Google Polywell Fusion Counter

[Art Carlson]

Using 1/8th the width, and ½ the length, and assuming 99%+ return efficiency on the electrons, we are down to ~the 40MW that Dr. B wrote of.

Why stop there? Let's just say the plasma pressure is 1/10 the magnetic pressure (even though they are in equilibrium) and the gamma factor in the speed of sound in 0.01 (even though the "standard theory" says it can't be less than 1). Then we are down to 400 kW. Wow, this thing just keeps looking better and better!

Please Art, I am trying to get to a real understanding here. My factors are not being pulled out of the aether. I explained my disagreement with your numbers and assumed only that a MaGrid was a bit better than a plain grid at returning electrons. I did not try to assume impossibilities. I am just concerned that your "standard theory" is standard magnetic confinement theory... and that is NOT what we have here!

It does seem like "standard magnetic confinement theory" is the only place to start. If you want to propose an alternate theory, then you need to get serious about it.

each somewhat less than a quarter circumference long,

I’d say WAY less, given the squared plan-form coils proposed by Dr. B.

Maybe I need to draw a picture for you, but this is simple geometry, not a guess. If you claim a significantly different number, how about you draw a picture to explain what you are thinking.

Multiply that times 8 (the fourth root of the deuteron/electron mass ratio) for the hybrid gyroradius, assuming standard theory holds. Makes 8 mm cusp width.

Why in the world would you do this? Everything I have read about the Polywell says the ions don’t get anywhere near the MaGrid. The only things near the cusps are electrons.

I must have missed your elucidation when I submitted my posts explaining why quasineutrality was unavoidable and citing the review paper giving the hybrid radius as the lower limit of the sheath thickness. If you're serious about contributing to the scientific discussion, you need to get in on the ground floor. I don't have time to repeat myself over and over.

What's the power loss through the cusp, again assuming standard theory (or worst case, depending on your point of view)? An area of 0,1 m^2. An energy density of (1 T)^2/(2mu_0) ~ 4e5 J/m^3. A sound speed of about 2e6 m/s. Adds up to 100 GW. We're gonna need a bigger boat!

Using 1/8th the width, and ½ the length, and assuming 99%+ return efficiency on the electrons, we are down to ~the 40MW that Dr. B wrote of.

The 99%+ figure, at least, was "pulled out of the aether". I have explained why I don't expect any recycling, and nobody has presented a counter-model in any helpful degree of detail. If you can do that, great! Otherwise, why don't we stick with known physics, or at least admit that anything else is unfounded speculation?

Multiply by the ~5 times improvement Dr.B expects from a less-quasi-more-spherical dodecahedral Magrid, and there you have it!

Another number from the aether. Bussard said a lot of things that were nonsense. I never heard how he arrived at that factor of 5. I can give you a cogent geometrical argument why I would expect a dodecahedron to be worse than a cube. If you want to "get to a real understanding", then start by being a little more critical of unsubstantiated claims.
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P.S. I seem to getting a little crotchety. I'll start back to my daytime job tomorrow. Maybe that will help.

[TallDave]

He assumed the cusp width was equal to the electron gyroradius, although there was published experimental and theoretical evidence that the hybrid radius (the factor of 8 here) was the lower bound.

Yes, but that was also assuming quasineutrality, was it not?

<sigh> Of course I assumed quasineutrality. I always assume quasineutrality. More precisely, I don't assume it, I estimate the parameters and conclude that the plasma must be quasineutral. Check the archives, I don't feel like presenting the calculations yet again.

If I recall correctly, Rick replied that quasineutrality only applied at the edge under the assumption of LTE, whch isn't true for a Polywell where we are constantly injecting more electrons (i.e., there shouldn't be many ions out near the cusps).

Of course, we'd all like to see some measurements from WB-7 showing that there is some level of ion focussing, but it's always been fairly obvious Polywell couldn't operate in LTE. The whole starting point for the Polywell concept is that electrons are easier to confine magnetically than ions. Assuming LTE is sort of like assuming flat tires and determining your car can't go more than 20mph.

Other experiments have shown you can get ion focussing with IEC, most notably the Japanese laser fluouroscopy measurements.

[rnebel]

People seem to be confusing quasi-neutrality with ambipolarity. They aren't the same thing, and one doesn't imply the other. Polywells are quasi-neutral. They aren't ambipolar.

[MSimon]

Google search on - ambipolarity plasma

http://prola.aps.org/abstract/PR/v188/i1/p288_1

Phys. Rev. 188, 288 - 290 (1969)

The following statement is offered as a conjecture. Given two otherwise identically prepared plasmas: If one has J→·dA→=0 at every point of the boundary (except those points that carry essential currents), and the other permits nonessential currents to the plasma boundaries, the former will be more stable and better confined. A general theoretical argument in support of this conjecture (not a rigorous proof) is offered, based on the principle of minimum entropy-production rate. Experimental evidence in support of the conjecture is cited.

==

http://plasmadictionary.llnl.gov/terms. ... age=detail

Term: Ambipolar plasma potential
Definition: Electric fields that are self-generated by the plasma and act to preserve charge neutrality through ambipolar diffusion.

Term: Ambipolar plasma diffusion
Definition: Diffusion process in which buildup of spatial electrical charge creates electric fields (see ambipolar potential) which cause electrons and ions to leave the plasma at the same rate.

[TallDave]

Ah, thanks for clarifying Rick.

http://en.wikipedia.org/wiki/Ambipolar_diffusion

That does sound more correct. Sorry if I'm muddying the debate with imprecise terminology.

[Billy Catringer]

Those are real options, but they have a certain ugliness about them (either radioactive waste or greenhouse gases). Why not solar power (thermal cycle, built in the desert with the electricity piped to civilization over HVDC lines)? Or off-shore wind? (I haven't given up on hot-dry-rock geothermal, either, although it's pretty iffy.)

There is a lot of potential for geothermal here in the US and in Australia--at least that is what I have been told. What I don't see or hear about is a power company leasing a drillilng rig to drill the necessary wells. Perhaps that is a "red berries" situation, I don't know. It could be the going rig rates, $300k/day, even in today's rather depressed drilling market.

We already have windmills all over Texas and are building more of them. They are not too terribly useful because no one has found a way to store some of the electricity they generate for use when the wind lays. Yes, there is a company seeking investment to build windmills off the Texas coast in the Gulf of Mexico. The winds out there are steady to too much. When there is too much wind, it's no different from when there is no wind, and the storage issue again raises its ugly head. Absent a storage device like the "Shipstone" dreamed up by Robert A. Heinlein, wind and all the other forms of solar-to-electrical are never going to be of much practical use.

I spent more than a little time looking at biomass, hoping that there might be a way to replace our use of crude for transport energy. It's a non-starter as best I can tell. The fastest growing best hydrocarbon producing plant on the planet, algea, is unlikely to meet demand until AFTER oil reaches $400-$800/bbl and then only because demand will have dropped rather dramatically.

None of these technologies will replace the energy placed on our grids by fossil fuels, let alone keep up with projected demand, especially if we begin to transfer transport energy needs over to the grid. The situation we are in is simple, but dire. We either build fusion plants or we build fission plants or our civilization will collapse. Come to that, we may already be witness to the second crumbling. What I am afraid we will do is try and use up all fossilf fuels to keep going and fail. What I am voting for and advocating is nuclear power of the best kind we can develop. If that isn't fusion, then it is fission supported by breeder reactors.

[icarus]

rnebel wrote:

Polywells are quasi-neutral. They aren't ambipolar.

Interesting.

And what of the magnetisation inside the wiffle-ball, can we consider that part of the plasma as magnetized?

I'm assuming a small boundary layer of magnetisation just interior to the boundary perhaps.

[rnebel]

This is all very simple. In steady-state, ions and electrons leave the device at the rate they are injected. For closed field line systems like tokamaks, you have to inject neutral particles in order to get them across the magnetic field. This is generally a gas puff, frozen DT pellets, or neutral beams. In other words, you inject the same number of electrons as deuterium (or tritium). Consequently, electrons and ions leave at the same rate (the rate they are injected) and the electric field adjusts itself to make that happen. This is ambipolar diffusion.

On the other hand, cusped systems are open field line systems. You can inject charged particles in these systems along the field lines, which is what is done with the electrons in the Polywell. The injection rate of ions doesn't have to be the same as the electrons. 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. This is what you want to do in a Polywell. This even works in the quasi-neutral limit where the number of electrons and ions are approximately the same (with just a few more electrons to make the potential well).

[icarus]

rnebel wrote:

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 agree.

Now the question is how much does "flooding the device with electrons" cost, energywise? I.e. how good is the electron confinement?

Art's contention is that it is gushing out electrons, along cusp lines, at rates greater than what will be required to ever make the device a feasible net generator.

Is it possible that self-magnetisation of the electron plasma (particularly in a layer at the WB boundary) will serve to provide the enhanced wiffle-ball confinement of the electrons (i.e. non-cusp like), reducing electron losses to feasible reactor levels?

[TallDave]

For anyone else trying to follow along at home, there's also a good bit on ambipolar diffusion in the previously mentioned Glasstone & Lovberg "Controlled Thermonuclear Reactions" text (12.21 - 12.33).

[Tom Ligon]

Treated as an electron trap, once a steady state is reached a Polywell should lose electrons as fast as they are injected, or conversely it will stop accepting electrons any faster than they are lost.

If you want to characterize the losses as "gushing", that may be OK, as long as the electrons make a very high number of transits across the interior of the machine first.

It is not a perpetual motion machine. The electrons must eventually lose energy, and if it were possible to "gush" the coldest ones, that would be wonderful. Did someone here recently model this behavior of cold electrons in the cusps?

[KitemanSA]

Please Art, I am trying to get to a real understanding here. My factors are not being pulled out of the aether. I explained my disagreement with your numbers and assumed only that a MaGrid was a bit better than a plain grid at returning electrons. I did not try to assume impossibilities. I am just concerned that your "standard theory" is standard magnetic confinement theory... and that is NOT what we have here!

It does seem like "standard magnetic confinement theory" is the only place to start. If you want to propose an alternate theory, then you need to get serious about it.

I realize I am not a physicist, but I was under the impression that the basic theory to be working with here is "electro-static" confinement, at least as far as the ions are concerned. Isn't that the basis of all fusors?

Multiply that times 8 (the fourth root of the deuteron/electron mass ratio) for the hybrid gyroradius, assuming standard theory holds. Makes 8 mm cusp width.

Why in the world would you do this? Everything I have read about the Polywell says the ions don’t get anywhere near the MaGrid. The only things near the cusps are electrons.

I must have missed your elucidation when I submitted my posts explaining why quasineutrality was unavoidable and citing the review paper giving the hybrid radius as the lower limit of the sheath thickness. If you're serious about contributing to the scientific discussion, you need to get in on the ground floor. I don't have time to repeat myself over and over.

Vailed snipe happily accepted. I will look for them and try to understand your points.

What's the power loss through the cusp, again assuming standard theory (or worst case, depending on your point of view)? An area of 0,1 m^2. An energy density of (1 T)^2/(2mu_0) ~ 4e5 J/m^3. A sound speed of about 2e6 m/s. Adds up to 100 GW. We're gonna need a bigger boat!

Using 1/8th the width, and ½ the length, and assuming 99%+ return efficiency on the electrons, we are down to ~the 40MW that Dr. B wrote of.

The 99%+ figure, at least, was "pulled out of the aether". I have explained why I don't expect any recycling, and nobody has presented a counter-model in any helpful degree of detail. If you can do that, great! Otherwise, why don't we stick with known physics, or at least admit that anything else is unfounded speculation?

Well, perhaps, but not whole cloth. My counter models include both the Hirsh-Farnsworth and Elmore-Tuck-Watson fusors. Many sources suggest they get effectively 100% "recirculation" except those members of the relevant species that run into the relavent grid. Such sources imply ~90%-95% even with grid losses. Yes I am assuming the magnetic field will protect the MaGrid at 80%-90% additional efficiency. Purely a guess, but not unreasonable! I mean surely it does SOMETHING to improve on the basic fusor!

Multiply by the ~5 times improvement Dr.B expects from a less-quasi-more-spherical dodecahedral Magrid, and there you have it!

Another number from the aether. Bussard said a lot of things that were nonsense. I never heard how he arrived at that factor of 5. I can give you a cogent geometrical argument why I would expect a dodecahedron to be worse than a cube. If you want to "get to a real understanding", then start by being a little more critical of unsubstantiated claims.

I will take your word that you think he spoke a lot of nonsense. I have no data to judge him that way. Until I get such data, I will think of it as him saying some things I don't fully understand.
It is my understanding that the ~5x improvement came mainly from improved sphericity. As you point out, neither of us have the data he had to make that claim. Until we do, I cannot gainsay it, I will merely quote it as his opinion.

[MSimon]

Well, perhaps, but not whole cloth. My counter models include both the Hirsh-Farnsworth and Elmore-Tuck-Watson fusors. Many sources suggest they get effectively 100% "recirculation" except those members of the relevant species that run into the relavent grid. Such sources imply ~90%-95% even with grid losses. Yes I am assuming the magnetic field will protect the MaGrid at 80%-90% additional efficiency. Purely a guess, but not unreasonable! I mean surely it does SOMETHING to improve on the basic fusor!

First off: by going to magnetic grids the grids get thicker. You go from 2% to 5% intercept to 20% intercept. Second off the non-leakage probability must be .9999 in order to keep drive energy reasonable. That is not just an additional 80% to 90% efficiency. Sadly.

[KitemanSA]

Well, perhaps, but not whole cloth. My counter models include both the Hirsh-Farnsworth and Elmore-Tuck-Watson fusors. Many sources suggest they get effectively 100% "recirculation" except those members of the relevant species that run into the relavent grid. Such sources imply ~90%-95% even with grid losses. Yes I am assuming the magnetic field will protect the MaGrid at 80%-90% additional efficiency. Purely a guess, but not unreasonable! I mean surely it does SOMETHING to improve on the basic fusor!

First off: by going to magnetic grids the grids get thicker. You go from 2% to 5% intercept to 20% intercept. Second off the non-leakage probability must be .9999 in order to keep drive energy reasonable. That is not just an additional 80% to 90% efficiency. Sadly.

I took that into account in my sWAG. We are talking about the % of the electrons that escape the cusps, not the total percent. The wider grid is already protected by the mag field, no?

[Tom Ligon]

The number I heard for the improvement going to a dodec was closer to 3, but my communications with Dr. Bussard suggested he really did not have a particularly trustworthy model for more than a rough estimate. That was the reason for wanting to build both WB7 and WB8 at the same size. It would be important to determine just what the improvement was before deciding on a design for what MSimon calls WB100.

With the factor, it becomes an economic choice to build more but smaller coils, with the attendant multiplication of mechanical challenges, or simply go a little bigger and let R^7 give the same performance increase.

It would also answer Art's challenge. If it works worse, it tells you something about cusp performance, and Art can say he told us so. If it works better, we could tell Art to sit down and shut up. In the absence of data, I think we should continue to hear him out, because he strikes me as a basically smart fellow who will keep us honest.