Relativistic backward-wave tube with mechanically tunable generation frequency over a 14% range

A tunable-frequency low-magnetic-field relativistic microwave oscillator is realized experimentally based on a relativistic backward-wave tube with a modulating resonance reflector. The generated frequency is tuned mechanically by moving the oscillator slow-wave structure relative to the reflector. At fixed parameters of the corrugations and of the electron bunch, a frequency tuning range of about 14% measured between -3-dB (relative to the maximum peak generated microwave power) points is realized. The maximum pulse power of 3.4 $\pm$ 0.7 GW was obtained at a carrier frequency of 3.65 GHz in a magnetic field of 0.44 T.