激光直接加速电子产生高品质伽马射线源研究

High-quality gamma-ray production driven by high power laser pulse in direct laser acceleration regime has become the focus of high energy density plasma physics. However, for electron acceleration and radiation production in direct laser acceleration regime, there are still two key issues to be solved. On one hand, because of the continuous injection process of electrons, the direct-laser accelerated electrons usually display Maxwellian distribution and only a small portion of the electrons can satisfy the resonance condition. On the other hand, when the ultra-intense ultra-short laser pulse propagates into the plasma, it will suffer from many instabilities, including the laser filamentation instability and hosing instability, which will terminate the electron acceleration process and influence the gamma ray properties. Thus, understanding how to improve the electron injection process and suppress the laser propagation instabilities is the key to improve the quality of gamma-ray sources generated by direct laser accelerated electrons. This project is proposed to make a study on the electron injection process and laser propagation instabilities in direct laser acceleration regime. The main research contents included in this project are as follows: study on the improvement of the electron injection process and enhancement of the number of resonant electrons by controlling the laser and plasma distributions; study on the characteristics of the nonlinear synchrotron radiation from direct laser accelerated electrons; study on the suppression of laser propagation instabilities in plasmas and the quality improvement of the gamma-rays by employing novel designed target configurations.

高功率激光直接加速电子产生高品质伽马射线源的研究是高能量密度等离子体物理领域的前沿热点。在激光直接电子加速及辐射源产生的研究中，主要面临两个关键问题：一是由于电子的连续注入过程，电子的能谱通常呈现为麦克斯韦分布，因此满足共振匹配条件的高能电子数目较少；二是超强超短激光脉冲在等离子体中的传播不稳定性过程、如水流管不稳定性等，将破坏电子的加速过程并影响伽马光源品质。如何改善电子注入过程、并抑制激光传播不稳定性，是提高激光直接加速电子产生伽马射线源品质的关键。本项目将对激光直接加速机制下电子的注入物理过程及激光不稳定性传播等新物理问题开展研究，具体包括：通过调控激光和等离子体密度分布，改善电子注入过程以提高共振电子的数目，并研究其辐射特征；研究新型靶结构，探索抑制激光传播不稳定性并提高伽马射线源品质的新物理方案。

高功率激光直接加速电子产生高品质伽马射线源的研究是高能量密度等离子体物理领域的前沿热点。在激光直接电子加速及辐射源产生的研究中，主要面临两个关键问题：一是由于电子的连续注入过程，电子的能谱通常呈现为麦克斯韦分布，因此满足共振匹配条件的高能电子数目较少；二是超强超短激光脉冲在等离子体中的传播不稳定性过程、如水流管不稳定性等，将破坏电子的加速过程并影响伽马光源品质。如何改善电子注入过程、并抑制激光传播不稳定性，是提高激光直接加速电子产生伽马射线源品质的关键。本项目围绕激光直接加速电子产生伽马辐射源研究，重点解决了抑制激光传输不稳定性过程、电子注入过程的调控及优化、以及伽马射线源的品质提升等关键问题，完成了多个方面的研究工作：（1）通过考虑电子运动相对论效应及激光有质动力排开等离子体作用，我们从理论上获得了超强激光脉冲在临界密度等离子体中的质心演化方程，掌握了强激光水流管不稳定性的发展规律，并提出采用非均匀等离子体密度通道抑制激光传输不稳定性的物理方案；（2）基于单粒子运动模型及三维粒子模拟结果，我们对激光直接加速机制下电子的注入机制开展了仔细研究，阐明了离子运动及角向磁场对电子注入的重要影响规律，并提出采用双束激光优化电子注入及加速过程的物理方案；（3）为了在提高伽马射线源转换效率的同时，降低伽马光源的发散角，我们提出了新型组合靶、涡旋激光等新物理方案，极大提高了激光驱动伽马射线源的品质。

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