中文摘要：

采用3维粒子软件VORPAL对微波阶梯阻抗变换器中的低气压电晕放电过程进行了粒子模拟，获得了放电过程中带电粒子实空间分布的时间演变图像，分析并解释了其中低气压电晕放电机理和微放机理之间的关系．模拟结果表明：低气压电晕放电的阂值电压随着气压的增长呈现先减小后增加的变化趋势；并且随着气压的增长，微放电作用减弱，低气压电晕放电作用增强．通过对银和铜两种器壁材料放电阈值的比较，获得了两种放电机理之间的临界气压．

英文摘要：

The corona discharge process in low pressure N2 in stepped impedance transformer （SIT） is simulated using 3-D particle-in-cell （PIC） software （VORPAL）. The evolution of the charged particle spatial distribution during the discharge is obtained. The two main discharge mechanisms, i.e., multipactor and corona discharge, are analyzed. From the simulation results, it can be found that the threshold voltage of breakdown of the SIT first decreases and then increases. In addition, with the increase of the pressure, the multipactor effect weakens while the corona discharge effect strengthens. Through the comparison of the threshold voltages between two kinds of wall materials, i.e., Ag and Cu, the critical pressures between the two discharge mechanisms are achieved.