Undulator radiation inside a dielectric waveguide

We investigate the radiation emitted by a charged particle moving along a helical orbit around a dielectric cylinder immersed into a homogeneous medium. Formulae are presented for the radiation intensity at large distances from the cylinder and for the radiation energy flux through the cross section of the cylinder. Under the Cherenkov condition for dielectric permittivity of the cylinder and the velocity of the particle image on the cylinder surface, strong narrow peaks appear in the angular distribution of the radiation in the exterior medium. The radiated energy inside the cylinder is redistributed among the cylinder modes and, as a result, the corresponding spectrum differs significantly from the homogeneous medium or free-space results. It is shown that the presence of the cylinder can lead to the considerable increase of the radiation intensity.