偏压电极对KT-5C装置等离子体边缘的影响

通过电极偏压来控制KT 5C装置边缘区等离子体的径向电场 ,发现在正偏压作用下 ,径向电场剖面由小的负阱状变成明显的山包结构 ,从而形成一个加强的E×B剪切层。剪切层附近的等离子体参数变陡 ,不仅等离子体极向流速度大大增加 ,而且其方向也由沿电子逆磁漂移方向改变为离子的逆磁漂移方向。这些变化导致等离子体边界横向输运被抑制、整体约束得到改善     

等离子体边界对线积分辐射率的影响

在托卡马克辐射诊断中,当探测束线的极向宽度与等离子体小半径要以比较时,等离子体边界会显著影响线积分辐射率,使其工度平均辐射率的带权重的线积分。本文给出了这种情况下的线积分辐射率明晰表达式。     

强流电子束自磁场对能量沉积的磁增强效应

一、引言 苏联的库尔恰托夫研究所最早报导了强流相对论电子束与等离子体相互作用过程中能量沉积的磁增强效应,该所于1976年发表了实验结果,增强因子是10;随后美国的Sandia实验室报导的磁增强因子是2—5;C.Peugnet和R.Bailly-Salins等人用强流电子束在薄金靶上做实验,获得了2—3倍的增强效应。他们的实验结果与理论计算结果是相符合的。本文主要是用蒙特卡罗方法对电子束在束自磁场的作用下的运动进行了模拟跟踪,计算了电子在薄铜靶中沉积能量的磁增强效应。     

磁场中等离子体鞘层的结构

采用流体力学理论，研究了斜磁场作用下的等离子体鞘层结构.在不同大小及方向的磁场作用下，对鞘层的离子，电子密度分布，离子流速度分布，电势分布和Bohm判据进行了讨 论.结果显示磁场对鞘层的结构有明显的影响.在静电力和洛仑兹力的作用下，离子流作螺旋进动，离子密度分布产生振荡. 关键词： 磁鞘 等离子体 磁场     

等离子体屏蔽效应对离子取出时间影响的实验研究

离子取出时间是原子法激光同位素分离（ＡＶＬＩＳ）过程中决定离子取出效率的关键参数之一，它主要受着等离子体屏蔽效应的影响。文中报告了这方面的实验研究结果。在阐述了等离子体屏蔽效应及存在条件的基础上，通过进行静电场（平行平板电场）收集铯（Ｃｓ）等离子体中铯离子的实验，发现在１０~９－１０~（１１）ｍ~（－３）等离子体密度范围内，离子取出时间与等离子体密度、收集场电压均是几何关系，即。     

外磁场作用下的磁等离子体动力学过程仿真

磁等离子体动力学推力器是空间高功率电推进装置的典型代表,磁等离子体动力学过程是其核心工作机制.为深入理解外磁场对其工作特性的影响,本文采用粒子云(particle in cell,PIC)方法结合基于自相似准则的缩比模型,进行外加磁场作用下磁等离子体动力学推力器工作过程的建模仿真,通过与实验结果对比验证模型和方法的可靠性,并重点分析推力器点火启动过程的等离子特性参数分布,以及外磁场和阴极电流对推力器工作性能的影响.研究结果表明:阴阳极放电电弧构建是推力器启动和高效工作的关键步骤;外磁场强度较低工况不利于构建稳定放电电弧,等离子体束流集中于轴线附近,推力主要产生机制是自身场加速;外磁场强度较高时,阴阳极放电电弧稳定,推力产生主要机制是涡旋加速,推力、比冲随外磁场强度线性增大;推力器效率随阴极电流和外磁场强度增大而增大;放电电压随阴极电流增大而增大,但随外磁场强度的增大表现出先减小后增大的趋势.     

外磁场作用下的磁等离子体动力学过程仿真

磁等离子体动力学推力器是空间高功率电推进装置的典型代表,磁等离子体动力学过程是其核心工作机制.为深入理解外磁场对其工作特性的影响,本文采用粒子云(particle in cell,PIC)方法结合基于自相似准则的缩比模型,进行外加磁场作用下磁等离子体动力学推力器工作过程的建模仿真,通过与实验结果对比验证模型和方法的可靠性,并重点分析推力器点火启动过程的等离子特性参数分布,以及外磁场和阴极电流对推力器工作性能的影响.研究结果表明:阴阳极放电电弧构建是推力器启动和高效工作的关键步骤;外磁场强度较低工况不利于构建稳定放电电弧,等离子体束流集中于轴线附近,推力主要产生机制是自身场加速;外磁场强度较高时,阴阳极放电电弧稳定,推力产生主要机制是涡旋加速,推力、比冲随外磁场强度线性增大;推力器效率随阴极电流和外磁场强度增大而增大;放电电压随阴极电流增大而增大,但随外磁场强度的增大表现出先减小后增大的趋势.     

高超声速磁流体力学控制霍尔效应影响

针对霍尔效应对高超声速磁流体力学控制的影响问题,考虑高超声速流动过程中高温化学反应、气体分子热力学温度激发(即平动、转动、振动以及电子温度能量模态之间的激发与松弛过程)及多电离组分等离子体霍尔系数分布,通过耦合求解各向异性霍尔电场泊松方程和带电磁源项的高温热化学非平衡流动控制方程组,建立了高超声速流动磁流体力学控制霍尔效应数值模拟方法,开展了多种条件下高超声速流动磁流体力学控制数值模拟,分析了霍尔效应"漏电"与"聚集"现象原理及其对气动力/热特性的影响机制,详细探讨了不同空域、速域和飞行器特征尺度条件下霍尔效应的作用机理和影响规律.研究表明:1)霍尔效应改变了流场等离子体洛伦兹力分布,削弱了整体的力学效果,使整体的磁阻特性降低; 2)霍尔效应对高超声速磁流体力学控制的影响,与壁面导电性和壁面附近漏电层的"漏电"现象紧密相关,要增强磁控效果,必须抑制壁面附近的"漏电"现象; 3)霍尔效应对磁控热防护效果的影响较为复杂,受"漏电"现象和电流"聚集"现象共同作用; 4)基于本文基准状态,当高度高于67 km或速度高于5.7 km/s或特征尺度大于0.5 m时,霍尔效应使磁控热防护效果增强,电...     

等离子体在磁场中能级分离可能产生的影响

考虑到磁场中的带电粒子在与磁场方向垂直的两个方向上的能级分离，采用玻耳兹曼统计分布，得到几个公式.说明了低温强磁场时可能出现的情况.据此说明了如何对磁流体方程给予一定的修正. 关键词：     

An exact solution of the moving boundary problem for the expansion of a plasma cylinder in a magnetic field

An exact analytic solution has been obtained for a uniformly expanding, neutral, infinitely conducting plasma cylinder in an external uniform and constant magnetic field. The electrodynamical aspects related to the emission and transformation of energy have been considered as well. The results obtained can be used in analysing the recent experimental and simulation data.     

能量输运对柱状等离子体开关磁场穿透过程的影响

 对于高密度、导通时间为μs级的柱状等离子体开关,利用磁流体动力学理论(MHD),对其导通阶段的磁场穿透过程进行了模拟,得到了磁场分布随时间的变化;研究了开关导通过程中能量输运导致的温度不均匀分布对磁场穿透过程的影响。模拟结果表明：对于高密度等离子体开关,磁场以远大于磁扩散速率的速度穿透到等离子体中;在磁压对等离子体产生的压缩效应和欧姆加热效应共同作用下,激波区域的等离子体温度显著升高,这进一步加速了磁场穿透;当考虑能量输运方程时,开关导通时间为0.87 μs,比等温模型的结果0.92 μs短,与实验结果0.87 μs相一致。     

带电粒子在正交电场和磁场中轨迹的形成及曲率半径

本文讨论了带电粒子在正交的电场和磁场中于不同条件下的旋轮线轨迹,并讨论了这些不同形状的旋轮线是怎样由圆轮的纯滚动形成的,使带电粒子的运动过程更加直观,并且运用物理方法导出了旋轮线曲率半径的普遍公式.     

空间电荷效应对热场致发射中诺廷汉效应的影响

热场致发射阴极所产生的强流电子束具有很强的空间电荷效应,为研究该效应对热场致发射过程中诺廷汉（Nottingham）效应的影响机理,在理论分析的基础上,用数值方法研究了不同逸出功和多个外加电场条件下考虑空间电荷效应对诺廷汉效应结果的影响,并与不考虑空间电荷效应时的情形进行了对比. 结果表明：空间电荷效应的强弱会显著影响到阴极表面的稳态电场,进而对诺廷汉效应产生不可忽略的影响;当逸出功在3.0–4.52 eV、外加电场在3×10⁹–9×10⁹ V/m范围内时,考虑空间电荷效应的影响后,热场致发射电子所带走的平均能量较不考虑空间电荷效应时增加0–2.5 eV,且温度越高或外加电场越大时,该增加值越大;考虑空间电荷效应对诺廷汉效应的影响后,热场致发射电子从阴极带走的平均能量随外加电场的增加呈非线性下降规律;当阴极表面温度较高时,诺廷汉效应中的冷却效应随二极管间隙距离的变大而增强. 关键词： 热场致发射 诺廷汉效应 空间电荷效应 阴极表面电场     

Effect of magnetic field on plasma control during CO2 laser welding

During high power CO₂ laser beam welding, the plasma above the keyhole has a shielding effect that it not only absorbs part of the laser energy but also defocuses the laser beam. As a result, the welding efficiency and the aspect ratio of the welds are influenced. In order to reduce the effect of plasma, helium as a plasma control gas has been used successfully and effectively. However, the cost of helium in Southeast Asia is extremely high and therefore the production cost is significantly increased when helium is used as a continuous bleeding plasma control gas. To search for an alternative plasma control technique, feasibility in using magnetic effect as a control tool is explored in this paper. The influences of the magnetic field strength, laser power, welding speed, field direction and shielding gas (e.g. helium and argon) on the penetration depth and the width of bead were also investigated. Experimental results indicated that the magnetic field can influence the shielding effect of the plasma without using plasma control gas. It was found that at a suitable magnetic field strength the penetration depth was increased by about 7%, but no significant difference on the width of bead was found. Moreover, it was shown that the plasma control effect can be achieved at low magnetic field strength and the penetration depth can be increased significantly under argon atmosphere.     

Studies on coherent and incoherent spin dynamics that control the magnetic field effect on photogenerated radical pairs

Since 1970s, magnetic field effects (MFEs) on photogenerated radical pairs have been the centre of focus in the field of spin chemistry. The MFE attributes to quantum mechanical interconversion between the singlet and triplet radical pair states and subsequent spin-selective recombination reactions. In this New View article, the author picks up two hot topics studied during the last two decades, which are (i) so-called low field effect (LFE) and (ii) 2J-resonance MFE on fixed distance donor–acceptor linked molecules. In both of the topics, quantum mechanical explanations are given referring to recent reports, and some novel calculations have been carried out for bridging theoretical and experimental data for long-lived radical pairs. For the first topic, time domain calculations of coherent state mixing have been carried out for elucidation of hyperfine (HF) structure dependence of the LFE. For the second topic, Monte Carlo simulations of the torsional motion of polyaromatic linker unit have been carried out for the demonstration of fast decoherence in such rigid molecules. From these considerations, future possibilities of MFE studies on photo-functional materials and biomolecules have been indicated.     

Electron g-factor in quantum wire in the presence of Rashba effect and magnetic field

In this paper, we study the electron effective Landé g-factor in the InAs quantum wire under an applied magnetic field and the Rashba effect. For this goal, we first present an analytic solution to one-particle Schrödinger equation in the presence of both magnetic field and spin-orbit interaction (SOI). Then, using the obtained energy levels, we study the electron effective Landé g-factor. It is found that: (i) The effective Landé g-factor decreases when magnetic field increases. (ii) By increasing the confinement length l₀, the electron g-factor decreases. (iii) By increasing the strength of SOI, the electron g-factor increases.     

Electron beam modeling and analyses of the electric field distribution and space charge effect

In electron beam technology, one of the critical focuses of research and development efforts is on improving the measurement of electron beam parameters. The parameters are closely related to the generation, emission, operation environment, and role of the electron beam and the corresponding medium. In this study, a field calculation method is proposed, and the electric field intensity distribution on the electron beam's cross-section is analyzed. The characteristics of beam diffusion caused by the space charge effect are investigated in simulation, and the obtained data are compared with the experiment. The simulation demonstrated that the cross-sectional electric field distribution is primarily affected by the electron beam current, current density distribution, and electron beam propagation speed.     

垂直磁场对光抽运信号的影响

保持扫场和垂直磁场合成的叠加磁场大小一定,定量研究了地磁场的垂直分量抵消不同时叠加磁场方向变化角度Δθ对光抽运信号幅度的影响.结果表明:光抽运信号幅度随叠加磁场方向变化角度Δθ的增大而增大,当Δθ=180°时,即地磁场的垂直分量完全抵消时,光抽运信号幅度最大,并用量子理论的观点解释了这一规律.     

Tuning the phase separation in La_(0.325)Pr_(0.3)Ca_(0.375)MnO_3 using the electric double-layer field effect

Electric double-layer field effect experiments were performed on ultrathin films of La0.325Pr0.3Ca0.375MnO3, which is noted for its micrometer-scale phase separation. A clear change of resistance up to 220% was observed and the characteristic metal–insulator transition temperature TPwas also shifted. The changes of both the resistance and TPsuggest that the electric field induced not only tuning of the carrier density but also rebalancing of the phase separation states. The change of the charge-ordered insulating phase fraction was estimated to be temperature dependent, and a maximum of 16% was achieved in the phase separation regime. This tuning effect was partially irreversible, which might be due to an oxygen vacancy migration that is driven by the huge applied electric field.