PIC方法在RFQ加速器z-code和t-code模拟程序中的应用研究

本文介绍了二维PIC(Particle in cell)方法,这种方法常用于粒子动力学模拟中空间电荷作用的计算。并比较了以时间为自变量(t-code)和以纵向位置为自变量(z-code)的两种动力学模拟程序;针对“国家重点基础研究发展规划”洁净核能项目中的射频四极(RFQ)加速器结构参数,给出了单束加速和正、负离子束同时加速两种情况下,t-code和z-code模拟得出的传输效率。结果表明,当束团的相位宽度大或能散大时,z-code在计算空间电荷作用时会引入相对较大的误差,从而应该使用t-code来进行动力学模拟,以获得更准确的结果。     

RFQ accelerators for ion implantation

Radiofrequency quadrupoles (RFQs) are low-energy rf accelerator structures which can efficiently transport and accelerate high-current ion beams. For a wide range of applications, RFQs can be designed that, like all rf accelerators, have a fixed output energy per amu, that can be varied by independently phased postaccelerator cavities. An attractive new development is an RFQ structure with variable energy which is achieved by frequency variation. The status of the work on fixed- and variable-energy RFQ applications is presented.     

分段共振耦合RFQ场调谐方法研究

强流质子加速器需要采用分段共振耦合RFQ作为其低能加速结构,为减少束流损失,RFQ加速器必须达到所要求的场分布。针对共振耦合结构的特殊性,在RFQ传输线模型的理论基础上,在一台RFQ冷模型上进行了场调谐的实验研究,获得了满意的实验结果。同时,也验证了作者用LabView编写的RFQ场调谐程序的正确性。     

Design study of a multibeam type IH-RFQ linac to accelerate high intensity and low energy heavy ion beams

A multibeam Radio Frequency Quadrupole (RFQ) linac with an Interdigital H-mode (IH) structure has been developed for high intensity heavy-ion beam acceleration. The defocusing force of space charge effect is proportional to the beam current and to the inverse square of the beam velocity. Therefore, multibeam acceleration is an attractive scheme to suppress this in the low energy region. The electromagnetic field distribution and the beam dynamics were studied for a prototype. We discuss the configuration of the multibeam IH-RFQ linac and the results of these simulations.     

Simulation of a low energy beam transport line

A 2.45 GHz electron cyclotron resonance intense proton source and a low energy beam transport line with dual-Glaser lens were designed and fabricated by Institute of Modern Physics for a compact pulsed hadron source at Tsinghua. The intense proton beams extracted from the ion source are transported through the transport line to match the downstream radio frequency quadrupole accelerator. Particle-in-cell code BEAMPATH was used to carry out the beam transport simulations and optimize the magnetic field structures of the transport line. Emittance growth due to space charge and spherical aberrations of the Glaser lens were studied in both theory and simulation. The results show that narrow beam has smaller aberrations and better beam quality through the transport line. To better match the radio frequency quadrupole accelerator, a shorter transport line is desired with sufficient space charge neutralization.     

CSNS/LRBT优化设计及空间电荷效应影响研究

中国散裂中子源（CSNS）直线加速器至快循环同步加速器（RCS）的束流输运线（LRBT）传输80 MeV H^-束流至RCS注入点,由于较小的束流发射度和较高的峰值流强,空间电荷效应在LRBT中的影响非常显著,是引起LRBT中发射度增长和束流损失的主要因素,也是LRBT优化设计中的重要问题。文章利用TRACE 3-D程序进行带有空间电荷效应的twiss参量和消色散匹配,比较研究LRBT不同聚焦结构和不同初始束流分布条件下发射度的增长情况。对于采用Triplet结构作为标准单元的结构,研究发现,通过优化LRBT前端匹配段能有效控制发射度的增长。多粒子模拟跟踪结果表明,峰值流强为15 mA时,现有物理孔径下基本无束流损失发生。对LRBT上散束器的参数和位置进行了优化设计,可减少动量散度和中心能量抖动,优化RCS注入束流参数。     

Assessment of pulse height defect in passivated implanted planar Si detectors used for channeling measurements with slow, highly charged heavy projectiles

The pulse height defect (PHD) of slow, highly charged ¹²C, ¹⁶O, ⁴⁰Ar and ⁸⁴Kr ions in a passivated implanted silicon detector has been measured. The detector is part of the channeling setup at the Frankfurt ECR/RFQ installation for beams of highly charged ions. In this experiment the modification of the charge states under channeling conditions in thin silicon membranes is measured. The charge states of the scattered ions are separated by post-acceleration. The PHD is an important input for the energy calibration. It allows the analysis via a parametrization which relates it to the true energy and the order number of the ions through a simple power law.     

CSRe分子离子研究装置低能传输线物理设计

本文完成了CSRe分子离子研究装置低能传输线的物理设计。采用Poisson/Superfish软件对150 kV倍压型高压加速器的电场分布进行了模拟,结果显示,加速器各区域空间电场强度均远低于击穿电场强度限值。利用Beampath程序对离子源引出的分子离子束在高压加速器中的传输进行了模拟,束流包络显示,加速区电场对分子离子束具有较强的聚焦作用,加速管出口束斑尺寸较小。采用Trace-3D程序设计了高分辨能力的磁分析系统和RFQ加速器的注入匹配段。通过Beampath程序的模拟,分析出了质量数为150的分子离子束,并由三单元四极透镜实现了分析束流与直线加速器RFQ的注入匹配。     

Numerical Simulation of the Effect of the Beam Space Charge on the Acceptance of a Storage Ring

A model based on the assumption that there exists a stationary particle distribution in the space of invariants is used to investigate numerically the effect of the space charge of a beam in storage rings. The model is used to develop a computer code that makes it possible to use a personal computer to investigate the dependence of the acceptance on the beam current, betatron frequency, and other machine parameters. The structure of the code and the results obtained using it for the ACR storage ring (RIKEN, Japan) and the accelerator-storage system at the Institute of Theoretical and Experimental Physics are described. The computational results show that this computer code is an effective tool for calculating and optimizing the parameters of high-current storage rings.     

Feasibility of an epithermal neutron source for BNCT based on RFQ accelerator

The use of boron neutron capture therapy for the treatment of deep-seated tumours, such as glioblastoma multiforme, requires neutron beams of suitable energy and intensity. The analysis of the therapeutic gain shows that a high tumour control probability with sublethal dose at healthy tissues can be achieved, in most cases, by using neutron beams of a few keV energy, with a flux of about 10⁹ neutrons/cm² s. Therapeutic neutron beams with high-spectral purity in this energy range could be produced by accelerator-based neutron sources through a suitable neutron-producing reaction. We investigate the feasibility of a solution based on a small radio frequency quadrupole for a proton beam current of 30 mA and an energy of 2 MeV. An appropriate choice of the function parameters of the RFQ (modulation, efficiency of acceleration, phase shift, etc., …) allows one to design relatively compact accelerators, which could eventually lead to setup hospital-based BNCT facilities.     

高流强RFQ质子加速器研制

在国家“973”计划洁净核能项目的支持下,中国科学院高能物理研究所与中国原子能科学研究院合作,建成了我国首台强流质子加速器。它是1台四翼型结构的射频四极（radio-frequencyqaudrupole,RFQ）加速器,这种先进加速结构可为来自离子源的低能强流束提供周期性强聚焦,并同时在纵向对束流进行聚束和加速。我国建成的这台RFQ加速器束流能量为3.5MeV,脉冲流强达46mA,束流工作比大于7%。本文将介绍这台RFQ加速器的物理设计、研制、调试和出束实验的结果。     

An ECR-RFQ ion beam facility for materials research with highly charged slow ions

An ion beam facility is described which can produce intense beams of very highly charged ions with variable energy in the keV and MeV regime. This facility consists of an electron cyclotron resonance ion source (ECR) and a radiofrequency quadrupole accelerating structure (RFQ). It provides a relatively cheap and compact device for material research with highly charged ions at surfaces as well as for deep-lying solid layers.     

Beam dynamics design and electromagnetic analysis of 3 MeV RFQ for TAC Proton Linac

A beam dynamics design of 352.2 MHz radio-frequency quadrupole(RFQ) of Turkish Accelerator Center(TAC) project which accelerates continuous wave(CW) proton beam with 30 m A current from 50 ke V to3 Me V kinetic energy has been performed in this study. Also, it includes error analysis of the RFQ, in which some fluctuations have been introduced to input beam parameters to see how the output beam parameters are affected, two-dimensional(2-D) and three-dimensional(3-D) electromagnetic structural design of the RFQ to obtain optimum cavity paramaters that agree with the ones of the beam dynamics. The beam dynamics and error analysis of the RFQ have been done by using LIDOS.RFQ. Electromagnetic design parameters have been obtained by using SUPERFISH for 2-D cavity geometry and CST Microwave Studio for 3-D cavity geometry.     

53.667 MHz重离子RFQ的不稳定性研究

采用多粒子跟踪程序BEAMPATH对53.667 MHz RFQ进行模拟计算,基于RFQ腔体冷测、机械测量的结果,在考虑其入口束流不稳定性、电压不平整度、高频系统稳定度、加工误差、安装误差等因素的情况下,对RFQ的出口束流品质和不稳定性进行了系统分析。结果表明,在现有的加工、安装水平下,提高RFQ入口束流稳定度和高频系统稳定度对束流在RFQ中的传输十分必要。     

A drift tube accelerating structure for CRYRING

A conceptual design has been developed for a driven (non-resonant) drift-tube (DD-T) accelerating structure for CRYRING. Because the ring is small and accelerating voltage requirements not too large, it is possible to use a DD-T to cover the broad frequency range required at modest cost. The control of the system requires only a frequency signal from a beam position pick up and a voltage level signal. With the DD-T can be provided nonsinusoidal wave forms for bunch shaping to improve the space charge limit. A full scale low power model was used to verify the essential features of the design.     

RFQ加速器高频测量软件和分析软件开发

强流RFQ加速器要求严格控制束流损失和束流发射度增长,因此必须准确测量和正确分析RFQ加速器的场分布和模式的场分量,并使它们符合设计要求。LebView是一个广泛应用于自动测量和数据处理的计算机软件平台,介绍了在此平台上开发的RFQ自动测量软件和数据分析软件,同时给出这些软件的一些应用实例。     

14MeV医用同源双模中能电子直线加速管的研制

医用同源双模中能电子直线加速管是影像引导放射治疗技术(Image Guide Radiation Therapy,IGRT)中的核心部件,为确保放射治疗直线加速器能够提供稳定和高品质的成像射束、双光子模式治疗射束以及多档电子射束,上海联影医疗科技有限公司研制了基于一种新型的能量开关技术的14 Me V医用双模驻波加速管。采用束流动力学程序Parmela对加速管整管的横向聚焦和纵向聚束进行了动力学设计分析,为优化加速管腔体几何结构提供了指标要求,最终利用电磁场仿真软件Superfish及CST(Computer Simulation Technology)优化腔体结构设计并得到了最优的微波参数。模拟计算结果表明,该加速管总长1.3 m,采用边耦合双周期?/2驻波结构,工作频率2.998 GHz,其输出束流能量可以实现多档可调,成像模式可输出低于3 MV的光子,治疗束可输出具有6 MV和10 MV两档的光子及4档能量电子束(最高能量可达14 Me V)。完成加工后,冷测结果与设计值符合得比较好,下一步将进行高功率微波老练。     

Experimental verification of an APF linac for a proton therapy facility

Alternating phase focusing (APF) is known as a beam focusing method; it was applied to an interdigital H-mode structure and successfully accelerated high current proton beams up to the desired energy for a medical synchrotron injector. A high-current APF linac was achieved by the optimal design of the cavity and the drift tubes themselves, as well as drift tube arrangement based on the co-iteration of a precise electromagnetic field and space charge beam dynamics.A proton injector for a medical accelerator complex was fabricated with the newly developed APF linac. The injector consists of an electron cyclotron resonance ion source, a radio-frequency quadrupole linac and the APF linac. The experimental results showed that over 10 mA proton beams were accelerated up to 7.4 MeV.     

Two-plane painting injection scheme for BRing of HIAF

The high-intensity heavy-ion accelerator facility(HIAF)is under design at the Institute of Modern Physics(IMP)and will provide an intense ion beam for nuclear physics,atomic mass measurement research,and other applications.As the main ring of HIAF,the BRing accumulates beams to high intensity and accelerates them to high energy.To achieve high intensities up to 1×10~(11)(~(238)U~(34+)),the injection gain of the BRing must be as high as 88.However,multiple multiturn injection supported by the electron cooling system takes a long time,causing substantial beam loss under a strong space charge effect.Hence,a two-plane painting injection scheme is proposed for beam accumulation in the BRing.This scheme uses a tilted injection septum and horizontal and vertical bump magnets to paint the beam into horizontal and vertical phase space simultaneously.In this paper,the two-plane painting injection parameters are optimized,and the resulting injection process is simulated using the Objective Ring Beam Injection and Tracking(ORBIT)code.An injection gain of up to 110.3 with a loss rate of 2:3%is achieved,meeting the requirements of BRing.