深等离子体通道中超强激光脉冲驱动尾场电子加速及其辐射的研究

The electron bunch generated from the laser-driven plasma accelerator will outrun the plasma wave and then disperse transversely because of the depletion and instabilities of the laser pulse, which limits the energy gain and broadens the energy spread. All these above-mentioned factors deteriorate the quality of the electron bunch. This project intends to overcome these problems by employing a deep plasma channel (DPC) driven by the ultraintense laser pulse. This allows a significant improvement of the acceleration because the DPC is devoid of electrons and ions near the propgating axis. In this case, the energy of laser near the axis can't be depleted. In addition, the transverse focusing force is almost zero. The longitudinal accelerating field is therefore steeped in the rear of the bubble. The self-injected electron bunch can achieve a quasi phase-stable acceleration forward and preserve its low emittance when the parameters of laser and DPC are optimized. In this project, we also introduce an optimum scheme to obtain high-quality electron bunch with high charge density. It is that the ultaintense laser pulse propagates in a DPC with dense-plasma wall. With the further increase of the laser intensity, we'll study the self-injection and acceleration of electron driven by an ultraintense laser pulse in the DPC including the effect of quantum electrodynamics (QED). It can be obtain the ultrahigh energetic electron bunch when the parameters of laser and plasma are optimized. We also introduce three optimum schemes to obtain ultrahigh peak brilliance and collimation gamma ray beam. One is that two ultraintense laser pulses counter-propagates in the DPC, the other is that an ultraintense laser pulse collides an energetic electron bunch driven by another ulstraintense laser pulse in the DPC, and the last is that an ultraintense laser pulse collides a solid target in the DPC. These high-quality electron bunches and gamma ray beams will be of important to the next-generation particle accelerators and light sources.

由于激光损耗和不稳定性的作用，激光在等离子体中产生的电子束将由尾场加速相位进入减速相位且横向发散，限制了其能量增益，增大了能散度和发散度，无法获得高品质电子束。本项目拟用深等离子体通道来解决这一重大问题，利用通道轴上密度很小甚至为零的特点，激光强度保持不变，空泡尾场纵向收缩，在激光与等离子体参量条件匹配时有望实现电子束在通道中的稳相加速且保持低能散度和发散度；提出增加通道边缘密度的方法，这种优化方案有望得到高电荷量的高品质电子束。在此基础上，随着激光强度的进一步增强，拟研究含量子电动力学(QED)效应的超强激光脉冲在深等离子体通道中捕获和加速电子，得到获得极高能量电子束的参量条件，再用两束相向传输的激光与等离子体作用、高能电子与强激光脉冲对撞以及超强激光脉冲与高密度靶作用等方案来获得高峰值亮度和准直伽马射线。本项目的研究成果有望为新一代台面型粒子加速器和辐射源的建造提供重要的理论指导。

超强激光脉冲与等离子体相互作用具有高度非线性，如何获得高能量、准单能电子束及其辐射高亮度、准直伽玛光源成为了强场物理研究的热点。本项目围绕超强激光脉冲在等离子体通道中非线性传输、电子加速并辐射伽玛光源展开研究。研究了自带轨道角动量的涡旋高斯激光脉冲在等离子体通道中的非线性传输特性，得到了其稳定传输的功率阈值；利用波动方程和电子动力学方程研究了纵向磁场对激光束在等离子体通道中准平衡传输和聚焦的影响，获得激光束腰匹配传输和准平衡传输的阈值条件，进一步研究了外加磁场对激光脉冲束腰宽度和脉冲宽度同时演化的特性，分析激光脉冲允许在磁化等离子体通道中传输的初始参量条件，确定得激光脉冲聚焦性准平衡传输的参量条件；提出了强激光脉冲在深等离子体通道中加速电子方案，通过参量优化获得了高品质电子束；提出了多个高能质子束在深等离子体通道中驱动高强度尾波场加速正电子束的方案，通过在深等离子体通道密度降低区域且位于正电子束前面适当距离注入高能电子束，使得正电子束随着高能质子束向前加速，最终获得极高的能量增益；提出了超强激光脉冲斜入射到固体靶产生超高亮度准直伽玛辐射源的方案，入射激光和反射激光电场在固体靶表面叠加，导致靶表面静电场强度显著增强，大量电子沿着靶表面加速的同时横向做振荡运动，获得了高亮度和准直的伽玛辐射源。本项目发表论文17篇，培养博士研究生2名、硕士研究生5名及本科生1名。相关研究成果对于超强激光脉冲在等离子体通道中非线性传输、粒子加速和辐射伽玛光源等实验方案具有重要的理论意义和应用价值。