charliem wrote: You agree that if you place an extra coil inside or near a corner of the cube (opposite N-S orientation to the 6 main ones), then it will deform the field so that it gets stronger in some places and weaker somewhere else.
Actually, I am not sure it would in fact have to get weaker anywhere. By turning the virtual coil real, it may just even things up and make the fields stronger.
charliem wrote: Then the question that remains is if you can think of a configuration where the lowered field regions are shielded with other of enhanced (or at least not diminished) field. No trivial thing to achieve.
I can’t help but feel that what we want to achieve, after the plasma has inflated the waffle ball, is as spherical a wiffleball as possible with as small a total cusp area as possible. I agree with what I think DrB said which is the quasi truncated cube format is NOT it.
charliem wrote:If you put an extra coil inside a corner, that would deforme the funny cusp creating a point cusp in its center (an enhancement, good thing), but also weaking the field in the line cusps between the primary magnets, that is WIDENING them (not so good).
Ok. It seems we have a disagreement here on terminology. The funny cusps are NOT at the corners of the cube. At the corners are the point cusps from the virtual out magnets. The things you call line cusps are where the funny cusps SHOULD be if the system were the true Polywell DrB stated that he wanted. But we are agreed that placing a magnet at the corner can be a good thing.
Re the “line” cusps, replacing the virtual magnet with a real one may “widen” the cusp, but it can also make it MUCH shorter. It is an area issue, and line cusps (according to DrB) are the dominant loss mechanism. He wanted to eliminate them in favor of funny cusps which had a very small area of null field.
I suspect you are currently locked into thinking the magnet must necessarily be toroidal. I don’t agree. I think it would be better to be triangular.
The other question is just exactly what you mean by “inside” a corner. I envision it to be at the same spherical standoff as the prime coils.
charliem wrote:And if we put the coils outside the corners then they'll "push" from the magnetic field lines created by the primary coils, and in doing so expanding the funny cusp mouth (very bad thing), and still weaking the field near the casings (and making easier for the E-field to get the electrons to the metal).
IBID re terminology. And I don’t understand what you mean by “push” but I disagree that it would grow the corner cusp. The fields will all be of proper sense to shrink ALL cusps.
charliem wrote:About "no metal thru the wiffleball": Its not just about the wiffleball not contacting with any metal structure, the ideal situation is that no metal in the magrid is unshielded from electrons; that includes its interior (where the wiffleball is supposed to form), but ALSO the cusp regions, AND even its exterior surfaces. Any metal of the magnets casings unprotected with a powerful enough B-field will suck electrons, because of the E-field.
Here we go with language again. To me, the wiffleball is the definition of that surface in space where the electrons cannot pass. Like the true waffle ball it has the inside surface, which is where most folks seem to stop thinking, but it also has a part of the surface that transits outward to an outer surface, thereby making holes (cusps) and continues across an outside surface (which in this case looks nothing like a wiffleball!). No metal should cross that surface, the wiffleball, unless it is remote enough from the cusps that the electrons have been returned thru the cusp by the electrostatic potential.
charliem wrote:A simulation with graphics could make all this much more evident... or disprove my intuition ...
Tell you what, give me ~$5000 so I can buy the necessary software and I will do the sim. And a juicy one back at ya!
Actually, the software is free, but it requires Wolfram Mathematica which is not