Studies of a high-efficiency, long-pulse relativistic backward wave oscillator

Abstract

A high-efficiency long-pulse relativistic backward wave oscillator (RBWO) operating in the C band is described. The electrodynamical structure of the RBWO consists of a resonance reflector, a slow-wave structure (SWS), an extractor, and a coaxial collector. To achieve high electron beam-electromagnetic wave interaction efficiency, a SWS for the RBWO is designed comprising of two structural segments with different corrugations that enables the gradually decreased electron beam axial velocity to better match the spatially constant electromagnetic wave phase velocity of the operating mode of the RBWO. To suppress electron emission and plasma formation on the inner surface of the electrodynamical structure, which is caused by a strong RF electric field, the RF electric field magnitude is optimized in computer simulations to be less than 700 kV/cm. A coaxial collector is designed to slow down the expansion of the collector plasma. The design of the RBWO is optimized in numerical simulations and its operation is validated in practical microwave-generation experiments. An output power of 3.3 GW is obtained in a practical experiment with a 796-kV, 10.3-kA electron beam guided by an external magnetic field of 2.2 T. The RBWO efficiency and microwave pulse width are measured in the experiment and found to be about 40% and 100 ns, respectively.