用于激光聚变的光电子筛选技术X射线飞秒条纹相机研究

In the field of laser fusion, the significance of an X-ray streak camera in obtaining the continuous spatial-temporal information through implosion and its property of national security make it be blocked by the West. Laser fast ignition must be diagnosed in femtosecond order. As the key part of the streak camera, the performance of streak tube is restricted by photoelectron energy dispersion and space charge effect. When the time resolution reaches femtosecond, the dynamic range is severely insufficient to be practical. Based on results of the preliminary research, the photoelectron filter technology is introduced to construct an evaluation of streak camera imaging system, and the methods to improve the dynamic range of the camera system are researched. Specifically as that the design of a novel type of photoelectron filter to reduce the photoelectron energy dispersion and the angular spread, the optimization of the planar focal high-voltage electronic optical system to reduce the space charge effect, and the development of improving the dynamic range of the other parts of the camera system. The results of our preliminary research have shown that the physical time resolution, spatial resolution and dynamic range of the streak tube are increased by the photoelectron filter technology by 28%, 90% and 181% respectively. The streak camera system is constructed and calibrated after the development of the novel streak tube and the optimization of fast sweep circuit, inducing the results of 700 fs time resolution and 100: 1 dynamic range. Finally, this project will provide a critical X-ray femtosecond streak camera for fast ignition diagnosis, and promote the process of laser fusion strategy research in China.

X射线条纹相机是激光聚变研究中获取内爆连续时空信息、是关乎我国国防安全并被西方封锁的重要核仪器。激光快点火必需飞秒诊断，条纹变像管作为相机核心部件，其性能受制于光电子能量色散和空间电荷效应，当时间分辨率达到飞秒时，动态范围严重受限，难以实用。本项目基于前期研究，引入光电子筛选技术构建条纹相机成像评价体系，研究提高相机系统动态范围的方法和途径。具体为：设计新型光电子筛选器以减小光电子能量色散和角度弥散；优化设计平面聚焦高压电子光学系统，降低空间电荷效应；探索相机系统其它部件提高动态范围的方案。初步研究表明光电子筛选技术将条纹变像管物理时间、空间分辨率、动态范围分别提高了28%、90%和181%。研制新型条纹变像管和优化快速扫描电路，组建条纹相机系统并实验标定，实现700fs时间分辨率和100：1的动态范围。本项目将为快点火诊断提供关键的X射线飞秒条纹相机，推动我国激光聚变战略研究的进程。

在激光惯性约束聚变研究中，条纹相机是唯一获取核爆辐射连续时空信息的诊断仪器，是一种具有我国安全背景且被西方封锁的核仪器。激光快点火技术需要对X射线辐射信息进行飞秒量级的诊断，受此需求研制X射线飞秒条纹相机。X射线条纹相机时间分辨率达到飞秒量级，但是动态范围太小的缺陷限制了相机在聚变诊断中的应用。条纹变像管是条纹相机的核心部件，其性能的提高受制于光电子能量色散和空间电荷效应的物理机制。本项目研究了一种X射线飞秒条纹变像管，引入光电子筛选机制研究，设计出新型光电子能量角度筛选器，提高条纹变像管性能。新型光电子筛选器对光电子迅速加速，同时对其能量和角度进行筛选，实现光电子能量色散、角度弥散的减小，结合优化平面聚焦高压电子光学系统对电子聚焦成像，提高条纹变像管时间分辨、动态范围等性能。制作了高量子效率Au光电阴极和P20荧光屏。改进了高精密高耐压的变像管装配工艺。研制成功了具有新型光电子筛选器的X射线飞秒条纹变像管。该新型条纹变像管长度273mm，其中光电子筛选器的狭缝宽度20μm，通道长度300μm，阴极和筛选器之间的加速电场达10kV/mm，5电极的平面聚焦高压电子光学系统匹配该光电子筛选器。制作了超快扫描脉冲发生电路，组建了飞秒条纹相机系统。使用266nm、130fs紫外激光光源，搭建了飞秒条纹相机标定系统，实验标定相机性能，结果显示光电子筛选技术的条纹相机时间分辨率为357fs、动态范围达182:1、空间偏转灵敏度为79.9mm/kV、扫描速度为2.5×10^8m/s。本研究的成功实施将为激光快点火诊断提供关键的X射线飞秒条纹相机，推动我国聚变诊断的研究进程。