Proposal for a compact FEL with electromagnetic-wave undulator

A proposal for a compact FEL based on an electromagnetic-wave undulator is presented. For a proof-of-principle experiment it is planned to scatter electrons with relatively low energy (< 10 MeV) from an intense microwave in order to realize an FEL in the infrared region. Calculation examples indicate that this experiment should be feasible with present technology. The long term goal of the project, however, is to use an infrared high-power laser as an undulator in order to advance to the soft X-ray spectral region. In this regime an additional problem occurs due to the diffraction of the undulator pulse, which can degrade the gain if the undulator power exceeds 1 GW. A method of compensating the diffraction effects is presented. A necessary pre-condition for experiments with electromagnetic undulators is the use of advanced electron beam sources which provide high currents with low emittance and low energy spread. (orig.)