I don't believe there is, at present, any consensus on the precise mechanism
of origin for the geomagnetic field. Although it's a good question, I
believe that the problem of ion distribution is best addressed by
considering the current vectors and convection currents in the outer core.
In addition, there is no radial ionic confinement zone.
Perhaps the geomagnetic field is best understood in terms of a self-exciting
dynamo model? Topological differences (e.g., the hole) and symmetry
considerations render it unlikely, however, that the geodynamo is like a
self-exciting disk dynamo.
Regardless, magnetohydrodynamic calculations are exceeding difficult. A
fair start on this topic can be obtained from a review of C.M.R. Fowler's
excellent text -- The Solid Earth (University of Cambridge Press, ISBN
0-521-38590-3).
This is the edge of the geophysics cognitive map for me -- beyond this point
there be dragons. Although I don't know his present status, for the email
ambitious, I believe that Dr... Fowler used to be at the University of
Saskatchewan.