Dynamical aspects of FEL interaction in single passage and storage ring devices

The dynamical behaviour of the free-electron lasers is investigated by using appropriate scaling relations valid for devices operating in the low and high gain regimes, including saturation. The analysis is applied to both single passage and storage ring configurations. In the latter case the interplay between the interaction of the electron beam with the laser field and with the accelerator environment is investigated. In particular we discuss the effect of FEL interaction on the microwave instability.