Polywell - Magnetic Electron Confinement or Magnetic Grid Shielding?

It may be difficult to separate "theory" from "application," but let''s see if this helps facilitate the discussion.
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Re: Polywell - Magnetic Electron Confinement or Magnetic Grid Shielding?

Post by MSimon » Wed Jan 16, 2008 1:55 pm

If you inject the D-D gas inside the positive grid the gas ionizes. The ions are attracted to the virtual cathode. Electrons are stripped off in the process.

With sufficient fusions alphas leaving the system will leave their electrons behind maintaining a net negative charge in the reaction area.

Electron guns may be needed for start up. If they are needed for running the device will not generate net power - in my estimation.

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Re: Polywell - Magnetic Electron Confinement or Magnetic Grid Shielding?

Post by MSimon » Wed Jan 16, 2008 2:02 pm

Look up double layer.

It has been known in electron tubes since the 20s.

You can't understand this device without a deep understanding of vacuum tube technology. Which is generally a lost art.

BTW the Japanese IEC folks proved the double layer (well formation) in 1999 with laser probes. Although Langmuir probes had been used since the 20s to map out charge vs distance in tubes. The problem with Langmuir probes is that they disturb the field so that the results are not definitive.

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Re: Polywell - Magnetic Electron Confinement or Magnetic Grid Shielding?

Post by MSimon » Wed Jan 16, 2008 2:09 pm

True. You need a significant size to produce net energy. Unless POPS gives you enough of a boost - sadly POPS is easy and yet table top experimenters seem uninterested. A very sad state of affairs IMO. In any case the POPS boys - Nebel and Park - are continuing Dr. B's work. There is hope.

The key is raising the density inside the reaction space without everything thermalizing. Bussard thought he had that figured out. We shall see.

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Re: Polywell - Magnetic Electron Confinement or Magnetic Grid Shielding?

Post by MSimon » Wed Jan 16, 2008 2:20 pm

Thermalization of ions happens near the grids where the energy is low.

Thermalization of electrons happens in the center where their energy is low.

Thus the energies are continuously renormalized.

The plasma so created tends to naturally form bunched beams. Those that have tried can listen to it on a HF receiver. With a little help from POPS it should be possible to add energy coherently to those beams increasing the collision density.

So add RF engineering to the talents required.

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Re: Polywell - Magnetic Electron Confinement or Magnetic Grid Shielding?

Post by Wilfried Heil » Wed Jan 16, 2008 3:01 pm

>I still question whether the magnetic confinement of electrons is required, although I concur that such an effect may occur .,.

Your question, if confinement is needed or just magnetic shielding of the grid, refers to the same thing.

The electrons are not confined forever, they will slow down and all of them will hit the "MaGrid" eventually. Confining the electrons in the magnetic field for some time has the effect of reducing the current which flows to the metal shell of the magnet structure AND increases the e-beam current which flows around the magnets, possibly many thousands of times.

The "MaGrid" is a magnetic storage trap for electrons, like Dave has pointed out. If the magnetic field is strong enough to hold the electrons for 10000 orbits, then the current flowing in the "MaGrid" assembly will be 10000 times stronger than the current delivered by the electron beam sources. This reduces the power needed to set up the electrostatic field to confine ions.

Tom Ligon has observed that after a while, the e-beam current suddenly drops, presumably when the "MaGrid"s electron trap is full. "All hell broke lose" when he switched the magnets off in this state.

Without the magnets, we have Farnsworth's "Multipactor" design, with crossing e-beams which form a potential well and also no need for a grid. Such beams are capable of melting and evaporating the hardest materials, but were not enough for fusion.

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Re: Polywell - Magnetic Electron Confinement or Magnetic Grid Shielding?

Post by Richard Hull » Wed Jan 16, 2008 3:48 pm

From the foregoing and as no one posting above has ever worked a polywell device, there seems to be a lot of ideas about how it might really be implemented.

If the grid structure, (the coil body), is the positive return then it will have to be made proof against heating which will occur from not only its own power input, but electron leakage, up converted ions and neutral bombardment. This magnetic structure demands a lot of power just to establish the field and a lot of cooling. It doesn't need parasitic leakage heating. (engineering and mechanical issues).

As Stefan mentioned above in his analysis, there are a lot of leak/loss paths. Some are common to even a simple fusor while others are generated by this polywell design and perhaps peculiar to it. They will drift out of the woodwork if the polywell is persued to any real degree.

Doubling the energy output per watt input over a fusor is a pyrrhic victory to say the least.

It looks like more ever insidious losses as in all fusion schemes. Do we just just keep making it bigger like the tokomaks and stellartors with the latest fixes in place on this newer device until we create a new billion dollar boon-doggle?

Real watts created in any device per unit viable volume would certainly thermalize this dream. Sometimes I think thermal is, indeed, the way to go, even if it is just to show it can't be done! (At some future point and after more big bucks are tossed into the fusion rat hole.)

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Re: Polywell - Magnetic Electron Confinement or Magnetic Grid Shielding?

Post by Wilfried Heil » Wed Jan 16, 2008 5:35 pm

So many here discussing the emperor's new clothes and with Richard, as always, firmly convinced that the guy is naked.

Apparently everyone has a different idea of what the "Polywell" is and how it might work. Part of the blame goes to Bussard who could have described it concisely. Instead of chasing a spectre I would much prefer to build such a device and discuss it in the process.

Richard, why do you think that the "Polywell" will be twice as efficient as the fusor?

The ions can fuse as long as they remain captured and if they are thermalized, then the energy of non-fusing collisions will not be lost. However, the fastest ions can escape from the well and take their energy with them.

There may be many paths to a successful fusion reactor. If Bussard's concept increases efficiency by 10000x compared to a Fusor, then we are half there, on a log scale at least. Scaling the thing up might do the rest. If nothing else works, it would still be a hell of a neutron source.

At present, unfortunately, there is no evidence that it works at all, just like Nebel's POPS, the Sandia Z-machine abused for fusion, and so on. All show minor effects which are then extrapolated to bombastic performance. The Z-machine at least sets all kinds of records unrelated to fusion.

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Re: Polywell - Magnetic Electron Confinement or Magnetic Grid Shielding?

Post by Richard Hull » Wed Jan 16, 2008 9:15 pm

.....Richard, why do you think that the "Polywell" will be twice as efficient as the fusor?

I do not look at the polywell as increasing fusion over the stock fusor though some might hope that this is the case.

What is claimed, but not proven, is that the polywell will virtually elimenate the electron loses suffered in a common fusor.

These losses were about half of the energy sucked up by a fusor. If these go away, you are now at a point where energy in to energy out is up by a factor of two. (Doubled the efficiency)

OOPS! We sorta', kinda, forgot that high current coil, magnetic field bill on the energy drag down, didn't we? Apparently we dropped the soap in the shower without watching out for the other guys in there with us. There is always another new loss jockeying for position that tends to screw th' pooch in the fusion reality chain. These are created in a virtual defacto manner with each new brainstorm that supposedly will plug the leak in the dike used to contain fusion.

Man is a creature of endless habituation once on the trail of something that looks like gold. The degree of repeated torture and loss of fortune willing to be suffered in getting at the golden substance separates the interested prospectors into strata that range from the true believers, 'no matter what', to those who claim to see only 'fools gold'.

Richard Hull
Progress may have been a good thing once, but it just went on too long. - Yogi Berra
Fusion is the energy of the future....and it always will be
Retired now...Doing only what I want and not what I should...every day is a saturday.

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Re: Polywell - Magnetic Electron Confinement or Magnetic Grid Shielding?

Post by stob » Wed Jan 16, 2008 11:30 pm

That's not quiet what is claimed.
The claim is that ion losses are virtually eliminated and electron losses remain constant with increasing magnetic field and go up with the square of the device size for a given geometry and drive voltage.

In a contest between a fusor and a polywell, both the size of an average fusor I doubt the polywell would stand a chance in terms of gain.
However the question is how it scales to higher fusion power.

Since for net power the ion density has to be increased by orders of magnetitude it's important to see how ion losses scale and because the reactor has to be quasi neutral the same goes for electrons losses. If these two don't scale very favorably (like claimed for the polywell and unlike the common fusor) there's no chance of net power, the reactor will prefer evaporating.
Losses which don't directly depend on plasma density probably won't increase as strongly as the ion density when scaling up, so they aren't quiet as interesting, but still have to be looked into of course.

Now I'm not sure what this other half of the losses consists of. Will these scale up dramatically with size and plasma density or are they more along the lines of vacuum pumps, measuring equipment and loss in power supplies?

Stefan

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Re: Polywell - Magnetic Electron Confinement or Magnetic Grid Shielding?

Post by SJSVOB » Fri Jan 18, 2008 3:05 pm

>We sorta', kinda, forgot that high current coil, magnetic field bill >on the energy drag down, didn't we?

Wasn't this the reason they wanted to use superconducting coils?

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