离子-离子声不稳定性对无碰撞冲击波形成和演化的影响研究

Collisionless shock waves have attracted a lot of research interests due to its richness in the nonlinear dynamics and micro-instability processes, as well as its potential in generating energetic particles such as cosmic rays in the astrophysics and high energy ions in the indirect-drive inertial-confinement-fusion (ICF). In collisionless shock waves, where particle collisions are rare, the exciting of plasma waves and the collective interactions between particles and electromagnetic fields are needed to provide the essential energy dissipation. Therefore, it is important to understand the development of micro-instabilities (e.g. ion-ion acoustic instability) in the collisionless shock wave as well as its potential impact on the shock evolution. Topics to be addressed in this proposal include: (1) The investigation of the development of ion-ion acoustic instabilities and their interplay with other nonlinear dynamic processes in the different stages of the collisionless shock evolution. (2) The investigation of the characteristic of ion-ion acoustic instabilities, as well as their coupling with other instability modes, in different regions (e.g. the upstream and downstream regions) of the collisionless shock. This proposal complements ongoing efforts to the theoretical understanding of the collisionless shock physics, as well as some important phenomenons such as the generation of high energy ions in the ICF.

无碰撞冲击波是蕴含着丰富的非线性动力学和微观不稳定性过程的非线性结构。无碰撞冲击波加速被认为是天体中宇宙射线和间接驱动激光聚变中超热离子等高能粒子产生的重要物理机制。与普通流体中的冲击波不同，无碰撞冲击波形成所需的能量耗散过程是通过等离子体中波的激发及其与带电粒子之间的集体相互作用完成，而不是通过粒子碰撞完成。因此，认识无碰撞冲击波中微观不稳定性（如离子-离子声不稳定性）的发展规律及其影响具有重要科学意义和应用价值。本项目拟主要研究：（1）无碰撞冲击波演化不同阶段，离子-离子声不稳定性的发展规律及其与其他非线性动力学过程的相互影响。（2）无碰撞冲击波不同区域（如上游、下游区域），离子-离子声不稳定性的发展特征及其与其他不稳定性模式的耦合关系。本项目研究结果将有助于促进对无碰撞冲击波基础物理的理解，以及对激光聚变中高能离子加速等现象的认识。

本项目中，我主要对惯性约束聚变条件下的等离子体冲击波问题进行了研究，主要包含以下工作：（1）结合理论和粒子模拟，研究了影响无碰撞静电冲击波演化的物理因素，发现离子——离子声不稳定性、Weibel不稳定性和带电粒子库伦碰撞通过影响静电冲击波的广义守恒关系，进而改变冲击波的传输速度、离子反射率等性质，该研究已用于惯性约束聚变黑腔动理学效应的评估；（2）利用粒子模拟，首次开展了全电离等离子体碰撞冲击波的全动理学模拟研究，发现高马赫数等离子体冲击波受到非局域等效应的影响。在此基础上，研究了冲击波电子——离子能量分配对电离度的依赖关系，给出了冲击波能量分配规律，该工作对认识惯性约束聚变内爆冲击波物理、发展辐射流体力学建模具有参考意义。