  We evaluate the renormalized vacuum expectation values (VEVs) of electric and
magnetic fields squared and the energy-momentum tensor for the electromagnetic
field in the geometry of two parallel conducting plates on background of cosmic
string spacetime. On the base of these results, the Casimir-Polder force on a
polarizable particle and the Casimir forces acting on the plates are
investigated. The VEVs are decomposed into the pure string and plate-induced
parts. The VEV of the electric field squared is negative for points with radial
distance to the string smaller than the distance to the plates and positive for
the opposite situation. On the other hand the VEV for the magnetic field
squared is negative everywhere. The boundary induced part in the VEV of the
energy-momentum tensor is different from zero in the region between the plates
only. Moreover, this part only depends on the distance from the string. The
boundary-induced part in the vacuum energy density is positive for points with
distance to the string smaller than the distance to the plates and negative in
opposite situation. The Casimir stresses on the plates depend non-monotonically
on the distance from the string. We show that the Casimir forces acting on the
plates are always attractive.
