Intense microwave generation with a free-electron laser amplifier

The free-electron laser (FEL) is a source of coherent radiation in which the electron beam is coupled to the radiation field by a trasverse periodic magnetic field. The frequency of the radiation is primarily determined by the magnetic field strength and period, and the electron beam energy. We are investigating an FEL operating at 34.6 GHz which utilizes a 3.5-MeV, 800-A electron beam. The FEL is designed to maintain resonance through the entire device; that is, the magnetic field is adjusted (tapered) as the electrons traverse the interaction region and lose energy. With the proper magnetic field profile, we have observed radiated power in excess of 1 GW and a conversion efficiency (electron beam to radiation) of 35%.