  The intensity of an electromagnetic wave interacting self-consistently with a
beam of charged particles, as in a Free Electron Laser, displays large
oscillations due to an aggregate of particles, called the macro-particle. In
this article, we propose a strategy to stabilize the intensity by destabilizing
the macro-particle. This strategy involves the study of the linear stability of
a specific periodic orbit of a mean-field model. As a control parameter - the
amplitude of an external wave - is varied, a bifurcation occur in the system
which has drastic effects on the self-consistent dynamics, and in particular,
on the macro-particle. We show how to obtain an appropriate tuning of the
control parameter which is able to strongly decrease the oscillations of the
intensity without reducing its mean-value.
