  It has been observed \cite{break} that breakdown in an 805 MHz pill-box cavi
ty occurs at much lower gradients as an external axial magnetic field is inc
reased. This effect was not observed with on open iris cavity. It is propose d
that this effect depends on the relative angles of the magnetic and maximu m
electric fields: parallel in the pill-box case; at an angle in the open ir is
case. If so, using an open iris structure with solenoid coils in the iris es
should perform even better. A lattice, using this principle, is presented, for
use in 6D cooling for a Muon Collider. Experimental layouts to test th is
principle are proposed.
