Core material for high power high frequency coil/solenoid

[artis]

I'm not sure I understood your remark, well the field lines are going to loop back anyway whether there is a disc or isn't one I was just thinking that maybe I can put them to good use, although on a second thought if they experience another disc in their path that would in total lessen the strength of the field and I'm not sure whether the effect of cancelling circumferential currents would outweigh the extra mechanical complexity and other factors, probably not.
If I make a slotted disc I would have to use some low permeability (the same as air) composite material disc on which to attach the multiple thin and slotted copper fragments that join at the center for more structural integrity, this way I could sandwich the thin copper plate between the non-conductive discs to make one larger rotating structure.

 

[Baluncore]

You need to specify exactly what you are trying to do. Many things are provably impossible. The design of magnetic machines is well defined. You need to shorten the magnetic field lines and you need to minimise the air gaps. You cannot get away with breaking the laws of physics by negotiating with the devil, or by getting a more expensive lawyer. Are you dreaming or engineering?