On possible use of an isochronously synchrotron radiation concentrator in the photoinjector of free electron lasers

The possible use of intrinsic synchrotron radiation of a cyclic FEL for the cathode illumination in the photoinjector - the electron source for the basic FEL electron accelerator - is analyzed. It is shown that it is necessary to collect the energy from the arc which is much larger than the intrinsic SR divergence and to use isochronous optics. A simple algorithm is proposed to define the isochronously focusing surface which transforms the SR evolvent to a compact area.