Spectroscopic Research of hot electron transport in Fast Igniter Plasmas

在激光核聚变研究中，快速点火器方案取得了较好的进展。在这个方案中，在燃料被压缩到固体密度的一千倍以上之后，燃料被一个佩瓦激光脉冲产生的高能电子强制加热。在该方案中，有效的能量传递和沉积是关键问题之一。建立了一种新的光谱方法，提供了时间和空间分辨的信息，比粒子测量提供了更多的定量理解能量沉积。此外，还开发了一种用于部分电离等离子体分析的原子动力学方程求解器，用于提取超高强度激光等离子体的温度等等离子体参数。用双层塑料靶或金属靶观察了氯或铝的k -α至He-α谱线，并测量了发射谱线强度与涂层厚度的关系。将塑料靶上的实验结果与试图模拟观测光谱的集成分析进行对比：首先，将实验热电子能量分布函数作为初始条件，进行一维（1D） Fokker-Planck输运计算，并耦合一维辐射流体动力学模拟。这提供了等离子体温度和密度随时间的变化。其次，将这些谱线作为原子动力学代码的输入，以提供谱线的时间演化。因此，我们计算了电离位移的Kα谱线，并与实验进行了比较。结果表明，该谱线与实验的Cl - k -α谱线一致，但与He-α谱线等高电离阶段的谱线不一致。

In laser fusion research, fast igniter scheme has shown a good progress. In this scheme, after compression of the fuel to more than a thousand times solid-density has occurred, the fuel is enforcedly heated with energetic electrons generated by a Peta-watt laser pulse. Efficient energy transfer to and deposition in the dense plasma is one of the critical issues in this scheme. A new spectroscopic method providing time-and space-resolved information has been established to provide a more quantitative understanding of the energy deposition than those provided by particle measurements. Moreover, an atomic kinetic equation solver, dedicated for analysis of partially ionized plasma, has been developed to extract plasma parameters such as temperature of ultra-high intensity laser produced plasma.X-ray spectra ranging from Kα to He-α lines of chlorine or aluminum were observed by using bi-layered plastic or metallic targets, and the dependence of the emitted line intensities on overcoat thickness was measured. The experimental results on the plastic targets were compared to an integrated analysis that attempted to simulate the observed spectrum: First, the experimental hot-electron energy distribution function was used as the initial condition to a one-dimensional (1D) Fokker-Planck transport calculation that is coupled to a 1D radiation hydrodynamic simulation. This provided the temporal evolution of temperature and density pro>les of the plasma. Second, these pro>les were given as input to an atomic kinetics code to provide temporal evolution of the spectra. Thus, the ionization-shifted Kα lines were calculated for comparison to experiments. The comparisons show a reasonable agreement with the experimental Cl Kα lines but not with those from higher ionization stages such as He-α line.