Focusing effect in synchrotron radiation

The distance dependence along the radial direction of the radiation emitted by a monoenergetic electron in a circular orbit is analyzed. It turns out that the angular spread of the radiation decreases with distance as we approach the orbit, while the radiation intensity increases. Near the orbit, this focusing effect of the radiation in the orbit plane is strongly dependent on distance, so it might be useful for studying the electron-beam structure in high-energy accelerators.