螺旋波纹波导被动式脉冲压缩模拟研究

研究了一种基于螺旋波纹波导特殊色散特性对输入微波脉冲进行压缩的新方法。利用3维全电磁粒子模拟软件对X波段螺旋波纹波导进行了建模,模拟分析了该波导的特殊色散特性及提高功率增益的方法,并将已有模型脉冲压缩增益提高了6.65。模拟结果表明:通过优化输入微波的频率调制特性,可以获得更加符合被动式脉冲压缩所需要的调频形式;采用改进后的椭圆波导,可以得到更有利于被动式脉冲压缩的本征模式;通过延长渐变段长度,可以减少规则段和渐变段之间不均匀性造成的微波反射,从而实现更高的脉冲压缩增益。     

轴对称系统等离子体数值模拟电荷、电流分配CIC方法

采用体积加权CIC方法,对轴对称系统等离子体模拟PIC方法中的节点电荷和电流计算进行了详细讨论,推导出节点电荷和电流的计算公式,可用于轴对称系统21／2维等离子体静电PIC模拟和电磁PIC模拟。     

无箔二极管电磁PIC模拟空间电荷限制发射模型比较

 为了在无箔二极管电磁PIC模拟中采用与电磁场自洽的空间电荷限制发射模型，对查尔特定律模型、高斯定律模型和一维二极管模型进行了理论分析和实例模拟比较。模拟结果表明，三种模型都能与电磁场自洽并反映外加磁场对发射电流的影响，但高斯定律模型受网格剖分粗细程度的影响较大且容易产生振荡，一维二极管模型在网格参数合理的情况下结果与查尔特定律模型基本接近，但需要求解超越方程，花费时间多。通过对模拟结果进行分析和比较，认为外加磁场对电子发射模型本身的影响很小，在电磁PIC数值模拟中可以不考虑，因此，查尔特定律模型更适合用于无箔二极管的电磁PIC模拟。     

Frequency Spectrum of Plasma-Filled Free-Electron Laser Pumped by Electromagnetic Wave

The frequency spectrum of free-electron laser pumped by electromagnetic wave with magnetized and unmagnetized background plasma is analyzed by the theory of three-wave interaction and PIC simulation, respectively. The frequencies of PIC simulation are in agreement with the results of the three-wave interaction theory. The results show that the frequency spectrum is very plentiful.     

相对论磁控管输出阻抗

 用二维全电磁PIC方法模拟了Palevky和Bekefi的A-6型的相对论磁控管实验, 分析了A-6磁控管的物理图象。同时以实验参数为基础, 特别研究了相对论磁控管输出阻抗对输出功率和运行模式的影响, 给出了最大输出功率时最佳阻抗匹配值。     

3维全电磁粒子模拟大规模并行程序NEPTUNE

 介绍了自主编制的3维全电磁粒子模拟大规模并行程序NEPTUNE的基本情况。该程序具备对多种典型高功率微波源器件的3维模拟能力,可以在数百乃至上千个CPU上稳定运行。该程序使用时域有限差分(FDTD)方法更新计算电磁场,采用Buneman-Boris算法更新粒子运动状态,运用质点网格法（PIC）处理粒子与电磁场的耦合关系,最后利用Boris方法求解泊松方程对电场散度进行修正,以确保计算精度。该程序初步具备复杂几何结构建模能力,可以对典型高功率微波器件中常见的一些复杂结构,如任意边界形状的轴对称几何体、正交投影面几何体,慢波结构、耦合孔洞、金属线和曲面薄膜等进行几何建模。该程序将理想导体边界、外加波边界、粒子发射与吸收边界及完全匹配层边界等物理边界应用于几何边界上,实现了数值计算的封闭求解。最后以算例的形式,介绍了使用NEPTUNE程序对磁绝缘线振荡器、相对论返波管、虚阴极振荡器及相对论速调管等典型高功率微波源器件进行的模拟计算情况,验证了模拟计算结果的可靠性,同时给出了并行效率的分布情况。     

Modeling of Laser Generation and Propagation of Electron Bunch Along Thin Irradiated Wire

Three-dimensional numerical PIC simulation allowed the detection and study of the formation of an electron bunch moving with relativistic velocity along a thin metal wire during its irradiation with a short laser pulse of relativistic intensity. The bunch motion is accompanied by electromagnetic surface-type pulses.     

Ka波段带状注相对论扩展互作用振荡器的模拟设计

利用三维粒子仿真软件,对工作在Ka波段的带状注相对论扩展互作用振荡器进行了模拟仿真设计。采用宽高比为30∶1的带状电子束以降低空间电荷效应,选择多间隙耦合腔为高频结构以增加器件功率容量,在电子束电压为400kV、束流为2kA、轴向引导磁感应强度为1T的情况下,器件输出微波功率为240 MW,频率为30GHz,效率为30%。     

High-current electron beam in medium-density plasma

Nonstationary effects under the injection of a high-current electron beam (HCEB) in medium-density plasma are considered. A computer simulation was performed using the KARAT electromagnetic PIC code.     

飞秒激光辐照铝靶产生快电子发射的实验和模拟研究

采用实验和数值模拟研究了飞秒激光辐照铝靶产生的快电子发射.实验中,在主脉冲前加上一个预脉冲产生预等离子体,然后主脉冲与预等离子体作用产生快电子.在激光反射方向附近,实验测量的快电子束发射与数值模拟的结果高度地一致;在靶背面,发射的快电子的数目小于数值模拟的结果,原因在于快电子在靶内输运受到电荷分离场和碰撞的影响;在数值模拟中未出现的,沿靶表面发射的快电子束,是由表面准静态电磁场的禁闭效应产生.     

飞秒激光辐照铝靶产生快电子发射的实验和模拟研究

采用实验和数值模拟研究了飞秒激光辐照铝靶产生的快电子发射。实验中,在主脉冲前加上一个预脉冲产生预等离子体,然后主脉冲与预等离子体作用产生快电子。在激光反射方向附近,实验测量的快电子束发射与数值模拟的结果高度地一致;在靶背面,发射的快电子的数目小于数值模拟的结果,原因在于快电子在靶内输运受到电荷分离场和碰撞的影响;在数值模拟中未出现的,沿靶表面发射的快电子束,是由表面准静态电磁场的禁闭效应产生。     

Transverse dynamics of space charge dominated beam during bunching

In this paper we present a technique to optimize the transport parameters for transverse matching of the space charge dominated beams in the presence of bunching. The increase in the current within the specified bunch width during the transport is obtained from the disc model and is included in the optimization method. A 2D particle in cell (PIC) code is then developed to study the details transverse dynamics of the bunch taking into account the effect of longitudinal compression by reweighting the charge and mass of macroparticles. The evolution of rms beam size obtained using PIC simulation agrees well with the results obtained by solving beam envelope equation. The PIC simulation shows emittance growth during bunching induced by the space charge effect for nonuniform distribution. The growth in the emittance increases with the nonlinearity of distribution and peaks near the time focus.     

Ka波段带状注相对论扩展互作用速调管放大器的分析与设计

带状注相对论扩展互作用速调管放大器是一种高功率、高频率的微波毫米波放大型器件, 具有广阔的应用前景. 本文分析了扩展互作用结构多间隙谐振腔的渡越时间效应, 推导了2π模场情况下谐振腔的能量交换系数和电子负载电导, 且通过计算表明工作在2π模式三间隙腔的电子负载电导是单间隙腔的9倍左右, 多间隙结构有利于提高器件效率. 利用三维粒子仿真软件, 对工作在Ka波段的带状注相对论扩展互作用速调管放大器进行了模拟研究, 采用宽高比为30:1的带状电子束以降低空间电荷效应, 在电子束电压为500 kV, 束流为1 kA, 轴向引导磁感应强度为0.8 T的情况下, 器件输出微波功率为190 MW, 频率为40 GHz, 器件效率为38%, 器件增益为69 dB.     

潘宁源放电的全三维电磁粒子模拟/蒙特卡罗碰撞数值算法研究

深入研究潘宁放电的物理机制, 研制了全三维高品质算法粒子模拟软件(PIC), 设计并添加了相应物理情景的蒙特卡罗碰撞模块(MCC), 并对电子、氢分子离子(H₂⁺)、氢正离子(H⁺)、氢三正离子(H₃⁺)同时进行了跟踪, 成功研制了全三维电磁PIC/MCC数值算法. 结合国内研究较热的潘宁放电模型, 对该算法进行模拟验证. 模拟结果显示: 采用有效的滤波算法能抑制电磁数值噪声, 电子能量呈麦克斯韦分布, 由于电子的径向漂移和加速导致离子源顶端H₂⁺产量较大. 关键词： 潘宁离子源 高品质算法 粒子模拟/蒙特卡罗     

Study of a rectangular coupled cavity extendedinteraction oscillator in sub-terahertz waves

An extended interaction oscillator （EIO） generating 120 GHz wave in sub-terahertz waves is studied by using the three-dimensional electromagnetic simulation software CST and PIC codes. A rectangular reentrant coupled-cavity is proposed as the slow-wave structure of EIO. By CST, the circuit parameters including frequency-phase dispersion, interaction impedance and characteristic impedance are simulated and calculated. The operation mode of EIO is chosen very close to the point where βL = 2π with corresponding frequency 120 GHz, the beam voltage 12 kV and the dimensions of the cavity with the period 0.5mm, the height 3mm and the width 1.4mm. Simulation results of beam-wave interaction by PIC show that the exciting frequency is 120.85 GHz and output peak power 465 W with 12-period coupled-cavity with the perveance 0.17 μP. Simulation results indicate that the EIO has very wide range of the operation voltage.     

Effects of Ion-to-Electron Mass Ratio on Electron Dynamics in Collisionless Magnetic Reconnection

A 2 1/2-dimensional electromagnetic particle-in-cell （PIC） simulation code is used to investigate electron behaviour in collisionless magnetic reconnectfon. The results show that the ion/electron mass ratio （mi/me） almost has no impact on the reconnection rate, however it can significantly affect electron behaviour in the diffusion region. For the case with larger mass ratio, the width of electron current sheet becomes smaller and the outflow region along the separatrix is smaller, hence the peak of the electron outflow speed is essentially larger. Density cavities and the parallel electric field E// along the separatrix can be found in the case with larger mass ratio, which may have significant influences on the acceleration and heating of the electrons near the X point.     

Three-dimensional electromagnetic PIC model of a compact ECR plasmasource

A three-dimensional electromagnetic particle-in-cell (PIC) model is developed and used to model a compact ECR plasma source. The finite-difference time-domain (FDTD) technique is used to model the microwave fields which excite the plasma at 2.45 GHz. The PIC technique is used to model the dynamics of both the electrons and ions in the plasma. The grid structure used is constructed using the cylindrical coordinate system. Techniques which permit stable numerical solutions in the cylindrical coordinate system are developed and described. The electromagnetic fields and the plasma dynamics are solved in a self-consistent manner. A compact ECR (electron cyclotron resonance) plasma source used for the generation of ions for materials processing is simulated. This source has a plasma size of 3.6 cm in diameter and 3 cm in height. Simulation results of microwave power absorption, plasma potential, and microwave electric fields are presented. Distributed computing techniques are explored to handle the large computer memory requirements and the long computer simulation times associated with the three-dimensional particle-in-cell plasma model     

Formation of electron depletion layer and parallel electric field in the separatrix region of anti-parallel magnetic reconnection

It is generally accepted that during collisionless magnetic reconnection, electrons flow toward the X line in the separatrix region, and then an electron depletion layer is formed.In this paper, with two-dimensional(2 D) particle-in-cell(PIC)simulation, we investigate the characteristics of the separatrix region during magnetic reconnection.In addition to the electron depletion layer, we find that there still exists an electric field parallel to the magnetic field in the separatrix region.Because a reduced ion-to-electron mass ratio and light speed are usually used in PIC simulation models, we also change these parameters to analyze the characteristics of the separatrix region.It is found that the increase in the ion-to-electron mass ratio makes the electron depletion layer and the parallel electric field more obvious, while the influence of light speed is less pronounced.     

Particle Simulation of a Millimeter Wave Multiwave Cerenkov Generator Producing Gigawatt Power Levels

The Multiwave Cerenkov Generator(MWCG) is investigated with a two and one half dimensional(2 1/2 D) electromagnetic relativistic Particle-in-Cell(PIC) simulation code. NonIinear beam-wave interaction is considered in the code. Deep insights into the MWCG are demonstrated by simulations. Some of the results agree with those of experiments. The radiation is generated with its dominant frequency at 35.5GHz. The power level of 3.8GW is achieved, with radiation efficiency up to 24%. The harmonics of both 71.0GHz and 106.5GHz are observed. The features of parameters dependency are presented. And reasonable explanation is put forward.     

W波段二次谐波突变复合腔回旋管数值模拟

 通过对二次谐波低电压突变结构复合腔回旋管中谐振腔结构、模式竞争以及电子注-波互作用的研究,分析了高频结构特性、寄生模式的抑制和工作参数优化等问题。给出了3 mm 二次谐波低损耗TE₀₂/TE₀₃模式回旋管的模拟设计结果。计算采用了坡度磁场,互作用效率得到显著提高。PIC粒子模拟结果表明:在电子注电压25 kV、电流4 A、纵横速度比1.6、工作磁场1.72 T时,回旋管可获得37 kW 的输出功率,横向运动能量转换效率高达51%,器件效率为37%。