中物院太赫兹自由电子激光(CTFEL)装置是我国第一台基于超导加速器的高重复频率、高平均功率太赫兹自由电子激光装置.CTFEL利用光阴极直流高压电子枪和超导加速器产生约8 MeV电子束在波荡器中产生自发太赫兹(THz)辐射,并在光腔中受激放大获得饱和输出.得益于在0.7～4.2 THz频谱范围内连续可调以及平均功率大于10 W的特性,CT-FEL为材料动力学、太赫兹成像、太赫兹生物学等领域提供了独特的研究平台.自2018年开放成为用户装置以来,每年提供不少于1000 h的稳定出光.未来CTFEL将在现有基础上升级成为红外太赫兹自由电子激光装置,实现太赫兹频率全覆盖以及最大功率大于100 W的目标,力争成为世界先进的长波长自由电子激光装置.

转换效率高、散热性能优异的辐射转换靶是高能微焦点工业CT的关键部件,本文设计了一种适用于高能(6 MeV)微焦点(直径约100μm)工业CT的先进旋转式辐射转换靶.通过模拟分析辐射转换靶X射线转换效率和热沉积,确定最优转换靶厚度,从而设计、加工出旋转式辐射转化靶,并成功应用于中国工程物理研究院应用电子学研究所高能微焦点工业CT验证装置.对比实验结果显示,在相同工况(电子束能量6 MeV,宏脉冲长度5 ms,宏脉冲流强1.5 mA,焦斑直径100μm)下,固定靶被电子束熔融,而旋转靶则能够承受电子束的轰击,验证了旋转式辐射转换靶的有效性和可靠性.

波荡器性能一般有多个指标要求,而这些指标往往是相互冲突的,因此在磁场垫补时难以对垫补量进行精确推算,导致磁场垫补耗时和低效.为解决该问题,本文将多目标遗传算法应用于波荡器磁场垫补量推算,并对波荡器U38-S磁场进行了垫补.根据波荡器磁场垫补结构建立了计算模型,并阐述了计算模型中的主要问题,给出了U38-S磁场的垫补过程.经过3次磁场垫补,U38-S的轨迹中心偏差 、相位误差和峰峰值误差分别减小到0.15 mm、1°和0.49％.由于遗传算法本身具有较强的可扩展性,本文所用方法也可应用于其他类型波荡器的磁场垫补.

本文基于微波零相位法,将中国工程物理研究院太赫兹自由电子激光(CTFEL)2×4-cell超导加速器的下游腔作为零相位腔,测量了上游腔增能后的电子束纵向长度,并通过束流动力学模拟证明,当两个超导腔正常工作时,上游腔出口处的电子束纵向长度与下游腔出口处的接近.实验结果表明,CTFEL 2×4-cell超导加速器能实现半高宽小于6.8 ps的电子束,满足装置出光要求.

束流变压器(BCT)在频域表现为带通特性,其低频截止特性会引起基线漂移现象,本文使用高通滤波器模型对低频截止特性对单束团和连续束团的影响进行了分析.采用基线操纵和一次谐波算法两种方法进行了基线修复,使BCT测量高重复频率连续束团的相对误差由20％下降至3％以内.

First lasing of the CAEP THz FEL (CTFEL) facility was obtained in August 29,2017.The facility consists of a GaAs photocathode high-voltage DC gun,a superconducting RF linac,a planar undulator and a quasi-concentric optical resonator.The central frequency of the first saturated lasing was 2.56 THz,with the spectral width about 1.9％.The average output power in the macro pulse was larger than 5.7 W.

中国工程物理研究院紧凑型自由电子激光太赫兹源装置采用了两路微波独立调谐热阴极微波电子枪作为注入器,一路由首腔馈入激励首腔和实现阴极表面建场并引出电子,另一路由后续腔馈入并通过腔间耦合激励各腔,两路微波互不耦合.对于这种微波激励方式,微波电子枪首腔的电场相位和幅度在实验中均可调节,因此可以通过实验研究来优化微波电子枪的工作参数,从而减小热阴极微波电子枪的电子反轰效应,提高束流品质.介绍了该热阴极微波电子枪热测实验研究的最新结果,通过BCT测得微波电子枪出口处束流强度超过400 mA,电子反轰效应随着首腔电场的相位和幅度调节发生显著变化,这些指标和实验现象与理论研究结果较为吻合.

基于负电子亲和势GaAs光阴极直流高压注入器,设计并搭建了国内首套光阴极量子效率分布测量系统.该系统利用单透镜实现逐点扫描,并采用LabVIEW进行控制和数据读写.实验表明,该系统单点采样时间小于2.3s,分辨率优于0.32 mm.初步测量了GaAs阴极的量子效率分布,观察到量子效率分布及其衰减的不均匀性,量子效率较高区域的衰减速率更低.

离子反轰会造成直流高压电子枪内光阴极的量子效率衰减,降低阴极的工作寿命和稳定性,是限制光阴极直流高压电子枪性能的重要因素之一.基于中国工程物理研究院太赫兹自由电子激光(THz-FEL)的直流高压电子枪,通过束流动力学模拟和阴极量子效率测量,研究了束流偏轴发射对离子反轰的抑制作用及其应用限制.模拟结果表明:束流偏轴发射时,离子主要轰击阴极的电中心附近,光电发射区域的离子通量较轴上发射时降低约95％;但束流发射度增大约4π mm·mrad,横向运动幅度增加约1倍.通过电子枪运行前后阴极量子效率测量,发现束流偏轴发射时离子反轰引起电中心附近量子效率大面积的衰减,而光电发射区域量子效率损失较小,验证了束流偏轴发射抑制离子反轰的可行性.

The beam dump is the primary assembly used at the end of the accelerator to absorb high power electrons .In this paper ,a beam dump was designed for 8 MV/5 mA CW electron beam of the terahertz free electron laser (FEL‐T Hz) facility in China Acad‐emy of Engineering Physics , whose inner surface absorbed average power is up to 40 kW .The beam dump design was based on a 1.2 m long copper cone whose inner sur‐face absorbs the beam .The beam dump cooling structure and flow rate were optimized , so that the beam dump temperature was controlled at 355 K ,to meet the requirements of high average power FEL‐T Hz facility .

主要介绍自由电子激光相干强太赫兹源(FEL-THz)装置上的砷化镓光阴极直流高压注入器的研究进展,并讨论其驱动未来高重复频率短波长自由电子激光器的差距.通过综合砷化镓阴极寿命的三大影响因素,提出了其工作寿命的定性物理模型;通过该模型对阴极和注入器进行优化,在直流高压电子枪上得到了5 mA,32 min的连续稳定输出;测量了电子束在4.8 mA下归一化发射度约为4.0π mm·mrad,阴极热发射度约为0.67πmm·mrad,电子束本征横向能量约为92 meV,250 keV电子束在距离阴极90.6 cm处纵向均方根长度约为11.5 ps.这一束流状态已经基本满足FEL-THz需求.

The temperature rise, caused by high power laser, would destroy the activation layer of the NEA GaAs photocathode. In this paper, the temperature rise is studied theoretically and experimentally. With some theoretical analysis, the thermal transfer between the NEA wafer and the puck is proved as the most important factors that affect the temperature. To the thermal transfer, the GaAs vacuum indium soldering chamber is built and the vacuum soldering technology is explored. Some comparative experiments with and without indium soldering are also presented in this paper. The results, both in the atmosphere and in vacuum, indicate that indium provides effective thermal contact between the GaAs cathode and the puck, enhancing the thermal transfer and slowing down the temperature rise. These studies increase the operational lifetime of NEA GaAs illuminated by several-watt laser more than 20 times eventually.

对比研究了真空管道中环形电子束与位于束团中心的实心束在管道壁上产生的场分布,证明束流位置探测(BPM)技术可用于电流密度均匀分布的环形电子束位置测量.采用点密度不均匀性模型,分析了环形电子束角向不均匀性对测量精确度的影响.结果显示,当环形电子束电流密度不均匀性为10％时,对位置分辨率精确度的影响为0.1 mm.初步开展了BPM系统设计,并对纽扣电极半径和输出端口半径进行了优化设计.

As one of the most important high average power electron source materials , the high brightness negative electron affinity (NEA ) gallium arsenide (GaAs) photo‐cathode becomes a researcher focus nowadays .The thermal emittance is the lower limit of emittance ,and its measurement is of great importance to determine the brightness that an injector can provide .In this paper ,based on the terahertz free electron laser (FEL‐T Hz) facility in China Academy of Engineering Physics ,some efforts were made to calculate and measure the thermal emittance of NEA‐GaAs photocathode . Under ultra‐low charge of 28 fC NEA‐GaAs photocathode ,the thermal emittance is (0.603 ± 0.002)μm/mm by the solenoid scan method .

The integrating current transformer (ICT ) is measurement devices used for accurate measurement of bunch charge ,and the precise calibration is needed before the use of ICT .The calibration of the ICT produced by Bergoz company was discussed in this paper ,and the problems appeared in calibration stage were analyzed .The research focused on baseline drift phenomenon when the input pulse repetition frequency increased to M Hz range ,and the mechanism of baseline drift and baseline restoration was analyzed .The results show that the ratio of the input pulse charge and output pulse charge is 9.67 .T he relative error of the pulse charge measurement is less than 5% .

This paper summarizes the results of the study of a bunch length monitor based on the button BPM (Beam Position Monitor). The monitor consists of a BPM installed on the beam pipe and a spectrum analyzer. We use the button-BPM's button pickups as the electrodes to pick up the signal. The bunch length can be derived from the spectrum of the beam-induced signal got by the spectrum analyzer. We show the theoretical results and the simulations performed by CST