We analyze the electromagnetic field of a charge crossing a boundary between a vacuum and cold plasma in a waveguide. We obtain exact expressions for the field components and the spectral density of the transition radiation. With the steepest descent technique, we investigate the field components. We show that the electromagnetic field has a different structure in a vacuum than in cold plasma. We also develop an algorithm for the computation of the field based on a certain transformation of the integration path. The behavior of the field depending on distance and time and the spectral density depending on frequency are explored for different charge velocities. Some important physical effects are noted. A considerable increase and concentration of the field near the wave front in the plasma is observed for the case of ultrarelativistic particles. In the plasma, the mode envelopes and spectral density show zero points when the charge velocity is within certain limits.
We analyze the electromagnetic field of a charged particle moving uniformly in a circular waveguide and crossing the boundary between a dielectric and a vacuum. Our study focuses on the case when Cherenkov radiation is generated in the dielectric. Analytical and numerical investigation of the waveguide modes is performed. We show that a large radiation can be excited in the vacuum area. The mode amplitudes in the vacuum can be greater than those in the dielectric. The field from a Gaussian bunch is also studied. We note that the effect under consideration can be used to generate a large quasimonochromatic or multimode radiation.
We analyze the interaction between a charge and its electromagnetic field in the case of the charge moving in a waveguide and intersecting a boundary between two nondispersive media. The total work done by the field on the charge is calculated both analytically and numerically. It is shown that the work is positive under certain conditions, that is the force actuating the charge is accelerating. A physical interpretation of this phenomenon from the point of view of energy conservation is given. The kinetic energy gain per unit length and for all time of motion is analyzed as well.
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