A hybrid fluid–kinetic neutral model based on a micro–macro decomposition in the SOLPS-ITER plasma edge code suite

We present a hybrid fluid–kinetic model for the hydrogenic atoms in the plasma edge that is implemented in SOLPS-ITER. A micro–macro decomposition of the kinetic equation leads to a fluid model with a continuity and parallel momentum equation (implemented in B2.5) coupled to a kinetic correction equation (implemented in EIRENE). We assess the hybrid model for a high recycling fixed background plasma. The hybrid approach leads to a reduction of the Central Processing Unit(CPU) time required to obtain the same statistical error as the full kinetic Monte Carlo (MC) simulation with approximate factors of 1.7, 4.9, and 1.9 for the particle, parallel momentum, and electron energy source, respectively. However, there is an increase in CPU time for the ion energy source. By comparing the results with our in-house plasma edge code, we conclude that the hybrid performance can be improved by adapting some default MC features in EIRENE.     

纳米晶粒生长的动力学蒙特卡罗模型

给出应用于纳米晶粒生长的动力学蒙特卡罗模型,并对模拟方法做了细致的讨论.作为一个应用实例,对薄膜生长做了分类模拟研究.结果显示,改变三维Ehrlich-Schwoebel势垒将导致薄膜生长过程中多层原子岛的结构相变.     

The Interface Kinetics of Crystal Growth Processes

A brief review of the present state of our understanding of the kinetic processes which take place on the atomic scale at the interface during crystal growth is presented in this paper. Computer simulations have played a central role in the development of this understanding. Three aspects will be discussed:(1) There are two classes of materials based on their different modes of crystallization. Molecular dynamics modeling has demonstrated that the growth rate for many simple materials is not thermally activated, but instead depends on the thermal velocity of the atoms.(2) The cooperative processes which give rise to the surface roughening transition. Kinetic Monte Carlo studies played a central role in the development of our understanding of how interface roughness dominates growth morphologies.(3) Solute trapping in alloys. Kinetic Monte Carlo simulations of alloys have led to an understanding of these kinetic effects during alloy crystallization.     

Pre-asymptotic corrections to fractional diffusion equations

The motion of contaminant particles through complex environments such as fractured rocks or porous sediments is often characterized by anomalous diffusion: the spread of the transported quantity is found to grow sublinearly in time due to the presence of obstacles which hinder particle migration. The asymptotic behavior of these systems is usually well described by fractional diffusion, which provides an elegant and unified framework for modeling anomalous transport. We show that pre-asymptotic corrections to fractional diffusion might become relevant, depending on the microscopic dynamics of the particles. To incorporate these effects, we derive a modified transport equation and validate its effectiveness by a Monte Carlo simulation.     

一类大气等离子体反应扩散模型的解法

研究了一类大气等离子体反应扩散模型. 利用奇摄动方法得到了问题的渐近解, 并用微分不等式理论证明了解的一致有效性.     

非均匀基底上三维薄膜生长的模拟研究

考虑原子在基底表面的扩散、沿岛周界的扩散和不同层间的扩散以及非均匀基底上表面吸附能分布的各向异性,建立起非均匀基底表面上原子扩散和三维薄膜生长的动力学蒙特卡罗模型.模拟得到在不同生长条件下出现的层状生长、岛状生长和混合生长三种生长模式和相应的多层薄膜生长形貌图.通过统计三维薄膜中原子在各层的分布,计算薄膜的表面粗糙度,得到薄膜生长模式与生长条件之间的关系.关键词：薄膜生长非均匀基底动力学蒙特卡罗模拟     

热辐射输运问题的高效蒙特卡罗模拟方法

惯性约束聚变研究中,热辐射光子在介质中的输运以及热辐射光子与介质的相互作用是重要研究课题,蒙特卡罗方法是该类问题的重要研究手段之一.隐式蒙特卡罗方法虽然能正确地模拟热辐射在介质中的输运过程,但当模拟重介质(材料的吸收系数大)问题时,该方法花费的计算时间将变得很长,导致模拟效率很低.本文以离散扩散蒙特卡罗方法为基础,开发...     

Tracer diffusion in concentrated lattice gas models. Rectangular lattices with anisotropic jump rates

An approximate theory is developed for tracer diffusion in rectangular lattice gas models with anisotropic jump rates to neighboring unoccupied sites in different directions. Comparison with Monte Carlo simulations on quadratic lattices with several ratios for the jump rates in orthogonal directions shows a satisfactory agreement in all cases investigated.     

The Lattice Model for Addressing Phenomenological Diffusion Problems Associated with Grain Boundaries

Mapping a phenomenological diffusion problem onto a lattice permits lattice-based random walk theory to address the problem. The solution is generally carried out using Monte Carlo methods. This paper reviews the substantial progress that has been made with this method for tracer diffusion associated with grain boundaries.     

Tracer diffusion of dimers on correlated heterogeneous surfaces

The diffusion of a single dimer adsorbed on highly correlated heterogeneous substrates is studied through Monte Carlo simulations. The topography has been characterized by patches of weak and strong adsorbing sites, arranged in a chessboard-like ordered structure. The time behavior of the mean-square displacement of the dimer is analyzed for different temperatures and patch size. Based on this analysis, a possible method for the characterization of the correlated heterogeneous topography from dimer diffusion measurements is discussed.     

沉积粒子能量对薄膜早期生长过程的影响

利用Monte Carlo(MC)模型研究了能量粒子对薄膜生长的初始阶段岛膜的形貌和岛的尺寸的影响,沉积粒子的能量范围为:0—0.7eV.在模型中考虑了原子沉积、吸附原子扩散和蒸发等过程,并详细考虑了临近和次临近原子的影响.结果表明,在所采用的参量范围内不同的基底温度情况下,能量粒子的影响有很大的区别.低基底温度情况下,沉积粒子强烈地影响着薄膜的生长过程中,岛膜的形貌、数量和尺寸随能量粒子的能量增加而有很大的变化.分析表明,这些变化都是由于能量粒子的介入使得表面吸附粒子的扩散能力增强所致关键词：薄膜生长Monte Carlo方法扩散     

漫射近似在测量生物组织光学性质中的适用范围

漫射近似理论经常被用来作为测量生物组织光学特性参数实验和方法的理论基础,但是漫射近似理论只是一种对辐射传输理论的近似结果,在一定条件下有其特定的适用范围.为了确定漫射近似理论在活体非侵入式无损测量要求下的适用范围,本文采用Monte Carlo模拟校验的方法,对漫射近似理论和Monte Carlo模拟计算的结果进行了比较,给出了基于单散射反照率a和各向异性因子g的漫射近似理论适用范围数值标准.这一标准为漫射理论的应用提供了参考依据.     

Further Monte Carlo calculations for the classical one-component plasma in the range 100 ⩽ Γ ⩽ 160: The FCC lattice

Very accurate Monte Carlo calculations for the one-component plasma (OCP) have been compared with the results of Slattery, Doolen, and DeWitt.^(1,2) We confirm their results and also find a slight dependence of the calculation of the internal energy per particle uponN, the number of particles. A detailed investigation forN=108 permits us to evaluate the Helmholtz free energy for an OCP fcc lattice. As is usually believed, we find that the bcc lattice is more stable than the fcc lattice. The transition from the liquid to the fcc lattice phase occurs when ^fcc = 196 ± 1. A three-dimensional modified cubic procedure, capable of achieving high accuracy in using tables of two-particle interaction potentials, is described in Appendix B.     

蒙特卡罗模拟在辉光放电鞘层离子输运研究中的应用

利用蒙特卡罗方法模拟氩气直流辉光放电鞘层内离子的运动过程.模拟基于离子与中性原子的电荷转移和弹性散射两种主要的散射过程,考虑了碰撞截面与能量相关和不相关两种情况,在弹性散射中采用了势场相互作用模型和刚性球碰撞两种模型.通过模拟得到不同气压和不同放电电压下离子入射阴极的能量分布和角度分布,并对几种模型的模拟结果进行了比较和讨论.关键词：辉光放电等离子体鞘层蒙特卡罗模拟