Computer simulations for intense continuous beam transport in electrostatic lens systems

A code LEADS based on the Lie algebraic analysis for the continuous beam dynamics with space charge effect in beam transport has been developed.The program is used for the simulations of axial-symmetric and unsymmetricalintense continuous beam in the channels including drift spaces.electrostatic lenses and DC electrostatic accelerating tubes.In order to get the accuracy required,all elements are divided into many small segments,and the electric field in the segments is regarded as uniform field,and the dividing points are treated as thin lenses.Iteration procedures are adopted in the program to obtain self-consistent solutions.The code can be used in the designs of low energy beam transport systems,electrostatic accelerators and ion implantation machines.     

Computer simulations for intense continuous beam transport in electrostatic lens systems

A code LEADS based on the Lie algebraic analysis for the continuous beam dynamics with space charge effect in beam transport has been developed. The program is used for the simulations of axial-symmetric and unsymmetrical intense continuous beam in the channels including drift spaces, electrostatic lenses and DC electrostatic accelerating tubes. In order to get the accuracy required, all elements are divided into many small segments, and the electric field in the segments is regarded as uniform field, and the dividing points are treated as thin lenses. Iteration procedures are adopted in the program to obtain self-consistent solutions. The code can be used in the designs of low energy beam transport systems, electrostatic accelerators and ion implantation machines.     

LEADS-DC: A computer code for intense dc beam nonlinear transport simulation

An intense dc beam nonlinear transport code has been developed. The code is written in Visual FORTRAN 6.6 and has ∼13000 lines. The particle distribution in the transverse cross section is uniform or Gaussian. The space charge forces are calculated by the PIC (particle in cell) scheme, and the effects of the applied fields on the particle motion are calculated with the Lie algebraic method through the third order approximation. Obviously, the solutions to the equations of particle motion are self-consistent. The results obtained from the theoretical analysis have been put in the computer code. Many optical beam elements are contained in the code. So, the code can simulate the intense dc particle motions in the beam transport lines, high voltage dc accelerators and ion implanters.

     

High performance computation on beam dynamics problems in high intensity compact cyclotrons

This paper presents the research progress in the beam dynamics problems for future high intensity compact cyclotrons by utilizing the state-of-the-art high performance computation technology. A “Start-to-Stop” model, which includes both the interaction of the internal particles of a single bunch and the mutual interaction of neighboring multiple bunches in the radial direction, is established for compact cyclotrons with multi-turn extraction. This model is then implemented in OPAL-CYCL, which is a 3D object-oriented parallel code for large scale particle simulations in cyclotrons. In addition, to meet the running requirement of parallel computation, we have constructed a small scale HPC cluster system and tested its performance. Finally, the high intensity beam dynamics problems in the 100 MeV compact cyclotron, which is being constructed at CIAE, are studied using this code and some conclusions are drawn.

     

Free vibration behaviour of multiphase and layered magneto-electro-elastic beam

Free vibration studies of multiphase and layered magneto-electro-elastic beam for BaTiO₃–CoFe₂O₄ composite is carried out. In-plane plate finite-element analysis is used to obtain the behaviour of magneto-electro-elastic beam. Studies are carried out for beams for different boundary conditions, as may be applicable in design of smart sensors/actuators. The ANSYS package is used to validate the results obtained by the computer code developed for piezoelectric (PE) beam. Plane stress condition is used for the Euler–Bernouli magneto-electro-elastic beam.     

HZE beam transport in multilayered materials

A nonperturbative analytic solution of the high charge and energy (HZE) Green's function is used to implement a computer code for laboratory ion beam transport in multiple-layered materials. The code is established to operate on the Langley nuclear fragmentation model used in space engineering applications. Computational procedures are established to generate linear energy transfer (LET) distributions for a specified ion beam and target for comparison with experimental measurement. Comparison with 56Fe ion with Pb-Al and Pb-(CH2)x targets shows reasonable agreement.     

Modeling of astigmatic-elliptical beam shaping during fs-laser waveguide writing including beam truncation and diffraction effects

In this work, we report a model for accurately calculating the focal volumes corresponding to astigmatic elliptical beams used in fs-laser waveguide writing. The model is based on the use of the ABCD matrix formalism for the propagation of a Gaussian beam. The code includes the effects of propagation on the astigmatic elliptical beam, and the effects of beam truncation and diffraction at the entrance pupil of the focusing objective due to beam clipping when overfilling the pupil. The results predict that for a given astigmatism value and propagation distance it is possible to efficiently suppress the astigmatic focus closer to the surface. This explains previous experimental results where single structure waveguides with controllable aspect-ratio were fabricated using astigmatic-elliptical beams. Furthermore, we investigate the respective roles of astigmatism and beam propagation, as well as the strong impact of truncation and diffraction effects caused by clipping the beam at the pupil of the focusing optics. Finally, based on the results from our model, we present some practical considerations in terms of beam propagation and phase wrapping constraints.     

Particle-in-cell mode beam dynamics simulation of the low energy beam transport for the SSC-linac injector

A new SSC-linac system (injector into separated sector cyclotron) is being designed in the HIRFL (heavy ion research facility of Lanzhou). As part of SSC-Linac, the LEBT (low energy beam transport) consists of seven solenoids, four quadrupoles, a bending magnet and an extra multi-harmonic buncher. The total length of this segment is about 7 meters. The beam dynamics in this LEBT has been studied using three-dimensional PIC (particle-in-cell) code BEAMPATH. The simulation results show that the continuous beam from the ion source is first well analyzed by a charge-to-mass selection system, and the beam of the selected charge-to-mass ratio is then efficiently pre-bunched by a multi-harmonic buncher and optimally matched into the RFQ (radio frequency quadrupole) for further acceleration. The principles and effects of the solenoid collimation channel are discussed, and it could limit the beam emittance by changing the aperture size.     

Particle-in-cell mode beam dynamics simulation of the low energy beam transport for the SSC-linac injector

A new SSC-linac system (injector into separated sector cyclotron) is being designed in the HIRFL (heavy ion research facility of Lanzhou). As part of SSC-Linac, the LEBT (low energy beam transport) consists of seven solenoids, four quadrupoles, a bending magnet and an extra multi-harmonic buncher. The total length of this segment is about 7 meters. The beam dynamics in this LEBT has been studied using three-dimensional PIC (particle-in-cell) code BEAMPATH. The simulation results show that the continuous beam from the ion source is first well analyzed by a charge-to-mass selection system, and the beam of the selected charge-to-mass ratio is then efficiently pre-bunched by a multi-harmonic buncher and optimally matched into the RFQ (radio frequency quadrupole) for further acceleration. The principles and effects of the solenoid collimation channel are discussed, and it could limit the beam emittance by changing the aperture size.     

A particle-in-cell mode beam dynamics simulation of medium energy beam transport for the SSC-Linac

A new linear accelerator system, called the SSC-Linac injector, is being designed at HIRFL (the heavy ion research facility of Lanzhou). As part of the SSC-Linac, the medium energy beam transport (MEBT) consists of seven magnetic quadrupoles, a re-buncher and a diagnose box. The total length of this segment is about 1.75 m. The beam dynamics simulation in MEBT has been studied using the TRACK 3D particle-in-cell code, and the simulation result shows that the beam accelerated from the radio frequency quadrupole (RFQ) matches well with the acceptance of the following drift tube linac (DTL) in both the transverse and longitudinal phase spaces, and that most of the particles can be captured by the final sector focusing cyclotron for further acceleration. The longitudinal emittance of the RFQ and the longitudinal acceptance of the DTL was calculated in detail, and a multi-particle beam dynamics simulation from the ion source to the end of the DTL was done to verify the original design.     

An identification method of positron production in laser beam interaction with targets

A simple electromagnetic transport system was constructed to identify very rare positrons produced in a powerful laser beam interaction with a target. Testing experiments were carried out with CO₂-laser (10¹² W/cm²) beam pulses (τ=50 ns,f=0.01 Hz) focused on the copper target, as well as with a 96 MeV alpha-particle beam irradiated carbon target. The results showed that the developed system could be effectively used for positron identification and evaluation of their energy by means of a time-of-flight method. The computerized system to deal with this problem, together with others related to the power laser beam interaction with targets, has been constructed.     

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。     

Space-time dynamics of nanoparticles of a magnetofluid in a laser beam

Laser-induced space-time dynamics of nanoparticles of a magnetofluid was observed. Visualization was effectuated and the redistribution of the particles was measured. These showed a strong decrease in the particle density on and around the periphery of the laser beam axis. A number of proofs showing that the thermal diffusion of nanoparticles plays the key role in determining the dynamics of the particle redistribution are presented. High-quality pictures taken of the self-modulation of the laser beam serve as a new and powerful method for investigating transport phenomena and the nonlinear interaction of light with colloids. Pis’ma Zh. éksp. Teor. Fiz. 68, No. 7, 594–598 (10 October 1998)     

Determination of the profile of energy release from a high-power electron beam in an aerogel

Optical methods are used to investigate the dynamics of the interaction of a high-current electron beam with an aerogel (a highly porous transparent dielectric with a low density ρ=0.36 g/cm³). The measured profile of the glow of the aerogel and the pattern of its expansion are compared with the results of a numerical simulation. The influence of the space charge on the profile of the energy absorption from the high-current relativistic electron beam is discussed. Zh. Tekh. Fiz. 67, 26–32 (November 1997)     

Nonlinear beam shaping by a cloud of cold Rb atoms

First experimental investigations are reported on nonlinear beam shaping due to the interaction between an intense laser beam and a cloud of laser cooled rubidium atoms. Resonant excitation of the F = 3 ↔ F ^′ = 4 hyperfine transition is considered. The single-pass interaction through the cold vapor causes an increase in the laser beam intensity in the forward direction (zero transverse wavevector component) when observed in Fourier space, for sufficiently high values of saturation. A qualitative explanation of the observations based on a two-level model for a resonantly excited transition proves acceptable. The observations are compatible with an interpretation based on nonlinear index-induced focusing of an incident beam with curved wavefront, as is used in z-scan measurements. Simple physical considerations allow us to deduce the conditions for the observability of optical patterns in the beam transmitted by a cold atomic cloud.     

EAST中性束注入快离子损失研究

利用经典导心轨道程序ORBIT,结合平衡程序EFIT和输运程序TRANSP,计算了EAST中性束注入后快离子的损失情况.结果表明,4MW(80keV)氘离子的损失份额为29％,2MW(50keV)氘离子的损失份额为31％,损失的快离子有很强的局域性.     

Temporal evolution of a long-pulse high-density electron beam

The temporal evolution of a long-pulse high-density electron beam in a high-power traveling-wave tube with a periodic magnetic focusing system is investigated. The relation between the variation of the characteristics of the electron beam and ionization of the residual gas and particles desorbed from the electrode surfaces is shown. A strong influence of the formation of the collector plasma and the flux of ions from its surface on the beam dynamics is revealed. The effect of microwave fields in the transport channel on the characteristics of the beam during its evolution is studied. Zh. Tekh. Fiz. 67, 54–58 (December 1997)     

直线感应加速器输运磁场遗传算法优化

以直线感应加速器（LIA）匹配磁场设计和束线调谐为背景,提出解决强流相对论电子束长距离、小波动、多元件磁约束的输运优化问题的数值优化办法,建立基于遗传算法的优化程序。结合束质心轨迹及束包络耦合模型,设计描述束传输半径波动大小的评价函数,采用励磁元件馈入电流为优化对象,解决LIA磁场配置组合爆炸优化问题。计算结果表明:优化程序可依据不同的初始束流,有针对性地快速给出一组符合束输运要求的励磁电流配置。研究成果为在建的LIA装置束线调谐提供一种重要的数值分析工具。     

Coulomb excitation of 74Ge beam

⁷⁴Ge beam was Coulomb-excited on a ^natPb target. Ten E2 matrix elements including diagonal matrix elements for 5 low-lying states have been determined using the least-squares search code GOSIA. The expectation values of the rotational invariants 〈Q ²〉 and 〈cos3δ〉 show the small and triaxial deformation of the two lowest members of the ground-state band , while the 0₂ ⁺ and 2₂ ⁺ states are found to be almost spherical. Received: 31 August 2000 / Accepted: 4 December 2000     

Transverse dynamics of space charge dominated beam during bunching

In this paper we present a technique to optimize the transport parameters for transverse matching of the space charge dominated beams in the presence of bunching. The increase in the current within the specified bunch width during the transport is obtained from the disc model and is included in the optimization method. A 2D particle in cell (PIC) code is then developed to study the details transverse dynamics of the bunch taking into account the effect of longitudinal compression by reweighting the charge and mass of macroparticles. The evolution of rms beam size obtained using PIC simulation agrees well with the results obtained by solving beam envelope equation. The PIC simulation shows emittance growth during bunching induced by the space charge effect for nonuniform distribution. The growth in the emittance increases with the nonlinearity of distribution and peaks near the time focus.