Radiation of charge moving through a dielectric spherical target: ray optics and aperture methods

Radiation of charged particles moving in the presence of dielectric targets is of significant interest for various applications in the accelerator and beam physics. The size of these targets is typically much larger than the wavelengths under consideration. This fact gives us an obvious small parameter of the problem and allows developing approximate methods for analysis. We develop two methods, which are called the "ray optics method" and the "aperture method". In the present paper, we apply these methods to analysis of Cherenkov radiation from a charge moving through a vacuum channel in a solid dielectric sphere. We present the main analytical results and describe the physical effects. In particular, it is shown that the radiation field possesses an expressed maximum at a certain distance from the sphere at the Cherenkov angle. Additionally, we perform simulations in COMSOL Multiphysics and show a good agreement between numerical and analytical results.