We consider an atom interacting with a quantized electromagnetic field insi
de a cavity with variable parameters. The atom in the ground state located
in the initially empty cavity can be excited by variation of cavity paramet
ers. We have discovered two mechanisms of atomic excitation. The first aris
es due to the interaction of the atom with the non-stationary electromagnet
ic field created by modulation of cavity parameters. If the characteristic
time of variation of cavity parameters is of the order of the atomic transi
tion time, the processes of photon creation and atomic excitation are going
on simultaneously and hence excitation of the atom cannot be reduced to tr
ivial absorption of the photons produced by the dynamical Casimir effect. T
he second mechanism is 'shaking' of the atom due to fast modulation of its
ground state Lamb shift which takes place as a result of fast variation of
cavity parameters. The last mechanism has no connection with the vacuum dyn
amical Casimir effect. Moreover, it opens a new channel of photon creation
in the non-stationary cavity. Nevertheless, the process of photon creation
is altered by the presence of the atom in the cavity, even if one disregard
s the existence of the new channel. In particular, it removes the restricti
on for creation of only even number of photons and also changes the expecta
tion value for the number of created photons. Our consideration is based on
a simple model of a two-level atom interacting with a single mode of the c
avity field. Qualitatively our results are valid for a real atom in a physi
cal cavity. (C) 2000 Elsevier Science B.V. All rights reserved.