Over-Sized Mode-Selective Relativistic Backward Wave Oscillator

An oversized mode-selective relativistic backward wave oscillator is proposed. This device operates using the pure TM
₀₂
mode in the beam-wave interaction area and transmits a pure TM
₀₁
mode in the output waveguide. In the beam-wave interaction area, mode selection is well realized through oversized slow-wave structures with a coaxial inner conductor that provides perfect boundary conditions for the TM
₀₂
mode and simultaneously eliminates other modes. A large proportion of the TM
₀₂
mode field is eventually exported into the output waveguide in the form of a pure TM
₀₁
mode. With the large diameter and high mode purity, the device can be expected to have high power capacity. With a 770 kV, 11.0 kA beam guided by a 3.5 T magnetic field, a 3.2 GW microwave at 9.42 GHz has been obtained in our simulation. The device efficiency is 38%.