Phase-locked high power microwave generator driven by kW level RF power
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摘要: 针对kW级微波驱动的锁相GW高功率微波,设计了一个高增益(大于50 dB)四腔相对论速调管放大器(RKA)。模拟表明,在此条件下高次模振荡严重影响器件的锁相实现。由此,将RKA结构与正反馈振荡电路结合起来,建立相应的等效电路来研究这种高次模激励的物理过程(即高次模的激励与中间腔之间耦合强度的相关性)。在高次模振荡的等效电路(即正反馈振荡电路)中,用衰减电阻代替结构中的微波吸收层来研究高次模振荡的抑制机理,衰减电阻通过对反馈过程的控制,提高了电路的自激振荡起振电流。在结构上按照衰减电阻要求设计了微波吸收层,将高次模振荡的起振电流提高到大于器件的工作电流,实现了高增益(约60 dB)条件下高次模激励的抑制。模拟获得了4 kW微波功率驱动的2.3 GW锁相高功率微波,增益接近60 dB。在LTD加速器平台的实验结果表明:注入微波由固态RF种子源提供(功率10 kW),输出功率达到1.8 GW,增益为52.6 dB,90 ns内输入和输出微波的相对相位差小于±10°,实验上实现了kW级注入微波对GW高功率微波的相位锁定。Abstract: In order to realize the phase locking of GW-level high power microwave (HPM) driven by kW-level RF source, a relativistic klystron amplifier (RKA) with four resonant cavities is designed. However, the particle in cell (PIC) simulation shows that high order mode oscillation in the device destroys the phase locking of HPM seriously. And this high order mode excitation is closely related to the coupling between middle cavities. Combining with the structure of RKA, an equivalent circuit model is built to study the process of high order mode excitation (positive feedback process). Simulations show that positive feedback process of high order mode can be controlled by adding RF lossy material to the RKA structure. And this measure increases the threshold current of the high order mode excitation. We have got a phase-locking output microwave of 2.3 GW with an input power of 4 kW in simulation. Experiments were performed on the LTD accelerator, and the input microwave was provided by a solid-state microwave source. Under the conditions of an input microwave of 10 kW, the output power achieved 1.8 GW with a gain of 52.6 dB; and the relative phase difference between input and output RF signals was about ±10° in the locking duration of 90 ns.
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表 1 吸波材料电导率与腔间耦合强度关系
Table 1. Relationship between conductance of lossy material and coupled strength
conductivity/(S·m-1) coupled strength Ist/(kA) 0.3 0.108 6 0.5 0.054 11 0.7 0.079 7 0.9 0.098 / -
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