束团序列发射的相干同步辐射强度数值计算

提出一个新颖的射频电子束团序列在偏转或者摇摆磁场中发射的相干同步辐射相干迭加导致辐射增强的理论模型,并基此分析和计算了利用BFEL装置的3?0MeV射频直线加速器产生的电子束团序列发射的相干辐射增强效应.由讨论可知,不同的束团产生的相干同步辐射之间存在相干性源于束团间的相干性;这种束团间的相干性引起的辐射增强迭加在单个束团产生的相干辐射功率谱上;随着波长的增长,这种辐射增强呈现规则的高速振荡效应;束团间相干性引起的强度增强近似约为宏脉冲内所含束团数的平方.最后提出利用所设计的毫米波Michelson干涉仪检测BFEL装置的电子束团序列的相干性的实验设想.     

合肥光源单束团下束团长度和能散的测量

根据同步光与储存环中的束流信号具有相同的时间结构的原理,测量同步光脉冲的半高全宽值可以计算出束团的长度。根据合肥光源的特点和实际需要,选择快速光电接收器搭配高速高带宽示波器作为在线测量束团长度和纵向分布等的主要手段。对单束团模式下束团长度随流强和高频腔腔压的变化趋势进行了测量。测量结果表明：束团长度与腔压的0.3次方成反比,比理论值0.5小;而束团长度随流强的增长率为2.0 ps/mA。通过测量纵向量子寿命进行了能散随流强变化的间接测量,结果表明,束团的拉伸是能散变化和势阱效应共同作用的结果。     

BEPCⅡ中电子云不稳定性模拟研究

正电子储存环在多束团运行时有可能发生电子云不稳定性(ECI)?.本文针对北京正负电子对撞机二期工程(BEPCⅡ)的具体条件,编写发展了模拟计算程序,以不同电子云密度抑制措施下的计算结果为基础,研究了耦合束团不稳定性和单束团不稳定性,给出了电子云不稳定性增长率和阈值密度以及色品对束团尺寸增长的抑制作用,为储存环中电子云不稳定性的前沿科学研究和BEPCⅡ工程设计提供了有意义的结果.     

First experimental research of the bunch compressor at CAEPLI

Magnetic bunch compressor is one of the key technologies on the path to next generation accelerator driven facilities. In this paper we report the design principles and the first experimental research of the bunch compressor developed at Chinese Academy of Engineering Physics (CAEP). The length of the bunch after compressor is found to be about 0.7 ps (rms) and the peak current exceeds 500 A when operated in the optimized condition. The sensitivity of the bunch length on the phase of the acceleration field and magnetic field of the bunch compressor was also measured and analyzed.     

电光采样(EOS)法测量超短电子束束团长度中的模拟计算与误差分析

随着高能物理的发展, 高能量正负电子对撞机, X射线自由电子激光器, 先进的同步光源等, 都需要产生高流强超短脉冲的相对论电子束团. 于是, 亚皮秒电子束束团诊断成为加速器物理新发展的关键技术, 电子束长度的监测是其中的一部分. 电光采样(EOS)法测量超短电子束团长度有非侵入、非破坏、实时测量的特点, 具有较好的应用前景. 本文介绍该方法的原理, 通过模拟计算分析电子束束团与探测光间距、电子束电场与电光晶体晶轴夹角、探测光偏振方向与电光晶体晶轴夹角等实验参数与束团长度测量的关系, 做系统误差分析, 对实际实验有指导意义.     

First experimental research of the bunch compressor at CAEP

Magnetic bunch compressor is one of the key technologies on the path to next generation accelerator driven facilities. In this paper we report the design principles and the first experimental research of the bunch compressor developed at Chinese Academy of Engineering Physics （CAEP）. The length of the bunch after compressor is found to be about 0.7 ps （rms） and the peak current exceeds 500 A when operated in the optimized condition. The sensitivity of the bunch length on the phase of the acceleration field and magnetic field of the bunch compressor was also measured and analyzed.     

Generation and measurement of sub-picosecond electron bunch in photocathode rf gun

We consider a scheme to generate a sub-picosecond electron bunch in the photocathode rf gun by im-proving the acceleration gradient in the gun, suitably tuning the bunch charge, the laser spot size and the acceleration phase, and reducing the growth of transverse emittance by laser shaping. A nondestructive technique is also reported to measure the electron bunch length, by measuring the high-frequency spectrum of wakefield radiation which is caused by the passage of a relativistic electron bunch through a channel surrounded by a dielectric.     

Possibility of the charge density modulation of an electron bunch in the electromagnetic wave field

We consider the problem of modulation of the electron density in a linear bunch after its interaction with a linearly polarized, monochromatic electromagnetic wave, as well as an opportunity to observe this effect. It is shown that one can achieve significant values of the modulation depth at high intensities of the electromagnetic wave.     

正弦波速调管聚束理论在ns-200加速器上的应用

阐述了正弦波速调管聚束理论及具体实现方法,给出了相应的计算公式。结合ns-200加速器的结构特点,运用该法确定了聚束装置的主要参数：聚束筒长度、等效漂移长度、聚束电压等,为ns-200加速器设计了聚束装置。将该装置安装于加速器,通过调试,获得了半宽为3.5ns的聚束脉冲,实现了纳秒脉冲运行方式。     

合肥光源测量束团纵向精细结构的单光子计数系统设计

本文介绍了用单光子计数法测量束团纵向精细结构的原理.介绍了合肥同步辐射光源测量束团纵向精细结构的单光子计数系统的设计.由于单光子计数法具有高时间分辨率(2ps)和大的动态测量范围(10⁵)等优点,所以该系统不仅可以测量束团长度,而且可以精密测量单束团的纯净度.最后,分析了该系统的性能,并讨论了该系统在尾场和纵向阻抗的研究、束团伸长效应的研究以及影响单束团不纯净机理的研究中的应用.     

可变参数磁压缩系统设计

北京大学30MeV超导加速器包含3个RF加速单元: 自主研发的1.5cell DC-SC(直流-超导)注入器, 经过升级的3.5cell DC-SC注入器, 以及1.3GHz 2×9cell Telsa型超导加速腔. 为充分利用该装置上高品质电子束, 计划压缩1.5cell注入器出口电子束用于产生相干THz光, 以及压缩2×9cell超导加速腔出口电子束产生红外自由电子激光. 通过理论计算及模拟计算相结合设计了一套可变参数磁压缩系统, 该系统可以同时满足两个RF加速单元后束团压缩的要求.     

Calculations for shortening the bunch length in storage rings using a harmonic cavity

Using the Hefei Light Source phase Ⅱ project （HLS- Ⅱ） as an example, a theoretical analysis of shortening the bunch lengths using a higher harmonic cavity （HHC） is given. The threshold voltage of an active HHC and the threshold tuning angle of a passive HHC are first analysed. The optimum tuning angle for the constant detuning scenario and the optimum harmonic voltage for the constant voltage scenario are presented. The calculated results show that the reduced bunch length is about half that of the nominal bunch. The bunch lengths vary from 11 mm at 0.1 A to 7 mm at 0.4 A for the constant detuning scenario, while the bunch lengths are around 7 mm over the beam current range for the constant voltage scenario. In addition, the synchrotron frequency spread is increased. It indicates that HHC may be used to reduce the bunch length and increase the Landau damping of synchrotron oscillations in a storage ring.     

合肥同步辐射光源的束团伸长效应初析

利用新理论,统一阐述了感抗壁效应和微波不稳定性,并着重证明窄带阻抗对束团伸长效应的重要贡献,在此基础上,解释了合肥同步辐射光源的束团伸长效应的初步实验结果,证明了束腔相互作用是导致该光源束团伸长的主要因素。     

粒子束团状态对测量束流发射度及能量的影响

为了验证国产质子注入器的参数是否满足需求,注入器团队设计了束流测量系统用于测量国产质子直线注入器束流的流强、发射度、能量以及能散等关键指标。此测量系统包含了采用变聚焦法测量发散度、采用分析磁铁测量束流能量和能散的主要功能。利用束流输运线设计软件Tracewin(版本2.11.4.1)进行了系统束线的物理设计,对束测系统测量质子束流的发散度和能量的精度进行了模拟计算。由于经过RFQ-(APF)DTL加速后的粒子束团为“拖尾”的非理想粒子束团,需要针对非理想束团对束测系统测量发射度和能量产生的影响进行分析。通过对模拟计算结果的分析,发现相对于测量理想粒子束团的结果非理想粒子束团对束测系统测量发射度精度影响较大;非理想粒子束团对束测系统测量能量精度影响较小。     

Formation of radiation spectrum at the planar channeling of a positron bunch with allowance for the medium inhomogeneity

The radiation of a positron in a planar channel of a crystal is studied, considering the dependence of the medium polarization on the transverse coordinate. The expression for the spectral distribution of the number of radiated photons is obtained for a single positron. It is shown that because of the medium polarization in the soft and hard regions not all positrons make a contribution to the radiation formation. An analytical formula for the total spectral distribution of the number of photons is obtained.     

束团伸长效应的理论研究

论述了束团伸长效应现有理论的不足和困难。在强流条件下,用统计力学理论解出粒子纵向分布函数,从而将目前关于束团伸长现象的平衡理论和微波不稳定性理论用统一的形式加以描述。并且在理论上证明了束团伸长效应在本质上是多束团效应,指出了窄带阻抗对束团伸长效应的重要贡献。     

CTF磁压缩器的误差研究

磁压缩器广泛应用在自由电子激光装置中. 电子束团的归一化发射度增长由二极磁铁的高阶分量误差及准直误差引起. 本文描述了CTF (CXFEL Test Facility)的第一个磁压缩器的误差研究.     

合肥同步辐射光源的束团伸长效应初析

利用新理论，统一阐述了感抗壁效应和微波不稳定性，并着重证明窄带阻抗对束团伸长效应的重要贡献，在此基础上，解释了合肥同步辐射光源的束团伸长效应的初步实验结果，证明了束腔相互作用是导致该光源束团伸长的主要因素。     

单谐振腔束团长度监测器的设计与仿真

提出了一种利用单个谐振腔测量直线加速器束团长度的新方法。不同于传统的双谐振腔束团长度监测器,该方法仅需要使用单个谐振腔,省去了用于辅助测量的参考腔,从而简化了装置结构,节省了空间。针对国家同步辐射实验室基于可调谐红外激光的能源化学研究大型实验装置进行了监测器的物理设计。通过设定同轴探针的插入位置,解决了双模信号互相干扰的问题,利用微扰金属改变调节工作频率,克服了双模难以同时谐振的困难。利用CST软件进行建模和仿真。仿真结果表明,该监测器可实现2～5 ps束团长度的诊断,测量误差小于5%。     

A new method to generate relativistic comb bunches with tunable subpicosecond spacing

We propose and analyze a scheme to produce comb bunches, i.e. a bunch consisting of micro-bunch trains, with tunable subpicosecond spacing. In the scheme, the electron beam is first deflected by a deflecting cavity which introduces a longitudinal-dependent linear transverse kick to the particles. After passing through a drift space, the transverse beam size is linearly coupled to the longitudinal position of the particle inside the beam, and a mask is placed there to tailor the beam, then the mask distribution is imprinted on the beam's longitudinal distribution. A quadrupole magnet and another deflecting cavity are used in the beam line to compensate the transverse angle due to the first deflecting cavity. Analysis shows that the number, length, and spacing of the trains can be controlled through the parameters of the deflecting cavity and the mask. Such electron bunch trains can be applied to an infrared free electron laser, a plasma-wakefield accelerator and a supper-radiance THz source.