Observation of coherent synchrotron radiation

Coherent effects in synchrotron radiation (SR) have been observed for the first time from 180-MeV short electron bunches of 2.4 mm using the Tohoku 300-MeV Linac. The intensity of the coherent SR was about ${10}^5$ times as strong as that of incoherent SR in the wavelengths of 0.4–2.2 mm. This enhancement factor corresponds to the number of electrons in a bunch. The SR intensity showed a quadratic dependence on the electron beam current. The radiation was mainly polarized in the orbital plane. The possibility of induced rf in a vacuum chamber was excluded experimentally.