Phase–velocity disk model for predicting output-gap velocity distribution for the design of high-efficiency Klystrons

Abstract

Abstract Klystrons require continued efficiency improvement to satisfy the growing demands of energy efficiency in modern high power microwave and accelerator systems. At the output gap, the phase–velocity distribution of the bunched electron beam governs beam-to-RF energy extraction and thus strongly affects electronic efficiency. In this work, a disk-based prediction model is developed to evaluate the phase and velocity distribution of beam disks at the output gap and to estimate the corresponding energy extraction behaviour. A novel diagnostic quantity, cavity energy transfer ratio, is developed as a figure of merit of the work for cavity wise energy transfer diagnosis and klystron efficiency optimization. The model incorporates RF gap interaction, drift-space phase slippage, velocity modulation, and space-charge-influenced bunch evolution in a self-consistent framework. Two drift-length cases are investigated to examine the role of space-charge-dominated bunching in efficiency enhancement using this model. The longer-drift configuration produces stronger bunch evolution before the output cavity, and yields improved electronic efficiency. The predicted disk energy-extraction efficiency agrees closely with KLyC and CST results, validating the proposed approach for rapid efficiency evaluation in klystron design