Boltzmann simulation of a storage ring laser

A numerical technique is described, which follows the motion of the entire electron distribution in a storage ring laser. The laser gain and electron distribution parameters such as energy spread, bunch length, damping rates, and containment time are discussed, both with and without the use of the gain expansion technique. The limits of validity of the onedimensional approximation are defined.     

气温和颗粒密度对声场中颗粒动力学影响的数值模拟

综合考虑黏性夹带力、Basset力、虚拟质量力和压力梯度力,建立颗粒在声场中的动力学模型,利用变步长四阶RungeKutta算法和二阶隐式Adams插值算法对颗粒的受力和运动进行数值模拟。将模拟和实验得到的颗粒运动特性进行对比,验证数值模拟的正确性。在此基础上,研究气温和颗粒密度对颗粒动力学的影响规律。结果表明,黏性夹带力对颗粒运动起主导作用;气温升高,压力梯度力与黏性夹带力之间的相位差减小,Basset力、虚拟质量力与黏性夹带力之间的相位差增大。研究还发现,气温较低时,颗粒密度对颗粒运动有重要影响,夹带系数随着密度的增加而迅速下降;气温较高时,颗粒密度对颗粒运动的影响较小,颗粒位移振幅和夹带系数相对低温时明显增加。     

Numerical simulation of space-charge dynamics in a gyrotron trap

The particle-in-cell (PIC) method is used to simulate the self-consistent accumulation and bunching of space charge in the trap of a gyrotron electron-optical system. It is shown that it is possible to generate charge bunches that oscillate along the direction of the magnetic field. The dependence of the characteristics of these oscillations on the magnitude of the electron current into the trap is determined, along with the effect of the accumulated charge on the velocity distribution of electrons in the current passing through the magnetic mirror. Satisfactory agreement with the experimental data is obtained. Zh. Tekh. Fiz. 67, 98–101 (September 1997)     

Numerical simulation of a triple laser beam particle sizing instrument

The Mississippi State University Particle Sizing Instrument (MSU-PSI) is designed to perform real-time measurement of the particle-size distributions by means of non-intrusive methods. The instrument is based upon the principles of forward scatter of a laser beam by a single particle. Three beams are used to illuminate the particle. The green central beam is used to measure particles in the range of 2–15 μm in diameter. Two crossed blue beams are used to validate the trajectory of particles through the green beam. The size of a particle is determined by the amount of light that it scatters. This scattered light is captured and processed electronically and eventually is converted to a histogram, which, when interpreted, will be a representation of the particle-size distribution. In this paper, the model used to simulate the instrument numerically in the Ripple Validated Small Angle Near Forward Scattering (RVSANFS) mode is explained.     

Numerical simulation of non-Abelian particle-field dynamics

Numerical 1D-3V solutions of the Wong-Yang-Mills equations with anisotropic particle momentum distributions are presented. They confirm the existence of plasma instabilities for weak initial fields and of their saturation at a level where the particle motion is affected, similar to Abelian plasmas. The isotropization of the particle momenta by strong random fields is shown explicitly, as well as their nearly exponential distribution up to a typical hard scale, which arises from scattering off field fluctuations. By variation of the lattice spacing we show that the effects described here are independent of the UV field modes near the end of the Brioullin zone.     

Numerical simulation of particle motion in an ultrasound field using the lattice Boltzmann model

In this paper we investigate the motion of small particles suspended in a fluid through which an ultrasound field is propagating. The application of the lattice Boltzmann model to this problem is considered using a two dimensional model. Particles in an ultrasound field are observed to move with a mean particle motion. Further, the time-averaged force on a fixed cylinder is computed and found to be in good agreement with a theoretical expression for the radiation force. Simulations are performed with a single particle, although the approach can equally be applied for a larger number of particles.     

Numerical simulation of solid-phase ignition of metallized condensed matter by a particle heated to a high temperature

Numerical simulation of the ignition of a composite propellant by a single “hot” particle of metal is carried out in the framework of the solid-phase model of ignition. The dependences of the ignition lag time for a metallized condensed matter on the initial temperature of a local energy source are determined. Close agreement of the obtained theoretical results with the known experimental data is found.     

物体色度值的计算机模拟表征

本文以国际标准CIE(国际照明委员会)所规定的XYZ空间体系为基础，结合计算机计算的方法，通过利用光栅光谱仪所测的透射光谱来计算出准确的颜色，并可直接在计算机屏幕上将颜色表达出来，最后结合例子给出实验结果和相应的理论分析，结果表明：实验结果和理论分析的符合是相当好的．     

不同振动模式下颗粒分离行为的数值模拟

利用三维离散元法对垂直方向上的直线、圆和椭圆振动模式颗粒分离过程进行了数值模拟研究,对直线振动时上层大颗粒的波动及圆和椭圆振动时出现的聚集、循环等现象的形成机理进行了分析,并讨论了振动强度对各振动模式下颗粒分离形态的影响规律. 研究表明,综合运用空隙填充、侧面驱动的颗粒运动和能量非均匀分布三种机理,并结合颗粒群的速度矢量分布情况能够较好地解释各振动模式下的颗粒分离行为. 振动强度对圆和椭圆振动模式的分离形态具有显著的影响,并在振动强度约为3时,各种振动模式均具有良好的颗粒分离效果和稳定的颗粒运动状态.     

夹套冰温库内流场的数值模拟

随着计算机技术的飞速发展,计算流体力学(CFD)越来越广泛地应用于各个领域。通过CFD对复杂流动问题进行研究,能够较精确地反映流场的流动情况。利用CFD技术对夹套冰温库内的流场进行了稳态数值模拟,分析了夹套冰温库内流场的分布情况,讨论了该库体结构下不同送风速度对库内流场均匀性的影响。研究表明,具有夹套结构的冰温库,库内流场分布均匀,采用顶部静压箱送风,底部四周回风的送回风方式,能够使库内形成自上而下的均匀活塞流,不同送风速度对冰温库内流场的影响很小。研究结果证明数值模拟能较好地反映现实情况。     

Experiments with longitudinally polarized electrons in a storage ring using a siberian snake

We report on first measurements with polarized electrons stored in a medium-energy ring and with a polarized internal target. Polarized electrons were injected at 442 MeV (653 MeV), and a partial (full) Siberian snake was employed to preserve the polarization. Longitudinal polarization at the interaction point and polarization lifetime of the stored electrons were determined with laser backscattering. Spin observables were measured for electrodisintegration of polarized 3He, with simultaneous detection of scattered electrons, protons, neutrons, deuterons, and 3He nuclei, over a large phase space.     

液氢贮箱零蒸发数值模拟与分析

采用CFD技术,对处于微重力下的零蒸发(ZBO)液氢贮箱内采用喷嘴棒强迫混合的流场进行稳态数值模拟,建立了二维轴对称模型,预测了在不同几何参数下贮箱内温度场及速度场分布情况。研究表明,喷嘴棒伸入贮箱长度、入口直径等因素均会对系统内温度场产生影响。贮箱内平均温度和最大温度随喷嘴棒长度和入口直径的增大而减小,而喷口直径对贮箱内温度场影响不明显。由上述可以看出,通过增大入口直径、选择合适的喷嘴棒伸入长度,可以改善系统性能。     

Dielectrophoretic and AC electroosmotic trapping of DNA: Numerical simulation incorporating fluid dynamics and steric particle effects

In this paper the Dielectrophoretic trapping of nanoparticles in parallel electrode arrays is investigated. The numerical simulations presented take into account the steric effect of the particle collection yielding more realistic results than the non-steric model. Furthermore, the effect of the AC electroosmotic motion of the electrolyte is taken into account. The model is then applied to Dielectrophoretic DNA trapping. The simulations are compared with experimental results and allow for a plausible explanation of observations inconsistent with simple Dielectrophoretic theory. It is demonstrated that the discrepancies can be attributed to a significant extent to the AC electroosmotic fluid motion.     

Numerical simulation of the intramolecular dynamics of photoisomerization

The results of mixed quantum-classical and quantum-mechanical numerical calculations of the intramolecular dynamics of photoisomerization under conditions similar to ordinary natural conditions, i.e., for irradiation of the molecule by a light pulse not shorter than the lifetime of the resonant excited electronic state of the molecule and with an intensity comparable to that of solar light at the Earth’s surface, are presented. It was concluded that the dynamics of such photoisomerization should be modeled using quantum-mechanical methods. The simplest approach to modeling the photoisomerization of a molecule with two isomeric forms can be based on the density matrix formalism for describing the interaction of a light pulse with a three-level system of Λ configuration.     

Director configuration and dynamics of a nematic liquid crystal around a two-dimensional spherical particle: Numerical analysis using adaptive grids

We study numerically the director and orientational order parameter configurations in a nematic liquid crystal around a two-dimensional spherical particle on the basis of the tensor order parameter formalism. To properly account for the large length scale difference between the particle and the accompanying orientational defect, we devise an adaptive grid scheme in which the lattice spacing is automatically and locally adjusted in response to the spatial gradient of the orientational order parameter. This adaptive grid scheme is useful in studying dynamical as well as static orientational structures. We present a simulation result which shows how a hedgehog defect of topological charge -1 becomes unstable in two dimensions, and splits into a defect pair of topological charge -1/2, located symmetrically around the particle. Received 14 September 2000 and Received in final form 27 December 2000     

A Monte Carlo simulation of a stroboscopic laser diagnostics of ordered ion beams in a storage ring

A Monte Carlo code combined with a particle tracking program has been used to study a stroboscopic laser diagnostic system that is able to detect a string-like ordered ion beam. Different ion species have been studied to evaluate the diagnostics capability. This revised version was published online in July 2006 with corrections to the Cover Date.     

Numerical simulation of intramolecular dynamics during dual fluorescence

The dynamics of transformation of a light pulse by a five-level model molecule whose secondary emission spectrum can contain two fluorescence bands is simulated. The system of equations that determine the time behavior of the matrix elements of the statistical operator of the molecule interacting with the light pulse is numerically solved. From this solution, the time dependences of the populations of the molecular states are determined for different values of the parameters of the irradiation pulse, which is described in terms of the classical theory, and of the parameters that characterize the rates of radiative and nonradiative spontaneous transitions of the molecule. Based on particular examples of the choice of these parameters, it is demonstrated that the mechanism by which dual fluorescence occurs in molecules with intramolecular hydrogen bonds can be efficiently established from the numerically simulated intramolecular dynamics.     

Beam dynamics of the superconducting wiggler on the SSRF storage ring

In the SSRF Phase-II beamline project, a superconducting wiggler(SW) will be installed in the electron storage ring. It may greatly impact on the beam dynamics due to the very high magnetic field. The emittance growth becomes a major problem, even after correction of the beam optics. A local achromatic lattice is studied, in order to combat the emittance growth and keep the performance of the SSRF storage ring as high as possible. Other effects of the SW are also simulated and optimized, including the beta beating, the tune shift, the dynamic aperture, and the field error effects.     

Beam dynamics of 20 MeV MIRRORCLE-type tabletop storage ring

An experimental study on beam dynamics in MIRRORCLE-20, a tabletop storage ring of 15 cm orbit radius, was performed. Measurement of the infrared (IR) synchrotron light is the tool of this study. The IR emission is enhanced by a circular optics, named photon storage ring (PhSR), placed around the electron orbit, and is collected by a magic mirror associated with two plane mirrors in the storage ring. The measured average IR power in mid-IR region (λ < 50 μm) is ～59 mW. The observed stored beam current is about 1.2 A at maximum, which represents a record for a storage ring. The observed beam size is about 74 × 3 mm². We conclude that this very long beam size is due to the large betatron oscillation of 2/3 resonance injection.     

Numerical simulation of the ionization dynamics of a two-electron quantum system in a femtosecond pulse

The ionization of a simple two-electron model system, viz., the one-dimensional negative hydrogen ion, is investigated using direct numerical integration of the time-dependent Schrödinger equation. The one-and two-electron ionization probabilities as functions of frequency and radiation intensity are obtained. It is shown that two-electron ionization is mediated by both direct and sequential mechanisms. The stabilization of the two-electron system against the ionization process is investigated. The data obtained are compared with calculations performed within the one-dimensional single-particle model of H^?. The photoelectron spectrum is analyzed in the region of parameters corresponding to the single-electron ionization regime.