Radiation of surface polaritons by annular beams in cylindrical waveguides

We investigate the radiation from a circular annular electron beam coaxially moving inside a dielectric cylinder immersed in a homogeneous medium. By using the electromagnetic field Green tensor the electric and magnetic fields are found inside and outside the cylinder for the general case of dispersion of exterior and interior dielectric permittivities. The energy losses of the beam are studied. Different types of radiations emitted by the beam are discussed. They include the Cherenkov radiation in the exterior medium, the radiation on guiding modes of the dielectric cylinder and radiation of surface polaritons confined on a cylindrical interface. The latter types of the waves are radiated in the spectral range where the real parts of the dielectric permittivities of the cylinder and surrounding medium have opposite signs. Numerical results for the spectral distribution of the radiated energy are presented for the Drude model of dielectric permittivity.