棒-板电极直流负电晕放电特里切尔脉冲的微观过程分析

本文基于流体动力学理论改进出一种新的棒-板电极负电晕放电混合数值模型, 模型中加入了27种主要碰撞反应, 并考虑了光电离和二次电子发射过程. 对棒-板间距3.3 mm, 施加电压-5.0 kV情况下进行数值计算, 得到负电晕放电的特里切尔脉冲. 重点分析了单个特里切尔脉冲持续过程中5个关键时刻的微观特征量发展规律, 丰富并量化描述了特里切尔脉冲的微观过程, 主要结论如下: 随着放电时间的发展, 电场集中分布区域向阳极移动且幅值变小, 这对电子崩的发展非常不利. 大部分放电区域都是电中性的, 只有在阴极鞘和阳极鞘附近有带正电的等离子体特性, 带负电的离子云随着放电时间的发展缓慢向阳极发散式移动. 整个特里切尔脉冲持续过程中, 阴极鞘内电子密度几乎为0; 特里切尔脉冲前期, 阴极鞘附近电子密度迅速增加至最大值并保持基本不变; 随着放电时间的增加, 放电间隙内电子密度整体增加, 并且向阳极发展. 在特里切尔脉冲后期, 电子的产生主要来自于N₂和O₂的碰撞电离, 电子的消失则主要由N₂⁺的复合决定, O₄⁺和O₂^-分别是数量最多的正离子和负离子. 关键词： 负电晕 混合模型 特里切尔脉冲 微观特征量     

多针电晕增强大气压辉光放电稳定性研究

利用多针电晕增强放电装置，在无气流和存在高速气流的情况下都得到了稳定的大气压辉光.通过纪录发光图片、电流-电压波形和伏安特性曲线的方法对影响放电稳定性的因素做了细致地研究，发现了在从电晕放电到辉光放电的过程中存在着过渡阶段，表现为出现带有直流成分的Trichel脉冲.气流速度、极板间距以及针尖锥度和凹坑曲率半径的匹配程度都对放电的稳定性和电流密度有着重要的影响. 关键词： 大气压辉光放电 多针电晕 等离子体     

The first Trichel pulse of negative corona discharge in N2 with a small admixture of SF6

Current growth waveforms of transient negative point-to-plane discharge in N₂ and in N₂ with 0·025-0·1% admixture of SF₆ at a pressure of 40 kPa have been measured and compared. The transient glow discharge regime in pure N₂ was found to be preceded by a peaked current signal of conspicuous similarity to the first Trichel pulse rise and its initial decay in N₂+SF₆ mixture. The results are in a basic agreement with a hypothesis on streamer mechanism for Trichel pulse and indicate occurrence of field emission during the rise of Trichel pulse current.     

On the Mechanism of Generation of Trichel Pulses in Atmospheric Air

JETP Letters - Discharge current pulse profiles have been recorded with a subnanosecond time resolution for a corona discharge from a negative-polarity needle functioning in the Trichel pulse...     

Negative coronas: Low current mode – pulse mode transition

In the paper the results of experimental study of negative corona in a point – plane gap in a dust-free air flow at atmospheric pressure are presented. Both the low current mode (LCM) of the discharge and Trichel pulses are externally triggered by UV light. Close to the inception voltage of Trichel pulses short-duration current spikes appear besides the steady component of the LCM which indicates to the switch-on of Fowler-Nordheim type emission mechanism. At the inception voltage spike – Trichel pulse transition is recorded. The influence of dielectric layers at the cathode on the discharge parameters is discussed.     

Total Variation Diminishing technique in numerical simulation of Trichel corona in air

This paper deals with the numerical simulation of the Trichel pulse corona discharge in air under the room temperature and atmospheric pressure in the pin-plane configuration. A simplified drift-diffusion model of the discharge is considered with three species: electrons, positive and negative ions. The Total Variation Diminishing algorithm is used to stabilize the charge transport equations. The effect of the voltage level and the external circuit parameters on the average corona current, pulse frequency and pulse parameters are presented. The results of numerical predictions are compared with the experimental data.     

针-板DBD微流注与微辉光交替生成的机理研究

在介质阻挡放电体系中产生辉光放电可以有效的提高放电体系产生高能电子的性能, 为等离子体化学反应提供更加丰富的活性粒子.本文对针-板介质阻挡放电体系下的放电模式进行了研究,实验发现放电正负半周期表现出不同的放电模式, 激励电压为3 kV时放电正负半周期分别为微流注放电和电晕放电(或者Trichel脉冲放电),激励电压为6 kV时放电正负半周期分别为微流注放电和微辉光放电.微辉光放电形貌具有与典型辉光放电相同的分层次放电结构, 分析了激励电压6 kV时的放电过程,认为足够强的阴极电场强度和裸露针状电极形成的有效的二次电子发射过程是形成微辉光放电的主要因素,绝缘介质层的存在避免了微辉光放电向弧光放电过渡.     

直流电源耦合高功率脉冲非平衡磁控溅射电离特性

采用直流电源放电形成高功率脉冲非平衡磁控溅射(dc-high power impulse unbalanced magnetron sputtering,dc-HPPUMS 或dc-HiPiUMS),利用雪崩放电的击穿机理形成深度自触发放电,同轴线圈和空心阴极控制放电特性和提高功率密度.磁阱俘获雪崩放电形成的二次电子和形成漂移电流,形成了大电流脉冲放电,放电脉冲电流密度峰值超过100 A/cm²,脉冲频率小于40 Hz.由于放电等离子体远没有达到平衡状态,放电电流主要受到空间电荷效应 关键词： 放电 脉冲技术     

Parametric study of the characteristics of Trichel pulses in the needle-plane negative corona discharge in atmospheric air

A numerical study of the impact of different model coefficients on the frequency, DC current, and the rise time of the Trichel pulses in a needle-plane negative corona discharge is presented here. The studied coefficients include the coefficients of the ionization and attachment reactions, the mobilities of the three charged species considered in the model (electrons and positive and negative ions), and the coefficient of the secondary emission of electrons. The characteristics of the pulses were also studied using another set of model coefficients which includes an extended number of reactions such as detachment of the electrons from negative ions.     

Erosion of a copper cathode in a negative corona discharge

The pulsed-periodic regime of a negative corona (Trichel pulses) in atmospheric-pressure air, which leads to explosion emission mechanisms (ecton generation) of pointed cathode erosion, is investigated. The jet erosion process at the copper cathode is discovered, and micrometer dendritelike structures formed by erosion products returning to the cathode are detected.     

超短强激光脉冲激励甲烷团簇的内电离机理

采用三维粒子动力学模拟方法研究了甲烷团簇在超短强激光脉冲激励下的爆炸动力学行为,重点讨论了几种典型的内电离机理对团簇爆炸过程中离子的价态和动能的影响.研究表明,在激光脉冲强度比较小的情况下,团簇中的原子主要是在光场作用下通过隧道电离的方式发生电离.当激光场进一步增强时,势垒压低电离是电离的主要方式.在相同的较高激光强度下,团簇更容易通过势垒压低电离达到高的电离价态.团簇发生电离后,其内部库仑电场的点火电离效应和内部滞留自由电子的碰撞电离效应也将增强团簇的再次电离过程. 关键词： 超短强激光脉冲 甲烷团簇 内电离     

Numerical modeling of the photoionization of Rydberg atoms by the field of an electromagnetic wave

The ionization of excited hydrogen-like atoms in a femtosecond laser pulse is studied by direct numerical integration of the time-dependent Schrödinger equation for a quantum system in the field of an electromagnetic wave. Expressions are obtained for the ionization probability of the system as a function of the parameters of the laser pulse and the initial state of the atom. Ionization suppression is found, confirming the basic premises of the theory of interference stabilization of Rydberg atoms.     

Action of corona discharges on bacteria and spores

We have measured the E.coli bactericidal efficiency of DC and AC point-to-plane coronas in air and in argon in the corona modes positive glow, positive streamer, negative Trichel pulse and negative glow. Negative Trichel pulse and positive streamer coronas are the most efficient for production of bactericidal agents in air. Less than 5 minute exposure to the products from 30 A of these coronas will sterilize the E.coli covered agar surfaces in a 3l volume to a survival ratio of 10^–5. Positive glow coronas are two orders of magnitude less efficient. 50 Hz AC coronas seem to mainly work during the negative half cycles. The bactericidal agent(s) produced by the coronas have not all been identified, but ozone O₃ with concentration 35–40 ppm is probably the most important one. We show that charged particles and photons can play only a minor role, so the agent(s) must be neutral particles. The main part of them must have a lifetime in the vessel of more than 3 minutes. The much smaller, and volume/distance dependent, efficiency of coronas in humid argon indicates that metastable neutrals or radicals from H₂O can play only a minor role. A preliminary test showed negligible effects of the corona treatment on the spores of Bacillus subtilis.     

Investigation of a single barrier discharge in submillimeter air gaps. Nonuniform field

Pulse characteristics of single barrier discharges as well as parameters of charges accumulated on the surface of a dielectric under the atmospheric pressure in the “needle-(0.1–2.0)-mm air gap-polymer barrier-plane” system are investigated. It is found experimentally that for the positive polarity of the needle, the voltage for the discharge initiation is higher than in the case of the negative polarity by ～25–35%. The reversal of the needle polarity from negative to positive increases the amplitude of the discharge current and the accumulated surface charge by ～1.5–3 times. For the positive polarity of the needle, the discharge is governed by a streamer mechanism, while for the negative polarity, the discharge is initiated by the formation of a single Trichel pulse. The single pulse regime is observed for the discharge current up to a certain electrode gap d _CR. For the positive needle and for air gap width d _air > d _CR ≈ 1.5 mm, a multipulse burst corona is formed, while for the negative needle and d _air > d _CR ≈ 0.9 mm, a damped sequence of Trichel pulses evolves in the system.     

初始电子密度对光学薄膜激光损伤机制的影响

光学元件的激光损伤问题是激光器件向高功率密度方向发展中必须认识和克服的问题.基于Forkker-Planck方程,研究了激光与材料相互作用时的雪崩电离机制、多光子电离机制以及联合两种机制的情况.雪崩电离的产生需要一定密度的初始自由电子存在,该自由电子可以是材料中原本就存在的,也可能是光电离产生的.着重分析了材料中的初始自由电子对材料电离机制的影响.结果表明,雪崩过程在激光作用一段时间后会达到一个稳定的电离阶段(以自由电子平均能量不随时间变化为特征,且此时雪崩电离为材料电离的主导机制),该时间与光电离速率、材料中初始自由电子密度有关.材料中的初始自由电子可以在一定程度上掩盖光电离的作用效果.     

初始电子密度对光学薄膜激光损伤机制的影响

光学元件的激光损伤问题是激光器件向高功率密度方向发展中必须认识和克服的问题.基于Forkker-Planck方程,研究了激光与材料相互作用时的雪崩电离机制、多光子电离机制以及联合两种机制的情况.雪崩电离的产生需要一定密度的初始自由电子存在,该自由电子可以是材料中原本就存在的,也可能是光电离产生的.着重分析了材料中的初始自由电子对材料电离机制的影响.结果表明,雪崩过程在激光作用一段时间后会达到一个稳定的电离阶段（以自由电子平均能量不随时间变化为特征,且此时雪崩电离为材料电离的主导机制）,该时间与光电离速率、材料中初始自由电子密度有关.材料中的初始自由电子可以在一定程度上掩盖光电离的作用效果.
关键词:初始电子;激光损伤;光电离;雪崩电离     

2D Simulations of Short‐Pulsed Dielectric Barrier Discharge Xenon Excimer Lamp

Self‐consistent two‐dimensional (2D) simulations of short‐pulsed dielectric barrier discharge (DBD) in pure xenon have been performed. It is shown that during short current pulse the traversal inhomogeneity of the plasma parameters can be important only at the end of the current pulse as an edge effect close to the side walls. During the current pulse, the gap voltage drops until the ionization wave reaches the cathode so the current in the cathode sheath is the displacement current. This means that almost all of the absorbed power is deposited into excitation of xenon atoms and not to the ion heating in the cathode sheath as in the traditional glow discharges. This fact is one of the reasons of high efficiency of short‐pulsed DBD. The developed model allows one to estimate the temporal position of the plasma‐sheath boundary. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

氢闸流管放电猝熄实验现象

 氢闸流管脉内放电猝熄给高功率氢闸流管的放电脉冲宽度和峰值电流或峰值功率能力设置了一定限制,造成工作不稳定。还观察到另一种不同的脉间猝熄现象。随着运行时间增加,由于氢吸除损失,点火延迟及跳动均逐渐增加,板耗明显上升。在正失配下,脉冲形成网络上的剩余正电压将增加,且往往不稳定。当氢压减小超过一定限度,脉冲漏失现象出现,这种脉间猝熄很不稳定。     

Quantum control by ultrafast polarization shaping

We demonstrate that the use of time-dependent light polarization opens a new level of control over quantum systems. With potassium dimer molecules from a supersonic molecular beam, we show that a polarization-shaped laser pulse increases the ionization yield beyond that obtained with an optimally shaped linearly polarized laser pulse. This is due to the different multiphoton ionization pathways in K2 involving dipole transitions which favor different polarization directions of the exciting laser field. This experiment is a qualitative extension of quantum control mechanisms which opens up new directions giving access to the three-dimensional temporal response of molecular systems.     

纳秒脉冲气体放电机理探讨

 经典Townsend机理和流注理论是气体放电研究的基础,但在解释纳秒脉冲气体放电时均存在一定缺陷。基于经典气体放电理论,探讨纳秒脉冲气体放电机理,分析流注理论判据在纳秒脉冲气体放电中的有效性,解释纳秒脉冲下电子逃逸现象和基于电子逃逸的快速电离波击穿理论,仿真计算高能快电子的逃逸过程。结果认为基于高能量快电子的逃逸击穿将是可能解释纳秒脉冲下气体放电现象的依据。