Properties of Some Chaotic Billiards with Time-Dependent Boundaries

A dispersing billiard (Lorentz gas) and focusing billiards (in the form of a stadium) with time-dependent boundaries are considered. The problem of a particle acceleration in such billiards is studied. For the Lorentz gas two cases of the time-dependence are investigated: stochastic perturbations of the boundary and its periodic oscillations. Two types of focusing billiards with periodically forced boundaries are explored: stadium with strong chaotic properties and a near-rectangle stadium. It is shown that in all cases billiard particles can reach unbounded velocities. Average velocities of the particle ensemble as functions of time and the number of collisions are obtained.     

Focusing of Macroparticle Projectiles

The electrostatic acceleration of small particles to hyper-velocities is a way to get high temperatures by hypervelocity impact. In order to get fusion these particles should be bunched together in order to check the Lawson criterion. The longitudinal focusing of a beam of macroparticles is discussed in analogy with klystron theory. An ideal potential law and a sinusoidal potential law are considered. Because of the low charge/mass ratio of macroparticles, the frequencies involved are extremely low.     

Simulation of the acceleration mechanism by light-propulsion for the powder particles at laser direct material deposition

The results of the numerical analysis of heat- and mass-transfer processes at powder particles' motion in a gas flow and laser beam by light-propulsion force during the laser cladding and direct material deposition are presented. Under consideration were the stainless steel particles, the radiation power range of the CO₂ laser were 1000, 3000 and 5000 W. Finally, the particles of 45 μm in diameter reach the maximum velocity of about 80, 220, 280 m/s. It is shown that as particles are heated by the laser up to the temperature approaching the boiling point, the particles' velocity in the light field by the vapor recoil pressure may increase significantly. The radius of the particles slightly varies due to the evaporation; the losses in the clad material mass are negligibly small. Comparisons of numerical results with known experimental data on light-propulsion acceleration of single particles (aluminum, aluminum oxide and graphite) under the influence of pulse laser radiation are also presented. Particle acceleration resulting from the laser evaporation depends on the particle diameter, powder material properties, focusing degree and attenuation laser beam intensity by the direction of its propagation.     

Mass-reflectron as an ion energy analyzer

The possibility of using the mass-reflectron as an analyzer for the kinetic energy of charged particles is demonstrated. The reflectron operating regime can be changed by varying the voltage across the reflecting system. The geometry of the system, in some cases, can remain the same. The time-of-flight focusing property of the analyzer is demonstrated for the case where ions of various initial energies simultaneously escape the same equipotential surface of the simple acceleration system.     

Direct acceleration of electrons by radially polarized laser pulse

Direct electron acceleration by highly focused ultrahigh-power laser pulses of radial polarization in the ultrarelativistic mode was studied. The mode at which the focusing spot size appears of the same order as the laser radiation wavelength was considered. Electromagnetic fields were calculated using exact Stratton-Chu diffraction integrals. Calculations showed that, as for the case of linear polarization, too sharp focusing (in the diffraction limit) is not optimum for electron acceleration, despite the strong axial field namely in the case of a submicrometer laser spot. At the same time, the case of moderate focusing is more attractive for electron acceleration.     

Space-time focusing of charged particles in radio-frequency linear electric fields

The properties of space-time focusing of nonmonoenergetic ions in linear high-frequency electric fields are studied. The degree of time focusing of ions in high-frequency fields of hyperboloidal analyzers belonging to the monopole and dipole types is estimated. The possibility of the time-of-flight mass separation of nonmonoenergetic ions in radio-frequency mass reflectors is substantiated.     

On the physical meaning of the Unruh effect

Simple arguments are presented that detectors moving with constant acceleration (even acceleration for a finite time) should detect particles. The effect is seen to be universal. Moreover, detectors undergoing linear acceleration and uniform circular motion both detect particles for the same physical reason. It is shown that the Unruh effect for a circularly orbiting electron in a constant external magnetic field used as a Unruh-DeWitt detector physically coincides with the experimentally verified Sokolov-Ternov effect.     

On the physical meaning of the Unruh effect

Simple arguments are presented that detectors moving with constant acceleration (even acceleration for a finite time) should detect particles. The effect is seen to be universal. Moreover, detectors undergoing linear acceleration and uniform circular motion both detect particles for the same physical reason. It is shown that the Unruh effect for a circularly orbiting electron in a constant external magnetic field used as a Unruh-DeWitt detector physically coincides with the experimentally verified Sokolov-Ternov effect. The text was submitted by the authors in English.     

Laser acceleration of light impurity from an ultrathin foil of complex ionic composition

The model of acceleration of light impurity particles from a planar ultrathin foil of complex ionic composition under an ultrashort high-power high-contrast laser pulse is proposed. Both the mode of pure Coulomb acceleration of ions, characteristic of extremely high electron energies, and acceleration under conditions of spatial charge separation controlled by a finite characteristic electron temperature are studied. Accurate and approximate analytical approaches for describing impurity particle acceleration are formulated. Spatial and spectral characteristics of accelerated particles are determined. Particle dynamics is studied in both the approximation of test impurity particles and taking into account their intrinsic electrostatic field, depending on the relative charge density of light particles.     

振动颗粒混合物中的三明治式分离

在竖直振动两种颗粒的混合物的实验中，观察到了一种新的分离现象——“三明治”式分离，即大而重的颗粒被夹在两层小的轻颗粒之间.这不同于“巴西果”效应导致的大而重的颗粒在上的两层有序结构.实验表明当振动加速度大于某个临界值时这种三层有序将取代两层结构，而且是稳定的.实验中观察到导致“三明治”式分离的两种不同的分离过程.对这两种过程的物理机理及其与振动加速度、振动频率及颗粒尺寸等因素的关系做了研究，并给出了相图. 关键词： 颗粒物质 振动 有序结构 三明治式分离 巴西果效应     

紧凑针孔中性粒子分析器标定系统的设计和研制

介绍了紧凑针孔中性粒子分析器(CP-NPA)标定系统,包括一套高能量、小流强的中性粒子束线源和一个配套旋转平台.束线源由高频离子源、电单透镜、速度选择器、加速管、电四极透镜和中性化室组成.高频离子源已经完成研制,并顺利建立起等离子体.单透镜已经完成仿真、制造和测试.实验中引出电压为1.0kV时,调整单透镜聚焦电压最高可...     

Acceleration and focusing of intense ion beams in rf undulator structures

Bunching, acceleration, and transverse focusing of intense ion beams in an undulator linac are considered. Such an accelerator features the absence of an rf field harmonic synchronous with the beam. A 3D equation of motion in the Hamiltonian form is derived in the smooth approximation, and the general conditions for ion beam acceleration and transverse focusing in the undulator linac are formulated. Basic analytical results are compared with the results of numerical simulation of the beam dynamics in the polyharmonic field of an accelerating cavity.     

Vacuum electron acceleration by coherent dipole radiation

The validity of the concept of laser-driven vacuum acceleration has been questioned, based on an extrapolation of the well-known Lawson-Woodward theorem, which stipulates that plane electromagnetic waves cannot accelerate charged particles in vacuum. To formally demonstrate that electrons can indeed be accelerated in vacuum by focusing or diffracting electromagnetic waves, the interaction between a point charge and coherent dipole radiation is studied in detail. The corresponding four-potential exactly satisfies both Maxwell's equations and the Lorentz gauge condition everywhere, and is analytically tractable. It is found that in the far-field region, where the field distribution closely approximates that of a plane wave, we recover the Lawson-Woodward result, while net acceleration is obtained in the near-field region. The scaling of the energy gain with wave-front curvature and wave amplitude is studied systematically.     

Gyroresonant surfing acceleration

We discuss a new acceleration or energization mechanism of charged particles in space and astrophysical plasmas. In the presence of an electrostatic potential gradient and a circularly polarized electromagnetic monochromatic wave, particles are accelerated efficiently by keeping cyclotron resonance with the wave due to the electrostatic dragging force. In addition, particles can propagate against the electrostatic potential even if they have smaller parallel energy. This mechanism is potentially widely applicable, in terms of particle acceleration and transport, to various space and astrophysical phenomena, such as shock environment and short-large amplitude magnetic structures. We introduce the basic physical process of the acceleration or energization mechanism theoretically and numerically.     

圆截面直流道中微粒黏弹性聚焦机理研究

微粒黏弹性聚焦技术近年来受到了广泛的研究重视, 但影响粒子聚焦特性的关键参数调控机理仍不清楚. 基于此目的, 本文量化研究了圆截面直流道中非牛顿流体诱导微粒黏弹性聚焦的行为, 给出了流速和流道长度对粒子聚焦特性的调控机理. 具体而言: 首先, 对比分析不同黏度牛顿流体(水和22 wt%甘油水溶液)和非牛顿流体(8 wt%聚乙烯吡咯烷酮水溶液)中粒子横向迁移行为, 发现非牛顿流体中粒子将在弹性力主导下聚焦至流道中心区域, 而牛顿流体中粒子则在惯性升力主导下迁移形成Segré-Silberberg圆环. 其次, 量化分析粒子尺寸和驱动流速对黏弹性聚焦效果的影响, 发现随着流速的增加, 粒子聚焦效果逐渐变好并最终趋于稳定, 且大粒子较小粒子具有更好的聚焦效果. 最后, 研究粒子沿流道长度的动态聚焦过程, 推导并验证了粒子聚焦所需安全流道长度的数学模型, 发现大粒子聚焦所需安全流道长度显著短于小粒子. 上述研究结果对于提升粒子黏弹性聚焦机理和过程的理解, 实现微粒聚焦特性的灵活控制具有非常重要的意义.     

强流离子注入机加速管的聚焦特性研究

 讨论了三间隙强流离子加速管的聚焦特性，计算了各种能量下离子束聚焦情况，并分析了抑制空间电荷效应所需要的电场强度。最后总结了三间隙加速管设计和调试应注意的问题。     

等单元长度多间隙加速结构的束流动力学特性

等单元长度多间隙加速结构是一种非同步加速结构,当粒子在加速结构中的速度变化很明显时,粒子在每个间隙的相位是不相同的,薄透镜近似下的束流纵向运动方程没有考虑粒子在加速结构中的速度变化,这在单腔的能量增益相对于粒子能量很小的情况下是合理的,但是当粒子在加速结构中的速度有明显变化时,这种处理方式是不够的.本文从带电粒子在电磁...     

非对称弯曲微流道中粒子惯性聚焦动态过程及流速调控机理研究

设计制作了一种具有非对称弯曲微流道结构的微流控芯片, 搭建实验平台定量表征聚苯乙烯粒子和血细胞沿流道的动态惯性聚焦过程, 并系统研究了流体流速和粒子尺寸对粒子聚焦特性的调控机理. 通过分析粒子荧光图谱和对应量化强度曲线, 将粒子沿流道长度的横向迁移过程分为形成聚焦和平衡位置调整两个阶段, 指出在整个聚焦过程中具有小曲率半径的流道结构起主导作用. 根据全流速段内粒子聚焦特性的演变, 重点分析潜在惯性升力和Dean 曳力的竞争机制, 提出了阐述粒子聚焦流速调控过程的三阶段模型. 进一步比较两种尺寸粒子聚焦位置和聚焦率随流速与流道长度的变化规律, 发现大粒子具有更好的聚焦效果和稳定性, 且两种粒子的相对位置可通过流速进行调整. 最后, 通过分析血细胞在非对称弯流道中的横向迁移特性, 验证了粒子惯性聚焦机理在复杂生物粒子操控方面的适用性. 上述结论为深入研究微流体环境下粒子的运动特性以及开发微流式细胞术等临床即时诊断器件提供了重要参考.     

Wave dispersion relation of two-dimensional plasma crystals in a magnetic field

The wave dispersion relation in a two-dimensional strongly coupled plasma crystal is studied by theoretical analysis and molecular dynamics simulation taking into account a constant magnetic field parallel to the crystal normal. The expression for the wave dispersion relation clearly shows that high-frequency and low-frequency branches exist as a result of the coupling of longitudinal and transverse modes due to the Lorenz force acting on the dust particles. The high-frequency and the low-frequency branches are found to belong to right-hand and left-hand polarized waves, respectively.     

Collective oscillations of the magnetic moments of a chain of spherical magnetic nanoparticles with uniaxial magnetic anisotropy

Magnetic particles moving freely in a fluid can organize dense phases (3D clusters or linear chains). We analyze the spectrum of magnetic oscillations of a chain of spherical magnetic particles taking into account the magnetic anisotropy of an individual particle for an arbitrary relation between the anisotropy energy and the energy of the dipole interaction of particles. For any relation between these energies, the spectrum contains three branches of collective oscillations: a high-frequency branch and a weakly split doublet of low-frequency branches. The frequency of the high-frequency branch is determined by a stronger interaction, while the frequencies of the low-frequency branches are determined by the weakest interaction. Accordingly, the dispersion is maximal for oscillations formed by the dipole-dipole interaction of particles, which have high frequencies in the case of a strong dipole interaction or low frequencies in the case of a strong anisotropy.