Measurement of Longitudinal Electron Beam Distributions for FELs

(TH-2-01) Presenting Author: Patrick O'Shea (Invited)

Patrick G. O'Shea  

Department of Electrical and Computer Engineering; University of Maryland

The performance of free-electron lasers depends critically on the quality of the electron beams used as drivers. In recent years, the growing requirements of short-pulse, high-gain FELs with sub-ps electron pulses have resulted in the developments of novel techniques for longitudinal pulse characterization. Such diagnostics range from simple FIR detectors to sophisticated optoelectronic devices. The ideal diagnostic should give us more information than just a single figure of merit $\ddot{o}$ it should give a phase space map that involves only the most minimal of a priori assumptions about the distribution. In practice, however, we may wish to have a more limited device for use during routine operation, while reserving the ideal diagnostic for initial setup and characterization. In this presentation we will outline the physical principles of longitudinal bunch measurements, and discuss the practical aspects of some devices currently in use or under development.