Microwave amplification with an intense relativistic electron beam

A linear microwave amplifier has been constructed using an intense relativistic electron beam (5 kA, 1.2 MV) as the active medium. Stable amplification of an externally applied 100‐kW signal at ∼ 3‐cm wavelength has been demonstrated with a spatial growth rate of 1 dB/cm and an over‐all gain in this single‐stage device of 16 dB. The amplifier appears to be a very wide band device having a bandwidth extending over several gigahertz. The measured characteristics of the amplifier have been compared with theoretical predictions for the relativistic electron cyclotron instability. Measurements of both the variation of amplifier gain with magnetic field strength and the linear spatial growth rate are in reasonable agreement with theoretical predictions.