Azimuthal asymmetry of coherent Cherenkov radiation from a tilted bunch

Modern accelerator technologies may provide electron beams consisting of ultrashort bunches with transverse sizes, which are much larger than longitudinal sizes. The spectral-angular characteristics of coherent Cherenkov radiation (CChR) produced by such bunches have thus been considered. We simulated the characteristics of CChR and those from a single charge on the basis of the polarization current model, which allowed us to consider finite sizes for the Cherenkov radiator. We calculated the angular distribution of the CChR from a bunch tilted by angle ψ with respect to the velocity direction, with the assumption of a 3-D Gaussian charge distribution in the bunch. Contrary to the azimuthally symmetrical distribution of conventional ChR, a strong azimuthal asymmetry was observed in the CChR from the tilted bunch. The maximal yield of the CChR may be achieved if the tilt angle ψ coincides with the Cherenkov angle Θ _ch =arccos⁡(1/nβ), βc is the charge velocity and n is the refraction index.