Claudio Pellegrini
UCLA, Dept. of Physics and Astronomy
The well developed theory of short wavelength SASE-FELs is now being used to design two X-ray lasers, LCLS and Tesla-FEL. However these projects present some unique technological and physical challenges, related to the very high peak current of the electron beam, the very long undulator needed to reach saturation, and the importance of preserving the beam phase-space density even in the presence of large wake-field effects. In the first part of this paper we review the theoretical scaling laws for an X-ray SASE-FEL, and the status of the experimental verification of the theory. We then discuss some of the most important issues for the design of these systems, including wake-fields in the undulator, and the choice of undulator type. In the last part we consider the options for extending the basic FEL performance, in particular the possibilities of shortening the radiation pulse duration to the femtosecond region, and reducing the pulse line-width.
