Ferroelectric electron beam sources

Ferroelectric materials offer the possibility of compact electron sources, with modest requirements to initiate the emission process. We are studying such sources as possible injectors for microwave generation. The source consists of a polarized ferroelectric ceramic disk with silver electrodes coated on both faces. The front electrode consists of a periodic grid created by etching the silver to expose a line pattern of ceramic. This electrode functions as the cathode in a planar diode geometry with an accelerating gap adjustable from 0.1 to 5 cm. A rapid change in the polarization state of the ceramic is achieved by applying a 1–2 kV, 150 ns pulse between the electrodes of the ferroelectric. Early work used a coaxial cable to maintain an anode potential of up to 1 kV across the A-K gap. The emitted electron current was measured as a function of the gap spacing and the anode potential. The current varies linearly with the anode voltage, up to 1 kV, for gaps < 10 mm, and typically exceeds the Child-Langmuir current density by at least two orders of magnitude. Current densities in excess of 70 A/cm² have been measured. More recent work has used a 300 ns pulse forming network to apply a potential of up to 15 k V at the anode. Results of emittance and´ scaling measurements under these conditions are reported.