Undulator and curvature radiation of a relativistic charge moving along the curved spiral trajectory

For the ultrarelativistic charged particle having a spiral trajectory, revolving around the curved magnetic field line, the contribution to radiation occurs from two types of motions: the motion with relativistic speed along the curved magnetic field line (curvature radiation) and the contribution to radiation from many revolutions of particle round a drift trajectory (undulator radiation). Characteristic frequencies for these two mechanisms are essentially various. Curvature radiation is linearly polarized, undulator radiation has circular polarization.