  We consider a gedanken experiment with a beam of atoms in their ground state
that are accelerated through a single-mode microwave cavity. We show that
taking into account of the ''counter-rotating'' terms in the interaction
Hamiltonian leads to the excitation of an atom with simultaneous emission of a
photon into a field mode. In the case of a slow switching on of the
interaction, the ratio of emission and absorption probabilities is
exponentially small and is described by the Unruh factor. In the opposite case
of sharp cavity boundaries the above ratio is much greater and radiation is
produced with an intensity which can exceed the intensity of Unruh acceleration
radiation in free space by many orders of magnitude. In both cases real photons
are produced, contrary to the opinion that a uniformly accelerated atom does
not radiate. The cavity field at steady state is described by a thermal density
matrix. However, under some conditions laser gain is possible. We present a
detailed discussion of how the acceleration of atoms affects the generated
cavity field in different situations, progressing from a simple physical
picture of Unruh radiation to more complicated situations.
