Temporal behaviour and longitudinal instabilities on the Super-ACO free electron laser

Abstract

In a Free Electron Laser (FEL) the amplification of a stored light pulse varies according to different conditions of gain. This implies, for a Storage Ring FEL (SRFEL), a particular behaviour of the temporal structure. Measurements of the temporal width of the laser pulse in the Super-ACO FEL versus stored ring current and versus the so called “detuning” have been performed with a dissector. The results presented here show how the temporal width is influenced by the evolution of the gain. The position of the laser pulse with respect to the center of the positron bunch in equilibrium condition has been also measured. These results seem to confirm, along with the existence of longitudinal instabilities of the laser pulse for a perfect synchronisation, the important role played by detuning in SRFEL saturation process.