The image of the plasma with the central coil on the right is consistent with my descriptions of the setup with essentially a linear variation of the Polywell. The properties of quasi spherical shape, favorable B field countours to prevent edge instabilities, high Beta, narrow line cusps, potential central focus are preserved. What is not apparent is if the plasma is neutral or electron rich. Mention of a potential well suggests it is electron rich- thus it is also a non neutral plasma. These characteristics are core to the Polywell concept - or any other that wishes to confine ions in a small reactor (excluding inertially confined or very short pulsation reactors like laser confinement or DPF?) due to ExB considerations.DeltaV wrote:Conjecture --
The larger diameter of the central coil increases the diameter and volume of the fusion region, compared to having a smaller central coil, making it less "2-lobed". Off-axis fusions become more likely, at the cost of higher central coil current. Coil currents will be tuned to obtain the optimum (highest fusion rate) compromise between active region volume and density. I'm guessing that the coil on the right in the T4 picture below is the central coil.
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Descriptions of more complex plasma confinement shapes- fields are perhaps consistent with the limited views and information but I wonder if they could work. Would the ExB losses be tolerable. It seems that there would be a lot of dense plasma near magnet can surfaces, and how would a potential well work in such a complicated plasma distribution? .
High Beta implies relatively high density which implies magnified ExB concerns for ions- unless they are confined in a potential well and kept out of the magnetic domain (?). At some point even the electron ExB losses could become dominate if the bulk plasma is to close to magnetic surfaces.
High Beta is possible in part, I believe, due to the quasi spherical shape of the contained plasma. The plasma pressure pushes outward symetrically against all magnetic surfaces equally. There are no weak points- excluding the cusps which are much less vunerable to the outwardly directed pressure, at least up to Beta exceeds 1.
It currently seems likely to me that recirculation in this concept may have greater importance than even in the Polywell. The 4th and 5th end magnets may reflect greater recirculation harvesting and control than in the Polywell. The illustration of a two magnet mirror machine, while generally considered as inadequate for containment might conceivably work if recirculation can be made good enough. This of course also requires an electron rich plasma. The electrons escape the magnetic containment, but recirculate while the ions are effectively contained by the potential well due to the maintained excess electrons. While the charged particles inside are within a 'Wiffleball' and thus non magnetic (not following magnetic lines), externally the conditions are low Beta, the B field gradient is shallow enough that charged particles (electrons) are captured on field lines and will flow around to the end point cusps and back in . Again the progressive upscattering of electrons would have to be controlled in some way. In this concept, the plasma (at least the electrons) is surrounding the magnets as quoted in the article.
This brings up a consideration of recirculation in general and electron upscatter also. In the Mini B and WB8(?) the electron guns seem to be at high negative voltage, while the magrid is presumed to be at ground. Here any electron that escaped would not have the high positive potential on the magrid to stop it and reverse it back through the same cusp like in WB6. With WB6 if the electron is upscattered enough it will lose a portion of it's outward KE but retain enough to reach the top of the magnetic loop outside the magrid, and then fall towards an adjacent grid, picking up additional KE as it does due to the positive charge on the magrid( back to its original already excessive energy). This can be a problem and so the upscattered electron must be picked off by a surface before it reaches the peak of the magnetic loop (surface such as a Faraday cage).
But with the magnets at zero potential (grounded) the escaped electrons would mostly stick on the magnetic line loops and renter an adjacent cusp at the same energy at which it escaped. Up scattered electrons would retain their excess energy, but at least they would not pick up an additional boost from a positively charged magrid. Collisional processes would complicate things, but to first order this may describe things. Art Carlson argued that progressive electron upscattering would destroy the system so there has to be some mechanism to prevent this. WB6 did this simply and directly by removing them . With the full looping recirculation system some other means for slowing or removing these upscattered electrons would be necessary. Simply removing them by intercepting a wall on the larger magnetic loops (which the higher energy electrons would follow- much like a mass spectrometer) might do this. This would be similar to the WB6 pick off mechanism but in a more selective fashion. I think this could also apply to the Polywell, thus satisfaction of my recirculation concerns about a grounded magrid. The collisional effects (such as electrons being scattered to the extent that they mirror without reenterering the interior) though may cause additional problems and any external grids for direct conversion would also complicate the system.
Dan Tibbets
