为进一步提高相对论速调管放大器(RKA)的工作频率和输出功率，开展了X波段GW级长脉冲多注RKA实验研究，对实验中出现的杂模振荡现象进行了模拟和实验分析。结果表明，电子回流是导致实验中出现杂模振荡的主要因素，采取了相应措施减少电子回流从而抑制杂模振荡，实现多注RKA输出微波功率约为0.98 GW，脉宽为95 ns，频率为9.405 GHz。

An X-band multi-beam relativistic klystron amplifier is designed to increase the output microwave power and the operating frequency of the amplifier tube, and an experimental study is performed on the long pulse accelerator. The parasitic oscillation of relativistic klystron amplifier is explored in particle-in-cell code and experiment, and the results indicate that the parasitic oscillation is mainly excited by retrograde electrons. Special measures are introduced in the device to suppress the retrograde electrons and avoid parasitic oscillation. Output power of 0.98 GW is obtained in the experiment, the microwave frequency is 9.405 GHz, the pulse width is 95 ns, and the amplifier gain is about 43 dB.