Ph.D Thesis

Ph.D StudentLahav Assaf
SubjectInteraction of Electromagnetic Wave with Electrons in a
Cross-Field Oscillator with Ferroelectric Cathode
DepartmentDepartment of Electrical and Computer Engineering
Supervisors PROF. Levi Schachter
PROFESSOR EMERITUS David Schieber (Deceased)


The ferroelectric cathode has a number of unique features which enables the design of miniature vacuum tubes: The electron emission is triggered by much lower field than other field emission cathode, the vacuum level needed for reliable operation is low (10-5 torr), and it can be operated at relatively high repletion rate. The most interesting feature of the ferroelectric cathode is the high current densities achieved for operation with voltages lower than 1kV. The measured current densities are higher by more than two orders of magnitude than the maximum current predicted by the Child-Langmuir law.

The important trade off between a space charge dominated beam, originated from a ferroelectric cathode in a miniature cross-field oscillator is presented in this work. The proposed device is combined from two planar ferroelectric cathodes facing each other. An annular anode is inserted between them. The anode supports a DC field and an RF mode that is specially designed to interact with the electrons flow.

It is shown that the electron flow in the oscillator is controlled by electrostatic energy, which is coupled from the ferroelectric cathode to the interaction region. Although that in the absence of magnetic field the measured current exceeds the estimated Child-Langmuir limit by more than two orders of magnitude; the device is shown to be insulated by a relatively low magnetic field. More over the cut-off field is controlled primarily by the anode voltage.

A macro-particle model was developed for the proposed miniature cross-field oscillator (<0.1cm3). The model calculates the 3D motion of electrons first under DC fields (Ferroelectric, anode and space charge fields) and second under the combined DC and AC fields. The conversion efficiency of this oscillator is than calculated for various electrical conditions. It is shown that the conversion efficiency is weakly dependent on the amount total space-charge in the diode with values up to 25%.