Abstract

Enhanced electron density and plasma dynamics are investigated for Helium discharges on nanosecond timescales with Particle-In-Cell simulations. The plasma discharges are driven between planar electrodes with DC, single pulses, and dynamic frequency square waves. It is assumed that the DC and pulse discharges operate in the glow regime. It is shown that as pressure increases with narrowing gap distance, the peak transient electron density rises. This is in contrast to what is observed under a constant pressure-gap (pd) and electric field reduced by neutral density (E/N) values at saturation time. It is shown that although the pd and E/N values and therefore the breakdown voltage are the same across cases, the plasma kinetics are different due to a change in the energy relaxation lengths. The cross-points between the sheath length and energy relaxation length move to higher electron energies at higher pressure. This facilitates high-energy electrons to undergo inelastic collisions and produces different rates of increasing electron density and temperature at nanosecond timescales. Moreover, using a plasma frequency-dependent square wave, the electron density can be increased to 50 times higher over that of the DC case because of a reverse electric field. The electron kinetics on nanosecond time scales can be exploited for high electron density and fast ionization applications.

Graphic abstract

中文翻译：

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氦等离子体放电中纳秒级时间尺度上增强的电子密度和等离子体动力学

摘要

通过粒子内模拟，研究了纳秒级时氦放电的增强的电子密度和等离子体动力学。等离子放电通过直流电，单脉冲和动态频率方波在平面电极之间驱动。假定直流和脉冲放电在辉光状态下工作。结果表明，随着压力随着间隙距离变窄而增加，峰值瞬态电子密度也随之升高。这与在恒定压力差（pd）下观察到的情况相反，电场在饱和时减小了中性密度（E / N）值。结果表明，尽管pd和E / N情况下的击穿电压值相同，因此击穿电压相同，由于能量弛豫长度的变化，等离子体动力学也不同。鞘长度和能量弛豫长度之间的交叉点在较高压力下移向较高的电子能量。这使高能电子易于发生非弹性碰撞，并在纳秒级时标上以不同的速率增加电子密度和温度。此外，由于等离子体的反向电场，使用与等离子体频率有关的方波，可以使电子密度比DC情况下的电子密度高50倍。纳秒级的电子动力学可用于高电子密度和快速电离应用。

图形摘要