强流脉冲束在静电加速管中传输研究及模拟计算

为了研究强流脉冲束流在静电加速管中的传输, 采用矩阵法分析了非强流脉冲束流与强流脉冲束流在静电加速管中的传输矩阵, 编写了束流在静电加速管等元件中传输的计算程序ACCT。 用优化方法实现给定的光学条件, 用迭代方法计算强流脉冲束流的空间电荷效应对束流传输的影响以获得自洽解。 在不同束流流强条件下, 利用ACCT、TRACE-3D和TRANSPORT等程序进行了模拟计算, 并对模拟结果进行了比较分析。 模拟结果表明, 提高加速电压比, 可以增强静电加速管的聚焦能力、 减少束流损失和提高传输效率。To study intense pulsed beam transfer in electrostatic accelerate tube, the matrix method was applied to analyze the transport matrixes in electrostatic accelerate tube of non-intense pulsed beam and intense pulsed beam, and a computer code was written for the intense pulsed beam transporting in electrostatic accelerate tube. Optimization techniques were used to attain the given optical conditions and iteration procedures were adopted to compute intense pulsed beam for obtaining self-consistent solutions in this computer code. The calculations were carried out by using ACCT, TRACE-3D and TRANSPORT for different beam currents, respectively. The simulation results show that improvement of the accelerating voltage ratio can enhance focusing power of electrostatic accelerate tube, reduce beam loss and increase the transferring efficiency.     

Transport of 3D space charge dominated beams

In this paper we present the theoretical analysis and the computer code design for the intense pulsed beam transport. Intense beam dynamics is a very important issue in low-energy high-current accelerators and beam transport systems. This problem affects beam transmission and beam qualities. Therefore, it attracts the attention of the accelerator physicists worldwide. The analysis and calculation for the intense beam dynamics are very complicated, because the state of particle motion is dominated not only by the applied electromagnetic fields, but also by the beam-induced electromagnetic fields (self-fields). Moreover, the self fields are related to the beam dimensions and particle distributions. So, it is very difficult to get the self-consistent solutions of particle motion analytically. For this reason, we combine the Lie algebraic method and the particle in cell (PIC) scheme together to simulate intense 3D beam transport. With the Lie algebraic method we analyze the particle nonlinear trajectories in the applied electromagnetic fields up to third order approximation, and with the PIC algorithm we calculate the space charge effects to the particle motion. Based on the theoretical analysis, we have developed a computer code, which calculates beam transport systems consisting of electrostatic lenses, electrostatic accelerating columns, solenoid lenses, magnetic and electric quadruples, magnetic sextupoles,octopuses and different kinds of electromagnetic analyzers. The optimization calculations and the graphic display for the calculated results are provided by the code.     

Intense DC beam nonlinear transport-analysis & simulation

The intense dc beam nonlinear transport was analyzed with the Lie algebraic method, and the particle trajectories of the second order approximation were obtained. Based on the theoretical analysis a computer code was designed. To get self-consistent solutions, iteration procedures were used in the code. As an example, we calculated a beam line (drift-electrostatic quadrupole doublet-drift). The results agree to the results calculated by using the PIC method.     

Comparison of the PIC model and the Lie algebraic method in the simulation of intense continuous beam transport

Both the PIC (Particle-In-Cell) model and the Lie algebraic method can be used to simulate the transport of intense continuous beams. The PIC model is to calculate the space charge field, which is blended into the external field, and then simulate the trajectories of particles in the total field; the Lie algebraic method is to simulate the intense continuous beam transport with transport matrixes. Two simulation codes based on the two methods are developed respectively, and the simulated results of transport in a set of electrostatic lenses are compared. It is found that the results from the two codes are in agreement with each other, and both approaches have their own merits.     

Lie algebraic analysis for intense bunched beam in the nonlinear transport of electrostatic quadrupoles

In this paper, the nonlinear transport of intense bunched beams in electrostatic quadrupoles is analyzed using the Lie algebraic method, and the results are briefly presented of the linear matrix approximation and the second order correction of particle trajectory in the state space. Beam having K-V distribution and Gaussian distribution approximation are respectively considered. A brief discussion is also given of the total effects of the quadrupole and the space charge forces on the evolution of the beam envelope.     

Numerical Simulation Multicomponent Ion Beam Transport form ECR Ion Source

In order to simulate the transport of multi-components ion beam extracted from an ECR ion source, we have developed a multi-charged ion beam transport program named MCIBS 1.0. The program is dedicated to numerical simulation of the behavior of highly-charged ion beam and optimization of beam optics in transport lines and is realized on a PC with Windows user interface of Microsoft Visual Basic. Among all the ions with different charge states in the beam, the exchanges of electrons between highly charged ions and low charged ions or neutral,atoms of residual gas are taken into account by using classical Molecular Over-barrier Model and Monte Carlo method. An advanced Windows graphical interface makes it; comfortable and friendly for the user to operate in an interactive mode. The present program is used for the numerical calculation and optimization of beam optics in a transport line consisting of various magnetic elements, such as dipole magnet, quadrupole and so on. It is possible to simultaneously simulate 200,000 particles, in a transport line of 340 m at most, and show every particle orbit. Beam cross section graphics and emittance phase pictures can be also shown at any position in the transport line.     

Numerical simulation for space charge dominated beam transport

To simulate the intense bunched beam transport, a computer program LEADS-3D has been developed. The particle trajectories are analysed with the Lie algebraic method. The third order approximation of the trajectory solutions is made with space charge forces off, and the second order approximation is made with space charge forces on. The particle distribution in the 3D ellipsoid is uniform or Gaussian. Most of the conventional beam optical elements are incorporated in the code. The optimization procedures are provided to fit the beam lines to satisfy the given optical conditions.     

强流束在二极磁场中传输的模拟计算

为了研究空间电荷力对束流在二极磁场中传输的影响,从理论上用矩阵法分析非强流脉冲束流与强流脉冲束流在二极磁场中的传输矩阵,编写了束流在二极磁场等元件中传输的计算程序。用Powell优化方法计算非强流束传输实现给定的光学条件,用迭代方法计算强流束传输获得自洽解。在不同束流流强条件下,运用该程序与其他程序进行了模拟计算,并对模拟结果进行了比较分析。模拟结果表明:束流流强越大,束流包络曲线横向发散越显著,空间电荷效应越强。     

用于强流中子发生器的低能束流传输线的设计模拟

兰州大学设计研发的ZF-400强流中子发生器设计D-T中子产额6×1012 n/s,主要由ECR离子源、低能束流传输线（LEBT）、加速管、旋转靶等部分组成。LEBT负责将从离子源引出的束流进行分析聚焦并注入到加速管中。LEBT对束流的聚焦及分析的好坏程度决定了加速管中束流的损失程度、中子的产额以及靶的寿命。本工作就该强流中子发生器所需的低能传输线进行了设计。使用螺线管、分析磁铁和四极透镜组合的方案。利用TRACK软件对此方案进行模拟,得到符合要求的束流线及元件的参数。用TraceWin进行了验证模拟,验证结果符合要求。另外,通过软件模拟确定了杂质离子损失的位置,据此设计了束流管道冷却方案。通过模拟发现,这种透镜的组合方式可以让整个LEBT以较低的功率获得低损失、高纯度的打靶束流。The ZF-400 Intense Neutron Generator, which is designed by Lanzhou University with an expected neutron yield of 6×1012 n/s, is consist of ECR ion source, low energy beam transport (LEBT) line, accelerating tube and rotating target. The beam extracted from ECR source is analyzed and focused through LEBT, then, the beam is introduced into the accelerating tube. The focus and analysis ability of LEBT is very important for the beam loss, neutron yield and target's life. A LEBT line for intense neutron generator is designed in this paper, the project consisted of a solenoid, a bend magnet and three quadrupole lens. The qualified LEBT and its parameters have been got through the simulation with TRACK code. Then TraceWin program was employed to check this simulation and the result satisfied our requirement. Besides, the loss position of impurity ions was known through the simulation, and a project of beam line's cooling system was designed according to this result. Through the simulation, we find the optimal lens combination plan which can obtain lower beam loss and higher beam purity at low running power of LEBT.     

TOPOPIC对强流束流在周期FODO结构中的传输研究

粒子云网格(Particle In cell,PIC) 方法是研究带电粒子在加速器中运动的关键工具之一。基于PIC 算法,开发了模拟强流条件下的束流动力学模拟程序TOPOPIC(Trace of Particle Orbit with PIC method),并且利用TOPOPIC,研究了束流在四极铁周期结构(FODO) 中的传输问题。结果表明,在强流条件下空间电荷效应显著地影响了束流的整体行为和单粒子的运动轨迹。最后比较了TOPOPIC 程序和通用的BEAMPATH 程序在相同条件下的计算结果,可以看到两个程序给出的模拟结果吻合得非常好,这表明TOPOPIC程序的计算结果是合理、可靠的。The Particle in cell (PIC) method is one of the key techniques in the research of charged particles in accelerators. Based on the PIC method, a new beam simulation code for high intensity beam named TOPOPIC (Trace of particle orbit with PIC method) has been developed. With the code TOPOPIC,the beam behavior during passing through the periodic quadrupole (FODO) structure has been studied. The results show that the nonlinear space charge affects the single particle behavior and beam envelope a lot. At last, the PIC code BEAMPATH is used for benchmark, the results given by TOPOPIC and BEAMPATH show good agreements,which means the code TOPOPIC is reliable.     

直线变压器驱动源磁芯能量传递效率

磁芯是直线变压器驱动源(LTD)的关键部件之一,起着初、次级能量传递和次级电压感应叠加的作用,磁芯的能量传递效率对LTD系统的效率、体积和重量影响显著。对LTD系统中影响磁芯能量传递效率的原因进行了初步的分析,并利用Pspice软件的非线性磁芯模型对磁芯的工作过程和损耗进行了模拟计算,最后对LTD磁芯的能量传递效率进行了初步的实验研究,在工作电压为20 kV时、脉宽约220 ns时,在2.8 Ω负载上获得了大于60%的能量传递效率。     

Pulsed intense electron beams generated in transient hollow cathodedischarges: fundamentals and applications

For the commercial application of pulsed power, material processing with intense pulsed particle beams is a very interesting subject. Recently, high-voltage (1-70 kV), low-pressure (1-100 Pa) transient hollow-cathode discharges turned out to be sources for pulsed intense electron beam generation suitable for this application. The remarkable parameters of these electron beams-beam currents of 50-1000 A (10-30% of the maximum discharge current) with a high energy component (mean energy of about 0.25-0.75 of maximum applied voltage) of 20-70% of the maximum beam current, power density up to 10 W/cm², beam diameters of 0.1-3 mm, beam charge efficiency of 3-5%-captured the attention not only of the scientific community in the last decade. The electron beam is emitted during the early phases of the discharge, and only weak dependence of the high energetic peak of the beam current was found on the external capacity, which determine the development of the later high-current phases. However, the beam parameters depend on the breakdown voltage, gas pressure, and discharge geometry (including self-capacity). In this paper, the characteristics of the pulsed intense electron beams generated in two configurations-multigap pseudosparks and preionization-controlled open-ended hollow-cathode transient discharges (PCOHC)-are described. Such electron beams already were used successfully in a variety of pulsed power applications in material processing, deposition of superconducting (YBaCuO) and diamond-like thin films, microlithography, electron sources for accelerators, and intense point-like X-ray sources, and some preliminary experiments revealed new potential applications such as pumping of short-wavelength laser active media. These pulsed electron beams could be used further in any kind of pulsed power applications that require high-power density, small or high electron energy, and small-beam diameters     

Lie algebraic analysis for the nonlinear transport of intense bunched beam in electrostatic quadrupoles

In this paper, the nonlinear transport of intense bunched beams in electrostatic quadrupoles is analyzed using the Lie algebraic method, and the results are briefly presented of the linear matrix approximation and the second order correction of particle trajectory in the state space. Beam having K-V distribution and Gaussian distribution approximation are respectively considered. A brief discussion is also given of the total effects of the quadrupole and the space charge forces on the evolution of the beam envelope.     

双圆筒加速透镜中强流束传输的模拟

用矩阵法分析非强流束流与强流束流在双圆筒加速透镜中的传输,编写束流在双圆筒加速透镜等元件中传输的计算程序DCALENS.采用优化方法实现给定的光学条件,用迭代方法计算强流束传输获得自洽解.在不同束流流强条件下,用DCALENS程序进行模拟计算,并对模拟结果进行比较分析.结果表明:束流流强越大,束流包络曲线横向发散越显著,空间电荷力越强;束流流强大于2 A时,束流包络曲线发散明显.     

APPLICATION OF PERMANENT MAGNET LENSES IN ACCELERATORS BEAM TRANSPORT AND FOCUSING

This paper presents the characteristics, structure and parameters of the permanent magnet quadrupole lenses which have been used as a beam transport element in our linac. The methods of connection and adjustment are discussed. After transporting 15MeV electron beams by 43cm, a improvement of 50%—80% of the primary beam profile was obtained.     

电子束在α-磁铁模型中传输模拟与优化

在电子直线加速器设计中,α-磁铁通常被用来压缩脉冲长度,采用热阴极微波电子枪和α-磁铁相结合的设计,可以获得皮秒或亚皮秒量级脉冲长度的电子束。电子束在α-磁铁中的传输过程较为复杂,相关文献介绍的研究成果均是基于理想模型,且有镜板开孔的α-磁铁的束流传输研究,对α-磁铁的使用具有重要的指导作用。本文首先简单介绍了用于高能电子成像装置的α-磁铁模型的设计,对电子束在理想模型与α-磁铁模型中传输模拟结果进行对比分析,验证了所构建模型可以有效地实现脉冲纵向压缩的结论。此外,对以优化角度进入α-磁铁和在空间电荷效应影响下的单束团及多束团束流动力学模拟结果进行了讨论,提出通过减小入射角度来补偿α-磁铁镜板上的束流进出孔对束流传输影响的方案。通过在α-磁铁与电子枪之间增加四极磁铁组,优化了束流发射度和束团尺寸。