EFFICIENCY ENHANCEMENT IN A CERENKOV LASER BY VARYING PERMITTIVITY - TAKING INTO CONSIDERATION MODE SCATTERING

This paper considers a model of a Cerenkov laser consisting of a relat ivistic electron beam and a parallel plate waveguide loaded with a die lectric thin film. By means of numerical analysis, the improvement of the growth characteristics for the electromagnetic wave and the effici ency in energy conversion is discussed. In the Cerenkov laser, the gro wth of the electromagnetic wave is caused by the transfer of the kinet ic energy of the electron beam to the electromagnetic energy. As a res ult, the drift velocity of the electron beam is decreased gradually so that the synchronism with the phase velocity of the electromagnetic w ave cannot be maintained and an efficient transfer of energy is preven ted. Thus, the permittivity of the dielectric material composing the w aveguide is increased gradually along the direction of the propagation for the electromagnetic wave to reduce the phase velocity of the elec tromagnetic wave. In this manner, the synchronism with the drift veloc ity of the electron beam is maintained, leading to an efficient transf er of energy. The variation of the permittivity causes power loss due to the mode scattering of the electromagnetic wave or the reflection o r conversion to higher-order modes. In this paper, the effect of the m ode scattering is taken into account for detailed numerical analysis o f the amplification characteristics for the electromagnetic wave. It i s shown that the efficiency in energy conversion from the electron bea m to the electromagnetic wave and the amplification characteristics of the electromagnetic wave can be significantly improved.