基于高频偏转腔的束团纵向整形及诊断研究

RF Deflecting cavity can be used for bunch longitudinal shaping which is an advanced technique to manipulate the electron bunch. This technique can be used to increase the energy transform ratio and the efficiency of beam-driven wakefield accelerator, or to generate high order harmonics by longitudinal modulation of the electron bunch for light sources. The study of this technique is very important to beam physics and has a bright future. This project is based on the existing beam line for Thomson scattering X-ray generation in Tsinghua Univserity and the development of a new RF deflecting cavity dedicated for this longitudinal shaping application. The detailed beam dynamics inside the new deflecting cavity will be calculated and used for designing a beam line to accomplish the shaping scheme more accurately. The beamline will be constructed and experiment will be done to measure the 3D distribution of the shaped bunch based on an existing RF deflecting cavity for beam diagnostics. Detailed parameters of the generated bunch will be measured and characterized for understanding the beam physics and for further optimization. Questions like the precise control of the RF deflecting, the diagnostics of the fine structure of the bunch will be studied. While finishing this project, a beamline that can generate required bunch shape will be completed for carrying out experiment such as the wakefield measurement, THz generation and so on.

基于高频偏转腔的电子束流纵向整形是一种对束流操控的前沿技术,可用于提高束流尾场加速的效率、也可用于纵向调制电子束产生各种高次谐波作为更好的光源驱动束流，对该技术的研究有很大的科学意义和广泛应用前景。本项目依托清华大学已有束流装置，以研制束流纵向整形用的偏转腔为基础，通过精确计算束团在偏转腔内部的动力学，结合现有参数，设计并搭建束团纵向整形的束线，开展实验研究，利用已有高频偏转腔作为诊断工具，对束流三维分布进行诊断，对纵向整形后的束流品质进行测量并开展优化工作。解决如偏转腔相位幅度的精确控制、束团三维精细结构测量等具体问题，最终搭建一条能产生所要求纵向分布的电子束团的束线，开展具体如尾场测量、太赫兹产生等应用实验研究。

项目基于高频偏转腔开展束团纵向整形和诊断，对于产生高亮度电子束及物理测量都有重要意义。项目完成了发射度交换束线关键微波原件——S波段偏转腔的物理设计，并已经加工成型。完成了基于清华加速器实验室直线加速器段的发射度交换束线的物理设计，可以实现纵向束团的整形。与美国阿贡实验室合作，完成了基于发射度交换的束团纵向整形实验研究，成功产生了纵向电流分布为三角形的电子束，首次实验验证了该电子束具有数值近似为5的高变压，突破了非对称束流对于变压比为2的限制。该结果证明可以提高同轴尾场加速器中驱动束能量利用效率，对于节约高能对撞机建设成本具有重要意义。通过利用纵向空间测量的方法，建立了精确测量尾场的新技术，对于尾场加速器研究利用具有重要的意义。

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