Study Of TM High Mode Double Gap Cavity For Multi-beam Klystron

πmode double gap cavity was wide used in high power broadband klystron for its characteristic impedance and peak power twice to the single gap cavity, in latest decade, double gap cavity was preferred output cavity in klystron design. The cavity size became smaller and smaller along with frequency heighten, which restrict to improve efficiency and power of klystron. Therefore, it is a necessity means that adopting high order mode cavity to improve high frequency klystron.Coaxial cavity was seductive due to its peak electric field symmetrical disperse around circle of the cavity section and convenient for electron beam hole disposal, but the uniformity of the characteristics impedance in each hole of cavity will be change worse while coupling with a waveguide. Therefore, it is not an optimal choice to adopt coaxial cavity coupling with waveguide. However, the difficult about asymmetric of characteristic impedance will be overcome while adopting high order mode double gap cavity coupling with coaxial line. The main works in this paper base on upwards are list as following:1,The eigenfrequency and the characteristic impedance ofπ-TM high order mode of rectangular double-gap cavity with a coupling slot in the center are calculated by analytic method. The influence of sizes and the position of the coupling slot on the frequency and the characteristic impedance ofπ-TM mode are discussed. The results of the analytic calculation are compared with ISFEL3D simulation results, and it is showed that the analytic results are close to the simulation results on the whole, especially for the TM₃₁₀ mode. Our research shows that the width of the coupling wall in double gap cavity has little influence, while the position and the sizes of the coupling slot have strong influence on the frequency and the characteristic impedance ofπ-TM modes. Meanwhile, we discover that, theπ1-TM mode of double gap cavity with a coupling slot in the center will vanish, and theπ1-TM mode of double gap cavity with two coupling slots on two sides also vanishes for high order modes.2,A double-gapπ-TM₆₁₀ mode coaxial cavity for X-band multi-beam klystron is designed. The coaxial line output circuit of double-gapπ-TM₆₁₀ mode coaxial cavity is studied. The results show that characteristics impedance of each hole in the output cavity is still very uniform after coupled with a coaxial line. The influence of the outer radius of the coaxial line coupling with cavity is inappreciable on characteristic impedance and its uniformity, but is strong on the external quality factor Qext. The size of coupling slots has strong influence on the frequency interval ofπ-TM₆₁₀ mode to other resonant mode. It is improper that coupling slots are too big or too small. The size of coupling slots should be moderate, there is an optimal size.