Electromagnetic field of a charge moving in a waveguide and intersecting a boundary between vacuum and a resonance dispersion medium

Electromagnetic field of a charge that uniformly moves in a circular waveguide from a vacuum into a dielectric possessing frequency dispersion of a resonant type is under consideration. The main attention is paid to the analytical and numerical investigation of the waveguide modes excited by the charge. It is shown that there is a region in the medium where partial compensation of Cherenkov radiation (CR) takes place similar to the case of a nondispersive dielectric. However, the electromagnetic field pattern is complex and the role of resonant dispersion is essential. In the vacuum area of the waveguide, the main part of the field is a response from the resonant medium with frequency which is close to the resonance frequency. This effect might be used for diagnostics of medium properties. The typical plots for the field demonstrate the process of forming the so-called 'wakefield' in the dielectric part of waveguide. (paper)