Electron beam properties and impedance characterization for storage rings used for free electron lasers

Good electron beam qualities and stability are the crucial features of Stor age Rings dedicated to synchrotron radiation sources or to Free Electron La ser. Most of these characteristics depend on the coupling of the e-beam wit h the machine environment, which can be in turn modelled in terms of a char acteristic impedance, whose absolute value and structure can be used to spe cify both the stability (longitudinal and transverse) of the beam and its q ualities (energy spread, bunch length, peak current, etc.). In this paper w e consider two specific examples of Storage Rings used for FEL operation an d analyze their performances by means of semianalytical and numerical metho ds. The analysis is aimed at clarifying the dependence of beam energy sprea d and bunch length on beam current and at providing a set of parameters use ful for the optimization of Free Electron Laser or synchrotron radiation so urces. (C) 2001 Elsevier Science B.V. All rights reserved.