用于离子直线加速器的高分辨纵向束团形状测量装置研究

The bunch shape in the longitudinal is a very important parameter for the Ion LINAC. According to measuring longitudinal bunch shape, the longitudinal emittance can be derived, and we can judge whether there will be the beam loss in the high energy beam transmission line, because of the mismatching in the longitudinal phase plane. However, it is very hard for beam diagnostics work, since the measuring need a very high bandwidth of the detector and a high resolution requirement. This project will develop a high resolution longitudinal bunch shape monitor applied in the Ion LINAC. The principle of operation is based on the analysis of secondary electrons produced by a primary beam hitting a wire target, to which a potential is applied. The longitudinal distribution of charge of the analyzed beam is coherently transformed into a spatial distribution of low energy secondary electrons through transverse rf modulation. The designed phase resolution is about 1°.Through the designing, the fabricated, the calibration and the tested on beam, we hope to realize the first accurate measuring the longitudinal bunch shape in the Ion LINAC, to get some useful theories and experiences for the beam diagnostic, and to solve the difficulty problem for the accurate measuring the longitudinal bunch shape in China.

对于离子直线加速器，束团纵向分布是一个非常重要的关键参数。通过测量纵向形状推算纵向发射度，可判断束流在纵向相空间是否存在失配而导致高能段逐渐发生束损。因此准确测量束团纵向形状是加速器物理的更高需求，但同时也因高分辨率的测量要求与物理探头需极高工作带宽的问题而成为束诊工作难点。本项目拟研制一套用于离子直线加速器的高分辨率纵向束团形状测量装置，利用待测束流轰击丝靶产生二次电子、经静电场加速、再通过射频偏转系统对二次电子进行横向调制、将待测束团小于纳秒量级的纵向时间信息转换为二次电子空间分布，最后利用探测装置记录偏转后二次电子的空间分布信号，即可直观得到离子束团的高分辨率纵向形状。该装置设计相位分辨率为1°左右，通过研制、加工、离线标定、在线测试实现国内离子加速器首次纵向束团形状的准确测量，为我国束流纵向特性诊断积累设计经验与工程基础，解决离子直线加速器纵向束团形状准确测量的难题。

对于离子直线加速器，束团纵向分布是一个非常重要的关键参数。通过测量纵向形状推算纵向发射度，可判断束流在纵向相空间是否存在失配而导致高能段逐渐发生束损。因此准确测量束团纵向形状是加速器物理的更高需求，但同时也因高分辨率的测量要求与物理探头需极高工作带宽的问题而成为束诊工作难点。本项目研制了一套用于离子直线加速器的高分辨率纵向束团形状测量装置。按照研究计划，首先根据被测束流动力学模拟确定测量精度与范围，分析影响分辨率的因素；数值求解RF Deflector 结构参数，包括谐振腔型的选择（QWR 或HWR）、偏转极板长度与宽度，以及确定丝靶与狭缝距离、狭缝缝宽等；模拟跟踪二次电子从丝靶产生、通过狭缝、进入射频偏转场偏转的轨迹。其次, 优化结构设计，详细确定整体装置参数，进行机械设计，装置加工，利用高压平台悬浮电流丝产生热电子,进行离线测试标定; 建立纵向束团形状测量系统控制框图，在线安装，实现束流在线纵向束团形状测试；在线测试结束后，发现问题总结经验，进行改版设计，并积极准备进行第二次上线束流测试。