Design considerations for x-ray free electron lasers

We develop design considerations on the possibility of generating free electron laser radiation in the x-ray region of the spectrum (50-60 Angstrom), by exploiting a frequency multiplier scheme. We propose a free electron device consisting of a relatively low energy linac (750 MeV) and three sections: an oscillator at 150 nm, an amplifier tuned at the fifth harmonic of the first and a second amplifier operating at a subharmonic of the second amplifier. The seedless amplification is ensured by the e-beam bunching, induced in the oscillator and in the second section, which plays the role of amplifier and modulator. We also explore the possibility of overcoming the problems associated with the bunching efficiency dilution, due to intracavity saturation of the first section, by discussing the regeneration of the bunching by the use of a cavity dumping, realized with a suitable e-beam energy or cavity detuning modulation. (C) 1999 American Institute of Physics. [S0021-8979(99)01622-9].