强激光在强磁化等离子体中能量输运特性研究

Under the background of new clear energy requirement based on magnetic inertial confinement fusion (ICF), the present project is to study the energy transport and relevant events in strongly magnetized high-energy-density laser-produced plasma, in which the issues are involved: 1) locally magnetized properties of laser-produced plasma under seeded and self-generated strong magnetic field topology, such as the magnetic field amplification and its saturation by magnetic flux compression, the dependent relations between magnetic flux compression and parameters of laser-plasma; 2) applying the generalized Ohm’s law in the MHD framework to explore the self-generated magnetic reconnection driven by two laser beams in plasma, energy conversion resulted from magnetic explosion process, and new mechanism of electron acceleration and transport by magnetic explosion; 3) characteristics of hot electron transport resulted from sideward Raman and weak-damped two-plasmon decay instabilities and competition between the processess in the developing of instabilities under the condition of strong topologic magnetic field, which will be experimentally examined by ultrafast time-resolved diagnosis; 4) harmonic radiation driven by strong laser field near the critical density and the radiation transport under the condition of strong topologic magnetic field. The investigations for these issues are of significance for further understanding the developing magnetic assistant ICF implosion and even for the design of new imploding targets.

基于磁约束辅助的惯性约束核聚变（ICF）的新能源背景，研究强激光产生的等离子体在强磁化条件下能量输运的相关物理问题，具体包括：外置的和自生的非定域强拓扑磁场对等离子体的局域磁化性质，如磁通收缩产生的磁场放大效应及其饱和条件、磁通收缩与激光等离子体参数的依赖关系等；应用磁流体动力学框架下的广义欧姆定律，研究双光束驱动靶等离子体中的自生磁场重联现象、重联引起的磁爆能量转换及其导致的磁爆电子加速与输运的新机制；在强拓扑磁场条件下侧向Raman散射和弱阻尼双等离子体衰变等不稳定性过程产生的超热电子输运新特性，考察不稳定性发展的过程竞争，同时从实验上进行超快时间分辨诊断予以验证；通过3D数值模拟并辅以适当的激光-固体靶实验，研究强拓扑磁场条件下在等离子体临界面由强激光场驱动的谐波辐射及输运。项目研究对于进一步理解和揭示磁约束辅助的ICF内爆物理乃至新兴ICF内爆靶设计将具有重要的理论参考意义。

本项目以激光聚变等离子体和高能粒子快点火方案为主体背景，通过各种等离子体靶型设计并结合理论解析和粒子模拟，研究在强磁场条件下强激光导致的超热电子产生及其输运、磁场放大、以及强激光驱动的固体密度表面结构靶产生的谐波辐射。获得的主要结果如下：. 1）在稳态和瞬态强磁场条件下，揭示了在强磁场并同时存在碰撞的条件下强激光等离子体中超热电子横向输运的规律，获得了不同电子密度分布时横向输运系数（即电导率及热导率）的解析公式；2）基于高能“快点火”设想，提出了一种在激光辐射压力加速机制下的增强质子加速方案，获得了高品质（准直）质子输运的重要结果；3）为了提高超热电子的输运效率，设计了一种含高密度夹层的低密度核心靶型，获得了高密度夹层对准静态自生磁场具有放大作用、对超热电子长距离输运具有明显“波导”效应和准直效果的新结论；4）将聚变压缩靶解析为具有周期性波纹结构表面的高密度光栅固体靶，获得了强激光驱动光栅固体靶谐波辐射输运的空间分布，提出了等效电偶极辐射的新机制，揭示了改变强激光入射角可有效控制谐波辐射输运空间分布的重要规律；5）作为项目研究计划外的拓展性探索，尝试考察了聚变等离子体中是否存在长程力效应的尚无触及问题，引入了非广延熵的统计力学描述并解析研究了激光诱导磁化等离子体的参量衰变不稳定性，获得了非广延效应和磁化强度对前向Raman散射不稳定性增长率的贡献很大、对双等离子体衰变不稳定性在短波方向的增长率的作用不可忽视、而对后向Brillouin散射不稳定性增长率的影响不明显的新理解；6）尤其在实验上，研究了强激光驱动的气体原子介质靶的高次谐波产生，通过不同靶型的优化设计获得了接近“水窗”波段的谐波辐射。