逃逸电子对纳秒短脉冲大气压空气击穿的影响

Effect of Runaway Electrons on the Breakdown of Nanosecond Short Pulse in Atmospheric Air

由于经典的流注放电理论难以解释纳秒短脉冲电压下气体快速击穿,人们提出了逃逸电子击穿理论。为了帮助读者理解逃逸电子击穿理论,首先简要介绍了逃逸电子击穿理论的发展历程,然后给出对纳秒短脉冲尖-板电极大气压空气放电的PIC/MCC模拟结果。在负极性下,随着击穿电压的升高,观察到了逃逸电子从无到有的演变过程,提出了逃逸电子产生的充分条件。发现了逃逸电子在放电通道头部前方产生的预电离通道,指出了它对气隙快速击穿的重要作用。比较了正负极性相同击穿电压下放电通道跨越气隙所需的时间,解释了击穿电压极性效应反转现象。在正极性电压下,重点关注最高能电子,发现它们仅出现在放电通道头部强电场区,即使该处电场超过临界值,电子也难以进入持续加速模式,因此最高能电子能量比负极性下小得多。最后指出了正极性下高能电子对气隙快速击穿的贡献。

Because the classical streamer discharge theory is difficult to explain the rapid breakdown of gas under nano-second short pulse voltage,the runaway electron breakdown theory is proposed.In order to help understand the theory of runaway electron breakdown,this paper first gives a brief introduction of its development history,and then presents our PIC/MCC simulation results for nanosecond short pulse discharge in atmospheric air.Under negative polarity,with the increase of breakdown voltage,the evolution of runaway electrons from nothing was observed,and sufficient conditions for the generation of runaway electrons were proposed.The pre-ionization channel generated by runaway electron in front of discharge channel head was found and its important role in the rapid breakdown of air gap was indicated.The time re-quired for the channel to cross the air gap under the positive and negative 26 kV breakdown voltage was compared,and the polarity effect reversal of the breakdown voltage was explained.It is found that the highest energy electrons only ap-pear in the strong electric field area at the head of the discharge channel.Even if the electric field there exceeds the critical value,it is difficult for the electrons to enter the continuous acceleration mode.Therefore,the energy of the highest energy electrons is much smaller than that in the negative polarity.Finally,the contribution of high-energy electrons to the rapid breakdown of the air gap is pointed out.