氢原子束在大气长程传输中自剥离效应研究

氢原子束在大气传输时,束流粒子与大气粒子碰撞电离形成的大气剥离效应,以及和大气剥离产生次级粒子碰撞电离形成的自剥离效应,是造成氢原子束能量损失的重要机制。考虑到自剥离效应成因复杂,虽然目前已有一些理论方面的研究结果,但对其发生机理和对束流损失效果尚未有实验或数值模拟方面的工作,因此,通过对自剥离效应的发生机理和对束流损失的影响进行分析,进一步完善了自剥离效应理论,在通过束流传输方程验证了粒子云网格-蒙特卡罗法对氢原子束大气传输仿真模拟适用的基础上,将仿真结果与自剥离理论进行了对比,验证了自剥离效应理论的适用性。模拟结果表明,自剥离效应是由束流被大气电离产生的带电次级粒子团在地磁场的影响不停地穿越束流导致的,且自剥离效应的强弱与原子束的密度有关,束流密度越大,自剥离效应越强,对束流的影响越大。     

非理想氢原子束真空环境长程传输模拟研究

模拟研究了非理想氢原子束在真空环境下的长程传输效应。根据中性化程度的不同,将非理想束分为欠中性束和过中性束。通过建立束流传输的准电磁模型,研究了束流密度、中性化因子、空间磁场和弹性散射等因素对非理想氢原子束的影响。结果表明:对于欠中性束,负氢离子的存在对氢原子的传输几乎没有影响,因此欠中性束的发射装置可以考虑去除偏置磁场,以减小设备体积和质量;对于过中性束,束流损失率与束流密度和中性化因子有关,即束流密度越大,束流损失越大;中性化因子越高,束流损失就越高;而无论是欠中性束还是过中性束,空间磁场和粒子间的弹性散射对其传输都没有影响。     

EAST-NBI磁偏转系统束传输特性模拟研究

根据EAST-NBI偏转系统工作原理,分析了束流在偏转系统传输的基本过程和特点。利用直接蒙特卡罗方法,发展了中性束注入器束偏转区域束流传输模拟程序。结果显示:EAST-NBI磁偏转系统可很好地剥离束流中的剩余离子;束偏转区域束流再电离损失约为2.43%;束流180°偏转所带来线聚焦过程使偏转磁体磁极护板局部面临较高的热流密度。     

低能强流带电粒子束的非线性空间电荷效应理论

本文用解析方法研究低能强流带电粒子束的非线性空间电荷效应。文中确定了粒子温度为零的束的发射度图形形状的变化和束的初始束流密度分布之间的关系,由此导出了计算粒子温度不很高的束在非线性空间电荷场作用下发射度图形变化和有效发射度增长的近似方法。     

相对论电子束在离子通道中的聚焦与输运

 基于单粒子理论,描述了相对论电子束在离子通道中的聚焦输运过程,讨论了离子-电子密度比、相对论因子、束加速电压和入射电流等系统参数对电子束的聚焦半径、纵向聚焦位置的影响。研究表明,离子通道对电子束具有强烈的聚焦效应,束流在离子通道内的传输是类周期波动传输,随传输距离增加,聚焦点处的半径逐渐增加,束流的波动幅度逐渐减小。选择适当的系统参数,可调节束聚焦点位置和聚焦点半径的大小,实现电子束的长距传输并且减少电子束的耗散。     

HIAF-BRing束团合并过程中的束流负载效应模拟

强流重离子加速器HIAF-BRing在加速完成后进行束团合并，为研究BRing中的束流负载效应对束团合并的影响，对238U35+束流进行了粒子跟踪模拟。模拟结果显示，在束团合并过程中，束流负载效应引起束团长度和束团中心位置的振荡，导致束流动量分散和束团长度的增长。束团合并过程中尾场电压以及不同束团间尾场的耦合导致的势阱畸变，是引起束团长度和束团中心振荡及束流发射度增长的原因。为了降低束流负载效应的影响，采用多谐波前馈系统进行补偿，达到了补偿束团合并过程中的束流负载效应的目的，从而确保了BRing中引出束流的品质，同时根据模拟结果确定了前馈系统需要覆盖的频率范围和需要补偿的最大尾场电压。     

Corkscrew运动影响束流发射度的数值分析

在直线加速器中，始终存在束流质心轴、束流传输管道几何轴、束流聚焦传输磁场磁轴等三轴不一致问题。当束轴与磁轴存在夹角，而且束流脉冲（平顶）期间存在能量差别时，将引起束心的Corkscrew运动。斜入射的束流在轴向磁场中传输时，由于束流脉冲（平顶）期间不可避免的能量差别，导致不同时刻的束片质心螺旋运动的相位不同，在束流到达同一个位置时，不同时刻束片的质心在同一个考察点具有不同的横向位置。束心Corkscrew运动会造成很多不良后果。针对束心Corkscrew运动造成束流积分发射度的增长情况开展数值模拟研究，为采取相应的抑制措施提供参考和依据。     

粒子束团状态对测量束流发射度及能量的影响

为了验证国产质子注入器的参数是否满足需求,注入器团队设计了束流测量系统用于测量国产质子直线注入器束流的流强、发射度、能量以及能散等关键指标。此测量系统包含了采用变聚焦法测量发散度、采用分析磁铁测量束流能量和能散的主要功能。利用束流输运线设计软件Tracewin(版本2.11.4.1)进行了系统束线的物理设计,对束测系统测量质子束流的发散度和能量的精度进行了模拟计算。由于经过RFQ-(APF)DTL加速后的粒子束团为“拖尾”的非理想粒子束团,需要针对非理想束团对束测系统测量发射度和能量产生的影响进行分析。通过对模拟计算结果的分析,发现相对于测量理想粒子束团的结果非理想粒子束团对束测系统测量发射度精度影响较大;非理想粒子束团对束测系统测量能量精度影响较小。     

光谱法测HT-7托卡马克诊断中性束的束成分

 实验测量了诊断中性束(DNB)中H0的4种主要能量成分(全能量，半能量，1/3能量，1/18能量)，运用光谱法来分析中性束的束成分所占百分数。根据多普勒效应，中性束中的氢粒子发出的Ha波长偏离本底的Ha波长，波长偏移量与氢粒子的能量相关，从而在光谱仪上得到多峰Ha谱线。通过编写程序并以此对实验的原始谱线进行了初步和精确拟合，最终准确有效地分析出中性束的束成分和束能量。实验测得DNB束流的中性氢粒子的全能量、半能量、1/3能量和1/18能量4种成分分别占15%,42%,35%,8%。     

HL—1M装置超声分子束流注入过程中的团簇现象

在环流器等离子体中用超声分子束流注入加料,引起密度峰化和约束改善,其主要机制归结为加料粒子的注入深化和密度上升率（注入效率）的提高。本文主要介绍经过改进的超声分子束流注入HL－1M装置等离子体利用边缘Hα线辐射、径向可伸缩的静电探针和顺着束流注入方向的CCD摄像等诊断技术,考察了粒子注入口及注入口附近区域电子温度和密度沿径向分布的变化,研究了分子束粒子注入等离子体的所谓“冷通道模型”及其效应。     

Modeling of beam ions loss and slowing down with Coulomb collisions in EAST

This paper uses the implicit Monte-Carlo full-orbit-following parallel program ISSDE to calculate the prompt loss and slowing down process of neutral beam injection (NBI)-generated fast ions due to Coulomb collisions in the equilibrium configuration of Experimental Advanced Superconducting Tokamak (EAST). This program is based on the weak equivalence of the Fokker-Planck equation under Rosenbluth MacDonald Judd (RMJ) potential and Stratonovich stochastic differential equation (SDE). The prompt loss with the LCFS boundary and the first wall (FW) boundary of the two co-current neutral injection beams are studied. Simulation results indicate that the loss behavior of fast ions using the FW boundary is very different from that of the LCFS boundary, especially for fast ions with a large gyration radius. According to our calculations, about 5.11% of fast ions generated by perpendicular injection drift out of the LCFS and then return inside the LCFS to be captured by the magnetic field. The prompt loss ratio of fast ions and the ratio of orbital types depend on the initial distribution of fast ions in the P_ζ-$\varLambda$ space. Under the effect of Coulomb collisions, the pitch-angle scattering and stochastic diffusion happens, which will cause more fast ion loss. For short time scales, among the particles lost due to collisions, the fraction of banana ions reaches 92.31% in the perpendicular beam and 58.65% in the tangential beam when the fraction of banana ions in the tangential beam is 3.4% of the total ions, which means that the effect of Coulomb collisions on banana fast ions is more significant. For long time scales, the additional fast ion loss caused by Coulomb collisions of tangential and perpendicular beams accounted for 16.21% and 25.05% of the total particles, respectively. We have also investigated the slowing down process of NBI fast ions.     

Modeling process of the neutral beam re-ionization loss

The basic process of re-ionization loss was studied. In the drift duct there are three processes leading to re-ionization loss: the collision of neutral beam particles with the molecules of background gas, similar collisions with released molecules from the inner wall of the drift duct and the ferret-collisions among particles with different energy of the neutral beam. Mathematical models have been developed and taking EAST-NBI parameters as an example, the re-ionization loss was obtained within these models. The result indicated that in the early stage of the neutral beam injector operation the released gas was quite abundant. The amount of re-ionization loss owing to the released gas can be as high as 60%. In the case of a long-time operation of the neutral beam injector, the total re-ionization loss decreases from 13.7% to 5.7%. Then the re-ionization loss originating mainly from the collisions between particles of the neutral beam and the background molecules is dominant, covering about 92% of the total re-ionization loss. The drift duct pressure was the decisive factor for neutral beam re-ionization loss.     

Locally Resolving Measurements of PSD,Particle Concentration and Particle Velocity by Means of TFS with Dual Beams

Transmission fluctuation spectrometry with spatial correlation (TFS‐SC) is based on transmitting two beams of radiation through a flowing suspension, whereby the distance of the beam centers is varied. Thus, the spatial correlation of the transmission fluctuations of the two beams is determined as a function of the beam distance. By numerical modeling, the transition functions of the correlation are found as a function of beam distance, beam diameters, particle diameter and beam intersection angle. Experimentally determined spatial correlation spectra can be inverted to obtain the particle concentration and particle size distribution by using the theoretical transition functions for mono‐sized particles. In addition, time correlations can be used to extract information on particle velocity. Some experimental results obtained by TFS‐SC are presented and discussed. This method appears promising for application in the local resolving of measurements of PSD, particle concentration and particle velocity in two‐phase flows, both in the laboratory and in process control.     

采用衍射掩模产生白光横向平顶光束

白光横向平顶光束在定向背光式自由立体显示器中有重要应用.本文提出一种采用带蝶形小孔阵列的衍射掩模片获得白光横向平顶光束的方法.根据广义惠更斯-菲涅耳衍射积分和多波长叠加原理,推导出光强分布计算式.设计一套实验装置,数值模拟并实验验证出射光束在不同距离的横向光强分布以及小孔蝶形凹度(蝶形中心高度与边长的比值)对横向光强分布的影响.结果表明:当选择小孔蝶形凹度为0.50—0.66时,可以得到平顶因子F 0.89的白光横向平顶光束,横向平顶光束的宽度随着传输距离的增大而增大,而平顶因子基本不变.实验还发现柱面透镜的折射色散和衍射色散可以互相抵消,使白光横向平顶光束基本无色散.     

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The fluid dynamics model was used to study the influence of the existence of the collisions on the dust particles in a dusty plasma sheath. The main collisions in this study consist of the ionization collision, the collision between electron and neutral particle, the collision between ion and neutral particle, the collision between electron and dust particle, the collision between ion and dust particle. Numerical calculation results are obtained by the fourth-order-Rung-Kutta method. It is shown that both the dust particles’ density and corresponding electricity quantity increase as the following collisions’ frequency enhances, such as ionization collision, the collision between electron and neutral particle, the collision between ion and neutral particle. The charge reduces due to the collisions concluding electron-dust particle and ion-dust particle. In addition, the effect produced by ions’ collision is much more obviously compared with electrons’ collision.     

碰撞对尘埃等离子体鞘层中尘埃颗粒影响

在一维平板鞘层中应用流体模型研究了尘埃等离子体鞘层中碰撞对尘埃颗粒密度和带电量的影响。 研究所涉及的碰撞主要有电离碰撞,电子、离子分别与中性粒子的碰撞,以及电子、离子分别与尘埃颗粒的碰撞。通过采用四阶龙格库塔法,得到了数值解。结果表明,随着电离碰撞或者电子、离子分别与中性粒子碰撞的频率 增加,都将导致鞘层中尘埃颗粒的数密度增大,数密度的极值位置向鞘边位置靠近,尘埃颗粒带电量增多。电子、离子与尘埃颗粒的碰撞,使得尘埃带电量减小。此外,从研究的结果来看,由离子产生的碰撞要比电子产生的碰 撞对尘埃颗粒的影响明显得多。     

Kinetic equation for a relativistic electron beam propagating along an external magnetic field in dense and rare gas-plasma media

A kinetic equation that describes the transverse dynamics of an axisymmetric paraxial relativistic electron beam propagating along an external magnetic field in a gas-plasma medium is derived with allowance for the influence of the self-consistent electromagnetic field on the beam, the effects related to the nonlaminar motion and rotation of the beam electrons at the exit from the injector, and the scattering and energy loss of the beam electrons in their collisions with the neutral particles of the background gas.     

Methods of geometrical integration in accelerator physics

In the paper we consider a method of geometric integration for a long evolution of the particle beam in cyclic accelerators, based on the matrix representation of the operator of particles evolution. This method allows us to calculate the corresponding beam evolution in terms of two-dimensional matrices including for nonlinear effects. The ideology of the geometric integration introduces in appropriate computational algorithms amendments which are necessary for preserving the qualitative properties of maps presented in the form of the truncated series generated by the operator of evolution. This formalism extends both on polarized and intense beams. Examples of practical applications are described.