First Beam Measurements of the S-Band photocathode Radio-Frequency Gun at Tsinghua University

During the last decades, photocathode rf gun has been proven to be successful in generating the high brightness electron beam （-lnC,-lπ mmmrad,-l ps） which is required by the ILC, XFEL, Thomson scattering x-ra y source, etc. A photocathode rf gun system is built to develop electron source for the Thomson scattering x-ray source at Accelerator Laboratory of Tsinghua University. The system consists of a BNL/ATF-type 1.6 cell S-band rf cavity, a solenoid for emittance compensation, a laser system and some simple equipments for beam diagnosis. The first beam measurements of the photocathode rf gun, including the dark current, transverse beam profile, charge and quantum efficiency, are reported.     

基于光纤合束器件的高功率全光纤相干合成技术研究进展与展望

介绍了目前研究中相干合成多采用空间结构的研究现状,分析了空间结构的相干合成方案需要复杂的光路调节且长时间工作稳定性欠缺,肯定了基于光纤合束器件的全光纤激光相干合成在相干合成光源中的稳定性与实用性,梳理了近年来基于光纤合束器件的全光纤激光相干合成方案,分别介绍了基于光纤耦合器、光子灯笼、相干信号合束器以及基于自成像效应实现全光纤合束的技术方案及研究现状,分析了不同光纤器件目前的主要限制因素和发展瓶颈,并展望了未来的发展方向。     

Vlasov方程的数值求解

研究环形加速器中的纵向微波不稳定性,发展了Vlasov方程在(J,φ)坐标下用正交多项式展开的数值计算程序,并把它用于对微波不稳定性的初步研究.     

三阶矢量有限元方法精确计算轴对称谐振腔高阶模

为了进一步提高数值求解谐振腔高阶模的精度，本文提出了三阶矢量有限元方法，并针对二阶矢量有限元轴对称谐振腔高阶模计算程序Cafe对曲线边界的计算能力较差和计算速度较慢的缺点做了改进. 在这些改进的基础上编制了三阶矢量有限元轴对称谐振腔高阶模计算程序meshmatrix3，得到了很好的结果.     

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.     

基于受激布里渊散射能量转移的冲击点火激光技术研究

提出一种新型的激光放大技术, 高效地实现冲击点火所需的10² ps级高功率激光脉冲. 该技术耦合了传统的激光驱动器放大技术和受激布里渊散射(SBS) 脉冲压缩技术, 在不改变现有激光装置主体结构的前提下, 使用长脉冲(数 ns) 充分提取主放大器储能, 然后在系统输出端通过SBS进行脉冲自抽运的能量转移, 将长脉冲能量转移给10² ps级的冲击脉冲, 实现高效放大的目的. 该技术在主动控制下实现能量转移, 将克服传统SBS压缩时间特性不可控的缺点, 输出满足冲击点火时域特性要求的精密控制激光脉冲.     

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.     

汤姆逊硬X射线源中锁模脉冲激光稳频方法

汤姆逊硬X射线源中,光阴极微波电子枪要求触发激光脉冲与腔中微波场相位的精确时间同步。理论分析了锁模脉冲激光器相位噪声,探讨了对激光脉冲相位探测和控制的方法,并通过实验构建了激光相位抖动测量系统和锁相环稳频回路,用基频鉴相信号驱动压电陶瓷晶体改变谐振腔长,实现了从开环3.42 ps到闭环1.46 ps的均方根相位抖动的测量和控制。     

Generating 10-40 MeV high quality monoenergetic electron beams using a 5 TW 60 fs laser at Tsinghua University

A unique facility for laser plasma physics and advanced accelerator research has recently been built at Tsinghua University. This system is based on a Tsinghua Thomson scattering X-ray source (TTX), which combines an ultrafast TW laser with a synchronized 45 MeV high brightness linac. In our recent laser wakefield acceleration experiments, we have obtained 10-40 MeV high quality monoenergetic electron beams by running the laser at 5 TW peak power. Under certain conditions a very low relative energy spread of a few percent can be achieved. Absolute charge calibration for three different scintillating screens has also been performed using the linac system.     

Design for the lattice with 4-DBA structure of the compact laser-electron storage ring

We try to design the lattice with 2 super periods and 4-DBA structure in order to provide more drifts for the future development of the TTX source. Due to the space limitation in the lab, the 4-DBA lattice is suitable.In the paper,we present the lattice design with a 4-DBA structure mainly for the pulse mode of the compact laser-electron storage ring (LESR). Element parameters of the lattice are optimized with the help of the professional software and beam dynamics such as intra-beam scattering (IBS) and Compton scattering (CS) are calculated. Besides, the fringe field effect is analyzed with the numerical method.