Multislit-Based Emittance Measurement of Electron Beam from a Photocathode Radio-Frequency Gun

Measurement of emittance for a space-charge dominated electron beam from a photocathode rf gun is performed by employing the multislit-based method at Accelerator Laboratory of Tsinghua University. We present the design considerations on the multislit system and the experimental results, with special attention to the study of space charge induced emittance growth. The experimental results are in reasonable agreement with the PARMELA simulations.     

北京大学高平均流强光阴极电子枪驱动激光系统

DC-SC超导光阴极注入器将直流光阴极电子枪和超导加速腔结合在一起,其特点之一是适合于提供高平均流强电子束.文中介绍了直流光阴极电子枪的驱动激光系统的研制.该驱动激光系统的主机为瑞士TBP公司的GE-100-XHP型激光器,是采用可饱和吸收镜技术的被动锁模激光器,其工作晶体为Nd:YVO₄,输出波长为1064nm,脉冲重复频率为81.25MHz,平均功率10W.该驱动激光系统配套的CLX-1100同步控制器可以将激光脉冲与射频参考信号严格锁定,随机抖动不大于1ps.根据使用要求,作者研制了高效的激光倍频器,获得了大于1W的266nm紫外激光.同时,激光到光阴极的传输设计中,采用了傅立叶光学技术,在紫外激光功率650mW左右的条件下,从自行研制的Cs₂Te光阴极上实现了大于500μA的光电流引出     

用于短波长FEL的光阴极微波电子枪设计研究

高增益、短波长自由电子激光器需要发射度低、峰值电流高的短脉冲电子束流.采用发射度补偿技术,设计了一台S波段、一个半腔体的光阴极微波电子枪以用于建议中的SDUV-FEL装置.POISSON,SUPERFISH和PARMELA程序的计算表明:当微脉冲电量为2nC时,这种设计能产生ε_n,rms=2.3π·mm·mrad、E_k=4.8MeV的电子束流.报道了该枪的设计考虑和模拟结果.     

光阴极微波电子枪优化设计的考虑

对光阴极微波电子枪进行了优化设计 ,给出了光阳极微波腔的形状、电参数和电场分布 .电子束团初始参数对束流横向发射度的影响 ,用 Parmela程序对其进行了优化 ,得到了一组最优参数 .考虑了补偿线圈对束流发射度的影响 ,对线圈的位置和电流的大小做了优化 .经过优化后得到腔出口处的横向发射度为 1 .39πmm.mrad,达到了设计时的要求. A 1.3 GHz photocathode RF gun is under study in peking University. The photocathode RF gun, composed of gun cavity, photocathode and Laser system, is expected to deliver a electron beam with a normalized transverse rms emittance of 1π mm·mrad at a charge of 1nC. Its performance has been studied by the space-charge tracking code PARMELA. The influences of the initialized electron beam were also studied. The emittance compensation technique is employed. After optimization of the parameters was...     

高能所光阴极驱动激光系统研制

能量回收型直线加速器(ERL)可能提供低发射度、高平均流强的连续电子束团,其电子枪的光阴极需要高重复频率、高平均功率的驱动激光系统。采用先进的光纤激光技术,特别是在激光系统中采用了掺镱光子晶体增益光纤,能实现高重复频率高平均功率激光输出。利用啁啾脉冲放大(CPA)技术,通过优化设计,将重复频率100 MHz和1.3 GHz的两套激光振荡源集成到同一个激光系统,整个激光系统的结构简化,使用方便。两种重复频率激光倍频效率分别达到50%和30%,绿光能达到5 W以上,满足光阴极实验平台的使用要求。     

基于碳纳米管场致发射的电子枪的初步研究

给出了基于碳纳米管场致发射电子枪的初步研究结果. 碳纳米管场致发射试验证明碳纳米管是一种很好的场致发射材料. 试验中, 在极间场强2.7MV/m的情况下得到的电流发射密度为0.5mA/cm².     

虚边界元法与强流电子枪的电子轨迹模拟

以位势问题为分析对象,从格林公式出发严格导出了虚边界元法的基本积分方程.并以虚边界元法基本积分方程为出发点,从理论上导出了虚边界元法对虚边界形状位置的基本要求.理论结果表明,虚边界元法本身是一种严格的方法,但在一定条件下,它是一种近似方法.基于虚边界元方法开发了一套适用于强流电子枪的电子轨迹模拟程序,并对强流电子枪进行了计算.对强流电子枪的计算表明,在同等条件下,取定最佳的虚实边界距离与边界单元数,虚边界元法较边界元法的精度要高.     

1.6Cell光阴极微波电子枪冷测及初步高功率实验研究

介绍了清华大学加速器实验室BNL/KEK/SHI型1.6cell微波枪调谐以及老练的初步结果. 调谐过程中, 测量了耦合孔尺寸与外部品质因数之间的关系; 给出了0模和π模的频率、单腔频率以及场分布. 目前, 该微波电子枪正在进行高功率微波老练, 给出了该枪初步的微波老练的情况及测量结果.     

微脉冲电子枪的初步实验研究

给出了微脉冲电子枪的模拟计算及其初步实验结果. 该电子枪采用铜铝镁合金作为冷阴极材料, 在以磁控管作为微波功率源的出束实验中得到了100mA/cm²的电流密度.实验结果与次级电子倍增解析计算和SEEG程序的模拟计算结果基本符合, 初步验证了微脉冲电子枪的基本原理, 为今后实验中得到更大的电流密度打下了基础.     

Design of a 325 MHz half wave resonator prototype at IHEP

A 325 MHz β=0.14 superconducting half-wave resonator prototype has been developed at the Institute of High Energy Physics,Beijing,which can be applied in the low energy section of continuous wave high current proton linear accelerators.The electromagnetic design,multipacting simulation,mechanical optimization and fabrication are introduced in detail.Test results at room temperature and 4.2 K,and a comparison between measured and simulated results,are analyzed in this paper.     

Design of a 325 MHz SC Spoke040 cavity at IHEP

A spoke cavity is a TEM-class superconducting resonator with particular advantages: compact structure and high shunt impedance. The 325 MHz β =0.40(β =v/c, v is the velocity of particle and c is the velocity of light)single spoke cavity(Spoke 040) is adopted for the Chinese ADS(Accelerator Driven Sub-critical System) project. The physics and mechanical design has been accomplished, and the fabrication of a prototype is currently in progress. In this paper, the optimization processes for the main radio frequency(RF) and mechanical parameters are analyzed in detail. Two kinds of cavity end-walls(flat and convex) are compared. The convex end-wall is preferred in order to improve mechanical performance of the cavity. Two prototypes of the Spoke 040 cavity are in the machining stage,and should be finished in early 2014.Vertical testing is also under preparation.     

电子帘加速器电子枪的研制

研究了电子帘加速器电子枪的束流传输特性,分析了影响束流纵向均匀性的几个因素,尤其对灯丝的下垂问题提出了一种理想的端约束模型.介绍了新研制的电子枪,其束流纵向不均匀度≤±10%.     

Electron-Optical System of a High-Power Gyrotron with Nonadiabatic Electron Gun

We describe a nonadiabatic electron gun operated in the mode of a currentconfined by spatial charge and intended for producing helical electron beams for high-power gyroresonantdevices.Results of numerical simulation of electron trajectories and electron-beam parameters arepresented. It is shown that for a high operating current, the pitch factor and the electronvelocity spread can be significantly better than in the conventional adiabatic systems. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 48,No. 6, pp. 517–522, June 2005     

Development and application of the intense slow positron beam at IHEP

This paper describes the development and application of an intense slow positron beam at IHEP with regard to its two main components.The Variable-Energy Positron Lifetime Spectroscopy (VEPLS) based on the pulsing system consisting of a chopper,a prebuncher and a buncher has been constructed in order to meet the needs of materials science development.At present,the time resolution of the VEPLS can easily reach about 386 ps with a peak-to-background ratio of about 600:1.A plugged-in 22Na positron source section for adjusting the newly built experimental station and for increasing the beam operation efficiency has been constructed.A slow positron beam with an intensity of 2.5x105 e+/s and the beam profile whose diameter is 10 mm has been obtained;the moderation efficiency of the tungsten mesh moderator reaches 5.1x 10-4 as calculated with an original positron source activity of 52 mCi.     

Development and application of the intense slow positron beam at IHEP

This paper describes the development and application of an intense slow positron beam at IHEP with regard to its two main components. The Variable-Energy Positron Lifetime Spectroscopy (VEPLS) based on the pulsing system consisting of a chopper, a prebuncher and a buncher has been constructed in order to meet the needs of materials science development. At present, the time resolution of the VEPLS can easily reach about 386ps with a peak-to-background ratio of about 600:1. A plugged-in ²²Na positron source section for adjusting the newly built experimental station and for increasing the beam operation efficiency has been constructed. A slow positron beam with an intensity of 2.5×10⁵e⁺/s and the beam profile whose diameter is 10mm has been obtained; the moderation efficiency of the tungsten mesh moderator reaches 5.1×10^－4 as calculated with an original positron source activity of 52mCi.     

表面势垒对梯度掺杂GaN光电阴极电子逸出几率的影响

研究表面势垒对梯度掺杂GaN光电阴极电子逸出几率的影响.计算梯度掺杂透射式GaN光电阴极的电子能量分布及逸出几率,结果显示梯度掺杂与均匀掺杂相比,可以获得更大的电子逸出几率;I势垒对电子逸出几率的影响显著,而Ⅱ势垒影响较小.利用GaN光电阴极多信息量测试系统,测试两种GaN阴极样品的光电流.实验结果表明,梯度掺杂GaN样品比均匀掺杂电子逸出几率更大;单独进行Cs激活形成的I势垒对电子逸出几率有显著影响,而Cs/O共同激活形成的Ⅱ势垒对其影响较小.     

脉冲光电子枪中光电子束性能研究

利用新设计的脉冲光电子枪,研究了光电子束的能量分布,光数密度与激光强度的关系和光电子在电离区内的滞留时间。大部分电子的能量为光发射电子的剩余能量,但量由于电子的空间电荷效应,电子能量分布具有加宽现象。每个激光脉冲发射到电离区内的光电子数密度在１０＾９／ｃｍ＾３以上。     

BEPCⅡ电子枪系统测试与运行

2004年7月BEPCⅡ新电子枪系统在测试台进行了测试, 同年11月投入BEPCⅡ直线加速器运行. 描述了新电子枪系统的测试与运行状态. 电子枪设计电流10A, 脉宽1ns,重复频率50Hz, 脉冲高压200kV, 提供单脉冲和双脉冲运行模式. 通过实验获取了一些重要的关系曲线, 同时进行了初步的双脉冲测试. 流强及发射度测量等测试结果表明设计阶段的计算机模拟数据与实际情况基本相符. 从电子枪实际运行状况来看, 其设计与制造是成功的.     

氮等离子体枪中电子输运行为的蒙特卡罗模拟

采用蒙特卡罗模拟,对氮等离子体枪的两个环形电极间的氮气辉光放电过程中电子的输运过程进行研究.计算在不同平均电场与粒子数密度的比值(E/N)下,电子与氮分子发生不同碰撞的概率、出射电子的平均能量、方向角分布和电子的能量分布.结果表明,电子能量近似服从玻尔兹曼分布.随着E/N的升高,电子平均能量升高,发生激发、离化、电离和离化电离碰撞的概率增大;非均匀分布的电场使分子获得更高的离化率,同时显著增强出射电子的能量.模拟结果为等离子体应用设计提供了参考依据.     

二次发射微波电子枪的数值计算方法

阐述了在rfz轴对称坐标系下,计算二次发射微波电子枪中电子束运动的一种数值方法.通过在束流运动区域建立网格,把空间中的电荷密度分布转化为网格上各顶点的电荷密度分布.在束团运动坐标系中,用多重网格法求解Poisson方程,得到束团的空间电荷场.用5阶Runge?Kutta法直接求解相对论下的电子运动方程.通过实例计算,并和MAFIA的计算结果对比,证明其是一种可靠的方法.