Runaway electron beams in nanosecond-pulse discharges

Abstract

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.

Mechanism of runaway electron generation in nanosecond pulsed plate-plate discharge at atmospheric-pressure air

“…会逃逸。如果忽略弹性散射，非弹性碰撞产生的有效摩擦力可以通过 Bethe 公式 由于空气的主要成分是氮气，取 Z=14，I=80eV [39] ，P=0.1Mpa，则第一电子逃逸 直到气隙击穿时，最大能量电子的最大能量为39.7keV，超过20keV，这表明 在放电发展过程中存在能量大于eU m 的电子，其中e是电子电荷，U m 是纳秒脉冲 电压幅值，这与许多实验和数值模拟结果一致 [18,19,22,42] ，这种异常现象被称为 Askaryan效应 [43]…”

Anode and Cathode Spots in High-Voltage Nanosecond-Pulse Discharge Initiated by Runaway Electrons in Air

“…The experimental results of the SAEB study in different gases are described in Refs. [4,[6][7][8]10,[12][13][14]17,18]. According to the nonlocal criterion for runaway electrons, the critical electric field strength for the runaway mode in atmospheric pressure nitrogen was ∼2 MV/cm.…”