Measurement of temperature of a dusty plasma from its configuration

A new concept called “configurational temperature” is introduced in the context of dusty plasma, where the temperature of the dust particles submerged in the plasma can be measured directly from the positional information of the individual dust particles and the interaction potential between the dust grains. This method does not require the velocity information of individual particles, which is a key parameter to measure the dust temperature in the conventional method. The technique is initially tested using two-dimensional (2D) OpenMP parallel molecular dynamics and Monte Carlo simulation and then compared with the temperature evaluated from experimental data. The experiment have been carried out in the Dusty Plasma Experimental (DPEx) device, where a 2D stationary plasma crystal of melamine formaldehyde particles is formed in the cathode sheath of a DC glow discharge argon plasma. The kinetic temperature of the dust is calculated using the standard particle image velocimetry technique at different pressures. An extended simulation result for the three-dimensional case is also presented, which can be employed for the temperature measurement of a three-dimensional dust crystal in laboratory devices.     

Relativistic BBGKY Theory and Collision Integral of Generalized Boltzmann Equation in a Relativistic Magnetized Plasma

Usually, only Coulomb interactions between charged particles which are independent of time are considered in BBGKY theory of a nonrelativistic plasma. In relativistic case, the induced electromagnetic forces between charged particles which are dependent on time obviously should be considered. A Lorentz-covariant generalized n-time Liouville equation for classical plasma is established. A convenient form applicable to the laboratory frame of this equation is also given. The relativistic BBGKY hierarchy is developed in which both Coulomb and electromagnetic forces between particles are included. A method for solving the relativistic pair correlation equation is given in polarization approximation. A new formula for calculating collision integral in terms of discrete particle Green functions is given. A number of generalized Boltzmann equations for relativistic plasmas are derived.     

Simultaneous measurement of particle size, velocity, andtemperature in thermal plasmas

The in-flight measurement of particle parameters (size, velocity, temperature, and local number density) can prove insight into the plasma processing of solid materials. A measurement technique for simultaneously obtaining the size, velocity, and temperature of particles entrained in high-temperature flow fields is described. Particle size and velocity are obtained from a combination laser-particle-sizing system and laser Doppler velocimeter. The particle temperature is determined by a two-color pyrometry technique and the data rate is a measure of relative particle number density. Typical measured temperatures and velocities for the 5-100 μm particles used in plasma spraying are 1600-3500 K and 100-300 m/s, respectively. Since particle size, velocity, and temperature are measured simultaneously, cold particles (<1600 K) are identified and their relative number density can be quantified. Data from two plasma spray systems, a metal one (Ni-Al) and a metal oxide one (Al₂O₃), are presented and their application to understanding the plasma spray-coating process is illustrated     

Siliconization for Wall Conditioning in the HL-2A Tokamak

The sputtering of impurities is caused by the interactions between plasma and the first wall, and the recycling of the gas affects the particle and energy transport of plasmas with a complicated mechanism in plasma operation. It is important for present tokarnaks to achieve a good confinement and high performance plasmas by means of controls of the vacuum condition, usage of low Z materials, control of the recycling of neutral particles and suppressions of the appearances and yield of impurities. For higher plasma parameters, some of the first wall of HL-2A is covered with graphite materials and carbon fiber tiles. Hence the studies on the in-situ coating application and development, and the interactions between the coating film and plasma are needed to effectively control the impurity, improve plasma confinement and achieve high performance plasma.     

Relativistic particle simulation of a coloured parton plasma

We propose a relativistic particle-in-cell (PIC) simulation method for investigating the non-perturbative dynamics and collective interactions in a classical coloured parton plasma. The method has the advantage of including quarks and both short and long scale gluons non-perturbatively, and may be used for the study of a number of conceptual questions relevant to evolution of a quark gluon plasma formed in ultrarelativistic heavy ion collisions. We illustrate the simulation method by a detailed study of the thermalization of a highly nonequilibrium coloured parton plasma due to collective non-abelian interactions.     

直接模拟离散颗粒对湍流射流的影响

发展了一种基于双向耦合的直接数值模拟方法,研究了两相湍流射流中离散颗粒对气相射流的影响。流场采用高分辨率的算法直接耦合求解,颗粒相采用拉格朗日方法跟踪。结果表明不同Stokes数的颗粒对射流的影响不同。所有的颗粒都降低了射流速度半宽,但对流向平均速度剖面的影响比较复杂.Stokes数为0.01和50的颗粒降低了横向平均速度,使得湍流强度剖面变的更宽更低;而Stokes数为1的颗粒则增加了横向平均速度,降低了湍流强度。     

The Influence of Particles Interaction in Low-Temperature Plasma on its Composition and Optical Properties

A model theory of the influence of particles interaction in plasma on its composition and optical properties is developed. The interaction of charged particles in plasma reduces the ionization energy of atoms and ions. The action of internal microfields in plasma on atoms and ions reduces the statistical weight of electron levels which affects the populations of excited states. The latter effect leads to an effective cutoff of partition functions and determines the behaviour of optical properties of plasma (of absorption coefficient and emissivity) at increased number densities of charged particles. The formulas are obtained for calculation of the continuous and discrete spectrum in plasma taking into account the particles interaction. A non-monotonic dependence of optical plasma density upon number density of charged particles is quantitatively explained. A satisfactory agreement is obtained with a large number of experimental data some of which were considered to be contradictory. The method developed can be used for calculations in the field of atomic spectroscopy and low-temperature plasma physics including increased densities of charged particles. The use of the formulas obtained in plasma diagnostics will enable one to avoid considerable errors.     

Improving the Sensitivity of Forward Light Scattering Technique to Large Particles

The detection of a small number of large particles whose size lies outside the required size distribution is important in the processing of many materials when those particles result in the deterioration of the product quality. Laser diffraction, which is a very popular technique for on-line monitoring and process control, has, however, limited sensitivity to those few large particles. This paper deals with the improvement of this sensitivity. The fluctuations of the signal received by the detectors were analyzed by both experiment and simulation. Two statistical approaches, cross-correlation and principal component analysis (PCA), were applied. A detection procedure is proposed which is based on the combination of sweep selection through PCA and an appropriate deconvolution of the selected sweeps. The preliminary experiments with Al₂O₃ powder showed an improved sensitivity to the large particles.     

Measurement of chemical potentials of systems with strong excluded volume interactions by computing the density of states

At high densities and low temperatures, the conventional Widom test particle method to compute the chemical potential of a system of particles with excluded volume interactions fails owing to bad statistics. A way to circumvent this problem is the use of expanded ensemble simulation techniques or thermodynamic integration. In this article, we will describe an alternative method to compute the chemical potential which is conceptually much easier, by computing the density of states of systems of N and N + 1 particles directly; and by performing a test particle simulation at very high temperature. The advantage of our technique is that the densities of states of the N and N + 1 particle system are computed in an ensemble in which particles can pass each other, resulting in a more efficient sampling. We will demonstrate our method not only for single particles but also for chain molecules with intramolecular interactions. By using an infinite temperature expansion and an extension of the density of states to very high energies, we will show that it is also possible to compute the chemical potential without having to compute the density of states for the N + 1 particle system.     

单链表在离子发动机光学系统粒子模拟中的应用

 目前离子发动机光学系统数值模拟大多采用PIC方法,由于该方法需要跟踪单个粒子的运动,因此需要存储每个粒子的位置信息与运动信息。传统的粒子模拟程序中,保存粒子信息大多采用数组的方式,但是采用这种方式存在弊端,例如对粒子总数变化的自适应不好。基于此开发了一种使用链式存储结构的粒子模拟程序,该程序使用带头节点的单向链表存储粒子信息。使用基于链式存储结构的PIC方法对离子发动机光学系统进行了粒子模拟,验证了链式粒子信息存储方法在粒子模拟中的可用性。模拟表明：（1）在粒子模拟中采用链式存储结构存储粒子信息,无需预先指定最大粒子总数,程序可自适应粒子总数的变化,因此无需进行试算,节省了计算时间;（2）在粒子模拟中采用链式存储结构,由于不存在内存资源的浪费,因而可显著提高程序的存储效率与计算效率。     

基于Geant4的反应堆临界及动态计算方法

Geant4是一款基于C++面向对象技术的蒙特卡罗开发程序包,可以模拟各种已知粒子与物质之间的相互作用。然而该程序包没有提供临界源功能,无法直接用于反应堆物理计算。因此,利用Geant4提供的基础物理模型和粒子跟踪控制等功能,用两种不同方法实现了临界源的设置,实现了基于Geant4的反应堆静态计算程序G4-RSM和反应堆动态计算程序G4-RDM。两个程序均可用于反应堆临界计算,与MCNP计算结果相对误差在5%以内。G4-RDM程序除可用于临界计算外,还可用于模拟堆内事故工况下的中子学瞬态变化。     

高速碰撞数值计算中的光滑粒子法

扼要讨论了改进的光滑粒子法的离散思想,给出了二维轴对称问题中连续介质力学守恒方程的离散过程及离散格式,提出了轴对称坐标下确定影响域内粒子数的方法.最后通过高速碰撞的系列算例说明,光滑粒子法不但适宜于计算大变形冲击力学问题,而且有着其它网格法所无法替代的优势.     

等离子体装置中粉尘问题研究进展

等离子体装置中,带电粒子与壁材料相互作用会导致粉尘的产生。综述了主要等离子体装置中粉尘问题的实验研究现状,对主要装置中使用的诊断方法和所得到的实验结果进行了评述。提出了等离子体装置粉尘研究中存在的问题以及未来研究的方向。