Dc Electric-Field Enhancement of Cherenkov-Radiation Output Power

The Cherenkov radiation in dielectric-lined waveguide with transverse magnetic (TM) mode coupling has been investigated by using a newly developed relativistic electromagnetic particle model. The parameters used in the simulation are relevant to a recent laboratory experiments. With a 12-A and 220-kV electron beams, the results show that the excited wave is at ¿¿ 26 GHz with 310-kW output power. The increase in electron momentum spread is observed to reduce the tightness of electron bunches and to enhance the energy spread of the electrons trapped in the potential well, which results in smaller gain per unit length and reduced nonlinear efficiency. It has also been demonstrated by computer simulations that the output power can be improved by an order of magnitude if in an amplifier configuration the interaction length without phase focusing is doubled and an axial dc electric field (30V/cm) is imposed right before the electron bunches reach the bottom of the potential well.