非均匀加速结构腔间耦合系数模拟计算

电子直线加速器的聚束段对于会聚入射电子相位,提高电子直线加速器出射束流性能起着至为关键的作用. 而准确计算聚束段腔间耦合系数又是设计聚束段耦合孔几何结构的关键. 本文利用电磁场计算软件MAFIA的特征值计算模块E模块, 分别计算出单腔频率, 双腔腔链的两个本征频率,从而得到聚束段腔间耦合系数. 采用该方法,可以设计聚束段腔间耦合孔的几何参数. 与实验结果的对照表明, 这是一种非常有效的非均匀加速结构腔间耦合孔设计方法.     

RF deffecting cavity for bunch length measurement in Tsinghua Thomson scattering X-ray source

An RF deffecting cavity used for bunch length measurement has been designed and fabricated at Tsinghua University for the Thomson Scattering X-Ray Source. The cavity is a 2856 MHz, π-mode, 3-cell standing-wave cavity, to diagnose the 3.5 MeV beam produced by photocathode electron gun. With a larger power source, the same cavity will again be used to measure the accelerated beam with energy of 50 MeV before colliding with the laser pulse. The RF design using MAFIA for both the cavity shape and the power coupler is reviewed, followed by presenting the fabrication procedure and bench measurement results of two cavities.     

Development of Mini-LIA and Primary Experiments

Mini-LIA is a miniature of a linear induction accelerator developed by China Academy of Engineering Physics and Tsinghua University in 2007. It has been constructed with a thermionic cathode in an electron injector and a metglas core in the induction accelerator cavities. A double-pulsed electron beam was produced for the first time in China on the Mini-LIA with a thermionic cathode in the electron gun and a metglas core in the induction accelerator cavities. A double-pulsed beam current of more than 1.1 A was obtained on condition of 80 k V double-pulsed high voltage produced by pulsed power system supplying to the injector and accelerating modules. Some primary experiments for measuring the parameters of Mini-LIA has been performed, and some beam characterizations of Mini-LIA are presented. Further improvement is underway.     

三频率法测量耦合器的定量分析

在已有三频率法的基础上,根据耦合腔链等效电路模型,推导出利用实验测量数据计算耦合器频偏△f和耦合度β的公式,首次把只能定性分析的三频率法定量化.根据此公式编写的软件,在一套微机控制下的测量系统上实现了实时测量和定量显示,取得了高效调配行波加速管耦合器的效果,为大型集装箱检测系统用行波加速器的产业化作出了贡献.     

向内发射同轴虚阴极振荡器理论分析与数值模拟

 针对向内发射同轴虚阴极振荡器进行了1维理论分析，给出了电流电压关系的数值解，估算了同轴漂移区空间电荷限制流及虚阴极位置；同时使用MAFIA程序进行了全3维PIC数值模拟研究，通过调节阴极电子发射区与阳极反射板之间距离进行了一系列计算，得到了圆波导中各传输模式频谱及功率。结果表明，尽管使用圆周对称的同轴结构，输出模式中TE₁₁和TM₀₁仍占主导地位，两种模式共同存在，相互竞争。在最佳情况下，当二极管电压为250 kV，电流为20 kA时，得到了微波输出总功率最高为740 MW，功率效率超过10%，主频为3.18 GHz，同时含有较强TE₁₁和TM₀₁模式成分的微波输出。     

Development of a ferroelectric cathode diode

As a promising kind of high current cold cathode, the Ferroelectric Cathode （FEC） has several significant advantages, such as a controllable trigger time, lower vacuum requirement and large emitting area fabricability. The emitting current density of the FEC fabricated at Tsinghua University was more than 200 A/cm^2. In order to make the ferroelectric cathode into practical applications, a high current density diode using a ferroelectric cathode was designed, based on the PIC simulation. The performance of the FEC diode was investigated experimentally. When the applied diode voltage was 60 kV, a current density of more than 250 A/cm^2 was obtained, and the current density distribution was also measured.     

双脉冲电子直线感应加速器实验研究

 Mini-LIA为MHz重复频率双脉冲电子直线感应加速器,由双脉冲功率系统、热阴极电子枪注入器及金属玻璃磁芯感应加速腔等组成。在此平台的实验获得了数百ns间隔（即MHz重复频率）的双脉冲高压,每个脉冲幅值达到80 kV,脉冲半高全宽为80 ns;在感应腔加速间隙处测得双脉冲加速电场;在加速器出口处测量得到流强约1.1 A的双脉冲电子束流。实验结果表明：利用硅堆隔离汇流装置可实现MHz重复频率的双脉冲高压,金属玻璃磁芯感应加速腔和六硼化镧热阴极电子枪均适合MHz重复频率双脉冲工作方式。     

RF deflecting cavity for bunch length measurement in Tsinghua Thomson scattering X-ray source

An RF deflecting cavity used for bunch length measurement has been designed and fabricated at Tsinghua University for the Thomson Scattering X-Ray Source. The cavity is a 2856 MHz, π-mode, 3-cell standing-wave cavity, to diagnose the 3.5 MeV beam produced by photocathode electron gun. With a larger power source, the same cavity will again be used to measure the accelerated beam with energy of 50~MeV before colliding with the laser pulse.     

X波段PBG加速结构的数值模拟和加工研究

利用3D电磁场模拟计算软件, 对X波段的金属PBG加速结构进行了模拟计算. 设计了11.42GHz的光速段行波加速腔, 并进行了耦合器调配的计算和模拟. 最后, 研究了电铸加工的方法, 并通过模拟计算给出了加工公差.     

同轴线法阻抗测量平台中高频接头的研制

研制宽带传输性能良好的高频接头是用同轴线法测量纵向阻抗的一个技术关键.介绍根据同轴器件设计中的错位过渡和共平面补偿的原理,利用MAFIA软件设计高频接头的方法.利用该方法,已成功地设计了一种可同时完成拉紧内导体细丝和阻抗匹配两种功能的高频接头;优化设计后,模拟计算结果为20GHz带宽内反射系数小于0.1,加工件初测已达到17GHz内反射系数基本小于0.2的良好效果.