Limitations on millimeter-wave power generation with spiraling electron beams

A study is made of the suitability of the interaction between a thin, solid, spiraling electron beam of 5-15-kV energy and a microwave cavity, for the purpose of generating watts of CW millimeter-wave power. The effect of finite energy spread in the electron beam is considered both theoretically and experimentally. Measured results are given for a prototype device operating at 9.4 GHz. Power outputs of 5 W and electronic efficiencies near 2 percent have been obtained. The data agree well with the theory, subject to some ambiguity in the energy-distribution parameters. The performance is strongly limited by the energy spread in the beam.