Constrained evolutionary optimization of the signal growth rate in an RKO with an axially varying waveguide diameter

Summary form only given. The relativistic klystron oscillator (RKO) is a high power microwave (HPM) source based on enhancing mature non-relativistic klystron technology, in which the kinetic energy of a population of electrons is converted into coherent microwave radiation. There is significant interest in maximizing the growth rate of the RKO\´s microwave signal as a function of the RKO design parameters. A model relating the growth rate to the beam voltage, beam current, and gap separation is generalized to reflect dependence on additional device parameters. Specifically, the lumped circuit model from which resonant frequencies of the cold tube are determined is extended to allow axial variation of the waveguide diameter, and to reflect the simultaneous existence of the "zero mode" and the "pi mode." These modes have associated frequencies that are up-shifted and downshifted symmetrically (though not necessarily respectively) from the (common) resonant frequency of the driver and booster cavities. The hot tube model is also generalized to reflect the dependence of the stop current on the beam diameter and axial variation of the waveguide diameter.