Observation of coherent synchrotron, Čerenkov, and wake-field radiation at millimeter wavelengths using anL-band linear accelerator

Spectra of synchrotron radiation (SR) and Čerenkov radiation (CR) in air have been observed in the wavelength range of 1.15–8 mm using bunched electrons accelerated by an L-band linac, whose energy and radio frequency are 40 MeV and 1300 MHz. The observed intensities of SR and CR at λ=4 mm are enhanced by factors of 9×${10}^7$ and 1×${10}^7$ in comparison with calculated intensities of ordinary SR and CR, respectively. Radiation of the rf wake induced in a chamber has also been observed. Bunch form factors are derived from the observed spectra, and the electron distribution in a bunch is discussed.