基于高能电子逃逸行为的纳秒脉冲放电特性分析

Analysis of the Characteristics of Nanosecond-pulse Discharge Based on Runaway Behaves of High-energy Electrons

为研究ns脉冲激励下的气体放电现象,近年来基于高能电子逃逸引导放电发展的相关研究受到了广泛关注。利用上升沿15ns,半高宽30～40ns的重复频率ns脉冲激励极不均匀电场下大气压空气放电,将实验测量和理论计算相结合,研究了基于高能电子逃逸击穿的ns脉冲气体放电特性。实验结果表明高重复频率下仍可获得大面积均匀的弥散放电,放电中存在能量范围为10～130keV的X射线。理论计算结果表明施加120kV负极性脉冲条件下电场强度最高可达718kV/cm,高于大气压空气中产生逃逸电子的场强阈值,放电中X射线与逃逸电子有关。进一步对从理论上对ns脉冲气体放电特性进行探索,极不均匀电场下的场致发射为放电提供初始电子,其中能量较高的电子在气隙运动过程中发生逃逸,与气体分子碰撞产生二次电子,并辐射出X射线。逃逸电子与X射线共同作用,有利于获得大面积的弥散放电。

In order to study the phenomenon of the gas discharge excited by nanosecond-pulse, the evolution of the nanosecond-pulse discharge based on runaway of the high-energy electron is focused on. In this paper, nanosecond- pulse discharge was generated by repetitive nanosecond-pulse with a rise time of about 15 ns and a full width at half maximum of 30~40 ns in inhomogeneous electric filed in atmospheric air, and the discharge characteristics based on runaway breakdown of high-energy electrons were investigated by experimental measurements and theoretical calculation. Experimental results showed that large-area diffuse discharge could be obtained when the pulse repetition reached 1 kHz, and x-rays ranged from 10 to 130 keV existed in the discharge. Furthermore, theoretical results demonstrated the maximum electric field could reach 717 kV/cm when a negative pulse of 120 kV was applied in the air gap, such an electric field was higher than the critical value of the electric fields for generating runaway electrons in air at atmospheric pressure. In addition, the characteristics of the nanosecond-pulse discharge were theoretically explored. The results indicated that initial electrons were generated by the field emission under inhomogeneous electric field, and part of the initial electrons with high energy run away in the motion process in the gap. Those runaway electrons collided with the gas molecule, from which the second electrons were generated, accompanying with the x-rays emission. Finally, both the runaway electrons and x-rays were responsible for the discharge evolution, which was beneficial for the generation of large-area diffuse discharge.