Why people are so optimistical to Polywell?

[Joseph Chikva]

As 93143 stated, the required features and the machines that addressed them ( to Bussard's satisfaction) have been referenced. More percisely, Bussard's Valencia paper is:

http://www.askmar.com/ConferenceNotes/2 ... 0Paper.pdf

Begining on ~ page 4, he presents the milestones and the machines that addressed them.

As far as density, I think that ~ 10^13 particles / CC was mentioned for WB6. This would be ~ 10^19 particles per cubic meter. This about a thousand fold lower density of what was predicted for a ~ 10T and 3 M diameter machine.

So, 10^19 reached. Am I understand correctly?

[TallDave]

How would you take a solicitation for yet another intermediate scale machine?

Another WB-8 sized machine, rather than WB-8.1? I think we could infer they probably don't think WB-8.1 can fuse p-B11, and further that there are problems that they are hoping to re-design their way around before upscaling to reactor.

Or do you mean larger than WB-8, but smaller than WB-D? I guess I'd be somewhat surprised they would do that. I don't think they can go much further on B without superconductors, which are going to be expensive and have a certain casing radius due to cooling at any machine size, and the volume scaling is probably less uncertain so there's probably not a lot of reason to make it bigger at the same magnet strength. I suppose it's possible, if WB-8 data is promising but still suggests some intermediate issues to be worked out, and the costs work out somehow, that they might go for a machine betweem 1KW and 1MW, maybe 1M radius and 1.5T, or something.

[TallDave]

Where is the magnetic pressure in reaction zone?

.1T at the edge for WB-6/7, .8T in WB-8. It's actually zero in the core (where most fusion takes place), though. The magnetic field mainly confines the electrons, the ions are mainly confined by the electrons.

So, 10^19 reached. Am I understand correctly?

Yes, and presumably something like 10^21 for WB-8. (Again, high beta.) I think this is at the edge...

You might find this comment by Rick enlightening.

viewtopic.php?p=4940&highlight=62500#4940

Actually, you need to click on “read more” under the design section, then “main parameters” then on the “more” button. What you will find is that the average density of ITER is ~ 1.0e20/m**3. If you use the formula I sent you for the Polywell [n*kBolt*Te = B**2/(2*mu0) to make it simple, let's use mks units and assume B = 10 Tesla, mu0 =4.0e-7*pi, Te = 1.0e4 eV and kBolt = 1.6022e-19 Joules per eV.], you will get a density ~ 2.5e22/m**3. The upshot of this is that the Polywell has a power density that is ~ 62500 times bigger than ITER EVEN IF THERE IS NO ION CONVERGENCE! Thus, a Polywell should far outperform a Tokamak even with a constant density Maxwellian plasma. Even if Rider and Nevins were correct (which Chacon has pretty clearly shown they aren’t) this isn’t a show stopper. It has a lot more significance for Hirsch/Farnsworth machines that have low average densities than it does for the Polywell.
The best analogy that I can think of is that the wiffleball mode is the jet engine and the ion convergence is the afterburner. The 2.5e22/m**3 density is what the Polywell should have on the edge, and then it hopefully goes up a few orders of magnitude as it goes into the interior. I don’t mean to imply that ion convergence isn’t important. This power density boost is what enables the Polywell to be built in small attractive unit sizes and to easily use advanced fuels.
However, the wiffleball mode is essential and the ion convergence simply makes things better. If we can’t get the wiffleball, then we can kiss our behinds goodbye. That’s why we are focused on achieving the wiffleball and we aren’t paying any attention to Rider and Nevins. They’re just a distraction. Does this kind of make sense?

[chrismb]

If you use the formula I sent you for the Polywell [n*kBolt*Te = B**2/(2*mu0) to make it simple, let's use mks units and assume B = 10 Tesla, mu0 =4.0e-7*pi, Te = 1.0e4 eV and kBolt = 1.6022e-19 Joules per eV.], you will get a density ~ 2.5e22/m**3. The upshot of this is that the Polywell has a power density that is ~ 62500 times bigger than ITER EVEN IF THERE IS NO ION CONVERGENCE! Thus, a Polywell should far outperform a Tokamak even with a constant density Maxwellian plasma.

Yeah. Sure! 10keV temp in a 1 millibar thermalised plasma. Oh, sure, that's easy.

[D Tibbets]

Thanks for recalling Nebel's quote. It looks like he was using an optimistic estimate for Tokamaks (I generally see 10^19 to 10^20 particles / M^3 for the upper end of obtainable densities of Tokamaks). I have heard that there is a "high Beta" version of a possibly functional Tokamak. I have no idea how much density advantage this would give, if any.
The Polywell fusion power density gain is a conservative estimate. So this is the minimal comparison, assuming the Wiffleball works. Improved performance with D-D fuel could push this gain significantly. But, at some point the thermal wall loading would limit the minimal size of the machine. Convergence may be more significant for P-B11 fusion as the fusion crossection is generally less than D-D fusion. I speculate that maintaining the average temperature around the P-B11 crossection resonance peak (~ 75KeV center of mass energy?) with convergence could result in greater fusion power density than the baseline D-D fusion. With direct conversion the final electrical output could be even greater and the limits on wall heat loading could be less. IE: the final size for any given power output could be smaller for a P-B11 Polywell, than for a steam generating D-D Polywell (at least if the D-D version is operating in the baseline mode mentioned by Nebel).

Dan Tibbets

[D Tibbets]

As 93143 stated, the required features and the machines that addressed them ( to Bussard's satisfaction) have been referenced. More percisely, Bussard's Valencia paper is:

http://www.askmar.com/ConferenceNotes/2 ... 0Paper.pdf

Begining on ~ page 4, he presents the milestones and the machines that addressed them.

As far as density, I think that ~ 10^13 particles / CC was mentioned for WB6. This would be ~ 10^19 particles per cubic meter. This about a thousand fold lower density of what was predicted for a ~ 10T and 3 M diameter machine.

So, 10^19 reached. Am I understand correctly?

Yes, I believe this was the ~ desity obtained in WB6. I don't know what densities may have been reached in the same sized WB7.

As far as Wiffleball formation due to the kinetic pressure of a plasma, A. Carlson was a vocal critic at one time, but even he was impressed by some simulations run by someone here on this site. He used a nother central magnetic field to demonstrate the effect, but the results were similar. Can anyone recall the author? Inderac (sp?) perhaps? I really ought to develop a bibliography.

A quick search of-
inflating a volume confined by magnetic field
revieled this article. The concept in astronomy is apparently mundane.

http://www.ess.washington.edu/Space/M2P ... slough.PDF



Dan Tibbets

[Ivy Matt]

Can anyone recall the author? Inderac (sp?) perhaps?

Indrek, I believe.

[D Tibbets]

Can anyone recall the author? Inderac (sp?) perhaps?

Indrek, I believe.

Thanks, that helps.

The model was, I think, produced by incarus, using Indrek's software and possible input. See this link. The image is ~ 2/3rds of the way down the page.

viewtopic.php?t=650&highlight=wiffle+ball

[EDIT] Or perhaps the work was done primarily by Indrek(?). In any case, here is a PDF made by Indrek :

http://www.mare.ee/indrek/ephi/images.pdf


Dan Tibbets

[Joseph Chikva]

Where is the magnetic pressure in reaction zone?

.1T at the edge for WB-6/7, .8T in WB-8. It's actually zero in the core (where most fusion takes place), though. The magnetic field mainly confines the electrons, the ions are mainly confined by the electrons.

So, 10^19 reached. Am I understand correctly?

Yes, and presumably something like 10^21 for WB-8. (Again, high beta.) I think this is at the edge...

I already learned out how Polywell should work according its authors idea. Thank you all.
And this is terminology issue. But beta parameter is used for magnetic confinement devices. Yes, it (words) have not a big matter, but beta there used for estimation of stability criteria. Stability is not the favorite issue here like to discuss.

So, 10^19 reached. Am I understand correctly?

Yes, I believe this was the ~ desity obtained in WB6. I don't know what densities may have been reached in the same sized WB7.

You believe that 10^22 m^-3, as I understand there is not any publication on it.
And in WB-8 obligatory 10 Tesla will be, not 2, not 6.
Will be the blanket between plasma and magnets?

[Joseph Chikva]

Where is the magnetic pressure in reaction zone?

.1T at the edge for WB-6/7, .8T in WB-8. It's actually zero in the core (where most fusion takes place), though. The magnetic field mainly confines the electrons, the ions are mainly confined by the electrons.

So, 10^19 reached. Am I understand correctly?

Yes, and presumably something like 10^21 for WB-8. (Again, high beta.) I think this is at the edge...

I already learned out how Polywell should work according its authors idea. Thank you all.
And this is terminology issue. But beta parameter is used for magnetic confinement devices -not for IEC. Yes, it (words) have not a big matter, but beta there used for estimation of stability criteria. Stability is not the favorite issue here like to discuss.

So, 10^19 reached. Am I understand correctly?

Yes, I believe this was the ~ desity obtained in WB6. I don't know what densities may have been reached in the same sized WB7.

You believe that 10^22 m^-3, as I understand there is not any publication on it.
And in WB-8 obligatory 10 Tesla will be, not 2, not 6.
Will be the blanket between plasma and magnets?

[TallDave]

I speculate that maintaining the average temperature around the P-B11 crossection resonance peak (~ 75KeV center of mass energy?) with convergence could result in greater fusion power density than the baseline D-D fusion. With direct conversion the final electrical output could be even greater and the limits on wall heat loading could be less. IE: the final size for any given power output could be smaller for a P-B11 Polywell, than for a steam generating D-D Polywell (at least if the D-D version is operating in the baseline mode mentioned by Nebel). Dan Tibbets

That's an interesting notion.

I got the impression the first wall load (at the Magrid) for P-B11 is negligible, since almost all the output is in alphas, which funnel out the cusps. Based on some comments from 93143 and others, I also got the impression neutroncity of the reactor materials is a concern for D-D, at least in terms of long-term operating costs. Those two factors combined make me think even a steam P-B11 (or one that has just has relatively low efficiency direct conversion) could potentially have some big cost advantages over D-D, even though the shielding advantage is apparently minimal. (Of course, this assumes you can afford to give up the power factor going from D-D to p-B11, which iirc is in the hundreds (or maybe smaller, with the resonance Dan refers to), but then power is only useful when controlled, as MSimon will tell you...)

But beta parameter is used for magnetic confinement devices -not for IEC. Yes, it (words) have not a big matter, but beta there used for estimation of stability criteria. Stability is not the favorite issue here like to discuss.

Polywells are a sort of magnetic/IEC hybrid. They have good magnetic curvature everywhere, so no ELMs, etc. Plus, the ion pressure is low at the edge.

I'll quote Rick again here:

Polywells have good curvature in their magnetic fields everywhere. Tokamaks have average good curvature. Consequently, tokamaks have some regions where localized modes (like elms) can be a problem.
It's unlikely that we will see elms on a Polywell. However, we might see other things. However, we don't expect to see catastropic things. What we may see is modes which increase losses through the cusps or cause cross-field transport across the magneitc field. These can affect the scaling laws. That's why the proposed phase II machine will be a steady-state machine at a considerably larger size. It should resolve these issues.

Also, note the implication that WB-8 is steady-state. I had been thinking it was probably pulsed until I read back through these recently.

[D Tibbets]

Joseph Chikva, I'm not sure what your trying to say in your last statement. WB8 is certainly [EDIT- certainly not] 10 Tesla, it probably is not even 1 Tesla. Hints are that it will be capable of ~ 8,000 Gauss, or 0.8 Tesla at the Wiffleball border. The 3 meter/10 T projected machine is just a example given by Bussard and which has become known as the 'WB100' as it was projected to produce ~ 100 MW of D-D fusion. It also would have ~ 100 X B- field, 100X the Wiffleball surface area compared to WB6.
Any combination of magnetic strength and diameter could be used in a machine limited only by engineering concerns.
As an example the B field could be 10T, the diameter could be 6 Meters. With the projected scaling of B^4 r^3/ B^0.25 r^2 scaling (note this is a more accurate description of the scaling, but as the B loss scaling is relatively small compared to the r^2 loss scaling it is often ignored for casual discussions). this machine would produce ~ 800 MW of fusion power.
If, in some way much stronger small magnets could be made and the thermal loads and arcing concerns could be handled, you could get ~ 100 MW from a WB6 (30 cm diameter) sized machine. I think the magnets would have to be ~ 60 T in strength.

I also think Beta is a straight forward ratio of plasma pressure / magnetic pressure. Beta= one means they are equal. While the desired value of Beta is certainly critical for various designs, I wouldn't go so far as to say it is a predictor of stability by itself. Of course, in the Polywell, if the Beta exceeds 1 by even a small amount the cusps open up and electron containment quickly suffers. If Beta is much less than one the Wiffleball effect is not maximized and obtainable density suffers, along with electron confinement per unit of volume.

Dan Tibbets

[Joseph Chikva]

Magnetic field
I am trying to say that even 10 Tesla will not help in case of instabilities. And superconducting magnets will not work if blanket or something else will not prevent them from neutrons.

High beta
Beta in Tokamaks as a rule does not exceed 0.1, nevertheless the number density there has an order of magnitude 10^19-10^20.
For TOKAMAKs there was proved theoretically that in case if beta exceeds 0.4 then various types of instabilities will occur. You are going to run at beta=1. I do not know is this possible or no.
And beta can't exceed 1 by definition.

Thermalization
I also do not see any mechanizm to avoid the thermalization. As that mainly caused by ion-ion collisions. No thermal energy dissipation mechanizm, no any forces returning scattered ions on previous direction.
I am sure that if we consider Polywell as the machine using the coherent movement of ions, it is obligatory. Otherwise - thermalization is inevitable.

Instabilities
I am more and more convinced that the instabilities issue hasn't been investigated at all. Or at least did not published.

And where did you read about 60 teslas strong magnets?

[chrismb]

Could someone just remind me how the curvature in a cusp is 'good curvature'?

[Joseph Chikva]

Could someone just remind me how the curvature in a cusp is 'good curvature'?

If you are asking regarding that I said above, I am declaring that regardless to the shape of mag field. Combination of 6 or more MaGrids is a certain one type of magnetic trap. And there are a lot of other types of traps that have been designed. As I know today all of them (open type magnetic traps) are in a limited consideration.