  A crucial part of the design of an FCC-ee detector is the minimisation of the
disruption of the beam due to the presence of a large and powerful detector
magnet. Indeed, the emittance blow-up of the few meters around the interaction
point (IP) at lower energies is comparable to the emittance introduced by the
rest of the 100 km ring. Vertical emittance is the single most important factor
in achieving high performance (luminosity, in this case) in a modern e^+ e^-
storage ring such as the FCC-ee. The design adopted is the simplest possible
arrangement that can nevertheless deliver high performance: two additional
coils per IP side. The performance achieved is such that vertical emittance
blow-up will not be a limiting performance factor even in the case of a ring
with four experiments, and even in the most demanding energy regime, that of
the Z running (about 45 GeV beam energy).
