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通过理论分析指出,单模相对论返波振荡器内的平均场强正比于其工作频率,工作在高频段难以实现长脉冲运行。采用电磁场仿真方法,比较了X波段单模和过模慢波结构的场分布特点,结果表明:增加过模比能有效减小慢波结构表面的射频场强,但由于场分布变化导致场强的减小与过模比的增加相比并不显著。利用过模比约为3的慢波结构设计了一种X波段长脉冲高功率微波源。实验中,在单次运行条件下,输出微波功率达到2 GW、脉宽80 ns;在20 Hz重复频率运行条件下,输出微波功率达到1.2 GW、脉宽100 ns。器件产生的微波频率为9.38 GHz,主模为TM01,效率约24%。微波窗口和慢波结构表面的射频击穿是目前实验中限制微波功率和脉宽增加的关键因素。
The theoretical analysis shows that the average field strength in the single-mode relativistic back-wave oscillator is proportional to its operating frequency, and it is difficult to achieve long-pulse operation in the high frequency range. The field distribution characteristics of X-band single-mode and over-mode slow-wave structures are compared using electromagnetic field simulation. The results show that increasing the over-mode ratio can effectively reduce the RF field strength on the surface of the slow-wave structure. However, The decrease is not significant compared to the increase of the over-mode ratio. An X-band long pulse high power microwave source is designed by using a slow-wave structure with an over-mode ratio of about 3. In the experiment, under a single operation condition, the output microwave power reaches 2 GW and the pulse width is 80 ns. Under the condition of 20 Hz repetition frequency, the output microwave power reaches 1.2 GW and the pulse width is 100 ns. The microwave frequency generated by the device is 9.38 GHz, the main mode is TM01, and the efficiency is about 24%. The radio frequency breakdown of the microwave window and the surface of the slow wave structure is the key factor that limits the microwave power and the pulse width increase in the present experiment.