The Problem of Coupling a 120-MHz RF Cavity to a 700-A, 6-MeV Pulsed Electron Beam

A 120-MHz cavity and RF system were built to modulate the beam energy of the Astron electron accelerator by ±5%. The beam pulse has a rise time of 20 ns which initiates a transient in the cavity. We designed the cavity to limit the transient voltage in order to avoid sparking. The excitation problem was studied both experimentally and theoretically. We established design criteria that allowed us to couple an RF cavity to a high-current beam as easily as to the low-current beams of the usual research accelerators.