Theory and design of a harmonic ubitron/free-electron laser

Summary Form only given, as follows. A fully three-dimensional nonlinear analysis of the harmonic ubitron/free-electron laser, which is valid for arbitrary harmonic number, is discussed. The analysis has been performed for a configuration consisting of a beam propagating through a loss-free rectangular waveguide in the presence of a planar wiggler field. The advantage of harmonic operation is that relatively high operating frequencies can be obtained with relatively modest beam energies; however, this occurs at the expense of a greater sensitivity to beam thermal effects. In addition to enhancing the extraction efficiency, a tapered wiggler has been shown to reduce the sensitivity of the interaction to such effects. Suppression of the fundamental is accomplished by the careful choice of the beam energy, waveguide radius, and wiggler period in order to ensure that no resonance is possible at the fundamental. A third-harmonic experiment operated at 15 GHz with a 55-keV electron beam is discussed.<>