Mode competition in highly overmoded klystron cavities

The importance of klystrons to high power levels and high frequency ranges stimulated an interest in alternative concepts of klystrons for a long time. Inspite of a long history of the interest to alternative concepts of klystrons, an analytical theory that can be used for analysing such important effects as excitation of so called monotron oscillations in klystron cavities can describe such processes only in traditional klystrons with a cylindrical symmetry of the interaction space. We present the analytical theory describing this self-excitation in such cavities and also some estimation of possible effects in the design of an 11.4 GHz sheet beam klystron.