Why people are so optimistical to Polywell?

[Giorgio]

Until we have those data all of our ideas can generate some nice discussions, but they will remain plain speculations.

One more time about injecting of electrons into background plasma:

Electron Beam Plasma Instability
...This initial configuration is unstable to an electrostatic plasma wave which grows by tapping the free energy of the electron beam. At early times, the unstable waves grow exponentially...

The full text you can read here: http://www.netlib.org/utk/lsi/pcwLSI/text/node180.html

That is just a simulation code.
We all know that (with the proper conditions) you can get any result you want with a simulation code. Unless you can support these simulations with experimental data in a polywell environment than it adds nothing new to the discussion.

But here people hope that next WB-8 will reach the density of 10^22 m^-3 explaining me beta=1, B=10T.
I also trust in God and and in miracles.

I am also not so much convinced that they can actually reach those values, but I also do not have any real indication that proves that it is not feasible.

[TallDave]

Electron Beam Plasma Instability
...This initial configuration is unstable to an electrostatic plasma wave which grows by tapping the free energy of the electron beam. At early times, the unstable waves grow exponentially..
The full text you can read here: http://www.netlib.org/utk/lsi/pcwLSI/text/node180.html

Mildly interesting, but it doesn't appear relevant to a well of magnetically confined electrons as in a Polywell.

And I suffered with the question: why soup has cooled in my pan?

I'm not sure you're understanding the concept of an electrostatic well. It isn't a Maxwellian distribution like a pot on a stove, it's more like ball bearings in a funnel-shaped bowl: as they fall down the sides of the bowl they gain kinetic energy, as they climb the sides of the bowl they lose kinetic energy.

Chacon's and Krall's simulations suggest that because the collision cross-section is much higher at the edge, where ions are slower, they will tend to thermalize there at low radial kinetic energy, which will tend to focus them at the core. I think there's some question as to how much ion focus we'll see due to this "annealing" in reactor-sized machines, but it's a reasonable notion.

[Joseph Chikva]

Until we have those data all of our ideas can generate some nice discussions, but they will remain plain speculations.

One more time about injecting of electrons into background plasma:

That is just a simulation code.
We all know that (with the proper conditions) you can get any result you want with a simulation code. Unless you can support these simulations with experimental data in a polywell environment than it adds nothing new to the discussion.

Yes that is simulation. But you know and me - not that any results may be gotten.
Conditions are the following: plasma and electron beam injected. As result - two stream instability.

[TallDave]

Here's Rick on two-stream, way back on the MSNBC article:

The machine does not use a bi-modal velocity distribution. We have looked at two-stream in detail, and it is not an issue for this machine. The most definitive treatise on the ions is : L. Chacon, G. H. Miley, D. C. Barnes, D. A. Knoll, Phys. Plasmas 7, 4547 (2000) which concluded partially relaxed ion distributions work just fine. Furthermore, the Polywell doesn’t even require ion convergence to work (unlike most other electrostatic devices). It helps, but it isn’t a requirement.

[Joseph Chikva]

Mildly interesting, but it doesn't appear relevant to a well of magnetically confined electrons as in a Polywell.

Please note me how does plasma confined in other devices? Not magnetically?
I am only putting the question: does in polywell electron beam injected into plasma? Or no?

And I suffered with the question: why soup has cooled in my pan?

I'm not sure you're understanding the concept of an electrostatic well. It isn't a Maxwellian distribution like a pot on a stove, it's more like ball bearings in a funnel-shaped bowl: as they fall down the sides of the bowl they gain kinetic energy, as they climb the sides of the bowl they lose kinetic energy.

Thanks. Some people are also worry on my education. Do not worry please. Potential well is not Maxwellian distribution and is a pot on a stove, is not bearings as well.

Chacon's and Krall's simulations suggest that because the collision cross-section is much higher at the edge, where ions are slower, they will tend to thermalize there at low radial kinetic energy, which will tend to focus them at the core. I think there's some question as to how much ion focus we'll see due to this "annealing" in reactor-sized machines, but it's a reasonable notion.

As I understand, at the edge arrange velocity of ions is near zero and they have larger cross section to pass radial energy for fast moving electrons? If yes, ions cooled at the expense of electrons thermalization?

[ladajo]

Furthermore, the Polywell doesn’t even require ion convergence to work (unlike most other electrostatic devices). It helps, but it isn’t a requirement

The source of much debate I think.

[Joseph Chikva]

Here's Rick on two-stream, way back on the MSNBC article:

The machine does not use a bi-modal velocity distribution. We have looked at two-stream in detail, and it is not an issue for this machine. The most definitive treatise on the ions is : L. Chacon, G. H. Miley, D. C. Barnes, D. A. Knoll, Phys. Plasmas 7, 4547 (2000) which concluded partially relaxed ion distributions work just fine. Furthermore, the Polywell doesn’t even require ion convergence to work (unlike most other electrostatic devices). It helps, but it isn’t a requirement.

It is really interesting. Can you please give a link?

[D Tibbets]

Chikva, you are taking things out of context.
Some values as I understand them:

Electron lifetimes (at ~ 10KeV average energies)

In a ~ 1 Meter machine diameter= ~ 5-6 passes in an opposing magnet mirror machine.= ~ 0.2 microseconds

In a Polywell with cusp confinement (No Wiffleball effect) ~ 60 passes= ~ 6 microseconds.

In a Polywell with Wiffleball effect (assume ~100 fold decrease in effective cusp hole size) = ~ 6,000 passes= ~ 600 microseconds

Note that roughly speaking, a Wiffleball could be achieved in a Mirror machine with confinement limited to the initial lower value, but you would have to throw 10 to 100 times (I'm not sure whether it is a linear or log rhythmic relationship) more electron current at it. Not good if you are trying to reach breakeven.

WB 8 is not expected by anyone to achieve 10^22 charged particles/ M^3 densities. If WB6 achieved ~ 10^19 then with B fields 8 times stronger (B^2 scaling) the density may reach ~ ~ 6 * 10^20 charged particles per M^3 in WB 8. This would be at the same drive energy (12 KeV). As Beta=1 is determined by the density *KE the achievable density would decrease as the drive voltage was increased. Having said that, if the test is done at 5 KeV the density would be relatively higher at the same B field strength.

Ions 'annealing' at the top edge of their potential well does not effect the electrons much because momentum transfer between heavy ions and light electrons is a bunch less than momentum transfer between same mass ions. The ions are not trading energy with the electrons so much as they are trading energy with themselves. The ions do not have time to thermalize completely on one pass in the bulk of the machine, but there are still a lot of upscattering and downscattering collisions. It is these two populations of ions that are exchanging energy in the low energy, high collisionality edge annealing region. This process dominates over the more rare collisions at higher energy areas. It would be reasonable to say that the ion population is indeed thermalized, but this thermalization spread is dominated by the low energy (and thus relatively low Maxwellian distribution range) ions at the top of their potential well. As machine size and density increases this dominance decreases but would never disappear entirely.

As has been referenced several times, if you wish to debate models, there is a contention that you have to use Fokker Plank formulas to accurately describe these dynamic systems. If you wish to argue the merits of this contention then you are out of my league.

As far as 0.4 Beta being an upper limit for Tokamaks before confinement suffers. I speculate this is due to the concave towards the center B fields. The Polywell does not have any concave towards the center B field lines. That is why it is claimed to be immune to MHD instabilities.

Dan Tibbets

[Giorgio]

Yes that is simulation. But you know and me - not that any results may be gotten.
Conditions are the following: plasma and electron beam injected. As result - two stream instability.

You can't just consider a generic plasma and electron beam interaction. It has very little to do with what happens (should happen) inside the Polywell.

[TallDave]

Please note me how does plasma confined in other devices? Not magnetically?

It depends on the device. I didn't see any sort of confinement mentioned in your link. But in a PW we're talking about electrons bouncing around inside the WB.

Thanks. Some people are also worry on my education. Do not worry please. Potential well is not Maxwellian distribution and is a pot on a stove, is not bearings as well.

Hmmm, somewhere between "well" and "stove" some confusion is arising. They are not analogous. Or maybe we just have dissimilar cooking methods. Perhaps your stove accelerates water toward the center of the pan?

As I understand, at the edge arrange velocity of ions is near zero and they have larger cross section to pass radial energy for fast moving electrons? If yes, ions cooled at the expense of electrons thermalization?

Yes, we have to keep injecting hot electrons to keep the distribution nonthermal.

Sorry, I don't have a link handy for the Chacon paper, but if you Google around you should find it.

[Giorgio]

Here's Rick on two-stream, way back on the MSNBC article:

The machine does not use a bi-modal velocity distribution. We have looked at two-stream in detail, and it is not an issue for this machine. The most definitive treatise on the ions is : L. Chacon, G. H. Miley, D. C. Barnes, D. A. Knoll, Phys. Plasmas 7, 4547 (2000) which concluded partially relaxed ion distributions work just fine. Furthermore, the Polywell doesn’t even require ion convergence to work (unlike most other electrostatic devices). It helps, but it isn’t a requirement.

It is really interesting. Can you please give a link?

http://adsabs.harvard.edu/abs/2000PhPl....7.4547C

In case you have an AIP account:
http://pop.aip.org/resource/1/phpaen/v7 ... horized=no

[Joseph Chikva]

You can't just consider a generic plasma and electron beam interaction. It has very little to do with what happens (should happen) inside the Polywell.

As I know regardless of device only different arrange velocities of electrons enough for creation of this type of instability at any conditionthat realy used in various devices. Including vacuum tubes, Astron of Nickolas Cristafilos, etc. And I am asking was this effect considered for Polywell or no? On base of what are declaring that "no"? Link? Article?

[Joseph Chikva]

As has been referenced several times, if you wish to debate models, there is a contention that you have to use Fokker Plank formulas to accurately describe these dynamic systems. If you wish to argue the merits of this contention then you are out of my league.

Again.
If you can I would be grateful for information, article, link where with usage of Fokker Plank equation or others is proved that Polywell at those and those condition has an immunity against something and something.
I will try to understand.
Thanks in advance.

[Joseph Chikva]

It depends on the device. I didn't see any sort of confinement mentioned in your link. But in a PW we're talking about electrons bouncing around inside the WB.

Just now I answered on two-stream instability in another post. That occurs in any device where electrons injected into media where another population of electrons is already exist.

As I understand, at the edge arrange velocity of ions is near zero and they have larger cross section to pass radial energy for fast moving electrons? If yes, ions cooled at the expense of electrons thermalization?

Yes, we have to keep injecting hot electrons to keep the distribution nonthermal.

If distribution - then thermal. Would you like to say non-maxwelian?
Yes, this may be will have some effect. But if fast electrons interact with slow ions and the other way around, I doubt that significant effect. Do not know.

[KitemanSA]

AFAIK, the primary force against thermalization is thermalization. See "Annealing" at this site:
http://www.ohiovr.com/polywell-faq/inde ... e#Glossary

Ok, thanks. I am heating my soup pan and in result that is cooling. Am I correct?

Counter-intuitive, isn't it. But remember that you are not "cooling" per-se, you are keeping the ions mono-energetic. Things trade kinetic and potential energy all the time. They do here too.

The thing to remember is that the collision cross section is much bigger at the cold end of this spectrum than the hot. So thermalization works better when cold. IIUIC.

A lot of people think of the fuel ions in a Polywell as ball bearings rolling up and down a bowl, but that isn't a good mental picture. Try thinking of them as ball bearings that get MUCH smaller at the bottom than the top. Thus, fewer collisions at the bottom and many more at the top. Ions catching up with ions (overtaking) have very small relative velocity so are bound to nudge and average the energy more often than ions in opposition spreading the energy.

All in all it makes sense, but still needs to be proved. And if it turns out not to be true, then it may be that the Polywell will not run steady state. Doesn't mean it won't work, just not steady state.