铁电阴极前电极表面等离子体横向扩散速度估算

分析了激励脉冲电压作用下铁电阴极电容的变化,即等离子体沿着铁电阴极前电极表面扩散而引起电容变化;建立了激励脉冲电压作用下铁电阴极等效电容模型并推导铁电阴极前电极表面等离子横向扩散速度表达式。采用传统固相烧结工艺制备的掺镧锆锡钛酸铅反铁电陶瓷作为阴极材料,通过测量激励脉冲电压作用下铁电阴极两端的电压及充放电电流,计算得到掺镧锆锡钛酸铅陶瓷表面等离子体横向扩散速度为1.89×106 cm/s。     

真空脉冲放电金属等离子体生成及传播特性

研究了采用放电电流为200 A,持续时间为13 s的单脉冲放电形式,在锥-板、锥-网两种电极结构下,等离子体生成及空间传播特性并使用探针法对生成等离子体的电子密度、电子温度、空间电位、离子能量等参数进行了测量。实验和仿真结果表明;锥-网电极的起始放电电压较高,生成的等离子密度较大,沿放电电极轴方向运动的等离子体的密度最大。然而,两种不同电极结构生成的等离子体的传播速度没有明显区别。     

脉冲放电等离子体光谱干扰机制及其修正方法研究

为解决脉冲放电击穿颗粒流的等离子体光谱(PF-SIBS)中钨电极激发引起的谱线干扰问题,研究了基于等离子体信号探测优化的谱线干扰修正方法。搭建PF-SIBS测量实验系统,以化学纯石墨的颗粒流为研究对象,根据电极间等离子体产生和消亡过程、各特征谱线在等离子体内的分布情况以及各特征谱线信号强度在电极间的变化规律,解析了放电等离子体内各特征元素蒸发、解离和激发的过程,并据此优化光谱探测位置以减弱谱线干扰。研究结果表明：电子在阴极斑点生成,向阳极发射的过程中与电极金属、石墨颗粒流和电极间空气介质发生碰撞电离,产生更多的电子发射,从而形成并维持从阴极向阳极的放电通道。在阴极区域,高能电场产生的焦耳热促使阴极尖端钨金属蒸发溅射,膨胀产生的冲击使得颗粒和空气被排出阴极区域,钨金属的原子及电子占据在阴极区域;在放电通道中部,电子与密集的石墨颗粒流发生碰撞电离;在阳极区域,剩余的放电能量难以蒸发阳极金属,电子主要电离空气介质。可将阴极到阳极的区域划分为阴极金属激发区、中部颗粒激发区和阳极空气激发区。被电离的电极金属、石墨颗粒、空气介质的离子和中性原子占据各自的激发区域,形成等离子体并辐射出对应的特征谱线...     

微腔等离子体放电过程的数值研究

采用2维自洽完全流体模型,数值研究了阳极为通孔的高气压微腔放电结构中等离子体参数的变化过程。模拟结果获得了当氩气压强为13.3 kPa时,放电中的电势分布、等离子体密度分布、径向电场分布和电子温度分布等重要参数的演化过程。模拟结果表明在放电过程中,阴极附近的电场由轴向电场逐步转变为径向电场,等离子体密度最大值位于放电腔中间处,并随时间推移由阳极附近向阴极附近移动,电子温度的最大值出现在阴极环形鞘层区域。     

同轴枪放电等离子体电流片的运动特性研究

同轴枪放电可以产生高速度、高密度的等离子体射流,在天体物理、核物理等研究领域具有广泛的应用.基于同轴枪放电等离子体运动的"雪犁模型"分析,本实验通过对等离子体光电信号和磁信号的测量及放电照片的拍摄,研究了不同放电电流和气压对同轴枪放电等离子体电流片的运动特性、电流通道分布的影响.实验结果发现:一次放电过程中,气压为10 Pa、放电电流为35.7—69.8 kA时,随着放电电流的增加,等离子体喷射速度增加,输运距离与离子携带的轴向动能成正比,大电流条件下,等离子体喷出枪口时易于在枪底端形成新的电流通道;气压为5—40 Pa、放电电流为49.8 kA时,随着气压的增加,等离子体喷射速度减小,输运距离缩短,高气压下,等离子体喷出枪口时在枪底端未产生新的放电通道,这与放电过程中遗留在枪底端的带电粒子和电流片渗漏残留在枪内的中性粒子共同形成的阻抗通道有关;电流反向时,二次放电击穿位置发生在电极头部,放电过程中存在多次放电现象.     

介质阻挡放电点燃大气压直流均匀放电的光谱研究

由于大气压均匀放电等离子体在工业领域具有广泛的应用前景,为了获得大尺寸的大气压均匀等离子体,采用氩气作为工作气体,在大气压空气环境中利用同轴介质阻挡放电点燃了针-板电极间的大气隙(气隙宽度达到5 cm)直流均匀放电。研究发现,同轴介质阻挡放电能够有效降低针-板电极间的击穿电压。该均匀放电由等离子体柱、等离子体羽、阴极暗区和阴极辉区组成。其中等离子体柱和阴极辉区都是连续放电。而等离子体羽不同位置的放电是不同时的。事实上,等离子体羽放电是由从阴极向着等离子体柱移动的发光光层(即等离子体子弹)叠加而成。利用电学方法测量了放电的伏安特性曲线,发现其与低气压正常辉光放电类似,均具有负斜率。采集了放电的发射光谱,发现存在N₂第二正带系、氩原子和氧原子谱线。通过Boltzmann plot方法对放电等离子体电子激发温度进行了空间分辨测量,发现等离子体柱的电子激发温度比等离子体羽的电子激发温度低。通过分析放电机制,对以上现象进行了定性解释。这些研究结果对大气压均匀放电等离子体源的研制和工业应用具有重要意义。     

强流电子束源阴极等离子体的粒子模拟

 模拟了强流电子束源阴极表面附近区域数密度约1014 cm-3的等离子体的膨胀过程,观察到等离子体膨胀速度约为1 cm/μs。通过观察不同时刻阴极附近电子和离子的相空间分布、数密度分布和轴向电场分布,分析了等离子体膨胀过程。结果表明:等离子体的产生使得阴极表面电场增强,进而增大阴极的电流发射密度,电流密度增加使得空间电荷效应增强,并使等离子体前沿处的电场减小,当等离子体前沿处的电场减小到零时等离子体向阳极膨胀。讨论了等离子体温度、离子质量、束流密度和离子产生率对等离子体膨胀速度的影响。结果表明:等离子体的膨胀速度随着等离子体温度升高而增大,随离子质量增大而减小,但膨胀速度不等于离子声速;等离子体产生率越小,等离子体膨胀速度越小。     

高功率单孔柱-孔汇聚传输结构的电磁粒子仿真

柱-孔汇聚结构(PHC)附近高功率脉冲电流的损失是脉冲功率技术领域的研究热点,是研制下一代大型脉冲功率装置的技术瓶颈.本文建立了单孔柱-孔汇聚结构的3维仿真模型,采用粒子(PIC)仿真算法,分别在阴极发射电子以及阴极等离子体等情况下,计算了单孔柱-孔汇聚结构的电流传输特性,首次在仿真过程中考虑了阴极负离子的运动对单孔PHC阴阳极间隙闭合的影响.仿真结果表明阴极等离子体导致了阴阳极间距明显地缩短,从而引起电流损失.同时获得了阴极等离子体平均扩展速度为3.76 cm/μs.更为重要的是,当阴极等离子体中含有负离子时,单孔柱-孔汇聚结构电流损失的现象更为显著.同时获得了负离子平均漂移速度约为10 cm/μs.仿真结果显示阴极负离子在PHC阴阳极间隙闭合过程中,同样发挥了显著的作用,是阴阳极间隙闭合的重要因素之一.研究结果有助于深入理解高功率PHC电流损失的物理机理,也可为高功率PHC的设计提供重要理论基础.     

大气压微波等离子体射流装置放电特性研究

基于同轴传输线结构设计了两种不同喷嘴结构的大气压微波等离子体射流(MW-APPJ)装置,其工作频率2.45 GHz,工作气体为氩气,分别研究了两种不同喷嘴结构对等离子体放电特性产生的影响。仿真结果表明,MW-APPJ在气体喷嘴处会产生高强度的电场,经过优化结构,实现在频率2.45 GHz下,喷嘴处的场强满足氩气电离的击穿场强阈值要求。同时,利用多物理场耦合仿真软件对装置的气流分布进行了稳态模拟,并通过实验对比分析了两种喷嘴结构下大气压氩等离子体射流的基本特性。实验结果表明,不同的喷嘴结构会影响等离子体装置的反射系数随输入功率的变化规律,但并不影响等离子体射流长度随输入功率的变化规律和反射功率随进气流量的变化规律;同时,在大气压下,稳态微波等离子体射流呈现出类金属性,等离子体中的电子只能在很薄的区域中吸收微波能量,因而造成微波的反射功率较大。     

含氢电极真空弧放电等离子体时空分布特性研究

真空弧离子源在真空镀膜、材料表面改性、真空大电流开关、加速器离子注入等领域有广泛应用,目前国内外对真空弧放电等离子体的研究主要针对纯金属或合金电极,对含氢电极的研究和公开报道较少.本文利用高时空分辨的四分幅图像诊断系统,结合氢和钛原子特征线单色器件,研究了含氢钛电极的真空弧微秒级脉冲放电等离子体的轴向和径向时空分布特性.研究表明:在真空击穿阶段,阳极区域发光更为明显,阳极电极解吸附释放的氢原子是引发击穿的主要放电介质;在真空弧阶段,阴极-绝缘-真空三结合点处产生圆锥状阴极斑,喷射出大量的等离子体以维持弧放电,同时电极内壁非阴极斑区域也有少量等离子体产生,等离子体中H原子的轴向和径向空间分布均比Ti原子均匀.     

Velocity distributions in magnetron sputter

Results of the particle simulation of magnetron sputter are presented. Using a kinetic code, we obtain the spatial profiles of plasma density, potential, and velocity distribution function, along with the electron temperature, the ion density, the current density, and the deposition profiles at the anode surface. The result of simulation is compared with the Child-Langmuir law applied to the magnetron discharge and the global model. The velocity distribution function of electrons is Maxwellian, but that of ions is non-Maxwellian near the cathode with the majority in the energy range below 50 eV     

直流辉光放电等离子体轴向动力学过程的研究

采用磁流体动力学理论,考虑了电子与中性粒子的非弹性碰撞,应用有限差分法研究了直流辉光放电氩等离子体的轴向动力学过程,得到了氩等离子体密度、输运速度、温度以及电位的轴向分布,发现了气体压强和电极间距的变化对阴极区的电子密度有较大的影响,而对阴极区的离子密度的影响甚微。 关键词：     

氮气开关流柱形成过程的理论研究

使用蒙特卡罗-粒子模拟方法对氮气开关中的流柱形成过程进行模拟, 并结合计算结果对其进行理论分析. 发现在流柱击穿发生前(即空间电荷场远小于本底电场), 等离子体的电离频率、电子平均能量及其迁移速度等都近似为常数, 因此可以解析求解电子数密度方程对等离子体的演化行为进行分析. 在击穿发生后, 随机碰撞过程会破坏初始等离子体区域分布的对称性, 并出现分叉的等离子体区域结构. 在放电过程中, 随着等离子体密度增加, 其内部基本保持电中性且电场不断减小, 靠近阴阳极两端电荷分离产生的净电荷密度不断增加, 场强也不断增加, 且靠近阳极端的电荷密度(绝对值)和场强都大于阴极端. 通过改变极板间电压发现, 平均电子能量随极板间场强增加而增加, 电子迁移速度随着场强近似线性增加, 电离频率随场强的变化快慢介于E⁴与E⁵之间.     

Simulation of radio-frequency atmospheric pressure glow discharge in γ mode

The existence of two diffe1：ent discharge modes has been verified in an rf （radio-frequency） atmospheric pressure glow discharge （APGD） by Shi [J. Appl. Phys. 97, 023306 （2005）]. In the first mode, referred to as a mode, the discharge current density is relatively low and the bulk plasma electrons acquire the energy due to the sheath expansion. In the second mode, termed γ mode, the discharge current density is relatively high, the secondary electrons emitted by cathodc under ion bombardment in the cathode sheath region play an important role in sustaining the discharge. In this paper, a one-dimensional self-consistent fluid model for rf APGDs is used to simulate the discharge mechanisms in the mode in helium discharge between two parallel metallic planar electrodes. The results show that as the applied voltage increases, the discharge current becomes greater and the plasma density correspondingly increases, consequentially the discharge transits from the a mode into the γ mode. The high collisionality of the APGD plasma results in significant drop of discharge potential across the sheath region, and the electron Joule heating and the electron collisional energy loss reach their maxima in the region. The validity of the simulation is checked with the available experimental and numerical data.     

Results of vacuum cleaning techniques on the performance of LiFfield-threshold ion sources on extraction applied-B ion diodes at 1-10TW

Uncontrolled plasma formation on electrode surfaces limits performance in a wide variety of pulsed power devices such as electron and ion diodes, transmission lines, radio frequency (RF) cavities, and microwave devices. Surface and bulk contaminants on the electrodes in vacuum dominate the composition of these plasmas, formed through processes such as stimulated and thermal desorption followed by ionization. We are applying RF discharge cleaning, anode heating, cathode cooling, and substrate surface coatings to the control of the effects of these plasmas in the particular case of applied-B ion diodes on the SABRE (1 TW) and PBFA-X (30 TW) accelerators. Evidence shows that our LiF ion source provides a 200-700 A/cm² lithium beam for 10-20 ns which is then replaced by a contaminant beam of protons and carbon. Other ion sources show similar behavior. Our electrode surface and substrate cleaning techniques reduce beam contamination, anode and cathode plasma formation, delay impedance collapse, and increase lithium energy, power, and production efficiency. Theoretical and simulation models of electron-stimulated and thermal-contaminant desorption leading to anode plasma formation show agreement with many features from experiment. Decrease of the diode electron loss by changing the shape and magnitude of the insulating magnetic field profiles increases the lithium output and changes the diode response to cleaning. We also show that the LiF films are permeable, allowing substrate contaminants to affect diode behavior. Substrate coatings of Ta and Au underneath the LiF film allow some measure of control of substrate contaminants, and provide direct evidence for thermal desorption. We have increased lithium current density by a factor of four and lithium energy by a factor of five through a combination of in situ surface and substrate cleaning, substrate coatings, and field profile modifications     

Intense emission from a grid-stabilized plasma cathode

Intense emission from a grid-stabilized plasma cathode based on a glow discharge with an expanded anode area is studied. In the electrode system of the ion source, the potential difference between a large-mesh grid electrode (a hole diameter of 4–6 mm) and cathode and anode plasma reaches 200 V and the glow discharge current is up to 1 A. The current distribution over the electrodes of the plasma cathode is taken, and the dependences of the electron extraction efficiency and electron-emitting-plasma potential on the gas pressure and discharge parameters are obtained. A relationship between the geometric parameters of the grid, cathode plasma potential, and efficiency of electron extraction from the plasma is derived. It is shown that stable intense emission from the plasma cathode can be provided in wide ranges of gas pressure and discharge current by varying the geometry and mesh size of the plasma cathode grid. Discharge contraction in the grid plane at elevated gas pressures is explained. It is assumed that the emitting plasma becomes inhomogeneous due to variation in the thickness of near-electrode layers in the holes of the grid, which makes the distribution of the emission current from the plasma more nonuniform.     

Cable guns as a plasma source in a plasma opening switch

The characteristics of a plasma generated by cable plasma guns have been studied by a laser interferometer. Cable plasma guns are frequently used as a plasma source in plasma opening switches. In our experiments, the plasma source consists of eight coaxial cable guns mounted on the outer electrode of concentric coaxial electrodes. The reproducibility of the gun in subsequent shots is found to be better than 10%, and the gun-to-gun difference is less than 15%. Assuming a symmetry of eight guns, the contour maps of the electron plasma density are plotted as functions of time. The plasma density becomes maximum near the gun nozzle and near the inner coaxial electrode. The plasma density is low in the area between the coaxial electrodes during the early time of the discharge. At a later time, the plasma fills the space between the two guns more uniformly. Still photographs of the plasma luminosity show a good correspondence with the plasma density plots which were taken 10 μs after the discharge initiation. The plasma gun system is designed for use in a 400-kA inductive voltage adder with the inductive energy storage system     

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The electric field strength and electron mean kinetic energy in co-axial dielectric barrier discharge (DBD) were estimated based on static electric filed model. Through the comparison of the single dielectric layer DBD with the double dielectric layer DBD, it was found the electric field strength and electron mean kinetic energy in double dielectric layer DBD are greater than that in the single dielectric layer DBD under the same electrode configuration and discharge conditions. The calculation results can successfully applied to explain the toluene degradation efficiency in double dielectric layer DBD is larger than that in the single dielectric layer DBD under the same discharge parameters.     

估算线筒式介质阻挡放电场强和电子平均动能的方法

利用静电场模型对线筒式介质阻挡放电电场强度进行了计算,并对电子平均动能进行了估算。通过对单双介质阻挡放电(DBD)的对比,发现在相同的放电条件下,双介质DBD产生的电场强度和电子平均动能比单介质DBD的要大。这就很好地解释了在相同的放电参数下,甲苯的降解效率在双介质DBD中要比单介质DBD中大。