超声分子束注入模型与流体输运程序的耦合

将超声分子束注入模型加入到流体输运程序ONETWO 中,为ONETWO 程序提供了重要的粒子源和电子、离子热源项。在ONETWO 程序物理模型中加入超声分子束注入模型,修改TPSMBI 程序并将其耦合到 ONETWO 程序中。运用耦合后的ONETWO 程序模拟研究了喷气法与超声分子束注入产生的源项。将超声分子束注入模型加入到ONETWO 程序中不仅可以为相关的实验分析提供一种重要的工具,也可为未来装置(如中国聚变工程实验堆)的物理设计提供重要的粒子和能量源信息。     

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.     

离子发动机交换电荷离子返流的粒子模拟

建立了离子发动机羽流的物理模型,采用粒子网格对羽流中的交换电荷离子的分布进行了模拟,电场方程使用完全近似格式的代数多重网格方法求解。利用计算设备统一架构技术开发出一套基于图形处理器的3维并行粒子模拟程序。计算结果表明,交换电荷离子在径向扩张型电势结构下会向束流区外运动,一部分交换离子在电场力作用下会向发动机上游运动,从而形成返流。发动机上游区域的交换电荷数密度与束流等离子体数密度相比降低了3~4个数量级。通过降低电子温度可有效降低返流电流。     

Formation of biaxial texture in metal films by selective ion beam etching

The formation of in-plane texture via ion bombardment of uniaxially textured metal films was investigated. In particular, selective grain Ar ion beam etching of uniaxially textured (0 0 1) Ni was used to achieve in-plane aligned Ni grains. Unlike conventional ion beam assisted deposition, the ion beam irradiates the uniaxially textured film surface with no impinging deposition flux. The initial uniaxial texture is established via surface energy minimization with no ion irradiation. Within this sequential texturing method, in-plane grain alignment is driven by selective etching and grain overgrowth. Biaxial texture was achieved for ion beam irradiation at elevated temperature.     

离子发动机交换电荷离子返流的粒子模拟

 建立了离子发动机羽流的物理模型,采用粒子网格对羽流中的交换电荷离子的分布进行了模拟,电场方程使用完全近似格式的代数多重网格方法求解。利用计算设备统一架构技术开发出一套基于图形处理器的3维并行粒子模拟程序。计算结果表明,交换电荷离子在径向扩张型电势结构下会向束流区外运动,一部分交换离子在电场力作用下会向发动机上游运动,从而形成返流。发动机上游区域的交换电荷数密度与束流等离子体数密度相比降低了3~4个数量级。通过降低电子温度可有效降低返流电流。     

黑腔中空间束匀滑光束成丝不稳定性的数值模拟北大核心CSCD

为深入研究黑腔内激光成丝不稳定性产生和发展,建立了空间束匀滑光束的传播模型,利用三维激光等离子体相互作用程序LAP3D模拟了黑腔物理条件下的大尺度成丝现象。模拟结果可正确描述成丝后光强的束发散现象及谱空间光强分布特征。从激光能量参数角度分析了导致成丝不稳定性发展的物理因素,并讨论了应用空间束匀滑技术抑制成丝不稳定性的局限性。研究表明:空间束匀滑光束发展成丝的能力取决于光斑内小焦斑的成丝表现,当具备成丝能力的小焦斑份额达到一定比例后,就会导致整个空间束匀滑光束成丝,因此对于光斑平均功率密度较高的光束,须考虑结合其他束匀滑手段来抑制成丝发展。     

Mathematical modeling of the heating of a fast ignition target by an ion beam

We develop a BIN computer code for simulating the interaction of a monochromatic ion beam with a plasma, which takes into account changes in the spatial distribution of the heated-plasma temperature. This enables us to calculate the heating of both homogeneous and inhomogeneous plasmas with parameters corresponding to their real spatial distributions at the time of maximum compression of the inertial confinement fusion (ICF) target. We present the results of a numerical simulation using the BIN code for the heating of a homogeneous deuterium–tritium plasma by a short pulse of monochromatic ions at various ion velocity and plasma–electron thermal velocity ratios. We also present the results of calculations for the heating of an inhomogeneous plasma of a non-cryogenic target formed as a beryllium deuteride–tritide shell by beams of light, medium, and heavy ions. As the initial distributions, we use the results of numerical simulations for such a target, precompressed by a laser pulse (carried out at the M. V. Keldysh Institute of Applied Mathematics using the DIANA code). We demonstrate the possibility of forming the central ignitor with the parameters sufficient for igniting the targets by beams of ions with energies E ~ 100 ? 400 MeV/u and specific energy densities of the beam Q ～ 5?20 GJ/cm². The required specific energy density drops with increase in the ion energy; however, due to the increased path length, larger-charge ions have to be used.     

Computer simulations of low-energy neon-ion scattering from nickel crystals

The model of successive single binary elastic collisions used by a computer code called ARGUS is sufficiently accurate to reproduce the salient features of energy spectra that result from ion-surface scattering for the neon on nickel system down to incidence energies of 600 eV. Agreement with experimental measurements is at least as good as that obtained by more detailed calculations, which include the interactions of many particles. Many features of the backscattered energy spectra can be associated with a single, or at most a few, specific collision sequences. ARGUS selects sampling areas that are orthogonal to the incident beam direction rather than parallel to the surface. These sampling areas are constructed from polygons formed by the intersection of the Wigner-Scitz cell of an atom with a plane perpendicular to the ion beam direction and passing through the center of the atom. These polygons of surface atoms form an overlapping mosaic. The irreducible portion of this mosaic (a type of primitive cell) that is visible along the ion beam direction is the required sampling area. This approach provides the most economical sampling of the surface.     

Optimization of accelerated charged particle beam for ADS energy production

A comparative analysis and optimization of energy efficiency for proton and ion beams in ADS systems is performed via simulation using a GEANT4 code with account for energy consumption for different accelerator types. It is demonstrated that for light nuclei, beginning from ⁷Li, with energies above 1 GeV/nucleon, ion beams are considerably (several times) more efficient than the 1–3 GeV proton beam. The possibility of achieving energy deposition equivalent to 1 GeV protons in a quasi-infinite uranium target with higher efficiency (and twice as small accelerator size) in the case of acceleration of light ions is substantiated.     

Analytical and simulation studies for diode and triode ion beam extraction systems

This work is concerned with ion beam dynamics and compares the emittance to aberration ratios of two-and three-electrode extraction systems. The study is conducted with the aid of Version 7 of SIMION 3D ray-tracing software. The beam dependence on various parameters of the extraction systems is studied and the numerical results lead to qualitative conclusions.     

Simulation of ion beam extraction and focusing system

The characteristics of ion beam extraction and focused to a volume as small as possible were investigated with the aid of computer code SIMION 3D version 7. This has been used to evaluate the extraction characteristics (accel-decel system) to generate an ion beam with low beam emittance and high brightness. The simulation process can provide a good study for optimizing the extraction and focusing system of the ion beam without any losses and transported to the required target. Also, a study of a simulation model for the extraction system of the ion source was used to describe the possible plasma boundary curvatures during the ion extraction that may be affected by the change in an extraction potential with a constant plasma density meniscus.     

Simulation of ion beam extraction and focusing system

The characteristics of ion beam extraction and focused to a volume as small as possible were investigated with the aid of computer code SIMION 3D version 7.This has been used to evaluate the extraction characteristics(accel-decel system)to generate an ion beam with low beam emittance and high brightness.The simulation process can provide a good study for optimizing the extraction and focusing system of the ion beam without any losses and transported to the required target.Also,a study of a simulation model for the extraction system of the ion source was used to describe the possible plasma boundary curvatures during the ion extraction that may be affected by the change in an extraction potential with a constant plasma density meniscus.     

Systematic investigation of the reactive ion beam sputter deposition process of SiO<Subscript>2</Subscript>

Ion beam sputter deposition (IBSD) is an established physical vapour deposition technique that offers the opportunity to tailor the properties of film-forming particles and, consequently, film properties. This is because of two reasons: (i) ion generation and acceleration (ion source), sputtering (target) and film deposition (substrate) are locally separated. (ii) The angular and energy distribution of sputtered target atoms and scattered primary particles depend on ion incidence angle, ion energy, and ion species. Ion beam sputtering of a Si target in a reactive oxygen atmosphere was used to grow SiO₂ films on silicon substrates. The sputtering geometry, ion energy and ion species were varied systematically and their influence on film properties was investigated. The SiO₂ films are amorphous. The growth rate increases with increasing ion energy and ion incidence angle. Thickness, index of refraction, stoichiometry, mass density and surface roughness show a strong correlation with the sputtering geometry. A considerable amount of primary inert gas particles is found in the deposited films. The primary ion species also has an impact on the film properties, whereas the influence of the ion energy is rather small.     

电子束相空间分布效应的三维计算

在386微机上建立了长脉冲单模的三维放大器数值模拟程序3DFEL,每个单程只需20分钟。模拟计算得出:(1)发射度对输出功率的影响几乎是指数式的。(2)电子相空间形状(相同发射度)对输出功率的重大影响主要表现为两方面:(a)不同相空间形状,等效能散度是不同的,(b)电子束包络和光场包络匹配关系。(3)非理想入射(偏入射和斜入射)超出一定范围之后将引起输出功率的指数下降。     

Central region design for a 10 MeV internal ion source cyclotron

Internal ion sources are widely adopted in commercial cyclotrons used for short-life isotopes produc-tion. Without beam manipulation provided by the external beam injection line, the central region of this type of cyclotron is more sensitive and should be carefully designed. A design study and beam dynamics simulation for the central region of a 10 MeV compact cyclotron is presented. The OPERA3D/TOSCA code was used to calculate the electric field from a parameterized three dimensional (3D) central region model. With iterative structure optimizations of the central region, the beam centering and vertical focusing is well controlled, and the RF phase acceptance is around 25° A c++ code for beam simulation in the central region was developed and tested.     

On the evaluation of ignition threshold in proton-carbon hybrid ignitor beam proposal

We may improve plasma ignition quality in a conically guided proton fast ignition scheme by the application of an extra lower intensity, secondary carbon beam. According to the experimental measurements on the number of laser-accelerated ions, the temporal evolution of the hot spot electron, ion, and radiation temperatures was examined using three-temperature plasma model, in radiation pressure acceleration (RPA) mechanisms for a proton-Carbon beam configuration, E_avg ≈ 10 MeV/nucleon. The hot spot ignition was evaluated by the well-known stopping power models proposed independently by Li–Petrasso (LP) and Brown–Preston–Singleton (BPS). Based on our analytical results, with time, plasma temperature in the LP model surpasses the BPS model. From this point of view, to compensate this deficiency in the BPS method, we will show that the density ratio of 17% is required when the energy spread is 10%. The results were also validated by the DEIRA-4 code. Moreover, the electron-ion equilibrium will decrease up to 9.3 and 4.4% for the LP and BPS methods, respectively. It is demonstrated that the key features of a higher average ion energy as well as the narrow beam profile in the RPA regime may effectively ignite hot spot much better than in the Target Normal Sheath Acceleration (TNSA) counterpart. It is estimated that the proton-Carbon beam proposal can reduce ion beam energy to 8.42 kJ, approximately saving 15% of ignitor energy.     

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.     

Beam loading in the nonlinear regime of plasma-based acceleration

A theory that describes how to load negative charge into a nonlinear, three-dimensional plasma wakefield is presented. In this regime, a laser or an electron beam blows out the plasma electrons and creates a nearly spherical ion channel, which is modified by the presence of the beam load. Analytical solutions for the fields and the shape of the ion channel are derived. It is shown that very high beam-loading efficiency can be achieved, while the energy spread of the bunch is conserved. The theoretical results are verified with the particle-in-cell code OSIRIS.