PERFORMANCE LIMITATIONS OF AN X-RAY FEL

In this paper we present simple design formulae for calcula-tion of characteristics of a self amplified spontaneous emis-sion (SASE) FEL operating in an X-ray wavelength band. It is shown also that the growth of the energy spread due to the quantum fluctuations of synchrotron radiation imposes fundamental limit on the minimal achievable value of the wavelength in the X-ray FEL.