为了探索相对论速调管放大器(RKA)的小型化技术, 开展了同轴RKA周期永磁聚焦的物理与设计技术研究。周期永磁聚焦系统采用Halbach阵列结构, 产生的磁场类型为周期性会切磁场。首先给出该系统的磁场各个分量的表达式, 分析该系统磁场分布的特点, 并推导得出该系统聚焦强流环形电子束的稳定条件。根据该稳定条件, 对Ka波段同轴RKA设计了一个周期永磁聚焦系统, 并优化了周期磁场参数, 确定了磁场系统设计的最佳周期和幅值。研究结果显示, 周期永磁(PPM)聚焦系统在周期长度18 mm和磁场幅值033 T的条件下可引导500 kV、6 kA的同轴RKA, 得到1 GW的微波输出功率, 物理分析确定了周期永磁聚焦系统应用于高功率同轴RKA的技术可能性。

In order to explore the miniaturized relativistic klystron amplifier(RKA), we develop the theoretical analysis and simulation on the periodic permanent magnet (PPM) of the coaxial RKA. The Halbach arrays are applied to this PPM system and generate periodic cusped magnetic field. We evaluate the radial and axial components of the PPM field and present the characteristics of the magnetic distribution. Based on our expressions of the magnetic distribution, we get the transmission stability condition of the annular IREB in the PPM system for the coaxial waveguide. According to the stability condition, we design and optimize a PPM system for a Ka band coaxial RKA. Then the optimized period and amplitude of the PPM system are obtained. The results of the research show that the PPM system can focus the electron beam with voltage of 500 kV and current of 6 kA in the Ka band coaxial RKA, while the period and amplitude of the PPM system are 18 mm, 0.33 T, respectively. In addition, the coaxial RKA can stably generate millimeter wave with power of 1 GW. In a word, it is possible that the PPM system can be applied to the high power coaxial RKA.