Design of large area electron beam guns

The factors which enter into the design of large area high voltage electron beam guns in which the beam emerges from vacuum into a gaseous environment through a thin foil window are reviewed. The following restraints are considered: The type of cathode which can be used, the restrictions imposed by voltage breakdown, the need for uniform current density distribution, the maintenance of uniformity during modulation, and the restrictions imposed by the foil window. The design of a 5-cm wide by 125-cm long gun for cw operation is described. (auth)