求解三种导体构形中相对论电子形成的空间电荷限制流

从Poisson方程及空间电荷限制流假设出发,推导了三种导体构形中相对论电子形成的空间电荷流密度的一般方程,给出了求解方法及解的基本特征、平板形阳极空间电荷限制流的具体表达式,研究了同轴圆筒形及共顶点同轴圆锥形导体空间电荷限制流关系表达式的极性效应、空间电荷密度及电场分布。     

空间电荷限制流与传导电流的定量关系

从空间电荷限制流假设、Poisson方程及电子正则动量守恒关系出发,推导了平板形、同轴圆柱和共顶点同轴圆锥三种导体构形的空间电荷流随传导电流变化的广义Poisson方程,给出了求解方法及解的基本特征,分析比较了三种导体构形空间电荷限制流的基本性质。通过推导,计算和分析可得：各种电压条件下传导电流对空间电荷限制（SCL） 流的作用效果不一样,电压越高传导电流提高磁绝缘程度的作用越显著;当几何因子(即高阻抗)较小时其它两种导体的SCL流与平板形相差较大,几何因子较大时与平板形十分接近;同样电压条件下负极性的SCL流比平板形小、正极形正好相反,而相同几何因子条件下同轴圆筒的SCL流比共顶点同轴圆锥的小;在分析研究低阻抗MITL时,采用SCL流的平板近似不会带来大的误差。在描述时变脉冲作用于MITL时,可以通过对SCL流随电压、传导电流变化的曲面函数插值的方法确定各个时刻的磁绝缘状态。     

空间电荷限制流与传导电流的定量关系

 从空间电荷限制流假设、Poisson方程及电子正则动量守恒关系出发,推导了平板形、同轴圆柱和共顶点同轴圆锥三种导体构形的空间电荷流随传导电流变化的广义Poisson方程,给出了求解方法及解的基本特征,分析比较了三种导体构形空间电荷限制流的基本性质。通过推导,计算和分析可得：各种电压条件下传导电流对空间电荷限制（SCL） 流的作用效果不一样,电压越高传导电流提高磁绝缘程度的作用越显著;当几何因子(即高阻抗)较小时其它两种导体的SCL流与平板形相差较大,几何因子较大时与平板形十分接近;同样电压条件下负极性的SCL流比平板形小、正极形正好相反,而相同几何因子条件下同轴圆筒的SCL流比共顶点同轴圆锥的小;在分析研究低阻抗MITL时,采用SCL流的平板近似不会带来大的误差。在描述时变脉冲作用于MITL时,可以通过对SCL流随电压、传导电流变化的曲面函数插值的方法确定各个时刻的磁绝缘状态。     

求解三种导体构形中相对论电子形成的空间电荷限制流

在无横向磁场作用下，真空中损失到金属导体阳极表面的空间电荷限制（SCL）流将达到最大。在无限大平板构形导体中，这个最大的SCL流只与阴阳极电压和间距相关；而对于在磁绝缘传输线（MITL）中广泛应用的同轴圆筒和共顶点同轴圆锥构形，其最大SCL流还与导体的几何因子及极性参量有关。研究这3种典型构形的最大SCL流，是研究横向磁场对SCL流影响规律的起点，是设计同类MITL构形的基础。     

轴对称真空二极管空间电荷限制流

基于ArcPIC代码采用PIC-MCC方法,模拟研究了轴对称真空二极管放电时电子密度和阴极表面场强分布情况,同时给出了二维空间电荷限制流的一阶和二阶拟合公式。研究发现,真空二极管放电时阴极表面电场会随阴极注入电流密度的增加而增加,而后出现振荡并趋于一个稳定状态;二维空间电荷限制流密度值随阴极发射半径的增大而减小,且阴极发射半径越大越接近一维空间电荷限制流值。     

电子初始能量对双向流二极管空间电荷限制流密度的影响

从理论上研究了阴极发射电子初始能量对一维平面非相对论性双向流二极管内空间电荷限制电子、离子流密度的影响,并与阴极发射电子初始能量为0情况下的空间电荷限制电子、离子流密度进行了比较。     

电子初始能量对双向流二极管空间电荷限制流密度的影响

 从理论上研究了阴极发射电子初始能量对一维平面非相对论性双向流二极管内空间电荷限制电子、离子流密度的影响,并与阴极发射电子初始能量为0情况下的空间电荷限制电子、离子流密度进行了比较。     

轴对称平板二极管空间电荷限制流的2维效应

应用精度较高的体积加权电荷、电流分配模型,对轴对称平板二极管的空间电荷限制流2维效应进行了粒子模拟研究。选取电压分别为100 kV和1 MV两种情况,对空间电荷限制流受二极管尺寸影响的规律进行了模拟。模拟结果表明,2维效应使空间电荷限制流密度随二极管形状因子(阴极发射半径与阴阳极间隙的比值)的减小而增大,且受相对论效应的影响不明显。经数值拟合得到了空间电荷限制流2维效应与形状因子相关的二阶经验公式,其一阶系数与一阶理论结果基本一致,约为1/4。     

轴对称平板二极管空间电荷限制流的2维效应

 应用精度较高的体积加权电荷、电流分配模型,对轴对称平板二极管的空间电荷限制流2维效应进行了粒子模拟研究。选取电压分别为100 kV和1 MV两种情况,对空间电荷限制流受二极管尺寸影响的规律进行了模拟。模拟结果表明,2维效应使空间电荷限制流密度随二极管形状因子(阴极发射半径与阴阳极间隙的比值)的减小而增大,且受相对论效应的影响不明显。经数值拟合得到了空间电荷限制流2维效应与形状因子相关的二阶经验公式,其一阶系数与一阶理论结果基本一致,约为1/4。     

基于库仑定律的二极管空间电荷限制效应研究

真空二极管是电子束源装置中的一个关键部件, 其阴极发射的电子束进入二极管阴阳极间隙区会产生很强的空间电荷限制效应. 本文针对平板真空二极管中的空间电荷限制效应物理模型, 从库仑定律的积分形式出发, 选取了不同参数的阴极半径与阴阳极间隙距离之比, 计算得到了真空二极管阴阳极间隙区的电场分布情况, 从而避免了采用Poisson方程求解时需要处理复杂的非线性偏微分方程这一问题. 结果表明, 基于库仑定律的计算结果与从Child-Langmuir定律分析得到的结果仅相差一个与二 极管极板边界条件有关的修正量. 当二极管阴极半径与阴阳极间隙距离之比 R/D>10时,一维空间电荷限制定律将是一个较好的近似结果,当 R/D较小时, 用该定律计算误差较大,在实际物理问题中需要谨慎使用.     

Collective flow in relativistic heavy-ion collisions

A brief introduction is given to the field of collective flow, currently being investigated experimentally at the Relativistic Heavy-Ion Collider, Brookhaven National Laboratory. It is followed by an outline of the work that I have been doing in this field, in collaboration with Nicolas Borghini and Jean-Yves Ollitrault.     

Electrical discharge characteristics of a dielectric liquid under external flow in a microchannel with planar electrode configuration

The effect of fluid flow on discharge characteristics in a dielectric liquid was determined. Tests were performed for flow in a 100 micron high, 5 mm wide, 50 mm long microchannel at Reynolds numbers up to 13 and applied DC potentials up to 1.5 kV through 100 micro planar electrode pairs along the floor of the channel. The current within the conduction regime increased as the flow rate increased for the case where the flow was in the same direction as the applied electric field. In the injection regime, there was an optimum flow rate for maximum current.     

Solution to the MHD flow over a non-linear stretching sheet by homotopy perturbation method

In this study,by means of homotopy perturbation method(HPM) an approximate solution of the magnetohydrodynamic(MHD) boundary layer flow is obtained.The main feature of the HPM is that it deforms a difficult problem into a set of problems which are easier to solve.HPM produces analytical expressions for the solution to nonlinear differential equations.The obtained analytic solution is in the form of an infinite power series.In this work,the analytical solution obtained by using only two terms from HPM soluti...     

Characteristics of the vibrational power flow propagation in a submerged periodic ring-stiffened cylindrical shell

By using space-harmonic analysis method, the characteristics of the vibrational power flow propagation in an infinite periodic ring-stiffened cylindrical shell immersed in water are studied. The harmonic motion of the shell and the sound pressure field in the fluid are described by Flügge shell equations and Helmholtz equation, respectively, and four kinds of the rings’ forces and moments are considered. Along the shell axial direction, the propagation of the power flow carried by different internal forces (moments) of the shell wall can be obtained, thus the total power flow in the shell wall and the ratios of the component power flow carried by different shell internal forces (moments) to the total power flow are also studied. It is found that characteristics of the vibrational power flow propagation vary with different circumferential modes order and different frequencies. Moreover, the presence of the stiffeners and structural damping will greatly influence the results.     

油-气-水三相流超声传感器持气率测量

为探索油-气-水三相流持气率测量难题,该文开展了脉冲透射式超声传感器持气率测量动态实验研究。首先,利用超声传感器与光纤传感器组合,测取了油-气-水三相流中段塞流、混状流、泡状流的响应信号;其次,提取了超声脉冲信号的最大值序列来反映不同流型时超声传感器响应特性,同时,借助双头光纤传感器与相关测速法,计算得到了流体中气泡弦长序列;最后,结合流型与泡径信息,利用超声传感器测量了不同流型下持气率,并分析了不同流型持气率预测的误差来源,为其他油-气-水三相流持气率测量传感器设计提供了借鉴。     

Fractional Quantum Conductance Plateaus in Mosaic‐Like Conductors and Their Similarities to the Fractional Quantum Hall Effect

A simple route to generate magnetotransport data is reported that results in fractional quantum Hall plateaus in the conductance without invoking strongly correlated physics. Ingredients to the generating model are conducting tiles with integer quantum Hall effect and metallic linkers, further Kirchhoff rules. When connecting few identical tiles in a mosaic, fractional steps occur in the conductance values. Richer spectra representing several fractions occur when the tiles are parametrically varied. Parts of the simulation data are supported with purposefully designed graphene mosaics in high magnetic fields. The findings emphasize that the occurrence of fractional conductance values, in particular in two‐terminal measurements, does not necessarily indicate interaction‐driven physics. The importance of an independent determination of charge densities is underscored and similarities with and differences to the fractional quantum Hall effect are critically discussed.