He/N $_2$中电压波形驱动的微atmospheric pressure等离子体射流中的电子功率吸收
Electron power absorption in micro atmospheric pressure plasma jets driven by tailored voltage waveforms in He/N$_2$
摘要：
在大气压电容耦合微等离子体射流中，电压波形剪裁（VWT）被证明可以提供对电子能量分布函数（EEDF）的最终控制，其允许通过控制电子功率吸收动力学来增强和调节所选中性物种的产生。然而，在基本层面上，VWT的这些影响的物理起源仍然不清楚。因此，在这项工作中，电子功率吸收动力学的研究在He/N $_2$射流与氮浓度为0.05\%驱动的谷波形在基频为13.56 MHz的不同数量的谐波使用自洽的粒子在细胞模拟耦合的时空分辨分析的电子功率吸收的动量平衡方程的基础上。由于在大气压下的传输的局部性质，欧姆功率吸收占主导地位。增加谐波的数量，由于激励波形的特殊形状，接地电极处的鞘层塌陷相对于通电电极处的鞘层塌陷缩短。因此，为了确保该电极处的电子和正离子的通量补偿，在该短鞘层塌陷时驱动高电流通过放电。该电流由高欧姆电场驱动。在靠近接地电极处，电子密度低，电场高，电子被加速到高能量，观察到强电离以及局部电子密度最大值的形成。该电子密度最大值导致局部双极电场，其充当电场反转并将电子加速到甚至更高的能量。详细了解这些效应，从根本上解释VWT在等离子体中用于EEDF控制的独特潜力。
英文摘要：
In atmospheric pressure capacitively coupled microplasma jets, Voltage Waveform Tailoring (VWT) was demonstrated to provide ultimate control of the Electron Energy Distribution Function (EEDF), which allows to enhance and adjust the generation of selected neutral species by controlling the electron power absorption dynamics. However, at the fundamental level, the physical origin of these effects of VWT remained unclear. Therefore, in this work, the electron power absorption dynamics is investigated in a He/N$_2$ jet with a nitrogen concentration of 0.05\% driven by a valleys waveform at a base frequency of 13.56 MHz for different numbers of harmonics using a self-consistent Particle in Cell simulation coupled with a spatio-temporally resolved analysis of the electron power absorption based on the momentum balance equation. Due to the local nature of the transport at atmospheric pressure, ohmic power absorption is dominant. Increasing the number of harmonics, due to the peculiar shape of the excitation waveform the sheath collapse at the grounded electrode is shortened relative to the one at the powered electrode. As a consequence, and in order to ensure flux compensation of electrons and positive ions at this electrode, a high current is driven through the discharge at the time of this short sheath collapse. This current is driven by a high ohmic electric field. Close to the grounded electrode, where the electron density is low and the electric field is high, electrons are accelerated to high energies and strong ionization as well as the formation of a local electron density maximum are observed. This electron density maximum leads to a local ambipolar electric field that acts as an electric field reversal and accelerates electrons to even higher energies. These effects are understood in detail to fundamentally explain the unique potential of VWT for EEDF control in such plasmas.
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