Study of T Mn,1,0 Mode Instabilities in the Annular Cavities of an S-Band High-Power Multibeam Klystron

IF 1.6 4区物理与天体物理 Q3 PHYSICS, FLUIDS & PLASMAS

IEEE Transactions on Plasma Science Pub Date : 2026-10-01 Epub Date: 2026-09-07 DOI:10.1109/TPS.2026.3728065

Shengchang Wang;Shuji Matsumoto;Takuya Natsui;Toshihiro Matsumoto;Takako Miura;Shigeki Fukuda;Tetsuo Shidara

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引用次数: 0

Abstract

This article investigates beam instabilities induced by

${TM}_{n,1,0}$

modes under asymmetric beam conditions in the annular cavity of an S-band multibeam klystron. In S-band or higher-frequency multibeam klystrons (MBKs), annular cavities exhibit a high density of higher-order modes (HOMs), particularly in high-power designs. The

${TM}_{n,{1},{0}}$

modes can potentially trigger beam breakup (BBU) instabilities within the penultimate cavity. We present an analytical study of the power transfer from the beam to the

${TM}_{{n},{1},{0}}$

mode, to clarify that azimuthal asymmetry in the beam currents is the premise to excite the unwanted

${TM}_{{n},{1},{0}}$

mode. Particle-in-cell (PIC) simulations of an S-band 8-beamlet MBK under a single-beam-loss scenario confirm the presence of instability in the penultimate cavity, driven by the

${TM}_{{7},{1},{0}}$

mode at the second harmonic frequency. A solution is proposed to mitigate this issue by introducing 14 evenly spaced fins on the outer boundary and 14 corresponding grooves on the inner boundary, which split the degenerate

${TM}_{{7},{1},{0}}$

mode into two. Additionally, we discuss mode competition between the

${TM}_{{0},{1},{0}}$

and

${TM}_{{1},{1},{0}}$

modes in a C-band annular cavity used for second-harmonic bunching, and this problem can be effectively solved by improving the azimuthal uniformity of the longitudinal electric field in the input cavity.

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s波段大功率多波束速调管环形腔中tmn，1,0模不稳定性研究

本文研究了非对称光束条件下s波段多速调管环形腔中${TM}_{n,1,0}$模引起的光束不稳定性。在s波段或更高频率的多波束速调管（mbk）中，环形腔表现出高密度的高阶模式（HOMs），特别是在高功率设计中。${TM}_{n,{1},{0}}$模式可以潜在地触发倒数第二腔内的束破裂（BBU）不稳定。本文对光束向${TM}_{{n},{1},{0}}$模式的能量传递进行了分析研究，阐明了光束电流的方位不对称是激发不需要的${TM}_{{n},{1},{0}}$模式的前提。对s波段8波束MBK在单波束损耗情况下的粒子池（PIC）模拟证实了次谐波频率下${TM}_{{7},{1},{0}}$模式驱动的第二腔中存在不稳定性。本文提出了一种解决方案，通过在外边界引入14个均匀间距的鳍片和在内边界引入14个相应的凹槽，将简并的${TM}_{{7},{1},{0}}$模式分成两个。此外，我们还讨论了用于二次谐波聚束的c波段环形腔中${TM}_{{0},{1},{0}}$和${TM}_{{1},{1},{0}}$模式之间的模式竞争问题，通过提高输入腔中纵向电场的方向均匀性可以有效地解决这一问题。

本文章由计算机程序翻译，如有差异，请以英文原文为准。

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来源期刊

IEEE Transactions on Plasma Science 物理-物理：流体与等离子体

CiteScore

3.00

自引率

20.00%

发文量

538

审稿时长

3.8 months

期刊介绍： The scope covers all aspects of the theory and application of plasma science. It includes the following areas: magnetohydrodynamics; thermionics and plasma diodes; basic plasma phenomena; gaseous electronics; microwave/plasma interaction; electron, ion, and plasma sources; space plasmas; intense electron and ion beams; laser-plasma interactions; plasma diagnostics; plasma chemistry and processing; solid-state plasmas; plasma heating; plasma for controlled fusion research; high energy density plasmas; industrial/commercial applications of plasma physics; plasma waves and instabilities; and high power microwave and submillimeter wave generation.