Nonlinear processes of probe formation of a beam with inhomogeneous phase density at nuclear microprobe

The work describes nonlinear processes of probe formation on the target with allowance for an inhomogeneous density of ion distribution in phase space in the object collimator plane taken from experimental data. The chromatic aberrations, intrinsic aberrations of the 3rd order and parasitic aberrations caused by sextupole and octupole components of the magnetic quadrupole lens field have been taken into account in the object-target phase coordinate transformation. The criterion of obtaining the optimal resolution was defined as the minimum spot size (FWHM) for a fixed ratio I_FWHM/I₀ of beam current in this spot to the total beam current. The conditions for which the initial density of ion distribution in phase space is matched with the ion-optical characteristics of the probe-forming system were considered. The influence of axial brightness and parasitic sextupole and octupole field components on the beam current distribution at the target has been determined.     

强流加速器D-Be中子源中子慢化引出研究

为优化成像中子束注量率和能谱,在考虑中子源能谱、角分布、面源结构及靶系统条件下,利用MCNP程序模拟源中子的慢化和输运过程,记录不同模型时慢化体内热中子注量率分布和成像中子束成分。结果表明,聚乙烯更适合用作小型热中子源慢化反射材料;D+束轰击靶面的束斑大小影响热中子在慢化体内的分布,束斑半径在1cm内变化对中子慢化影响较小;增加热中子引出孔道与D+束轴线的夹角能有效提高引出热中子束的纯度。     

First results obtained using the CENBG nanobeam line: Performances and applications

A high resolution focused beam line has been recently installed on the AIFIRA (“Applications Interdisciplinaires des Faisceaux d’Ions en Région Aquitaine”) facility at CENBG. This nanobeam line, based on a doublet-triplet configuration of Oxford Microbeam Ltd. OM-50™ quadrupoles, offers the opportunity to focus protons, deuterons and alpha particles in the MeV energy range to a sub-micrometer beam spot. The beam optics design has been studied in detail and optimized using detailed ray-tracing simulations and the full mechanical design of the beam line was reported in the Debrecen ICNMTA conference in 2008. During the last two years, the lenses have been carefully aligned and the target chamber has been fully equipped with particle and X-ray detectors, microscopes and precise positioning stages. The beam line is now operational and has been used for its first applications to ion beam analysis. Interestingly, this set-up turned out to be a very versatile tool for a wide range of applications. Indeed, even if it was not intended during the design phase, the ion optics configuration offers the opportunity to work either with a high current microbeam (using the triplet only) or with a lower current beam presenting a sub-micrometer resolution (using the doublet-triplet configuration).The performances of the CENBG nanobeam line are presented for both configurations. Quantitative data concerning the beam lateral resolutions at different beam currents are provided. Finally, the first results obtained for different types of application are shown, including nuclear reaction analysis at the micrometer scale and the first results on biological samples.     

基于束流环形高斯模型对上海硬X射线自由电子激光装置的束流刮束器进行活化分析

在建的上海硬X射线自由电子激光装置(Shanghai HIgh repetition rate XFEL aNd Extreme light facility,SHINE)的加速器隧道内,采用束流刮束器刮掉束晕外围张角比较大的电子,刮束器的束流损失率为0.1‰。本文采用蒙特卡洛程序FLUKA,用SOURCE程序实现电子束在3σ_beam外的高斯分布,以尽量真实模拟电子在束流刮束器处的丢失情况,解决了低功率刮束情况下蒙特卡洛模拟无统计性结果的难题。利用束流环形高斯模型对刮束器的活化进行了分析,结果表明环形高斯模型可以更真实地再现电子在束流刮束器的丢失情况;5年运行后距刮束器30 cm处的剩余剂量率达到了数百μSv/h至数mSv/h,和国外类似装置计算结果相当;通过对放射性核素的种类分析,结果证明刮束器(钨)的放射性废物处置难度不大。     

强流束晕-混沌的模糊逻辑控制研究

以周期性磁场聚焦传输通道中的K-V(Kapchinskij-Vladimirskij)分布离子束为例,引入带偏置的升余弦函数近似刻画实际磁场,理论分析了通道中强流离子束的束晕-混沌动力学行为。针对束晕-混沌的控制问题,提出了束晕-混沌的模糊逻辑控制方法。模糊控制器采用Mamdani推理系统,其输出作为控制因子线性调整外部磁场强度。用模糊相平面法分析了控制系统的稳定性。仿真结果显示：在控制条件下,混沌变化的束包络半径被稳定控制;将该方法应用于多粒子模型,消除了束晕及其再生现象,束的品质获得较大提高。该模糊控制方法具有不依赖束输运数学模型、控制器简单、磁场调节呈线性关系、易于工程实现等优点。     

Consideration about the Single-neutron Microbeam Facility

A conception of the single-neutron microbeam facility was put forward in this paper. The specific particle (e.g. H^ , ^2d^ or α ) bombarding a specific target can generate neutron, when the particle energy is more than a threshold (e.g., H^ energy is more than 2 MeV). And if the specific beam spot on the target is very small, the neutron beam along the direction of the specific beam spot will be very small too. If the neutron beam is weak and a neutron detector is mounted after the specific neutron collimator, the single- neutron will be obtained. Therefore, if the specific target and the neutron detector are installed after the proton accelerator and the microbeam system, the single-neutron microbeam will probably be obtained.     

利用多毛细管准直器测量X射线光源焦斑尺寸

设计了一种测量X射线光源焦斑尺寸的方法：多毛细管准直器法。整体玻璃毛细管X射线准直器是由数10⁵根内径为几微米的单玻璃毛细管组成的X射线光学器件,X射线光源发出的发散X射线光束被多毛细管准直器约束后变为准平行束。准平行束的截面直径是X射线光源焦斑直径的函数,通过测量准平行束不同位置处的截面直径,利用线性拟合可得到X射线光源的焦斑直径。分别利用多毛细管准直器法和常用的小孔成像法测量了同一微焦斑X射线光源的焦斑直径,测量结果分别为60.8和59.4μm。多毛细管准直器法对焦斑直径在亚微米量级或更小X射线源的焦斑尺寸测量中将显示出更多的优势。     

400 kV强流中子发生器的物理设计

对400 kV强流中子发生器进行了物理设计。采用Poisson/Superfish软件对中子发生器高压电极和加速管的电场分布进行了模拟,结果显示,各关键区域的空间电场最大值远低于击穿电场限值。以强流束旁轴包络方程为基本模型,发展了强流束传输系统束包络的计算机模拟程序IONB1.0,模拟了中子发生器传输系统中40 mA的D束流包络。结果显示,设计方案中所采取的两间隙高梯度加速结构有较强的聚焦性能,能有效抵消强流束空间电荷效应造成的束流发散,加速管出口处的束包络半径约3 cm,由加速管出口处的空间电荷透镜和三重四极磁透镜组成的传输系统能将束流聚焦在约140 cm处的靶上,且束斑直径小于2 cm。     

Investigations on the time evolution of the plasma density in argon electron-beam plasma at intermediate pressure

The time evolution of the argon electron-beam plasma at intermediate pressure and low electron beam intensity was presented.By applying the amplitude modulation with the frequency of 20 Hz on the stable beam current,the plasma evolution was studied.A Faraday cup was used for the measurement of the electron beam current and a single electrostatic probe was used for the measurement of the ion current.Experimental results indicated that the ion current was in phase with the electron beam current in the pressure range from 200 Pa to 3000 Pa and in the beam current range lower than 20 mA,the residual density increased approximately linearly with the maximum density in the log-log plot and the fitting coefficient was irrelative to the pressure.And then three kinds of kinetic models were developed and the simulated results given by the kinetic model,without the consideration of the excited atoms,mostly approached to the experimental results.This indicated that the effect of the excited atoms on the plasma density can be ignored at intermediate pressure and low electron beam current intensity,which can greatly simplify the kinetic model.In the end,the decrease of the plasma density when the beam current was suddenly off was studied based on the simplified model and it was found that the decease characteristic at intermediate pressure was approximate to the one at high pressure at low electron beam intensity,which was in good accordance with the experimental results.     

The plume diagnostics of 30 cm ion thruster with an advanced plasma diagnostics system

In order to achieve a better understanding of plume characteristics of LIPS-300 ion thruster, the beam current density, ion energy and electron number density of LIPS-300 ion thruster plume are studied with an Advanced Plasma Diagnostics System(APDS) which allows for simultaneous in situ measurements of various properties characterizing ion thruster, such as plasma density, plasma potential, plasma temperature and ion beam current densities, ion energy distribution and so on. The results show that the beam current density distribution has a double‘wing' shape. The high energy ions were found in small scan angle, while low energy ions were found in greater scan angle. Electron number density has a similar shape with the beam current density distribution.     

扫描式质子束剂量分布成像仪的研制及性能分析

在重离子癌症治疗技术中,保证重离子束的质量（均匀性、束斑大小和位置、能量等）非常重要。为满足临床对重离子束质量的要求,本文设计了一种新型质子束剂量分布成像仪。该剂量分布成像仪基于闪烁屏、镜面反射屏与光学信号采集装置,将重离子束通过硫氧化钆闪烁屏转化为可见光,通过采集可见光信号,对重离子束予以质量控制。同时通过精密的电动位移平台对闪烁屏、镜面反射屏与光学信号采集装置的相对位置进行遥控从而调整设备视野。结果表明,该剂量分布成像仪在布拉格峰后沿的能量分辨率为0.22 mm等效水深,空间分辨率为0.35 mm,对单一光源响应的均匀性在图像视野中心10 cm×10 cm的区域内为±3.5%,并可通过算法对测量结果进行修正。该剂量分布成像仪能完成对重离子束质量的各项关键指标的测试,可用于医用质子束的质量控制。     

Enhancement of proton collimation and acceleration by an ultra-intense laser interacting with a cone target followed by a beam collimator

A special method is proposed of a laser-induced cavity pressure acceleration scheme for collimating, accelerating and guiding protons, using a single-cone target with a beam collimator through a target normal sheath acceleration mechanism. In addition, the problems involved are studied by using two-dimensional particle-in-cell simulations. The results show that the proton beam can be collimated, accelerated and guided effectively through this type of target. Theoretically, a formula is derived for the combined electric field of accelerating protons. Compared with a proton beam without a beam collimator, the proton beam density and cut-off energy of protons in the type II are increased by 3.3 times and 10% respectively. Detailed analysis shows that the enhancement is mainly due to the compact and strong sheath electrostatic field, and that the beam collimator plays a role in focusing energy. In addition, the simulation results show that the divergence angle of the proton beam in type II is less than 1.67 times that of type I. The more prominent point is that the proton number of type II is 2.2 times higher than that of type I. This kind of target has important applications in many fields, such as fast ion ignition in inertial fusion, high energy physics and proton therapy.     

微波离子源聚焦离子束光学系统的研究

设计了一种微波离子源的聚焦离子束光学系统,分析计算了光学系统的束径。并数值模拟了由空间电荷作用造成的束径增宽效应,找出了影响束斑大小的主要因素和减小束径的方法。测试结果表明,在束能在２５ｋｅＶ时,束流为１４８ｎＡ,束径约为２０μｍ左右。     

Thermal analysis and tests of W/Cu brazing for primary collimator scraper in CSNS/RCS

To the transverse beam collimation system in a rapid cycling synchrotron,an important component is the primary collimator,which improves emittance of the beam halo particles such that the particles outside the predefined trajectory can be absorbed by the secondary collimators.Given the material properties and power deposition distribution,the beam scraper of the primary collimator is a0.17 mm tungsten foil on a double face-wedged copper block of 121.5 mm x 20 mm.The heat is transferred to the outside by a φ34 mm copper rod.In this paper,for minimizing brazing thermal stress,we report our theoretical analysis and tests on brazing the tungsten and copper materials which differ greatly in size.We show that the thermal stress effect can be controlled effectively by creating stress relief grooves on the copper block and inserting a tungsten transition layer into the copper block.This innovation contributes to the successful RD of the primary collimator.And this study may be of help for working out a brazing plan of similar structures.     

Analysis of an electrostatic column used to produce a microfocused ion beam

This paper presents an analysis of a column employing an asymmetric three-element electrostatic lens and a liquid metal ion source designed to produce a microfocused gallium ion beam. The study includes both theoretical calculations and experimental measurements from working columns. Even though the column design has low chromatic aberration, the spot size is dominated by this aberration throughout the usual range of operation. The column can generate gallium current densities in excess of 1.5 A/cm² into a 0.2 μm spot size.     

箍缩反射离子二极管产生的强流脉冲离子束特性

通过对离子束流密度分布的测量和对被离子束轰击的铜箔不同半径处表面微观形貌的分析,研究了200kV箍缩反射离子二极管产生的离子束特性。结果表明：轴线上离子束流密度最大。     

Experiment and analysis of the neutralization of the electron cyclotron resonance ion thruster

An electron cyclotron resonance ion thruster must emit an electron current equivalent to its ion beam current to prevent the thruster system from being electrically charged.This operation is defined as neutralization.The factors which influence neutralization are categorized into the ion beam current parameters,the neutralizer input parameters,and the neutralizer position.To understand the mechanism of neutralization,an experiment and a calculation study on how these factors influence thruster neutralization are presented.The experiment results show that the minimum bias voltage of the neutralizer was-60 V at the ion beam current of 80 mA for the argon propellant,and a critical gas flow rate existed,below which the coupling voltage increased sharply.Based on the experiment,the neutralization was analyzed by means of a onedimensional calculation model.The computation results show that the coupling voltage was influenced by the beam divergence and the negative potential zone near the grids.     

The effects of beam line pressure on the beam quality of an electron cyclotron resonance ion source

The results of a series of measurements studying the possibility to use neutral gas feeding into the beam line as a way to improve the quality of the heavy ion beams produced with an electron cyclotron resonance ion source (ECRIS) are presented. Significant reduction of the beam spot size and emittance can be achieved with this method. The observed effects are presumably due to increased space charge compensation degree of the ion beam in the beam line section between the ion source and the analyzing magnet. This is the region where the neutral gas was injected. It is shown that the effects are independent of the ion source tuning. Transmission measurements through the beam line and K-130 cyclotron have been carried out to study the effects of improved ion beam quality to the transmission efficiency.     

Numerical Study on the Two-Dimensional Temperature Fields of Titanium/Aluminum Double-Layer Target Irradiated by High-Intensity Pulsed Ion Beam

Interaction between high-intensity pulsed ion beam (HIPIB) and a double-layer target with titanium film on top of aluminum substrate was simulated. The two-dimensional nonlinear thermal conduction equations, with the deposited energy in the target taken as source term, were derived and solved by finite differential method. As a result, the two-dimensional spatial and temporal evolution profiles of temperature were obtained for a titanium/aluminum double-layer target irradiated by a pulse of HIPIB. The effects of ion beam current density on the phase state of the target materials near the film and substrate interface were analyzed. Both titanium and aluminum were melted near the interface after a shot when the ion beam current density fell in the range of 100A/cm2 to 200A/cm2.