Numerical Analysis of Resonant Multipolar Instabilities in High Power Klystrons

The monopole monotron instability is a well-known phenomenon in linear beam devices. In recent development of high-efficiency 50-MW X-band klystron, such instabilities were found and mitigated special second-harmonic multicell cavities triplet that used to improve the klystron's performance. further simulations using 3-D particle-in-cell computer codes, more rare complicated phenomenon, previously unreported nonrelativistic devices, associated with rotating multipolar was discovered. this article, qualitative quantitative analysis these oscillations presented. Various resonant suppression strategies are introduced discussed detail.