Relativistic Cherenkov Microwave Oscillator Without a Guiding Magnetic Field

In this paper, microwave oscillation in which an electromagnetic wave and a continuous cylindrical relativistic electron beam (REB) with no magnetic field are in Cherenkov synchronism was studied. Analytical estimates of the beam-transport length were given, and analysis of the effect of electron-beam premodulation on the oscillator starting current and linear efficiency was made. Using numerical simulation, the oscillator geometry with a slow wave structure of length about three times the wavelength and with an efficiency of 30%-44% was determined. In experiment, the transport of a continuous cylindrical high-current REB over a distance about two times greater than the drift-tube diameter was demonstrated. Stable oscillation with ap 10% efficiency was obtained, taking into account the total current of a planar diode producing the electron beam. The microwave peak power for the operating TM₀₁ mode was 1.3 plusmn 0.3 GW at 4.03 GHz.