高功率微波及材料特性参数对沿面击穿的影响

Numerical investigation of dielectric window breakdown with different high-power microwave and material characteristic parameters

为研究高功率微波及材料特性参数对介质沿面闪络击穿过程的影响,采用自编的1D3VPIC-MCC程序,通过粒子模拟手段,得到了电子与离子数目、电子及离子密度分布、空间电荷场时空分布、电子平均能量、放电功率、表面沉积功率、激发电离损耗功率、电离频率等重要物理量。结果表明:电离频率随场强增加而增加,达到饱和后缓慢下降,强场诱发的二次电子数目更多导致本底沉积功率增高;电离频率随频率减小而增加,达到饱和后缓慢下降,频率太高会抑制次级电子倍增;因此,低频强场下击穿压力较大;反射引发表面电场下降及磁场增加效应,降低表面场强虽使表面击穿压力下降,但磁场的增加会导致二次电子倍增起振时间缩短,且会增加器件内部击穿风险;圆极化相对线极化诱导二次电子数目更多、本底沉积功率更高,击穿风险增加;短脉冲产生电子、离子总数少,平均能量低,沉积功率低,击穿风险低于长脉冲;脉冲上升时间的缩短和延长,只会提前或推后击穿时间,并不会改善击穿压力;材料二次电子发射率的增加会给击穿造成巨大压力,表面光滑度对击穿过程影响不大;电离频率和电子平均能量随释气压强增加均先增加后减小,低气压二次电子倍增占优,高气压碰撞电离占优。

For investigating the influence of high-power microwave and material characteristic parameters on flashover and breakdown on dielectric surfaces, a 1D3V PIC-MCC code is adopted in this simulation. By using this code, the number of electrons and ions, electron and ion density distributions, time and space distribution of space charge field, average electron energy, discharge power, deposited power, excitation and ionization loss power, and ionization frequency are studied numerically in detail. Ionization frequency increases with electric-field increasing, and then reaches to saturation and decreases slowly; higher value of electric-field causes more secondary electrons to form higher deposited power. Ionization frequency increases with microwave frequency decreasing, and then reaches to saturation and decreases slowly; higher frequency may suppress multipactor discharge. Thus high-power microwaves with higher value of electric-field and lower frequency is easier to induce breakdown. Reflection causes electric-field decrease and magnetic-filed increase on dielectric surfaces, which leads to the decrease of ionization frequency and secondary electron decrease, the shortening of the oscillation time of multipactor discharge, and the breakdown risk increase of the inner region of device. Compared with linear polarization, circular polarization causes more secondary electrons to form higher deposited power, and the breakdown risk increases. Shorter pulses produce fewer electrons and ions with lower average energy, which form lower deposited power, so high-power microwaves with long pulses are easier to induce breakdown. Longer rise time of pulses causes longer breakdown time, but could not decrease the breakdown risk. Compared with surface roughness, higher value of materials secondary emission yield increases breakdown risk markedly. Ionization frequency and average electron energy increase firstly, and then decrease with gas pressure increasing. Multipactor discharge dominates at low pressure, and ionization dominates at high pressure.