基于自聚焦效应的大电量高能电子束研究

超短强脉冲微焦点轫致辐射X射线源的产生需要紧聚焦、大电量、能量可调的高能电子束。本项目围绕这一目标开展研究。针对超高强激光产生高能电子束的两种不同途径所面临的问题，本项目提出利用超强激光与大尺度预等离子体相互作用中的自聚焦效应改善激光脉冲的聚焦状态，提高激光功率密度并产生大电量的高能电子束；同时利用可控的大尺度预等离子体减小激光预脉冲的影响；自聚焦后的激光与高Z靶作用，产生另一束能量稍低的电子束，激光能量转化率将有效提高，其产生的自生磁场还可进一步箍缩预等离子体中产生的高能电子束。因此，将有望获得适合X射线源产生的高品质电子束。本项目拟利用理论分析和数值模拟手段细致研究激光与大尺度预等离子体混合靶作用产生的紧聚焦，大电量、高能电子束的物理机制,得出有关规律，并在SILEX-I飞秒装置上开展相关实验进行验证。

For generating a laser based hard X-ray source, a tightly focused, tunable energy, tightly focused and high charge hot electron beam is required. To overcome the intrinsic faults of the interaction between laser and planar metallic target or gas target, we propose the high Z solid target with large scale pre-plasma. The large-scale preplasma reduces the prepulse effects effectively and accelerates more fast electrons inthe self-focusing channel. Furthermore, the self-focusing effect reduces wings of the laser spot and enhances laser intensity. When the self-focused laser arrives at the high Z target surface, another high energy electron beam with lower energy is produced therefore the total amount of electrons which enter the solid target increases. Additionally, the self-generated magnetic field on the target surface also pinches the bunch from the preplasma. Generally, a tightly focused, high charge electron bunch with high energy can be produced this way.Theoretical analyses and particle-in-cell simulations will be performed to investigate the physical mechanism in the high power laser interaction with the target and related experiments will be carried out to check the physical model and get a tightly focused, tunable energy,and high charge hot electron beam.