THz波段高梯度加速结构物理与实验研究

The high-gradient accelerating structure is the cutting-edge research area in the field of linear accelerators in the world. The traditional linear accelerator operating frequency is in the range of 1 to 12 GHz with an accelerating gradient of up to approximately 100 MV/m, which does not meet the requirements for future linear colliders and hard X-rays for electron beam energy. According to the RF characteristics of the acceleration structure, the higher the operating frequency, the higher the RF breakdown threshold. When the accelerating gradient is increased, the operation of the accelerating structure is stable. This project intends to carry out physical and experimental research on high gradient accelerating structures in the THz wave (0.3 THz). Because of the low pulse energy of the THz source, an energy conservation method is proposed to analyze the relationship between the transient field and the accelerating structure, optimize the accelerating structure, increase the impedance, decrease the filling time, reduce the THz pulse energy loss during transient field changes, and increase the transformation efficiency from the THz pulse power into electron beam power. The introduction of the Choke-Mode structure eliminates higher-order modes in the wake field and improves beam quality. The LIGA technology is used to fabricate and measure the THz wave accelerating structure. It is of great theoretical significance and engineering application value to study the accelerating structure of THz band through this subject. It lays a foundation for the development of high-gradient accelerating structure of THz band and develop the reserve technology route of high-energy electron accelerator.

高梯度加速结构是目前世界上直线加速器领域的前沿研究方向。传统的直线加速器工作频率在1-12GHz，加速梯度最高约100MV/m，不能满足未来直线对撞机以及硬X射线对电子束能量的要求。根据加速结构的RF特性，工作频率越高，RF击穿阈值越高，加速梯度增高时，保证加速结构工作稳定性。本课题拟开展THz波段(0.3THz)高梯度加速结构的物理与实验研究。由于THz源脉冲能量低，提出利用能量守恒法分析瞬态场与加速结构之间的关系，优化加速结构，提高分路阻抗，降低建场时间，减小瞬态场变化过程中THz脉冲能量损耗，提高THz脉冲功率转化为电子束流功率的效率。引入Choke-Mode结构，消除尾场中的高阶模，提高束流品质。采用LIGA技术加工制备THz波加速结构并测量。通过本课题的探索研究，为THz波段高梯度加速结构的研制奠定基础和发展高能电子加速器储备技术路线，具有重要的理论意义和工程应用价值。

本项目基于能量守恒分析腔体建场的瞬态过程，优化腔体参数，基于束流负载分析束流在加速结构中的稳态分析和瞬态分析。基于上述瞬态场建立和束流瞬态分析，完成加速结构的建模分析，仿真计算与理论分析结果吻合。基于上述理论和分析方法，提出基于THz加速产生飞秒束团的太赫兹电子枪。该方法不依赖于驱动激光系统以及传统的热阴极系统，产生飞秒束团的方法较为简单。因此对于很多需要飞秒束团的应用具有非常重要的意义。与北京高能所联合利用LIGA技术进行腔体制备，仅能制备准3D的样品，同时THz测量设备较为昂贵，本单位实验室未有相关设备，因此未能进行相关测量实验。