PREBUNCHED HIGH-HARMONIC FEL FOR SHORT-PULSE MILLIMETER-WAVE EMISSION

A novel wide-band millimeter-wave source is described where a ''point- charge'' electron beam rotating within a bifilar wiggler will generate a short-pulse TE(mn) wavepacket at the mth-harmonic of the fundamenta l free electron laser (FEL) frequency. In this first-order interaction , all electrons lose energy to the wave if the electron bunch size is much less than the wavelength. For a grazing intersection of the beam mode with the waveguide mode, there is no slippage of the electron bun ch in the wave and the narrow width of the broad-band output pulse is limited only by the waveguide's dispersion. A linear theory of this ne w interaction is presented along with the design for a prebunched tent h-harmonic FEL proof-of-principle experiment that is predicted to gene rate a 140-ps pulsewidth 30-GHz wavepacket at kilowatt power levels.