超高速碰撞产生等离子体电磁特性的研究进展

 综述了国外在超高速碰撞产生等离子体的电磁特性研究方面的现状,主要包括电子温度、等离子体的粒子密度、等离子体的振荡频率及产生的磁场特征等方面。利用等离子体特征参量诊断的扫描Langmuir探针系统、磁感应强度测量的线圈系统及实验系统,进行了超高速碰撞产生等离子体实验,分析了实验中产生等离子体的电磁特性。     

超高速碰撞产生弱磁场线圈测量系统

为了测量超高速碰撞过程中产生瞬态弱磁场的磁感应强度,设计了弱磁场测量的线圈系统。阐述了线圈的设计、线圈等效电路的分析、运算放大器的选择及其功能。理论上探讨了自积分电阻对测量频率的影响。通过超高速碰撞实验得到了产生的弱磁场信号,实验记录的测量信号光滑,表明该测量系统具有较好的抗干扰性能。该测量系统的建立将为超高速碰撞产生等离子体的性能研究提供新的手段。     

碎片云问题的三维欧拉数值模拟

针对材料超高速碰撞产生碎片云问题进行了多介质弹塑性流体力学欧拉方法数值模拟,介绍了所采用的数学模型、材料模型及相应的计算方法,模拟了铝球超高速碰撞铝板和斜铜柱高速撞击铝板形成碎片云的实验现象。进行了不同碰撞速度下模拟的碎片云形状和实验结果比较,利用经验公式对数值模拟的板靶开孔尺寸进行了分析。数值结果与实验结果、经验公式结果比较,说明多介质弹塑性流体力学欧拉方法能够较好地模拟超高速碰撞产生的碎片云问题,验证了数值方法的有效性。     

超高速碰撞产生等离子体云的粒子能量时空分布

为了研究超高速碰撞产生等离子体的粒子能量对航天器电路中元器件的毁伤,获得超高速碰撞产生等离子体粒子能量的时空分布特性是十分必要的。基于超高速碰撞产生稀薄等离子体中带电粒子的运动速度、等离子体的扩散特点,推导出等离子体的粒子能量密度与带电粒子密度及带电粒子运动速度的关系式。进而通过对超高速碰撞2024-T4铝靶实验采集的原始数据分析,利用Matlab编程得到了超高速碰撞2024-T4铝靶产生膨胀等离子体云物理过程中,等离子体的粒子能量密度与带电粒子持续时间及被测点到碰撞点距离的时空分布规律。     

超高速碰撞LY12铝靶产生膨胀等离子体云的电导率测量

 为了研究超高速碰撞过程中产生的膨胀等离子体云的电导率,设计了适用于瞬态等离子体电导率测量的扫描电探针系统。通过二级轻气炮加载LY12球形铝弹丸,运用设计的扫描电探针系统分别进行了相同入射角度和不同碰撞速度条件下超高速碰撞产生等离子体电导率的实验测量。通过对探针等效电路的分析,获得了在整个物理过程中给定探针位置处产生膨胀等离子体云的电导率随时间的变化关系。实验结果表明：在碰撞角度(与靶板平面的夹角)相同、传感器布局相同的条件下,碰撞速度越大,产生膨胀等离子体云的电导率相对越大。     

膨胀等离子体云的粒子密度时空分布

为了获得超高速碰撞产生等离子体粒子密度的时空分布特性,利用点电荷电场的1维理论模型,综合运用质量守恒方程、动量守恒方程、能量守恒方程和麦克斯韦方程,推导出了等离子体在膨胀过程中粒子密度的时空分布规律。通过对超高速碰撞2024-T4铝靶实验采集的原始数据分析,得到了超高速碰撞2024-T4铝靶产生膨胀等离子体云粒子密度的时空演化规律。     

超高速碰撞产生等离子体的频谱响应特征

 针对探针与接地极板间的阻抗匹配问题,通过对超高速碰撞产生等离子体特征参量诊断系统的理论分析,获得了超高速碰撞产生等离子体的频率组成特征;基于该理论特征建立了一种适用于超高速碰撞产生等离子体的探针测量系统,并利用该探针测量系统进行了LY12实心球形铝弹丸超高速碰撞LY12铝靶实验,得到了该实验中超高速碰撞产生等离子体的功率谱特征。理论分析及实验获得的功率谱结果均表明超高速碰撞产生的等离子体具有低频为主的频谱特征：当频率低于5.8 kHz时,功率谱线比较平滑且幅值较小;频率达到11.0 kHz时,功率谱线的峰值和功率全谱峰值相近。因此频率在5.8~11.0 kHz范围的低频频段对功率谱线的峰值贡献较大,频率超过11.0 kHz时,功率谱线的大幅度抖动对功率谱线的峰值贡献较小。理论及实验结果证明了实验系统的可靠性和实现过程的合理性。     

超高速碰撞2024-T4铝靶产生的等离子体对逻辑芯片的干扰

 为了掌握超高速碰撞产生等离子体对航天器上常用典型逻辑芯片产生的干扰,利用自主设计的朗缪尔三探针诊断系统,进行了弹丸（入射速度为6.10 km/s,入射角度为30°）超高速碰撞2024-T4铝产生等离子体的特征参量诊断,测量了给定位置和方位角处等离子体的电子密度,利用数据采集系统对实验给定位置和方位角处逻辑芯片的干扰情况进行了评价。实验结果表明,超高速碰撞产生的等离子体对航天器上常用的逻辑芯片将产生严重干扰。     

超高速碰撞2A12铝靶过程中Al~+的光谱辐射特征

材料受到强冲击会产生闪光和等离子体效应。通过超高速碰撞实验并结合多种先进测试手段,推导出了适用于计算超高速碰撞产生等离子体电离度的沙哈(Saha)公式,为超高速碰撞过程中弹丸和靶板的物质组成分析提供了强有力的工具。基于二级轻气炮加载系统结合等离子体特征参量诊断的Triple Langmuir probe诊断系统和光谱辐射测量的ESA4000光谱仪系统,进行了3种不同碰撞速度条件下的超高速碰撞实验。实验结果表明,超高速碰撞2A12铝靶产生闪光辐射中包含Al+的光谱辐射;通过实验数据的解析进一步揭示了光谱强度与弹丸速度的关系。随着弹丸速度的增加,Al+的辐射光谱强度增大,由2A12铝激发的Al+光谱中小波长所对应谱线的辐射光谱强度比长波长所对应谱线的辐射光谱强度增加更快。关于2A12铝靶在超高速撞击载荷下产生铝离子的光谱辐射特征以及辐射温度研究在航天器防护空间碎片、导弹拦截、天体物理及深空探测领域具有重要的应用价值,此外,等离子体的特征参量测量和光谱辐射特征研究,对于在微观层面深刻揭示超高速碰撞现象具有重要的理论意义。     

超高速碰撞喷出物气化与等离子体形成的物理机制

 为了了解超高速碰撞产生等离子体的物理机制,采用理论方法对超高速碰撞LY12铝靶各物理过程的能量分配进行了分析,涉及到熔化相变、气化相变及等离子体形成过程的能量消耗。揭示了碰撞喷出物形成过程中各物理阶段对气化、等离子体形成的影响因素,包括碰撞的附加热机制、材料碰撞后等离子体羽的形成及等离子体羽膨胀的物理机制,并给出了模型描述。     

A multi-energy-level lattice Boltzmann model for Maxwell’s equations without sources

A lattice Boltzmann model for the Maxwell’s equations without sources is proposed by taking separate sets of distribution functions for the electric and magnetic fields and using the higher-order moment method. The higher-order moment method is based on the solution of a series of partial differential equations obtained by multi-energy-level techniques, multi-scale techniques, and Chapman–Enskog expansion, As numerical examples, some classical electromagnetic phenomena, such as the electric field and equipotential lines around an electrostatic dipole, the electric and magnetic fields around oscillating dipoles are given. These numerical results agree well with classical ones.     

Dielectric tensor elements for the description of waves in rotating inhomogeneous magnetized plasma spheroids

The dielectric permittivity tensor elements of a rotating cold collisionless plasma spheroid in an external magnetic field with toroidal and axial components are obtained. The effects of inhomogeneity in the densities of charged particles and the initial toroidal velocity on the dielectric permittivity tensor and field equations are investigated. The field components in terms of their toroidal components are calculated and it is shown that the toroidal components of the electric and magnetic fields are coupled by two differential equations. The influence of thermal and collisional effects on the dielectric tensor and field equations in the rotating plasma spheroid are also investigated. In the limiting spherical case, the dielectric tensor of a stationary magnetized collisionless cold plasma sphere is presented.     

Poloidal–toroidal decomposition in a finite cylinder. I: Influence matrices for the magnetohydrodynamic equations

The Navier–Stokes equations and magnetohydrodynamics equations are written in terms of poloidal and toroidal potentials in a finite cylinder. This formulation insures that the velocity and magnetic fields are divergence-free by construction, but leads to systems of partial differential equations of higher order, whose boundary conditions are coupled. The influence matrix technique is used to transform these systems into decoupled parabolic and elliptic problems. The magnetic field in the induction equation is matched to that in an exterior vacuum by means of the Dirichlet-to-Neumann mapping, thus eliminating the need to discretize the exterior. The influence matrix is scaled in order to attain an acceptable condition number.     

Generation of perturbations by means of decoupled equations and their adjoints

It is shown that the procedure introduced by Wald for constructing solutions of a coupled system of linear partial differential equations from the solution of a single equation, based on the concept of the adjoint of a linear partial differential operator, can be extended to equations involving spinor fields, matrix fields and two or more fields. Some results concerning massless spinor fields are presented and the application of the method to linear perturbations of Yang-Mills fields and of Einstein-Maxwell fields is indicated.     

Poloidal–toroidal decomposition in a finite cylinder. I: Influence matrices for the magnetohydrodynamic equations

The Navier–Stokes equations and magnetohydrodynamics equations are written in terms of poloidal and toroidal potentials in a finite cylinder. This formulation insures that the velocity and magnetic fields are divergence-free by construction, but leads to systems of partial differential equations of higher order, whose boundary conditions are coupled. The influence matrix technique is used to transform these systems into decoupled parabolic and elliptic problems. The magnetic field in the induction equation is matched to that in an exterior vacuum by means of the Dirichlet-to-Neumann mapping, thus eliminating the need to discretize the exterior. The influence matrix is scaled in order to attain an acceptable condition number.     

Perturbation technique for unsteady MHD mixed convection periodic flow, heat and mass transfer in micropolar fluid with chemical reaction in the presence of thermal radiation

An analytical study is presented for the problem of unsteady hydromagnetic heat and mass transfer for a micropolar fluid bounded by semi-infinite vertical permeable plate in the presence of first-order chemical reaction, thermal radiation and heat absorption. A uniform magnetic field acts perpendicularly to the porous surface which absorbs the micropolar fluid with a time-dependent suction velocity. The basic partial differential equations are reduced to a system of nonlinear ordinary differential equations which are solved analytically using perturbation technique. Numerical calculations for the analytical expressions are carried out and the results are shown graphically. The effects of the various dimensionless parameters related to the problem on the velocity, angular velocity, temperature and concentration fields are discussed in detail.