High-efficiency relativistic backward wave oscillator: theory and design

Backward wave oscillators (BWOs) driven by high-current relativistic electron beams are capable of producing high-power coherent radiation in the centimeter and millimeter wavelength regions. However, the efficiency of these devices is usually limited to 15-20% when a homogeneous slow-wave structure is used. Utilizing a two-section slow-wave structure, where the spatial period of the second section is larger than that of the first section, a BWO efficiency of greater than 50% was calculated. A conceptual design of a high-efficiency S-band BWO driven by a 500-kV 5-kA electron beam has been developed and analyzed.