NEW RESULTS ON ELECTRON EMISSION FROM PZT

Ferroelectric cathodes may offer a source of high current density electron beams for applications where the use of conventional cathodes is limited by the required current density, cathode poisoning, or lifetime. In a ferroelectric cathode, electrons are emitted when the spontaneous polarization is rapidly changed by a pulsed electric field applied across the ferroelectric. When no additional voltage is applied to a planar diode gap, emission current densities are on the order of w 1 Alcm'. When an additional field is applied to the gap, we have measured current densities of up to 100 Alcm'. In this paper we report on two topics:(l) beam extraction into a drift tube at low (10-20kV ) voltage and, (2) electron emission, transverse to an applied magnetic field, from a cylindrical ferroelectric cathode. In the former case we report on emission of a 20A beam current in a 300ns pulse repetitively pulsed at rates up to a power supply limited - 50Hz. The cathode is located in the fringing region of a 3kG solenoid magnetic field. In the second case we find, at low applied gap voltages, that the magnetic field required to suppress the radial current flow is considerably in excess of that predicted for the applied electric field.