  Ferroelectric ceramics are tested as photocathodes at INFN Frascati
Laboratories. In order to characterize them for use in linac injectors it is
important to measure the temporal shape of the emitted current. With a duration
of the laser pulse of 25 ps, the required resolution is a few ps. An apparatus
has been set up for the purpose, consisting of a 30 kV electron gun, a
microwave deflecting cavity which translates the temporal distribution of the
electron bunch into a spatial one, a fluorescent screen on which the deflected
beam traces a sector of a circle and various focusing and charge measuring
items. The image on the screen is detected via a CCD camera and a frame
grabber. We describe the performance of the apparatus and some preliminary
temporal distribution measurements.
