Bunch length measurement at Tsinghua Thomson scattering X-ray source

The length of electron beam from a photocathode RF gun is determined by a spectrometer, according to the relative energy spread induced by the bunch length during the acceleration in a linac. For a photocathode RF gun, different laser injected phase and beam charge are studied. The compression is changed for the different laser phases, as from 10° to 30°, and the bunch length is lengthened due to the strong longitudinal space charge force, caused by the increased charge.     

Physics design of a 10 MeV, 6 kW travelling wave electron linac for industrial applications

We present the physics design of a 10 MeV, 6 kW S-band (2856 MHz) electron linear accelerator (linac), which has been recently built and successfully operated at Raja Ramanna Centre for Advanced Technology, Indore. The accelerating structure is a 2π/3 mode constant impedance travelling wave structure, which comprises travelling wave buncher cells, followed by regular accelerating cells. The structure is designed to accelerate 50 keV electron beam from the electron gun to 10 MeV. This paper describes the details of electromagnetic design simulations to fix the mechanical dimensions and tolerances, as well as heat loss calculations in the structure. Results of design simulations have been compared with those obtained using approximate analytical formulae. The beam dynamics simulation with space charge is performed and the required magnetic field profile for keeping the beam focussed in the linac has been evaluated and discussed. An important feature of a travelling wave linac (in contrast with standing wave linac) is that it accepts the RF power over a band of frequencies. Three-dimensional transient simulations of the accelerating structure along with the input and output couplers have been performed using the software CST-MWS to explicitly demonstrate this feature.     

W–band光注入器的模拟研究

模拟研究了1.6个腔、高梯度的W-band光阴极微波电子枪系统,该系统能产生和加速300pC的电子束团.设计系统由频率91.392GHz光阴极微波电子枪以及频率91.392GHz行波加速结构组成.基于射频直线加速器标度律与数值模拟结果,设计系统能产生能量1.74MeV,电量300pC,束团长度0.72ps,归一化横向发射度0.55mm·mrad的电子束团.研究了高频、高梯度下的束流动力学.由于高梯度,有质动力效应在束流动力学中起重要作用,且由于横向与纵向之间的耦合,在基次空间谐波的情形下,仍然存在着有质动力聚焦效应.     

直线加速器中的非线性空间电荷效应和发射度增长

直线加速器中束团的非线性空间电荷效应是引起发射度增长的重要原因之一．根据计算在屏蔽筒中非均匀分布京团的空间电荷效应的普遍方法，推导了直线加速器圆波导中几种非均匀分布束团的非线性场能公式，并给出数值计算结果．讨论了由非线性所引起发射度增长．     

Research on a novel compact linac

This work looks at a new type of electron linear accelerator. Compared with the traditional electron linac, it has only two main parts: a klystron and an accelerating tube, without the electron gun element. This new kind of linac could perform just like its predecesors but reduce cost and space. The preliminary design and simulation have been accomplished. In this paper, an overview discussion about the performance tests and some improvements to increase the beam current are presented.     

Research on a novel compact linac

This work looks at a new type of electron linear accelerator.Compared with the traditional electron linac,it has only two main parts:a klystron and an accelerating tube,without the electron gun element.This new kind of linac could perform just like its predecesors but reduce cost and space.The preliminary design and simulation have been accomplished.In this paper,an overview discussion about the performance tests and some improvements to increase the beam current are presented.     

束流传输管道孔径变化引起的束团场能差

由直线加速器提供的用于自由电子激光(FEL)的电子束团,在其传输过程中常会遇到传输管道孔径变化的情况.本文在电荷密度均匀分布假定下,应用直线加速器中空间电荷束团的有限长柱模型,推导得到了束流传输管道孔径变化引起的束团场能变化及场能差公式.数值计算结果表明,它与国外以往所采用的以连续束流来代表直线加速器中电荷束团而得到的结果,有很大的差别,并且是更符合直线加速器中的电荷束团的实际情况,因而是更精确和可靠的.     

准周期聚焦–加速耦合系统的均温设计方法

强流质子直线加速器要求严格控制束流损失和束流发射度增长.理论已经证明,强的空间电荷作用在不同自由度之间的耦合,会因为其间的温度差异,通过束流的相干不稳定性,使束流发射度增长.因此,有必要按照均温的原则设计强流加速器.但是,由于质子直线加速器的各种加速结构均为准周期耦合系统,使得均温设计十分繁琐而难以达到完全均温.我们利用国际上通用的束流动力学软件TRACE3-D,给它补充了均温设计功能,通过与PARMILA程序的配合使用,可以方便地在加速器设计中实现均温条件.本文将介绍我们对TRACE3-D的修改补充,并以强流质子直线加速器设计实例,说明均温设计的必要性.     

PIC mode simulation of solenoid collimation channel

A new SSC(Separated Sector Cyclotron)-Linac is being designed to serve as an injector for the SSC at the HIRFL(Heavy Ion Research Facility Lanzhou).The beam intensity at the LEBT(Low Energy Beam Transport)for the heavy ions after the selection is typically low and the space charge effects are inconspicuous.The space charge effects become obvious when the beam current increases to a few hundred microamperes.The emittance growth deriving from the space charge effects may be particularly troublesome for the following linac and cyclotron.An optical system containing three solenoids has been designed for the LEBT to limit the beam emittance and to avoid the unnecessary beam loss in the cyclotron,as well as for the purpose of immunizing the LEBT emittance growth due to the space charge effects.The results of the PIC(Particle-In-Cell)mode simulation illustrate that this channel could limit the beam emittance growth and increase the beam brightness.     

The Effect of High Spatial Harmonics in RF Linac

The effect of high spatial harmonics on beam dynamics in a axisymmetric radio frequency linear accelerator (RF linac) is examined. The high spatial harmonics forms the second order ponderomotive focusing for the relativistical particle beam when the transverse motion is averaged over the period of RF structure, the beam transverse envelop equation is obtained including the ponderomotive focusing force which is useful for the design of RF gun and linac. Under a certain of high spatial harmonics coefficients, the high spatial harmonics increase the energy spread due to the stochasitical beam energy diffusion.     

100 MeV电子直线加速器的物理设计

 能量为100 MeV左右的高性能电子直线加速器是第三代同步辐射光源注入器和自由电子激光注入器的重要组成部分,采用热阴极栅控电子枪、聚束系统和4根SLAC型加速管作为加速器主体结构,一套45 MW的速调管调制器系统和波导系统作为微波功率源系统。设计中,使用了国际通用的模拟软件对加速器的动力学特性进行了数值模拟和参数优化,电子束能量达到100 MeV以上,能散小于1%,归一化发射度小于30 mm·mrad。     

BEPCⅡ Positron Source

BEPCⅡ— an upgrade project of the Beijing Electron Positron Collider (BEPC) is a factory type of e^＋e^－ collider. The fundamental requirements for its injector linac are the beam energy of 1.89GeV for on-energy injection and a 40mA positron beam current at the linac end with a low beam emittance of 1.6μm and a low energy spread of ±0.5% so as to guarantee a higher injection rate (≥50mA/min) to the storage ring. Since the positron flux is proportional to the primary electron beam power on the target, we will increase the electron gun current from 4A to 10A by using a new electron gun system and increase the primary electron energy from 120MeV to 240MeV. The positron source itself is an extremely important system for producing more positrons, including a positron converter target chamber, a 12kA flux modulator, the 7m focusing module with DC power supplies and the support. The new positron production linac from the electron gun to the positron source has been installed into the tunnel. In what follows, we will emphasize the positron source design, manufacture and tests.     

微脉冲电子枪的动力学研究

 利用SEEG程序模拟计算了微脉冲电子枪束流动力学问题。在不考虑空间电荷效应的情况下，模拟了在微脉冲电子枪中电子纵向聚束的过程。进而详细研究了在空间电荷效应作用及相聚过程共同作用下形成饱和电流的过程。在此基础上，给出了经过优化后的微脉冲电子枪腔型特性,使用SEEG程序对该枪进行束流动力学模拟计算。最后给出一个实验用微脉冲电子枪的物理设计。     

A Particle-in-cell scheme of the RFQ in the SSC-Linac

A 52 MHz Radio Frequency Quadrupole(RFQ)linear accelerator(linac)is designed to serve as an initial structure for the SSC-Linac system(injector into Separated Sector Cyclotron).The designed injection and output energy are 3.5 keV/u and 143 keV/u,respectively.The beam dynamics in this RFQ have been studied using a three-dimensional Particle-In-Cell(PIC)code BEAMPATH.Simulation results show that this RFQ structure is characterized by stable values of beam transmission efficiency(at least 95%)for both zerocurrent mode and the space charge dominated regime.The beam accelerated in the RFQ has good quality in both transverse and longitudinal directions,and could easily be accepted by Drift Tube Linac(DTL).The effect of the vane error and that of the space charge on the beam parameters have been studied as well to define the engineering tolerance for RFQ vane machining and alignment.     

SSC-LINAC重离子RFQ动力学模拟与研究

采用多粒子跟踪程序BEAMPATH 对SSC-LINAC 重离子RFQ 直线加速器进行动力学模拟,分别对RFQ 的接受度、高频特性、束流稳定性、空间电荷效应等进行了分析。该RFQ具有很大的纵向接受度,有利于束流在RFQ中的传输;高频特性研究表明,翼间电压设定在理论值以上时,该RFQ都能保持较好的束流特性;束流稳定性分析结果表明,该RFQ具有很大的束流失配容忍度;空间电荷效应研究表明,当束流强度低于0.5 mA时,束流传输不受影响。综合研究结果表明,53.667 MHz重离子RFQ具有较好的动力学特性,满足SSC-LINAC直线加速器的设计要求。The RFQ beam dynamics of a heavy ion linac was investigated in this paper and the BEAMPATH code was employed in this study. The main research was focused on the beam performances depending on longitudinal acceptance, RF properties, beam instability and space charge effect. The RFQ has large longitudinal acceptance in design, which brings the beam performances well. In the RF parameter study, the beam can keep good transmission in the acceleration even the vane voltage is larger than the theoretical value. It is also shown that the RFQ has a large robustness for the mismatch of the input beam by the analysis of the beam instability.Furthermore, the beam evolution is independent on the space charge effect when the beam current is less than 0.5 emA. The preliminary analysis of the beam dynamics shows that the 53.667 MHz heavy ion RFQ has a promising performance, which meets the requirements of SSC-LINAC.     

HIRFL-CSR电子冷却系统空心电子束性能研究

 电子冷却系统中冷却力的大小与电子束的温度密切相关。由于强流电子束自身产生的空间电荷场,使得电子束的速度离散,增加了电子束温度,降低了冷却效率。为了减小空间电荷效应,HIRFL CSR的电子冷却系统将首次采用空心电子束对储存环中的重离子束流进行冷却。通过分析实心电子束和空心电子束的空间电荷场,研究了其对电子束速度和温度的影响。     

直线加速器中双向高斯密度分布电荷束团发射度增长的比率关系

采用直线加速器中的空间电荷束团的有限圆柱模型，并假设该有限圆柱体电荷密度分布在横向ｒ和纵向ｚ都满足高期分布，推导得到了该电荷束团的自场能与发射度增长公式；通过数值模拟计算，给出了束流发射度增长随束团参数和加速器系统参数变化的图表曲线，讨论了该双向高期密度分布电荷束团发射度增长的比率关系．     

S波段6 MeV边耦合电子直线加速器的设计研究（英文）北大核心CSCD

近年来,对紧凑、稳定及可靠型电子直线加速器的需求越来越多,其能量主要分布在几百keV到十几个MeV的范围内,其中需求最多的则是能量在MeV量级的微波电子直线加速器。在这种形势下,中国科学院高能物理研究所正在研制一台S波段6 MeV的边耦合电子直线加速器,本文对基于该加速器的模拟计算研究进行了介绍。EGUN和HFSS分别用来设计电子枪和边耦合加速结构。通过将EGUN计算得到的电子束流参数和HFSS计算得到的三维电磁场分布数据引入到PARMELA中,完成了对该加速器的多粒子动力学研究。模拟结果显示,所设计的加速器完全能够满足设计指标的要求。最终,在考虑束流负载效应的因素后,完成了边耦合加速结构的微波结构设计。     

Emittance coupling driven by space charge in the CSNS linac

In the conventional design of RF linacs, the bunched beams are not in thermal equilibrium. The space charge forces couple the particle motions between the transverse and the longitudinal directions. Fur-thermore it will cause the equipartitioning process which leads to emittance growth and halo formation. In the design of the China Spallation Neutron Source (CSNS) linac, three cases are investigated using the Hofmann stability charts. In this paper, we present the equipartitioning beam study of the CSNS Alvarez DTL linac.     

NEPCⅡ新电子枪热结构分析与测试

北京正负电子对撞机重大改造工程(BEPCⅡ)要求其直线注入器提供更高的能量和流强, 为此必须设计大电流和小发射度的新电子枪, 以提高正电子的产额. 利用ANSYS对BEPCⅡ新电子枪的温度场分布及结构的热变形进行了模拟分析. 对于电子枪复杂的内部结构形态以及能量转换方式, 分析了传导传热方式对温度场的影响. 在此基础上进行了温度场与结构变形的耦合分析, 利用EGUN对电子枪形变前后束流光学特性进行模拟分析, 并对模拟结果与试验 测试结果进行了分析比较.