-Wasters section also ... just one more poster to scroll on by.

[Aero]

If every effect that exists that no-one can prove/disprove goes into the model you are not doing physics ... I thought you knew what you were talking about but you have come here to spout off like so many others .... haven't you?

Somehow that doesn't seem right to me. I don't know if it qualifies as "Flaming" but it seems to me to be discourteous in the extreme.

Very little Polywell theory can be proven or disproven due to the lack of experimental data. This missing data will be the rule by which all theory is measured, once such data becomes available or comes into existence.

If such an influence exists then it seems to me to behoove the proponent of that influence to cast the influence into the language of physics, that is, mathematics, in such a way that others could see how it might fit into their models. English is a very weak language for physics, but it is not unheard of for theories in physics to come before the observation, or contrarily, for observations to come before the theory. Start at the root of the idea and expound mathematically to the point of the influence so that it can be traced back to first principles. If the influence is real the review of the derivation will test it and the data will show it to be so. If it is not real, then so be it.

[Giorgio]

Giorgio:

If this has any effect is something no one at this moment can probably prove or disprove, but it exist and should enter the model.

If every effect that exists that no-one can prove/disprove goes into the model you are not doing physics ...

You are missing the whole point of my post, probably due to my poor english.

1) The effect exist, so you must consider it when you theorize an idea. You cannot just consider the increase of Magnetic Pressure and discard the presence of the Magnetic Tension without explaining why. They are one thing.

2) If the Magnetic Tension will have any effect on the working of the Polywell is somethink no one can prove or disprove at this moment.

But again, I am probably unable to correctly express what I mean.

I thought you knew what you were talking about but you have come here to spout off like so many others .... haven't you?

Maybe we should create a Theory for Time-Wasters section also ... just one more poster to scroll on by.

That is exactly my point.
If you hope to find theoretical answers in this section you are loosing your time as we have no data, we have no model, we have just ideas on how it might work, and any idea might be correct or wrong.

[Giorgio]

Very little Polywell theory can be proven or disproven due to the lack of experimental data. This missing data will be the rule by which all theory is measured, once such data becomes available or comes into existence.

Yep, exactly what I meant to say.