【作者】 李骥；

【导师】 尚雷；

【作者基本信息】 中国科学技术大学 ， 核技术及应用， 2014， 博士

【摘要】 为满足自由电子激光器对高品质电子束流的要求,高性能电子枪的研究已经得到了广泛重视。本文就应用于自由电子激光器的三种高性能电子枪开展了设计和研究工作。论文第一部分介绍了15keV强流栅控电子枪,它作为独立调谐微波电子枪的外注入式电子源,为远红外自由电子激光器提供高品质的电子束流。我们提出了一种双阳极结构,即在常规栅控枪结构的基础上增加了中间电极,使得束流在电子枪内经过加速再减速的过程,提高了电子枪的发射能力和聚焦性能,成功实现了高导流系数和大面积压缩比电子枪的设计。这种结构还可以根据实际需要,通过调整中间电极的电压来调节电子枪的最佳输出电流而能量保持不变。通过对远红外自由电子激光注入器的束流动力学计算和优化,可以使系统对电子枪的输出流强由设计值4.2A降低至2.45A。双阳极方案的电子枪结构复杂、紧凑,为了避免可能出现的真空击穿和绝缘陶瓷表面爬电现象,我们采用双脉冲电源对阴极和中间电极供电,栅控信号叠加在高压脉冲信号上。这种方式既降低了打火和爬电的风险,又保证了输出束流的具有良好的上升沿和下降沿,并能实现脉宽可调。为了测量提供给独立调谐微波单元的脉冲束流品质,我们根据该栅控电子枪的输出束流能量低、流强高的特点,设计了一套电子枪测量装置测量阳极出口处,即独立调谐微波电子枪入口处的束流流强和束斑尺寸。该装置通过一段陶瓷腔与电子枪连接,电子枪阳极固定在陶瓷腔法兰上。步进装置驱动荧光屏从阳极下游的真空室移动至陶瓷腔内的阳极出口处,通过后方的观察窗和反射镜采集束斑信号。该方案省去了屏蔽罩,将FCT直接套在陶瓷真空室外,可以使FCT的位置贴近阳极出口。另外,我们还在高压电源回路中放置了三个束流流强检测器,可以通过测量高压电源和灯丝电源的负载电流,测得阴极的发射电流、栅网的截获电流、以及电子枪内电极上损失的电流,为获得最佳的电子束输出提供参考依据。论文第二部分介绍了500kV脉冲高压电子枪系统。为了获得较低初始发射度的3A脉冲束流,该电子枪选用发射性能优异、抗中毒能力良好的单晶CeB6作为阴极材料,阴极发射面直径3mmm；通过对枪体内电场分布的计算,优化了电子枪的电极形状,给出了束流动力学计算结果。我们设计了一套双缝法发射度测量装置平台,给出了装置的布局。另外,我们还完成了基于500kV脉冲高压电子枪的预注入器的物理设计,验证了该枪作为短波长自由电子激光器电子源的可行性。论文的第三部分介绍了对光阴极微波电子枪中的类肖特基效应的初步研究。我们针对ASTRA对PITZ光阴极微波电子枪中类肖特基效应的模拟结果与实验数据不一致的情况,对PARMELA程序进行了拓展,使其能用简单的模型模拟类肖特基效应,模拟结果与实验数据吻合较好。最后,针对三个部分已经完成的工作进行了分析和讨论,指出了下一步需要解决的问题,并给出了相应的解决方法。更多还原

【Abstract】 To meet the requirements of high-quality electron beam for free electron lasers (FELs), the study of high-performance electron guns has been paid extensive attentions. In this paper, three different types of electron guns for FELs have been studied.A15keV gridded high-perveance electron gun is described firstly in this thesis This gun plays a key role as the external injecting electron source of the independently-tunable-cells (ITC) RF gun, the performance of which determines the beam quality in the injector for far IR radiation source. We proposed a double-anode structure with an intermediate electrode to overcome the strong longitudinal space-charge force on the emission surface and to improve the transverse focusing, which makes the goal of high perveance and high compression ratio achieved. This double-anode structure can adjust the voltage on intermediate electrode to beam outputs with different beam current at15keV. Through the beam dynamics simulations and opitmizations of the injector, the minimum output current could be reduced from4.2A to2.45A.The double-anode scheme makes the electrodes structure compact and complex. In order to avoid the possible breakdown in vacuum and creepage on the ceramic surface, two pulsed power supplies are employed for cathode and intermediate electrode. And the grid-controlled signal is superposed on the high-voltage pulsed signals. This approach not only can reduce the risk of berakdown and creepage, but also ensures that the output beam with good rising and falling edges.Considering the output beam is low-energy and high-current, we designed a test stand to measure the quality of the beam injected to ITC RF gun at the exit of anode.The measurement system is connected to the gridded gun through a ceramic chamber with a FCT outside. The anode is fixed on the flange of the ceramic chamber. The YAG screen can be drived from the downstream vacuum chamber to the position close to the anode. Besides, three beam current monitors were used in the power circuits to measure the values of the current emitted from the cathode and beam current lost on the electrodes, which gives a reference for gun tuning.The500kV high-voltage pulsed electron gun system is introduced in the second part of the thesis. In order to obtain the3A beam with low intial emittance, we used monocrystal CeB6as the cathode material basing on its excellent emission ability and anti-poisoning characteristic.The diameter of the cathode is3mm.The electrodes of the gun were optimized on the basis of gun simulations.We also designed an emittance measurement line using double-slit method. In addition, we finished the physical design of a pre-injector for XFEL and testified the possibility of using the500kV gun as the electron source for XFEL.The Schottky-like effect in photocathode RF gun is studied in the third part of the thesis. Considering the discrepancies between measured extracted charge and simulated results with Schottky-like effect from ASTRA code, PARMELA code was applied as benchmark. Since PARMELA cannot be used to simulate Schottky-like effect with its own modules, MATLAB scripts have been developed to implement this feature. The simulation results fit the experimental data well.Finally, the finished work has been summarized. The suggestions of problems to be solved in the next step and corresponding solutions are provided.更多还原