Re: Charge distribution on a Toroid (was spheres vs toroids)

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "Jim Lux" <jimlux-at-earthlink-dot-net> 

 >
 >  > I noticed then that if I reduce the thickness of the tubes for the
 >  > Pjj terms to about 1/3 of the distance to the adjacent ring the
 >  > oscillations disappear, and I obtain very good results with the
 >  > rings right at the surface.
 >
 > At some tube radius, presumably, the self potential of the tube
 > ring becomes equal to the self potential of the tape ring, so I
 > guess you've found the correct 'equivalent tube' in this instance.
 >
 > Wonder if the 1/3rd is generally valid?  One might expect it to
 > depend on curvature of the surface in some way.

This seems quite similar to the guidelines used in modeling conductive
surfaces using wires in method of moments codes.  You generally look for
half the circumference of the "wire" to be the spacing between the wires
(i.e. diameter=spacing).  I don't know that there is real analytical backup
for this "rule of thumb" or just that it empirically produces the "right
results".  There certainly is a fair amount of literature on wiregrid models
for surfaces in MoM codes, but I haven't looked into it in any detail.