Abstract
Annular relativistic electron beams carrying currents of 30–40 kA at energies of 200–500 keV have been propagated through a cylindrically symmetric, annular, ridged waveguide. An interaction between the electron beam and a backward wave in the guide has been observed. This leads to oscillations in the range 7.8–9.7 GHz at power levels of about 10 MW in a 30‐nsec pulse.