Compound-lens injector for a 19-MeV, 700-kA electron beam

A robust injector capable of controlling the radius and angle of incidence of the intense, pulsed, annular electron beam extracted from the HERMES-III accelerator is described. The injector, called the compound lens, uses a tapered anode to control the beam electrostatically, followed by a gas cell with externally applied current to control the beam magnetically. Adjustment of the anode-cathode gap and external current of the injector permits the mean radius and injection angle of the beam to be defined independently of one another. Measurements of these quantities confirm model expectations