Radio-frequency beam conditioner for fast-wave free-electron generators of coherent radiation

A method for conditioning electron beams is proposed to enhance gain in resonant electron-beam devices by introducing a correlation between betatron amplitude and energy. This correlation reduces the axial-velocity spread within the beam, and thereby eliminates an often severe constraint on beam emittance. Free-electron-laser performance with a conditioned beam is examined and analysis is performed of a conditioner consisting of a periodic arry of ‘‘FODO’’ channels and idealized microwave cavitites excited in the ${\mathrm{TM}}_{210}$ mode. Numerical examples are discussed.