Stimulated Cherenkov emission in dielectric-lined waveguides

Abstract

Particle-in-cell simulations of a dielectric Cherenkov maser experiment are used to analyze the emissive characteristics of an annular relativistic beam in a dielectric-lined waveguide. Good agreement with recent experimental results is obtained. The large gain in the device follows linear theory until saturation, when particle bunching and trapping is observed. The beam density becomes highly modulated with pulse length \ensuremath{\sim}\ensuremath{\lambda}/2, where \ensuremath{\lambda} is the guide wavelength. The performance of the device in the high-current regime is highly nonlinear. A simple nonlinear theory, confirmed by numerical results, shows that the field saturates at a value corresponding to ${\mathrm{\ensuremath{\omega}}}_{\mathit{b}}$=\ensuremath{\Delta}\ensuremath{\omega}/2, where ${\mathrm{\ensuremath{\omega}}}_{\mathit{b}}$ is the electron bounce frequency in the wave and \ensuremath{\Delta}\ensuremath{\omega} is the detuning parameter.