Polywell FAQ wrote:Related to the above question, wouldn't the ions thermalize after a while of constant collision?
Hanelyp wrote:The collision cross section for ions is much greater at low energies than at higher energies. Thus the ions thermalize much faster at low energies at the edge than at the high energies at the core. Thus the ions assume a narrow energy distribution associated with thermalization at a lower energy.
Yes, because Bussard believed the losses were only of electrons to unshielded areas or through cross-field transport (electrons going out through cusps "recirculated"). One of the odd things about Valencia is that Bussard really hardly talks about ion losses at all. Almost everything he says about "losses" refers to electrons. The gmj factor he refers to doesn't appear to include ions either. Bussard seems to have looked at this from a perspective of a machine that only leaks/loses significant numbers of electrons.Again though, I'll restate my understanding of Bussard's emphasis on the Wiffleball trapping factor being more important for practical fusion levels, not for minimizing energy loss.
In a Faraday cage, I think the "lumpiness" acceptable depends on the wavelength of the EM radiation that will be blocked. I'm not sure the balance of forces from on or outside the Magrid is equivalent everywhere inside (especially since in WB-8 the coil casings may not even be connected to one another). I remember 93143 expressing some doubt on that point, and I don't think Art agreed either because otherwise ions inside the Magrid would see no force from those exterior electron sheaths he was calculating forces for.As far as Gauss's Law. In several threads here in the last ~1-2 years I have been informed that the lumpiness or continuity of the shell is not important. A wire grid would do as well. In fact the Faraday cage in the WB6 experiments was a rectangular wire mesh grid.and acted via Gauss's law.
Rick seemed to think so. IIRC, he posted words to the effect that longitudinal velocity was high and radial low in the area of higher collisionality. Maybe I'll dig that up. That would probably be the best cite for the FAQ. I'll try to get to that this wknd, Kite.Annealing- I think I have seen mention of edge annealing moderating the thermalization via upscattering or downscattering. I'm not sure if it has a similar effect on angular thermalization.
Yes, except you need to know the velocity to pick which crossection value you choose.hanelyp wrote:To partly answer Chris' objection: A fast particle sweeps though volume faster. But the slower particle will have more time for collisions as it sweeps through a distance. So the number of collisions is proportional to distance covered * cross section, velocity canceling out.
After some discussion here over the years the consensus here seems to be that that doesn't happen. For one thing, the field lines for WB-7 go into the wall. The new hotness is cusp-plugging (with oscillation rather than recirculation all the way 'round the fieldlines). That seem to explains Tom's PZL observation better too.WizWom wrote:The electrons will find a cusp line, and be puled (rather forcefully) along it out of the core; then they will recirculate to a face along the magnetic field lines outside the core,
This, I suspect, is because they did not understand what Bussard was driving at. He expected the linear cusps to leak. The reason he wanted to go to a dodecahedron is because a pentagon fits around a circle better than a triangle or square. Circular coils are easiest to engineer. Instead they thought it was about chopping off the "cusps" with a magnetic block. I've seen at least one web page with a truncated cube suggestion.TallDave wrote:After some discussion here over the years the consensus here seems to be that that doesn't happen. For one thing, the field lines for WB-7 go into the wall. The new hotness is cusp-plugging (with oscillation rather than recirculation all the way 'round the fieldlines). That seem to explains Tom's PZL observation better too.WizWom wrote:The electrons will find a cusp line, and be puled (rather forcefully) along it out of the core; then they will recirculate to a face along the magnetic field lines outside the core,
I treated the 0.1 C as a point charge using Gauss' law. Then, the force exerted on a charge of +1eV by it at one meter is easily calculated 0.1*charge/(4pi*ep-nought)/r^2; choosing 1m removed r^2Interesting numbers. Are you calculating just the force of the electrons there, or the well from the electron/ion differential?
There is no easy answer to this, it is a multiple variable partial differential equation, and we don't even know what functions to put into that equation until we see a Polywell operating and take some density/velocity/plasma parameter measurements of it. There are too many variables, too many unknowns at this time.
However, there is a hypothesis that such thermalization is counter-acted by thermalization itself in a process called annealing.
The basis of annealing is that the collision cross section for ions is much greater at low energies than at higher energies. Thus the ions thermalize much faster at low energies at the edge than at the high energies at the core. And while the spread of energies in a thermalized high temperature plasma (at the core) is quite wide, the spread at low temperatures (at the edge) is quite low. Thus the wide distribution from whatever amount of thermalization at occurs at the core assumes a narrower energy distribution by thermalization at the lower energy of the edge. The ions then fall back into the core with the energy of the potential well plus a SMALL thermal distribution, remaining effectively mono-energetic. Hypothetically.