A compact and economical injector for free electron lasers

Abstract The various successful demonstrations of FEL oscillation have verified the theory and established practical design techniques. FELs should now move into the realm of user devices, whether scientific or commercial. Potential users will be looking for sources of electron beams which are both compact in size and economical to manufacture. The present paper suggests a type of recirculating linac which could give energies in the range of 50 to several hundred MeV using a single klystron, whilst maintaining all the desirable properties given to the beam by the preinjection system. The latter could incorporate, for instance, the proposals of Stanford (HEPL) or Los Alamos for the production of very low emittance, low energy spread beams with high peak currents. The klystron would essentially have a long macropulse (∼ 100 μs) and could be either L-band or S-band, the former having some advantages at high peak currents. In principle the device could be cw, using either conventional or superconducting technology, although this would be more costly. The proposed accelerator might well be the best means of achieving a VUV FEL, if sufficiently low emittance electron beams can be produced.