慢波结构爆炸发射对高功率太赫兹表面波振荡器的影响

随着真空电子学器件的工作频率达到太赫兹波段, 表面波振荡器的横截面尺寸变小, 慢波结构的加工精度难以得到保证, 同时由于表面波振荡器的电磁场集中在慢波结构表面, 在高电压工作情况下, 太赫兹波段的表面波振荡器慢波结构爆炸发射电子会影响器件的工作特性. 本文分析了高电压工作情况下0.14 THz表面波振荡器慢波结构中电场的分布特性, 研究表明, 在慢波结构区域沿着轴线方向上存在电场幅度的包络分布, 在慢波结构中心位置处靠近慢波结构内半径处电场的幅度最大, 最易爆炸发射产生电子, 采用粒子模拟软件UNIPIC模拟了慢波结构处爆炸发射的电子对器件工作特性的影响, 同时考虑了电子回流所产生的二次电子倍增效应, 数值模拟结果表明, 慢波结构电子产生会导致器件的输出功率下降, 从数十兆瓦下降到兆瓦量级.

Influence of slow wave structure explosive emission on high-power surface wave oscillator

As the working frequency of a vacuum electron device reaches the terahertz frequency band, the cross section of the surface wave oscillators (SWO) becomes very small, and the micro-fabrication precision of the device cannot be guaranteed, at the same time, because the electromagnetic field of SWO concentrates on the inner surface in slow wave structure, when the working voltage of surface wave oscillator is very high, the explosive emission probability of the slow wave structure increases greatly, and the explosive emission can influence the working characteristic of the device. This paper analyses the distributing property of the electrical field in the slow wave structure of 0.14 THz SWO. Parameters of the SWO under study are as follows: working voltage is 312 kV, explosive emitted current is 1.67 kA, periodic length of the slow wave structure is 0.7 mm, width of the slot is 0.4 mm, and the height of it is 0.3 mm; cold-test results indicate that the amplitude of the electrical field in the slow wave structure varies sinusoidally; the amplitude of the electrical field reaches a maximum value in the middle of the slow wave structure near its inner surface, and the explosive electron emission can occur most possibly in this position, because the electrical field in the slow wave structure varies with very high working frequency. The explosive emitted electron may bombard back the slow wave structure, and the secondary electrons will be emitted at a certain probability, for which the formula proposed by Vaughan is used to compute the secondary emission yield, and this formula is implemented in the self-developed particle-in-cell code UNIPIC; while the code is used to simulate 0.14 THz SWO with explosive emission in the slow wave structure. In the simulation, the slow wave structure multipactor discharge induced by electrons is also considered; the phase space of the electrons emitted from the slow wave structure shows that the energy of secondary electrons is below 5 keV, so the validity for secondary electron yield is affirmed. Numerical simulation results indicate that because the emitted electrons from the slow wave structure change the distribution character of the electrical field in the slow wave structure, especially the amplitude of the electrical field in the middle of the slow wave structure, the beam-wave interaction is weakened, and as a result, output power decreases from about 22.6 megawatts to only 1.89 megawatts.