Cyclotron-Cherenkov and Cherenkov instabilities

The effect of the conventional Cherenkov instability on the cyclotron-Cherenkov maser is investigated for the case of a relativistic electron beam propagating along a background magnetic field in a dielectric using particle simulations. Both Cherenkov and cyclotron-Cherenkov instabilities are excited when the phase velocity of light in the dielectric is less than the beam velocity. It is demonstrated in the high-power regime, where the cyclotron-Cherenkov mode has the higher growth rate, that the Cherenkov mode has little effect on the nonlinear efficiency of the cyclotron-Cherenkov mode. High-efficiency is possible, confirming previous predictions based on single mode calculations. The effect of beam momentum spread is studied.>