纳秒脉冲气体放电中逃逸电子束流的研究

Runaway electron beams in nanosecond-pulse discharges

经典的放电理论(Townsend和流注理论)不能很好地解释纳秒脉冲放电中的现象,近年来基于高能量电子逃逸击穿的纳秒脉冲气体放电理论研究受到广泛关注,有研究发现,高能逃逸电子是纳秒脉冲气体放电中的新特征参数,本文研制了用于测量纳秒脉冲放电中逃逸电子束流的收集器,并对脉宽3—5ns、上升沿1.2—1.6 n8激励的大气压纳秒脉冲气体放电中逃逸电子束流进行了测量,收集器采用类似法拉第杯的原理,利用金属极收集纳秒脉冲放电中的高能电子,并转换为电信号后由示波器采集,为了获得更好的逃逸电子束流波形,对逃逸电子束流收集器进行了优化设计,提高了收集器的阻抗匹配特性,基于上述的逃逸电子束流收集器,研究了纳秒脉冲气体放电中逃逸电子的特征,实验结果表明,所设计的收集器可以有效地测量到逃逸电子束流,改进设计后收集器测得的逃逸电子柬流的时间分辨率和幅值均得到提高,施加电压约80 kV时,大气压空气中的逃逸电子束流幅值可达160 mA,脉宽小于1ns,多个脉冲激励放电的结果表明逃逸电子束流收集器具有较好的可靠性,其瞬态响应与时间分辨率比较稳定。

Conventional discharge （Townsend and streamer mechanisms） theories are not able to well explain the phenomenon in nanosecond-pulse discharges. Recently, much attention has been paid to the runaway breakdown due to high-energy electrons in nanosecond-pulse discharges, and some experimental data confirm that high-energy runaway electron beam is an important characteristic parameter for nanosecond-pulse discharges. In this paper, two designed collectors are used for detecting runaway electron beams in nanosecond-pulse discharges. These collectors are used to measure the runaway electron beams in discharges driven by a nanosecond-pulse generator with a pulse width of 3-5 ns and a rise time of 1.2-1.6 ns. The measuring principle of both two collectors is similar to that of Faraday cup, where high-energy electrons are collected by a metal cone, and converted into an electric signal that can be recorded by an oscilloscope. Furthermore, optimal designs of collectors are conducted in order to improve the impedance matching characteristics and to obtain better recording data. Using the above two collectors, characteristics of runaway electron beams are investigated. Experimental results show that runaway electron beams can be effectively measured by the collectors, and the optimized collector has a shorter time resolution and higher amplitude of the runaway electron beam current. When the applied voltage is 80 kV, the electron beam current can be measured with an amplitude of 160 mA and a full width at half maximum of less than 1 ns. In addition, experimental results with pulse sequences prove that the collectors have excellent reliability, and both the transient response and the time resolution are stable.