设计了工作在X波段的相对论速调管放大器同轴双间隙输出结构，并采用3维PIC程序对其进行了粒子模拟，分析了输出微波功率随直流渡越角、输出腔品质因数值等相关参数的变化，对输出腔体结构进行了优化设计。模拟结果表明：同轴双间隙输出结构可以降低束流的势能，增加束流与腔体的作用时间，提高速调管的微波提取效率。模拟中采用束压600 kV、束流5 kA、调制深度100%和峰值频率9.37 GHz的电子束以及1T的轴向引导磁场强度，得到了周期平均功率1.2 GW、峰值频率9.37 GHz、效率40%的微波输出。

With 3D full electromagnetic particle-in-cell code, an X-band coaxial double-gap output cavity of klystron amplifier has been designed and simulated. It is found that the microwave extraction power and efficiency is increased by employing the coaxial double-gap output cavity. The relation between output power and modulation depth of current, and the relation between output power and the distance from electron beam outer radius to drifting wall are obtained. Furthermore, the relation between output power and DC transitional angle is presented. A 1.2 GW averaged power over the oscillator period is generated by simulation with 600 kV electron beam voltage, 5 kA current, 100% modulation depth of current and 1 T leading magnetic field density. The peak frequency is 9.37 GHz and the efficiency is 40%.