超短脉冲强激光与结构靶相互作用产生高品质电子束和超快X射线的模拟研究

Hard-x-ray emissions from femtosecond (fs) laser-produced plasmas have been extensively studied in past years. These kinds of intense and ultrafast hard-x-ray sources have a number of characteristics: (i) they can provide very short pulse durations from tens of femtoseconds to a few subpicoseconds;(ii) bright micro-focus x-ray sources can be generated with source sizes as small as a few microns, and (iii) laser-plasma x-ray sources can be accurately dynchronized with other events that can be driven, triggered, or stimulated by the same laser light. They make them valuable in imaging applications and diagnostic technique. The hard-x-ray emission produced by high intensity laser-solid interactions relies on hot electrons, which penetrate into the solid target and produce hard-x-ray emission via K-shell ionization and bremsstrahlung. In order to achieve high quality electron beam and ultrafast bright x-ray, we will carry out the modeling studies of an ultra-short intense laser pulse interaction with the structured targets and the electron propagation to generate x-ray emission, the abilities of both the separated and integrated simulations will also be acquired. The generation of electron beam will be studied by particle-in-cell (PIC) method, the emission of x-ray will be investigated by electron beam transport hybrid code and Monte-Carlo code, and the integraged simulation will be performed by coupling PIC code to hybrid code. The matching condition between target parameters and laser conditions will be explored and the target design will be optimized to increase laser absorption and x-ray emission. The results may be useful for the experiments in high energy density physics .

以超短脉冲强激光产生高品质电子束和超快X射线以及它们的诊断应用为牵引，建立分段模拟和集成模拟能力，深入开展强激光与结构靶相互作用产生高品质电子束的物理机制以及超热电子在靶中传输、转换成X射线相关物理的数值模拟研究。用粒子模拟程序研究超热电子束的产生过程，获得电子束品质（包括能谱、能散度、产额和发散角等）与靶参数、激光参数的关系。用电子束混合输运程序和蒙特卡洛程序研究微焦斑超快X射线产生的物理过程，获得X射线特性（亮度、能谱、角分布和脉宽等）与超热电子参数、靶参数的依赖关系，并开展集成模拟研究。通过大量的数值实验，结合理论分析，获得靶参数与激光参数的匹配条件，提出优化方案和新颖结构靶设想，为进一步的物理实验提供新的思路和理论参考，为高能量密度物理实验诊断提供理论依据。

研究工作以超短脉冲强激光产生高品质电子束和超快X射线及诊断应用为牵引，完善了激光-靶相互作用产生电子束的粒子模拟程序，建立了快电子束产生Ka或X射线研究的蒙特卡洛模拟能力，深入开展了超强激光与平面靶、纳米刷靶、周期结构靶等结构靶相互作用产生高品质电子束物理机制的理论和数值模拟研究，获得了电子束品质（能谱、产额、发散角和转换效率等）与靶参数、激光参数的关系。开展了快电子在固体靶、纳米刷靶中传输产生Ka X 射线物理过程的理论和蒙特卡洛数值模拟研究，研究了电子refluxing效应、电子双麦克斯韦分布对Ka X射线品质的影响，通过大量数值模拟获得了Ka 和X 射线特性（亮度、能谱、角分布和脉宽等）与超热电子参数、靶参数的依赖关系。提出了外加磁场提高电子束或质子束品质的理论方案和设想，为进一步的物理实验提供新的思路和理论参考，为高能量密度物理实验诊断提供理论依据。