Significance of Electron Recirculation Revisited

Discuss how polywell fusion works; share theoretical questions and answers.

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MSimon
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Post by MSimon »

I've been rude, again. My apologies. I'll try to be a better person in the future.


Why? A man should be at home in his skin.
Engineering is the art of making what you want from what you can get at a profit.

MSimon
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Post by MSimon »

Say the ions are confined in the reaction space. And the electrons go in an out. That might tell us that we have an alternating polarity at the edge.

Maybe the whole thing works because the various conditions are transient. The electrons leave. The reaction space at the edge gets a net positive charge. The electrons come back.

For the sake of argument assume the device works. How?

I'm of the opinion that static analysis is useless except for start up conditions.
Engineering is the art of making what you want from what you can get at a profit.

KitemanSA
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Post by KitemanSA »

Indrek wrote: This is actually why I entered my very first question - what is the true lifecycle of electrons. How do they leave the system so that they can avoid this "thermalization" everyone seems to be obsessed about? Now in our pipe dreams they hit the coils and go away before bad things(tm) happen. But coils are protected by a powerful jedi force-shield.

So they thermalize, destroy the effective potential well and no fusion can happen. Maybe there is salvation, but I can't see it.

Sorry for the long comment. I know noone wants to read other's comments and only write their own. I'm guilty of that too.
First, WELCOME BACK!

I was under the impression that Dr. N. answered this already. He says the electron "flow thru" as opposed to "current" needs to be optimized by permitting a number of the upscattered electrons to reach the wall, i.e. ground, thus recycling MOST of the energy while removing part of the thermalized population. Not sure where the lower energy electrons go. Joel seems to have them congregate at the edge of the well, IIRC.

As I understand this, Dr. N. considers electrons sent to the wall, "flow thru" which is used to optimize the system and not very lossy, and electrons that hit the MaGrid "current" which is energy lost. Hope I am quoting him correctly.

By the way, a lot of this was in posts relative to optimization against brem.

chrismb
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Post by chrismb »

Indrek wrote:I know noone wants to read other's comments and only write their own. I'm guilty of that too.
I like reading the comments of others(!) [despite the erroneous criticism that I don't see other points of view (which is a false axiom as there is only one point of view if I have a point of view! :lol:)].

I'm still waiting on the sidelines for something tangible to help change my mind on this hocus-pocus. Something solid. Something tangible. Anything!?! (Like, the sort of thing rnebel promised after a peer review).

Your static analysis seems correct and the dynamic case will only be worse. I presume you are being a little mocking on the comment of "thermalisation" because, of course, any "non-thermal" system will try to thermalise. That is just the 2nd law. Hence, thermo-nuclear fusion is conceptually preferable.

Any electrons lost through cusps will [obviously] encourage ambipolar diffusion, whether directly or otherwise lagging behind in their space-charged wake, and once outside the magrid, what possible physics will bring all that back into the magrid, a region of higher magnetic fields??

I mean, if Polywell is based on known physics, as is oft posited, then how does it manage to invert grad B drift?? By what means does it turn F=-µ.grad(B) into F=+µ.grad(B)?

D Tibbets
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Post by D Tibbets »

The population of the highest energy upscattered electrons have speeds too high to be reversed and recirculated. Also, they have to much energy to stay on a magnetic field line and be orbited back inside (if thay are on a field line away from the center of the cusp where the field lines curve more (field line doesn't hit the wall)). I have read this in several Bussard, etel papers or heard it mentioned. I have't sseen how the low energy electrons are removed. I guess thay become 'stuck' on a field line (instead of bouncing off) and are then lost through transport through the magnetic field till they ground on the coil. This could happen at the cusps or other areas of the wiffleball surface. Recirculation would recycle the electrons (99%?) that exit the magrid at cusps, essentially ejecting the 1% of electrons that have the highest energy. This would selectively reject the progressively upscattering electrons before they built up so much velocity that they would carry away alot of energy. How significant this preventive action would be depends on some number crunching with the total electron population lifetimes ( eg: 1000 bounces * 100 X recirculation) vs. the lifetimes of the electrons that reach this threashold ( 1000 bounces * 1X recirculation).

I don't know if low energy electrons traveling on deeper field lines might exit the grid and thus get a boost back up to the drive potential and then exit the B field, on a shallower vector back into the wiffleball. Bussard talked about the dispersion of the electrons from a radial path as they were initially injected because few of them could actually be persicely centered in a cusp and this is why the potential well is only about 85% of the drive voltage. This also implies (I think) that the radial nature of the electron vectors establishes the elliptical potential well (due to the electrons slowing as they approach the center- thereby spending more time there with subsequent concentration). If the electrons were moving randomely around inside the wiffleball, I think that the ions, due to their greater inertia and Gauss's law conciderations would travel outside the electron cloud before reversing. Generally it is claimed that the ions are electrostatically contained and generally do not see the magnetic field. This seems impossible with my understanding of square potential wells consisting of a bag of randomized electrons. This proves that the electrons must retain at least a portion of their radial vectors throughout their primary lifetimes (before recirculation)- based on my convient reverse logic. This also enters into arguments about bremsstrulung, and ion focusing (?).

Dan Tibbets
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KitemanSA
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Post by KitemanSA »

chrismb wrote: Any electrons lost through cusps will [obviously] encourage ambipolar diffusion, whether directly or otherwise lagging behind in their space-charged wake, and once outside the magrid, what possible physics will bring all that back into the magrid, a region of higher magnetic fields??
+12kV of electro-static charge?

PS: Dr. N. seems to disagree with your "obviously". As he stated, Polywells are quasi-neutral, NOT ambi-polar. Ok, so I emphasized some stuff.

D Tibbets
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Post by D Tibbets »

KitemanSA wrote:
chrismb wrote: Any electrons lost through cusps will [obviously] encourage ambipolar diffusion, whether directly or otherwise lagging behind in their space-charged wake, and once outside the magrid, what possible physics will bring all that back into the magrid, a region of higher magnetic fields??
+12kV of electro-static charge?

PS: Dr. N. seems to disagree with your "obviously". As he stated, Polywells are quasi-neutral, NOT ambi-polar. Ok, so I emphasized some stuff.
Once I find some references I'll explain why I am in the non-ambipolar camp. As for what possible physical force that can get the electrons back into the magrid-
Obvously, it is exactly the same force that 'pulls' the virgin electrons inside. The electeron gun releases low voltage electrons, and they are accelerated by the positive potential on the magrid. They are not going through the magfnetic field per sa, but traveling nearely parellel to it in the cusp regions. Just as the cusps are a hole that the electrons can escape through from the inside, the reverse is also true. I think that because of the configuration of the opposing magnetic fields, the electrons go down a focused funnel to get inside, but are trying to flow out through the small end of the funnel, which is quite small (wiffleball hole). Keep in mind that the potential on the magrid is up to several thousand more volts than the potential well. So, at least in theory the positive charged magrid will dominate over the space charge inside the machine if the electrons are not upscattered too much. Also keep in mind that the excess of negative charge inside the magrid is only ~one part in a million*. And, again, as Dr Bussard emphasized, don't think electrostatic, but electrodynamic.

* I'm not sure what the electrodynamic situation is while the wiffleball is being established.

Dan Tibbets
To error is human... and I'm very human.

Art Carlson
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Post by Art Carlson »

BenTC wrote:To what degree would the positive HV electric field from the coils balance those electrons, rather than needing ions to do it?
If you play through the geometry with some model calculations, you will see that will hardly make any difference at all.

If I am able to get across one piece of plasma physics before I go my way,* I hope it is the way quasi-neutrality works. I've explained it so often, and always somebody pops up that doesn't get it. Let me try one last time.

It is really just as basic and nearly as simple as Coulomb's Law, which establishes a relationship between charge, potential, and geometry. If you choose any two of these, the third is automatically and unavoidably determined. It does not depend in any way on the velocity distribution of the particles or on whether or not things are changing in time.

The way I like to think about it is to set the maximum potential difference allowed, the charge density, and the shape, and then calculate the maximum scale size. Let's assume spherical symmetry because it is simplest and most optimistic, in the sense of yielding the smallest value for the characteristic scale. For a sphere with radius R and a uniform charge density rho, the potential difference between the center of the sphere and infinity is

Phi = 0.5*(rho/epsilon_0)*R^2

Take Phi and rho as given, and solve for R:

R = sqrt( 2*(e*Phi) / (rho*e/epsilon_0) )

If we ignore the numerical factor and replace e*Phi with k*T_e, and rho*e with n_e*e^2, then we have - not coincidently - the formula for the Debye length.

If we apply this to a polywell, we might take Phi no larger than 100 kV, and n in the range of 1e22 m^-3 (figuring B = 1 T, beta = 1, <E> = 10 keV). Then we find

R >= sqrt( 2*(e*Phi) / (rho*e/epsilon_0) )
= sqrt( 2*(1e5) / ( (rho/n*e)*(1.6e-19)*(1e22)/(8.854e-12) ) )
= sqrt(rho/n*e) * 3 microns

You can play with the assumptions, but obviously your polywell as a whole is much bigger than 3 microns, so rho = e*(n_i-n_e) will have to be much smaller than n*e. That's the meaning of quasineutrality. If you want to even start a discussion of non-neutral plasmas in a polywell, the best you can do is look at the cusps, but I have given arguments why the thickness of the cusps must be much larger than microns, and the 1-D or 2-D geometry will make things rather worse than the calculation I did here.

In brief:
As a simple consequence of Coulomb's Law, coupled with an upper limit for the potential and a lower limit for the density, non-neutral structures in a polywell reactor can never be bigger than a few microns.

--------------------------------------------------------------

* When I came here, I brought with me a satchel full of physics arguments, why polywell would not work. In the ensuing months I beat on these arguments and let them be beaten on, looking for rotten parts. A few were rejected, a few new ones were added to the list, but on the whole my original analysis held up. Of course I was also exposed to claims that, whatever my theory says, the experiments show something different. I waited through a few countdowns for new and solid data, but they all fizzled. I'm not getting anything out of this anymore, so it is time to move on. I hope to put at least some of my energy into investigating the current prospects for FRC fusion. If something ever really does happen here, I suppose I'll find out about it through my Wikipedia watch list, or through a PM from some kind soul here. If you really need me, you can send a PM, or shine the Bat-Signal on the sky.

Oh, and thanks for all the fish.

chrismb
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Post by chrismb »

I'm 100% with Art on this. It's one thing to be discussing something eruditely whilst waiting for info, but why should I bother sticking around when nothing happens to discuss further or to progress the discussion? Speculations on top of speculations on top of...&c..

I came on to discuss some seemingly obvious show stoppers as well;
  • - the thermalising centripetal and oscillatory motions (that are all supposedly smoothed out by "annealing", this magic process never seen before in plasma, but somehow will happen for Polywell),
    - the megaamp proton fluxes though the centre (that, apparently, generate no magnetic fields)
    - the trillion litre per second vacuum pump requirement
to name but a few.

So I, also, plan to stay schtum while you guys hang about for Godot.

Incidentally, here are pictures of my experiment whilst operating (seeing as some have asked, sneeringly, something like "what are you doing [whilst EMC2 is so successful]?"). Yes, it is a toroidally shaped glow plasma with no visible glow contact with the chamber. Yes, it is a continuously sustained plasma, no pulses here (- in fact the picture is a 15 second exposure as it emits very little light). Yes, that is mostly H Balmer alpha (and a little beta and gamma), and, yes, there are very little thermalising energy-wasting electron recombinations going on, hence no blueness to it. Oh, and, yes, I have done diagnostics on it and it all looks very interesting, but maybe if I told you about it then it'd hold my research up....

...so I'll now let you get on with your speculations, which seems to be largely preferred here rather that to push to get real data.

cheers for now!

Chris MB.

Image

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domoarrigato
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Post by domoarrigato »

Art Carlson wrote: In brief:
As a simple consequence of Coulomb's Law, coupled with an upper limit for the potential and a lower limit for the density, non-neutral structures in a polywell reactor can never be bigger than a few microns.
Forgive me for asking what may be a completely dumb question, but why does this argument not also rule out fusion in a farnsworth-hirch fusor?

MSimon
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Post by MSimon »

Art Carlson wrote: In brief:
As a simple consequence of Coulomb's Law, coupled with an upper limit for the potential and a lower limit for the density, non-neutral structures in a polywell reactor can never be bigger than a few microns.
Art,

What difference does it make? We know a well forms (Japanese and other experiments).

I'm probably just thick - but isn't the important question the scaling of losses?

To get the reaction currents at the magnet faces (caused by lots of electrons moving slowly in a wire) you need few electrons (plus counter rotating ions?) moving very fast in the plasma.

Now that says there is a lot of stored energy in the electrons (ions?). Tom Ligon reported just such an anecdote about device shut down. Obviously without measurement there is no way to be sure of what Tom thought he saw.
Engineering is the art of making what you want from what you can get at a profit.

MSimon
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Post by MSimon »

Art,

It reminds me of the bumble bee question. For the longest time the flight of the bumble bee did not match what was known about aerodynamics.

It did not mean aerodynamics was wrong or that the bumble bee didn't fly.

All it meant was that there were gaps in our understanding.

I take the engineering approach. If physics can't explain how such a device works there are gaps in our knowledge of how the device works.

Now the bumble bee question may be apocryphal but the thrust of the argument holds.
Engineering is the art of making what you want from what you can get at a profit.

Indrek
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Post by Indrek »

Art Carlson wrote:In brief:
As a simple consequence of Coulomb's Law, coupled with an upper limit for the potential and a lower limit for the density, non-neutral structures in a polywell reactor can never be bigger than a few microns.
I haven't really been following the discussions as I've been away. And your messages are usually too hard for me to follow as you use too much random ascii-math. I apologize if you've been through this before. If you have perhaps anyone can spot it and let me know.

What you are saying is basically that my electrostatics simulation is wrong. The one at
http://www.mare.ee/indrek/ephi/pef8/
This is why I'm replying.

Now but why didn't you say so before? Either you are also one of those people who likes to write but not read other's stuff. Or you think I'm a complete nutcase and it's better to keep your distance and silence.

Anyways on the second account I can admit that this simulation was done using quite an unconventional technique. That was because I was a complete idiot back then and had no idea how to tackle PDE-s. I know better now. But I still think it is roughly correct - all the boundary conditions are satisfied. Therefore this is a solution to the problem at hand. And we all know the Poisson/Laplace's equation only has one solution - the right one.

I also tried to look into the math you offered. I found some errors. I couldn't get the results you get, but probably got what you intended, yes? Also where does this 1e22m^-3 pop out from?

Image

Why don't you write and format equations like this? Don't you care that other people read your messages?

Anyways let me point out the error in your thinking.

Take a +5V battery. Attach a large metal plate to one of the electrodes. How much charge moves into the plate? Hardly any. Now. Attach a second metal plate to the battery's second electrode and bring it close to the first plate. Something amazing happens. Large quantities of charge move into the plates. The net charge in individual plates is humungous, despite them only being at +5V.

But you just proved this can't happen. You just proved capacitors can't work.

And I didn't bring out this ridiculous example of capacitors for nothing. The polywell (as an ideal) is a sort of a capacitor. One plate is the coils. The other plate is the magnetic field against which the (net) electrons squeeze.

Then again. You are a plasma physicist. And I haven't really received any education in that domain. Maybe I misunderstood you. Maybe there is no hope for me.

edit: added proper equation. note to self: send hate-mail to devious people.
Last edited by Indrek on Thu Apr 01, 2010 10:46 pm, edited 1 time in total.

Art Carlson
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Post by Art Carlson »

@ MSimon (blowing my cover):

Never use a supercomputer when the back of an envelope will do. Just because there are equations you can't solve with the best theories and faster computers (like Navier-Stokes = bumble bees), doesn't mean you should doubt solutions you can obtain on the back of an envelope (like Coulomb).

If the polywell works, then there are gaps in our knowledge. We don't have the data yet showing it does work. If it has to violate Coulomb's law to work, I'll bet my life on Coulomb's law.

@Indrek:

The hour is too late (where I live) to give you a decent answer tonight. I'll get back to you. It's not there aren't plenty of nutcases around here, but I never saw any reason think you were one of them.

One final comment for today. You write "Why don't you write and format equations like this? Don't you care that other people read your messages?" What I see immediately above that is a red box containing the text, "Only texify.com can mimetex on this server. Please read read www.forkosh.com/mimetex.html and install mimetex.cgi on your own server. Thank you, John Forkosh." That does not seem to be a great improvement over ascii math.

MSimon
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Post by MSimon »

Art,

I'll bet on Coulomb too. I'm also betting that when we understand the device Coulomb will be satisfied.

As far as I'm concerned all that is proven so far is that the current understanding is wrong.

So do we say the bumble bee can't fly or do we look for a better explanation of why it does? Well of course we are going to need some data....

BTW I designed vacuum tube circuits for years without being concerned about quasi-neutrality. I just thought about electrons.
Engineering is the art of making what you want from what you can get at a profit.

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