A Large Signal Theory of Multiple Cascaded Bunching Cavities for High-Efficiency Triaxial Klystron Amplifier

Abstract

This paper presents a large signal theory of multiple cascaded bunching cavities for the design of high-efficiency triaxial klystron amplifiers (TKAs). The theoretical analysis of multiple cascaded bunching cavities is presented, focusing on the relationship between gap voltage and first harmonic current and velocity dispersion, which can exactly describe the clustering state of intense relativistic electron beams. The theoretical results of the first harmonic current and velocity dispersion are basically consistent with its simulation results, which can justify a high degree of confidence in the validity of that theory. This theory can predict the possibility of deep modulation of intense relativistic electron beams when the depth of the first harmonic current is about 150% by multiple cascaded bunching cavities. By properly accounting for this theory, we can design a Ku-band TKA with nearly 60% microwave conversion efficiency, which can provide theoretical and simulation guidance for the design of high-efficiency TKAs. More importantly, when we increase the electron beam voltage from 300 kV to 600 kV and keep the relativistic perveance constant, this device also can obtain more than 50% efficiency and 40 dB gain. As a result, we can design a Ku-band TKA with high average output power of about 1.5 GW, 52% efficiency and 46 dB gain.